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                                                                     Exhibit 4.5

                             THIRD AMENDMENT TO THE
                  INFORMATION AND REGISTRATION RIGHTS AGREEMENT

               This Third Amendment to the Information and Registration Rights
Agreement, as amended (the "Amendment"), is made as of March 23, 1998, by and
among Biosource Technology, Inc., a California corporation (the "Company"), and
the persons listed on the attached Schedule A, including amendments thereto, who
become signatories to this Amendment (collectively, the "Investors").

                                 R E C I T A L S

               A. The Company and the Investors have entered into agreements for
sale by the Company and purchase by the Investors of the Company's Convertible
Securities.

               B. The Company and the Investors desire to provide for the rights
of the Investors with respect to registration of the shares of common stock (the
"Common Stock") issued upon conversion of the Company's Series F Preferred Stock
according to the terms of the Information and Registration Rights Agreement
dated as of October 11, 1990, as amended by the Amendment to the Information and
Registration Rights Agreement dated as of October 11, 1990 and the Second
Amendment to the Information and Registration Rights Agreement dated October 10,
1991 (collectively, the "Agreement").

               C. The Company and the Investors desire to amend the Agreement to
grant to certain persons acquiring up to one million (1,000,000) shares of
Series F Preferred Stock of the Company, (the "Series F Investors") on or after
March 6, 1998, for a total aggregate consideration of $7.00 per share, or
approximately $7,000,000, Registration Rights in accordance with the Agreement.


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               THE PARTIES AGREE AS FOLLOWS:

               1. Definitions. The capitalized terms used in this Amendment
without definition shall have the same meanings as set forth in the Agreement.

               2. Grant of Registration Rights. In accordance with Section 9 of
the Agreement, each of the Series F Investors hereto shall be considered an
Investor for all purposes of the Agreement.

               3. Counterparts. This Amendment 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.

               4. Governing Law. This Amendment shall be governed by and
construed in accordance with the laws of the state of California applicable to
contracts entered into and wholly to be performed within the state of
California.

               5. Headings. The headings of the Sections of this Amendment are
for convenience and shall not by themselves determine the interpretation of this
Agreement.


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               IN WITNESS WHEREOF, the parties hereto have executed this
Amendment as of the day and year first above written.

THE COMPANY:                         BIOSOURCE TECHNOLOGIES, INC.


                                     By: /s/ Robert L. Erwin
                                        ----------------------------------------
                                        Robert L. Erwin, Chairman of the Board
                                        and Chief Executive Officer

INVESTOR:

                                     -------------------------------------------
                                     Type or Print Name of Investor


                                     -------------------------------------------
                                     Signature of Investor


                                     -------------------------------------------
                                     Type or Print Name and Title of Signer
                                     (if applicable)




              Signature Page for Third Amendment to the Information
                        and Registration Rights Agreement