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                                                                   EXHIBIT 10.21


     THIS WARRANT AND THE SECURITIES ISSUABLE UPON THE EXERCISE HEREOF HAVE
     NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933. THEY MAY NOT BE
     SOLD, OFFERED FOR SALE, PLEDGED, HYPOTHECATED, OR OTHERWISE
     TRANSFERRED EXCEPT PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT
     UNDER THE SECURITIES ACT OF 1933, OR AN OPINION OF COUNSEL REASONABLY
     SATISFACTORY TO THE COMPANY THAT REGISTRATION IS NOT REQUIRED UNDER
     SUCH ACT OR UNLESS SOLD PURSUANT TO RULE 144 UNDER SUCH ACT.

                      WARRANT TO PURCHASE PREFERRED STOCK
                                      of
                               PETOPIA.COM, INC.

                          Void after January 21, 2005

          This Warrant is issued to ((Name)) ("Series D Purchaser"), or its
registered assigns ("Holder") by Petopia.com, Inc., a Delaware corporation (the
"Company"), on January 21, 2000 (the "Warrant Issue Date").  This Warrant is
issued pursuant to Section 6.3 of that certain Series D Preferred Stock Purchase
Agreement dated November 29, 1999, as amended as of the date hereof (the
"Purchase Agreement").  The Company is valuing the Warrant at the price of $0.01
per share for all purposes, including with respect to financial statements
and/or tax purposes.

1.   Purchase Shares.  Subject to the terms and conditions hereinafter set forth
     ---------------
and set forth in the Purchase Agreement, the Holder is entitled, upon surrender
of this Warrant at the principal office of the Company (or at such other place
as the Company shall notify the holder hereof in writing), to purchase from the
Company (((NumberofShares))) (((Shares))) fully paid and nonassessable shares of
Series D Preferred Stock of the Company, as constituted on the Warrant Issue
Date (the "Preferred Stock"). The number of shares of Preferred Stock issuable
pursuant to this Section 1 (the "Shares") shall be subject to adjustment
pursuant to Section 8 hereof.

2.   Exercise Price.  The purchase price for the Shares shall be equal to
     --------------
$5.6061, as adjusted from time to time pursuant to Section 8 hereof (the
"Exercise Price").

3.   Exercise Period.  This Warrant shall be exercisable, in whole or in part,
     ---------------
during the term commencing on the Warrant Issue Date and ending at 5:00 p.m. on
January 21, 2005.

4.   Method of Exercise.  While this Warrant remains outstanding and exercisable
     ------------------
in accordance with Section 3 above, the Holder may exercise, in whole or in
part, the purchase rights evidenced hereby.  Such exercise shall be effected by:

     (a)  the surrender of the Warrant, together with a duly executed copy of
the form of Notice of Exercise attached hereto, to the Secretary of the Company
at its principal offices; and
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     (b)  the payment to the Company of an amount equal to the aggregate
Exercise Price for the number of Shares being purchased.

If the Warrant shall be exercised for less than the total number of shares of
Preferred Stock then issuable upon exercise, promptly after surrender of the
Warrant upon such exercise (but no later than twenty (20) days after such
surrender), the Company will execute and deliver a new Warrant, dated the date
hereof, evidencing the right of the Holder to the balance of the Preferred Stock
purchasable hereunder upon the same terms and conditions set forth herein.
Notwithstanding anything to the contrary contained herein, the Holder may elect
to receive a net issuance of Preferred Stock pursuant to Section 5 when
converting this Warrant in part.

5.   Net Exercise.  In lieu of exercising this Warrant pursuant to Section 4,
     ------------
the Holder may elect to receive, without the payment by the Holder of any
additional consideration, shares of Preferred Stock equal to the value of this
Warrant (or the portion thereof being canceled) by surrender of this Warrant at
the principal office of the Company together with the Notice of Exercise, in
which event the Company shall issue to the holder hereof a number of shares of
Preferred Stock computed using the following formula:

                              Y (A - B)
                              ---------
                       X =        A

     Where:    X =  The number of shares of Preferred Stock to be issued to the
                    Holder pursuant to this net exercise;

               Y =  The number of Shares in respect of which the net issue
                    election is made;

               A =  The fair market value of one share of the Preferred Stock at
                    the time the net issue election is made;

               B =  The Exercise Price (as adjusted to the date of the net
                    issuance).

For purposes of this Section 5, the fair market value of one share of Preferred
Stock (or, to the extent all such Preferred Stock has been converted into the
Company's Common Stock) as of a particular date shall be determined as follows:
(i) if traded on a securities exchange or through the Nasdaq National Market,
the value shall be deemed to be the closing price of the securities on such
exchange on the trading day immediately preceding the date of delivery of the
Notice of Exercise (it being understood that the original Warrant may be
surrendered on the subsequent day if such original Warrant is provided to an
overnight courier service (eg, Federal Express); (ii) if traded over-the-
counter, the value shall be deemed to be the average of the closing bid or sale
prices (whichever is applicable) on the trading day immediately preceding the
date of delivery of the Notice of Exercise (it being understood that the
original Warrant may be surrendered on the subsequent day if such original
Warrant is provided to an overnight courier service (eg, Federal Express); and
(iii) if there is no active public market for the Common Stock, the value shall
be the fair market value thereof, as determined in good faith by the Board of
Directors of the Company; provided, that, if the Warrant is being exercised upon
the closing of the Company's
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first underwritten public offering of common stock (the "IPO"), the value will
be the initial "Price to Public" of one share of such Preferred Stock (or Common
Stock issuable upon conversion of such Preferred Stock) specified in the final
prospectus with respect to such offering.

6.   Certificates for Shares.  Upon the exercise of the purchase rights
     -----------------------
evidenced by this Warrant, one or more certificates for the number of Shares so
purchased shall be issued as soon as practicable thereafter (with appropriate
restrictive legends, if applicable), and in any event within twenty (20) days of
the delivery of the Notice of Exercise.

7.   Issuance of Shares.  The Company covenants that the Shares, when issued
     ------------------
pursuant to the exercise of this Warrant, will be duly and validly issued, fully
paid and nonassessable and free from all taxes, liens, and charges with respect
to the issuance thereof.  The Company shall pay all taxes and any and all United
States federal, state and local taxes and other charges that may be payable in
connection with the preparation, issuance and delivery of the certificates
representing Preferred Stock issued hereunder.

8.   Adjustment of Exercise Price and Number of Shares.  The number of and kind
     -------------------------------------------------
of securities purchasable upon exercise of this Warrant and the Exercise Price
shall be subject to adjustment from time to time as follows:

          (a)  Subdivisions, Combinations and Other Issuances.  If the
               ----------------------------------------------
     Company shall at any time prior to the expiration of this Warrant
     subdivide its Preferred Stock, by split or otherwise, or combine its
     Preferred Stock, or issue additional shares of its Preferred Stock or
     Common Stock as a dividend with respect to any shares of its Preferred
     Stock, the number of Shares issuable on the exercise of this Warrant
     shall forthwith be proportionately increased in the case of a
     subdivision or stock dividend, or proportionately decreased in the
     case of a combination. Appropriate adjustments shall also be made to
     the Exercise Price, but the aggregate Exercise Price for the total
     number of Shares purchasable under this Warrant (as adjusted) shall
     remain the same. Any adjustment under this Section 8(a) shall become
     effective at the close of business on the date the subdivision or
     combination becomes effective, or as of the record date of such
     dividend, or in the event that no record date is fixed, upon the
     making of such dividend.

          (b)  Reclassification, Reorganization and Consolidation. In case
               --------------------------------------------------
     of any reclassification, capital reorganization, merger, consolidation
     or other change in the Preferred Stock of the Company (other than as a
     result of a subdivision, combination, or stock dividend provided for
     in Section 8(a) above), then, as a condition of such reclassification,
     reorganization, merger, consolidation or other change, lawful
     provision shall be made, and duly executed documents evidencing the
     same from the Company or its successor shall be delivered to the
     Holder, so that the Holder shall have the right at any time prior to
     the expiration of this Warrant to purchase, at a total price equal to
     that payable upon the exercise of this Warrant, the kind and amount of
     shares of stock and other securities and property receivable in
     connection with such reclassification, reorganization, merger or

<PAGE>

     change by a holder of the same number of shares of Preferred Stock as were
     purchasable by the Holder immediately prior to such reclassification,
     reorganization, merger or change. In any such case appropriate provisions
     shall be made with respect to the rights and interest of the Holder so that
     the provisions hereof shall thereafter be applicable with respect to any
     shares of stock or other securities and property deliverable upon exercise
     hereof, and appropriate adjustments shall be made to the Exercise Price
     hereunder, provided the aggregate Exercise Price shall remain the same.

          (c)  No Impairment.  The Company shall not, by amendment of its
               -------------
     Certificate of Incorporation or through a reorganization, transfer of
     assets, consolidation, merger, dissolution, issue or sale of
     securities or any other voluntary action, avoid or seek to avoid the
     observance or performance of any of the terms to be observed or
     performed under this Warrant by the Company, but shall at all times in
     good faith assist in carrying out of all the provisions of this
     Section 8 and in taking all such action as may be necessary or
     appropriate to protect the Holder's rights under this Section 8
     against impairment. If the Company takes any action affecting
     Preferred Stock other than as described above that adversely affects
     Holder's rights under this Warrant, the Exercise Price shall be
     adjusted downward.

          (d)  Notice.  Upon any adjustment of the Exercise Price and any
               ------
     increase or decrease in the number of shares of Preferred Stock
     purchasable upon the exercise or conversion of this Warrant, then, and
     in each such case, the Company, as promptly as practicable thereafter,
     shall give written notice thereof to the Holder of this Warrant at the
     address of such Holder as shown on the books of the Company which
     notice shall state the Exercise Price as adjusted and the increased or
     decreased number of shares purchasable upon the exercise or conversion
     of this Warrant, setting forth in reasonable detail the method of
     calculation of each.

9.   No Fractional Shares or Scrip.  No fractional shares or scrip representing
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fractional shares shall be issued upon the exercise of this Warrant, but in lieu
of such fractional shares the Company shall make a cash payment therefor on the
basis of the Exercise Price then in effect.

10.  No Stockholder Rights.  Prior to exercise of this Warrant, the Holder shall
     ---------------------
not be entitled to any rights of a stockholder with respect to the Shares,
including (without limitation) the right to vote such Shares, receive dividends
or other distributions thereon, exercise preemptive rights or be notified of
stockholder meetings, and such holder shall not be entitled to any notice or
other communication concerning the business or affairs of the Company. However,
nothing in this Section 10 shall limit the right of the Holder to be provided
the Notices required under this Warrant or the Purchase Agreement.

11.  Transfers of Warrant.  This Warrant and all rights hereunder may not be
     --------------------
transferred by Holder either in whole or in part; provided however, that subject
to compliance with applicable federal and state securities laws, and upon ten
written notice to the Company, Holder may transfer this Warrant in whole (i) to
a wholly-owned subsidiary of the Holder, (ii) to an entity or
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corporation that acquires all or substantially all of the assets of the Holder,
or (iii) to the surviving corporation of a merger or consolidation of the Holder
as a result of which the stockholders of the Holder immediately prior to such
transaction hold less than fifty percent (50%) of the voting power of the
surviving corporation. The transfer shall be recorded on the books of the
Company upon the surrender of this Warrant, properly endorsed, to the Company at
its principal offices, and the payment to the Company of all transfer taxes and
other governmental charges imposed on such transfer.

12.  Successors and Assigns.  The terms and provisions of this Warrant and the
     ----------------------
Purchase Agreement shall inure to the benefit of, and be binding upon, the
Company and the Holders hereof and their respective successors and assigns.

13.  Amendments and Waivers.  Any term of this Warrant may be amended and the
     ----------------------
observance of any term of this Warrant may be waived (either generally or in a
particular instance and either retroactively or prospectively), with the written
consent of the Company and the holders of a majority of shares of Preferred
Stock issued or issuable upon exercise of Warrants issued pursuant to the
Purchase Agreement.  Any waiver or amendment effected in accordance with this
Section shall be binding upon each holder of any Shares purchased under this
Warrant at the time outstanding (including securities into which such Shares
have been converted), each future holder of all such Shares, and the Company.

14.  Effect of Amendment or Waiver.  The Holder acknowledges that by the
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operation of Section 13 hereof, the holders of a majority of shares of Preferred
Stock issued or issuable upon exercise of Warrants issued pursuant to the
Purchase Agreement will have the right and power to diminish or eliminate all
rights of such holder under this Warrant or under the Purchase Agreement.

15.  Notices.  All notices required under this Warrant shall be deemed to have
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been given or made for all purposes (i) upon personal delivery, (ii) upon
confirmation receipt (or oral confirmation) that the communication was
successfully sent to the applicable number if sent by facsimile; (iii) one day
after being sent, when sent by professional overnight courier service, or (iv)
five days after posting when sent by registered or certified mail.  Notices to
the Company shall be sent to the principal office of the Company (or at such
other place as the Company shall notify the Holder hereof in writing).  Notices
to the Holder shall be sent to the address of the Holder on the books of the
Company (or at such other place as the Holder shall notify the Company hereof in
writing).

16.  Reservation of Stock.  On and after the Warrant Issuance Date, the Company
     --------------------
will reserve from its authorized and unissued Preferred Stock a sufficient
number of shares to provide for the issuance of Preferred Stock upon the
exercise of this Warrant and will reserve form its authorized and unissued
Common Stock a sufficient number of shares to provide for the issuance of Common
Stock upon the conversion of the Preferred Stock represented by this Warrant.
Issuance of this Warrant shall constitute full authority to the Company's
officers who are charged with the duty of executing stock certificates to
execute and issue the necessary certificates for shares of Preferred Stock
issuable upon the exercise or conversion of this Warrant.
<PAGE>

17.  Captions.  The section and subsection headings of this Warrant are inserted
     --------
for convenience only and shall not constitute a part of this Warrant in
construing or interpreting any provision hereof.

18.  Representation and Warranties.  The Company hereby makes all the
     -----------------------------
representations and warranties set forth in Section 2 of the Series D Preferred
Stock Purchase Agreement dated November 29, 1999, as amended on the date hereof,
by and among the Company, the Holder and certain other investors, except as set
forth on a Schedule of Exceptions attached thereto as Exhibit C.
                                                      ---------

19.  Loss, Theft, Destruction or Mutilation of Warrant.  Upon receipt by the
     -------------------------------------------------
Company of evidence reasonably satisfactory to it of the loss, theft,
destruction or mutilation of this Warrant, and in case of loss, theft or
destruction, of indemnity or security reasonably satisfactory to it,  and upon
surrender and cancellation of this Warrant, if mutilated, the Company will make
and deliver a new Warrant of like tenor and dated as of such cancellation or
delivery, in lieu of this Warrant.

20.  Saturdays, Sundays, Holidays, etc.  If the last or appointed day for the
     ---------------------------------
taking of any action or the expiration of any right required or granted herein
shall be a Saturday or a Sunday or shall be a legal holiday in San Francisco,
California,  then such action may be taken or such right may be exercised on the
next succeeding day not a legal holiday in San Francisco, California.

21.  Governing Law.  This Warrant shall be governed by the laws of the State of
     -------------
California as applied to agreements among California residents made and to be
performed entirely within the State of California.



                 [Remainder of page intentionally left blank.]
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          IN WITNESS WHEREOF, Petopia.com, Inc. caused this Warrant to be
executed by an officer thereunto duly authorized.

                                   PETOPIA.COM, INC.


                                   By:__________________________________
                                   Name:  Andrea C. Reisman
                                   Title: Chief Executive Officer