ADMINISTRATION AGREEMENT ADDENDUM NUMBER ONE

                                                       EXHIBIT NO. EX-99.h.3.z.1

                      DFA INVESTMENT DIMENSIONS GROUP INC.

                      TAX-MANAGED U.S. MARKETWIDE PORTFOLIO

                            ADMINISTRATION AGREEMENT
                               ADDENDUM NUMBER ONE

     THIS ADDENDUM made this 21st day of September, 2001, by and between DFA
INVESTMENT DIMENSIONS GROUP INC., a Maryland corporation (the "Fund"), on behalf
of:

                     "TAX-MANAGED U.S. MARKETWIDE PORTFOLIO"

(the "Portfolio"), a separate series of the Fund, and DIMENSIONAL FUND ADVISORS
INC., a Delaware corporation (the "Administrator").

     WHEREAS, the Fund and the Administrator have previously entered into an
Administration Agreement, dated August 1, 2001 (the "Administration Agreement"),
pursuant to which the Administrator has agreed to provide the services,
assistance and facilities of an administrator, and to perform various
administrative and other services for the Portfolio; and

     WHEREAS, the administrator has been informed by the Fund that the Portfolio
desires to change its name;

     NOW, THEREFORE, in consideration of the terms and conditions hereinafter
set forth, it is hereby agreed as follows:

     1.   The name of the Portfolio shall be changed from "Tax-Managed U.S.
Marketwide Portfolio" to "Tax-Managed U.S. Equity Portfolio," and all references
in the Administration Agreement to "Tax-Managed U.S. Marketwide Portfolio" shall
be changed to "Tax-Managed U.S. Equity Portfolio."

     2.   The effective date of this Addendum shall be September 21, 2001.

     3.   The parties hereby further agree that no other provisions of the
Administration Agreement are in any way modified by this Addendum, and that all
other provisions of the Administration Agreement remain in full force and
effect.

     IN WITNESS WHEREOF, the parties hereby have caused this Addendum Number One
to be executed this 21st day of September, 2001.

DFA INVESTMENT DIMENSIONS                     DIMENSIONAL FUND ADVISORS
GROUP INC.                                    INC.


By: /s/ Xxxxxxx X. Xxxxxxxx                   By:  /s/ Xxxxxxxxx X. Xxxxxx
    -----------------------------------            ---------------------------
    Xxxxxxx X. Xxxxxxxx                             Xxxxxxxxx X. Xxxxxx
    Vice President, Chief Financial Officer         Vice President and Secretary
    and Treasurer