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)
                                                                   
                                   1987 STOCK 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,      439,650         $22.25 (1)     $9,782,212.50 (1)   $3,374
  $.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 1987 Stock 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 pos]t-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.
  
       Signature                      Title                             Date
                                                                     
  /s/ Lowell B. Hawkinson             Chairman of the Board,         May 15, 1996
  - -----------------------------        Chief Executive 
  Lowell B. Hawkinson                  Officer, Treasurer            
                                       and Secretary                 
                                       (Principal Executive          
                                        Officer)                     
                                                
                                                                     
  /s/ Robert L. Moore                 President and                  May 15, 1996
  - ------------------------------       Director                         
  Robert L. Moore, Ph.D.                                   
                                       
                                
  /s/ Stephen N. Gregorio             Vice President,                May 15, 1996
  - ------------------------------       Finance and Chief   
  Stephen N. Gregorio                  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-
  <PAGE>   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-
metadata_documents: [{"type": "S-8", "sequence": "1", "description": "GENSYM COPRORATION", "secsgml_size_bytes": 21909}]
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": "333-03861", "film-number": "96568526"}, "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)
                                                                   
                                   1987 STOCK 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,      439,650         $22.25 (1)     $9,782,212.50 (1)   $3,374
  $.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 1987 Stock 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 pos]t-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
  - -----------------------------        Chief Executive 
  Lowell B. Hawkinson                  Officer, Treasurer            
                                       and Secretary                 
                                       (Principal Executive          
                                        Officer)                     
                                                
                                                                     
  /s/ Robert L. Moore                 President and                  May 15, 1996
  - ------------------------------       Director                         
  Robert L. Moore, Ph.D.                                   
                                       
                                
  /s/ Stephen N. Gregorio             Vice President,                May 15, 1996
  - ------------------------------       Finance and Chief   
  Stephen N. Gregorio                  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-