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  <TITLE>IDENIX PHARMACEUTICALS, INC.</TITLE>
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  <DIV style="font-family: 'Times New Roman',Times,serif">
  
  <P align="center" style="font-size: 10pt">As filed with the
  Securities and Exchange Commission on August&nbsp;18, 2004
  
  
  
  <P align="right" style="font-size: 10pt">Registration No.&nbsp;333-_____
  
  
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  <P align="center" style="font-size: 14pt"><B>SECURITIES AND EXCHANGE COMMISSION</B>
  
  <DIV align="center" style="font-size: 12pt"><B>Washington, D.C. 20549</B>
  </DIV>
  
  <P align="center" style="font-size: 18pt"><B>FORM S-8</B>
  
  
  <P align="center" style="font-size: 10pt"><B>REGISTRATION STATEMENT UNDER<BR>
  THE SECURITIES ACT OF 1933</B>
  
  
  <P align="center" style="font-size: 24pt"><B>Idenix Pharmaceuticals, Inc.</B>
  
  <DIV align="center" style="font-size: 10pt">(Exact Name of Registrant as Specified in Its Charter)</DIV>
  
  
  <DIV align="center">
  <TABLE style="font-size: 10pt" cellspacing="0" border="0" cellpadding="0" width="100%">
  
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  <TR valign="bottom">
      <TD align="center" valign="top"><B>Delaware</B>
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top"><B>45-0478605</B></TD>
  </TR>
  
  <TR valign="bottom">
      <TD align="center" valign="top">(State or Other Jurisdiction of Incorporation<BR>
  or Organization)
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">(I.R.S. Employer<BR>
  Identification No.)</TD>
  </TR>
  
  <TR valign="bottom">
      <TD align="center" valign="top">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">&nbsp;</TD>
  </TR>
  
  <TR valign="bottom">
      <TD align="center" valign="top">60 Hampshire Street</TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">&nbsp;</TD>
  </TR>
  
  <TR valign="bottom">
      <TD align="center" valign="top">Cambridge, MA
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">02139</TD>
  </TR>
  
  <TR valign="bottom">
      <TD align="center" valign="top">(Address of Principal Executive Offices)
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">(Zip Code)</TD>
  </TR>
  
  
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  </TABLE>
  </DIV>
  
  
  
  <P align="center" style="font-size: 10pt"><B>1998 Equity Incentive Plan<BR>
  2004 Stock Incentive Plan</B><BR>
  (Full Title of the Plan)
  
  
  
  <P align="center" style="font-size: 10pt"><B>Jean-Pierre Sommadossi<BR>
  President and Chief Executive Officer<BR>
  Idenix Pharmaceuticals, Inc.<BR>
  60 Hampshire Street<BR>
  Cambridge, MA 02139</B><BR>
  (Name and Address of Agent For Service)<BR>
  <B>617-995-9800</B><BR>
  (Telephone Number, Including Area Code, of Agent For Service)
  
  
  
  <P align="center" style="font-size: 10pt"><B>CALCULATION OF REGISTRATION FEE</B>
  
  
  <DIV align="center">
  <TABLE style="font-size: 10pt" cellspacing="0" cellpadding="0" width="100%" border="0">
  
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  <TR style="font-size: 1px" valign="bottom">
      <TD nowrap align="left" colspan="15" style="border-bottom: 3px solid #000000">&nbsp;</TD>
  </TR>
  <TR style="font-size: 8pt" valign="bottom">    <TD width="1%">&nbsp;</TD>
  
      <TD>&nbsp;</TD>
      <TD style="border-right: 1px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD style="border-right: 1px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center"><B>Proposed Maximum</B></TD>
      <TD style="border-right: 1px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center"><B>Proposed Maximum</B></TD>
      <TD style="border-right: 1px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center"><B>&nbsp;</B></TD>
      <TD width="1%">&nbsp;</TD>
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      <TD nowrap align="left"><B>Title of Securities</B></TD>
      <TD style="border-right: 1px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center"><B>Amount to be</B></TD>
      <TD style="border-right: 1px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center"><B>Offering Price Per</B></TD>
      <TD style="border-right: 1px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center"><B>Aggregate Offering</B></TD>
      <TD style="border-right: 1px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center"><B>Amount of</B></TD>
      <TD width="1%">&nbsp;</TD>
  </TR>
  <TR style="font-size: 8pt" valign="bottom">    <TD width="1%">&nbsp;</TD>
  
      <TD nowrap align="left"><B>to be Registered</B></TD>
      <TD style="border-right: 1px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center"><B>Registered(1)</B></TD>
      <TD style="border-right: 1px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center"><B>Share</B></TD>
      <TD style="border-right: 1px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center"><B>Price</B></TD>
      <TD style="border-right: 1px solid #000000">&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center"><B>Registration Fee</B></TD>
      <TD width="1%">&nbsp;</TD>
  </TR>
  
  
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  <TD valign="top" style="border-top: 1px solid #000000" nowrap><DIV style="margin-left:0px; text-indent:-0px">Common Stock,
  $0.001 par value per share
  </DIV></TD>
      <TD style="border-right: 1px solid #000000; border-top: 1px solid #000000">&nbsp;</TD>
      <TD style="border-top: 1px solid #000000">&nbsp;</TD>
  
  <TD align="center" valign="top" style="border-top: 1px solid #000000" nowrap>3,962,335&nbsp;shares(2)
  </TD>
      <TD style="border-right: 1px solid #000000; border-top: 1px solid #000000">&nbsp;</TD>
      <TD style="border-top: 1px solid #000000">&nbsp;</TD>
      <TD align="center" valign="top" style="border-top: 1px solid #000000">$8.495(3)
  </TD>
      <TD style="border-right: 1px solid #000000; border-top: 1px solid #000000">&nbsp;</TD>
      <TD style="border-top: 1px solid #000000">&nbsp;</TD>
  
  <TD align="center" valign="middle" style="border-top: 1px solid #000000" nowrap>$33,660,035.825(3)
  </TD>
      <TD style="border-right: 1px solid #000000; border-top: 1px solid #000000">&nbsp;</TD>
      <TD style="border-top: 1px solid #000000">&nbsp;</TD>
      <TD align="center" valign="top" style="border-top: 1px solid #000000">$4,264.73</TD>
      <TD width="1%" style="border-top: 1px solid #000000">&nbsp;</TD>
  </TR>
  
  <TR style="font-size: 1px" valign="bottom">
      <TD nowrap align="left" colspan="15" style="border-top: 3px solid #000000">&nbsp;</TD>
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  </DIV>
  
  
  
  
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  <TR valign="top">
      <TD width="1%" nowrap align="right">(1)</TD>
      <TD width="3%">&nbsp;</TD>
      <TD width="96%">In accordance with Rule&nbsp;416 under the Securities Act of 1933, as amended,
  this registration statement shall be deemed to cover any additional
  securities that may from time to time be offered or issued to prevent
  dilution resulting from stock splits, stock dividends or similar
  transactions.</TD>
  </TR>
  
  <TR><TD>&nbsp;</TD></TR>
  
  <TR valign="top">
      <TD width="1%" nowrap align="right">(2)</TD>
      <TD width="3%">&nbsp;</TD>
      <TD width="96%">Consists of (i)&nbsp;3,067,395&nbsp;shares subject to options outstanding under
  the 1998 Equity Incentive Plan, (ii)&nbsp;94,940&nbsp;shares issuable under the
  1998 Equity Incentive Plan; and (iii)&nbsp;800,000 shares issuable under the
  2004 Stock Incentive Plan.</TD>
  </TR>
  
  <TR><TD>&nbsp;</TD></TR>
  
  <TR valign="top">
      <TD width="1%" nowrap align="right">(3)</TD>
      <TD width="3%">&nbsp;</TD>
      <TD width="96%">Estimated solely for the purpose of calculating the registration fee
  pursuant to Rules 457(c) and 457(h) of the Securities Act of 1933, as
  amended, and based upon the average of the high and low prices of the
  Registrant&#146;s Common Stock as reported on the Nasdaq National Market on
  August&nbsp;11, 2004.</TD>
  </TR>
  
  </TABLE>
  
  
  
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  <P align="center" style="font-size: 10pt">&nbsp;
  </DIV>
  
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  <!-- TOC -->
  <A name="toc"><DIV align="CENTER" style="page-break-before:always"><U><B>TABLE OF CONTENTS</B></U></DIV></A>
  
  <P><CENTER>
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  </TR>
  <TR><TD colspan="9"><A HREF="#000">PART I</A></TD></TR>
  <TR><TD></TD><TD colspan="8"><A HREF="#001">Item&nbsp;1. Plan Information.</A></TD></TR>
  <TR><TD></TD><TD colspan="8"><A HREF="#002">Item&nbsp;2. Registrant Information and Employee Plan Annual Information.</A></TD></TR>
  <TR><TD colspan="9"><A HREF="#003">PART II</A></TD></TR>
  <TR><TD></TD><TD colspan="8"><A HREF="#004">Item&nbsp;3. Incorporation of Documents by Reference.</A></TD></TR>
  <TR><TD></TD><TD colspan="8"><A HREF="#005">Item&nbsp;4. Description of Securities.</A></TD></TR>
  <TR><TD></TD><TD colspan="8"><A HREF="#006">Item&nbsp;5. Interests of Named Experts and Counsel.</A></TD></TR>
  <TR><TD></TD><TD colspan="8"><A HREF="#007">Item&nbsp;6. Indemnification of Directors and Officers.</A></TD></TR>
  <TR><TD></TD><TD colspan="8"><A HREF="#008">Item&nbsp;7. Exemption from Registration Claimed.</A></TD></TR>
  <TR><TD></TD><TD colspan="8"><A HREF="#009">Item&nbsp;8. Exhibits.</A></TD></TR>
  <TR><TD></TD><TD colspan="8"><A HREF="#010">Item&nbsp;9. Undertakings.</A></TD></TR>
  <TR><TD colspan="9"><A HREF="#011">SIGNATURES</A></TD></TR>
  <TR><TD colspan="9"><A HREF="#012">INDEX TO EXHIBITS</A></TD></TR>
  <TR><TD colspan="9"><A HREF="b51481ipexv5.txt">EX-5 OPINION OF WILMER CUTLER PICKERING HALE AND DORR LLP</A></TD></TR>
  <TR><TD colspan="9"><A HREF="b51481ipexv23w2.txt">EX-23.2 CONSENT OF PRICEWATERHOUSECOOPERS LLP</A></TD></TR>
  </TABLE>
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  <H5 align="left" style="page-break-before:always"><A HREF="#toc">Table of Contents</A></H5><P>
  
  
  
  
  <!-- link1 "PART I" -->
  <DIV align="left"><A NAME="000"></A></DIV>
  
  <P align="center" style="font-size: 10pt"><B>PART I</B>
  
  
  <DIV align="center" style="font-size: 10pt"><B>INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS</B></DIV>
  
  
  <!-- link2 "Item&nbsp;1. Plan Information." -->
  <DIV align="left"><A NAME="001"></A></DIV>
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>Item&nbsp;1. Plan Information.</B>
  
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The information required by Item&nbsp;1 is included in documents sent or given
  to participants in the plans covered by this registration statement pursuant to
  Rule&nbsp;428(b)(1) of the Securities Act of 1933, as amended (the &#147;Securities
  Act&#148;).
  
  <!-- link2 "Item&nbsp;2. Registrant Information and Employee Plan Annual Information." -->
  <DIV align="left"><A NAME="002"></A></DIV>
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>Item&nbsp;2. Registrant Information and Employee Plan Annual Information.</B>
  
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The written statement required by Item&nbsp;2 is included in documents sent or
  given to participants in the plans covered by this registration statement
  pursuant to Rule&nbsp;428(b)(1) of the Securities Act.
  
  <!-- link1 "PART II" -->
  <DIV align="left"><A NAME="003"></A></DIV>
  
  <P align="center" style="font-size: 10pt"><B>PART II</B>
  
  
  <DIV align="center" style="font-size: 10pt"><B>INFORMATION REQUIRED IN THE REGISTRATION STATEMENT</B></DIV>
  
  
  <!-- link2 "Item&nbsp;3. Incorporation of Documents by Reference." -->
  <DIV align="left"><A NAME="004"></A></DIV>
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>Item&nbsp;3. Incorporation of Documents by Reference.</B>
  
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The registrant is subject to the informational and reporting requirements
  of Sections&nbsp;13(a), 14, and 15(d) of the Securities Exchange Act of 1934, as
  amended (the &#147;Exchange Act&#148;), and in accordance therewith files reports, proxy
  statements and other information with the Securities and Exchange Commission
  (the &#147;Commission&#148;). The following documents, which are on file with the
  Commission, are incorporated in this registration statement by reference:
  
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(a)&nbsp;The registrant&#146;s latest annual report filed pursuant to Section 13(a)
  or 15(d) of the Exchange Act or the latest prospectus filed pursuant to Rule
  424(b) under the Securities Act that contains audited financial statements for
  the registrant&#146;s latest fiscal year for which such statements have been filed.
  
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(b)&nbsp;All other reports filed pursuant to Section 13(a) or 15(d) of the
  Exchange Act since the end of the fiscal year covered by the document referred
  to in (a)&nbsp;above.
  
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(c)&nbsp;The description of the securities contained in the registrant&#146;s
  registration statements on Form 8-A filed under the Exchange Act, including any
  amendment or report filed for the purpose of updating such description.
  
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;All documents subsequently filed by the registrant pursuant to Sections
  13(a), 13(c), 14 and 15(d) of the Exchange Act, prior to the filing of a
  post-effective amendment which indicates that all securities offered hereby
  have been sold or which deregisters all securities then remaining unsold, shall
  be deemed to be incorporated by reference in this registration statement and to
  be part hereof from the date of the filing of such documents. Any statement
  contained in a document incorporated or deemed to be incorporated by reference
  herein shall be deemed to be modified or superseded for the purposes of this
  registration statement to the extent that a statement contained herein or in
  any other subsequently filed document which also is or is deemed to be
  incorporated by reference herein modifies or supersedes such statement. Any
  statement so modified or superseded shall not be deemed, except as so modified
  or superseded, to constitute a part of this registration statement.
  
  <!-- link2 "Item&nbsp;4. Description of Securities." -->
  <DIV align="left"><A NAME="005"></A></DIV>
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>Item&nbsp;4. Description of Securities.</B>
  
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Not applicable.
  
  
  <P align="center" style="font-size: 10pt">-1-
  </DIV>
  
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  <DIV style="font-family: 'Times New Roman',Times,serif">
  <!-- link2 "Item&nbsp;5. Interests of Named Experts and Counsel." -->
  <DIV align="left"><A NAME="006"></A></DIV>
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>Item&nbsp;5. Interests of Named Experts and Counsel.</B>
  
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Wilmer Cutler Pickering Hale and Dorr LLP has opined as to the legality of
  the securities being offered by this registration statement. Ambassador
  Charlene Barshefsky, a member of the registrant&#146;s board of directors, is a
  partner in the law firm of Wilmer Cutler Pickering Hale and Dorr LLP and
  beneficially owns 61,343 shares of the registrant&#146;s common stock.
  
  <!-- link2 "Item&nbsp;6. Indemnification of Directors and Officers." -->
  <DIV align="left"><A NAME="007"></A></DIV>
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>Item&nbsp;6. Indemnification of Directors and Officers.</B>
  
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Section&nbsp;145 of the General Corporation Law of the State of Delaware
  permits a corporation, under specified circumstances, to indemnify its
  directors, officers, employees or agents against expenses (including attorney&#146;s
  fees), judgments, fines and amounts paid in settlements actually and reasonably
  incurred by them in connection with any action, suit or proceeding brought by
  third parties by reason of the fact that they were or are directors, officers,
  employees or agents of the corporation, if such directors, officers, employees
  or agents acted in good faith and in a manner they reasonably believed to be in
  or not opposed to the best interests of the corporation and, with respect to
  any criminal action or proceeding, had no reason to believe their conduct was
  unlawful. In a derivative action, i.e., one by or in the right of the
  corporation, indemnification may be made only for expenses actually or
  reasonably incurred by directors, officers, employees or agents in connection
  with the defense or settlement of an action or suit, and only with respect to a
  matter as to which they shall have acted in good faith and in a manner they
  reasonably believed to be in or not opposed to the best interests of the
  corporation, except that no indemnification shall be made if such person shall
  have been adjudged liable to the corporation, unless and only to the extent
  that the court in which the action or suit was brought shall determine upon
  application that the defendant directors, officers, employees or agents are
  fairly and reasonably entitled to indemnify for such expenses despite such
  adjudication of liability.
  
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The registrant&#146;s restated certificate of incorporation, as amended, states
  that the registrant&#146;s directors will not have personal liability for monetary
  damages for any breach of fiduciary duty as a director, except to the extent
  that the General Corporation Law of the State of Delaware prohibits the
  elimination or limitation of liability of directors for breaches of fiduciary
  duty.
  
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The registrant also carries liability insurance covering each of its directors and officers.
  
  <!-- link2 "Item&nbsp;7. Exemption from Registration Claimed." -->
  <DIV align="left"><A NAME="008"></A></DIV>
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>Item&nbsp;7. Exemption from Registration Claimed.</B>
  
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Not applicable.
  
  <!-- link2 "Item&nbsp;8. Exhibits." -->
  <DIV align="left"><A NAME="009"></A></DIV>
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>Item&nbsp;8. Exhibits.</B>
  
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The Exhibit&nbsp;Index immediately preceding the exhibits is incorporated herein by reference.
  
  <!-- link2 "Item&nbsp;9. Undertakings." -->
  <DIV align="left"><A NAME="010"></A></DIV>
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>Item&nbsp;9. Undertakings.</B>
  
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;1.&nbsp;<I>Item&nbsp;</I><I>512(a)</I><I> of Regulation&nbsp;S-K</I>. The undersigned registrant hereby
  undertakes:
  
  
  
  <P align="left" style="margin-left:3%; font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(1) To file, during any period in which offers or sales are being
  made, a post-effective amendment to this registration statement:
  
  
  
  <P align="left" style="margin-left:3%; font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(i) To include any prospectus required by Section&nbsp;10(a)(3) of the
  Securities Act;
  
  
  <P align="center" style="font-size: 10pt">-2-
  </DIV>
  
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  <DIV style="font-family: 'Times New Roman',Times,serif">
  
  
  <P align="left" style="margin-left:3%; font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(ii) To reflect in the prospectus any facts or events arising after
  the effective date of the registration statement (or the most recent
  post-effective amendment thereof) which, individually or in the
  aggregate, represent a fundamental change in the information set forth in
  the registration statement; and
  
  
  
  <P align="left" style="margin-left:3%; font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(iii) To include any material information with respect to the plan
  of distribution not previously disclosed in the registration statement or
  any material change to such information in the registration statement;
  
  
  
  <P align="left" style="margin-left:3%; font-size: 10pt"><I>provided, however, </I>that paragraphs (i)&nbsp;and (ii)&nbsp;do not apply if the
  information required to be included in a post-effective amendment by
  those paragraphs is contained in periodic reports filed with or furnished
  to the Commission by the registrant pursuant to Section&nbsp;13 or Section
  15(d) of the Exchange Act that are incorporated by reference in the
  registration statement.
  
  
  
  <P align="left" style="margin-left:3%; font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(2) That, for the purpose of determining any liability under the
  Securities Act, each such post-effective amendment shall be deemed to be
  a new registration statement relating to the securities offered therein,
  and the offering of such securities at that time shall be deemed to be
  the initial <I>bona fide </I>offering thereof.
  
  
  
  <P align="left" style="margin-left:3%; font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(3) To remove from registration by means of a post-effective
  amendment any of the securities being registered which remain unsold at
  the termination of the offering.
  
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;2.&nbsp;<I>Item&nbsp;</I><I>512(b)</I><I> of Regulation&nbsp;S-K</I>. The undersigned registrant hereby
  undertakes that, for purposes of determining any liability under the Securities
  Act, each filing of the registrant&#146;s annual report pursuant to Section 13(a) or
  Section 15(d) of the Exchange Act that is incorporated by reference in the
  registration statement shall be deemed to be a new registration statement
  relating to the securities offered therein, and the offering of such securities
  at that time shall be deemed to be the initial <I>bona fide </I>offering thereof.
  
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3.&nbsp;<I>Item&nbsp;</I><I>512(h)</I><I> of Regulation&nbsp;S-K</I>. Insofar as indemnification for
  liabilities arising under the Securities Act may be permitted to directors,
  officers and controlling persons of the registrant pursuant to the foregoing
  provisions, or otherwise, the registrant has been advised that in the opinion
  of the Securities and Exchange Commission such indemnification is against
  public policy as expressed in the Securities Act and is, therefore,
  unenforceable. In the event that a claim for indemnification against such
  liabilities (other than the payment by the registrant of expenses incurred or
  paid by a director, officer or controlling person of the registrant in the
  successful defense of any action, suit or proceeding) is asserted by such
  director, officer or controlling person in connection with the securities being
  registered, the registrant will, unless in the opinion of its counsel the
  matter has been settled by controlling precedent, submit to a court of
  appropriate jurisdiction the question whether such indemnification by it is
  against public policy as expressed in the Securities Act and will be governed
  by the final adjudication of such issue.
  
  
  <P align="center" style="font-size: 10pt">-3-
  </DIV>
  
  <!-- PAGEBREAK -->
  <P><HR noshade><P>
  <H5 align="left" style="page-break-before:always"><A HREF="#toc">Table of Contents</A></H5><P>
  
  <DIV style="font-family: 'Times New Roman',Times,serif">
  <!-- link1 "SIGNATURES" -->
  <DIV align="left"><A NAME="011"></A></DIV>
  
  <P align="center" style="font-size: 10pt"><B>SIGNATURES</B>
  
  
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Pursuant to the requirements of the Securities Act of 1933, the registrant
  certifies that it has reasonable grounds to believe that it meets all of the
  requirements for filing on Form S-8 and has duly caused this registration
  statement to be signed on its behalf by the undersigned, thereunto duly
  authorized, in the City of Cambridge, Commonwealth of Massachusetts, on this
  18th&nbsp;day of August, 2004.
  
  
  <TABLE width="100%" border="0" cellspacing="0" cellpadding="0" style="font-size: 10pt">
  <TR>
      <TD width="48%">&nbsp;</TD>
      <TD width="1%">&nbsp;</TD>
      <TD width="1%">&nbsp;</TD>
      <TD width="35%">&nbsp;</TD>
      <TD width="15%">&nbsp;</TD>
  </TR>
  <TR>
      <TD valign="top">&nbsp;</TD>
      <TD colspan="3">IDENIX PHARMACEUTICALS, INC.<BR>
  &nbsp;</TD>
      <TD>&nbsp;</TD>
  </TR><TR>
      <TD>&nbsp;</TD>
      <TD valign="top">By:&nbsp;&nbsp;</TD>
      <TD colspan="2" style="border-bottom: 1px solid #000000">/s/ Jean-Pierre Sommadossi
  &nbsp;</TD>
      <TD>&nbsp;</TD>
  </TR><TR>
      <TD>&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD colspan="2">Jean-Pierre Sommadossi&nbsp;</TD>
      <TD>&nbsp;</TD>
  </TR><TR>
      <TD>&nbsp;</TD>
      <TD>&nbsp;</TD>
      <TD colspan="2">President and Chief Executive Officer&nbsp;</TD>
      <TD>&nbsp;</TD>
  </TR>
  <TR>
      <TD colspan="5">&nbsp;</TD>
  </TR>
  </TABLE>
  
  <P align="center" style="font-size: 10pt"><B>POWER OF ATTORNEY AND SIGNATURES</B>
  
  
  
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;We, the undersigned officers and directors of Idenix Pharmaceuticals,
  Inc., hereby severally constitute and appoint Jean-Pierre Sommadossi and Andrea
  J. Corcoran, and each of them singly, our true and lawful attorneys with full
  power to them, and each of them singly, to sign for us and in our names in the
  capacities indicated below, the registration statement on Form S-8 filed
  herewith and any and all subsequent amendments to said registration statement,
  and generally to do all such things in our names and on our behalf in our
  capacities as officers and directors to enable Idenix Pharmaceuticals, Inc. to
  comply with the provisions of the Securities Act of 1933, as amended, and all
  requirements of the Securities and Exchange Commission, hereby ratifying and
  confirming our signatures as they may be signed by our said attorneys, or any
  of them, to said registration statement and any and all amendments thereto.
  
  
  <P align="left" style="font-size: 10pt">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Pursuant to the requirements of the Securities Act of 1933, this
  registration statement has been signed by the following persons in the
  capacities and on the dates indicated.
  
  <DIV align="center">
  <TABLE style="font-size: 10pt" cellspacing="0" border="0" cellpadding="0" width="100%">
  
  <!-- Begin Table Head --><TR valign="bottom">
      <TD width="38%">&nbsp;</TD>
      <TD width="5%">&nbsp;</TD>
      <TD width="30%">&nbsp;</TD>
      <TD width="5%">&nbsp;</TD>
      <TD width="22%">&nbsp;</TD>
  </TR>
  <TR style="font-size: 8pt" valign="bottom">
      <TD nowrap align="left"><B>Signature</B><HR size="1" noshade></TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center"><B>Title</B><HR size="1" noshade></TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="center"><B>Date</B><HR size="1" noshade></TD>
  </TR>
  
  
  <!-- End Table Head -->
  
  <!-- Begin Table Body -->
  <TR><TD>&nbsp;</TD></TR>
  <TR><TD>&nbsp;</TD></TR>
  <TR valign="bottom">
      <TD align="center" nowrap valign="top">/s/ Jean-Pierre Sommadossi<BR><HR size="1" noshade>
      Jean-Pierre Sommadossi</TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">
  President and Chief<BR>
  Executive Officer<BR>
  (Principal executive<BR>
  officer)
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">August&nbsp;18,&nbsp;2004</TD>
  </TR>
  
  <TR valign="bottom" style="padding-top: 1em">
      <TD align="center" nowrap valign="top">/s/ David A. Arkowitz<BR>
  <HR size="1" noshade>
  David A. Arkowitz</TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">
  Chief Financial Officer<BR>
  and Treasurer (Principal<BR>
  financial and accounting<BR>
  officer)
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">August&nbsp;18,&nbsp;2004</TD>
  </TR>
  
  <TR valign="top" style="padding-top: 1em">
      <TD align="center" nowrap valign="top">/s/ Charlene Barshefsky<br>
  <HR size="1" noshade>Charlene Barshefsky</td>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">Director
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">August&nbsp;18,&nbsp;2004</TD>
  </TR>
  
  
  <TR valign="top" style="padding-top: 1em">
      <TD align="center" nowrap valign="top">/s/ Charles W. Cramb<br>
  <HR size="1" noshade>Charles W. Cramb</td>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">
  Director
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">August&nbsp;18,&nbsp;2004</TD>
  </TR>
  
  <TR valign="top" style="padding-top: 1em">
      <TD align="center" nowrap valign="top">/s/ Thomas Ebeling<br>
  <HR size="1" noshade>Thomas Ebeling</td>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">
  Director</TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">August&nbsp;18,&nbsp;2004</TD>
  </TR>
  
  <!-- End Table Body -->
  </TABLE>
  </DIV>
  
  
  
  <P align="center" style="font-size: 10pt">-4-
  </DIV>
  
  <!-- PAGEBREAK -->
  <P><HR noshade><P>
  <H5 align="left" style="page-break-before:always"><A HREF="#toc">Table of Contents</A></H5><P>
  
  <DIV style="font-family: 'Times New Roman',Times,serif">
  <DIV align="center">
  <TABLE style="font-size: 10pt" cellspacing="0" border="0" cellpadding="0" width="100%">
  
  <!-- Begin Table Head --><TR valign="bottom">
      <TD width="38%">&nbsp;</TD>
      <TD width="5%">&nbsp;</TD>
      <TD width="30%">&nbsp;</TD>
      <TD width="5%">&nbsp;</TD>
      <TD width="22%">&nbsp;</TD>
  </TR>
  
  <!-- End Table Head -->
  
  <!-- Begin Table Body -->
  <TR valign="bottom" style="padding-top: 1em">
      <TD align="center" nowrap valign="top">/s/ Ansbert Gadicke<BR>
  <HR size="1" noshade>Ansbert Gadicke</TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">
  Director
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">August&nbsp;18,&nbsp;2004</TD>
  </TR>
  
  <TR valign="bottom" style="padding-top: 1em">
      <TD align="center" nowrap valign="top">/s/ Wayne T. Hockmeyer<BR>
  <HR size="1" noshade>Wayne T. Hockmeyer</TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">
  Director
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">August&nbsp;18,&nbsp;2004</TD>
  </TR>
  
  <TR valign="bottom" style="padding-top: 1em">
      <TD align="center" nowrap valign="top">/s/ Thomas R. Hodgson<BR>
  <HR size="1" noshade>Thomas R. Hodgson</TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">
  Director
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">August&nbsp;18,&nbsp;2004</TD>
  </TR>
  
  <TR valign="bottom" style="padding-top: 1em">
      <TD align="center" nowrap valign="top">/s/ Robert E. Pelzer<BR>
  <HR size="1" noshade>Robert E. Pelzer</TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">
  Director
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">August&nbsp;18,&nbsp;2004</TD>
  </TR>
  
  <TR valign="bottom" style="padding-top: 1em">
      <TD align="center" nowrap valign="top">/s/ Denise Pollard-Knight<BR>
  <HR size="1" noshade>Denise Pollard-Knight</TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">
  Director
  </TD>
      <TD>&nbsp;</TD>
      <TD align="center" valign="top">August&nbsp;18,&nbsp;2004</TD>
  </TR>
  
  
  
  <!-- End Table Body -->
  </TABLE>
  </DIV>
  
  
  
  <P align="center" style="font-size: 10pt">-5-
  </DIV>
  
  <!-- PAGEBREAK -->
  <P><HR noshade><P>
  <H5 align="left" style="page-break-before:always"><A HREF="#toc">Table of Contents</A></H5><P>
  
  <DIV style="font-family: 'Times New Roman',Times,serif">
  <!-- link1 "INDEX TO EXHIBITS" -->
  <DIV align="left"><A NAME="012"></A></DIV>
  
  <P align="center" style="font-size: 10pt"><B>INDEX TO EXHIBITS</B>
  
  
  <DIV align="center">
  <TABLE style="font-size: 10pt" cellspacing="0" border="0" cellpadding="0" width="100%">
  
  <!-- Begin Table Head --><TR valign="bottom">
      <TD width="8%">&nbsp;</TD>
      <TD width="2%">&nbsp;</TD>
      <TD width="90%">&nbsp;</TD>
  </TR>
  <TR style="font-size: 8pt" valign="bottom">
      <TD nowrap align="left"><B>Number</B><HR size="1" noshade></TD>
      <TD>&nbsp;</TD>
      <TD nowrap align="left"><B>Description</B><HR size="1" noshade></TD>
  </TR>
  
  
  <!-- End Table Head -->
  
  <!-- Begin Table Body -->
  <TR valign="bottom">
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">4.1(1)
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">Restated Certificate of Incorporation of the Registrant, as amended</TD>
  </TR>
  
  <TR valign="bottom">
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">4.2(1)
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">Amended and Restated By-Laws of the Registrant</TD>
  </TR>
  
  <TR valign="bottom">
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">5
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">Opinion of Wilmer Cutler Pickering Hale and Dorr LLP, counsel to
  the Registrant</TD>
  </TR>
  
  <TR valign="bottom">
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">23.1
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">Consent of Wilmer Cutler Pickering Hale and Dorr LLP
  (included in Exhibit&nbsp;5)</TD>
  </TR>
  
  <TR valign="bottom">
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">23.2
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">Consent of PricewaterhouseCoopers LLP</TD>
  </TR>
  
  <TR valign="bottom">
      <TD valign="top"><DIV style="margin-left:0px; text-indent:-0px">24
  </DIV></TD>
      <TD>&nbsp;</TD>
      <TD align="left" valign="top">Power of attorney (included on the signature pages of this
  registration statement)</TD>
  </TR>
  
  
  <!-- End Table Body -->
  </TABLE>
  </DIV>
  
  
  
  
  <P>
  
  <HR size="1" width="18%" align="left" noshade>
  
  
  <TABLE width="100%" border="0" cellpadding="0" cellspacing="0" style="font-size: 10pt">
  
  <TR valign="top">
      <TD width="1%" nowrap align="right">(1)</TD>
      <TD width="3%">&nbsp;</TD>
      <TD width="96%">Previously filed with the Securities and Exchange Commission as an
  Exhibit to the Registrant&#146;s Registration Statement on Form S-1, as amended
  (File No.&nbsp;333-111157) and incorporated herein by reference.</TD>
  </TR>
  
  </TABLE>
  
  
  
  
  <P align="center" style="font-size: 10pt">&nbsp;</DIV>
  
  
  </BODY>
  </HTML>
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metadata_filer: {"company-data": {"conformed-name": "IDENIX PHARMACEUTICALS INC", "cik": "0001093649", "assigned-sic": "2834", "irs-number": "450478605"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-118341", "film-number": "04984466"}, "business-address": {"street1": "60 HAMPSHIRE STREET", "street2": ".", "city": "CAMBRIDGE", "state": "MA", "zip": "02139", "phone": "(617) 250-3100"}, "mail-address": {"street1": "60 HAMPSHIRE STREET", "city": "CAMBRIDGE", "state": "MA", "zip": "02139"}, "former-company": {"former-conformed-name": "NOVIRIO PHARMACEUTICALS LTD", "date-changed": "19990820"}}
text: IDENIX PHARMACEUTICALS, INC.
  Table of Contents
  As filed with the
  Securities and Exchange Commission on August 18, 2004
  Registration No. 333-_____
  SECURITIES AND EXCHANGE COMMISSION
  Washington, D.C. 20549
  FORM S-8
  REGISTRATION STATEMENT UNDER
  THE SECURITIES ACT OF 1933
  Idenix Pharmaceuticals, Inc.
  (Exact Name of Registrant as Specified in Its Charter)
  Delaware
  45-0478605
  (State or Other Jurisdiction of Incorporation
  or Organization)
  (I.R.S. Employer
  Identification No.)
  60 Hampshire Street
  Cambridge, MA
  02139
  (Address of Principal Executive Offices)
  (Zip Code)
  1998 Equity Incentive Plan
  2004 Stock Incentive Plan
  (Full Title of the Plan)
  Jean-Pierre Sommadossi
  President and Chief Executive Officer
  Idenix Pharmaceuticals, Inc.
  60 Hampshire Street
  Cambridge, MA 02139
  (Name and Address of Agent For Service)
  617-995-9800
  (Telephone Number, Including Area Code, of Agent For Service)
  CALCULATION OF REGISTRATION FEE
  Proposed Maximum
  Proposed Maximum
  Title of Securities
  Amount to be
  Offering Price Per
  Aggregate Offering
  Amount of
  to be Registered
  Registered(1)
  Share
  Price
  Registration Fee
  Common Stock,
  $0.001 par value per share
  3,962,335 shares(2)
  $8.495(3)
  $33,660,035.825(3)
  $4,264.73
  (1)
  In accordance with Rule 416 under the Securities Act of 1933, as amended,
  this registration statement shall be deemed to cover any additional
  securities that may from time to time be offered or issued to prevent
  dilution resulting from stock splits, stock dividends or similar
  transactions.
  (2)
  Consists of (i) 3,067,395 shares subject to options outstanding under
  the 1998 Equity Incentive Plan, (ii) 94,940 shares issuable under the
  1998 Equity Incentive Plan; and (iii) 800,000 shares issuable under the
  2004 Stock Incentive Plan.
  (3)
  Estimated solely for the purpose of calculating the registration fee
  pursuant to Rules 457(c) and 457(h) of the Securities Act of 1933, as
  amended, and based upon the average of the high and low prices of the
  Registrant's Common Stock as reported on the Nasdaq National Market on
  August 11, 2004.
  TABLE OF CONTENTS
  PART I
  Item 1. Plan Information.
  Item 2. Registrant Information and Employee Plan Annual Information.
  PART II
  Item 3. Incorporation of Documents by Reference.
  Item 4. Description of Securities.
  Item 5. Interests of Named Experts and Counsel.
  Item 6. Indemnification of Directors and Officers.
  Item 7. Exemption from Registration Claimed.
  Item 8. Exhibits.
  Item 9. Undertakings.
  SIGNATURES
  INDEX TO EXHIBITS
  EX-5 OPINION OF WILMER CUTLER PICKERING HALE AND DORR LLP
  EX-23.2 CONSENT OF PRICEWATERHOUSECOOPERS LLP
  Table of Contents
  PART I
  INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS
  Item 1. Plan Information.
  The information required by Item 1 is included in documents sent or given
  to participants in the plans covered by this registration statement pursuant to
  Rule 428(b)(1) of the Securities Act of 1933, as amended (the "Securities
  Act").
  Item 2. Registrant Information and Employee Plan Annual Information.
  The written statement required by Item 2 is included in documents sent or
  given to participants in the plans covered by this registration statement
  pursuant to Rule 428(b)(1) of the Securities Act.
  PART II
  INFORMATION REQUIRED IN THE REGISTRATION STATEMENT
  Item 3. Incorporation of Documents by Reference.
  The registrant is subject to the informational and reporting requirements
  of Sections 13(a), 14, and 15(d) of the Securities Exchange Act of 1934, as
  amended (the "Exchange Act"), and in accordance therewith files reports, proxy
  statements and other information with the Securities and Exchange Commission
  (the "Commission"). The following documents, which are on file with the
  Commission, are incorporated in this registration statement by reference:
  (a) The registrant's latest annual report filed pursuant to Section 13(a)
  or 15(d) of the Exchange Act or the latest prospectus filed pursuant to Rule
  424(b) under the Securities Act that contains audited financial statements for
  the registrant's latest fiscal year for which such statements have been filed.
  (b) All other reports filed pursuant to Section 13(a) or 15(d) of the
  Exchange Act since the end of the fiscal year covered by the document referred
  to in (a) above.
  (c) The description of the securities contained in the registrant's
  registration statements on Form 8-A filed under the Exchange Act, including any
  amendment or report filed for the purpose of updating such description.
  All documents subsequently filed by the registrant pursuant to Sections
  13(a), 13(c), 14 and 15(d) of the Exchange Act, prior to the filing of a
  post-effective amendment which indicates that all securities offered hereby
  have been sold or which deregisters all securities then remaining unsold, shall
  be deemed to be incorporated by reference in this registration statement and to
  be part hereof from the date of the filing of such documents. Any statement
  contained in a document incorporated or deemed to be incorporated by reference
  herein shall be deemed to be modified or superseded for the purposes of this
  registration statement to the extent that a statement contained herein or in
  any other subsequently filed document which also is or is deemed to be
  incorporated by reference herein modifies or supersedes such statement. Any
  statement so modified or superseded shall not be deemed, except as so modified
  or superseded, to constitute a part of this registration statement.
  Item 4. Description of Securities.
  Not applicable.
  -1-
  Table of Contents
  Item 5. Interests of Named Experts and Counsel.
  Wilmer Cutler Pickering Hale and Dorr LLP has opined as to the legality of
  the securities being offered by this registration statement. Ambassador
  Charlene Barshefsky, a member of the registrant's board of directors, is a
  partner in the law firm of Wilmer Cutler Pickering Hale and Dorr LLP and
  beneficially owns 61,343 shares of the registrant's common stock.
  Item 6. Indemnification of Directors and Officers.
  Section 145 of the General Corporation Law of the State of Delaware
  permits a corporation, under specified circumstances, to indemnify its
  directors, officers, employees or agents against expenses (including attorney's
  fees), judgments, fines and amounts paid in settlements actually and reasonably
  incurred by them in connection with any action, suit or proceeding brought by
  third parties by reason of the fact that they were or are directors, officers,
  employees or agents of the corporation, if such directors, officers, employees
  or agents acted in good faith and in a manner they reasonably believed to be in
  or not opposed to the best interests of the corporation and, with respect to
  any criminal action or proceeding, had no reason to believe their conduct was
  unlawful. In a derivative action, i.e., one by or in the right of the
  corporation, indemnification may be made only for expenses actually or
  reasonably incurred by directors, officers, employees or agents in connection
  with the defense or settlement of an action or suit, and only with respect to a
  matter as to which they shall have acted in good faith and in a manner they
  reasonably believed to be in or not opposed to the best interests of the
  corporation, except that no indemnification shall be made if such person shall
  have been adjudged liable to the corporation, unless and only to the extent
  that the court in which the action or suit was brought shall determine upon
  application that the defendant directors, officers, employees or agents are
  fairly and reasonably entitled to indemnify for such expenses despite such
  adjudication of liability.
  The registrant's restated certificate of incorporation, as amended, states
  that the registrant's directors will not have personal liability for monetary
  damages for any breach of fiduciary duty as a director, except to the extent
  that the General Corporation Law of the State of Delaware prohibits the
  elimination or limitation of liability of directors for breaches of fiduciary
  duty.
  The registrant also carries liability insurance covering each of its directors and officers.
  Item 7. Exemption from Registration Claimed.
  Not applicable.
  Item 8. Exhibits.
  The Exhibit Index immediately preceding the exhibits is incorporated herein by reference.
  Item 9. Undertakings.
  1.
  Item
  512(a)
  of Regulation S-K
  . The undersigned registrant hereby
  undertakes:
  (1) To file, during any period in which offers or sales are being
  made, a post-effective amendment to this registration statement:
  (i) To include any prospectus required by Section 10(a)(3) of the
  Securities Act;
  -2-
  Table of Contents
  (ii) To reflect in the prospectus any facts or events arising after
  the effective date of the registration statement (or the most recent
  post-effective amendment thereof) which, individually or in the
  aggregate, represent a fundamental change in the information set forth in
  the registration statement; and
  (iii) To include any material information with respect to the plan
  of distribution not previously disclosed in the registration statement or
  any material change to such information in the registration statement;
  provided, however,
  that paragraphs (i) and (ii) do not apply if the
  information required to be included in a post-effective amendment by
  those paragraphs is contained in periodic reports filed with or furnished
  to the Commission by the registrant pursuant to Section 13 or Section
  15(d) of the Exchange Act that are incorporated by reference in the
  registration statement.
  (2) That, for the purpose of determining any liability under the
  Securities Act, each such post-effective amendment shall be deemed to be
  a new registration statement relating to the securities offered therein,
  and the offering of such securities at that time shall be deemed to be
  the initial
  bona fide
  offering thereof.
  (3) To remove from registration by means of a post-effective
  amendment any of the securities being registered which remain unsold at
  the termination of the offering.
  2.
  Item
  512(b)
  of Regulation S-K
  . The undersigned registrant hereby
  undertakes that, for purposes of determining any liability under the Securities
  Act, each filing of the registrant's annual report pursuant to Section 13(a) or
  Section 15(d) of the Exchange Act that is incorporated by reference in the
  registration statement shall be deemed to be a new registration statement
  relating to the securities offered therein, and the offering of such securities
  at that time shall be deemed to be the initial
  bona fide
  offering thereof.
  3.
  Item
  512(h)
  of Regulation S-K
  . Insofar as indemnification for
  liabilities arising under the Securities Act may be permitted to directors,
  officers and controlling persons of the registrant pursuant to the foregoing
  provisions, or otherwise, the registrant has been advised that in the opinion
  of the Securities and Exchange Commission such indemnification is against
  public policy as expressed in the Securities Act and is, therefore,
  unenforceable. In the event that a claim for indemnification against such
  liabilities (other than the payment by the registrant of expenses incurred or
  paid by a director, officer or controlling person of the registrant in the
  successful defense of any action, suit or proceeding) is asserted by such
  director, officer or controlling person in connection with the securities being
  registered, the registrant will, unless in the opinion of its counsel the
  matter has been settled by controlling precedent, submit to a court of
  appropriate jurisdiction the question whether such indemnification by it is
  against public policy as expressed in the Securities Act and will be governed
  by the final adjudication of such issue.
  -3-
  Table of Contents
  SIGNATURES
  Pursuant to the requirements of the Securities Act of 1933, the registrant
  certifies that it has reasonable grounds to believe that it meets all of the
  requirements for filing on Form S-8 and has duly caused this registration
  statement to be signed on its behalf by the undersigned, thereunto duly
  authorized, in the City of Cambridge, Commonwealth of Massachusetts, on this
  18th day of August, 2004.
  IDENIX PHARMACEUTICALS, INC.
  By:
  /s/ Jean-Pierre Sommadossi
  Jean-Pierre Sommadossi
  President and Chief Executive Officer
  POWER OF ATTORNEY AND SIGNATURES
  We, the undersigned officers and directors of Idenix Pharmaceuticals,
  Inc., hereby severally constitute and appoint Jean-Pierre Sommadossi and Andrea
  J. Corcoran, and each of them singly, our true and lawful attorneys with full
  power to them, and each of them singly, to sign for us and in our names in the
  capacities indicated below, the registration statement on Form S-8 filed
  herewith and any and all subsequent amendments to said registration statement,
  and generally to do all such things in our names and on our behalf in our
  capacities as officers and directors to enable Idenix Pharmaceuticals, Inc. to
  comply with the provisions of the Securities Act of 1933, as amended, and all
  requirements of the Securities and Exchange Commission, hereby ratifying and
  confirming our signatures as they may be signed by our said attorneys, or any
  of them, to said registration statement and any and all amendments thereto.
  Pursuant to the requirements of the Securities Act of 1933, this
  registration statement has been signed by the following persons in the
  capacities and on the dates indicated.
  Signature
  Title
  Date
  /s/ Jean-Pierre Sommadossi
  Jean-Pierre Sommadossi
  President and Chief
  Executive Officer
  (Principal executive
  officer)
  August 18, 2004
  /s/ David A. Arkowitz
  David A. Arkowitz
  Chief Financial Officer
  and Treasurer (Principal
  financial and accounting
  officer)
  August 18, 2004
  /s/ Charlene Barshefsky
  Charlene Barshefsky
  Director
  August 18, 2004
  /s/ Charles W. Cramb
  Charles W. Cramb
  Director
  August 18, 2004
  /s/ Thomas Ebeling
  Thomas Ebeling
  Director
  August 18, 2004
  -4-
  Table of Contents
  /s/ Ansbert Gadicke
  Ansbert Gadicke
  Director
  August 18, 2004
  /s/ Wayne T. Hockmeyer
  Wayne T. Hockmeyer
  Director
  August 18, 2004
  /s/ Thomas R. Hodgson
  Thomas R. Hodgson
  Director
  August 18, 2004
  /s/ Robert E. Pelzer
  Robert E. Pelzer
  Director
  August 18, 2004
  /s/ Denise Pollard-Knight
  Denise Pollard-Knight
  Director
  August 18, 2004
  -5-
  Table of Contents
  INDEX TO EXHIBITS
  Number
  Description
  4.1(1)
  Restated Certificate of Incorporation of the Registrant, as amended
  4.2(1)
  Amended and Restated By-Laws of the Registrant
  5
  Opinion of Wilmer Cutler Pickering Hale and Dorr LLP, counsel to
  the Registrant
  23.1
  Consent of Wilmer Cutler Pickering Hale and Dorr LLP
  (included in Exhibit 5)
  23.2
  Consent of PricewaterhouseCoopers LLP
  24
  Power of attorney (included on the signature pages of this
  registration statement)
  (1)
  Previously filed with the Securities and Exchange Commission as an
  Exhibit to the Registrant's Registration Statement on Form S-1, as amended
  (File No. 333-111157) and incorporated herein by reference.