Exhibit B-4


                             TPG PARTNERS III, L.P.
                           201 MAIN STREET, SUITE 2420
                             FORT WORTH, TEXAS 76102


                                                     May 17, 2000


Board of Directors
Petco Animal Supplies, Inc.
9125 Rehco Road
San Diego, California 92121

Ladies and Gentlemen:

                  This letter sets forth the commitment of TPG Partners III,
L.P. ("TPG"), subject to the terms and conditions contained herein, to purchase
certain securities of BD Recapitalization Corp. ("MERGERSUB") in connection with
the recapitalization (the "RECAPITALIZATION") of Petco Animal Supplies, Inc.
(the "COMPANY"). The Recapitalization will occur under the Agreement and Plan of
Merger, dated as of even date herewith (the "MERGER AGREEMENT"), pursuant to
which MergerSub will merge with and into the Company, with the Company as the
surviving entity. Unless otherwise defined herein, all capitalized terms used
herein shall have the meanings set forth in the Merger Agreement.

                  1. COMMITMENT. TPG hereby commits, subject to the terms and
conditions set forth herein, to purchase, upon the consummation of the Merger,
common stock and preferred stock of MergerSub (the "EQUITY SECURITIES") for
consideration of up to $92,500,000, which Equity Securities shall represent at
least a 50% equity interest in MergerSub immediately prior to the Merger. TPG
may effect its purchase of the Equity Securities directly or indirectly through
one or more affiliated entities.

                  2. CONDITIONS. TPG's commitment hereunder to purchase the
Equity Securities shall be subject to compliance with the terms of the Merger
Agreement by the parties thereto, satisfaction of each of the conditions to
MergerSub's obligations to consummate the transactions under the Merger
Agreement, MergerSub's receipt of the Financing on the terms set forth in the
Financing Letters, and consummation of the Merger.

                  3. SOLE BENEFICIARY. TPG's commitment hereunder is provided
for your sole benefit and shall not benefit, be disclosed to, or be assigned to,
any other party without our written consent, except that the terms of this
letter may be disclosed (i) to your accountants, attorneys, investment banks and
other advisors or (ii) as required by law or legal process.

                  4. NO MODIFICATION; ENTIRE AGREEMENT. No modification of this
letter shall be binding upon or enforceable against TPG without the written
approval of TPG. This agreement


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represents the entire agreement between us with respect to the matters set forth
herein, and shall replace and supersede any and all discussions and written
communications regarding such matters.

                  5. COUNTERPARTS. This letter may be executed in counterparts,
each of which, when so executed, shall be deemed to be an original and all of
which taken together shall constitute one and the same agreement.

                  6. GOVERNING LAW; CONSENT TO JURISDICTION; WAIVER OF JURY
TRIAL. (a) The terms of this letter shall be governed by the laws of the State
of New York applicable to contracts made and to be performed in such state.

                  (b) Any dispute arising under or with respect to this letter
or the subject matter hereof shall be brought exclusively in the state or
federal courts located in the State of New York, New York County.

                  (c) Each party hereto waives all right to trial by jury in any
action, proceeding and counterclaim (whether based upon contract, tort or
otherwise) related to or arising out of this letter, any of the transactions
contemplated hereby or TPG's commitment hereunder.

                  7. TERMINATION. TPG's commitment hereunder shall terminate
contemporaneously with the termination or expiration of the Merger Agreement,
but in any event on November 1, 2000 (or if earlier, the Terminal Date), if the
Merger has not been consummated by such date.


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                  If the terms of this letter are acceptable to you, please
indicate by signing below and returning a copy of this letter to us.

                                         Sincerely,

                                         TPG PARTNERS III, L.P.

                                         By:  TPG GenPar III, L.P.,
                                              General Partner

                                         By:  TPG Advisors III, Inc.
                                              General Partner

                                         By:  /s/ Jonathan J. Coslet
                                            -------------------------------
                                            Name:  Jonathan Coslet
                                            Title:  Vice President



Agreed to and accepted:

Petco Animal Supplies, Inc.



By:  /s/ James M. Myers
   -----------------------------------
   Name:  James Myers
   Title: Senior VP & CFO


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