EXHIBIT 4.5

                         [DONLAR CORPORATION LETTERHEAD]

April ___, 2002


CONFIDENTIAL
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_____________________

_____________________

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Dear _____________:

         Currently, you own convertible debt of Donlar Corporation ("Donlar")
evidenced by a note dated ______________ in the face amount of _________________
(the "Convertible Note"). This letter agreement (this "Letter Agreement") sets
forth certain understandings between you and Donlar, an Illinois corporation,
regarding the terms upon which you shall surrender the Convertible Note in
exchange for shares of senior convertible preferred stock of Donlar ("Senior
Preferred") containing the terms attached hereto as Exhibit A and surrender for
cancellation all options and warrants you hold to purchase common or preferred
stock of Donlar. Upon the completion of certain transactions whereby Donlar's
majority owned subsidiary Donlar Bioysntrex Corporation, a Nevada corporation,
is merged into Donlar, the capitalization of Donlar shall be as set forth on
Exhibit B.

         Accordingly, you agree to surrender for cancellation: (a) the
Convertible Note to Donlar in exchange for shares of Senior Preferred in the
face amount of $ ____________ convertible into _______________ shares of common
stock of the Donlar; and (b) all warrants and options you hold to purchase
shares of common or preferred stock of Donlar.

         If the foregoing is in accordance with your understanding of our
agreement, please sign where indicated below and deliver a copy of this Letter
Agreement as provided for herein, whereupon this Letter Agreement shall
represent a binding agreement between us and shall be governed by the internal
laws of the State of Illinois.

                                                     Very truly yours,

                                                     DONLAR CORPORATION


                                                     By:________________________
                                                        Name: Larry Koskan
                                                        Title: President and CEO