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                                  EXHIBIT 10.1

Amendment No. 1 to Research and Development Agreement by and between Monsanto
Company and Ecogen Inc. dated May 22, 1997.


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                               AMENDMENT NO. 1 TO
                       RESEARCH AND DEVELOPMENT AGREEMENT


     This Amendment No. 1 to Research and Development Agreement ("Amendment") is
made as of May 22, 1997 by and between Monsanto Company, a Delaware corporation,
with its general offices at 800 North Lindbergh Boulevard, St. Louis, Missouri
63167 ("Monsanto"), and Ecogen Inc., a Delaware corporation having its principal
office at 2005 Cabot Boulevard West, Langhorne, PA 19047 ("Ecogen").


                                   WITNESSETH


     WHEREAS, Monsanto and Ecogen are parties to that certain Research and
Development Agreement dated as of January 24, 1996 (the "Original Agreement");
and

     WHEREAS, Monsanto and Ecogen wish to amend the Original Agreement as set
forth herein;

     NOW, THEREFORE, in consideration of the mutual covenants contained herein,
Monsanto and Ecogen agree as follows:

     1. Capitalized terms used herein but not defined herein shall have the
respective meanings ascribed thereto in the Original Agreement.

     2. On the date hereof, Monsanto is transferring to Ecogen, as an advance
payment, $1,424,000 of the funds scheduled to be disbursed by Monsanto to Ecogen
under the Research Budget during the third and fourth quarters of the Budget
Year currently in effect. Monsanto further agrees that if Monsanto shall elect,
in its sole discretion, but consistent with the Research Plan as determined by
the Supervisory Committee, to increase the aggregate amount of funds scheduled
to be disbursed by Monsanto to Ecogen under the Research Budget during the
Budget Year currently in effect, then Monsanto shall disburse such funds to
Ecogen within ten days following notification by Monsanto to Ecogen of such
election.


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     3. Section 3.5 of the Original Agreement is hereby amended to insert the
phrase "and other than a termination of this Agreement by Monsanto pursuant to
Section 5.7 following a Change of Control (as hereinafter defined) of Ecogen"
immediately after the words "Section 5.3" appearing therein.

     4. A new Section 5.7 is added to the Original Agreement to read as follows:

5.7 Termination of Agreement upon Change of Control. Notwithstanding anything
contained in this Agreement to the contrary, Monsanto shall have the right to
terminate this Agreement effective upon written notice of such termination from
Monsanto at any time following the occurrence of a Change of Control of Ecogen.
For purposes of this Agreement, the term "Change of Control" shall mean the
occurrence of any of the following events with respect to Ecogen: (i) there
shall be consummated (A) any merger, consolidation or combination involving
Ecogen in which Ecogen is not the continuing or surviving corporation, or
pursuant to which shares of Ecogen's voting stock would be converted in whole or
in part into cash (excluding any such transaction in which only fractional
shares are so converted to cash), or (B) any sale, lease, exchange or transfer
(in one transaction or a series of related transactions) of all or substantially
all of the assets of Ecogen, or (ii) any person, company, corporation or other
entity shall become the beneficial owner (within the meaning of Rule 13d-3 under
the Securities Exchange Act of 1934) of securities of Ecogen representing 50% or
more of the combined voting power of then outstanding securities ordinarily (and
apart from rights accruing in special circumstances) having the right to vote in
the election of directors, as a result of a tender or exchange offer, open
market purchases, privately negotiated purchases or otherwise. The parties
hereto agree that a sale, lease, exchange or transfer of all or substantially
all of the Intellectual Property Rights of Ecogen shall constitute a sale,
lease, exchange or transfer (as the case may be) of all or substantially all of
the assets of Ecogen for purposes hereof. The parties hereto further agree that
a sale, lease, exchange or transfer of Ecogen assets which does not include all
or substantially all of the Intellectual Property Rights of Ecogen shall not
constitute a sale, lease, exchange or transfer (as the case may be) of all or
substantially all of the assets of Ecogen for purposes hereof, unless after
giving effect to such transaction, Ecogen would be unable to pay its debts as
they become due, would become insolvent or would cease operations as a going
concern.


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     IN WITNESS WHEREOF, each party has caused this Amendment to be executed by
its duly authorized representative effective on the date set forth first above.



MONSANTO COMPANY                    ECOGEN INC.



By:/s/ Derek K. Rapp                By:/s/ James P. Reilly, Jr.
   ---------------------------         -------------------------------
   Name:  Derek K. Rapp                Name:  James P. Reilly, Jr.
   Title: Director, Mergers            Title: Chairman and Chief
          and Acquisitions                    Executive Officer


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