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                                                                 EXHIBIT 10.12


                              SECURITY AGREEMENT


     The Security Agreement is made as of November 30, 1999 between Kiva
Genetics, Inc., a Delaware corporation ("Pledgee"), Gregory T. Went
("Pledgor"), and Secretary of Pledgee, as the agent of Pledgee and holder of
the Securities pledged hereunder ("Pledgeholder").

                                   RECITALS

     Pursuant to the Restricted Stock Purchase Agreement dated November 30,
1999 (the "Agreement"), between Pledgor and Pledgee under Pledgee's 1998
Incentive Stock Plan and Pledgor's election under the terms of the Agreement
to pay for such shares with Pledgor's promissory note (the "Note"), Pledgor
has purchased 250,000 shares of Pledgee's Common Stock (the "Shares") at a
price of $0.40 per share, for a total purchase price of $100,000.00. The Note
and the obligations thereunder are as set forth in EXHIBIT A to the Agreement.

     NOW, THEREFORE, it is agreed as follows:

     1.  CREATION AND DESCRIPTION OF SECURITY INTEREST. In consideration of
the transfer of the Shares to Pledgor under the Agreement, Pledgor, pursuant
to the California Uniform Commercial Code, hereby pledges all of such Shares
(herein sometimes referred to as the "Collateral") represented by certificate
number 35, and herewith delivers said certificate to Pledgeholder, who shall
hold said certificate on behalf of Pledgee subject to the terms and
conditions of this Security Agreement.

     The Shares (together with an executed blank stock assignment or
assignments) shall be held by Pledgeholder on behalf of Pledgee as security
for the repayment of the Note, and any extensions or renewals thereof, to be
executed by Pledgor pursuant to the terms of the Agreement, and Pledgeholder
shall not encumber or dispose of such Shares except in accordance with the
provisions of this Security Agreement.

     2.  PLEDGOR'S REPRESENTATIONS AND COVENANTS. To induce Pledgee to enter
into this Security Agreement, Pledgor represents and covenants to Pledgee,
its successors and assigns, as follows:

         (a)  PAYMENT OF INDEBTEDNESS. Pledgor will pay the principal sum of
the Note secured hereby, and interest thereon, at the time and in the manner
provided in the Note.

         (b)  ENCUMBRANCES. The Shares are free of all other adverse claims,
encumbrances, defenses and liens (other than restrictions on transfer
imposed by applicable securities laws), except for (i) Pledgee's rights to
repurchase Shares pursuant to Section 3 of the Agreement and (ii) the pledge
of the Shares hereunder as security for payment of the Note, and Pledgor will
not further encumber the Shares without prior written consent of Pledgee.


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     3.  VOTING RIGHTS.  During the term of this pledge and so long as all
payments of principal and interest are made as they become due under the terms
of the Note, Pledgor shall have the right to vote all of the Shares pledged
hereunder.

     4.  STOCK ADJUSTMENTS.  In the event that during the term of the pledge
any stock dividend, reclassification, readjustment or other changes are
declared or made in the capital structure of Pledgee, all new, substituted
and additional shares or other securities issued by reason of any such change
shall be delivered to and held by the Pledgee under the terms of this
Security Agreement in the same manner as the Shares originally pledged
hereunder. In the event of substitution of such securities, Pledgor, Pledgee
and Pledgeholder shall cooperate and execute such documents as are reasonable
so as to provide for the substitution of such Collateral and, upon such
substitution, reference to "Shares" in this Security Agreement shall include
the substituted shares of capital stock of Pledgor as a result thereof.

     5.  OPTIONS AND RIGHTS.  In the event that, during the term of this
pledge, subscription Options or other rights or options shall be issued in
connection with the pledged Shares, such rights, Options and options shall be
the property of the Pledgor and, if exercised by Pledgor, all new stock or
other securities so acquired by Pledgor as it relates to the pledged Shares
then held by Pledgeholder shall be immediately delivered to Pledgeholder, to
be held under the terms of this Security Agreement in the same manner as the
Shares pledged.

     6.  DEFAULT.  Pledgor shall be deemed in default of the Note and of
this Security Agreement in the event:

         (a)  Payment of principal or interest on the Note shall be
delinquent for a period of 10 days or more; or

         (b)  Pledgor fails to perform any of the covenants set forth in the
Agreement or contained in this Security Agreement for a period of 10 days
after written notice thereof from Pledgee; or

         (c)  A bankruptcy or insolvency proceeding is instituted by or
against Pledgor, or if a receiver is appointed for the property of Pledgor; or

         (d)  Pledgor makes an assignment for the benefit of creditors.

     In the case of a default, as set forth above, Pledgee shall have the
right to accelerate payment of the Note, and Pledgee shall thereafter be
entitled to pursue its remedies under the California Uniform Commercial Code.

     7.  RELEASE OF COLLATERAL.  Subject to any applicable contrary rules
under Regulation G, there shall be released from this pledge a portion of the
pledged Shares held by Pledgeholder hereunder upon payments of the principal
of the Note. The number of the pledged Shares which shall be released shall
be that number of full Shares which bears the same proportion to the initial
number of Shares pledged hereunder as the payment of principal bears to the
initial full principal amount of the Note. Notwithstanding the foregoing,
upon any release of pledged Shares hereunder


                                                                        Page 2

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any such Shares which shall continue to constitute Unreleased Shares as
defined in the Agreement shall continue to be held in escrow pursuant to
Sections 3 and 6 of the Agreement.

     8.  WITHDRAWAL OR SUBSTITUTION OF COLLATERAL.  Pledgor shall not sell,
withdraw, pledge, substitute or otherwise dispose of all or any part of the
Collateral without the prior written consent of Pledgee.

     9.  TERM.  The within pledge of Shares shall continue until the payment
of all indebtedness secured hereby, subject to the provisions for prior
release of a portion of the Collateral as provided in paragraph 7 above.

    10.  INSOLVENCY.  Pledgor agrees that if a bankruptcy or insolvency
proceeding is instituted by or against Pledgor, or if a receiver is appointed
for the property of Pledgor, or if Pledgor makes an assignment for the
benefit of creditors, the entire amount unpaid on the Note shall become
immediately due and payable, and Pledgee many proceed as provided in the case
of default.

    11.  PLEDGEHOLDER LIABILITY.

         (a)  Pledgeholder shall not be liable to any party for any of his
acts, or omissions to act, as Pledgeholder unless Pledgeholder is proved to
have acted in bad faith. Any act done or omitted pursuant to the advice of
legal counsel, other than an act or omission involving gross or willful
negligence, shall be deemed to be done or omitted in good faith.

         (b)  Pledgeholder shall be entitled to employ such legal counsel and
other experts as Pledgeholder may deem necessary properly to advise
Pledgeholder in connection with its obligations hereunder, and Pledgeholder
may rely upon the advice of such counsel. Such counsel's reasonable fees and
costs shall be borne 50% by Pledger and 50% by Pledgee.

         (c)  It is understood and agreed that should any dispute arise with
respect to the delivery and/or ownership or right of possession of the
securities held by Pledgeholder hereunder, Pledgeholder is authorized and
directed to retain in Pledgeholder's possession as agent of Pledgee without
liability to anyone all or any part of said securities until such disputes
shall have been settled either by mutual written agreement of the parties
concerned or by a final order, decree or judgment of the arbitrator provided
for in Section 13 of the Agreement or of a court of competent jurisdiction
after the time for appeal has expired and no appeal has been perfected, but
Pledgeholder shall be under no duty whatsoever to institute or defend any
such proceedings.

     In addition, upon any dispute Pledgeholder should be entitled to engage
legal counsel, one-half of whose fees and expenses shall be borne by Pledgor
and one-half by Pledgee.

    12.  INVALIDITY OF PARTICULAR PROVISIONS.  Pledgor and Pledgee agree that
the enforceability or invalidity of any provision or provisions of this
Security Agreement shall not render any other provision or provisions herein
contained unenforceable or invalid.

    13.  SUCCESSOR OR ASSIGNS.  Pledgor and Pledgee agree that all of the
terms of this Security Agreement shall be binding on their respective
successors and assigns, and that the term


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"Pledgor" and the term "Pledgee" as used herein shall be deemed to include,
for all purposes, the respective designees, successors, assigns, heirs,
executors and administrators.

    14.  GOVERNING LAW.  This Security Agreement shall be interpreted and
governed under the laws of the State of California.

    IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of
the day and year first above written.

   "PLEDGOR"                           By: /s/ Gregory T. Went
                                          ------------------------------------
                                           Gregory T. Went

                                          2375 Garcia Ave
                                          ------------------------------------
                                          (Address)

                                          Mountain View, CA  94043
                                          ------------------------------------



"PLEDGEE"                                 Kiva Genetics, Inc.
                                          a Delaware corporation


                                          By: /s/ Hugh Y. Rienhoff
                                             ---------------------------------

                                          Title: CEO
                                                ------------------------------



"PLEDGEHOLDER"                            /s/ Michael O'Donnell
                                          ------------------------------------
                                          Secretary of Pledgee


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                                  EXHIBIT A

                               PROMISSORY NOTE

                                                              November 30, 1999

$100,000.00

     For value received, the undersigned promises to pay to Kiva Genetics,
Inc., a Delaware corporation (the "Company"), or order, at its principal
office the principal sum of $100,000.00 with interest thereof at the rate of
6.1% per annum, compounded annually.

     Principal and interest shall be due and payable on November 1, 2004.
Should the undersigned fail to make full payment of principal or interest for
a period of 10 days or more after the due date thereof, the whole unpaid
balance on this Note of principal and interest shall become immediately due
at the option of the holder of this Note. Payments of principal and interest
shall be made in lawful money of the United States of America.

     So long as the undersigned remains an employee or consultant of the
Company, the Company shall forgive the loan over the course of five (5)
years, according to the following schedule: the Company shall forgive twenty
percent (20%) of the principal and accrued interest commencing November 1,
2000 and each November 1 thereafter for the following four (4) years.

     The undersigned may at any time repay all or any portion of the
principal or interest owing hereunder.

     This Note is secured by a pledge of the Company's Common Stock under the
terms of a Security Agreement of even date herewith and is subject to all the
provisions thereof.

     The holder of this Note shall have full recourse against the
undersigned, and shall not be required to proceed against the collateral
securing this Note in the event of default.

     In the event of any voluntary or involuntary termination of the
undersigned's employment by or services to the Company for any or no reason,
or upon the sale or transfer of the pledged shares of Common Stock, this Note
shall, at the option of the Company, be accelerated, and the whole unpaid
balance on this Note (to the extent not forgiven) of principal and accrued
interest shall be immediately due and payable.

     Should any action be instituted for the collection of this Note, the
reasonable costs and attorneys' fees therein of the holder shall be paid by
the undersigned.


                                               /s/ Gregory T. Went
                                               --------------------------------
                                               Gregory T. Went