content: <PAGE>   1
                  As filed with the Securities and Exchange Commission
                                     on May 16, 1996
  
                                                   Registration No. 333-
  ================================================================================
  
                         SECURITIES AND EXCHANGE COMMISSION
                               Washington, D.C. 20549
  
                                      FORM S-8
  
                            REGISTRATION STATEMENT UNDER
                             THE SECURITIES ACT OF 1933
  
                                 Gensym Corporation
               (Exact name of registrant as specified in its charter)
  
                   Delaware                                04-2932756
           (State or other jurisdiction of             (I.R.S. Employer
           incorporation or organization)              Identification Number)
  
              125 CambridgePark Drive
              Cambridge, Massachusetts                        02140
        (Address of Principal Executive Offices)            (Zip Code)
  
                               1994 STOCK OPTION PLAN
                              (Full title of the Plan)
  
                               Mr. Lowell B. Hawkinson
                    Chairman of the Board and Chief Executive Officer
                                 Gensym Corporation
                               125 CambridgePark Drive
                           Cambridge, Massachusetts 02140
                       (Name and address of agent for service)
  
                                     (617) 547-2500
              (Telephone number, including area code, of agent for service)
  ================================================================================
  
                           CALCULATION OF REGISTRATION FEE
  <TABLE>
  <CAPTION>
                                       Proposed        Proposed
           Title of                    maximum         maximum
           securities     Amount       offering        aggregate      Amount of
           to be          to be        price           offering       registration
           registered     registered   per share       price          fee
           ----------     ----------   ---------       ---------      ------------
  <S>                      <C>         <C>          <C>                  <C>
           Common Stock,   534,750     $22.25(1)    $11,898,187.50(1)    $4,103
           $.01 par        shares                 
           value per
           share
  </TABLE>
  
  
           ------------------------------------------------------------------
           (1)  Estimated solely for the purpose of calculating the registration
                fee, and based upon the average of the high and low prices of the
                Registrant's Common Stock as reported by the Nasdaq National
                Market on May 10, 1996 in accordance with Rules 457(c) and
                457(h) of the Securities Act of 1933.
  ================================================================================
  <PAGE>   2
           PART I.  INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS
  
                     The information required by Part I of Form S-8 is included in
           documents sent or given to participants in the 1994 Stock Option Plan
           of Gensym Corporation, a Delaware corporation (the "Registrant")
           pursuant to Rule 428(b)(1) of the Securities Act of 1933, as amended
           (the "Securities Act").
  
           PART II.  INFORMATION REQUIRED IN THE REGISTRATION STATEMENT
  
                Item 3.  Incorporation of Certain Documents by Reference
  
                     The following documents, which are filed with the Securities
           and Exchange Commission (the "Commission"), are incorporated in this
           Registration Statement by reference:
  
                     (1) The Registrant's latest annual report filed pursuant to
                Section 13(a) or 15(d) of the Securities Exchange Act of 1934, as
                amended (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.
  
                     (2) All other reports filed pursuant to Sections 13(a) or
                15(d) of the Exchange Act since the end of the fiscal year covered
                by the annual reports or the prospectus referred to in (1) above.
  
                     (3) The description of the common stock of the Registrant,
                $.01 par value per share (the "Common Stock"), contained in a
                registration statement 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
           shares of Common Stock offered hereby have been sold or which
           deregisters all shares of Common Stock then remaining unsold, shall be
           deemed to be incorporated by reference herein and to be part hereof
           from the date of the filing of such documents.
  
                Item 4.  Description of Securities
  
                     Not applicable.
  
                                         -2-
  <PAGE>   3
                Item 5.  Interests of Named Experts and Counsel
  
                The legality of the Common Stock being offered by this
           Registration Statement will be passed upon by Hale and Dorr (a
           partnership which includes professional corporations), 60 State Street,
           Boston, Massachusetts 02109. As of the date of this Registration 
           Statement, H&D Investments I, a partnership comprised of certain
           partners of Hale and Dorr, owns 6,784 shares of the Registrant's
           Common Stock.
  
                Item 6.  Indemnification
  
                Section 145 of the Delaware General Corporation Law provides that
           a corporation has the power to indemnify a director, officer, employee
           or agent of the corporation and certain other persons serving at the
           request of the corporation in related capacities against amounts paid
           and expenses incurred in connection with an action or proceeding to
           which such person is or is threatened to be made a party by reasons of
           such position, if such person shall have acted in good faith and in a
           manner believed to be in or not opposed to the best interests of the
           corporation, and, in any criminal proceeding, if such person had no
           reasonable cause to believe his or her conduct was unlawful; provided
           that, in the case of actions brought by or in the right of the
           corporation, no indemnification shall be made with respect to any
           matter as to which such person shall have been adjudged to be liable to
           the corporation unless and only to the extent that the adjudicating
           court determines that such indemnification is proper under the
           circumstances.
  
                Article EIGHTH of the Registrant's Certificate of Incorporation
           provides that, except to the extent that the General Corporation Law of
           Delaware prohibits the elimination or limitation of liability of
           directors for breach of fiduciary duty, no director of the Registrant
           shall be personally liable to the Registrant or its stockholders for
           any monetary damages for any breach of fiduciary duty as a director.
  
                Article NINTH of the Registrant's Certificate of Incorporation
           provides that a director or officer of the Registrant (a) shall be
           indemnified by the Registrant against all expenses (including
           attorneys' fees), judgments, fines and amounts paid in settlement
           reasonably incurred in connection with any litigation or other legal
           proceeding (other than an action by or in the right of the Registrant)
           brought against such director or officer by virtue of his position as a
           director or officer of the Registrant if such director or officer acted
           in good faith and in a manner he reasonably believed to be in, or not
           opposed to, the best interests of the Registrant, and, with respect to
           any criminal action or proceeding, had no reasonable cause to believe
           his conduct was unlawful and (b) shall be indemnified by the Registrant
           against expenses (including attorneys' fees) and amounts paid in
           settlement reasonably incurred in connection with any action by or in
           the right of the Registrant by virtue of his position as a director or
           officer of the Registrant if such director or officer of the Registrant
           acted in good faith and in a manner reasonably believed to be in or not
           opposed to the best interests of the Registrant, except that no
           indemnification shall
  
                                         -3-
  <PAGE>   4
           be made with respect to any matter as to which such director or officer
           shall have been adjudged to be liable to the Registrant, unless and
           only to the extent that a court determines that, despite such
           adjudication but in view of all of the circumstances of the case, such
           person is fairly and reasonably entitled to indemnification for such
           expenses as the court deems proper. Notwithstanding the foregoing, to
           the extent that a director or officer has been successful, on the
           merits or otherwise, such person shall be indemnified against all
           expenses (including attorneys' fees) reasonably incurred by such person
           in connection therewith. Expenses incurred in defending a civil or
           criminal action, suit or proceeding shall be advanced by the Registrant
           to a director or officer, at such person's request, upon receipt of an
           undertaking by the director or officer to repay the amount if it is
           ultimately determined that such person is not entitled to
           indemnification.
  
                Indemnification is required to be made unless the Registrant
           determines that the applicable standard of conduct required for
           indemnification has not been met. In the event of a determination by
           the Registrant that the director or officer did not meet the applicable
           standard of conduct required for indemnification, or if the Registrant
           fails to make an indemnification payment within 60 days after such
           payment is claimed by such person, such person is permitted to petition
           a court to make an independent determination as to whether such person
           is entitled to indemnification. As a condition precedent to the right
           of indemnification, the director or officer must give the Registrant
           notice of the action for which indemnity is sought and the Registrant
           has the right to participate in such action or assume the defense
           thereof.
  
                Article NINTH of the Registrant's Certificate of Incorporation
           further provides that the indemnification provided therein is not
           exclusive, and provides that in the event that the Delaware General
           Corporation Law is amended to expand the indemnification permitted to
           directors or officers, the Registrant must indemnify those persons to
           the fullest extent permitted by such law as so amended.
  
                The Registrant carries a general liability insurance policy which
           covers certain liabilities of directors and officers of the Registrant
           arising out of claims based on acts or omissions in their capacity as
           directors or officers.
  
                Item 7.  Exemption from Registration Claimed
  
                     Not applicable.
  
                                         -4-
  <PAGE>   5
                Item 8.  Exhibits
  
                     The Exhibit Index immediately preceding the exhibits is
           incorporated herein by reference.
  
                Item 9.  Undertakings
  
                1.   The 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;
  
                   (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 Registration Statement is on Form S-3 or Form S-8, and the
                information required to be included in a post-effective amendment
                by those paragraphs is contained in periodic reports filed 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.  The 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
  
                                         -5-
  <PAGE>   6
           Section 15(d) of the Exchange Act (and, where applicable, each filing
           of an employee benefit plan's annual report pursuant to 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. 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
           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.
  
                                         -6-
  <PAGE>   7
                                     SIGNATURES
  
                Pursuant to the requirements of the Securities Act, 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 the 15th day of May, 1996.
  
                                              GENSYM CORPORATION
  
  
  
  
                                              By: /S/ Lowell B. Hawkinson
                                                 ------------------------------
                                                 Lowell B. Hawkinson
                                                 Chairman of the Board and
                                                 Chief Executive Officer
  
                                  POWER OF ATTORNEY
  
                We, the undersigned officers and directors of Gensym Corporation,
           hereby severally constitute and appoint Lowell B. Hawkinson, Robert L.
           Moore and Stephen N. Gregorio, 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 and in our capacities
           as officers and directors to enable Gensym Corporation 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.
  
                                         -7-
  <PAGE>   8
       Pursuant to the requirements of the Securities Act, this Registration
  Statement has been signed below by the following persons in the capacities and
  on the dates indicated.
  <TABLE>
  <CAPTION>
                Signature                Title                       Date
                ---------                -----                       ----
  <S>                                    <C>                      <C>  
  /S/ Lowell B. Hawkinson           
  - ---------------------------------      Chairman of the Board,   May 15, 1996
      Lowell B. Hawkinson                 Chief Executive
                                          Officer, Treasurer
                                          and Secretary
                                          (Principal Executive
                                           Officer)
  /S/ Robert L. Moore
  - ---------------------------------      President and            May 15, 1996
      Robert L. Moore, Ph.D.              Director
  
  /S/ Stephen N. Gregorio
  - ---------------------------------      Vice President,          May 15, 1996
      Stephen N. Gregorio                 Finance and Chief
                                          Financial Officer
                                          (Principal Financial
                                           and Accounting
                                           Officer)
  /S/ John A. Shane
  - ---------------------------------      Director                 May 15, 1996
      John A. Shane
  
  /S/ Edward Fredkin
  - ---------------------------------      Director                 May 15, 1996
      Edward Fredkin
  
  /S/ Theodore G. Johnson
  - ---------------------------------      Director                 May 15, 1996
      Theodore G. Johnson
  
  /S/ Nancy E. Pfund
  - ---------------------------------      Director                 May 15, 1996
      Nancy E. Pfund
      
  </TABLE>
  
                                           -8-
  <PAGE>   9
                                    Exhibit Index
  
  <TABLE>
  <CAPTION>
  
      Exhibit
      Number       Description                                         
      ------       -----------                                         
  
  <S>    <C>       <C>                                                 
         4.1 (1)   Amended and Restated Certificate of Incorporation   
                   of the Registrant
  
         4.2 (1)   Amended and Restated By-Laws of the Registrant     
  
         4.3 (1)   Specimen Stock Certificate of Common Stock         
                   of the Registrant
  
         5         Opinion of Hale and Dorr
  
        23.1       Consent of Hale and Dorr (included in Exhibit 5)
  
        23.2       Consent of Arthur Andersen LLP
  
        24         Power of Attorney (included on the signature
                   page of this Registration Statement)
  </TABLE>
  
           ----------------------
           (1)  Incorporated herein by reference to the Registrant's
                Registration Statement on Form S-1 (File No. 33-80727) filed
                on December 21, 1995.
  
                                         -9-
metadata_documents: [{"type": "S-8", "sequence": "1", "description": "GENSYM CORPORATION", "secsgml_size_bytes": 21690}]
metadata_filer: {"company-data": {"conformed-name": "GENSYM CORP", "cik": "0001005387", "assigned-sic": "7372", "irs-number": "042932756", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-03855", "film-number": "96568522"}, "business-address": {"street1": "125 CAMBRIDGE PARK DR", "city": "CAMBRIDGE", "state": "MA", "zip": "02140", "phone": "6175472500"}, "mail-address": {"street1": "125 CAMBRIDGE PARK DR", "city": "CAMBRIDGE", "state": "MA", "zip": "02140"}}
text: 1
                  As filed with the Securities and Exchange Commission
                                     on May 16, 1996
  
                                                   Registration No. 333-
  ================================================================================
  
                         SECURITIES AND EXCHANGE COMMISSION
                               Washington, D.C. 20549
  
                                      FORM S-8
  
                            REGISTRATION STATEMENT UNDER
                             THE SECURITIES ACT OF 1933
  
                                 Gensym Corporation
               (Exact name of registrant as specified in its charter)
  
                   Delaware                                04-2932756
           (State or other jurisdiction of             (I.R.S. Employer
           incorporation or organization)              Identification Number)
  
              125 CambridgePark Drive
              Cambridge, Massachusetts                        02140
        (Address of Principal Executive Offices)            (Zip Code)
  
                               1994 STOCK OPTION PLAN
                              (Full title of the Plan)
  
                               Mr. Lowell B. Hawkinson
                    Chairman of the Board and Chief Executive Officer
                                 Gensym Corporation
                               125 CambridgePark Drive
                           Cambridge, Massachusetts 02140
                       (Name and address of agent for service)
  
                                     (617) 547-2500
              (Telephone number, including area code, of agent for service)
  ================================================================================
  
                           CALCULATION OF REGISTRATION FEE
  Proposed        Proposed
           Title of                    maximum         maximum
           securities     Amount       offering        aggregate      Amount of
           to be          to be        price           offering       registration
           registered     registered   per share       price          fee
           ----------     ----------   ---------       ---------      ------------
  Common Stock,   534,750     $22.25(1)    $11,898,187.50(1)    $4,103
           $.01 par        shares                 
           value per
           share
  ------------------------------------------------------------------
           (1)  Estimated solely for the purpose of calculating the registration
                fee, and based upon the average of the high and low prices of the
                Registrant's Common Stock as reported by the Nasdaq National
                Market on May 10, 1996 in accordance with Rules 457(c) and
                457(h) of the Securities Act of 1933.
  ================================================================================
  2
           PART I.  INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS
  
                     The information required by Part I of Form S-8 is included in
           documents sent or given to participants in the 1994 Stock Option Plan
           of Gensym Corporation, a Delaware corporation (the "Registrant")
           pursuant to Rule 428(b)(1) of the Securities Act of 1933, as amended
           (the "Securities Act").
  
           PART II.  INFORMATION REQUIRED IN THE REGISTRATION STATEMENT
  
                Item 3.  Incorporation of Certain Documents by Reference
  
                     The following documents, which are filed with the Securities
           and Exchange Commission (the "Commission"), are incorporated in this
           Registration Statement by reference:
  
                     (1) The Registrant's latest annual report filed pursuant to
                Section 13(a) or 15(d) of the Securities Exchange Act of 1934, as
                amended (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.
  
                     (2) All other reports filed pursuant to Sections 13(a) or
                15(d) of the Exchange Act since the end of the fiscal year covered
                by the annual reports or the prospectus referred to in (1) above.
  
                     (3) The description of the common stock of the Registrant,
                $.01 par value per share (the "Common Stock"), contained in a
                registration statement 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
           shares of Common Stock offered hereby have been sold or which
           deregisters all shares of Common Stock then remaining unsold, shall be
           deemed to be incorporated by reference herein and to be part hereof
           from the date of the filing of such documents.
  
                Item 4.  Description of Securities
  
                     Not applicable.
  
                                         -2-
  3
                Item 5.  Interests of Named Experts and Counsel
  
                The legality of the Common Stock being offered by this
           Registration Statement will be passed upon by Hale and Dorr (a
           partnership which includes professional corporations), 60 State Street,
           Boston, Massachusetts 02109. As of the date of this Registration 
           Statement, H&D Investments I, a partnership comprised of certain
           partners of Hale and Dorr, owns 6,784 shares of the Registrant's
           Common Stock.
  
                Item 6.  Indemnification
  
                Section 145 of the Delaware General Corporation Law provides that
           a corporation has the power to indemnify a director, officer, employee
           or agent of the corporation and certain other persons serving at the
           request of the corporation in related capacities against amounts paid
           and expenses incurred in connection with an action or proceeding to
           which such person is or is threatened to be made a party by reasons of
           such position, if such person shall have acted in good faith and in a
           manner believed to be in or not opposed to the best interests of the
           corporation, and, in any criminal proceeding, if such person had no
           reasonable cause to believe his or her conduct was unlawful; provided
           that, in the case of actions brought by or in the right of the
           corporation, no indemnification shall be made with respect to any
           matter as to which such person shall have been adjudged to be liable to
           the corporation unless and only to the extent that the adjudicating
           court determines that such indemnification is proper under the
           circumstances.
  
                Article EIGHTH of the Registrant's Certificate of Incorporation
           provides that, except to the extent that the General Corporation Law of
           Delaware prohibits the elimination or limitation of liability of
           directors for breach of fiduciary duty, no director of the Registrant
           shall be personally liable to the Registrant or its stockholders for
           any monetary damages for any breach of fiduciary duty as a director.
  
                Article NINTH of the Registrant's Certificate of Incorporation
           provides that a director or officer of the Registrant (a) shall be
           indemnified by the Registrant against all expenses (including
           attorneys' fees), judgments, fines and amounts paid in settlement
           reasonably incurred in connection with any litigation or other legal
           proceeding (other than an action by or in the right of the Registrant)
           brought against such director or officer by virtue of his position as a
           director or officer of the Registrant if such director or officer acted
           in good faith and in a manner he reasonably believed to be in, or not
           opposed to, the best interests of the Registrant, and, with respect to
           any criminal action or proceeding, had no reasonable cause to believe
           his conduct was unlawful and (b) shall be indemnified by the Registrant
           against expenses (including attorneys' fees) and amounts paid in
           settlement reasonably incurred in connection with any action by or in
           the right of the Registrant by virtue of his position as a director or
           officer of the Registrant if such director or officer of the Registrant
           acted in good faith and in a manner reasonably believed to be in or not
           opposed to the best interests of the Registrant, except that no
           indemnification shall
  
                                         -3-
  4
           be made with respect to any matter as to which such director or officer
           shall have been adjudged to be liable to the Registrant, unless and
           only to the extent that a court determines that, despite such
           adjudication but in view of all of the circumstances of the case, such
           person is fairly and reasonably entitled to indemnification for such
           expenses as the court deems proper. Notwithstanding the foregoing, to
           the extent that a director or officer has been successful, on the
           merits or otherwise, such person shall be indemnified against all
           expenses (including attorneys' fees) reasonably incurred by such person
           in connection therewith. Expenses incurred in defending a civil or
           criminal action, suit or proceeding shall be advanced by the Registrant
           to a director or officer, at such person's request, upon receipt of an
           undertaking by the director or officer to repay the amount if it is
           ultimately determined that such person is not entitled to
           indemnification.
  
                Indemnification is required to be made unless the Registrant
           determines that the applicable standard of conduct required for
           indemnification has not been met. In the event of a determination by
           the Registrant that the director or officer did not meet the applicable
           standard of conduct required for indemnification, or if the Registrant
           fails to make an indemnification payment within 60 days after such
           payment is claimed by such person, such person is permitted to petition
           a court to make an independent determination as to whether such person
           is entitled to indemnification. As a condition precedent to the right
           of indemnification, the director or officer must give the Registrant
           notice of the action for which indemnity is sought and the Registrant
           has the right to participate in such action or assume the defense
           thereof.
  
                Article NINTH of the Registrant's Certificate of Incorporation
           further provides that the indemnification provided therein is not
           exclusive, and provides that in the event that the Delaware General
           Corporation Law is amended to expand the indemnification permitted to
           directors or officers, the Registrant must indemnify those persons to
           the fullest extent permitted by such law as so amended.
  
                The Registrant carries a general liability insurance policy which
           covers certain liabilities of directors and officers of the Registrant
           arising out of claims based on acts or omissions in their capacity as
           directors or officers.
  
                Item 7.  Exemption from Registration Claimed
  
                     Not applicable.
  
                                         -4-
  5
                Item 8.  Exhibits
  
                     The Exhibit Index immediately preceding the exhibits is
           incorporated herein by reference.
  
                Item 9.  Undertakings
  
                1.   The 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;
  
                   (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 Registration Statement is on Form S-3 or Form S-8, and the
                information required to be included in a post-effective amendment
                by those paragraphs is contained in periodic reports filed 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.  The 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
  
                                         -5-
  6
           Section 15(d) of the Exchange Act (and, where applicable, each filing
           of an employee benefit plan's annual report pursuant to 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. 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
           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.
  
                                         -6-
  7
                                     SIGNATURES
  
                Pursuant to the requirements of the Securities Act, 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 the 15th day of May, 1996.
  
                                              GENSYM CORPORATION
  
                                              By: /S/ Lowell B. Hawkinson
                                                 ------------------------------
                                                 Lowell B. Hawkinson
                                                 Chairman of the Board and
                                                 Chief Executive Officer
  
                                  POWER OF ATTORNEY
  
                We, the undersigned officers and directors of Gensym Corporation,
           hereby severally constitute and appoint Lowell B. Hawkinson, Robert L.
           Moore and Stephen N. Gregorio, 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 and in our capacities
           as officers and directors to enable Gensym Corporation 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.
  
                                         -7-
  8
       Pursuant to the requirements of the Securities Act, this Registration
  Statement has been signed below by the following persons in the capacities and
  on the dates indicated.
  Signature                Title                       Date
                ---------                -----                       ----
  /S/ Lowell B. Hawkinson           
  - ---------------------------------      Chairman of the Board,   May 15, 1996
      Lowell B. Hawkinson                 Chief Executive
                                          Officer, Treasurer
                                          and Secretary
                                          (Principal Executive
                                           Officer)
  /S/ Robert L. Moore
  - ---------------------------------      President and            May 15, 1996
      Robert L. Moore, Ph.D.              Director
  
  /S/ Stephen N. Gregorio
  - ---------------------------------      Vice President,          May 15, 1996
      Stephen N. Gregorio                 Finance and Chief
                                          Financial Officer
                                          (Principal Financial
                                           and Accounting
                                           Officer)
  /S/ John A. Shane
  - ---------------------------------      Director                 May 15, 1996
      John A. Shane
  
  /S/ Edward Fredkin
  - ---------------------------------      Director                 May 15, 1996
      Edward Fredkin
  
  /S/ Theodore G. Johnson
  - ---------------------------------      Director                 May 15, 1996
      Theodore G. Johnson
  
  /S/ Nancy E. Pfund
  - ---------------------------------      Director                 May 15, 1996
      Nancy E. Pfund
  -8-
  9
                                    Exhibit Index
  Exhibit
      Number       Description                                         
      ------       -----------
  4.1 (1)   Amended and Restated Certificate of Incorporation   
                   of the Registrant
  
         4.2 (1)   Amended and Restated By-Laws of the Registrant     
  
         4.3 (1)   Specimen Stock Certificate of Common Stock         
                   of the Registrant
  
         5         Opinion of Hale and Dorr
  
        23.1       Consent of Hale and Dorr (included in Exhibit 5)
  
        23.2       Consent of Arthur Andersen LLP
  
        24         Power of Attorney (included on the signature
                   page of this Registration Statement)
  ----------------------
           (1)  Incorporated herein by reference to the Registrant's
                Registration Statement on Form S-1 (File No. 33-80727) filed
                on December 21, 1995.
  
                                         -9-