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                                                                   Exhibit 10.43



                                OPTION AGREEMENT


         THIS OPTION AGREEMENT (the "AGREEMENT") is made as of the 24th day of
September, 1997 (the "EFFECTIVE DATE"), by and between CHEMTRAK INCORPORATED, a
Delaware corporation ("CHEMTRAK") and ASTRA MERCK INC. ("AMI"), a Delaware
corporation.

                                    RECITALS

         WHEREAS, the parties have agreed to terminate the Distribution and
Supply Agreement between the parties dated March 1, 1995 ("DISTRIBUTION AND
SUPPLY AGREEMENT"), as amended, regarding the distribution, marketing and sale
of ChemTrak's Heliobacter pylori (H. pylori) assay device ("HP PRODUCT");

         WHEREAS, ChemTrak has agreed that AMI may retain certain rights to the
Hp Product allowing AMI to regain the right to distribute, market, and sell the
Hp Product;

         NOW, THEREFORE, in consideration of the foregoing premises, the
covenants set forth below and for good and valuable consideration, the receipt
and sufficiency of which is hereby acknowledged, the parties hereby agree as
follows:

1.       OPTION RIGHTS.

         1.1. For one (1) year from the Effective Date ("Option Period"),
ChemTrak hereby grants AMI an option ("Option") to obtain non-exclusive rights
to distribute, market and sell the Hp Product.

         1.2. AMI may exercise the Option within the Option Period by notifying
ChemTrak thereof in writing and by indicating the date within the Option Period
on which AMI desires to commence the distribution, marketing and sale of the Hp
Product; provided, however, that such date shall be no later than ninety (90)
days from the date of such written notice.

2.       TERMS OF DISTRIBUTION.

         Prior to the inception of the distribution, marketing and sale of the
Hp Product by AMI and no later than the ninety (90) day period set forth in
Section 1.2 above, the parties shall negotiate and agree on the terms under
which AMI shall distribute, market and sell the HP Product on a non-exclusive
basis in the Territory.

3.       TERMINATION OF OPTION RIGHTS.

         3.1. This Agreement shall terminate on the first anniversary of the
Effective Date.




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         3.2. At any time during the Option Period, ChemTrak may request in
writing that AMI exercise its option as set forth in Section 1.2 above. If
within fourteen (14) days from receipt of such written request, AMI has not
notified ChemTrak of its exercising the Option, this Agreement shall terminate
and the Option shall be deemed to have expired at the end of such fourteen (14)
day period.

4.       MISCELLANEOUS

         4.1. Any notices to be delivered under this Agreement shall be made in
writing and shall be effective if received by the other party within the periods
specified herein.

         4.2. Capitalized terms used but not defined herein shall have the
meaning set forth in the Distribution and Supply Agreement.

         4.3. This Option Agreement shall be governed by and construed in
accordance with the laws of the State of California, without regard to the
conflicts of law provisions thereof.


         IN WITNESS WHEREOF, the parties have each caused this Agreement to be
signed and delivered by their duly authorized representatives as of the date
first written above.


CHEMTRAK INCORPORATED                      ASTRA MERCK INC.



By:  /s/ Edward F. Covell                  By:  /s/ Matthew W. Emmens
   ------------------------------             ----------------------------------

Title:  President/Chief                    Title:  President and Chief
        Executive Officer                          Executive Officer
      ---------------------------                -------------------------------




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