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                                                                    Exhibit 4.03


                             BROOKS AUTOMATION, INC.
                          AMENDMENT TO RIGHTS AGREEMENT

      This Amendment (this "Agreement"), dated as of October 23, 2001, to the
Rights Agreement dated as of July 23, 1997 (the "Rights Agreement"), between
Brooks Automation, Inc., a Delaware corporation (the "Company"), and Equiserve
Trust Company, N.A. successor Rights Agent (the "Rights Agent").

                                    RECITALS

      WHEREAS, the board of directors of the Company has approved a certain
agreement and plan of merger (the "Merger Agreement") by and among the Company,
PRI Automation, Inc., a Massachusetts corporation ("PRI"), Pontiac Acquisition
Corp., a Massachusetts corporation wholly owned by the Company ("Brooks Merger
Sub") at a meeting of the board of directors of the Company held on October 23,
2001 (the "Meeting"), pursuant to which Brooks Merger Sub will be merged with
and into PRI (the "Merger"), and the stockholders of PRI will become
stockholders of the Company.

      WHEREAS, upon the effectiveness of the Merger, PRI may acquire more than
15% of the outstanding shares of the Company's Common Stock, $.01 par value per
share (the "Company's Common Stock").

      WHEREAS, the acquisition of more than 15% of the outstanding shares of the
Company's Common Stock would result in the acquiring entity or entities being
deemed to be an "Acquiring Person" under the Rights Agreement, which would
trigger certain events pursuant to the terms of the Rights Agreement.

      WHEREAS, at the Meeting the board of directors of the Company determined
that it is in the best interest of the Company to amend the Rights Agreement
prior to the Company entering into the Merger Agreement so that PRI and its
Affiliates will not become Acquiring Persons under the Rights Agreement.

      WHEREAS, capitalized terms used but not otherwise defined in this
Amendment No. 1 shall have the meanings given them in the Rights Agreement.

      NOW, THEREFORE, in consideration of the promises and agreements set forth
herein, and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto agree as
follows:

      1. AMENDMENT OF FIRST SUBPARAGRAPH OF SECTION 1. The first subparagraph of
Section 1, definition of "Acquiring Person," is hereby amended and restated so
that such subparagraph reads in its entirety as follows:

            "Acquiring Person" shall mean any Person who or which, together with
            all Affiliates and Associates of such Person, shall be the
            Beneficial Owner of 15% or more of the Common Shares of the Company
            then outstanding, but shall not


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            include (i) the Company, (ii) any Subsidiary of the Company, (iii)
            any employee benefit plan of the Company or any Subsidiary of the
            Company, (iv) any entity holding Common Shares for or pursuant to
            the terms of any such employee benefit plan, (v) Robert J. Therrien,
            any members of his immediate family or any of his or their
            Affiliates or Associates, (vi) any person that is the Beneficial
            Owner of 15% or more of the Common Shares of the Company outstanding
            as of the close of the Nasdaq National Market on the date hereof;
            provided, however, that after such date such person does not become
            the Beneficial Owner of additional Common Shares of the Company in
            an aggregate amount (net of any sales) of the greater of 200,000
            Common Shares or the number of Common Shares equal to 2.6% of the
            then outstanding Common Shares (as measured as of the date of the
            then acquisition of Common Shares by the Beneficial Owner); and
            provided, further that such person shall be treated as any other
            holder of Common Shares of the Company and shall no longer be
            entitled to the exclusion set forth in this clause (vi) after such
            time as such person becomes the Beneficial Owner of less than 15% of
            the Common Shares of the Company then outstanding or (vii) PRI
            Automation, Inc., a Massachusetts corporation ("PRI"), or any of its
            Affiliates if and only if, PRI or such Affiliates shall become the
            Beneficial Owner of 15% or more of the Common Shares of the Company
            then outstanding as a result of the execution of the Agreement and
            Plan of Merger authorized and approved by the Board of Directors of
            the Company at the meeting of the Board of Directors held on October
            23, 2001, as it may be amended from time to time (the "Merger
            Agreement"), or the consummation of the transactions contemplated
            thereby, and/or any options to purchase or proxies to vote Common
            Shares of the Company granted by the Company or any stockholder of
            the Company to PRI in connection with the Merger Agreement or any
            agreements or arrangements entered into by the Company and PRI in
            connection therewith. Notwithstanding the foregoing, (1) no Person
            shall become an "Acquiring Person" as the result of an acquisition
            of Common Shares by the Company which, by reducing the number of
            shares outstanding, increases the proportionate number of shares
            beneficially owned by such Person to 15% or more of the Common
            Shares of the Company then outstanding; provided, however, that if a
            Person shall so become the Beneficial Owner of 15% or more of the
            Common Shares of the Company then outstanding by reason of an
            acquisition of Common Shares by the Company and shall, after such
            share purchases by the Company, become the Beneficial Owner of an
            additional 1% of the outstanding Common Shares of the Company, then
            such Person shall be deemed to be an "Acquiring Person"; (2) if the
            Board of Directors of the Company determines in good faith that a
            Person who would otherwise be an "Acquiring Person," as defined
            pursuant to the foregoing provisions of this paragraph, has become
            such inadvertently, and such Person divests as promptly as
            practicable a sufficient number of Common Shares so that such Person
            would no longer be an "Acquiring Person," as defined pursuant to the
            foregoing provisions of this paragraph, then such Person shall not
            be deemed to have become an "Acquiring Person" for any purposes of
            this Agreement; and (3) an underwriter or underwriters which become
            the Beneficial Owner of 15% or more of the Common Shares of the
            Corporation then outstanding in connection


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            with an underwritten public offering with a view to the public
            distribution of such Common Shares shall not become an "Acquiring
            Person" hereunder."

      2. REAFFIRMATION OF RIGHTS AGREEMENT. Except as specifically amended by
this Amendment, the Rights Agreement shall remain in full force and effect.


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      IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed as of the date first above written.

                                    BROOKS AUTOMATION, INC.

                                    By:   /s/ Ellen B. Richstone
                                       -----------------------------------------
                                          Name:   Ellen B. Richstone
                                          Title:  Senior Vice President of
                                                  Finance and Administration and
                                                  Chief Financial Officer


                                    EQUISERVE TRUST COMPANY, N.A

                                    By:   /s/ Margaret Prentice
                                       -----------------------------------------
                                          Name:   Margaret Prentice
                                          Title:  Managing Director


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