Document:

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                                                                  Exhibit 10.157

                          REGISTRATION RIGHTS AGREEMENT

                  This Registration Rights Agreement (this "Agreement") is made
and entered into as of February 14, 2000, between Ecogen Inc., a Delaware
corporation (the "Company"), and Amro International, S.A., a corporation
incorporated under the laws of Switzerland, Aspen International, Ltd. and
Markham Holdings Limited (collectively, the "Purchaser").

                  This Agreement is made pursuant to the Convertible Preferred
Stock Purchase Agreement, dated as of the date hereof between the Company and
the Purchaser (as amended, modified or supplemented from time to time, the
"Purchase Agreement").

                  The Company and the Purchaser hereby agree as follows:

         1.       Definitions

                  Capitalized terms used and not otherwise defined herein that
are defined in the Purchase Agreement shall have the meanings given such terms
in the Purchase Agreement. As used in this Agreement, the following terms shall
have the following meanings:

                  "Advice" shall have meaning set forth in Section 3(m).

                  "Affiliate" means, with respect to any Person, any other
Person that directly or indirectly controls or is controlled by or under common
control with such Person. For the purposes of this definition, "control," when
used with respect to any Person, means the possession, direct or indirect, of
the power to direct or cause the direction of the management and policies of
such Person, whether through the ownership of voting securities, by contract or
otherwise; and the terms of "affiliated," "controlling" and "controlled" have
meanings correlative to the foregoing.

                  "Business Day" means any day except Saturday, Sunday and any
day which shall be a legal holiday or a day on which banking institutions in the
state of New York generally are authorized or required by law or other
government actions to close.

                  "Closing Date" shall have the meaning set forth in the
Purchase Agreement.

                  "Commission" means the Securities and Exchange Commission.

                  "Common Stock" means the Company's common stock, $.01 par
value.

                  "Effectiveness Date" means (i) with respect to the Registrable
Securities issuable upon conversion of the Preferred Stock and exercise of the
Warrant, the 90th day following the

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Closing Date and (ii) with respect to the Registrable Securities issuable upon
exercise of the Trigger Warrants, the 90th day following the issuance of Trigger
Warrants.

                  "Effectiveness Period" shall have the meaning set forth in
Section 2(b).

                  "Exchange Act" means the Securities Exchange Act of 1934, as
amended.

                  "Filing Date" means (i) with respect to the Registrable
Securities issuable upon conversion of the Preferred Stock and exercise of the
Warrant, the 30th day following the Closing Date and (ii) with respect to the
Registrable Securities issuable upon exercise of the Trigger Warrants, the 30th
day following the issuance of Trigger Warrants.

                  "Holder" or "Holders" means the holder or holders, as the case
may be, from time to time of Registrable Securities.

                  "Indemnified Party" shall have the meaning set forth in
Section 5(c).

                  "Indemnifying Party" shall have the meaning set forth in
Section 5(c).

                  "Losses" shall have the meaning set forth in Section 5(a).

                  "Person" means an individual or a corporation, partnership,
trust, incorporated or unincorporated association, joint venture, limited
liability company, joint stock company, government (or an agency or political
subdivision thereof) or other entity of any kind.

                  "Preferred Stock" means the Company's shares of 7% Series
2000-A Preferred Stock, $.01 par value, to be issued to the Purchaser pursuant
to the Purchase Agreement (including any shares of Preferred Stock issued in
payment of dividends on the Preferred Stock).

                  "Proceeding" means an action, claim, suit, investigation or
proceeding (including, without limitation, an investigation or partial
proceeding, such as a deposition), whether commenced or threatened.

                  "Prospectus" means the prospectus included in the Registration
Statement (including, without limitation, a prospectus that includes any
information previously omitted from a prospectus filed as part of an effective
registration statement in reliance upon Rule 430A promulgated under the
Securities Act), as amended or supplemented by any prospectus supplement, with
respect to the terms of the offering of any portion of the Registrable
Securities covered by the Registration Statement, and all other amendments and
supplements to the Prospectus, including post-effective amendments, and all
material incorporated by reference or deemed to be incorporated by reference in
such Prospectus.

                  "Registrable Securities" means the shares of Common Stock
issuable upon (i) conversion in full of the Preferred Stock, and (ii) exercise
in full of each of the Warrant and the Trigger Warrants, provided that in order
to account for the fact that the number of shares of

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Common Stock that is issuable upon conversion of the Preferred Stock is
determined in part upon the market price of the Common Stock at the time of
conversion, Registrable Securities contemplated by clause (i) above, shall
include (but not be limited to) a number of shares of Common Stock equal to no
less than 175% of the number of shares of Common Stock into which the shares of
Preferred Stock (including shares of Preferred Stock issuable as dividends) are
convertible, assuming such conversion occurred on the Closing Date or the Filing
Date, whichever yields a lower Conversion Price and assuming all dividends for a
two year period are paid in shares of Preferred Stock and that all such shares
of Preferred Stock are outstanding. Notwithstanding anything herein contained to
the contrary, if the actual number of shares of Common Stock into which the
shares of Preferred Stock are convertible exceeds twice the number of shares of
Common Stock into which the shares of Preferred Stock are convertible based upon
a computation at a particular Closing Date, the term "Registrable Securities"
shall be deemed to include such additional shares of Common Stock. With respect
to the Registration Statement filed with respect to the Registrable Securities
issuable upon conversion of the Preferred Stock and exercise of the Warrant, the
Company shall be required to file additional Registration Statements to the
extent the actual number of shares of Common Stock into which the Preferred
Stock is convertible and Warrants are exercisable exceeds the number of shares
of Common Stock registered in the initial Registration Statement hereunder. The
Company shall have ten (10) Business Days to file such additional Registration
Statements after notice of the requirement thereof, which the Holders may give
at such time when the number of shares of Common Stock as are issuable upon
conversion of Preferred Stock plus the number of shares of Common Stock issuable
upon exercise in full of the Warrant, exceed 85% of the number of shares of
Common Stock registered in the initial Registration Statement hereunder.

                  "Registration Statement" means the registration statement and
any additional registration statements contemplated by Section 2(a), including
(in each case) the Prospectus, amendments and supplements to such registration
statement or Prospectus, including pre- and post-effective amendments, all
exhibits thereto, and all material incorporated by reference or deemed to be
incorporated by reference in such registration statement.

                  "Rule 144" means Rule 144 promulgated by the Commission
pursuant to the Securities Act, as such Rule may be amended from time to time,
or any similar rule or regulation hereafter adopted by the Commission having
substantially the same effect as such Rule.

                  "Rule 415" means Rule 415 promulgated by the Commission
pursuant to the Securities Act, as such Rule may be amended from time to time,
or any similar rule or regulation hereafter adopted by the Commission having
substantially the same effect as such Rule.

                  "Securities Act" means the Securities Act of 1933, as amended.

                  "Special Counsel" means one special counsel to the Holders,
for which the Holders will be reimbursed by the Company pursuant to Section 4.

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                  "Trigger Warrants" means the common stock purchase warrants
issuable to the Purchaser pursuant to Section 5(a)(iii) of the Certificate of
Designations filed in connection with the authorization of the Preferred Stock.

                  "Warrant" means the Warrant to be issued to the Purchaser
pursuant to the Purchase Agreement.

         2.       Shelf Registrations

                  (a) On or prior to each applicable Filing Date, the Company
shall prepare and file with the Commission a "Shelf" Registration Statement
covering all Registrable Securities required to be included herein in such
Registration Statement for an offering to be made on a continuous basis pursuant
to Rule 415. Each Registration Statement shall be on Form S-3 (except if
otherwise directed by the Holders of a majority in interest of the applicable
Registrable Securities in accordance herewith or if the Company is not then
eligible to register for resale the Registrable Securities on Form S-3, in which
case such registration shall be on another appropriate form in accordance
herewith). Each Registration Statement shall state, to the extent permitted by
Rule 416 under the Securities Act, that it also covers such indeterminate number
of shares of Common Stock as may be required to effect (i) conversion of the
Preferred Stock to prevent dilution resulting from stock splits, stock dividends
or similar events, or by reason of changes in the Conversion Price in accordance
with the terms of the Certificate of Designations (as defined in the Purchase
Agreement) and (ii) exercise of the Warrant in full to prevent dilution
resulting from stock splits, stock dividends or similar events, or by reason of
changes in the Exercise Price (as defined in the Warrant) in accordance with the
terms of the Warrant, provided that any Registration Statements covering
Registrable Securities issuable upon exercise of Trigger Warrants will state, to
the extent permitted by Rule 416 under the Securities Act, that it also covers
such indeterminate number of shares of Common Stock as may be required to effect
exercise of Trigger Warrants in full to prevent dilution resulting from stock
splits, stock dividends or similar events, or by reason of changes in the
Exercise Price (as defined in the Trigger Warrants) in accordance with the terms
of the Trigger Warrants.

                  (b) The Company shall use its reasonable best efforts to cause
each Registration Statement to be declared effective under the Securities Act as
promptly as possible after the filing thereof, but in any event prior to each
applicable Effectiveness Date, and shall use its reasonable best efforts to keep
such Registration Statement continuously effective under the Securities Act
until the date which is five years after the date that such Registration
Statement is declared effective by the Commission or such earlier date when all
Registrable Securities covered by such Registration Statement have been sold or
may be sold without volume restrictions pursuant to Rule 144(k) as determined by
the counsel to the Company pursuant to a written opinion letter to such effect,
addressed and acceptable to the Company's transfer agent (the "Effectiveness
Period"), provided, however, that the Company shall not be deemed to have used
its best efforts to keep the Registration Statement effective during the
Effectiveness Period if it voluntarily takes any action that would result in the
Holders not being able to sell the Registrable Securities covered by such
Registration Statement during the Effectiveness Period, unless such action is
required under

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applicable law or the Company has filed a post-effective amendment to the
Registration Statement and the Commission has not declared it effective.

         3.       Registration Procedures

                  In connection with the Company's registration obligations
hereunder, the Company shall:

                  (a) Prepare and file with the Commission on or prior to each
Filing Date, a Registration Statement on Form S-3 in accordance with Section
2(a) and the method or methods of distribution thereof as specified by the
Holders (except if otherwise directed by the Holders), and cause the
Registration Statement to become effective and remain effective as provided
herein; provided, however, that not less than seven (7) Business Days prior to
the filing of the Registration Statement or any related Prospectus or any
amendment or supplement thereto (including any document that would be
incorporated or deemed to be incorporated therein by reference), the Company
shall, (i) furnish to the Holders and their Special Counsel copies of all such
documents proposed to be filed, which documents (other than those incorporated
or deemed to be incorporated by reference) will be subject to the review of such
Holders and their Special Counsel, and (ii) cause its officers and directors,
counsel and independent certified public accountants to respond to such
inquiries as shall be necessary, in the reasonable opinion of respective counsel
to such Holders, to conduct a reasonable investigation within the meaning of the
Securities Act. The Holders or their Special Counsel will provide the Company
with their comments on the proposed Registration Statement within five (5)
Business Days of their receipt thereof (the "Review Period") and if the Holders
and their Special Counsel provide their comments to the Company after the end of
the Review Period, the Filing Date shall be extended by the number of Business
Days after the Review Period before which such comments were provided. The
Company shall not file the Registration Statement or any such Prospectus or any
amendments or supplements thereto to which the Holders of a majority of the
Registrable Securities, their Special Counsel, shall reasonably object on a
timely basis.

                  (b) (i) Prepare and file with the Commission such amendments,
including post-effective amendments, to the Registration Statement as may be
necessary to keep the Registration Statement continuously effective as to the
applicable Registrable Securities for the Effectiveness Period and prepare and
file with the Commission such additional Registration Statements in order to
register for resale under the Securities Act all of the Registrable Securities;
(ii) cause the related Prospectus to be amended or supplemented by any required
Prospectus supplement, and as so supplemented or amended to be filed pursuant to
Rule 424 (or any similar provisions then in force) promulgated under the
Securities Act; (iii) respond as promptly as reasonably possible to any comments
received from the Commission with respect to the Registration Statement or any
amendment thereto and as promptly as reasonably possible provide the Holders
true and complete copies of all correspondence from and to the Commission
relating to the Registration Statement; and (iv) comply in all material respects
with the provisions of the Securities Act and the Exchange Act with respect to
the disposition of all Registrable Securities covered by the Registration
Statement during the applicable period in accordance with the intended

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methods of disposition by the Holders thereof set forth in the Registration
Statement as so amended or in such Prospectus as so supplemented.

                  (c) Notify the Holders of Registrable Securities to be sold
and their Special Counsel as promptly as reasonably possible (and, in the case
of (i)(A) below, not less than five (5) days prior to such filing) and (if
requested by any such Person) confirm such notice in writing no later than one
(1) Business Day following the day (i)(A) when a Prospectus or any Prospectus
supplement or post-effective amendment to the Registration Statement is proposed
to be filed; (B) when the Commission notifies the Company whether there will be
a "review" of such Registration Statement and whenever the Commission comments
in writing on such Registration Statement (the Company shall provide true and
complete copies thereof and all written responses thereto to each of the
Holders); and (C) with respect to the Registration Statement or any
post-effective amendment, when the same has become effective; (ii) of any
request by the Commission or any other Federal or state governmental authority
for amendments or supplements to the Registration Statement or Prospectus or for
additional information; (iii) of the issuance by the Commission of any stop
order suspending the effectiveness of the Registration Statement covering any or
all of the Registrable Securities or the initiation of any Proceedings for that
purpose; (iv) of the receipt by the Company of any notification with respect to
the suspension of the qualification or exemption from qualification of any of
the Registrable Securities for sale in any jurisdiction, or the initiation or
threatening of any Proceeding for such purpose; and (v) of the occurrence of any
event that makes any statement made in the Registration Statement or Prospectus
or any document incorporated or deemed to be incorporated therein by reference
untrue in any material respect or that requires any revisions to the
Registration Statement, Prospectus or other documents so that, in the case of
the Registration Statement or the Prospectus, as the case may be, it will not
contain any untrue statement of a material fact or omit to state any material
fact required to be stated therein or necessary to make the statements therein,
in light of the circumstances under which they were made, not misleading.

                  (d) Use its reasonable best efforts to avoid the issuance of,
or, if issued, obtain the withdrawal of (i) any order suspending the
effectiveness of the Registration Statement, or (ii) any suspension of the
qualification (or exemption from qualification) of any of the Registrable
Securities for sale in any jurisdiction, at the earliest practicable moment.

                  (e) Furnish to each Holder and their Special Counsel, without
charge, at least one conformed copy of each Registration Statement and each
amendment thereto, including financial statements and schedules, all documents
incorporated or deemed to be incorporated therein by reference, and all exhibits
to the extent requested by such Person (including those previously furnished or
incorporated by reference) promptly after the filing of such documents with the
Commission.

                  (f) Promptly deliver to each Holder and their Special Counsel,
without charge, as many copies of the Prospectus or Prospectuses (including each
form of prospectus) and each amendment or supplement thereto as such Persons may
reasonably request; and the Company hereby consents to the use of such
Prospectus and each amendment or supplement thereto by each

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of the selling Holders in connection with the offering and sale of the
Registrable Securities covered by such Prospectus and any amendment or
supplement thereto.

                  (g) Prior to any public offering of Registrable Securities,
use its best efforts to register or qualify or cooperate with the selling
Holders and their Special Counsel in connection with the registration or
qualification (or exemption from such registration or qualification) of such
Registrable Securities for offer and sale under the securities or Blue Sky laws
of such jurisdictions within the United States as any Holder requests in
writing, to keep each such registration or qualification (or exemption
therefrom) effective during the Effectiveness Period and to do any and all other
acts or things necessary or advisable to enable the disposition in such
jurisdictions of the Registrable Securities covered by a Registration Statement;
provided, however, that the Company shall not be required to qualify generally
to do business in any jurisdiction where it is not then so qualified or to take
any action that would subject it to general service of process in any such
jurisdiction where it is not then so subject or subject the Company to any
material tax in any such jurisdiction where it is not then so subject.

                  (h) Cooperate with the Holders to facilitate the timely
preparation and delivery of certificates representing Registrable Securities to
be delivered to a transferee pursuant to a Registration Statement, which
certificates shall be free, to the extent permitted by applicable law, of all
restrictive legends, and to enable such Registrable Securities to be in such
denominations and registered in such names as Holders may request at least two
(2) Business Days prior to any sale of Registrable Securities.

                  (i) Upon the occurrence of any event contemplated by Section
3(c)(v), as promptly as reasonably possible, prepare a supplement or amendment,
including a post-effective amendment, to the Registration Statement or a
supplement to the related Prospectus or any document incorporated or deemed to
be incorporated therein by reference, and file any other required document so
that, as thereafter delivered, neither the Registration Statement nor such
Prospectus will contain an untrue statement of a material fact or omit to state
a material fact required to be stated therein or necessary to make the
statements therein, in light of the circumstances under which they were made,
not misleading.

                  (j) Use its best efforts to cause all Registrable Securities
relating to such Registration Statement to be listed on the Nasdaq National
Market (the "NASDAQ") and any other securities exchange, quotation system,
market or over-the-counter bulletin board, if any, on which similar securities
issued by the Company are then listed as and when required pursuant to the
Purchase Agreement.

                  (k) Make available for inspection by the selling Holders, any
representative of such Holders, and any attorney or accountant retained by such
selling Holders, at the offices where normally kept, during reasonable business
hours, all financial and other records, pertinent corporate documents and
properties of the Company and its subsidiaries, and cause the officers,
directors, agents and employees of the Company and its subsidiaries to supply
all information in each case reasonably requested by any such Holder,
representative, attorney or accountant in connection with the Registration
Statement; provided, however, that any information that is

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determined in good faith by the Company in writing to be of a confidential
nature at the time of delivery of such information shall be kept confidential by
such Persons, unless (i) disclosure of such information is required by court or
administrative order or is necessary to respond to inquiries of regulatory
authorities; (ii) disclosure of such information, in the opinion of counsel to
such Person, is required by law; (iii) such information becomes generally
available to the public other than as a result of a disclosure or failure to
safeguard by such Person; or (iv) such information becomes available to such
Person from a source other than the Company and such source is not known by such
Person to be bound by a confidentiality agreement with the Company. In the event
that any Person is requested or required to disclose any such information as
described in clause (i) or (ii) of the immediately preceding sentence, such
Person shall provide the Company with prompt prior notice so that the Company
may seek a protective order or other appropriate remedy and/or waive compliance
with the provisions of this Agreement. If such protective order or other remedy
is not obtained, or if the Company waives compliance with the provisions of this
Agreement, such Person shall furnish only that portion of such confidential
information that is advised by such Person's counsel is legally required and
shall exercise its best efforts to obtain a protective order or other reliable
assurance that confidential treatment will be accorded to such confidential
information.

                  (l) Comply with all applicable rules and regulations of the
Commission in connection with the Registration Statement.

                  (m) The Company may require each selling Holder to furnish to
the Company such information regarding the distribution of such Registrable
Securities and the beneficial ownership of Common Stock held by such Holder as
is required by law to be disclosed in the Registration Statement, and the
Company may exclude from such registration the Registrable Securities of any
such Holder who unreasonably fails to furnish such information within a
reasonable time after receiving such request. The parties agree that the "Plan
of Distribution" section of each Prospectus shall be substantially in the form
of Annex A attached hereto.

                  If the Registration Statement refers to any Holder by name or
otherwise as the holder of any securities of the Company, then such Holder shall
have the right to require (if such reference to such Holder by name or otherwise
is not required by the Securities Act or any similar Federal statute then in
force) the deletion of the reference to such Holder in any amendment or
supplement to the Registration Statement filed or prepared subsequent to the
time that such reference ceases to be required.

                  Each Holder covenants and agrees that (i) it will not sell any
Registrable Securities under the Registration Statement until it has received
copies of the Prospectus as then amended or supplemented as contemplated in
Section 3(i) and notice from the Company that such Registration Statement and
any post-effective amendments thereto have become effective as contemplated by
Section 3(c) and (ii) it and its officers, directors or Affiliates, if any, will
comply with the prospectus delivery requirements of the Securities Act as
applicable to it in connection with sales of Registrable Securities pursuant to
the Registration Statement.

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                  Each Holder agrees by its acquisition of such Registrable
Securities that, upon receipt of a notice from the Company of the occurrence of
any event of the kind described in Section 3(c)(ii), 3(c)(iii), 3(c)(iv), or
3(c)(v), such Holder will forthwith discontinue disposition of such Registrable
Securities under the Registration Statement until such Holder's receipt of the
copies of the supplemented Prospectus and/or amended Registration Statement
contemplated by Section 3(i), or until it is advised in writing (the "Advice")
by the Company that the use of the applicable Prospectus may be resumed, and, in
either case, has received copies of any additional or supplemental filings that
are incorporated or deemed to be incorporated by reference in such Prospectus or
Registration Statement.

         4.       Registration Expenses. All fees and expenses incident to the
performance of or compliance with this Agreement by the Company, shall be borne
by the Company whether or not the Registration Statement is filed or becomes
effective and whether or not any Registrable Securities are sold pursuant to the
Registration Statement. The fees and expenses referred to in the foregoing
sentence shall include, without limitation, (i) all registration and filing fees
(including, without limitation, fees and expenses (A) with respect to filings
required to be made with the NASDAQ or each other securities exchange or market
on which Registrable Securities are required hereunder to be listed and (B) in
compliance with state securities or Blue Sky laws (including, without
limitation, fees and disbursements of counsel for the Holders in connection with
Blue Sky qualifications or exemptions of the Registrable Securities and
determination of the eligibility of the Registrable Securities for investment
under the laws of such jurisdictions as the Holders of a majority of Registrable
Securities may designate)), (ii) printing expenses (including, without
limitation, expenses of printing certificates for Registrable Securities and of
printing prospectuses if the printing of prospectuses is requested by the
holders of a majority of the Registrable Securities included in the Registration
Statement), (iii) messenger, telephone and delivery expenses, (iv) fees and
disbursements of counsel for the Company and Special Counsel for the Holders (in
the case of Special Counsel for the Holders, such fees and disbursements shall
not exceed $5,000), (v) Securities Act liability insurance, if the Company so
desires such insurance, and (vi) fees and expenses of all other Persons retained
by the Company in connection with the consummation of the transactions
contemplated by this Agreement. In addition, the Company shall be responsible
for all of its internal expenses incurred in connection with the consummation of
the transactions contemplated by this Agreement (including, without limitation,
all salaries and expenses of its officers and employees performing legal or
accounting duties), the expense of any annual audit, the fees and expenses
incurred in connection with the listing of the Registrable Securities on any
securities exchange as required hereunder.

         5.       Indemnification

                  (a) Indemnification by the Company. The Company shall,
notwithstanding any termination of this Agreement, indemnify and hold harmless
each Holder, the officers, directors, agents, brokers (including brokers who
offer and sell Registrable Securities as principal, in connection with a block
trade or as a result of a pledge or any failure to perform under a margin call
of Common Stock), investment advisors and employees of each of them, each Person
who controls any such Holder (within the meaning of Section 15 of the Securities
Act or Section 20 of the Exchange Act) and the officers, directors, agents and
employees of each such controlling

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Person, to the fullest extent permitted by applicable law, from and against any
and all losses, claims, damages, liabilities, costs (including, without
limitation, costs of preparation and attorneys' fees) and expenses
(collectively, "Losses"), as incurred, arising out of or relating to any untrue
or alleged untrue statement of a material fact contained in the Registration
Statement, any Prospectus or any form of prospectus or in any amendment or
supplement thereto or in any preliminary prospectus, or arising out of or
relating to any omission or alleged omission of a material fact required to be
stated therein or necessary to make the statements therein (in the case of any
Prospectus or form of prospectus or supplement thereto, in light of the
circumstances under which they were made) not misleading, except to the extent,
but only to the extent, that such untrue statements or omissions are based
solely upon information regarding such Holder furnished in writing to the
Company by such Holder expressly for use therein, which information was
reasonably relied on by the Company for use therein or to the extent that such
information relates to such Holder or such Holder's proposed method of
distribution of Registrable Securities and was reviewed and expressly approved
in writing by such Holder expressly for use in the Registration Statement, such
Prospectus or such form of Prospectus or in any amendment or supplement thereto.
The Company shall notify the Holders promptly of the institution, threat or
assertion of any Proceeding of which the Company is aware in connection with the
transactions contemplated by this Agreement.

                  (b) Indemnification by Holders. Each Holder shall, severally
and not jointly, indemnify and hold harmless the Company, its directors,
officers, agents and employees, each Person who controls the Company (within the
meaning of Section 15 of the Securities Act and Section 20 of the Exchange Act),
and the directors, officers, agents or employees of such controlling Persons, to
the fullest extent permitted by applicable law, from and against all Losses (as
determined by a court of competent jurisdiction in a final judgment not subject
to appeal or review) arising solely out of or based solely upon any untrue
statement of a material fact contained in the Registration Statement, any
Prospectus, or any form of prospectus, or in any amendment or supplement
thereto, or arising solely out of or based solely upon any omission of a
material fact required to be stated therein or necessary to make the statements
therein not misleading to the extent, but only to the extent, that such untrue
statement or omission is contained in any information regarding such Holder so
furnished in writing by such Holder to the Company specifically for inclusion in
the Registration Statement or such Prospectus and that such information was
reasonably relied upon by the Company for use in the Registration Statement,
such Prospectus or such form of prospectus or to the extent that such
information relates to such Holder or such Holder's proposed method of
distribution of Registrable Securities and was reviewed and expressly approved
in writing by such Holder expressly for use in the Registration Statement, such
Prospectus or such form of Prospectus, or in any amendment or supplement
thereto. In no event shall the liability of any selling Holder hereunder be
greater in amount than the dollar amount of the net proceeds received by such
Holder upon the sale of the Registrable Securities giving rise to such
indemnification obligation.

                  (c) Conduct of Indemnification Proceedings. If any Proceeding
shall be brought or asserted against any Person entitled to indemnity hereunder
(an "Indemnified Party"), such Indemnified Party shall promptly notify the
Person from whom indemnity is sought (the "Indemnifying Party") in writing, and
the Indemnifying Party shall assume the defense thereof,

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including the employment of counsel reasonably satisfactory to the Indemnified
Party and the payment of all fees and expenses incurred in connection with
defense thereof; provided, that the failure of any Indemnified Party to give
such notice shall not relieve the Indemnifying Party of its obligations or
liabilities pursuant to this Agreement, except (and only) to the extent that it
shall be finally determined by a court of competent jurisdiction (which
determination is not subject to appeal or further review) that such failure
shall have proximately and materially adversely prejudiced the Indemnifying
Party.

                  An Indemnified Party shall have the right to employ separate
counsel in any such Proceeding and to participate in the defense thereof, but
the fees and expenses of such counsel shall be at the expense of such
Indemnified Party or Parties unless: (1) the Indemnifying Party has agreed in
writing to pay such fees and expenses; or (2) the Indemnifying Party shall have
failed promptly to assume the defense of such Proceeding and to employ counsel
reasonably satisfactory to such Indemnified Party in any such Proceeding; or (3)
the named parties to any such Proceeding (including any impleaded parties)
include both such Indemnified Party and the Indemnifying Party, and such
Indemnified Party shall have been advised by counsel that a conflict of interest
is likely to exist if the same counsel were to represent such Indemnified Party
and the Indemnifying Party (in which case, if such Indemnified Party notifies
the Indemnifying Party in writing that it elects to employ separate counsel at
the expense of the Indemnifying Party, the Indemnifying Party shall not have the
right to assume the defense thereof and such counsel shall be at the expense of
the Indemnifying Party). The Indemnifying Party shall not be liable for any
settlement of any such Proceeding effected without its written consent, which
consent shall not be unreasonably withheld. No Indemnifying Party shall, without
the prior written consent of the Indemnified Party, effect any settlement of any
pending Proceeding in respect of which any Indemnified Party is a party, unless
such settlement includes an unconditional release of such Indemnified Party from
all liability on claims that are the subject matter of such Proceeding.

                  All fees and expenses of the Indemnified Party (including
reasonable fees and expenses to the extent incurred in connection with
investigating or preparing to defend such Proceeding in a manner not
inconsistent with this Section) shall be paid to the Indemnified Party, as
incurred, within ten (10) Business Days of written notice thereof to the
Indemnifying Party (regardless of whether it is ultimately determined that an
Indemnified Party is not entitled to indemnification hereunder; provided, that
the Indemnifying Party may require such Indemnified Party to undertake to
reimburse all such fees and expenses to the extent it is finally judicially
determined that such Indemnified Party is not entitled to indemnification
hereunder).

                  (d) Contribution. If a claim for indemnification under Section
5(a) or 5(b) is unavailable to an Indemnified Party (by reason of public policy
or otherwise), then each Indemnifying Party, in lieu of indemnifying such
Indemnified Party, shall contribute to the amount paid or payable by such
Indemnified Party as a result of such Losses, in such proportion as is
appropriate to reflect the relative fault of the Indemnifying Party and
Indemnified Party in connection with the actions, statements or omissions that
resulted in such Losses as well as any other relevant equitable considerations.
The relative fault of such Indemnifying Party and Indemnified Party shall be
determined by reference to, among other things, whether any action in question,
including any untrue or alleged untrue statement of a material fact or omission
or

                                       11
<PAGE>   12
alleged omission of a material fact, has been taken or made by, or relates to
information supplied by, such Indemnifying Party or Indemnified Party, and the
parties' relative intent, knowledge, access to information and opportunity to
correct or prevent such action, statement or omission. The amount paid or
payable by a party as a result of any Losses shall be deemed to include, subject
to the limitations set forth in Section 5(c), any reasonable attorneys' or other
reasonable fees or expenses incurred by such party in connection with any
Proceeding to the extent such party would have been indemnified for such fees or
expenses if the indemnification provided for in this Section was available to
such party in accordance with its terms.

                  The parties hereto agree that it would not be just and
equitable if contribution pursuant to this Section 5(d) were determined by pro
rata allocation or by any other method of allocation that does not take into
account the equitable considerations referred to in the immediately preceding
paragraph. Notwithstanding the provisions of this Section 5(d), no Holder shall
be required to contribute, in the aggregate, any amount in excess of the amount
by which the proceeds actually received by such Holder from the sale of the
Registrable Securities subject to the Proceeding exceeds the amount of any
damages that such Holder has otherwise been required to pay by reason of such
untrue or alleged untrue statement or omission or alleged omission. No Person
guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of
the Securities Act) shall be entitled to contribution from any Person who was
not guilty of such fraudulent misrepresentation.

                  The indemnity and contribution agreements contained in this
Section are in addition to any liability that the Indemnifying Parties may have
to the Indemnified Parties.

         6.       Miscellaneous

                  (a) Remedies. In the event of a breach by the Company or by a
Holder, of any of their obligations under this Agreement, each Holder or the
Company, as the case may be, in addition to being entitled to exercise all
rights granted by law and under this Agreement, including recovery of damages,
will be entitled to specific performance of its rights under this Agreement. The
Company and each Holder agree that monetary damages would not provide adequate
compensation for any losses incurred by reason of a breach by it of any of the
provisions of this Agreement and hereby further agrees that, in the event of any
action for specific performance in respect of such breach, it shall waive the
defense that a remedy at law would be adequate.

                  (b) No Inconsistent Agreements. Neither the Company nor any of
its subsidiaries has, as of the date hereof, nor shall the Company or any of its
Subsidiaries, on or after the date of this Agreement, enter into any agreement
with respect to its securities that is inconsistent with the rights granted to
the Holders in this Agreement or otherwise conflicts with the provisions hereof.
Except as and to the extent specified in Schedule 6(b) hereto, neither the
Company nor any of its Subsidiaries has previously entered into any agreement
granting any registration rights with respect to any of its securities to any
Person. Without limiting the generality of the foregoing, without the written
consent of the Holders of a majority of the then outstanding Registrable
Securities, the Company shall not grant to any Person the right to request

                                       12
<PAGE>   13
the Company to register any securities of the Company under the Securities Act
unless the rights so granted are subject in all respects to the prior rights in
full of the Holders set forth herein, and are not otherwise in conflict or
inconsistent with the provisions of this Agreement.

                  (c) No Piggyback on Registrations. Except as and to the extent
specified in Schedule 6(c) hereto, neither the Company nor any of its security
holders (other than the Holders in such capacity pursuant hereto) may include
securities of the Company in the Registration Statement other than the
Registrable Securities, and the Company shall not after the date hereof enter
into any agreement providing any such right to any of its security holders.

                   (d) Piggy-Back Registrations. If at any time when there is
not an effective Registration Statement covering all of the Registrable
Securities and the Underlying Shares, the Company shall determine to prepare and
file with the Commission a registration statement relating to an offering for
its own account or the account of others under the Securities Act of any of its
equity securities, other than on Form S-4 or Form S-8 (each as promulgated under
the Securities Act) or their then equivalents relating to equity securities to
be issued solely in connection with any acquisition of any entity or business or
equity securities issuable in connection with stock option or other employee
benefit plans, then the Company shall send to each holder of Registrable
Securities written notice of such determination and, if within twenty (20) days
after receipt of such notice, any such holder shall so request in writing, the
Company shall include in such registration statement all or any part of such
Registrable Securities such holder requests to be registered; provided, however,
that the Company shall not be required to register any Registrable Securities
pursuant to this Section 7(d) that are eligible for sale pursuant to Rule 144(k)
under the Securities Act.

                   (d) Amendments and Waivers. The provisions of this Agreement,
including the provisions of this sentence, may not be amended, modified or
supplemented, and waivers or consents to departures from the provisions hereof
may not be given, unless the same shall be in writing and signed by the Company
and the Holders of at least two-thirds of the then outstanding Registrable
Securities; provided, however, that, for the purposes of this sentence,
Registrable Securities that are owned, directly or indirectly, by the Company,
or an Affiliate of the Company are not deemed outstanding. Notwithstanding the
foregoing, a waiver or consent to depart from the provisions hereof with respect
to a matter that relates exclusively to the rights of certain Holders and that
does not directly or indirectly affect the rights of other Holders may be given
by Holders of at least a majority of the Registrable Securities to which such
waiver or consent relates; provided, however, that the provisions of this
sentence may not be amended, modified, or supplemented except in accordance with
the provisions of the immediately preceding sentence.

                   (e) Notices. Any and all notices or other communications or
deliveries required or permitted to be provided hereunder shall be in writing
and shall be deemed given and effective on the earliest of (i) the date of
transmission, if such notice or communication is delivered via confirmed
facsimile at the facsimile telephone number specified in this Section prior to
8:00 p.m. (New York City time) on a Business Day, (ii) the Business Day after
the date of transmission, if such notice or communication is delivered via
confirmed facsimile at the facsimile

                                       13
<PAGE>   14
telephone number specified in the Purchase Agreement later than 8:00
p.m. (New York City time) on any date and earlier than 11:59 p.m. (New York City
time) on such date, (iii) the Business Day following the date of mailing, if
sent by nationally recognized overnight courier service, or (iv) upon actual
receipt by the party to whom such notice is required to be given. The address
for such notices and communications shall be as follows:

         If to the Company:   Ecogen, Inc.
                              2000 Cabot Boulevard West
                              Suite 170
                              Langhorne, PA  19047
                              Facsimile No.:(215) 757-3339
                              Attn:  Chief Financial Officer

         With copies to:      Paul, Hastings, Janofsky & Walker LLP
                              1055 Washington Boulevard
                              Stamford, CT  06901
                              Facsimile No.: (203) 359-3031
                              Attn: Elizabeth A. Brower, Esq.

         If to Purchaser:     Amro International, S.A.
                              c/o Ultra Finance, Ltd.
                              Grossmuenster Platz 26, P.O. Box 4401
                              Zurich, Switzerland, CH 8022
                              Facsimile No.: ( )
                              Attn: Thomas Badian

                              Aspen International, Ltd.
                              Charlotte House, Charlotte St.
                              Nassau Bahamas
                              Facsimile No.: (242) 323-7918

                                       14
<PAGE>   15
                              Markham Holdings Limited
                              Suite 7B and 8B
                              50 Town Range
                              Gibraltar
                              Facsimile No.: 011-350-40-40-4
                              Attention: J. David Hassan

         If to any other Person who is then the registered Holder:

                              To the address of such Holder as it appears in the
                              stock transfer books of the Company

or such other address as may be designated in writing hereafter, in the same
manner, by such Person.

                   (f) Successors and Assigns. This Agreement shall inure to the
benefit of and be binding upon the successors and permitted assigns of each of
the parties and shall inure to the benefit of each Holder. The Company may not
assign its rights or obligations hereunder without the prior written consent of
each Holder. Each Holder may assign their respective rights hereunder in the
manner and to the Persons as permitted under the Purchase Agreement.

                  (g) Assignment of Registration Rights. The rights of each
Holder hereunder, including the right to have the Company register for resale
Registrable Securities in accordance with the terms of this Agreement, shall be
automatically assignable by each Holder to any Affiliate of such Holder, any
other Holder or Affiliate of any other Holder and up to four other assignees of
all or a portion of the shares of Preferred Stock, the Warrants, the Trigger
Warrants or the Registrable Securities if: (i) the Holder agrees in writing with
the transferee or assignee to assign such rights, and a copy of such agreement
is furnished to the Company within a reasonable time after such assignment, (ii)
the Company is, within a reasonable time after such transfer or assignment,
furnished with written notice of (a) the name and address of such transferee or
assignee, and (b) the securities with respect to which such registration rights
are being transferred or assigned, (iii) following such transfer or assignment
the further disposition of such securities by the transferee or assignees is
restricted under the Securities Act and applicable state securities laws, (iv)
at or before the time the Company receives the written notice contemplated by
clause (ii) of this Section, the transferee or assignee agrees in writing with
the Company to be bound by all of the provisions of this Agreement, and (v) such
transfer shall have been made in accordance with the applicable requirements of
the Purchase Agreement. The rights to assignment shall apply to the Holders (and
to subsequent) successors and assigns.

                  (h) Counterparts. This Agreement may be executed in any number
of counterparts, each of which when so executed shall be deemed to be an
original and, all of which taken together shall constitute one and the same
Agreement. In the event that any signature is delivered by facsimile
transmission, such signature shall create a valid binding obligation of the

                                       15
<PAGE>   16
party executing (or on whose behalf such signature is executed) the same with
the same force and effect as if such facsimile signature were the original
thereof.

                  (i) Governing Law. This Agreement shall be governed by and
construed in accordance with the laws of the State of New York, without regard
to principles of conflicts of law.

                  (j) Cumulative Remedies. The remedies provided herein are
cumulative and not exclusive of any remedies provided by law.

                  (k) Severability. If any term, provision, covenant or
restriction of this Agreement is held by a court of competent jurisdiction to be
invalid, illegal, void or unenforceable, the remainder of the terms, provisions,
covenants and restrictions set forth herein shall remain in full force and
effect and shall in no way be affected, impaired or invalidated, and the parties
hereto shall use their reasonable efforts to find and employ an alternative
means to achieve the same or substantially the same result as that contemplated
by such term, provision, covenant or restriction. It is hereby stipulated and
declared to be the intention of the parties that they would have executed the
remaining terms, provisions, covenants and restrictions without including any of
such that may be hereafter declared invalid, illegal, void or unenforceable.

                  (l) Headings. The headings in this Agreement are for
convenience of reference only and shall not limit or otherwise affect the
meaning hereof.

                  (m) Shares Held by The Company and its Affiliates. Whenever
the consent or approval of Holders of a specified percentage of Registrable
Securities is required hereunder, Registrable Securities held by the Company or
its Affiliates (other than any Holder or transferees or successors or assigns
thereof if such Holder is deemed to be an Affiliate solely by reason of its
holdings of such Registrable Securities) shall not be counted in determining
whether such consent or approval was given by the Holders of such required
percentage.

                   [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK
                            SIGNATURE PAGE TO FOLLOW]

                                       16
<PAGE>   17
                  IN WITNESS WHEREOF, the parties have executed this
Registration Rights Agreement as of the date first written above.

                                       ECOGEN INC.

                                       By:
                                          -------------------------------------
                                          Name:  James P. Reilly, Jr.
                                          Title: Chairman and CEO

                                       AMRO INTERNATIONAL, S.A.

                                       By:
                                          -------------------------------------
                                          Name:
                                          Title:

                                      ASPEN INTERNATIONAL, LTD.

                                       By:
                                          -------------------------------------
                                          Name:
                                          Title:

                                       MARKHAM HOLDINGS LIMITED

                                       By:
                                          -------------------------------------
                                          Name:
                                          Title:
<PAGE>   18
                                                                         Annex A

                              Plan of Distribution

                  The Selling Stockholders and any of their pledgees, assignees
         and successors-in-interest may, from time to time, sell any or all of
         their shares of Common Stock on any stock exchange market or trading
         facility on which the shares are traded or in private transactions.
         These sales may be at fixed or negotiated prices. The Selling
         Stockholders may use any one or more of the following methods when
         selling shares:

         -        ordinary brokerage transactions and transactions in which the
                  broker-dealer solicits purchasers;

         -        block trades in which the broker-dealer will attempt to sell
                  the shares as agent but may position and resell a portion of
                  the block as principal to facilitate the transaction;

         -        purchases by a broker-dealer as principal and resale by the
                  broker-dealer for its account;

         -        an exchange distribution in accordance with the rules of the
                  applicable exchange;

         -        privately negotiated transactions;

         -        short sales;

         -        broker-dealers may agree with the Selling Stockholders to sell
                  a specified number of such shares at a stipulated price per
                  share;

         -        a combination of any such methods of sale; and

         -        any other method permitted pursuant to applicable law.

                  The Selling Stockholders may also sell shares under Rule 144
         under the Securities Act, if available, rather than under this
         prospectus.

                  The Selling Stockholders may also engage in short sales
         against the box, puts and calls and other transactions in securities of
         the Company or derivatives of Company securities and may sell or
         deliver shares in connection with these trades. The Selling
         Stockholders may pledge their shares to their brokers under the margin
         provisions of customer agreements. If a Selling Stockholders defaults
         on a margin loan, the broker may, from time to time, offer and sell the
         pledged shares.
<PAGE>   19
                  Broker-dealers engaged by the Selling Stockholders may arrange
         for other brokers-dealers to participate in sales. Broker-dealers may
         receive commissions or discounts from the Selling Stockholders (or, if
         any broker-dealer acts as agent for the purchaser of shares, from the
         purchaser) in amounts to be negotiated. The Selling Stockholders do not
         expect these commissions and discounts to exceed what is customary in
         the types of transactions involved.

                  The Selling Stockholders and any broker-dealers or agents that
         are involved in selling the shares may be deemed to be "underwriters"
         within the meaning of the Securities Act in connection with such sales.
         In such event, any commissions received by such broker-dealers or
         agents and any profit on the resale of the shares purchased by them may
         be deemed to be underwriting commissions or discounts under the
         Securities Act.

                  The Company is required to pay all fees and expenses incident
         to the registration of the shares, including fees and disbursements
         (not to exceed $5,000) of counsel to the Selling Stockholders. The
         Company has agreed to indemnify the Selling Stockholders against
         certain losses, claims, damages and liabilities, including liabilities
         under the Securities Act.
<PAGE>   20
                                  SCHEDULE 6(b)

                               REGISTRATION RIGHTS

         The following parties have registration rights:

                           Monsanto Company (with respect to 943,397 shares of
         Common Stock).

                           United Equities (Commodities) Company (with respect
         to shares of Common Stock issuable upon conversion of 32,354 shares of
         Ecogen's 8% 1998-C Convertible Preferred Stock (shares have been
         registered)).

                           KA Investments LDC (with respect to shares of Common
         Stock issuable upon conversion of Ecogen's 8% Series 1998-A Convertible
         Preferred Stock and 7% Series 1999-A Convertible Preferred Stock).

                           Momar Corporation (with respect to 200,000 shares of
         Common Stock issuable upon exercise of a warrant).
<PAGE>   21
                                  SCHEDULE 6(c)

         The following will parties will be able to piggyback on Registrations:

         Jesup & Lamont Securities Corporation (with respect to 20,000 shares of
Common Stock);

         Momar Corporation (with respect to 200,000 shares of Common Stock
issuable upon exercise of a warrant);

         Mycogen Corporation (with respect to approximately 1,400,000 shares of
Common Stock to be issued in connection with the purchase of a business).

         In addition approximately 1,750,000 shares of Common Stock or Common
Stock equivalents to be sold to investors within six months of the Closing Date
may piggyback on Registrations.<PAGE>   1
                                                                  EXHIBIT 10.158

NEITHER THESE SECURITIES NOR THE SECURITIES INTO WHICH THESE SECURITIES ARE
EXERCISABLE HAVE BEEN REGISTERED WITH THE SECURITIES AND EXCHANGE COMMISSION OR
THE SECURITIES COMMISSION OF ANY STATE IN RELIANCE UPON AN EXEMPTION FROM
REGISTRATION UNDER SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"),
AND, ACCORDINGLY, MAY NOT BE OFFERED OR SOLD EXCEPT PURSUANT TO AN EFFECTIVE
REGISTRATION STATEMENT UNDER THE SECURITIES ACT OR PURSUANT TO AN AVAILABLE
EXEMPTION FROM THE REGISTRATION REQUIREMENTS THEREUNDER AND IN COMPLIANCE WITH
APPLICABLE STATE SECURITIES OR BLUE SKY LAWS.

                                   ECOGEN INC.

                                     WARRANT

                            Dated: February 14, 2000

         Ecogen Inc., a Delaware corporation (the "Company"), hereby certifies
that, for value received, Amro International, S.A., or its registered assigns
("Holder"), is entitled, subject to the terms set forth below, to purchase from
the Company up to a total of 106,667 shares of Common Stock, $.01 par value per
share (the "Common Stock"), of the Company (each such share, a "Warrant Share"
and all such shares, the "Warrant Shares") at an exercise price equal to $2.66
per share (as adjusted from time to time as provided in Section 11, the
"Exercise Price"), at any time and from time to time from and after the date
hereof and through and including February 14, 2005 (the "Expiration Date"), and
subject to the following terms and conditions:

                  1. Registration of Warrant. The Company shall register this
Warrant, upon records to be maintained by the Company for that purpose (the
"Warrant Register"), in the name of the record Holder hereof from time to time.
The Company may deem and treat the registered Holder of this Warrant as the
absolute owner hereof for the purpose of any exercise hereof or any distribution
to the Holder, and for all other purposes, and the Company shall not be affected
by notice to the contrary.

                  2. Registration of Transfers and Exchanges.

                     (a) The Company shall register the transfer of any portion
of this Warrant in the Warrant Register, upon surrender of this Warrant, with
the Form of Assignment attached hereto duly completed and signed, to the
Transfer Agent or to the Company at the office specified in or pursuant to
Section 3(b). Upon any such registration or transfer, a new warrant to purchase
<PAGE>   2
Common Stock, in substantially the form of this Warrant (any such new warrant, a
"New Warrant"), evidencing the portion of this Warrant so transferred shall be
issued to the transferee and a New Warrant evidencing the remaining portion of
this Warrant not so transferred, if any, shall be issued to the transferring
Holder. The acceptance of the New Warrant by the transferee thereof shall be
deemed the acceptance of such transferee of all of the rights and obligations of
a holder of a Warrant.

                     (b) This Warrant is exchangeable, upon the surrender hereof
by the Holder to the office of the Company specified in or pursuant to Section
3(b) for one or more New Warrants, evidencing in the aggregate the right to
purchase the number of Warrant Shares which may then be purchased hereunder. Any
such New Warrant will be dated the date of such exchange.

                     3. Duration and Exercise of Warrants.

                     (a) This Warrant shall be exercisable by the registered
Holder on any business day before 5:30 P.M., Eastern time, at any time and from
time to time on or after the date hereof to and including the Expiration Date.
At 5:30 P.M., Eastern time on the Expiration Date, the portion of this Warrant
not exercised prior thereto shall be and become void and of no value. Prior to
the Expiration Date, the Company may not call or otherwise redeem this Warrant
without the prior written consent of the Holder.

                     (b) Subject to Sections 2(b) and 6, upon surrender of this
Warrant, with the Form of Election to Purchase attached hereto duly completed
and signed, to the Company at its address for notice set forth in Section 11 and
upon payment of the Exercise Price multiplied by the number of Warrant Shares
that the Holder intends to purchase hereunder, in lawful money of the United
States of America, in cash, by certified or official bank check or checks or
wire transfer of immediately available funds, all as specified by the Holder in
the Form of Election to Purchase, the Company shall promptly (but in no event
later than five (5) business days after the Date of Exercise) issue or cause to
be issued and cause to be delivered to or upon the written order of the Holder
and in such name or names as the Holder may designate, a certificate for the
Warrant Shares issuable upon such exercise, free of restrictive legends other
than as required by applicable law. Any person so designated by the Holder to
receive Warrant Shares shall be deemed to have become holder of record of such
Warrant Shares as of the Date of Exercise of this Warrant.

                     A "Date of Exercise" means the date on which the Company
shall have received (i) this Warrant (or any New Warrant, as applicable), with
the Form of Election to Purchase attached hereto (or attached to such New
Warrant) appropriately completed and duly signed, and (ii) payment of the
Exercise Price for the number of Warrant Shares so indicated by the holder
hereof to be purchased.

                     (c) Notwithstanding anything in this Section 3 to the
contrary, if a registration statement contemplated by the Registration Rights
Agreement between the Company and the Holder dated as of February 14, 2000 (the
"Registration Rights Agreement") which includes the Warrant Shares, is not
declared effective by the Effectiveness Date (as defined in the Registration
Rights Agreement), or if declared effective, such effectiveness lapses, then the
Holder hereof may exercise this Warrant, in whole or in part, by surrender to
the Company for cancellation of a portion

                                       2
<PAGE>   3
of this Warrant representing that number of Warrant Shares which is equal to the
quotient obtained by dividing (A) the product obtained by multiplying the
Exercise Price by the number of Warrant Shares being purchased upon such
exercise by (B) the difference obtained by subtracting the Exercise Price from
the Current Market Price per Warrant Share as of the date of such exercise.

                     For purposes of this Section 3, "Current Market Price per
Warrant Share" means (a) the closing bid price per share of the Common Stock on
such date on the NASDAQ or the Nasdaq SmallCal Market, as the case may be, or
any other stock exchange or quotation system on which the Common Stock is then
listed, or if there is no such price on such date, then the closing bid price on
such exchange or quotation system on which the Common Stock is listed for
trading on the date nearest preceding such date, or (b) if the Common Stock is
not listed then on the NASDAQ or the Nasdaq SmallCap Market or any stock
exchange or quotation system, the closing bid price for a share of Common Stock
in the over-the-counter market, as reported the National Quotation Bureau
Incorporated or similar organization or agency succeeding to its functions of
reporting prices) at the close of business on such date, or (c) if the Common
Stock is not then reported by the National Quotation Bureau Incorporated (or
similar organization or agency succeeding to its functions of reporting prices),
then the average of the "Pink Sheet" quotes for the relevant conversion period,
as determined in good faith by the Company, or (d) if the Common Stock is not
then publicly traded the fair market value of a share of Common Stock as
determined by an appraiser selected in good faith by the Company.

                     (d) This Warrant shall be exercisable, either in its
entirety or, from time to time, for a portion of the number of Warrant Shares.
If less than all of the Warrant Shares which may be purchased under this Warrant
are exercised at any time, the Company shall issue or cause to be issued, at its
expense, a New Warrant evidencing the right to purchase the remaining number of
Warrant Shares for which no exercise has been evidenced by this Warrant.

                     (e)(i) The Holder may not exercise this Warrant to the
extent such exercise would result in the Holder, together with any affiliate
thereof, beneficially owning (as determined in accordance with Section 13(d) of
the Securities Exchange Act of 1934, as amended (the "Exchange Act"), and the
rules thereunder) in excess of 4.999% of the then issued and outstanding shares
of Common Stock. The Holder shall have the sole authority and obligation to
determine whether the restriction contained in this Section applies and to the
extent that the Holder determines that the limitation contained in this Section
applies, the determination of which portion of this Warrant is exercisable shall
be in the sole discretion of the Holder, and the Company shall have no
obligation to verify or confirm the accuracy of any such determination. The
provisions of this Section may be waived by the Holder (but only as to itself
and not to any other Holder) upon not less than 75 days prior notice to the
Company, and the provisions of this Section shall continue to apply until such
75th day (or later, if stated in the notice of waiver).

                     (ii) The Holder may not exercise this Warrant to the extent
such exercise would result in the Holder, together with any affiliate thereof,
beneficially owning (as determined in accordance with Section 13(d) of the
Exchange Act and the rules thereunder) in excess of 9.999% of the then issued
and outstanding shares of Common Stock. The Holder shall have the sole

                                       3
<PAGE>   4
authority and obligation to determine whether the restriction contained in this
Section applies and to the extent that the Holder determines that the limitation
contained in this Section applies, the determination of which portion of this
Warrant is exercisable shall be in the sole discretion of the Holder and the
Company shall have no obligation to verify or confirm the accuracy of any such
determination. The provisions of this Section may be waived by the Holder (but
only as to itself and not to any other Holder) upon not less than 75 days prior
notice to the Company and the provisions of this Section shall continue to apply
until such 75th day (or later, if stated in the notice of waiver).

                     (iii) Notwithstanding anything herein to the contrary,
unless the Company shall have previously (A) received the shareholder approval
as may be required under Rule 4310(H)(i)(b) of the NASDAQ Stock Market or (B)
obtained an exemption from the requirement from the NASDAQ Stock Market for such
shareholder approval, the Holder shall not exercise this Warrant to the extent
such exercise would result in the Holder holding in excess of 25% of the number
of shares of Common Stock outstanding on the date hereof.

                  4. No Voting or Dividend Rights; Limitation of Liability.
Nothing contained in this Warrant shall be construed as conferring upon the
Holder the right to vote or to consent or to receive notice as a stockholder in
respect of meetings of stockholders for the election of directors of the Company
or any other matters or any rights whatsoever as a stockholder of the Company.
No cash dividends shall be payable or accrued in respect of this Warrant or the
Warrant Shares until, and only to the extent that, this Warrant shall have been
exercised. No provisions hereof, in the absence of affirmative action by the
Holder to purchase shares of Common Stock, and no mere enumeration herein of the
rights or privileges of the Holder hereof, shall give rise to any liability of
the Holder for the Exercise Price or as a stockholder of the company whether
such liability is asserted by the Company or by its creditors.

                  5. Registration Rights. The Warrant Shares are entitled to
certain registration rights pursuant to that certain Registration Rights
Agreement, dated as of February 14, 2000, between the Company and the Purchaser
named therein (as may be amended, modified or supplemented from time to time,
the "Registration Rights Agreement"). Pursuant to the terms of the Registration
Rights Agreement, the Company is obligated, among other things, to file a
registration statement registering for resale the Warrant Shares and naming the
Holder as a selling stockholder thereunder.

                  6. Payment of Taxes. The Company will pay all documentary
stamp taxes attributable to the issuance of Warrant Shares upon the exercise of
this Warrant; provided, however, that the Company shall not be required to pay
any tax which may be payable in respect of any transfer involved in the
registration of any certificates for Warrant Shares or Warrants in a name other
than that of the Holder, and the Company shall not be required to issue or cause
to be issued or deliver or cause to be delivered the certificates for Warrant
Shares unless or until the person or persons requesting the issuance thereof
shall have paid to the Company the amount of such tax or shall have established
to the satisfaction of the Company that such tax has been paid. The Holder shall
be responsible for all other tax liability that may arise as a result of holding
or transferring this Warrant or receiving Warrant Shares upon exercise hereof.

                                        4
<PAGE>   5
                  7. Replacement of Warrant. If this Warrant is mutilated, lost,
stolen or destroyed, the Company shall issue or cause to be issued in exchange
and substitution for and upon cancellation hereof, or in lieu of and
substitution for this Warrant, a New Warrant, but only upon receipt of evidence
reasonably satisfactory to the Company of such loss, theft or destruction and
indemnity and/or bond, if requested, satisfactory to it. Applicants for a New
Warrant under such circumstances shall also comply with such other reasonable
regulations and procedures and pay such other reasonable charges as the Company
may prescribe.

                  8. Reservation of Warrant Shares. The Company covenants that
it will at all times reserve and keep available out of the aggregate of its
authorized but unissued Common Stock, solely for the purpose of enabling it to
issue Warrant Shares upon exercise of this Warrant as herein provided, the
number of Warrant Shares which are then issuable and deliverable upon the
exercise of this entire Warrant, free from preemptive rights or any other actual
contingent purchase rights of persons other than the Holder (taking into account
the adjustments and restrictions of Section 9) The Company covenants that all
Warrant Shares that shall be so issuable and deliverable shall, upon issuance
and the payment of the applicable Exercise Price in accordance with the terms
hereof, be duly and validly authorized, issued and fully paid and nonassessable.

                                       5
<PAGE>   6
                  9. Certain Adjustments. The Exercise Price and number of
Warrant Shares issuable upon exercise of this Warrant are subject to adjustment
from time to time as set forth in this Section 9. Upon each such adjustment of
the Exercise Price pursuant to this Section 9, the Holder shall thereafter prior
to the Expiration Date be entitled to purchase, at the Exercise Price resulting
from such adjustment, the number of Warrant Shares obtained by multiplying the
Exercise Price in effect immediately prior to such adjustment by the number of
Warrant Shares issuable upon exercise of this Warrant immediately prior to such
adjustment and dividing the product thereof by the Exercise Price resulting from
such adjustment.

                     (a) If the Company, at any time while this Warrant is
outstanding, (i) shall pay a stock dividend (except scheduled dividends paid on
outstanding preferred stock as of the date hereof which contain a stated divided
rate) or otherwise make a distribution or distributions on shares of its Common
Stock (as defined below) or on any other class of capital stock and not the
Common Stock) payable in shares of Common Stock, (ii) subdivide outstanding
shares of Common Stock into a larger number of shares, or (iii) combine
outstanding shares of Common Stock into a smaller number of shares, the Exercise
Price shall be multiplied by a fraction of which the numerator shall be the
number of shares of Common Stock (excluding treasury shares, if any) outstanding
before such event and of which the denominator shall be the number of shares of
Common Stock (excluding treasury shares, if any) outstanding after such event.
Any adjustment made pursuant to this Section shall become effective immediately
after the record date for the determination of stockholders entitled to receive
such dividend or distribution and shall become effective immediately after the
effective date in the case of a subdivision or combination, and shall apply to
successive subdivisions and combinations.

                     (b) In case of any reclassification of the Common Stock,
any consolidation or merger of the Company with or into another person, the sale
or transfer of all or substantially all of the assets of the Company or any
compulsory share exchange pursuant to which the Common Stock is converted into
other securities, cash or property, then the Holder shall have the right
thereafter to exercise this Warrant only into the shares of stock and other
securities and property receivable upon or deemed to be held by holders of
Common Stock following such reclassification, consolidation, merger, sale,
transfer or share exchange, and the Holder shall be entitled upon such event to
receive such amount of securities or property equal to the amount of Warrant
Shares such Holder would have been entitled to had such Holder exercised this
Warrant immediately prior to such reclassification, consolidation, merger, sale,
transfer or share exchange. The terms of any such consolidation, merger, sale,
transfer or share exchange shall include such terms so as to continue to give to
the Holder the right to receive the securities or property set forth in this
Section 9(b) upon any exercise following any such reclassification,
consolidation, merger, sale, transfer or share exchange.

                     (c) If the Company, at any time while this Warrant is
outstanding, shall distribute to all holders of Common Stock (and not to holders
of this Warrant) evidences of its indebtedness or assets or rights or warrants
to subscribe for or purchase any security (excluding those referred to in
Sections 9(a), (b) and (d)), then in each such case the Exercise Price shall be
determined by multiplying the Exercise Price in effect immediately prior to the
record date fixed for

                                       6
<PAGE>   7
determination of stockholders entitled to receive such distribution by a
fraction of which the denominator shall be the Exercise Price determined as of
the record date mentioned above, and of which the numerator shall be such
Exercise Price on such record date less the then fair market value at such
record date of the portion of such assets or evidence of indebtedness so
distributed applicable to one outstanding share of Common Stock as determined by
the Company's independent certified public accountants that regularly examines
the financial statements of the Company (an "Appraiser").

                     (d) If, at any time while this Warrant is outstanding, the
Company shall issue or cause to be issued rights or warrants to acquire, or
securities convertible into, or otherwise sell or distribute, shares of Common
Stock for a consideration per share less than the Market Value in effect on the
date of issuance of such rights, warrants or shares, then, forthwith upon such
issue or sale, the Exercise Price shall be reduced to the price (calculated to
the nearest cent) determined by multiplying the Exercise Price in effect
immediately prior thereto by a fraction, the numerator of which shall be the sum
of the number of shares of Common Stock which the aggregate consideration
received (or to be received, assuming exercise or conversion in full of such
rights, warrants and convertible securities) for the issuance of such additional
shares of Common Stock would purchase at such Market Value, and the denominator
of which shall be the sum of the number of shares of Common Stock outstanding
immediately after the issuance of such additional shares. Such adjustment shall
be made successively whenever such an issuance is made. For purposes hereof, the
"Market Value" of the Common Stock as at a date of determination shall mean the
arithmetic average of the Per Share Market Value (as defined in the Convertible
Preferred Stock Purchase Agreement, dated as of February 14, 2000, between the
Company and the original Holder of this Warrant) for the ten (10) business days
preceding the date of determination.

                     (e) For the purposes of this Section 9, the following
clauses shall also be applicable:

                         (i) Record Date. In case the Company shall take a
record of the holders of its Common Stock for the purpose of entitling them (A)
to receive a dividend or other distribution payable in Common Stock or in
securities convertible or exchangeable into shares of Common Stock, or (B) to
subscribe for or purchase Common Stock or securities convertible or exchangeable
into shares of Common Stock, then such record date shall be deemed to be the
date of the issue or sale of the shares of Common Stock deemed to have been
issued or sold upon the declaration of such dividend or the making of such other
distribution or the date of the granting of such right of subscription or
purchase, as the case may be.

                         (ii) Treasury Shares. The number of shares of Common
Stock outstanding at any given time shall not include shares owned or held by or
for the account of the Company, and the disposition of any such shares shall be
considered an issue or sale of Common Stock.

                     (f) All calculations under this Section 9 shall be made to
the nearest cent or the nearest 1/100th of a share, as the case may be.

                                       7
<PAGE>   8
                     (g) Whenever the Exercise Price is adjusted pursuant to
Section 9(c) above, the Holder, after receipt of the determination by the
Appraiser, shall have the right to select an additional appraiser (which shall
be a nationally recognized accounting firm), in which case the adjustment shall
be equal to the average of the adjustments recommended by each of the Appraiser
and such appraiser. The Holder shall promptly mail or cause to be mailed to the
Company, a notice setting forth the Exercise Price after such adjustment and
setting forth a brief statement of the facts requiring such adjustment. Such
adjustment shall become effective immediately after the record date mentioned
above.

                     (h) If:

                            (i)   the Company shall declare a dividend (or any
                                  other distribution) on its Common Stock; or

                            (ii)  the Company shall declare a special
                                  nonrecurring cash dividend on or a redemption
                                  of its Common Stock; or

                            (iii) the Company shall authorize the granting to
                                  all holders of the Common Stock rights or
                                  warrants to subscribe for or purchase any
                                  shares of capital stock of any class or of any
                                  rights; or

                            (iv)  the approval of any stockholders of the
                                  Company shall be required in connection with
                                  any reclassification of the Common Stock of
                                  the Company, any consolidation or merger to
                                  which the Company is a party, any sale or
                                  transfer of all or substantially all of the
                                  assets of the Company, or any compulsory share
                                  exchange whereby the Common Stock is converted
                                  into other securities, cash or property; or

                            (v)   the Company shall authorize the voluntary
                                  dissolution, liquidation or winding up of the
                                  affairs of the Company,

then the Company shall cause to be mailed to each Holder at their last addresses
as they shall appear upon the Warrant Register, at least ten (10) business days
prior to the applicable record or effective date hereinafter specified, a notice
stating (x) the date on which a record is to be taken for the purpose of such
dividend, distribution, redemption, rights or warrants, or if a record is not to
be taken, the date as of which the holders of Common Stock of record to be
entitled to such dividend, distributions, redemption, rights or warrants are to
be determined or (y) the date on which such reclassification, consolidation,
merger, sale, transfer or share exchange is expected to become effective or
close, and the date as of which it is expected that holders of Common Stock of
record

                                       8
<PAGE>   9
shall be entitled to exchange their shares of Common Stock for securities, cash
or other property deliverable upon such reclassification, consolidation, merger,
sale, transfer, share exchange, dissolution, liquidation or winding up;
provided, however, that the failure to mail such notice or any defect therein or
in the mailing thereof shall not affect the validity of the corporate action
required to be specified in such notice.

                           (i) No adjustment in the Exercise Price under
Sections 9(c) or (d) shall be required to be made if such adjustment would
result in a change of less than $.10 in the Exercise Price, but any adjustments
not made by reason of this clause (i) shall be carried forward and shall be made
at the time of and together with the next subsequent adjustment(s) which,
together with any adjustment(s) so carried forward, shall require an increase or
decrease of at least $.10 in the Exercise Price then in effect.

                  10. Fractional Shares. The Company shall not be required to
issue or cause to be issued fractional Warrant Shares on the exercise of this
Warrant. The number of full Warrant Shares which shall be issuable upon the
exercise of this Warrant shall be computed on the basis of the aggregate number
of Warrant Shares purchasable on exercise of this Warrant so presented. If any
fraction of a Warrant Share would, except for the provisions of this Section 10,
be issuable on the exercise of this Warrant, the Company shall pay an amount in
cash equal to the Exercise Price multiplied by such fraction.

                  11. Notices. Any and all notices or other communications or
deliveries hereunder shall be in writing and shall be deemed given and effective
on the earliest of (i) the date of transmission, if such notice or communication
is delivered via confirmed facsimile at the facsimile telephone number specified
in this Section prior to 8:00 p.m. (New York City time) on a business day, (ii)
the business day after the date of transmission, if such notice or communication
is delivered via confirmed facsimile at the facsimile telephone number specified
in this Section later than 8:00 p.m. (New York City time) on any date and
earlier than 11:59 p.m. (New York City time) on such date, (iii) the business
day following the date of mailing, if sent by nationally recognized overnight
courier service, or (iv) upon actual receipt by the party to whom such notice is
required to be given. The addresses for such communications shall be: (i) if to
the Company, to Ecogen Inc., 2000 Cabot Boulevard West, Suite 170, Langhorne, PA
19047, Attention: Chief Financial Officer, or to facsimile no. (215) 757-3339,
or (ii) if to the Holder, to the Holder at the address or facsimile number
appearing on the Warrant Register or such other address or facsimile number as
the Holder may provide to the Company in accordance with this Section 11.

                  12. Warrant Agent.

                       (a) The Company shall serve as warrant agent under this
Warrant. Upon not less than thirty (30) days' notice to the Holder, the Company
may appoint a new warrant agent.

                       (b) Any corporation into which the Company or any new
warrant agent may be merged or any corporation resulting from any consolidation
to which the Company or any new warrant agent shall be a party or any
corporation to which the Company or any new warrant

                                       9
<PAGE>   10
agent transfers substantially all of its corporate trust or shareholders
services business shall be a successor warrant agent under this Warrant without
any further act. Any such successor warrant agent shall promptly cause notice of
its succession as warrant agent to be mailed (by first class mail, postage
prepaid) to the Holder at the Holder's last address as shown on the Warrant
Register.

                  13. Miscellaneous.

                       (a) This Warrant shall be binding on and inure to the
benefit of the parties hereto and their respective successors and permitted
assigns. This Warrant may be amended only in writing signed by the Company and
the Holder.

                       (b) Subject to Section 13(a) above, nothing in this
Warrant shall be construed to give to any person or corporation other than the
Company and the Holder any legal or equitable right, remedy or cause under this
Warrant. This Warrant shall inure to the sole and exclusive benefit of the
Company and the Holder.

                       (c) This Warrant shall be governed by and construed and
enforced in accordance with the internal laws of the State of New York without
regard to the principles of conflicts of law thereof.

                       (d) The headings herein are for convenience only, do not
constitute a part of this Warrant and shall not be deemed to limit or affect any
of the provisions hereof.

                       (e) In case any one or more of the provisions of this
Warrant shall be invalid or unenforceable in any respect, the validity and
enforceability of the remaining terms and provisions of this Warrant shall not
in any way be affected or impaired thereby and the parties will attempt in good
faith to agree upon a valid and enforceable provision which shall be a
commercially reasonable substitute therefor, and upon so agreeing, shall
incorporate such substitute provision in this Warrant.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK,
                             SIGNATURE PAGE FOLLOWS]

                                       10
<PAGE>   11
                  IN WITNESS WHEREOF, the Company has caused this Warrant to be
duly executed by its authorized officer as of the date first indicated above.

                                       ECOGEN INC.

                                       By:
                                          ----------------------------------
                                       Name:
                                       Title:
<PAGE>   12
                          FORM OF ELECTION TO PURCHASE

(To be executed by the Holder to exercise the right to purchase shares of Common
Stock under the foregoing Warrant)

To Ecogen Inc.

         In accordance with the Warrant enclosed with this Form of Election to
Purchase, the undersigned hereby irrevocably elects to purchase _____________
shares of Common Stock ("Common Stock"), $.01 par value per share, of Ecogen
Inc. and, if such Holder is not utilizing the cashless exercise provisions set
forth in this Warrant, encloses herewith $________ in cash, certified or
official bank check or checks or wire transfer of immediately available funds,
which sum represents the aggregate Exercise Price (as defined in the Warrant)
for the number of shares of Common Stock to which this Form of Election to
Purchase relates, together with any applicable taxes payable by the undersigned
pursuant to the Warrant.

         The undersigned requests that certificates for the shares of Common
Stock issuable upon this exercise be issued in the name of:

                                              PLEASE INSERT SOCIAL SECURITY OR
                                              TAX IDENTIFICATION NUMBER

                                              ----------------------------------

--------------------------------------------------------------------------------
                         (Please print name and address)

         If the number of shares of Common Stock issuable upon this exercise
shall not be all of the shares of Common Stock which the undersigned is entitled
to purchase in accordance with the enclosed Warrant, the undersigned requests
that a New Warrant (as defined in the Warrant) evidencing the right to purchase
the shares of Common Stock not issuable pursuant to the exercise evidenced
hereby be issued in the name of and delivered to:

--------------------------------------------------------------------------------
                         (Please print name and address)

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

Dated:                     ,        Name of Holder:
       ---------------------
                                    (Print)
                                           -------------------------------------
                                    (By:)
                                         ---------------------------------------
                                    (Name:)
                                    (Title:)
                                    (Signature must conform in all respects to
                                    name of holder as specified on the face of
                                    the Warrant)
<PAGE>   13
                               FORM OF ASSIGNMENT

           [To be completed and signed only upon transfer of Warrant]

         FOR VALUE RECEIVED, the undersigned hereby sells, assigns and transfers
unto ________________________________ the right represented by the within
Warrant to purchase ____________ shares of Common Stock of Ecogen Inc. to which
the within Warrant relates and appoints ________________ attorney to transfer
said right on the books of [ ] with full power of substitution in the premises.

Dated:

---------------, ----

                                      ---------------------------------------
                                      (Signature must conform in all respects to
                                      name of holder as specified on the face
                                      of the Warrant)

                                      ---------------------------------------
                                      Address of Transferee

                                      ---------------------------------------

                                      ---------------------------------------

In the presence of:

--------------------------

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