Document:

UNCONDITIONAL GUARANTEE OF PAYMENT
                                     (Brown)

TO:  IMPERIAL BANK, a California banking corporation

     1.  FOR  VALUABLE  CONSIDERATION,   the  undersigned   (hereinafter  called
"Guarantor"),  whose  address is set forth after  Guarantor's  signature  below,
jointly and severally,  and  unconditionally,  guarantees and promises to pay to
IMPERIAL BANK, a California banking  corporation  (hereinafter called "Lender"),
or order, upon demand, in lawful money of the United States, (i) that Promissory
Note dated July 13, 2000, made by MAIN STREET AND MAIN INCORPORATED,  a Delaware
corporation  (hereinafter  called  "Borrower"),  in favor of  Lender in the face
amount  of  FIVE  MILLION  AND  NO/100  DOLLARS  ($5,000,000.00)  (the  "Note"),
principal and interest and all other sums payable thereunder, or at the election
of Lender any one or more installments thereof, in the event that Borrower fails
to punctually pay any one or more  installments  of the Note  (principal  and/or
interest),  or any other sum  payable  thereunder  at the time and in the manner
provided therein;  and (ii) all other indebtedness of Borrower to Lender arising
under or in connection  with the Note, any loan agreement  between  Borrower and
Lender  executed and delivered in connection with the Note and any deed of trust
or other  security  document or instrument  given in connection  therewith  (the
indebtedness  evidenced  by  the  Note  together  with  all  other  indebtedness
specified above is hereinafter collectively called the "Indebtedness").  This is
an absolute, continuing and unconditional guarantee of payment and not merely of
collection.

     2. The  obligations  of  Guarantor  hereunder  are  joint  and  several  if
Guarantor is more than one person or entity, are separate and independent of the
obligations  of Borrower and of any other  guarantor,  and a separate  action or
actions  may be brought  and  prosecuted  against  Guarantor  whether  action is
brought against Borrower or any other guarantor or whether Borrower or any other
guarantor  is joined in any action or  actions.  The  obligations  of  Guarantor
hereunder  shall  survive and continue in full force and effect until payment in
full of the  Indebtedness is actually  received by Lender and the period of time
has expired during which any payment made by Borrower or Guarantor to Lender may
be determined to be a Preferential Payment (defined below),  notwithstanding any
release or  termination  of  Borrower's  or any other  guarantor's  liability by
express  or  implied   agreement   with  Lender  or  by  operation  of  law  and
notwithstanding that the Indebtedness or any part thereof is deemed to have been
paid or  discharged  by  operation of law or by some act or agreement of Lender.
For purposes of this Guarantee, the Indebtedness shall be deemed to be paid only
to the extent that Lender actually receives  immediately  available funds and to
the extent of any credit bid by Lender at any  foreclosure  or trustee's sale of
any security for the Indebtedness.

     3.  Guarantor  agrees that to the extent  Borrower or  Guarantor  makes any
payment to Lender in connection  with the  Indebtedness,  and all or any part of
such  payment  is  subsequently  invalidated,   declared  to  be  fraudulent  or
preferential,  set  aside or  required  to be repaid by Lender or paid over to a
trustee,  receiver or any other  entity,  whether  under any  bankruptcy  act or
<PAGE>
otherwise  (any such  payment  is  hereinafter  referred  to as a  "Preferential
Payment"),  then this  Guarantee  shall  continue  to be  effective  or shall be
reinstated,  as the case may be, and, to the extent of such payment or repayment
by Lender,  the  Indebtedness  or part thereof  intended to be satisfied by such
Preferential  Payment shall be revived and continued in full force and effect as
if said Preferential Payment had not been made.

     4.  Guarantor  is providing  this  Guarantee at the instance and request of
Borrower to induce  Lender to extend or  continue  financial  accommodations  to
Borrower.  Guarantor  hereby  represents and warrants that Guarantor is and will
continue to be fully informed  about all aspects of the financial  condition and
business affairs of Borrower that Guarantor deems relevant to the obligations of
Guarantor  hereunder and hereby waives and fully discharges  Lender from any and
all obligations to communicate to Guarantor any information whatsoever regarding
Borrower or Borrower's financial condition or business affairs.

     5.  Guarantor  authorizes  Lender,  without  notice or demand  and  without
affecting  Guarantor's  liability  hereunder,  from time to time, to: (a) renew,
modify, compromise,  extend, accelerate or otherwise change the time for payment
of, or  otherwise  change  the terms of the  Indebtedness  or any part  thereof,
including  increasing or decreasing the rate of interest  thereon;  (b) release,
substitute or add any one or more endorsers,  Guarantor or other guarantors; (c)
take and hold  security for the payment of this  Guarantee or the  Indebtedness,
and  enforce,  exchange,  substitute,  subordinate,  waive or  release  any such
security;  (d) proceed  against such  security and direct the order or manner of
sale of such security as Lender in its discretion  may determine;  and (e) apply
any and all  payments  from  Borrower,  Guarantor  or any  other  guarantor,  or
recoveries  from  such  security,  in such  order or  manner  as  Lender  in its
discretion may determine.

     6.  Guarantor  waives and  agrees  not to assert:  (a) any right to require
Lender to proceed against Borrower or any other guarantor, to proceed against or
exhaust any security for the Indebtedness,  to pursue any other remedy available
to Lender,  or to pursue any remedy in any particular  order or manner;  (b) the
benefit of any statute of limitations  affecting Guarantor's liability hereunder
or the  enforcement  hereof;  (c) demand,  diligence,  presentment  for payment,
protest  and  demand,  and  notice  of  extension,  dishonor,  protest,  demand,
nonpayment  and  acceptance  of this  Guarantee;  (d)  notice of the  existence,
creation or incurring of new or additional  indebtedness  of Borrower to Lender;
(e) the benefits of any statutory  provision limiting the liability of a surety;
(f) any defense arising by reason of any disability or other defense of Borrower
or by reason of the cessation from any cause  whatsoever  (other than payment in
full) of the liability of Borrower for the Indebtedness; and (g) the benefits of
any  statutory  provision  limiting  the right of Lender to recover a deficiency
judgment,  or to otherwise  proceed  against any person or entity  obligated for
payment of the  Indebtedness,  after any  foreclosure  or trustee's  sale of any
security  for the  Indebtedness.  Guarantor  hereby  expressly  consents  to any
impairment of  collateral,  including,  but not limited to, failure to perfect a
security  interest and release  collateral  and any such  impairment  or release
shall not affect Guarantor's obligations hereunder. Until payment in full of the
Indebtedness, Guarantor shall have no right of subrogation and hereby waives any
right to enforce any remedy which Lender now has, or may hereafter have, against

                                      -2-
<PAGE>
Borrower,  and  waives any  benefit  of,  and any right to  participate  in, any
security now or hereafter held by Lender.

     7. All existing and future  indebtedness of Borrower to Guarantor is hereby
subordinated to the Indebtedness and such indebtedness of Borrower to Guarantor,
if Lender so requests, shall be collected, enforced and received by Guarantor as
trustee  for  Lender  and  shall  be  paid  over to  Lender  on  account  of the
Indebtedness,  but without  reducing or affecting in any manner the liability of
Guarantor under the other provisions of this Guarantee.

     8. In addition to all liens upon, and rights of setoff against, the monies,
securities or other property of Guarantor  given to Lender by law,  Lender shall
have a lien and a right of setoff against, and Guarantor hereby grants to Lender
a security  interest in, all monies,  securities and other property of Guarantor
now and hereafter in the  possession of or on deposit with Lender,  whether held
in a general or special  account or deposit,  or for  safekeeping  or otherwise;
every such lien and right of setoff may be exercised upon Borrower's  default in
the payment of the  Indebtedness  or upon the occurrence of any event of default
under this Guarantee or any other document or instrument  executed and delivered
in connection with the Indebtedness.  No lien or right of setoff shall be deemed
to have been waived by any act or conduct on the part of Lender,  by any neglect
to exercise  such right of setoff or to enforce such lien, or by any delay in so
doing.

     9. If Borrower is a corporation,  limited liability company, partnership or
trust,  it is not necessary for Lender to inquire into the powers of Borrower or
the officers,  directors, members, managers, partners, trustees or agents acting
or purporting to act on its behalf,  and any of the Indebtedness made or created
in reliance  upon the  professed  exercise of such  powers  shall be  guaranteed
hereunder.

     10. Guarantor agrees to deliver to Lender financial statements,  income tax
returns  and  other  financial  information  in form and  level of  detail,  and
containing certifications,  as and to the extent required pursuant to the Credit
Agreement  between  Borrower  and Lender  dated April 2, 1999 (as  amended,  the
"Credit Agreement").

     11. All  financial  statements,  income  tax  returns  and other  financial
information previously or hereafter given to Lender by or on behalf of Guarantor
are and shall be true, complete and correct as of the date thereof.

     12.  Guarantor  agrees to pay all  attorneys'  fees and all other costs and
expenses  which may be  incurred by Lender in  enforcing  this  Guarantee  or in
collecting all or any part of the Indebtedness.

     13. This Guarantee sets forth the entire  agreement of Guarantor and Lender
with  respect to the subject  matter  hereof and  supersedes  all prior oral and
written agreements and  representations by Lender to Guarantor.  No modification
or waiver of any  provision of this  Guarantee or any right of Lender  hereunder
and no release of Guarantor from any obligation

                                      -3-
<PAGE>
hereunder  shall be  effective  unless in a writing  executed  by an  authorized
officer  of  Lender.  There  are  no  conditions,  oral  or  otherwise,  on  the
effectiveness of this Guarantee.

     14. This Guarantee  shall inure to the benefit of Lender and its successors
and  assigns  and  shall be  binding  upon  Guarantor  and its  heirs,  personal
representatives,  successors  and assigns.  Lender may assign this  Guarantee in
whole or in part without notice.

     15. Guarantor shall not, without Lender's prior written consent, enter into
any merger or  consolidation  (if Guarantor is other than a natural  person) or,
except in the ordinary course of business,  sell, lease or otherwise transfer or
dispose of a material portion of Guarantor's assets.

     16. Guarantor  represents and warrants to Lender that: (a) (if Guarantor is
not a  natural  person)  it is  duly  organized,  validly  existing  and in good
standing under the laws of the jurisdiction of its  organization;  (b) Guarantor
has full capacity and authority to execute,  deliver and perform this Guarantee,
and the  execution,  delivery and  performance  of this  Guarantee  will not (i)
violate  any law or  regulation,  (ii) (if  Guarantor  is not a natural  person)
violate any provision of Guarantor's  organizational documents, (iii) violate or
constitute  (with  due  notice  or lapse of time or both) a  default  under  any
indenture,  agreement, license or other instrument to which Guarantor is a party
or by which  Guarantor  or any of  Guarantor's  properties  may be  bound,  (iv)
violate  any order of any court,  tribunal  or  governmental  agency  binding on
Guarantor  or any of  Guarantor's  properties,  (v)  result in the  creation  or
imposition of any lien of any nature whatsoever on any of Guarantor's properties
or assets,  (vi) render Guarantor  insolvent under generally accepted accounting
principles,  (vii)  leave  Guarantor  with  remaining  assets  which  constitute
unreasonably small capital given the nature of its business, or (viii) result in
the   incurrence  of  debts  (whether   matured  or  unmatured,   liquidated  or
unliquidated,  absolute,  fixed or contingent) beyond Guarantor's ability to pay
them when and as they  become  due;  (c) no approval or consent of, or filing or
registration with, any federal,  state or local regulatory authority is required
in connection  with the execution,  delivery and  performance of this Guarantee;
(d) the value to  Guarantor of the  advances of the  Indebtedness  being made to
Borrower is worth at least as much as the liability and obligations of Guarantor
hereunder  and may  reasonably  be  expected  to benefit  Guarantor  directly or
indirectly;  and (e) this  Guarantee  constitutes  the legal,  valid and binding
obligation of Guarantor,  enforceable  against  Guarantor in accordance with its
terms. These  representations and warranties shall survive the execution of this
Guarantee.  As  used in this  paragraph,  "insolvent"  means  the  present  fair
saleable value of assets is less than the probable amount required to be paid on
existing debts when and as they mature.

     17. This Guarantee shall be governed by and construed according to the laws
of the State of Kentucky. Guarantor represents and warrants that the domicile of
Guarantor and Guarantor's spouse is the State of Kentucky.

     18. All claims or controversies of any type regarding  matters occurring at
any time arising under or relating to this Guarantee (including, but not limited
to, claims under  contract,  law or statute),  except the parties rights to seek
injunctive relief between Guarantor and the Lender (including claims against any
shareholders  or  affiliated  entities  of the  Lender  in  claims  against  any

                                      -4-
<PAGE>
directors,  officers,  employees  or  agents of the  Lender or their  affiliated
entities), shall be settled and finally determined by one arbitrator in Campbell
County, Kentucky, in accordance with the arbitration rules of JAMS/Endispute and
judgment by the  arbitrator  may be entered into any court  having  jurisdiction
thereof.  This agreement to arbitrate  includes all claims of breach of contract
and  all  other  claims  of any  type to the  maximum  extent  permissible.  The
prevailing party in any such  arbitration  shall be awarded its reasonable costs
and attorneys' fees as determined by the arbitrator.

     IN WITNESS  WHEREOF these presents are executed as of the 18th day of July,
2000.

                                        GUARANTOR:

                                        /s/ Bart A. Brown, Jr.
                                        ----------------------------------------
                                        BART A. BROWN, JR.

                                        Address: 140 Highland Avenue
                                                 Ft. Thomas, Kentucky 41075<PAGE>   1

                                                                    EXHIBIT 4.11

                          BIOSOURCE TECHNOLOGIES, INC.

================================================================================

                              COMMON STOCK WARRANT
                                    AGREEMENT

================================================================================

<PAGE>   2

                                TABLE OF CONTENTS

<TABLE>
<CAPTION>

                                                                                          Page
                                                                                          ----
<S>     <C>                                                                               <C>
ARTICLE I GRANT OF WARRANT...................................................................1
        Section 1.1 Issuance of Warrant to Purchase Common Stock.............................1
        Section 1.2 Closing..................................................................1
ARTICLE II DEFINITIONS.......................................................................2
        Section 2.1 Definitions and References...............................................2
ARTICLE III COVENANTS OF TDCC AND BIOSOURCE..................................................3
        Section 3.1 Right to Purchase Additional Securities..................................3
        Section 3.2 Board Seat...............................................................4
        Section 3.3 Initial Public Offering..................................................5
        Section 3.4 Information and Registration Rights Agreement............................5
        Section 3.5 Co-Sale Rights...........................................................5
        Section 3.6 Purchase of Securities by TDCC...........................................7
        Section 3.7 Right to Make Offer......................................................8
        Section 3.8 Expiration of Rights.....................................................8
ARTICLE IV REPRESENTATIONS AND WARRANTIES....................................................9
        Section 4.1 Representations and Warranties of Biosource..............................9
        Section 4.2 Representations and Warranties of TDCC..................................13
ARTICLE V MISCELLANEOUS.....................................................................14
        Section 5.1 Successors and Assigns..................................................14
        Section 5.2 Governing Law...........................................................14
        Section 5.3 Counterparts............................................................14
        Section 5.4 Titles and Subtitles....................................................14
        Section 5.5 Notices.................................................................14
        Section 5.6 Expenses................................................................15
        Section 5.7 Entire Agreement; Amendment.............................................15
        Section 5.8 Severability............................................................16
        Section 5.9 Delays or Omissions.....................................................16
        Section 5.10 Exhibits...............................................................16
        Section 5.11 Corporate Securities Law...............................................16
        Section 5.12 Publicity..............................................................16
        Section 5.13 Regulatory Approval....................................................16
        Section 5.14 Compliance Certificate.................................................16
        Section 5.15 Survival...............................................................17
        Section 5.16 Dispute Resolution.....................................................17
        Section 5.17 HSR Filings............................................................17
</TABLE>

Exhibit A      Common Stock Purchase Warrant

Exhibit B      Schedule of Exceptions

Exhibit C      Fourth Amendment to the Information and Registration Rights
               Agreement

                                       i
<PAGE>   3

                          BIOSOURCE TECHNOLOGIES, INC.

                              COMMON STOCK WARRANT
                                    AGREEMENT

               THIS COMMON STOCK WARRANT AGREEMENT is made as of the 1st day of
September, 1998, by and between Biosource Technologies, Inc., a California
corporation ("Biosource"), The Dow Chemical Company, a Delaware corporation
("TDCC"), Technology Directors II, LLC, a Delaware limited liability company,
Technology Directors II BST, LLC, a Delaware limited liability company
(Technology Directors II, LLC and Technology Directors II BST, LLC herein
referred to as "Technology Directors") and Robert L. Erwin, an individual
residing in the State of California.

                                    RECITALS

               WHEREAS, Biosource and TDCC have entered into that certain
Collaboration and License Agreement (the "Collaboration Agreement") of even date
herewith (capitalized terms not otherwise defined herein being used herein as
therein defined); and

               WHEREAS, in connection with the Collaboration Agreement,
Biosource desires to grant to TDCC a warrant to purchase common stock of
Biosource as set forth below.

               NOW, THEREFORE, in consideration for the execution by Biosource
and TDCC of the Collaboration Agreement and the mutual covenants and agreements
contained herein, intending to be legally bound, Biosource, TDCC, Technology
Directors and Robert L. Erwin do hereby agree as follows:

                                    ARTICLE I
                                GRANT OF WARRANT

        Section 1.1   Issuance of Warrant to Purchase Common Stock. Subject to
the terms and conditions of this Agreement and in consideration of the
Collaboration Agreement and certain amounts which TDCC has agreed to pay
thereunder, Biosource agrees to issue to TDCC at the Closing (as defined below)
a warrant in the form attached hereto as Exhibit A (the "Warrant") to purchase,
for the periods and prices set forth in the Warrant, 1,232,061 shares of Common
Stock as set forth in such Warrant.

        Section 1.2   Closing. The issuance of the Warrant shall take place
concurrently with the Effective Date of the Collaboration Agreement upon payment
of the $10,000,000 technology access fee contemplated by Section 6.1 thereof or
at such other time and place as Biosource and TDCC agree in writing (which time
and place are designated as the "Closing"). At the Closing, Biosource shall
deliver to TDCC the Warrant.

<PAGE>   4

                                   ARTICLE II
                                   DEFINITIONS

        Section 2.1   Definitions and References. For the purposes of this
Agreement, in addition to the definitions set forth above and elsewhere herein,
the following terms shall have the following respective meanings:

               "Additional Sale Closing" shall mean the closing of any sale of
Additional Securities by Biosource.

               "Additional Securities" shall mean all common stock of Biosource
("Common Stock") and any other capital stock, debenture or warrant convertible
into or exchangeable for Common Stock (collectively "Securities") which are
issued by Biosource after the date hereof other than (i) any Securities issued
or issuable to all of the holders of Securities then outstanding on a
proportionate basis (based on such holders' respective ownership of the
Securities); (ii) any Securities issued or issuable to any employees, officers
or directors pursuant to any stock option, benefit or incentive compensation
plan approved by the Board of Directors of Biosource (collectively, a "Plan");
(iii) Securities which are reissued by Biosource to employees pursuant to a Plan
following the repurchase, redemption or other acquisition of such Securities by
Biosource from any employee; (iv) any Securities issued in connection with a
merger, purchase of assets, business combination, or collaboration with a third
party; and (v) any Securities issued upon the conversion or exercise of
Securities of Biosource outstanding at the date hereof.

               "Affiliate" shall mean, with respect to TDCC, an entity
controlled by or under common control of TDCC including, but not limited to, Dow
AgroSciences LLC.

               "Commission" shall mean the U.S. Securities and Exchange
Commission and any successor agency.

               "Exchange Act" shall mean the Securities Exchange Act of 1934, as
amended, or similar federal statute, and the rules and regulations of the
Commission thereunder, all as the same shall be in effect at the time.

               "Outstanding Securities" shall mean outstanding Securities of
Biosource.

               "Securities Act" shall mean the Securities Act of 1933, as
amended or any similar federal statute, and the rules and regulations of the
Commission thereunder, all as the same shall be in effect at the time.

               "TDCC's Pro Rata Share" shall mean TDCC's percentage ownership of
Biosource's fully diluted capital stock, assuming exercise of the Warrant, with
all convertible or exchangeable instruments or securities calculated as if
converted to Biosource Common Stock. TDCC's percentage ownership shall include
the Common Stock issued to TDCC upon any exercise of the Warrant but not any
capital stock of Biosource purchased by TDCC or any Affiliate of TDCC in
violation of the terms of this Agreement.

               "Warrant Stock" shall mean the Common Stock issuable upon
exercise of the Warrant.

                                       2.
<PAGE>   5

                                   ARTICLE III
                         COVENANTS OF TDCC AND BIOSOURCE

        Section 3.1   Right to Purchase Additional Securities.

               (a) Biosource shall give TDCC written notice of Biosource's
intention to issue Additional Securities (the "Issuance Notice") at least thirty
(30) business days (or such shorter period as may be necessary under the
circumstances) prior to the anticipated Additional Sale Closing, of the sale of
such Additional Securities, describing the type of Additional Securities, the
anticipated price at which the Additional Securities will be issued and the
general terms upon which Biosource proposes to issue the Additional Securities,
including the anticipated date of such Additional Sale Closing.

               (b) Except as otherwise provided herein, upon any Additional Sale
Closing TDCC shall have the option (the "Option") to purchase from Biosource a
number of shares of Additional Securities up to TDCC's Pro Rata Share of the
number of shares of Additional Securities to be sold by Biosource plus the
number of shares of Additional Securities equal to ten percent (10%) of such
Additional Securities to be sold at such Additional Sale Closing (the "Optioned
Shares"), at a price per share equal to the price per share at which the
Additional Securities were sold to other purchasers in the Additional Sale
Closing. The aggregate price paid by TDCC for the purchase of such Additional
Securities concurrent with the Additional Sale Closing is hereinafter referred
to as the "Purchase Price."

               (c) TDCC shall have twenty (20) business days from the date it
receives the Issuance Notice to elect to purchase the Optioned Shares by giving
written notice to Biosource of its desire to purchase the Optioned Shares,
stating the quantity of Optioned Shares to be purchased. Such written notice
shall constitute the irrevocable agreement of TDCC to purchase the quantity of
Optioned Shares indicated in such response notice at the price stated in the
Issuance Notice (or if such shares are issued to other purchasers at a lower
price, at the price so issued). Any purchase by TDCC of Optioned Shares shall be
consummated on or prior to the date of such Additional Sale Closing of the sale
of the Additional Securities set forth in the Issuance Notice, on the same terms
(including registration and other investor rights) as the Additional Securities
are issued to other purchasers at the Additional Sale Closing.

               (d) Any Additional Sale Closing of the sale and purchase of the
Additional Securities pursuant to Section 3.1 shall be held at the principal
executive offices of Biosource, unless otherwise determined by the Board of
Directors of Biosource.

               (e) At any Additional Sale Closing, subject to the terms and
conditions of this Agreement, Biosource shall deliver to TDCC a certificate
registered in TDCC's name representing the Optioned Shares purchased at the
Additional Sale Closing, and TDCC shall deliver the Purchase Price to Biosource
by certified check payable to Biosource or by wire transfer of immediately
available funds to an account specified by Biosource in the Issuance Notice.

               (f) TDCC hereby acknowledges and agrees that it will, in
connection with the exercise of any purchase of Additional Securities, enter
into such security purchase and other

                                       3.
<PAGE>   6

investor agreements as may be entered into by the other purchasers of Additional
Securities on the same terms as such other purchasers.

        Section 3.2   Board Seat. Provided TDCC exercises all Warrants acquired
pursuant to this Agreement and does not dispose of any shares of Common Stock
received upon such exercise, and subject to expiration pursuant to Sections 3.8
(i), 3.8 (iii) and 3.8 (iv) of this Agreement, Biosource will make available to
TDCC one seat on its Board of Directors at TDCC's option on the following terms:

               (a) TDCC shall propose a business person who has substantial
business management or business development experience and the Board of
Directors shall appoint the person proposed by TDCC to the Board for election
until the next meeting of Shareholders to elect directors.

               (b) The Nominating Committee, or if there is no Nominating
Committee the Board of Directors, will nominate the person proposed by TDCC to
the Board for election at the next meeting of Shareholders to elect directors,
provided such person meets the qualifications specified in Section 3.2(a) above.

               (c) In connection with each successive shareholder meeting, the
TDCC nominee will be included in the management proxy to shareholders with the
same recommendation as other management nominees; provided, however, that no
officer or director of Biosource shall be required to extend such recommendation
if doing so would, in the reasonable judgment of such officer or director, cause
such officer or director to breach his fiduciary duty to Biosource or its
shareholders.

               (d) If elected, the TDCC nominee will be expected to recuse
himself or herself from any matter where the interests of TDCC may be adverse to
the interest of shareholders generally and from any matter involving a material
collaboration or contract between Biosource and a direct competitor of TDCC.

               At all times that TDCC does not have a TDCC representative on the
Board of Directors of Biosource during and for two years after the expiration of
the term of the Research Collaboration (as defined in the Collaboration
Agreement), but in no event after the occurrence of the events of expiration set
forth in Sections 3.8(iii) and 3.8(iv) of this Agreement, and provided TDCC
either owns or retains the right to purchase by exercise of the Warrant at least
10% of the Outstanding Securities of Biosource (or less than 10%, of the
Outstanding Securities of Biosource, provided that TDCC has not disposed of any
shares of Warrant Stock) Biosource will allow one representative of TDCC to
observe the meetings of the Board of Directors of Biosource. The representative
of TDCC may attend meetings of Biosource's Board of Directors in a nonvoting
observer capacity and, in this respect, Biosource shall give such representative
copies of all notices, minutes, consents and other material that it provides to
its directors, at the same time such materials are provided to directors, for
all meetings of the Board of Directors; provided, however, that Biosource
reserves the right to exclude such representative from access to any material or
meeting or portion thereof if the Board of Directors of Biosource believes based
upon advice of counsel that such exclusion is necessary to preserve the
attorney-client privilege or to protect highly confidential proprietary
information. Upon reasonable notice, such

                                       4.
<PAGE>   7

representative may address the Board of Directors with respect to significant
business issues facing Biosource.

        Section 3.3   Initial Public Offering.

               (a) Biosource agrees to use reasonable business efforts to effect
an effective registration statement under the Securities Act (an "IPO") not
later than December 31, 2008. In the event that Biosource is unsuccessful in
effecting an IPO by December 31, 2008, and cannot otherwise arrange the private
sale of Warrant Stock then held by TDCC, Biosource shall repurchase the shares
of Warrant Stock then held by TDCC or its Affiliates at the fair market value
thereof as determined by a mutually agreed upon nationally recognized investment
bank and calculated based on a sale of all Outstanding Securities of Biosource
with no discount for illiquidity or minority interest.

               (b) TDCC further acknowledges and agrees that it will enter into
such customary agreements so requested by the managing underwriter in connection
with the closing of a firm commitment underwritten public offering of Common
Stock of or for the account of Biosource pursuant to an IPO, including an
agreement restricting the sale or disposition of any Securities held by TDCC for
the same period of time following the IPO as agreed by the officers of Biosource
and the other parties to this Agreement, as applicable to the Securities held by
the other parties to this Agreement.

        Section 3.4   Information and Registration Rights Agreement. TDCC shall
have the same rights conferred by the Information and Registration Rights
Agreement of Biosource as amended as of April 13, 1998. TDCC will be made a
party to such agreement by the execution of the Fourth Amendment to the
Information and Registration Rights Agreement to be effective as of the date
hereof in the form attached hereto as Exhibit C.

        Section 3.5   Co-Sale Rights. In the event of any offer by any of TDCC
or Technology Directors or Robert L. Erwin (each an "Offeror") to sell Common
Stock or Preferred Stock (an "Offer"), the other parties (TDCC, Technology
Directors or Robert L. Erwin, as the case may be, (the "Right Holder")) may
elect to exercise the right of co-sale set forth below "Co-Sale Rights").
Co-Sale Rights shall apply where the putative buyer is a party to this
Agreement. Subject to the terms and conditions hereof, the Right Holder will
have the right, exercisable upon written notice to Offeror within thirty (30)
days after the date when the Offeror's notice is effective, to participate in
the Offeror's sale of stock pursuant to the specified terms and conditions of
Offeror's notice. To the extent the Right Holder exercises such right of
participation in accordance with the terms and conditions set forth below, the
number of shares of Common Stock or Preferred Stock that the Offeror may sell
pursuant to such Offer shall be correspondingly reduced. The right of
participation of the Right Holder shall be subject to the following terms and
conditions:

               (a) Calculation of Shares. The Right Holder may sell all or any
part of that number of shares of Common Stock and/or Preferred Stock of
Biosource equal to the product obtained by multiplying (i) the aggregate number
of shares of Common Stock and/or Preferred Stock covered by the Offer by (ii) a
fraction, the numerator of which is the number of shares of Common Stock of
Biosource then owned by such Right Holder (assuming conversion of all

                                       5.
<PAGE>   8

outstanding shares of Preferred Stock, but excluding any unexercised portion of
TDCC's Warrant to purchase Common Stock) and the denominator of which is the
aggregate number of shares of Common Stock of Biosource then owned by the
Offeror and all Right Holders who desire to sell. Notwithstanding the foregoing,
however, no Right Holder may elect to sell shares of any class or series of
stock in lieu of shares of a particular class or series specified in the Offer
unless the proposed transferee agrees to accept shares of such other series or
class in lieu of the class or series of stock specified in the Offer.

               (b) Delivery of Certificates. The Right Holder may effect its
participation in the sale by delivering to the Offeror for transfer to the
proposed transferee one or more certificates, properly endorsed for transfer,
which represent:

                           (i) the number of shares of Common Stock or Preferred
               Stock that the Right Holder elects to sell pursuant to this
               Section 3.5; or

                           (ii) to the extent the Offer specifies shares of
               Common Stock and the Right Holder desires to sell shares of
               Preferred Stock, that number of shares of Preferred Stock that is
               at such time convertible into the number of shares of Common
               Stock that such Right Holder elects to sell pursuant to this
               Section 3.5, provided that if the proposed transferee objects to
               the delivery of Preferred Stock in lieu of Common Stock, such
               Right Holder may convert such Preferred Stock and deliver Common
               Stock as provided in subparagraph (i) above.

               (c) The stock certificate or certificates that the Right Holder
delivers to the Offeror pursuant to Section 3.5 shall be transferred by the
Offeror to the transferee in consummation of the sale of the Common Stock and/or
Preferred Stock pursuant to the terms and conditions specified in Offeror's
Notice, and the Offeror shall promptly thereafter remit to such Right Holder
that portion of the sale proceeds to which a Right Holder is entitled by reason
of its participation in such sale.

               (d) The exercise or nonexercise of the rights of a Right Holder
hereunder to participate in one or more sales of stock made by the Offeror shall
not adversely affect his or its rights to participate in subsequent sales
pursuant to Section 3.5 hereof.

               (e) The participation rights of the Right Holder shall not apply
to:

                           (i) shares of Common Stock held by a party (including
               shares of Common Stock into which shares of Preferred Stock are
               convertible at the time of transfer), until such sales or
               transfers by such party aggregate a total of 10,000 shares of
               Common Stock (including Common Stock into which Preferred Stock
               was converted as provided above);

                           (ii) any repurchase of stock by Biosource from any
               shareholder other than a party to this Agreement;

                           (iii) any transfer to the transferring holder's
               ancestors or descendants or spouse or to a trustee for their
               benefit, or any bona fide gift;

                                       6.
<PAGE>   9

                           (iv) any transfer by a Right Holder that is a
               partnership or limited liability company to its constituent
               partners or members or third parties for no consideration;

                           (v) any transfer by Robert L. Erwin to the Marti
               Nelson Medical Foundation;

                           (vi) any transfer by TDCC to an Affiliate of TDCC; or

                           (vii) any transfer by Technology Directors to an
               affiliate of Technology Directors;

provided that (i) each Right Holder shall inform Biosource and the others of
such transfer or gift prior to effecting it and (ii) the transferee or donee
(collectively, "Permitted Transferees"), except transferees pursuant to Sections
3.5(e)(iv) and 3.5(e)(v) hereof, shall furnish the parties hereto with a written
agreement to be bound by and comply with all provisions of this Agreement as
though such Permitted Transferee were a party to this Agreement; provided
further that in the case of a distribution pursuant to Section 3.5(e)(iv),
recipients of shares of Biosource distributed by Technology Directors or its
affiliates in respect of, and to the extent of, John Maki's economic interest in
Technology Directors or its affiliates shall be bound by and comply with all
provisions of this Agreement as though such recipients were a party to this
Agreement.

        Section 3.6 Purchase of Securities by TDCC.

               (a) Subject to the terms of this Section 3.6, TDCC agrees that,
from the date of this Agreement until the earliest of: (i) an IPO, (ii) the date
of expiration of the Warrant provided no shares of Warrant Stock have been
acquired, (iii) the date of disposition by TDCC or its Affiliates of all of the
Warrant Stock, or (iv) December 31, 2008, it will not, nor will it permit any of
its Affiliates, without the prior approval of a majority of the Board of
Directors of Biosource, excluding for such purposes any director employed by or
affiliated in any way with TDCC or its Affiliates to:

                           (i) acquire, directly or indirectly, any outstanding
               Common Stock or any other Common Stock of Biosource except
               through a purchase program approved by the Board of Directors of
               Biosource or from a party to this Agreement;

                           (ii) acquire, directly or indirectly, by purchase or
               otherwise, of record or beneficially, any Securities of Biosource
               or rights or options to acquire any Securities, if as a result
               thereof (after giving effect to the exercise of options or other
               rights by all holders, including the Warrant issued hereunder)
               TDCC and its Affiliates would, in the aggregate, own more than
               19.9% of the Outstanding Securities of Biosource (calculated on
               an as converted to Common Stock or exercised basis); or

                                       7.
<PAGE>   10

                           (iii) initiate, propose or otherwise solicit any
               shareholder (other than a party to this Agreement) for the
               approval of one or more shareholder proposals at any time, or
               induce or attempt to induce any other person (other than a party
               to this Agreement) to initiate any shareholder proposal.

               (b) Notwithstanding subsection (a) above, if a third party makes
a tender offer or exchange offer for more than 50% of Biosource's outstanding
voting Securities, or Biosource announces a transaction pursuant to which a
third party not a shareholder of Biosource on the date hereof has or will
acquire, whether through merger, tender offer or exchange offer, more than 50%
of Biosource's voting Securities or all or substantially all of Biosource's
assets, then the restrictions set forth in this Section 3.6 shall be tolled
until such time, if any, as such transaction or transactions are withdrawn or
abandoned, at which time such restrictions shall be reinstated. Any
reinstatement of such restrictions shall not affect TDCC's ability to continue
to pursue any transaction it announced prior to such reinstatement; provided,
that, such announcement did not violate this Section 3.6, and provided further
that such transaction is completed within six (6) months from the date of
announcement.

        Section 3.7   Right to Make Offer. If, during the term of the Research
Collaboration and two years after the termination of the Research Collaboration,
the Board of Directors of Biosource shall determine that it is in the best
interest of its shareholders to merge into, or sell substantially all of its
assets to, a third party (collectively, a "Sale Transaction"), then Biosource
shall provide TDCC a reasonable opportunity to make an offer to purchase
Biosource prior to notifying any other person or entity of the Sale Transaction.
After receiving and reviewing such offer, Biosource shall negotiate in good
faith with TDCC and may negotiate contemporaneously with other persons or
entities with respect to a Sale Transaction. The parties acknowledge and agree
that in such negotiations Biosource shall be entitled to act in the best
interest of its shareholders other than TDCC, which interest may be different
than the interest of TDCC; furthermore, during the term of the Research
Collaboration, Biosource shall not grant any superior rights with respect to a
Sale Transaction to any person or entity, including without limitation, a right
of first refusal. Nothing herein shall be deemed to restrict TDCC from making an
offer to the Board of Biosource.

        Section 3.8    Expiration of Rights. Subject to the qualification of the
following sentence, the provisions of Sections 3.1, 3.2(a), (b), (c) and (d),
3.5 and 3.7 shall expire upon the earliest to occur of (i) two years after the
date of the termination of the Research Collaboration (as such termination is
defined in the Collaboration Agreement), (ii) August 31, 2003, (iii) upon the
initial closing of a firm commitment underwritten public offering of Common
Stock for the account of Biosource pursuant to an IPO the gross proceeds of
which exceed $15,000,000; or (iv) the consummation of a merger or other business
combination if, as a result of such merger or business combination, the
shareholders of Biosource immediately prior to the consummation of such
transaction hold less than fifty percent (50%) of the outstanding securities of
the surviving corporation. The provisions of Sections 3.2(a), (b), (c) and (d)
and Section 3.7 shall not expire as a result of Section 3.8(ii).

                                       8.
<PAGE>   11

                                   ARTICLE IV
                         REPRESENTATIONS AND WARRANTIES

        Section 4.1   Representations and Warranties of Biosource. As of the
date of this Agreement and as of the date of each exercise of a Warrant by TDCC,
except as set forth on the Schedule of Exceptions attached hereto as Exhibit B
and as updated upon each such exercise on Exhibit B, Biosource represents and
warrants to TDCC as follows:

               (a) Organization, Good Standing and Qualification. Biosource is a
corporation duly organized, validly existing and in good standing under the laws
of the State of California and has all requisite corporate power and authority
to carry on its business as now conducted and as proposed to be conducted.
Biosource is not qualified to transact business as a foreign corporation in any
jurisdiction and such qualification is not presently required.

               (b) Corporate Power. Biosource has all requisite legal and
corporate power to execute and deliver this Agreement, to issue the Warrants,
and to carry out and perform its obligations under the terms of this Agreement
and the Warrants.

               (c) Financial Statements. Biosource has prepared audited
financial statements for the periods ending December 31, 1997, 1996 and 1995
("Biosource's Financial Statements"), which have been made available to TDCC. To
Biosource's knowledge, Biosource's Financial Statements have been prepared in
accordance with generally accepted accounting principles, consistently applied.
Since December 31, 1997 there has been no development that had, or with the
passage of time would have, a material adverse effect on Biosource's financial
condition.

               (d) Liabilities. Biosource has no material liabilities required
by generally accepted accounting principles to be reflected in Biosource's
balance sheet or notes thereto except as disclosed on Biosource's Financial
Statements or incurred after December 31, 1997 in the normal course of business
and, to its knowledge, has no material contingent liabilities.

               (e) Taxes. Biosource has accurately prepared and timely filed all
income tax returns and other tax returns which are required to be filed, and has
paid, or made provision for the payment of, all taxes which have or may have
become due as shown on said returns or pursuant to any assessment which has been
received by it. No federal or state income or sales tax return of Biosource has
been audited, no deficiency assessment or proposed adjustment of Biosource's
United States income tax, state or municipal taxes or sales taxes is pending and
Biosource has no knowledge of any proposed liability for any tax to be imposed
on its property or assets other than taxes not yet due and payable.

               (f) Litigation. There is no action, suit, proceeding or
investigation pending or currently threatened against Biosource which questions
the validity of this Agreement or the right of Biosource to enter into it, or to
consummate the transactions contemplated hereby, or which might result, either
individually or in the aggregate, in any material adverse changes in the assets,
condition, affairs or prospects of Biosource, financially or otherwise, or which
might result, either individually or in the aggregate, in any material
impairment of the right or ability of Biosource to carry on its business as now
conducted or as proposed to be conducted, nor is there any litigation pending or
threatened.

                                       9.
<PAGE>   12

               (g) Capitalization. As of the date hereof (without giving effect
to the Warrants), the authorized capital stock of Biosource consists of
20,000,000 shares of Common Stock, of which 6,122,786 shares were issued and
outstanding; and 10,000,000 shares of preferred stock, no par value ("Existing
Preferred Stock"), of which 666,667 shares have been designated as Series A
Preferred Stock, all of which were issued and outstanding; 878,003 shares have
been designated as Series B Preferred Stock, all of which were issued and
outstanding; 344,050 shares have been designated as Series C Preferred Stock,
340,908 shares of which were issued and outstanding; 750,000 shares have been
designated as Series D Preferred Stock, 435,173 of which shares were issued and
outstanding; 146,875 shares have been designated Series E Preferred Stock, none
of which were issued and outstanding; and 1,000,000 shares have been designated
Series F Preferred Stock, all of which are issued and outstanding. All shares of
capital stock outstanding have been duly and validly authorized and issued and
are fully paid and nonassessable and were issued in compliance with all
applicable federal and state securities laws.

               As of the date hereof (without giving effect to the Warrants),
the following warrants, options and similar rights to purchase capital stock
were outstanding: a warrant to purchase 29,322 shares of Common Stock; warrants
to purchase up to an aggregate of 146,875 shares of Series E Preferred Stock;
and options to purchase up to 1,439,300 shares of Common Stock held by
employees, directors, officers and consultants of Biosource. There are no other
outstanding options, warrants, rights (including conversion or preemptive
rights) or agreements for the purchase or acquisition from Biosource of any
shares of its capital stock (or other securities of Biosource).

               (h) Subsidiaries. Biosource does not presently own or control,
directly or indirectly, any interest in any other corporation, association or
other business entity. Biosource is not a participant in any joint venture or
partnership.

               (i) Authorization. All corporate action on the part of Biosource,
its officers, directors and shareholders necessary for the authorization,
execution and delivery of this Agreement, the performance of all obligations of
Biosource hereunder and the authorization, issuance (or reservation for
issuance) and delivery of the Warrants being sold hereunder and the Common Stock
issuable upon exercise of the Warrants has been taken or will be taken prior to
the Closing, and this Agreement constitutes a valid and legally binding
obligation of Biosource, enforceable in accordance with its terms, subject to
the laws of general application relative to bankruptcy, insolvency and the
relief of debtors.

               (j) Governmental Consents. No consent, approval, order or
authorization of, or registration, qualification, designation, declaration or
filing with, any federal, state, local or provincial governmental authority on
the part of Biosource is required in connection with the consummation of the
transactions contemplated by this Agreement, except for the filing pursuant to
Section 25102(f) of the California Corporate Securities Law of 1968, as amended,
and the rules thereunder, which filing will be effected within 15 days of the
Closing, and such other notices as may be required by the securities or Blue Sky
laws of the various states or pursuant to the Hart-Scott-Rodino Antitrust
Improvements Act of 1976, as amended, (the "HSR Act").

               (k) Patents, Trademarks and Trade Secrets. There are no pending
or overtly threatened claims against Biosource alleging that the conduct of
Biosource's business infringes

                                      10.
<PAGE>   13

or conflicts with the rights of others under patents, trademarks, copyrights and
trade secrets. To Biosource's knowledge, Biosource's business as now conducted
and as proposed to be conducted will not infringe or conflict with the rights of
others, including rights under patents, trademarks, copyrights and trade
secrets. Biosource is not aware of any violation by a third party of any of
Biosource's patents, licenses, trademarks, service marks, tradenames,
copyrights, trade secrets or other proprietary rights.

               (l) Compliance with Other Instruments. Biosource is not in
violation of any provisions of its Amended and Restated Articles of
Incorporation or Bylaws or of any term contained in any instrument or contract
to which it is a party, the damages arising from which could exceed
individually, or in the aggregate, $25,000, and to its knowledge, is not in
violation of any order, statute, rule or regulation applicable to Biosource. The
execution, delivery and performance of this Agreement and the consummation of
the transactions contemplated hereby will not result in any such violation or be
in conflict with or constitute, with or without the passage of time and giving
of notice, either a default under any such provision or an event which results
in the creation of any lien, charge or encumbrance upon any assets of Biosource;
and there is no such violation or default, nor any such term which materially
and adversely affects the business of Biosource as presently conducted or as
proposed to be conducted or any of its assets.

               (m) Contracts and Other Commitments. Biosource does not have any
contract, agreement, lease, or other commitment, written or oral, absolute or
contingent, other than contracts for the purchase of supplies and services that
were entered into in the ordinary and usual course of business, that involve any
of Biosource's officers, directors, affiliates (as that term is defined in Rule
405 under the Securities Act), and that involve more than $25,000.

               (n) Disclosure. Biosource has previously delivered to TDCC its
Confidential Private Investment Memorandum dated February 25, 1998, (the
"Memorandum"). The Memorandum has been prepared by the management of Biosource
in good faith. To Biosource's knowledge, neither the Memorandum nor any
representation or warranty by Biosource contained in this Agreement, nor any
other statement or certificate furnished or to be furnished to TDCC pursuant
hereto or in connection with the transactions contemplated hereby by Biosource,
contains or will contain any untrue statement of a material fact or, when read
together, omits or will omit to state a material fact necessary to make the
statements contained therein or herein not misleading in light of the
circumstances under which they were made.

               (o) Registration Rights. Except as provided in the Series A
Preferred Stock Purchase Agreement, the Series B Preferred Stock Purchase
Agreement, the Series C Preferred Stock Purchase Agreement, the Series D
Preferred Stock Purchase Agreement, the Series E Preferred Stock Purchase
Agreement, and the Series F Stock Purchase Agreement, the Warrant to purchase
29,329 shares of Common Stock issued to Equitec Leasing Company and the
Information and Registration Rights Agreement, as amended, Biosource has not
granted or agreed to grant any registration rights, including piggyback rights,
to any person or entity.

               (p) Offering. Based on the representations of TDCC set forth in
Section 4.2 hereof and in written responses to Biosource's inquiries, if any,
the offer, sale and issuance of the Warrants and the Common Stock issuable upon
exercise of the Warrants constitute transactions

                                      11.
<PAGE>   14

exempt from the registration requirements of Section 5 of the Securities Act
pursuant to Section 4(2) of the Securities Act.

               (q) Title to Property and Assets. Biosource owns its property and
assets free and clear of all mortgages, liens, loans and encumbrances, except
such encumbrances and liens which arise in the ordinary course of business and
do not materially impair Biosource's ownership or use of such property or
assets. With respect to the property and assets it leases, Biosource is in
compliance with such leases and, to the best of its knowledge, holds a valid
leasehold interest free of any liens, claims or encumbrances, except such
encumbrances and liens which arise in the ordinary course of business and do not
materially impair Biosource's use of such property or assets.

               (r) Brokerage. There are no valid claims for brokerage
commissions, finders' fees or similar compensation in connection with
transactions contemplated by this Agreement based on any arrangement or
agreement made by or on behalf of Biosource, and Biosource will indemnify and
hold TDCC harmless against any liability or expense arising out of, or in
connection with any such claim.

               (s) Insurance. Biosource has fire and casualty insurance
policies, with extended coverage, sufficient in amount to allow it to replace
any of its properties that might be damaged or destroyed.

               (t) Employees; Employee Compensation. There is no strike or other
labor dispute pending or, to the knowledge of Biosource, threatened, between it
and its employees. None of Biosource's employees belongs to any union or
collective bargaining unit. All technical employees, other key employees and
officers of Biosource have signed nondisclosure and assignment of inventions
agreements with Biosource. To its knowledge, Biosource has complied with all
applicable state and federal equal employment opportunity and other laws related
to employment. To Biosource's knowledge, no employee of Biosource is or will be
in violation of any judgment, decree or order, or any term of any employment
contract, patent disclosure agreement or other contract or agreement relating to
the relationship of any such employee with Biosource or any other party because
of the nature of the business conducted or to be conducted by Biosource or to
the utilization by the employee of his or her best efforts with respect to such
business. Biosource is not party to or bound by any currently effective
employment contract, deferred compensation agreement, bonus plan, incentive
plan, profit sharing plan, retirement agreement or other employee compensation
agreement.

               (u) Valid Issuance of Preferred and Common Stock. All issued and
outstanding Series A, B, C, D, E and F Preferred Stock has been duly authorized
and validly issued, is fully paid and nonassessable and was issued in compliance
with all applicable federal and state securities laws. The Warrants to be
acquired by TDCC, when issued, sold and delivered in accordance with the terms
hereof for the consideration expressed herein, will be duly and validly issued,
fully paid and nonassessable and, based in part upon the representations of TDCC
in this Agreement, will be issued in compliance with all applicable federal and
state securities laws. Biosource has reserved 666,667 shares of its Common Stock
for issuance upon conversion of the Series A Preferred Stock; 878,003 shares of
its Common Stock for issuance upon conversion of the Series B Preferred Stock;
361,022 shares of Common Stock for issuance upon conversion of

                                      12.
<PAGE>   15

the Series C Preferred Stock; 437,044 shares of Common Stock for issuance upon
conversion of the Series D Preferred Stock; 146,875 shares of Common Stock
reserved for issuance upon conversion of Series E Preferred Stock; 1,000,000
shares of Common Stock for issuance upon conversion of Series F Preferred Stock;
29,322 shares of Common Stock for issuance upon exercise of warrants; and, as of
the date hereof, 1,668,700 shares of Common Stock for issuances to employees,
directors and officers of, and consultants to Biosource. The Common Stock
issuable upon exercise of the Warrant purchased under this Agreement has been
duly and validly reserved for issuance and, upon issuance in accordance with the
terms of this Agreement, assuming such shares of Common Stock were issued as of
the date hereof, shall be duly and validly issued, fully paid and nonassessable,
and issued in compliance with all applicable securities laws, as presently in
effect.

        Section 4.2   Representations and Warranties of TDCC. TDCC represents
and warrants to Biosource as follows:

               (a) TDCC is an "accredited investor" within the meaning of
Regulation D under the Securities Act. TDCC is knowledgeable in matters related
to the business of Biosource, has had an opportunity to conduct such
investigation and ask such questions as it deemed appropriate, and has received
information satisfactory to it in connection therewith.

               (b) TDCC understands that shares of Common Stock of Biosource
issuable upon exercise of the Warrants are "restricted" securities within the
meaning of Rule 144 under the Securities Act, may only be resold if such sale is
registered under the Securities Act or exempt from such registration and an
opinion of counsel to TDCC (which shall include an opinion from an attorney in
the law department of TDCC) is delivered to such effect, and will bear
restrictive legends to that effect.

               (c) TDCC understands the risks inherent in investing in the
securities of privately held emerging development companies such as Biosource,
including the fact that there is no market for such securities, which are
inherently illiquid, and that there is no assurance that Biosource will be
successful in executing its business plan to create value for its shareholders
through the development and exploitation of its technologies. TDCC has the
knowledge and experience to evaluate the merits and risks of investing in
Biosource.

               (d) Any Outstanding Securities acquired by TDCC will be acquired
for investment purposes, for its own account, and not with a view to the sale or
distribution thereof.

               (e) Legends. TDCC understands that the certificates evidencing
the Warrant and any Common Stock issued upon exercise of the Warrant may bear
one or all of the following legends:

                           (i) "THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER
               THE SECURITIES ACT OF 1933, AS AMENDED. THEY MAY NOT BE SOLD,
               OFFERED FOR SALE, PLEDGED OR HYPOTHECATED IN THE ABSENCE OF A
               REGISTRATION STATEMENT IN EFFECT WITH RESPECT TO THE SECURITIES
               UNDER SUCH ACT OR AN OPINION OF COUNSEL SATISFACTORY TO BIOSOURCE
               THAT SUCH

                                      13.
<PAGE>   16

                REGISTRATION IS NOT REQUIRED OR UNLESS SOLD PURSUANT TO RULE
                144 OF SUCH ACT."

                           (ii) "THESE SECURITIES ARE SUBJECT TO THE TERMS AND
               CONDITIONS OF A CERTAIN INFORMATION AND REGISTRATION RIGHTS
               AGREEMENT WHICH INCLUDES A MARKET STAND-OFF AGREEMENT. COPIES OF
               THE AGREEMENT MAY BE OBTAINED UPON WRITTEN REQUEST TO BIOSOURCE'S
               SECRETARY."

                           (iii) "THESE SECURITIES ARE SUBJECT TO THAT CERTAIN
               COMMON STOCK WARRANT AGREEMENT DATED AS OF SEPTEMBER 1, 1998,
               COPIES OF WHICH ARE AVAILABLE UPON WRITTEN REQUEST TO BIOSOURCE'S
               SECRETARY."

               (f) Any legend required by the laws of the State of California,
including any legend required by the California Department of Corporations and
Sections 417 and 418 of the California Corporations Code.

                                    ARTICLE V
                                  MISCELLANEOUS

        Section 5.1   Successors and Assigns. Except as otherwise provided
herein, the terms and conditions of this Agreement shall inure to the benefit of
and be binding upon the respective successors and assigns of the parties
(including transferees of any shares of Common Stock issued upon exercise of the
Warrants). Nothing in this Agreement, express or implied, is intended to confer
upon any party other than the parties hereto or their respective successors and
assigns any rights, remedies, obligations, or liabilities under or by reason of
this Agreement, except as expressly provided in this Agreement.

        Section 5.2   Governing Law. This Agreement shall be governed by and
construed in accordance with the laws of the State of California as applied to
agreements among California residents entered into and to be performed entirely
within California.

        Section 5.3   Counterparts . This Agreement may be executed in two or
more counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

        Section 5.4   Titles and Subtitles. The titles and subtitles used in
this Agreement are used for convenience only and are not to be considered in
construing or interpreting this Agreement.

        Section 5.5   Notices. All notices hereunder shall be in writing and
shall be deemed given if delivered personally or by facsimile transmission
(receipt verified), telexed, mailed by registered or certified mail (return
receipt requested), postage prepaid, or sent by express courier service, to
Biosource and to TDCC at the addresses set forth below (or at such other address
for a party as shall be specified by like notice; provided that notices of a
change of address shall be effective only upon receipt thereof):

                                      14.
<PAGE>   17

             If to Biosource:

             Biosource Technologies, Inc.
             3333 Vaca Valley Parkway
             Vacaville, CA 95688
             Attention:  Robert L. Erwin
             Telephone: (707) 446-5501
             Telecopy:  (707) 446-3917

             With a copy to:

             Brobeck, Phleger & Harrison LLP
             One Market, Spear Street Tower
             San Francisco, CA 94105
             Attention:  Ronald B. Moskovitz, Esq.
             Telephone:  (415) 442-0900
             Telecopy:   (415) 442-1010

             If to TDCC:

             The Dow Chemical Company
             2030 Dow Center
             Midland, MI 48674
             Attention:  Manager, Financial Law
             Telephone: (517) 636-0752
             Telecopy:  (517) 636-0861

             With a copy to:

             Mayer, Brown & Platt
             190 South LaSalle Street
             Chicago, IL 60603
             Attention:  Scott J. Davis, Esq.
             Telephone:  (312) 782-0600
             Telecopy:  (312) 701-7711

        Section 5.6   Expenses. Except as provided in the Collaboration
Agreement, the parties shall bear their own expenses incurred with respect to
this Agreement and the transactions contemplated hereby.

        Section 5.7   Entire Agreement; Amendment. This Agreement and the other
documents delivered pursuant hereto constitute the full and entire understanding
and agreement between the parties with regard to the subject matter hereof and
thereof. Except as otherwise provided in the Information and Registration Rights
Agreement, as amended, any term of this Agreement may be amended and the
observance of any term of this Agreement may be waived (either generally or in a
particular instance and either retroactively or prospectively), only with the
prior written consent of Biosource and TDCC.

                                      15.
<PAGE>   18
        Section 5.8   Severability. If one or more provisions of this Agreement
are held to be unenforceable under applicable law, such provision shall be
excluded from this Agreement and the balance of the Agreement shall be
interpreted as if such provision were so excluded and shall be enforceable in
accordance with its terms.

        Section 5.9   Delays or Omissions. No delay or omission to exercise any
right, power or remedy accruing to any holder of the Warrants, upon any breach
or default of Biosource under this Agreement, shall impair any such right, power
or remedy of TDCC nor shall it be construed to be a waiver of any such breach or
default, or an acquiescence therein, or of or in any similar breach or default
thereunder occurring; nor shall any waiver of any single breach or default be
deemed a waiver of any other breach or default theretofore or thereafter
occurring. Any waiver, permit, consent or approval of any kind or character on
the part of TDCC of any breach or default under this Agreement, or any waiver on
the part of TDCC of any provisions or conditions of this Agreement, must be in
writing and shall be effective only to the extent specifically set forth in such
writing. All remedies, either under this Agreement, or by law or otherwise
afforded to TDCC, shall be cumulative and not alternative.

        Section 5.10  Exhibits. Each reference in this Agreement to an Exhibit
shall mean an Exhibit attached to this Agreement. All such Exhibits are
incorporated into this Agreement by such reference.

        Section 5.11  Corporate Securities Law. THE SALE OF THE SECURITIES WHICH
ARE THE SUBJECT OF THIS AGREEMENT HAS NOT BEEN QUALIFIED WITH THE COMMISSIONER
OF CORPORATIONS OF THE STATE OF CALIFORNIA AND THE ISSUANCE OF SUCH SECURITIES
OR THE PAYMENT OR RECEIPT OF ANY PART OF THE CONSIDERATION FOR SUCH SECURITIES
PRIOR TO SUCH QUALIFICATION IS UNLAWFUL, UNLESS THE SALE OF SECURITIES IS EXEMPT
FROM QUALIFICATION BY SECTION 25100, 25102 OR 25105 OF THE CALIFORNIA
CORPORATIONS CODE. THE RIGHTS OF ALL PARTIES TO THIS AGREEMENT ARE EXPRESSLY
CONDITIONED UPON SUCH QUALIFICATION BEING OBTAINED, UNLESS THE SALE IS SO
EXEMPT.

        Section 5.12  Publicity. Biosource and TDCC each agree not to disclose
the existence of, or any terms or conditions of, this Agreement or the Warrant,
or any results arising from the Research Collaboration, to any third party
without the agreement of the other prior to such disclosure. Notwithstanding the
foregoing, Biosource and TDCC shall agree upon the substance of information that
can be used as a routine reference in the usual course of business to describe
the terms of this transaction, and Biosource and TDCC may disclose such
information, as modified by mutual agreement from time to time, without
consulting the other party.

        Section 5.13  Regulatory Approval. Notwithstanding any other provisions
of this Agreement, in no event shall the exercise of the Warrants for the
purchase of Common Stock be effective until the date all applicable regulatory
approvals have been received by TDCC including, without limitation, the
expiration of any waiting period under the HSR Act.

        Section 5.14  Compliance Certificate. Upon request of TDCC in connection
with any proposed exercise of the Warrant, the Chairman of the Board of
Biosource shall deliver to

                                      16.
<PAGE>   19

TDCC, as soon as practicable after each request, a certificate certifying that
the representations and warranties contained in Section 4.1 hereof (subject to
the qualifications of Exhibit B, the Schedule of Exceptions, as of such date)
shall be true on and as of the date of TDCC's exercise of the Warrant with the
same effect as though such representations and warranties had been made on and
as of the date of such exercise and such representations and warranties shall be
given with respect to Biosource's then most current audited financial statements
and most current unaudited interim financial statements.

        Section 5.15  Survival. The warranties, representations and covenants of
Biosource and TDCC contained in or made pursuant to this Agreement shall survive
the execution and delivery of this Agreement and the closing and shall in no way
be affected by an investigation of the subject matter thereof made by or on
behalf of TDCC or Biosource.

        Section 5.16  Dispute Resolution. The parties hereto shall in good faith
to resolve any dispute that arises under this Agreement or the Warrant. If the
parties fail to resolve the dispute by negotiation, either party may initiate
binding arbitration by written notice to the other party or parties. Such
arbitration shall be conducted by JAMS/Endispute before a single arbitrator
selected by agreement of the parties hereto in accordance with the rules of
JAMS/Endispute Comprehensive Rules of Commercial, Real Estate and Construction
Cases (www.jamsendispute.com). If the parties are unable to agree to a single
arbitrator within sixty (60) days of demand for arbitration, the office of
JAMS/Endispute where the arbitration is to be held shall appoint the arbitrator
who shall be experienced with resolving private investment disputes. If TDCC
initiates the arbitration with Biosource, it shall be conducted in San
Francisco, California, and if Biosource initiates the arbitration, it shall be
conducted in San Francisco, California or in Chicago, Illinois at TDCC's option.
The arbitrator shall not be empowered to award damages in excess of compensatory
damages. Judgment upon any decision rendered by the arbitrator may be entered by
any court having jurisdiction. The procedures set forth in this Section 5.16 are
the sole and exclusive procedures for the resolution of disputes among the
parties arising out of or related to this Agreement; provided, however, that any
party may seek a preliminary injunction or other provisional judicial relief if,
in its sole judgment, such action is necessary to avoid irreparable damage or to
preserve the status quo. All pending court action shall be stayed and all
applicable statutes of limitation and defenses based on the passage of time
shall be tolled while alternative dispute resolution efforts are pursued. The
parties shall take such action, if any, necessary to effectuate such stay or
tolling.

        Section 5.17  HSR Filings. The parties to this Agreement acknowledge
that in connection with the future exercise by TDCC, if applicable, of its
rights pursuant to the Warrant, the parties may be required to file Notification
Forms or otherwise comply with the provisions of the HSR Act. Each party agrees
that in connection with any such exercise by TDCC it will act in good faith to
analyze and evaluate its resulting obligations under the HSR Act. In the event
either party reasonably determines that it is required to make any filing under
the HSR Act in connection with such exercise, it will so notify the other party;
and the other party will reasonably cooperate with the filing party, and each
party will expeditiously comply with its respective filing requirements.
Notwithstanding any other provision of this Agreement, the time periods during
which TDCC is entitled to exercise its rights pursuant to the Warrant shall be
tolled for the duration of any application HSR Act waiting period (and any
related investigative period imposed by the FTC with respect to any such
filing).

                                      17.
<PAGE>   20

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

<TABLE>
<CAPTION>

BIOSOURCE TECHNOLOGIES, INC.                     THE DOW CHEMICAL COMPANY

<S>                                              <C>
By                                               By
  ------------------------------------------       ------------------------------------------
    Name:   Robert L. Erwin                          Name:   William S. Stavrolopoulous
    Title:  Chairman of the Board and Chief          Title:  President and CEO
            Executive Officer

TECHNOLOGY DIRECTORS II, LLC

By
  ------------------------------------------       ------------------------------------------
    Name:   John Maki                                Robert L. Erwin
    Title:  Managing Member

TECHNOLOGY DIRECTORS II BST, LLC

By
  ------------------------------------------
    Name:   John Maki
    Title:  Managing Member
</TABLE>

               Signature Page for Common Stock Warrant Agreement

<PAGE>   21

                                    EXHIBIT A

                        WARRANT TO PURCHASE COMMON STOCK

                                      A-1

<PAGE>   22

                                    EXHIBIT B

                             SCHEDULE OF EXCEPTIONS

               The exceptions set forth below are made to the representations
and warranties of Biosource Technologies, Inc. ("Biosource") in Section 4.1 of
the Common Stock Warrant Agreement dated as of September 1, 1998 (the
"Agreement") to which a copy of this Schedule of Exceptions is attached. Except
as otherwise stated herein, all capitalized terms used herein shall have the
meanings given them in the Agreement. Section numbers used herein correspond to
section numbers in the Agreement.

Effective date of Schedule of Exceptions:
                                         ------------------------------

                                      B-1

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