EXHIBIT 4.9

                   [DONLAR BIOSYNTREX CORPORATION LETTERHEAD]

August 15, 2002

CONFIDENTIAL

Mr. Kenneth Hubbard
Hubbard Healthcare
P.O. Box 2210
206 Southgate Dr.
Boone, NC  28607

Dear Mr. Hubbard:

         The boards of directors of Donlar Corporation ("Donlar") and Donlar's
majority owned subsidiary, Donlar Biosyntrex Corporation ("Donlar Biosyntrex"),
have unanimously approved that certain Amended and Restated Agreement and Plan
of Merger dated as of June 7, 2002 (the "Merger Agreement"), that provides for
the merger of Donlar Biosyntrex with and into Donlar (the "Merger") with Donlar
being the surviving corporation (the "Combined Company"). Currently, you own
5,000 shares of series A preferred stock of Donlar Biosyntrex ("Donlar
Biosyntrex Series A Shares"). This letter agreement (this "Letter Agreement")
sets forth certain understandings between you and Donlar Biosyntrex regarding
the terms upon which you shall surrender the Donlar Biosyntrex Series A Shares
in exchange for 5,000 shares of common stock of the Combined Company ("Combined
Company Common Shares") pursuant to the terms of the Merger Agreement.

         Accordingly, you agree: (a) to surrender for cancellation the Donlar
Biosyntrex Series A Shares in exchange for Combined Company Common Shares issued
upon the completion of the Merger; (b) to vote any shares of voting securities
of Donlar Biosyntrex owned by you in favor of the approval of the Merger and the
equity incentive plan; and (c) to appoint Larry P. Koskan as proxy with full
power of substitution, to vote at the special meeting of the shareholders of
Donlar Biosyntrex, all of the Donlar Biosyntrex Series A Shares which you have
power to vote at the special meeting of shareholders, or any adjournment
thereof, in favor of the approval of the Merger and the equity incentive plan.

         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 BIOSYNTREX CORPORATION


                                                  By: /s/ Larry P. Koskan
                                                      -------------------------
                                                  Name: Larry Koskan
                                                        Title: President and CEO


Accepted and agreed to as of the date first above written:


/s/ Kenneth S. Hubbard
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