EXHIBIT 4 to
                                                              AMENDMENT NO. 1 to
                                                                    Schedule 13D

                           PROBUSINESS SERVICES, INC.

         AMENDMENT TO AMENDED AND RESTATED REGISTRATION RIGHTS AGREEMENT

         The undersigned, being parties to that certain Amended and Restated
Registration Rights Agreement (the "Agreement") dated March 12, 1997, by and
among ProBusiness, Inc., a California corporation (the "Company"), General
Atlantic Partners 39, L.P. ("GAP L.P.") and GAP Coinvestment Partners, L.P.
("GAP Coinvestment") (collectively, the "Purchasers"), and the Holders (as
defined in the Registration Rights Agreement, dated December 1, 1989, as
amended, between the Company and the Original Holders) (the "Original Holders"),
in consideration of valuable consideration, the receipt and sufficiency of which
is hereby acknowledged, hereby agree and consent to the following amendments to
the Agreement:

         1. General Atlantic Partners 70, L.P., GAP Coinvestment Partners II,
L.P., and GapStar, LLC, shall each have the rights and obligations of a
"Purchaser," as defined in the Agreement.

         2. Section 1.2 "REGISTRABLE SECURITIES" shall be deleted and replaced
with the following Section 1.2 "REGISTRABLE SECURITIES":

         "REGISTRABLE SECURITIES" means (i) shares of the Company's Common Stock
issued or issuable pursuant to the conversion of the Company's Preferred Stock,
(ii) any Common Stock of the Company issued or issuable in respect of the shares
of the Company's Common Stock or other securities issued or issuable pursuant to
the conversion of the Company's Preferred Stock upon any stock split, stock
dividend, reapitalization or similar event, (iii) shares of the Company's Common
Stock issued or issuable pursuant to the conversion of the Company's 6.9% Senior
Convertible Preferred Stock issued on August 1, 2000 (the "Senior Preferred
Stock"), and (iv) any Common Stock of the Company issued or issuable in respect
of the shares of the Company's Common Stock or other securities issued or
issuable pursuant to the conversion of the Senior Preferred Stock upon any stock
split, stock dividend, reapitalization or similar event; provided, however,
Registrable Securities shall not include any such shares that were transferred
by a Holder to a transferree that did not comply with Section 1.15 hereof or of
the Original Agreement.

         3. The following provision shall be added to the Agreement below
Section 1.7.2 as Section 1.7.3:

                  1.7.3  SHELF REGISTRATION

                  (a) FILING AND EFFECTIVENESS OF SHELF REGISTRATION. As soon as
practicable following the conversion of the Senior Preferred Stock into shares
of Common Stock (the "CONVERSION SHARES") the Company shall file a shelf
registration statement solely

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with respect to the Conversion Shares and pursuant to Rule 415 under the
Securities Act (the "SHELF REGISTRATION") on Form S-3 (or any successor form).
The Company shall use its reasonably commercial best efforts to have the Shelf
Registration declared effective as soon as practicable after such filing, and
shall use its reasonably commercial best efforts to keep the Shelf Registration
effective and updated, from the date such Shelf Registration is declared
effective (the "EFFECTIVE DATE") until the second anniversary of the Effective
Date (the "EFFECTIVE PERIOD"); PROVIDED, that if the Company declares a Blackout
Period (as defined below) during the Effective Period, the Effective Period
shall be extended by the number of days equal to the length of time that any
Blackout Periods were in effect. Notwithstanding the foregoing, if the Board of
Directors makes a good faith determination that a filing of the Shelf
Registration or the sale of any Conversion Shares under an effective Shelf
Registration would interfere with any material financing or material investment
transaction, business combination or material acquisition then under
consideration, involving the Company or any of its affiliates, and the Company
provides written notice (the "SHELF NOTICE") to the holders containing a general
statement of the reasons for such determination (which shall be kept
confidential by such holders), the Company may postpone the filing of the Shelf
Registration for the period indicated in the Shelf Notice (which shall be kept
confidential by such holders), which period shall in no event exceed 90 days (a
"BLACKOUT PERIOD").

                  (b) SUPPLEMENTS AND AMENDMENTS; EXPENSES. The Company shall
supplement or amend, if necessary, the Shelf Registration, as required by the
instructions applicable to such registration form or by the Securities Act or as
reasonably required by the holders of (or any underwriter for) more than 50% of
the Conversion Shares and the Company shall furnish to the holders of the
Conversion Shares to which the Shelf Registration relates copies of any such
supplement or amendment prior to its being used and/or filed with the
Commission. The Company shall pay all Registration Expenses in connection with
the Shelf Registration, whether or not it becomes effective, and whether all,
none or some of the Conversion Shares are sold pursuant to the Shelf
Registration.

                  (c) EFFECTIVE SHELF REGISTRATION STATEMENT. A Shelf
Registration pursuant to this Section 1.7.3 shall not be deemed to have been
effected (i) unless a Shelf Registration has become effective and remained
effective in compliance with the provisions of the Securities Act with respect
to the disposition of all Conversion Shares and until such time as all of such
Conversion Shares have been disposed of under the Shelf Registration or (ii) if
after it has become effective, the Shelf Registration is interfered with by any
stop order, injunction or other order or requirement of the Commission or other
governmental agency or court and has not thereafter become effective."

         4. Section 1.11.2 under the heading "LOCK-UP AGREEMENT" shall be
deleted and replaced with the following Section 1.11.2:

         "In consideration for the Company agreeing to its obligations under
this Section 1, each Purchaser and each transferee of such Purchaser pursuant to
Section 1.15 hereof agrees (but only if each officer, director, shareholder
owning beneficially ten percent (10%) or more

                                       -2-

<PAGE>

of the Company's equity securities, and each shareholder selling shares in such
offering also agrees), in connection with the first registration (an "Initial
Public Offering") of the Company's securities for its own account to be offered
to the general public (other than a registration relating to a Rule 145
transaction or with respect to an employee benefit plan) and in connection with
any subsequent registration of the Company's securities that occurs within the
five-year period after the closing of an Initial Public Offering, not to sell,
make any short sale of, loan, grant any option for the purchase of, or otherwise
dispose of any Registrable Securities or other securities of the Company (other
than those included in the registration) without the prior written consent of
the underwriters, for one hundred eighty (180) days from the date of the final
prospectus related to the offering. The Company may impose stop-transfer
instructions with respect to such securities subject to the foregoing
restriction until the end of said period."

                                       -3-

<PAGE>

         IN WITNESS WHEREOF, the parties hereto have executed this Agreement as
of the 1st of August, 2000.

PROBUSINESS SERVICES, INC. (successor to ProBusiness, Inc.)

By   /s/ Thomas H. Sinton
     --------------------------------
Thomas H. Sinton
President and Chief Executive Officer

GENERAL ATLANTIC PARTNERS, 39, L.P.
GAP COINVESTMENT PARTNERS, L.P.
General Atlantic Service Corporation
3 Pickwick Plaza
Greenwich, Connecticut 06830

--------------------------------
    (Printed Name of Purchaser)

--------------------------------
    (Signature)

--------------------------------
    (Title, if Applicable)

                                       -4-

<PAGE>

         IN WITNESS WHEREOF, the parties hereto have executed this Agreement as
of the 1st of August, 2000.

                                   GENERAL ATLANTIC PARTNERS 39, L.P.

                                   By:  GENERAL ATLANTIC PARTNERS, LLC,
                                        its General Partner

                                        By:  /s/ Steven A. Denning
                                             -----------------------------------
                                             Name:  Steven A. Denning
                                             Title: A Managing Member


                                   GAP COINVESTMENT PARTNERS, L.P.

                                   By:  /s/ Steven A. Denning
                                        ----------------------------------------
                                        Name:  Steven A. Denning
                                        Title: A General Partner


                                       -5-

<PAGE>


         IN WITNESS WHEREOF, the parties hereto have executed this Agreement as
of the 1st of August, 2000.

                                   GENERAL ATLANTIC PARTNERS 70, L.P.

                                   By:  GENERAL ATLANTIC PARTNERS, LLC,
                                        its General Partner

                                        By:  /s/ Steven A. Denning
                                             -----------------------------------
                                             Name:  Steven A. Denning
                                             Title: A Managing Member


                                   GAP COINVESTMENT PARTNERS II, L.P.

                                   By:  /s/ Steven A. Denning
                                        ----------------------------------------
                                        Name:  Steven A. Denning
                                        Title: A General Partner


                                   GAPSTAR, LLC

                                   By:  GENERAL ATLANTIC PARTNERS, LLC
                                        its Managing Member

                                        By:  /s/ Steven A. Denning
                                             -----------------------------------
                                             Name:  Steven A. Denning
                                             Title: A Managing Member


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