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                                                                Exhibit 4.2

                                 AMENDMENT TO

              AMENDED AND RESTATED PREFERRED STOCK RIGHTS AGREEMENT

         This amendment (the "AMENDMENT"), dated as of January 5, 2003, to the
Amended and Restated Preferred Stock Rights Agreement (the "RIGHTS AGREEMENT"),
dated as of December 19, 2001, between ProBusiness Services, Inc., a Delaware
corporation (the "COMPANY"), and Wells Fargo Bank, MN N.A., is being executed at
the direction of the Company.

         WHEREAS, the Company, Automatic Data Processing, Inc., a Delaware
corporation ("PARENT"), and ADP Merger Corp., a Delaware corporation and
indirect wholly owned subsidiary of Parent ("MERGER SUB"), intend to enter into
an Agreement and Plan of Merger pursuant to which, among other things, Merger
Sub will merge with and into the Company and each remaining share of capital
stock of the Company will be converted into the right to receive cash, upon the
terms and subject to the conditions of the Merger Agreement;

         WHEREAS, on January 5, 2003, the Board of Directors of the Company
resolved to amend the Rights Agreement to render the Rights inapplicable to the
Merger Agreement (as defined below), the Merger (as defined below) and the other
transactions contemplated by the Merger Agreement; and

         WHEREAS, Section 27 of the Rights Agreement permits the Company from
time to time to supplement and amend the Rights Agreement.

         NOW, THEREFORE, in consideration of the foregoing and the agreements,
provisions and covenants herein contained, the parties agree as follows:

         1. Section 1(q) of the Rights Agreement is hereby amended to read in
its entirety as follows:

         "EXPIRATION DATE" shall mean the earliest to occur of: (i) the Close of
Business on the Final Expiration Date, (ii) the Redemption Date, (iii) the time
at which the Board of Directors orders the exchange of the Rights as provided in
Section 24 hereof, or (iv) upon the Effective Time (as such term in defined in
the Agreement and Plan of Merger, dated as of January 5, 2003, including any
amendment or supplement thereto (the "MERGER AGREEMENT") by and among the
Company, Automatic Data Processing, Inc., a Delaware corporation ("PARENT"), and
ADP Merger Corp., a Delaware corporation and indirect wholly owned subsidiary of
Parent).

         2. Section 1 of the Rights Agreement is hereby amended by adding the
following new paragraph at the end of Section 1:

         "Notwithstanding anything in this Agreement that might otherwise be
deemed to the contrary, neither Parent nor any of its Affiliates or Associates
shall be deemed an Acquiring Person and none of the Distribution Date, Shares
Acquisition Date, Section 13 Event or Triggering Event shall be deemed to occur,
in each such case, by the approval, execution, delivery or performance of the
Merger Agreement among Parent, ADP Merger Corp., an indirect wholly owned
subsidiary of Parent, and the Company, the announcement or consummation of the
Merger (as defined in the Merger
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Agreement) or the other transactions specifically contemplated by the Merger
Agreement, including the approval, execution, delivery or performance of the
Stockholder Agreements (as defined in the Merger Agreement), between Parent and
certain stockholders of the Company. No such event shall entitle or permit the
holders of the Rights to exercise the Rights or otherwise affect the rights of
the holders of Rights, including giving the holders of the Rights the right to
acquire securities of any party to the Merger Agreement."

         5. The Rights Agreement shall not otherwise be supplemented or amended
by virtue of this Amendment, but shall remain in full force and effect. This
Amendment may be executed in one or more counterparts, all of which shall be
considered one and the same amendment and each of which shall be deemed an
original.

         6. This Amendment shall be deemed a contract made under the laws of the
State of Delaware and for all purposes shall be governed by and construed in
accordance with the laws of such State applicable to contracts to be made and
performed entirely within such State.

                           [SIGNATURE PAGE TO FOLLOW]

                                       2.
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         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed and attested, all as of the day and year first above written.

PROBUSINESS SERVICES, INC.                       WELLS FARGO BANK, MN N.A.
                                                 as Rights Agent

By: /s/ Thomas H. Sinton                         By: /s/ John Baker
    -----------------------------                    ---------------------------
Name:  Thomas H. Sinton                          Name:  John Baker
Title: President and Chief                       Title:  Assistant Vice
       Executive Officer                                 President