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                                                                     EXHIBIT 4.3

                                 PETS.COM, INC.

                          REGISTRATION RIGHTS AGREEMENT


        This Registration Rights Agreement (the "Agreement") is made as of the
13th day of July, 2000, by and among Pets.com, Inc., a Delaware corporation (the
"Company") and Petstore.com, Inc., a Delaware corporation ("Holder").

                                    RECITALS

        The Company, Holder and P-Sub Corporation, a Delaware corporation and
wholly owned subsidiary of the Company, have entered into an Asset Purchase
Agreement (the "Purchase Agreement") dated as of June 12, 2000 pursuant to which
P-Sub Corporation desires to purchase from Holder, and Holder desires to sell to
P-Sub Corporation, certain assets, properties and businesses of Holder (the
"Assets") in exchange for 5,243,752 of the Company's shares of Common Stock,
$0.00125 par value (the "Shares"). A condition to Holder's obligations under the
Purchase Agreement is that the Company and Holder enter into this Agreement in
order to provide Holder with certain rights to register the Shares. The Company
desires to induce Holder to sell the Assets pursuant to the Purchase Agreement
by agreeing to the terms and conditions set forth herein.

                                    AGREEMENT

        In consideration of the mutual promises and covenants hereinafter set
forth, and for certain other valuable considerations, the receipt of which is
hereby acknowledged, the parties hereby agree as follows:

        1.     DEFINITIONS.

               (a) The terms "register," "registered," and "registration" refer
to a registration effected by preparing and filing a registration statement or
similar document in compliance with the Securities Act of 1933, as amended (the
"Securities Act"), and the declaration or ordering of effectiveness of such
registration statement or document;

               (b) The term "Registrable Securities" means the Shares.
Notwithstanding the foregoing, the Shares shall only be treated as Registrable
Securities if and so long as they have not been (A) sold to or through a broker
or dealer or underwriter in a public distribution or a public securities
transaction, or (B) sold in a transaction exempt from the registration and
prospectus delivery requirements of the Securities Act under Section 4(1)
thereof so that all transfer restrictions, and restrictive legends with respect
thereto, if any, are removed upon the consummation of such sale;

               (c) The term "Form S-3" means such form under the Securities Act
as in effect on the date hereof or any successor form that permits significant
incorporation by reference



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of a company's filings under the Securities Exchange Act of 1934, as amended
(the "Exchange Act");

               (d) The term "SEC" means the Securities and Exchange Commission;
and

               (e) The term "Affiliate" means, with respect to a specified
entity, any other entity directly or indirectly controlling or controlled by or
under direct or indirect common control with such specified entity. For purposes
of this definition, "control" when used with respect to any specified entity
means the power to direct the management and policies of such entity, whether
through the ownership of voting securities, by contract or otherwise; and the
terms "controlling" and "controlled" have meanings correlative to the foregoing.

        2. FORM S-3 REGISTRATION. In case the Company shall receive from Holder
written notice (the "Notice") providing a detailed description of an intended
transaction through which Holder intends to sell or distribute all or a part of
the Registrable Securities together with a written request that the Company
effect a registration on Form S-3 and any related qualification or compliance
with respect to all or a part of the Registrable Securities owned by Holder at
any time after the first anniversary of the Closing (as defined in the Purchase
Agreement), the Company will either within thirty (30) days:

               (a) provide Holder a legal opinion from one of the law firms
listed on Exhibit O to the Purchase Agreement stating that the transaction
contemplated by Holder is exempt from the registration requirements of the
Securities Act; or

               (b) effect such registration and all such qualifications and
compliances as may be so requested and as would permit or facilitate the sale or
distribution of all or such portion of Holders' Registrable Securities as are
specified in such Notice; provided, however, that the Company shall not be
obligated to effect any such registration, qualification or compliance pursuant
to this Section 2: (i) if Form S-3 is not available for such offering by Holder;
(ii) if Holder, together with the holders of any other securities of the Company
entitled to inclusion in such registration, propose to sell Registrable
Securities and such other securities (if any) at an aggregate price to the
public (net of any underwriters' discounts or commissions) of less than
$5,000,000; (iii) if the Company shall furnish to Holder a certificate signed by
the President of the Company stating that in the good faith judgment of the
Board of Directors of the Company, it would be detrimental to the Company and
its stockholders for such Form S-3 Registration to be effected at such time, in
which event the Company shall have the right to defer the filing of the Form S-3
registration statement for a period of not more than 90 days after receipt of
the request of Holder under this Section 2; provided, however, that the Company
shall not utilize this right more than once in any twelve month period; (iv) if
the Company has, within the twelve (12) month period preceding the date of such
request, already effected two registrations on Form S-3 for Holder pursuant to
this Agreement; (v) in any particular jurisdiction in which the Company would be
required to qualify to do business or to execute a general consent to service of
process in effecting such registration, qualification or compliance; or (vi) to
the extent the holders of registrable securities under the Company's Amended and
Restates Investors' Rights Agreement dated as of January 18, 2000, as amended
from time to time thereafter, are prevented from



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registering or qualifying registrable securities thereunder as a result of the
registration or qualification of the Shares under this Agreement.

        3. OBLIGATIONS OF THE COMPANY. Whenever required under this Agreement to
effect the registration of any Registrable Securities, the Company shall, as
expeditiously as reasonably possible:

               (a) Prepare and file with the SEC a registration statement with
respect to such Registrable Securities and use its best efforts to cause such
registration statement to become effective, and, upon the written request of
Holder, keep such registration statement effective for up to one hundred twenty
(120) days.

               (b) Prepare and file with the SEC such amendments and supplements
to such registration statement and the prospectus used in connection with such
registration statement as may be necessary to comply with the provisions of the
Securities Act with respect to the disposition of all securities covered by such
registration statement for such period of time as the registration statement
remains effective.

               (c) Furnish to Holder such number of copies of a prospectus,
including a preliminary prospectus, in conformity with the requirements of the
Securities Act, and such other documents as they may reasonably request in order
to facilitate the disposition of the Registrable Securities.

               (d) Use its best efforts to register and qualify the securities
covered by such registration statement under such other securities or Blue Sky
laws of such jurisdictions as shall be reasonably requested by Holder, provided
that the Company shall not be required in connection therewith or as a condition
thereto to qualify to do business or to file a general consent to service of
process in any such states or jurisdictions.

               (e) In the event of any underwritten public offering, enter into
and perform its obligations under an underwriting agreement, in usual and
customary form, with the managing underwriter of such offering. Holder shall
also enter into and perform its obligations under such an agreement.

               (f) Cause all such Registrable Securities registered pursuant
hereunder to be listed on each securities exchange on which similar securities
issued by the Company are then listed.

               (g) Provide a transfer agent and registrar for all Registrable
Securities registered pursuant hereunder and a CUSIP number for all such
Registrable Securities, in each case not later than the effective date of such
registration.

               (h) Use its best efforts to furnish, at the request of Holder, on
the date that such Registrable Securities are delivered to the underwriters for
sale in connection with a registration pursuant to this Agreement, if such
securities are being sold through underwriters, or, if such securities are not
being sold through underwriters, on the date that the registration



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statement with respect to such securities becomes effective, (i) an opinion,
dated such date, of the counsel representing the Company for the purposes of
such registration, in form and substance as is customarily given to underwriters
in an underwritten public offering, addressed to the underwriters, if any, and
to Holder and (ii) a letter dated such date, from the independent certified
public accountants of the Company, in form and substance as is customarily given
by independent certified public accountants to underwriters in an underwritten
public offering, addressed to the underwriters, if any, and to Holder.

        4. FURNISH INFORMATION. It shall be a condition precedent to the
obligations of the Company to take any action pursuant to this Agreement with
respect to the Registrable Securities that Holder shall furnish to the Company
such information regarding itself, the Registrable Securities held by it, and
the intended method of disposition of such securities as shall be required to
effect the registration of Holder's Registrable Securities. The Company shall
have no obligation with respect to any registration requested pursuant to this
Agreement if, as a result of the application of the preceding sentence, the
number of shares or the anticipated aggregate offering price of the Registrable
Securities to be included in the registration does not equal or exceed the
number of shares or the anticipated aggregate offering price required to
originally trigger the Company's obligation to initiate such registration as
specified in subsection 2(b)(ii).

        5. EXPENSES OF REGISTRATION. All expenses incurred in connection with a
registration requested pursuant to Section 2, including (without limitation) all
registration, filing, qualification, printers' and accounting fees and the
reasonable fees and disbursements of one counsel for the selling Holder or
Holders selected by them with the approval of the Company, which approval shall
not be unreasonably withheld, and counsel for the Company, and any underwriters'
discounts or commissions associated with Registrable Securities, shall be borne
by the Holder.

        6. REPORTS UNDER SECURITIES EXCHANGE ACT OF 1934. With a view to making
available to Holder the benefits of Rule 144 promulgated under the Securities
Act and any other rule or regulation of the SEC that may at any time permit
Holder to sell securities of the Company to the public without registration, the
Company agrees to:

               (a) make and keep public information available, as those terms
are understood and defined in SEC Rule 144, at all times so long as the Company
remains subject to the periodic reporting requirements under Sections 13 or
15(d) of the Exchange Act;

               (b) file with the SEC in a timely manner all reports and other
documents required of the Company under the Securities Act and the Exchange Act;
and

               (c) furnish to Holder, so long as Holder owns any Registrable
Securities, forthwith upon request (i) a written statement by the Company that
it has complied with the reporting requirements of SEC Rule 144, the Securities
Act and the Exchange Act (so long as it remains subject to such reporting
requirements), or that it qualifies as a registrant whose securities may be
resold pursuant to Form S-3 (at any time after it so qualifies), (ii) a copy of
the most recent annual or quarterly report of the Company and such other reports
and documents so filed by the Company, and (iii) such other information as may
be reasonably requested in



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availing Holder of any rule or regulation of the SEC which permits the selling
of any such securities without registration or pursuant to such form.

        7. TERMINATION OF REGISTRATION RIGHTS. The Holder shall not be entitled
to exercise any right provided for in this Agreement after the earlier of (i)
February 9, 2007, or (ii) such time as Rule 144 or another similar exemption
under the Securities Act is available for the sale of all of Holder's shares
during a three (3)-month period without registration.

        8. MISCELLANEOUS.

               (a) SUCCESSORS AND ASSIGNS. Except as otherwise provided in this
Agreement, the terms and conditions of this Agreement shall inure to the benefit
of and be binding upon the respective permitted successors and assigns of the
parties. Subject to the threshold provisions generally included above herein,
the parties agree that the Investors may assign their rights and obligations
under this Agreement to any of their current or former partners, members or
affiliates, including to any corporation or limited liability company which is
an Affiliate of such Investor. Nothing in this Agreement, express or implied, is
intended to confer upon any party other than the parties hereto or their
respective successors and assigns any rights, remedies, obligations, or
liabilities under or by reason of this Agreement, except as expressly provided
in this Agreement.

               (b) NOTICES. Unless otherwise provided, any notice required or
permitted by this Agreement shall be in writing and shall be deemed sufficient
upon delivery, when delivered personally or by overnight courier, or forty-eight
(48) hours after being deposited in the U.S. mail, as certified or registered
mail, with postage prepaid, and addressed to the party (with a copy to such
party's counsel at such counsel's address as set forth in the Purchase
Agreement) to be notified at such party's address as set forth on the signature
page or as subsequently modified by written notice.

               (c) SEVERABILITY. If one or more provisions of this Agreement are
held to be unenforceable under applicable law, the parties agree to renegotiate
such provision in good faith. In the event that the parties cannot reach a
mutually agreeable and enforceable replacement for such provision, then (a) such
provision shall be excluded from this Agreement, (b) the balance of the
Agreement shall be interpreted as if such provision were so excluded and (c) the
balance of the Agreement shall be enforceable in accordance with its terms.

               (d) GOVERNING LAW. This Agreement and all acts and transactions
pursuant hereto shall be governed, construed and interpreted in accordance with
the laws of the State of California, without giving effect to principles of
conflicts of laws.

               (e) COUNTERPARTS. This Agreement may be executed in two or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.



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               (f) TITLES AND SUBTITLES. The titles and subtitles used in this
Agreement are used for convenience only and are not to be considered in
construing or interpreting this Agreement.

               (g) AGGREGATION OF STOCK. All shares of the Preferred Stock held
or acquired by affiliated entities or persons shall be aggregated together for
the purpose of determining the availability of any rights under this Agreement.

               (h) EXPENSES. If any action at law or in equity is necessary to
enforce or interpret the terms of this Agreement, the prevailing party shall be
entitled to reasonable attorneys' fees, costs and necessary disbursements in
addition to any other relief to which such party may be entitled.

                            [Signature Page Follows]



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        The parties have executed this Registration Rights Agreement as of the
date first above written.

                                        COMPANY:

                                        PETS.COM, INC.


                                        By:      /s/  Paul Manca
                                             -----------------------------------

                                        Name:         Paul Manca
                                             -----------------------------------

                                        Title:        Chief Financial Officer
                                              ----------------------------------

                                        Address:      435 Brannan Street
                                                      San Francisco, CA  94107



                                        HOLDER:

                                        PETSTORE.COM, INC.


                                        By:      /s/  Joshua M. Newman
                                             -----------------------------------

                                        Name:         Joshua M. Newman
                                             -----------------------------------

                                        Title:        Chief Executive Officer
                                              ----------------------------------

                                        Address:      1545 Park Avenue
                                                      Emeryville, CA 94608