UNITED STATES 
                    SECURITIES AND EXCHANGE COMMISSION 
                          Washington, D.C. 20549 
                                                                 
                                                      
                              SCHEDULE 13D 
                Under the Securities Exchange Act of 1934 
                           (Amendment No. 1)* 
                                     
                              GENSYM CORP. 
                            (Name of Issuer) 
                                     
                      Common Stock, $.01 Par Value 
                     (Title of Class of Securities) 
                                     
                                37245R107 
                             (CUSIP Number) 
                                     
       Austin W. Marxe, 153 East 53rd Street, New York, NY  10022 

                             (212) 832-5300 
              (Name, Address and Telephone Number of Person 
            Authorized to Receive Notices and Communications) 
                                     
                                     
                             March 16, 1999 
             (Date of Event Which Requires Filing Statement) 
                                     
If the filing person has previously filed a statement on Schedule
13G to report the acquisition which is the 
subject of this Schedule 13D, and is filing this schedule because
of S240.13d-(e), 240.13d-1(f) or 240.13d-(g), 
check the following box  . 
 
Note: Six copies of this statement, including all exhibits,
should be filed with the Commission.  See 
S240.13d-7(b) for other parties to whom copies are to be sent. 
 
*The remainder of this cover page shall be filled out for a
reporting person's initial filing on this form with 
respect to the subject class of securities, and for any
subsequent amendment containing information which 
would alter the disclosures provided in a prior cover page. 
 
The information required in the remainder of the cover page shall
not be deemed to be "filed" for the 
purpose of Section 18 of the Securities Exchange Act of 1934
("Act") or otherwise subject to the liabilities of 
that section of the Act but shall be subject to all other
provisions of the Act (however, see the Notes). 

 
Item 1. Security and Issuer. 
 
   No change. 
 
Item 2. Identity and Background. 
 
   No change. 
 
Item 3. Source and Amount of Funds or Other Consideration. 
 
   No change. 
 
Item 4. Purpose of the Transaction. 
 
   On February 24, 1999, the Reporting Persons, as represented by
David Greenhouse, furnished a letter to management of the Company
for the purpose of seeking appropriate responses from such 
management with respect to the concerns of the Reporting Persons
relating to the poor performance of the Company.  In that letter,
Mr. Greenhouse demanded a reconstitution of the Board of
Directors of the Issuer as necessary to improve shareholders'
value and to respond to the interests of shareholders.  
In the absence of a satisfactory response, Special Situations
Fund III, L.P. has requested a list of the Issuer's stockholders
from the Issuer so that the Reporting Persons, as represented by
David Greenhouse, may communicate their concerns and address
appropriate action with certain of such stockholders. 
 
   The Reporting Persons, depending upon the outcome of such
communications, may or may not acquire additional Securities or
take other actions.  Alternatively, the Reporting Persons may
determine to sell or otherwise dispose of some or all of the
Securities owned by them, depending upon a continued 
assessment of such communications or other developments.  In
making any such determinations, the Reporting Persons will
consider their goals and objectives, other investment
opportunities available to them, as well as other factors. 
 
   The foregoing actions may be taken by one or more of the
Reporting Persons and, while currently there are no plans to do
so, possibly in combination with others.  The Reporting Persons
may also consider whether or not other stockholders of the
Company will become members of their group. 
 
   Except as set forth herein, the Reporting Persons have no
present plans or proposals to engage in any transactions
involving the Issuer or the Securities of the Issuer. 
 
Item 5. Interest in Securities of the Issuer. 
 
   No change. 

 
        Item 6. Contracts, Arrangements, Understandings or
Relationships with Respect to Securities 
        of the Issuer. 
 
   No change. 
 
        Item 6. Material to be Filed as Exhibits. 
 
   None.
                             SIGNATURE 
 
   After reasonable inquiry and to the best of the knowledge and
belief of the undersigned, the 
undersigned hereby certifies that the information set forth in
this Statement is true, complete and 
correct. 
 
Dated: March 17, 1999 
 
                            SPECIAL SITUATIONS FUND III, L.P. 
                            By MGP Advisers Limited Partnership, 

                                  General Partner 
 
 
 
                            By:  /s/ David M. Greenhouse         
                         
                                 David M. Greenhouse 
                                 Managing Director 
 
 
 
                            SPECIAL SITUATIONS CAYMAN FUND, L.P. 
                            By AWM Investment Company, Inc.,
                              General Partner 
 
 
                            By: /s/ David M. Greenhouse          
                              
                                 David M. Greenhouse 
                                 Managing Director 
 
 
 
                            By: /s/ Austin W. Marxe              
                                 
                                                                 
                              Austin W. Marxe, individually 
 
 
                            By: /s/ David M. Greenhouse          
                             
                                                                 
                              David M. Greenhouse, individually