<PAGE>

                                                                Exhibit 10.507

                               OPTION AGREEMENT

     Agreement made as of the   day of   , 1983, by and between Cetus
Corporation ("Cetus") and the limited partner of Cetus Healthcare Limited
Partnership (the "Partnership") listed on Schedule A hereto (the "Limited
Partner").

                                  RECITALS:

     A.   Pursuant to the Subscription Agreement and Investment
Representation between the Limited Partner and Cetus, the Partnership, Lehman
Brothers Kuhn Loeb Incorporated and Oppenheimer & Co., Inc., the Limited
Partner has subscribed for and agreed to acquire certain warrants (the
"Warrants") to purchase shares of Cetus Common Stock, in payment for which
the Limited Partner has agreed to grant Cetus the Purchase Option referred to
below.

     B.   Option Agreements substantially identical to this Agreement (the
"Option Agreements") are being executed by the other limited partners of the
Partnership.

     NOW, THEREFORE, the parties agree as follows:

1.   GRANT OF OPTION.

     In consideration of the issuance and sale to the Limited Partner by
Cetus of the Warrants on the date hereof, the Limited Partner hereby grants
to Cetus an irrevocable option (the "Purchase Option") to purchase all of the
Limited Partner's interest in the Partnership.

2.   TIME FOR EXERCISE.

     The Purchase Option may be exercised at any time during the period
commencing on June 30, 1987 and expiring at the close of business on August
31, 1987. Cetus may exercise the Purchase Option with respect to the Limited
Partner's interest only if it exercises all of its purchase options granted
by all other limited partners of the Partnership under the Option Agreements.

3.   MANNER OF EXERCISE.

     Cetus may exercise the Purchase Option only by delivery to Cetus
Development Corporation (the "General Partner") or any successor general
partner of the Partnership, who is hereby authorized by the Limited Partner
to accept such delivery on its behalf, of (i) a notice of exercise and (ii)
two copies of an executed Purchase Agreement, dated as of the date of the
notice of exercise and substantially in the form attached hereto as Exhibit
A. The General Partner shall forward both copies of the Purchase Agreement to
the Limited Partner requesting that the Limited Partner execute both copies
and return one original to Cetus. Upon the delivery of the executed Purchase
Agreement by Cetus to the General Partner, the Purchase Agreement
automatically will be effective, without the necessity of any action on the
part of the General Partner or the Limited Partner or any further action on
the part of Cetus: provided, however, that Cetus shall not be obligated to
pay to the Limited Partner any amounts under the Purchase Agreement until
Cetus shall have received from the Limited Partner a Purchase Agreement
executed by the Limited Partner.

4.   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,
when taken together, shall constitute this Agreement.

-------------------
- To be dated by the General Partner on and as of the Closing Date.

                                      I-1

<PAGE>

5.   GOVERNING LAW.

     This Agreement shall be governed by and construed in accordance with the
laws of the State of California as applied to residents of that state
entering into contracts wholly to be performed in that state.

6.   VALIDITY OF PROVISIONS, SEVERABILITY.

     If any provision of this Agreement is or becomes or is deemed invalid,
illegal, or unenforceable in any jurisdiction, (i) such provision will be
deemed amended to conform to applicable laws of such jurisdiction so as to be
valid and enforceable or, if it cannot be so amended without materially
altering the intention of the parties, it will be stricken, (ii) the
validity, legality and enforceability of such provision will not in any way
be affected or impaired thereby in any other jurisdiction, and (iii) the
remainder of this Agreement will remain in full force and effect.

7.   AMENDMENTS.

     No amendment, modification or addition hereto shall be effective or
binding unless set forth in a writing and executed by a duly authorized
representative of the party against whom such change is asserted.

8.   HEADINGS.

     The section headings contained in this Agreement are included for
convenience only and form no part of the agreement between the parties.

9.   ASSIGNMENT.

     Cetus may not assign its rights hereunder without the prior written
consent of a majority in interest of the limited partners of the Partnership,
which consent may not be unreasonably withheld, except to a person or entity
(i) with which Cetus is merged or consolidated or which purchases all or
substantially all of the assets of Cetus or (ii) which purchases all or
substantially all of Cetus' human healthcare business, which assumes in
writing Cetus' obligations hereunder, and which has a net worth of at least
$250,000,000 at the date of such purchase. Any consent of a majority in
interest of the limited partners shall be binding on the Limited Partner,
whether or not the Limited Partner in fact consented.

     IN WITNESS WHEREOF, the parties have executed this Agreement as of the
date first above written.

                                        CETUS CORPORATION


                                                 -----------------------------
                                                           President


                                                 -----------------------------
                                                        (Limited Partner)

--------------------------
*   The name, address and pro rata share of payments for each Limited Partner
    will be listed on Schedule A to that Limited Partner's Option Agreement and
    attached to that Limited Partner's Purchase Agreement.


                                      I-2

<PAGE>

                                                                      EXHIBIT A
                                                                   TO EXHIBIT I

                              PURCHASE AGREEMENT

    AGREEMENT made as of the ___*___ day of _______*______, 1987, by and
between Cetus Corporation ("Cetus") and the limited partner of Cetus
Healthcare Limited Partnership ("the Partnership") listed on Schedule A
hereto (the "Limited Partner").

                                  RECITALS:

    A.  Pursuant to an Option Agreement, the Limited Partner has granted to
Cetus an option (the "Purchase Option") to purchase the Limited Partner's
interest in Cetus Healthcare Limited Partnership (the "Partnership").

    B.  In accordance with the Option Agreement, Cetus has exercised the
Purchase Option and the parties are to execute this Agreement.

    C.  Purchase Agreements substantially identical to this Agreement (the
"Purchase Agreements") are being executed by the other limited partners of
the Partnership.

    NOW, THEREFORE, the parties agree as follows:

 1. DEFINITIONS.

    1.1  "Affiliate" shall mean a corporation or any other business entity
that directly, or indirectly through one or more intermediaries, controls, is
controlled by or is under common control with, the designated party.
"Control" shall mean ownership of at least 50% of the shares entitled to vote
for the election of directors in the case of a corporation and at least 50%
of the beneficial interests in the case of a business entity other than a
corporation.

    1.2  "Combination Product" shall mean a human diagnostic kit or reagent
or a product for the prevention, treatment or mitigation of disease in
humans that incorporates one or more Human Healthcare Products, Competing
Products or Interferon Products with one or more other human diagnostic kits
or reagents or human therapeutic products in respect of which Cetus is not
obligated to make payments to the Limited Partner hereunder.

    1.3  "Competing Product" shall mean, on a country by country basis, a
product other than an Interferon System Agent or an Interferon Product (i)
that has the same primary therapeutic indication or primary human diagnostic
use as a Human Healthcare Product and (ii) that Cetus either (a) purchases or
licenses from a third party or (b) develops other than with Partnership
funds of $150,000 or more, in each case only if the efforts to complete the
corresponding Human Healthcare Product has not been abandoned under Section 7
hereof or under Section 2.5 of the Development Contract, and development of
such product by or on behalf of the Partnership has not been recommended,
prior to the date of such purchase or license or the commencement of such
development by Cetus. Under the foregoing, primary diagnostic use or primary
therapeutic indication shall mean (i) in the case of a Competing Product,
such use or indication as approved by the FDA or, if not yet approved by the
FDA, as approved by a comparable foreign regulatory authority and (ii) in the
case of all other products, as approved by the FDA or, if not yet approved by
the FDA, as approved by a comparable foreign regulatory authority or, if not
yet approved by any regulatory authority, as set forth in the corresponding
Product Development Program.

    1.4  "Completion" of a product shall mean the obtaining of FDA approval
to market the product.

    1.5  "Development Contract" shall mean the Restated Research and
Development Agreement between Cetus and the Partnership.

----------
*   To be dated in accordance with Section 3 of the Option Agreement.


                                      I-3

<PAGE>

    1.6  "FDA" shall mean the United States Food and Drug Administration and
each successor regulatory authority.

    1.7  "Human Healthcare Product" shall mean a human diagnostic kit or
reagent or a product for the prevention, treatment or mitigation of disease
in humans that is not a Competing Product or an Interferon System Agent or
an Interferon Product and that is either (i) a Planned Product or
Substituted Product, or (ii) utilizes a specific molecular structure towards
the development of which at least $150,000 has been expended between April
15, 1983 and August 31, 1987 either (a) under its Product Development Program
or (b) otherwise by or on behalf of Cetus with Cetus' funds (but not third
party funds), or (iii) is actually Reduced to Practice prior to August 31,
1987 by or on behalf of the Partnership or Cetus (other than pursuant to an
agreement with a third party).

    1.8  "Interferon Product" shall mean a product for the diagnosis,
treatment, prevention or mitigation of disease in humans that (i) has as an
active ingredient any material that is instrumental in achieving beneficial
results through mechanisms attributed to the human interferon system,
including, without limitation, interferons (including gamma interferon),
interferon-like substances, derivatives of interferons, inducers for the
production by the human body of interferons, and the like, (ii) toward the
development of which $150,000 or more of Partnership funds is expected
between April 15, 1983 and August 31, 1987 and (iii) that is marketed by
Cetus, its Affiliates or sublicensees.

    1.9  "Interferon System Agent" shall mean any material that is
instrumental in achieving beneficial results through mechanisms attributed to
the human interferon system including, without limitation, interferons
(including gamma interferon), interferon-like substances, derivatives of
interferons, inducers for the production by the human body of interferons,
and the like, but excluding immunotoxins and molecules which are currently
described as lymphokines, such as Interleukin-2, Macrophage Activating
Factor, Tumor Necrosis Factor and Colony Stimulating Factor, unless such
molecules turn out to be interferons once isolated and analyzed.

    1.10 "Net Sales" shall mean the amount received from commercial sales
(worldwide for diagnostic products and in the United States for therapeutic
products) after the date of this Agreement to independent, unrelated parties
in bona fide arm's-length transactions, less the following deductions: (i)
trade and/or quantity discounts actually allowed and taken in amounts as are
customary in the trade; (ii) commissions paid or allowed to independent
brokers and agents; (iii) sales and other excise taxes and duties paid,
absorbed or allowed; (iv) license, sublicense or distribution fees payable to
third parties in respect of the product; (v) amounts separately billed to
cover transportation costs; (vi) three percent of the amounts invoiced to
cover transportation costs, if such charges are not separately billed; (vii)
amounts repaid or credited by reason of rejections, defects or returns or
because of retroactive price reductions; and (viii) in the case of Competing
Products or products purchased or licensed by Cetus from third parties, an
amount equal to three times the amount of any periodic payments to any third
parties from whom such product was purchased or licensed and three times the
annual amortization, over the remaining estimated useful life of such
product, of any lump sum payments made to such third parties.

    1.11 "Product License Agreement" shall mean any license agreement between
Cetus and the Partnership for the license of any Product.

    1.12  All other capitalized terms shall have the meanings set forth in the
Development Contract.

 2. PURCHASE AND SALE OF PARTNERSHIP INTEREST.

    Effective as the date of exercise of the Purchase Option, Cetus hereby
purchases, and the Limited Partner hereby sells to Cetus, all of such Limited
Partner's interest in the Partnership.

 3. PURCHASE PRICE; PAYMENT.

    The purchase price for the Limited Partner's interest shall be as follows:


                                     I-4


<PAGE>

     3.1  LUMP SUM PAYMENT. The Limited Partner's PRO RATA share, as set
forth on Schedule A, of nineteen million dollars ($19,000,000), payable upon
receipt by Cetus from the Limited Partner of an original of this Agreement
executed by the Limited Partner. Such payment shall be credited against all
payments due under the remainder of this Section 3 until the full amount of
such payment has been so credited; provided, however, that the total credit
taken hereunder in any calendar quarter shall not exceed 10% of the payments
otherwise due under this Section 3 for such quarter.

     3.2  ADDITIONAL PAYMENTS. The Limited Partner's PRO RATA share of the
following:

          (a)    in the case of therapeutic products and       in the case of
     diagnostic products, of the Net Sales, from and after the date of this
     Agreement, by Cetus and its Affiliates of all Human Healthcare Products,
     Interferon Products and Competing Products.

          (b)    in the case of therapeutic products and        in the case of
     diagnostic products, of all royalties received by Cetus and its
     Affiliates under any license for the manufacture, use or sale, after the
     date of this Agreement, of Human Healthcare Products, Interferon
     Products and Competing Products (worldwide for diagnostic products and
     in the United States for therapeutic products).

          (c)    in the case of therapeutic products and        in the case of
     diagnostic products of any front-end fees, distribution fees, prepaid
     royalties or similar one-time, infrequent or special payments received
     by Cetus and its Affiliates and not included in (b) above, for the
     manufacture, use or sale, after the date of this Agreement, of any Human
     Healthcare Product, Competing Product or Interferon Product (worldwide
     for diagnostic products and in the United States for therapeutic
     products), but only to the extent that such payments are not designated
     and used for research, development, testing or obtaining regulatory
     approval of the Human Healthcare Product, Competing Product or
     Interferon Product.

          (d)  Any payments not previously made (i) that were due on August
     31, 1987 or which became due thereafter to the Partnership under any
     Product License Agreement, at the same time and in the same amounts as
     would have been payable under such Product License Agreement had it not
     terminated on August 31, 1987 and (ii) any Excess Cash (as defined in
     the Agreement of Limited Partnership, as amended, of the Partnership)
     that had not been distributed on August 31, 1987 or such earlier date as
     Cetus exercises the Purchase Option.

Notwithstanding Section 3.4, in the case of any Interferon Product, if Shell
Oil Company ("Shell") exercises its option to license such product pursuant
to the Agreement dated as of April 15, 1983 between Cetus and Shell, for
purposes of this Section 3.2 in determining Net Sales of, and the other
payments described in (b) and (c) above received by Cetus and its Affiliates
in respect of such product, such items shall be deemed to include,
respectively, Net Sales of, and such other payments received by, Shell and by
any joint venture between Cetus and Shell.

     3.3  CERTAIN FOREIGN PAYMENTS. Notwithstanding the provisions of Section
3.2, if any therapeutic Human Healthcare Product is not approved for sale in
the United States, but is approved for sale in any other country, payments
shall be made to the Limited Partner in respect of such product in such
country at one-half the rates set forth in Section 3.2; provided, however,
that payments of the type described in Section 3.2(c) shall be amortized over
a five year period from the date of the payment and paid only for months
before the month in which foreign payments in respect of the product become
no longer payable. However, once such therapeutic Human Healthcare Product is
approved for sale in the United States, all payments in respect of such
product in countries other than the United States shall cease, and payments
shall be made solely in respect of such product in the United States;
provided, however, that in the case of Interleukin-2, the payments described
in the first sentence of this Section 3.3 shall continue until such time as
payments to the Limited Partner in respect of United States sales by Cetus
and United States sublicensing and other payments received by Cetus in
respect of Interleukin-2 for any quarter equal or exceed the payments made by
Cetus to the Limited Partner in respect of foreign sales made by Cetus and
foreign sublicensing and other payments received by Cetus in respect of
Interleukin-2 for the quarter in which FDA approval to market the product was
granted.

                                      I-5

<PAGE>

     3.4  JOINT VENTURES. If Cetus or any of its Affiliates commercializes a
Human Healthcare Product, Interferon Product or Competing Product through a
joint venture arrangement with an unrelated third party or parties, any joint
venture Net Sales of such product made directly by Cetus or any Affiliate
shall be deemed for purposes of Section 3.2 to be Net Sales of Cetus, and all
amounts received by Cetus or such Affiliate in respect of its interest in
such joint venture from such product (other than amounts attributable to Net
Sales made directly by Cetus or such Affiliate) shall be deemed for purposes
of Section 3.2 to be sublicensing royalties received by Cetus.

      3.5 CREDITS AGAINST PAYMENTS DUE. Notwithstanding the foregoing, Cetus
shall receive, as a credit against payments otherwise due in respect of any
product in any country other than the United States an amount equal to 50% of
Cetus' and its Affiliates' costs and expenses of obtaining regulatory
approval of such product in such country; provided, however, that in the case
of a therapeutic product, such amounts shall be amortized over a five year
period and credited only through the month during which foreign payments in
respect of the product become no longer payable. In each case, such credit
shall not exceed in any calendar year more than 25% of the payments otherwise
due in respect of such product in such country, with any balance being
carried over to subsequent years.

     3.6  COMBINATION PRODUCTS. Notwithstanding Sections 3.2 and 3.3, in
respect of Combination Products, the payments to be made by Cetus under
Section 3.2 or 3.3 shall be prorated on the basis of the relative values of
the various component products of the Combination Product, in each case
taking into consideration, without limitation, relative cost of goods,
relative sales prices if the components were sold separately, incremental
diagnostic or therapeutic value of each component, relative prices of
products competitive with the various components and relative profit margins
of the various components if sold separately. If a majority in interest of
the limited partners disagree with any proration by Cetus, the matter shall
be submitted to arbitration in accordance with Section 10 hereof.

     3.7  INTEREST. The parties agree that each payment received under
Sections 3.2(a), (b) and (c) and Section 3.3 includes simple interest at a
rate of 9% per annum from the date of this Agreement.

     3.8  REDUCTION IN PAYMENT RATES. Notwithstanding the remainder of this
Section 3, if and when the aggregate of all payments to the limited partners
(or their assignees) made under this Agreement and all other Purchase
Agreements and from the Partnership in respect of royalties and other
payments received from all Product License Agreements between Cetus and the
Partnership aggregate       all of the payment rates under Section 3 shall be
reduced to       of Net Sales and      of all other payments described in
Section 3; and if and when all such payments aggregate      all of such
payment rates shall be reduced to      of Net Sales and      of all other
payments described in Section 3; provided, however, that if such payments
under this Agreement and all other Purchase Agreements and all Product
License Agreements do not aggregate       on or before       then the first
reduction described above will not occur until such payments aggregate
; and if the payments under this Agreement and such other agreements do not
aggregate       on or before       then the second reduction described above
will not occur until such payments aggregate        .

4.   TERM OF PAYMENTS.

     Notwithstanding any other provision of this Agreement, the obligation to
make payments under this Agreement in respect of sales of any product shall
continue until the earlier of (i) the expiration of the last to expire of all
patents covering the product (but only if such product is covered by a
patent) and (ii) December 31, 2001.

5.   ACCOUNTING.

     Within 90 days after the close of each calendar quarter during the term
of this Agreement, Cetus shall render an accounting to the Limited Partner
with respect to all payments due and all credits taken for such quarter. Such
report shall indicate for such calendar quarter the quantity and amount of
sales of each product by Cetus, its Affiliates and sublicensees on which
payments are due hereunder; provided, however, that if Cetus shall not have
received from any sublicensee a report of such sales, then such sales may be
included in the next quarterly report. In addition, Cetus will provide the
Limited Partner with a brief

                                      I-6

<PAGE>

summary of the manner in which payments have been prorated under Section 3.5.
In case no payment is due for any calendar quarter, Cetus shall so report.
Cetus shall keep accurate records in sufficient detail to enable its payments
due hereunder to be determined.

    6. TIME AND CURRENCY OF PAYMENT.

         6.1  PAYMENTS. Payments shown by each calendar quarter report to
have accrued shall be due and payable on the date such report is due and
shall be paid in United States dollars. Any and all taxes due or payable on
such payments or with respect to the remittance thereof, and required by law
to be paid by Cetus, shall be deducted from such payments and shall be paid
by Cetus to the proper taxing authorities. Proof of such payments shall be
secured and sent to the Limited Partner as evidence of payment. The rate of
exchange to be used in computing the amount of the United States dollars due
in satisfaction of payment obligations with respect to foreign countries, if
any, shall be calculated at the exchange rate set by Citibank, N.A., New
York, New York for the purchase of United States dollars with respect to the
currency of the country of origin of such payment on the last business day of
the calendar quarter for which the payment is made. Settlement of payment
obligations shall be made by check.

         6.2  CERTAIN FOREIGN PAYMENTS. If governmental regulations prevent
remittance from any foreign country of amounts due under Section 3 in respect
of that country, Cetus shall so notify the Limited Partner in writing, and
subject to the remainder of this Section 6.2, the obligation under this
Agreement to make payments in respect of sales in that country shall be
suspended (but the amounts due but not paid shall continue to accrue) until
such remittances are possible; provided, however, that to the extent Cetus
invests its own blocked funds in passive investments in such country or
liquidates its own blocked funds at available rates, Cetus shall do the same
with the Limited Partner's blocked funds. In addition, on or before December
31 of each calendar year. Cetus shall liquidate any blocked funds of the
Limited Partner at available rates and pay any amounts received on
liquidation to the Limited Partner. Cetus shall in any event liquidate all
such amounts and pay all amounts received as soon as practicable after
December 31, 2001. All payments by Cetus under this Section 6.2 shall be
deemed to be payment in full of the amounts so paid or liquidated, and Cetus
shall have no liability to the Limited Partner for any actions taken in
accordance with this Section 6.2.

         6.3  LATE PAYMENTS. Any payments due hereunder that are not made
when due shall bear interest at the lesser of 15% per annum or the maximum
rate as may be allowed by law.

    7.  COMPLETION AND COMMERCIALIZATION OF PRODUCTS.

         Cetus agrees to Complete all Planned Products and Substituted
Products; provided that, if Cetus determines in its reasonable business
judgment that Completion of any such product is not technically feasible or,
if Completed, the product will have insufficient commercial value to the
limited partners as a group (assuming for this purpose the limited partners
were to pay all amounts necessary to Complete such product) because of
anticipated Completion costs, including costs of funds, or market or other
factors affecting the possible commercialization of such product, Cetus may
abandon its efforts to Complete such product. Cetus will use its best
efforts, and will require its sublicensees to use their best efforts, in each
case within the standards of commercial reasonableness, to commercialize each
Human Healthcare Product and Interferon Product; provided that, if Shell
exercises its option to license any such Interferon Product referred to in
Section 3.2, Cetus shall only be required to use its best efforts to require
Shell to comply with the provisions of such license.

    8.  PATENT INFRINGEMENT.

         If a third party infringes, by the manufacture or sale of a product
competitive with a Human Healthcare Product (in the United States for a
therapeutic product or in any country for a diagnostic product) any patent
covering any Human Healthcare Product, Cetus shall have the sole right, at
its own expense, to bring legal action to restrain such infringement and for
damages. The parties shall share in any recovery from any such action as
follows: (i) first 100% to Cetus to the extent of its costs and expenses,
including attorneys' fees, of the action and (ii) thereafter, ninety percent
(90%) to Cetus and ten percent (10%) to the limited partners PRO RATA.

                                 I-7

<PAGE>

     9. EFFECTIVE DATE AND TERM.

         This Agreement will become effective on the day and year first above
written in accordance with Section 9.3 of the Partnership Agreement and shall
remain in full force and effect until December 31, 2001.

    10. ARBITRATION.

         10.1  DISPUTES. If any dispute arises out of this Agreement, the
parties will endeavor to settle such dispute amicably. The Limited Partner
acknowledges that this Agreement is identical (except as to Schedule A) to
the agreements between Cetus and the other limited partners of the
Partnership. The Limited Partner agrees that if any dispute arises under this
Agreement, the Limited Partner will confer with the other limited partners
and will agree to settle such dispute in such manner as may be agreed to by a
majority in interest of the limited partners. The Limited Partner agrees to be
bound by any such settlement.

         10.2  ARBITRATION. If the parties shall fail to settle any dispute
in accordance with Section 10.1, such dispute shall be finally settled by
arbitration conducted in San Francisco, California in accordance with the
then existing rules of the American Arbitration Association, subject to
Section 10.3, and judgment upon the award rendered by the arbitrators
may be entered in any court having jurisdiction thereof. In the case of any
such arbitration, a representative (the "Representative") shall be appointed
by a majority in interest of the limited partners. The parties hereby agree
that service of any notices in the course of such arbitration at their
respective addresses as provided for in Section 11 shall be valid and
sufficient.

         10.3  ARBITRATION. In any arbitration pursuant to Section 10.1, the
award shall be rendered by a majority of the members of a board of
arbitration consisting of three members, all of whom will be appointed by
Cetus and the Representative jointly or, if Cetus and the Representative
cannot agree as to three arbitrators within 30 days after commencement of the
arbitration proceeding, one arbitrator shall be appointed by each of them
within 45 days after the commencement of the arbitration proceeding, and the
third shall be appointed by mutual agreement of the two appointed
arbitrators. In the event of failure of said two arbitrators to agree upon
the third arbitrator within 75 days after commencement of the arbitration
proceeding, the third arbitrator shall be appointed by the American
Arbitration Association in accordance with its then existing rules.
Notwithstanding the foregoing, if Cetus or the Representative shall fail to
appoint an arbitrator within the specified time period, such arbitrator as
well as the third arbitrator shall be appointed by the American Arbitration
Association in accordance with its then existing rules. For the purposes of
this Section 10.3 the "commencement of the arbitration proceeding" shall be
deemed to be the date upon which a written demand for arbitration is received
by one party from the other. The decision of the Representative shall be
final and binding on each Limited Partner.

    11.  NOTICES.

         Any notice, payment or other communication required or permitted to
be given hereunder shall be given in writing and shall be delivered by hand
or by registered or certified mail, postage prepaid and return receipt
requested, addressed to the Limited Partner at the address set forth on
Schedule A hereto and to Cetus at the address set forth below, or such other
address as may be designated by either party by notice pursuant to this
Section 11.

         If to Cetus:

                      Cetus Corporation
                      1400 Fifty-third Street
                      Emeryville, California 94608
                      Attention: President

Any notice given in conformity with this Section 11 shall be deemed to be
effective when received by the addressee, if delivered by hand, and five days
after mailing, if mailed. The Limited Partner will notify Cetus in writing of
any change of address of the Limited Partner, and Cetus shall be entitled to
rely on the last address so given in making payments hereunder.

                                  I-8

<PAGE>

12. 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,
when taken together, shall constitute this Agreement.

13. GOVERNING LAW.

    This Agreement shall be governed by and construed in accordance with the
laws of the State of California as applied between residents of that State
entering into contracts wholly to be performed in that State.

14. VALIDITY OF PROVISIONS, SEVERABILITY.

    If any provision of this Agreement is or becomes or is deemed invalid,
illegal, or unenforceable in any jurisdiction, (a) such provision will be
deemed amended to conform to applicable laws of such jurisdiction so as to be
valid and enforceable or, if it cannot be so amended without materially
altering the intention of the parties, it will be stricken, (b) the validity,
legality and enforceability of such provision will not in any way be affected
or impaired thereby in any other jurisdiction, and (c) the remainder of this
Agreement will remain in full force and effect.

15. AMENDMENTS.

    No amendment, modification or addition hereto shall be effective or
binding unless set forth in a writing and executed by a duly authorized
representative of each party.

16. ASSIGNMENT.

    Cetus may not assign its rights hereunder without the prior written
consent of a majority in interest of the Limited Partners, which consent
shall not be unreasonably withheld, except to a person or entity (i) with
which Cetus is merged or consolidated or which purchases all or substantially
all of its assets or (ii) which purchases all or substantially all of Cetus'
human healthcare business, which assumes in writing all of Cetus' obligations
hereunder, and which has, on the date of the purchase, a net worth of at
least $250,000,000. Any consent of a majority in interest of the limited
partners shall be binding on the Limited Partner, whether or not the Limited
Partner in fact consented.

    IN WITNESS WHEREOF, the parties have executed this Agreement on the date
first above written.

                                       CETUS CORPORATION


                                       By:
                                          -------------------------------------
                                                         President

                                          -------------------------------------
                                                     (Limited Partner)


                                      I-9

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                                   SCHEDULE A

           LIMITED PARTNER                            PRO RATA SHARE
          NAME AND ADDRESS                             OF PAYMENTS
          ----------------                            --------------













                                     I-10