<PAGE>

                                                                     EXHIBIT 4.3

THE WARRANT EVIDENCED OR CONSTITUTED HEREBY, AND ALL SHARES OF COMMON STOCK
ISSUABLE HEREUNDER, HAVE BEEN AND WILL BE ISSUED WITHOUT REGISTRATION UNDER THE
SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT") AND MAY NOT BE SOLD,
OFFERED FOR SALE, TRANSFERRED, PLEDGED OR HYPOTHECATED WITHOUT REGISTRATION
UNDER THE ACT UNLESS EITHER (i) THE COMPANY HAS RECEIVED AN OPINION OF COUNSEL,
IN FORM AND SUBSTANCE REASONABLY SATISFACTORY TO THE COMPANY, TO THE EFFECT THAT
REGISTRATION IS NOT REQUIRED IN CONNECTION WITH SUCH DISPOSITION OR (ii) THE
SALE OF SUCH SECURITIES IS MADE PURSUANT TO SEC RULE 144.

                       WARRANT TO PURCHASE COMMON STOCK
                                      OF
                         BIOSOURCE INTERNATIONAL, INC.

NO.                                                            February __, 2000

THIS CERTIFIES THAT, for value received by BioSource International, Inc., a
Delaware corporation (the "Company"), Stargen II LLC, or its permitted
                           -------
registered assigns ("Holder"), is entitled, subject to the terms and conditions
                     ------
of this Warrant, at any time or from time to time after the issuance date of
this Warrant (the "Effective Date"), and before 5:00 p.m. Pacific Time on the
                   --------------
fifth (5th) anniversary of the Effective Date (the "Expiration Date"), to
                                                    ---------------
purchase from the Company 24,458 shares of Common Stock of the Company, at a
price per share of $7.77 (the "Purchase Price").  Both the number of shares of
                               --------------
Common Stock purchasable upon exercise of this Warrant and the Purchase Price
are subject to adjustment and change as provided herein.

     1.  CERTAIN DEFINITIONS. As used in this Warrant the following terms shall
have the following respective meanings:

         1.1  "Fair Market Value" of a share of Common Stock as of a particular
              -------------------
date shall mean:

              (a)  If traded on a securities exchange or the Nasdaq National
Market, the Fair Market Value shall be deemed to be the average of the closing
prices of the Common Stock of the Company on such exchange or market over the
five (5) trading days ending immediately prior to the applicable date of
valuation;

              (b)  If actively traded over-the-counter, the Fair Market Value
shall be deemed to be the average of the closing bid prices over the thirty
(30)-day period ending immediately prior to the applicable date of valuation;
and

              (c)  If there is no active public market, the Fair Market Value
shall be the value thereof, as agreed upon by the Company and the Holder;
provided, however, that if the Company and the Holder cannot agree on such
value, such value shall be determined by an independent valuation firm
experienced in valuing businesses such as the Company and jointly selected in
good faith by the Company and the Holder. Fees and expenses of the valuation
firm shall be paid for by the Company.
<PAGE>

         1.2   "Registered Holder" shall mean any Holder in whose name this
                -----------------
Warrant is registered upon the books and records maintained by the Company.

         1.3   "Warrant" as used herein, shall include this Warrant and any
                -------
warrant delivered in substitution or exchange therefor as provided herein .

         1.4   "Common Stock" shall mean the Common Stock of the Company and any
                ------------
other securities at any time receivable or issuable upon exercise of this
Warrant.

     2.  EXERCISE OF WARRANT.

         2.1  Payment. Subject to compliance with the terms and conditions of
              -------
this Warrant and applicable securities laws, this Warrant may be exercised, in
whole or in part at any time or from time to time, on or before the Expiration
Date by the delivery (including, without limitation, delivery by facsimile) of
the form of Notice of Exercise attached hereto as Exhibit A (the "Notice of
                                                  ---------      -------
Exercise"), duly executed by the Holder, at the principal office of the Company,
--------
and as soon as practicable after such date, surrendering

              (a)  this Warrant at the principal office of the Company, and

              (b)  payment, (i) in cash (by check) or by wire transfer, (ii) by
cancellation by the Holder of indebtedness of the Company to the Holder; or
(iii) by a combination of (i) and (ii), of an amount equal to the product
obtained by multiplying the number of shares of Common Stock being purchased
upon such exercise by the then effective Purchase Price (the "Exercise Amount").
                                                              ---------------

         2.2  Net Issue Exercise. In lieu of the payment methods set forth in
              ------------------
Section 2.1(b) above, the Holder may elect to exchange all or some of this
Warrant for shares of Common Stock equal to the value of the amount of the
Warrant being exchanged on the date of exchange. If Holder elects to exchange
this Warrant as provided in this Section 2.2, Holder shall tender to the Company
                                 -----------
the Warrant for the amount being exchanged, along with written notice of
Holder's election to exchange some or all of the Warrant, and the Company shall
issue to Holder the number of shares of the Common Stock computed using the
following formula:

                  X =  Y (A-B)
                      ---------
                          A

          Where:   X =  the number of shares of Common Stock to be issued to
                        Holder.

                   Y =  the number of shares of Common Stock purchasable under
                        the amount of the Warrant being exchanged (as adjusted
                        to the date of such calculation).

                   A =  the Fair Market Value of one share of the Common Stock.

                   B =  Purchase Price (as adjusted to the date of such
                        calculation).

         2.3  "Easy Sale" Exercise. In lieu of the payment methods set forth in
              --------------------
Sections 2.1(b) and 2.2, above, when permitted by law and applicable regulations
-----------------------
(including Nasdaq and NASD rules), the Holder may pay the Purchase Price through
a "same day sale" commitment from the Holder (and if applicable a broker-dealer
that is a member of the National Association of

                                       2
<PAGE>

Securities Dealers (an "NASD Dealer")), whereby the Holder irrevocably elects to
                        -----------
exercise this Warrant and to sell a portion of the shares so purchased to pay
the Purchase Price and the Holder (or, if applicable, the NASD Dealer) commits
upon sale (or, in the case of the NASD Dealer, upon receipt) of such shares to
forward the Purchase Price directly to the Company.

         2.4  Stock Certificates; Fractional Shares. As soon as practicable on
              -------------------------------------
or after the date of any exercise of this Warrant, the Company shall issue and
deliver to the person or persons entitled to receive the same a certificate or
certificates for the number of whole shares of Common Stock issuable upon such
exercise, together with cash in lieu of any fraction of a share equal to such
fraction of the current Fair Market Value of one whole share of Common Stock as
of such date of exercise. No fractional shares or scrip representing fractional
shares shall be issued upon an exercise of this Warrant.

         2.5  Partial Exercise; Effective Date of Exercise. In case of any
              --------------------------------------------
partial exercise of this Warrant, the Company shall cancel this Warrant upon
surrender hereof and shall execute and deliver a new Warrant of like tenor and
date for the balance of the shares of Common Stock purchasable hereunder. This
Warrant shall be deemed to have been exercised immediately prior to the close of
business on the date of its surrender for exercise as provided above. The person
entitled to receive the shares of Common Stock issuable upon exercise of this
Warrant shall be treated for all purposes as the holder of record of such shares
as of the close of business on the date the Holder is deemed to have exercised
this Warrant.

         2.6  Vesting. This Warrant shall vest fully upon issuance.
              -------

     3.  VALID ISSUANCE: TAXES. All shares of Common Stock issued upon the
exercise of this Warrant shall be validly issued, fully paid and non-assessable,
and the Company shall pay all taxes and other governmental charges that may be
imposed in respect of the issue or delivery thereof. The Company shall not be
required to pay any tax or other charge imposed in connection with any transfer
involved in the issuance of any certificate for shares of Common Stock in any
name other than that of the Registered Holder of this Warrant, and in such case
the Company shall not be required to issue or deliver any stock certificate or
security until such tax or other charge has been paid, or it has been
established to the Company's reasonable satisfaction that no tax or other charge
is due.

     4.  ADJUSTMENT OF PURCHASE PRICE AND NUMBER OF SHARES. The number of shares
of Common Stock issuable upon exercise of this Warrant (or any shares of stock
or other securities or property receivable or issuable upon exercise of this
Warrant) and the Purchase Price are subject to adjustment upon occurrence of the
following events:

         4.1  Adjustment for Stock Splits, Stock Subdivisions or Combinations of
              ------------------------------------------------------------------
Shares. The Purchase Price of this Warrant shall be proportionally decreased and
------
the number of shares of Common Stock issuable upon exercise of this Warrant (or
any shares of stock or other securities at the time issuable upon exercise of
this Warrant) shall be proportionally increased to reflect any stock split or
subdivision of the Company's Common Stock. The Purchase Price of this Warrant
shall be proportionally increased and the number of shares of Common Stock
issuable upon exercise of this Warrant (or any shares of stock or other
securities at the time issuable upon exercise of this Warrant) shall be
proportionally decreased to reflect any combination of the Company's Common
Stock.

                                       3
<PAGE>

         4.2  Adjustment for Dividends or Distributions of Stock or Other
              -----------------------------------------------------------
Securities or Property. In case the Company shall make or issue, or shall fix a
----------------------
record date for the determination of eligible holders entitled to receive, a
dividend or other distribution with respect to the Common Stock (or any shares
of stock or other securities at the time issuable upon exercise of the Warrant)
payable in (a) securities of the Company or (b) assets or (c) cash dividends
paid or payable solely out of retained earnings, but only if such cash dividends
are Extraordinary Dividends (as defined below), then, in each such case, the
Holder of this Warrant on exercise hereof at any time after the consummation,
effective date or record date of such dividend or other distribution, shall
receive, in addition to the shares of Common Stock (or such other stock or
securities) issuable on such exercise prior to such date, and without the
payment of additional consideration therefor, the securities, assets or cash to
which such Holder would have been entitled upon such date if such Holder had
exercised this Warrant on the date hereof and had thereafter, during the period
from the date hereof to and including the date of such exercise, retained such
shares and all such additional securities, assets or cash distributed with
respect to such shares as aforesaid during such period giving effect to all
adjustments called for by this Section 4. "Extraordinary Dividends" shall mean
                               ---------
dividends or distributions declared with respect to the Common Stock that are in
an amount greater than 3% of the aggregate Fair Market Value of the shares of
capital stock receiving such dividends as of the trading day prior to the
declaration of such dividends or distributions.

         4.3  Reclassification. If the Company, by reclassification of
              ----------------
securities or otherwise, shall change any of the securities as to which purchase
rights under this Warrant exist into the same or a different number of
securities of any other class or classes, this Warrant shall thereafter
represent the right to acquire such number and kind of securities as would have
been issuable as the result of such change with respect to the securities that
were subject to the purchase rights under this Warrant immediately prior to such
reclassification or other change, and the Purchase Price therefor shall be
appropriately adjusted, all subject to further adjustment as provided in this
Section 4. No adjustment shall be made pursuant to this Section 4.3 upon any
---------                                               -----------
conversion or redemption of the Common Stock which is the subject of Section
                                                                     -------
4.5.
---

         4.4  Adjustment for Capital Reorganization, Merger or Consolidation. In
              --------------------------------------------------------------
case of any capital reorganization of the capital stock of the Company (other
than a combination, reclassification, exchange or subdivision of shares
otherwise provided for herein), or any merger or consolidation of the Company
with or into another corporation, or the sale of all or substantially all the
assets of the Company then, and in each such case, as a part of such
reorganization, merger, consolidation, sale or transfer, lawful provision shall
be made so that the Holder of this Warrant shall thereafter be entitled to
receive upon exercise of this Warrant, during the period specified herein and
upon payment of the Purchase Price then in effect, the number of shares of stock
or other securities or property of the successor corporation resulting from such
reorganization, merger, consolidation, sale or transfer that a holder of the
shares deliverable upon exercise of this Warrant would have been entitled to
receive in such reorganization, consolidation, merger, sale or transfer if this
Warrant had been exercised immediately before such reorganization, merger,
consolidation, sale or transfer, all subject to further adjustment as provided
in this Section 4. The foregoing provisions of this Section 4.4 shall similarly
        ---------                                   -----------
apply to successive reorganizations, consolidations, mergers, sales and
transfers and to the stock or securities of any other corporation that are at
the time receivable upon the exercise of this Warrant. If the per-share
consideration payable to the Holder hereof for shares in connection with any
such transaction is in a form other than cash or marketable securities, then the
value of such consideration shall be determined in good faith by the Company's
Board of Directors. In all events, appropriate adjustment (as determined in good
faith by the Company's Board of Directors) shall be made in the application of
the provisions of this Warrant with respect

                                       4
<PAGE>

to the rights and interests of the Holder after the transaction, to the end that
the provisions of this Warrant shall be applicable after that event, as near as
reasonably may be, in relation to any shares or other property deliverable after
that event upon exercise of this Warrant.

         4.5  Conversion of Common Stock. In case all or any portion of the
              --------------------------
authorized and outstanding shares of Common Stock of the Company are redeemed or
converted or reclassified into other securities or property pursuant to the
Company's Certificate of Incorporation or otherwise, or the Common Stock
otherwise ceases to exist, then, in such case, the Holder of this Warrant, upon
exercise hereof at any time after the date on which the Common Stock is so
redeemed or converted, reclassified or ceases to exist (the "Termination Date"),
                                                             ----------------
shall receive, in lieu of the number of shares of Common Stock that would have
been issuable upon such exercise immediately prior to the Termination Date, the
securities or property that would have been received if this Warrant had been
exercised in full and the Common Stock received thereupon had been
simultaneously converted immediately prior to the Termination Date, all subject
to further adjustment as provided in this Warrant. Additionally, the Purchase
Price shall be immediately adjusted to equal the quotient obtained by dividing
(x) the aggregate Purchase Price of the maximum number of shares of Common Stock
for which this Warrant was exercisable immediately prior to the Termination Date
by (y) the number of shares of Common Stock of the Company for which this
Warrant is exercisable immediately after the Termination Date, all subject to
further adjustment as provided herein.

         4.6  Issuances Below Market. In case the Company shall issue or sell
              ----------------------
(a) Common Stock, (b) rights, warrants or options entitling the holders thereof
to subscribe for or purchase shares of Common Stock or (c) any security
convertible into Common Stock, in each case at a price, or having an exercise or
conversion price, per share less than the Purchase Price (excluding any issuance
for which an appropriate and full adjustment has been made pursuant to Section
4.2), the Purchase Price shall be immediately reduced by multiplying the
Purchase Price by a fraction of which (A) the numerator shall be the number of
shares of Common Stock outstanding immediately prior to such issuance or sale
plus the number of shares of Common Stock which the aggregate consideration
received or receivable (I) for the total number of shares of Common Stock,
rights, warrants or options or convertible securities so issued or sold and (II)
upon the exercise or conversion of all such rights, warrants, options or
securities, would purchase at such Purchase Price, and (B) the denominator shall
be the number of shares of Common Stock outstanding immediately prior to such
issuance plus (without duplication) the number of shares of Common Stock subject
to all such rights, warrants, options and convertible securities. The issuance
of any shares of Common Stock or other rights, warrants, options or convertible
securities pursuant to (a) the effectuation of a split or subdivision of the
outstanding shares of Common Stock or a dividend or other distribution payable
in additional shares of Common Stock or other securities or rights convertible
into, or entitling the holder thereof to receive directly or indirectly,
additional shares of Common Stock, (b) Common Stock (or securities exercisable
or convertible into Common Stock) issuable or issued to employees, consultants
or directors of the Company after the Purchase Date directly or pursuant to a
stock option plan or restricted stock plan approved by the Board of Directors of
the Company, (c) securities issued pursuant to the conversion or exercise of
convertible or exercisable securities outstanding or deemed outstanding on the
date of this Warrant, and (d) securities issued or issuable in connection with
the acquisition, merger, consolidation, or other business combination by or of
the Company with, by, or of any person, shall not be deemed to constitute an
issuance or sale to which this Section 4.6 applies.

                                       5
<PAGE>

         5.   CERTIFICATE AS TO ADJUSTMENTS. In each case of any adjustment in
the Purchase Price, or number or type of shares issuable upon exercise of this
Warrant, the Chief Financial Officer or Controller of the Company shall compute
such adjustment in accordance with the terms of this Warrant and prepare a
certificate setting forth such adjustment and showing in detail the facts upon
which such adjustment is based, including a statement of the adjusted Purchase
Price. The Company shall promptly send (by facsimile and by either first class
mail, postage prepaid or overnight delivery) a copy of each such certificate to
the Holder.

         6.   LOSS OR MUTILATION. Upon receipt of evidence reasonably
satisfactory to the Company of the ownership of and the loss, theft, destruction
or mutilation of this Warrant, and of indemnity reasonably satisfactory to it,
and (in the case of mutilation) upon surrender and cancellation of this Warrant,
the Company will execute and deliver in lieu thereof a new Warrant of like tenor
as the lost, stolen, destroyed or mutilated Warrant.

         7.   RESERVATION OF COMMON STOCK. The Company hereby covenants that at
all times there shall be reserved for issuance and delivery upon exercise of
this Warrant such number of shares of Common Stock or other shares of capital
stock of the Company as are from time to time issuable upon exercise of this
Warrant and, from time to time, will take all steps necessary to amend its
Certificate of Incorporation to provide sufficient reserves of shares of Common
Stock issuable upon exercise of this Warrant, including, without limitation,
engaging in best efforts to obtain the requisite stockholder approval of any
necessary amendment to the Certificate of Incorporation. All such shares shall
be duly authorized, and when issued upon such exercise, shall be validly issued,
fully paid and non-assessable, free and clear of all liens, security interests,
charges and other encumbrances or restrictions on sale and free and clear of all
preemptive rights, except encumbrances or restrictions arising under federal or
state securities laws. Issuance of this Warrant shall constitute full authority
to the Company's Officers who are charged with the duty of executing stock
certificates to execute and issue the necessary certificates for shares of
Common Stock upon the exercise of this Warrant.

         8.   TRANSFER AND EXCHANGE. Subject to the terms and conditions of this
Warrant and compliance with all applicable securities laws, this Warrant and all
rights hereunder may be transferred to any Registered Holder's parent,
subsidiary or affiliate, or, if the Registered Holder is a partnership, to any
partner of such Registered Holder, or, if the Registered Holder is a limited
liability company, to any member of such Registered Holder, in whole or in part,
on the books of the Company maintained for such purpose at the principal office
of the Company referred to above, by the Registered Holder hereof in person, or
by duly authorized attorney, upon surrender of this Warrant properly endorsed
and upon payment of any necessary transfer tax or other governmental charge
imposed upon such transfer. Upon any permitted partial transfer, the Company
will issue and deliver to the Registered Holder a new Warrant or Warrants with
respect to the shares of Common Stock not so transferred. Each taker and holder
of this Warrant, by taking or holding the same, consents and agrees that when
this Warrant shall have been so endorsed, the person in possession of this
Warrant may be treated by the Company, and all other persons dealing with this
Warrant, as the absolute owner hereof for any purpose and as the person entitled
to exercise the rights represented hereby, any notice to the contrary
notwithstanding; provided, however that until a transfer of this Warrant is duly
registered on the books of the Company, the Company may treat the Registered
Holder hereof as the owner for all purposes.

         9.   RESTRICTIONS ON TRANSFER. The Holder, by acceptance hereof, agrees
that, absent an effective registration statement filed with the Securities and
Exchange Commission

                                       6
<PAGE>

(the "SEC") under the Securities Act of 1933, as amended (the "Securities Act")
      ---                                                      --------------
covering the disposition or sale of this Warrant or the Common Stock issued or
issuable upon exercise hereof, as the case may be, and registration or
qualification under applicable state securities laws, such Holder will not sell,
transfer, pledge, or hypothecate any or all of this Warrant or such Common
Stock, as the case may be, unless either (i) the Company has received an opinion
of counsel, in form and substance reasonably satisfactory to the Company, to the
effect that such registration is not required in connection with such
disposition, (ii) the sale of such securities is made pursuant to SEC Rule 144or
(iii) such sale or transfer is to the Holder's parent, subsidiary or affiliate,
or, if the Holder is a partnership, to any partner of such Holder, or, if the
Holder is a limited liability company, to any member of such Holder, pursuant to
an exemption under the Securities Act.

         10.  COMPLIANCE WITH SECURITIES LAWS. By acceptance of this Warrant,
the Holder hereby represents, warrants and covenants that any shares of stock
purchased upon exercise of this Warrant shall be acquired for investment only
and not with a view to, or for sale in connection with, any distribution
thereof; that the Holder has had such opportunity as such Holder has deemed
adequate to obtain from representatives of the Company such information as is
necessary to permit the Holder to evaluate the merits and risks of its
investment in the Company; that the Holder is able to bear the economic risk of
holding such shares as may be acquired pursuant to the exercise of this Warrant
for an indefinite period; that the Holder understands that the shares of stock
acquired pursuant to the exercise of this Warrant will not be registered under
the Securities Act (unless otherwise required pursuant to exercise by the Holder
of the registration rights, if any, granted to the Registered Holder) and will
be "restricted securities" within the meaning of Rule 144 under the Securities
Act and that the exemption from registration under Rule 144 will not be
available for at least one (1) year from the date of exercise of this Warrant,
subject to any special treatment by the SEC for exercise of this Warrant
pursuant to Section 2.2, and even then will not be available unless a public
            -----------
market then exists for the stock, adequate information concerning the Company is
then available to the public, and other terms and conditions of Rule 144 are
complied with; and that all stock certificates representing shares of stock
issued to the Holder upon exercise of this Warrant or upon conversion of such
shares may have affixed thereto a legend substantially in the following form:

     THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE
     SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"), OR UNDER THE
     SECURITIES LAWS OF ANY STATE.  THESE SECURITIES ARE SUBJECT TO RESTRICTIONS
     ON TRANSFERABILITY AND RESALE AND MAY NOT BE TRANSFERRED OR RESOLD EXCEPT
     AS PERMITTED UNDER THE ACT AND THE APPLICABLE STATE SECURITIES LAWS,
     PURSUANT TO REGISTRATION OR EXEMPTION THEREFROM.  INVESTORS SHOULD BE AWARE
     THAT THEY MAY BE REQUIRED TO BEAR THE FINANCIAL RISKS OF THIS INVESTMENT
     FOR AN INDEFINITE PERIOD OF TIME.  THE ISSUER OF THESE SECURITIES MAY
     REQUIRE AN OPINION OF COUNSEL IN FORM AND SUBSTANCE SATISFACTORY TO THE
     ISSUER TO THE EFFECT THAT ANY PROPOSED TRANSFER OR RESALE IS IN COMPLIANCE
     WITH THE ACT AND ANY APPLICABLE STATE SECURITIES LAWS.

         11.  NO RIGHTS OR LIABILITIES AS STOCKHOLDERS. This Warrant shall not
entitle the Holder to any voting rights or other rights as a stockholder of the
Company. In the

                                       7
<PAGE>

absence of affirmative action by such Holder to purchase Common Stock by
exercise of this Warrant or Common Stock upon conversion thereof, no provisions
of this Warrant, and no enumeration herein of the rights or privileges of the
Holder hereof shall cause such Holder hereof to be a stockholder of the Company
for any purpose.

         12.  REPRESENTATIONS AND WARRANTIES OF THE COMPANY. The Company hereby
represents and warrants to Holder that:

              12.1   Due Authorization; Consents. All corporate action on the
                     ---------------------------
part of the Company, its officers, directors and shareholders necessary for (a)
the authorization, execution and delivery of, and the performance of all
obligations of the Company under, this Warrant, and (b) the authorization,
issuance, reservation for issuance and delivery of all of the Common Stock
issuable upon exercise of this Warrant, has been duly taken. This Warrant
constitutes a valid and binding obligation of the Company enforceable in
accordance with its terms, subject, as to enforcement of remedies, to applicable
bankruptcy, insolvency, moratorium, reorganization and similar laws affecting
creditors' rights generally and to general equitable principles. All consents,
approvals and authorizations of, and registrations, qualifications and filings
with, any federal or state governmental agency, authority or body, or any third
party, required in connection with the execution, delivery and performance of
this Warrant and the consummation of the transactions contemplated hereby and
thereby, including, without limitation, the issuance and delivery of all of the
Common Stock issuable upon exercise of this Warrant, have been obtained.

              12.2   Organization. The Company is a corporation duly organized,
                     ------------
validly existing and in good standing under the laws of the State of Delaware
and has all requisite corporate power to own, lease and operate its property and
to carry on its business as now being conducted and as currently proposed to be
conducted.

              12.3   Valid Issuance of Stock. The outstanding shares of the
                     -----------------------
capital stock of the Company are duly and validly issued, fully paid and non-
assessable, and such shares, and all outstanding options and other securities of
the Company, have been issued in full compliance with the registration and
prospectus delivery requirements of the Securities Act and the registration and
qualification requirements of all applicable state securities laws, or in
compliance with applicable exemptions therefrom, and all other provisions of
applicable federal and state securities laws, including without limitation,
anti-fraud provisions.

              12.4   Governmental Consents. All consents, approvals, orders,
                     ---------------------
authorizations or registrations, qualifications, declarations or filings with
any federal or state governmental authority on the part of the Company required
in connection with the consummation of the transactions contemplated herein,
including, without limitation, those under the Securities Act and all applicable
state securities laws, shall have been obtained prior to and be effective as of
the Effective Date.

              12.5   Listing on Nasdaq or Securities Exchange. The Company shall
                     ----------------------------------------
use its best efforts to list any shares of Common Stock issuable upon exercise
of this Warrant on Nasdaq or such other national securities exchange on which
shares of Common Stock are then listed. The Company will at its expense cause
all shares of Common Stock issued upon exercise of this Warrant to be listed on
Nasdaq and/or such other national securities exchange on which shares of Common
Stock are then listed at the time of such issuance and shall maintain such
listing.

                                       8
<PAGE>

              12.6   No Impairment. The Company further covenants that it will
                     -------------
not, by amendment of its Certificate of Incorporation or through reorganization,
consolidation, merger, dissolution or sale of assets, or by any other voluntary
act, avoid or seek to avoid the observance or performance of any of the
covenants, stipulations or conditions to be observed or performed hereunder by
the Company.

         13.  NOTICES. Except as may be otherwise provided herein, all notices,
requests, waivers and other communications made pursuant to this Agreement shall
be in writing and shall be conclusively deemed to have been duly given (a) when
hand delivered to the other party; (b) when received when sent by facsimile at
the address and number set forth below; (c) three business days after deposit in
the U.S. mail with first class or certified mail receipt requested postage
prepaid and addressed to the other party as set forth below; or (d) the next
business day after deposit with a national overnight delivery service, postage
prepaid, addressed to the parties as set forth below with next-business-day
delivery guaranteed, provided that the sending party receives a confirmation of
delivery from the delivery service provider.

<TABLE>
<CAPTION>
<S>      <C>                                                 <C>
          To Holder:                                         To the Company:
          Stargen II LLC                                     BioSource International, Inc.
                                                             820 Flynn Road
                                                             Camarillo, California 93012
                                                             Telephone No.:  (805)
                                                             Facsimile No.:   (805)
                                                             Attention:  James Chamberlain
                                                             President and Chief Executive Officer

          With copies to (which shall not                    With copies to (which shall not
          constitute notice):                                constitute notice):
          Latham & Watkins                                   Troop Steuber Pasich Reddic & Tobey,
          505 Montgomery Street, Suite 1900                  LLP
          San Francisco, CA 94111-2562                       2029 Century Park East, 24th Floor
          Telephone No.:  (415) 391-0600                     Los Angeles, CA  90067
          Facsimile No.:   (415) 395-8095                    Telephone No.:  (310) 728-3222
          Attention:  Scott Haber, Esq.                      Facsimile No.:  (310) 728-2222
                                                             Attention: Scott W. Alderton Esq.

</TABLE>

Each person making a communication hereunder by facsimile shall promptly confirm
by telephone to the person to whom such communication was addressed each
communication made by it by facsimile pursuant hereto but the absence of such
confirmation shall not affect the validity of any such communication.  A party
may change or supplement the addresses given above, or designate additional
addresses, for purposes of this Section 14 by giving the other party written
                                ----------
notice of the new address in the manner set forth above.

         14.  HEADINGS. The headings in this Warrant are for purposes of
convenience in reference only, and shall not be deemed to constitute a part
hereof.

         15.  LAW GOVERNING. This Warrant shall be construed and enforced in
accordance with, and governed by, the laws of the State of California, with
regard to conflict of law principles of such state.

                                       9
<PAGE>

         16.  NO IMPAIRMENT. The Company will not, by amendment of its
Certificate of Incorporation or bylaws, or through reorganization,
consolidation, merger, dissolution, issue or sale of securities, sale of assets
or any other voluntary action, avoid or seek to avoid the observance or
performance of any of the terms of this Warrant, but will at all times in good
faith assist in the carrying out of all such terms and in the taking of all such
action as may be necessary or appropriate in order to protect the rights of the
Registered Holder of this Warrant against impairment. Without limiting the
generality of the foregoing, the Company (a) will not increase the par value of
any shares of stock issuable upon the exercise of this Warrant above the amount
payable therefor upon such exercise, and (b) will take all such action as may be
necessary or appropriate in order that the Company may validly and legally issue
fully paid and non-assessable shares of Common Stock upon exercise of this
Warrant.

         17.  NOTICES OF RECORD DATE.  In case:

              17.1  the Company shall take a record of the holders of its Common
Stock (or other stock or securities at the time receivable upon the exercise of
this Warrant), for the purpose of entitling them to receive any dividend or
other distribution, or any right to subscribe for or purchase any shares of
stock of any class or any other securities or to receive any other right; or

              17.2  of any consolidation or merger of the Company with or into
another corporation, any capital reorganization of the Company, any
reclassification of the capital stock of the Company, or any conveyance of all
or substantially all of the assets of the Company to another corporation in
which holders of the Company's stock are to receive stock, securities or
property of another corporation; or

              17.3  of any voluntary dissolution, liquidation or winding-up of
the Company; or 17.4 of any redemption or conversion of all outstanding Common
Stock;

then, and in each such case, the Company will mail or cause to be mailed to the
Registered Holder of this Warrant a notice specifying, as the case may be, (i)
the date on which a record is to be taken for the purpose of such dividend,
distribution or right, or (ii) the date on which such reorganization,
reclassification, consolidation, merger, conveyance, dissolution, liquidation,
winding-up, redemption or conversion is to take place, and the time, if any is
to be fixed, as of which the holders of record of Common Stock or (such stock or
securities as at the time are receivable upon the exercise of this Warrant),
shall be entitled to exchange their shares of Common Stock (or such other stock
or securities), for securities or other property deliverable upon such
reorganization, reclassification, consolidation, merger, conveyance,
dissolution, liquidation or winding-up.  The Company shall use all reasonable
efforts to ensure such notice shall be delivered at least thirty (30) days prior
to the date therein specified.

         18.  SEVERABILITY. If any term, provision, covenant or restriction of
this Warrant is held by a court of competent jurisdiction to be invalid, void or
unenforceable, the remainder of the terms, provisions, covenants and
restrictions of this Warrant shall remain in full force and effect and shall in
no way be affected, impaired or invalidated.

         19.  COUNTERPARTS. For the convenience of the parties, any number of
counterparts of this Warrant may be executed by the parties hereto and each such
executed counterpart shall be, and shall be deemed to be, an original
instrument.

                                       10
<PAGE>

         20.  NO INCONSISTENT AGREEMENTS. The Company will not on or after the
date of this Warrant enter into any agreement with respect to its securities
which is inconsistent with the rights granted to the Holders of this Warrant or
otherwise conflicts with the provisions hereof. The rights granted to the
Holders hereunder do not in any way conflict with and are not inconsistent with
the rights granted to holders of the Company's securities under any other
agreements, except rights that have been waived.

         21.  SATURDAYS, SUNDAYS AND HOLIDAYS. If the Expiration Date falls on a
Saturday, Sunday or legal holiday, the Expiration Date shall automatically be
extended until 5:00 p.m. the next business day.

         22.  ENTIRE AGREEMENT. This Warrant, the Securities Purchase Agreement
dated as of January 10, 2000 by and among the Company and the Holder, and the
Investor Rights Agreement dated as of February __, 2000 by and among the Company
and the Holder, contain the sole and entire agreement and understanding of the
parties with respect to the entire subject matter of this Warrant, and any and
all prior discussions, negotiations, commitments and understandings, whether
oral or otherwise, related to the subject matter of this Warrant are hereby
merged herein.

     IN WITNESS WHEREOF, the Company has caused this Warrant to be duly executed
as of the Effective Date.

BIOSOURCE INTERNATIONAL, INC.


-------------------------------------------
By
Printed Name
Title

                                       11
<PAGE>

                                   EXHIBIT A
                                   ---------

                              NOTICE OF EXERCISE
                   (To be executed upon exercise of Warrant)

BioSource International, Inc.

The undersigned hereby irrevocably elects to exercise the right of purchase
represented by the within Warrant Certificate for, and to purchase thereunder,
the securities of BioSource International, Inc., as provided for therein, and
(check the applicable box):


[ ]     tenders herewith payment of the exercise price in full in the form of
        cash or a certified or official bank check in same-day funds in the
        amount of $____________ for _________ such securities.

[ ]     Elects the [Net Issue Exercise][Easy Sale Exercise] option pursuant to
        Section 2.2 or 2.3 of the Warrant, and accordingly requests delivery of
        a net of ______________ of such securities.

Please issue a certificate or certificates for such securities in the name of,
and pay any cash for any fractional share to (please print name, address and
social security number):

Name:         ------------------------------------------------------------------

Address:      ------------------------------------------------------------------

Signature:    ------------------------------------------------------------------

Note:  The above signature should correspond exactly with the name on the first
page of this Warrant Certificate or with the name of the assignee appearing in
the assignment form below.

If said number of shares shall not be all the shares purchasable under the
within Warrant Certificate, a new Warrant Certificate is to be issued in the
name of said undersigned for the balance remaining of the shares purchasable
thereunder rounded up to the next higher whole number of shares.

                                       12
<PAGE>

                                   EXHIBIT B
                                   ---------

                                   ASSIGNMENT

          (To be executed only upon assignment of Warrant Certificate)

For value received, hereby sells, assigns and transfers unto _______________ the
within Warrant Certificate, together with all right, title and interest therein,
and does hereby irrevocably constitute and appoint ____________________________
attorney, to transfer said Warrant Certificate on the books of the within-named
Company with respect to the number of Warrants set forth below, with full power
of substitution in the premises:

--------------------------------------------------------------------------------
  Name(s) of Assignee(s)             Address                   # of Warrants
--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

And if said number of Warrants shall not be all the Warrants represented by the
Warrant Certificate, a new Warrant Certificate is to be issued in the name of
said undersigned for the balance remaining of the Warrants registered by said
Warrant Certificate.

              ------------------------------------------------------------------

Dated:        ------------------------------------------------------------------

Signature:    ------------------------------------------------------------------

Notice:  The signature to the foregoing Assignment must correspond to the name
as written upon the face of this security in every particular, without
alteration or any change whatsoever; signature(s) must be guaranteed by an
eligible guarantor institution (banks, stock brokers, savings and loan
associations and credit unions with membership in an approved signature
guarantee medallion program) pursuant to Securities and Exchange Commission Rule
17Ad-15.

                                       13