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                                                                    Exhibit 10.1

                      SECOND AMENDMENT TO CREDIT AGREEMENT

      THIS SECOND AMENDMENT TO CREDIT AGREEMENT (this "Amendment") is entered
into as of February 1, 2004, by and between FAIR ISAAC CORPORATION (FORMERLY
KNOWN AS FAIR, ISAAC AND COMPANY, INCORPORATED), a Delaware corporation
("Borrower"), and WELLS FARGO BANK, NATIONAL ASSOCIATION ("Bank").

                                    RECITALS

      WHEREAS, Borrower is currently indebted to Bank pursuant to the terms and
conditions of that certain Credit Agreement between Borrower and Bank dated as
of November 1, 2002, as amended from time to time ("Credit Agreement").

      WHEREAS, Bank and Borrower have agreed to certain changes in the terms and
conditions set forth in the Credit Agreement and have agreed to amend the Credit
Agreement to reflect said changes.

      NOW, THEREFORE, for valuable consideration, the receipt and sufficiency of
which are hereby acknowledged, the parties hereto agree that the Credit
Agreement shall be amended as follows:

      1.    Section 1.1.(a) is hereby amended by deleting "February 1, 2004" as
the last day on which Bank will make advances under the Line of Credit, and by
substituting for said date "February 1, 2006," with such change to be effective
upon the execution and delivery to Bank of a promissory note dated February 1,
2004 (which promissory note shall replace and be deemed the Line of Credit Note
defined in and made pursuant to the Credit Agreement) and all other contracts,
instruments and documents required by Bank to evidence such change.

      2.    Section 1.2.(a) is hereby deleted in its entirety, and the following
substituted therefor:

                  "(a)  Foreign Exchange Facility. Subject to the terms and
            conditions of this Agreement, Bank hereby agrees to make available
            to Borrower a facility (the "Foreign Exchange Facility") under which
            Bank, from time to time up to and including February 1, 2006, will
            enter into foreign exchange contracts for the account of Borrower
            for the purchase and/or sale by Borrower in United States dollars of
            Euro, Pound, Japanese yen, Australian dollars, Rand, Canadian
            dollars, Mexican Peso, Singapore dollars and Brazilian real;
            provided however, that the maximum amount of all outstanding foreign
            exchange contracts shall not at any time exceed an aggregate of
            Twenty-five Million United States Dollars (US$25,000,000.00). No
            foreign exchange contract shall be executed for a term which extends
            beyond February 1, 2006. Borrower shall have a "Delivery Limit"
            under the Foreign Exchange Facility not to exceed at any time the
            aggregate principal amount of Five Million United States Dollars
            (US$5,000,000.00), which Delivery Limit reflects the maximum
            principal amount of Borrower's foreign exchange contracts which

                                      -1-
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            may mature during any two (2) day period. All foreign exchange
            transactions shall be subject to the additional terms of a Foreign
            Exchange Agreement, substantially in the form of EXHIBIT B attached
            hereto ("Foreign Exchange Agreement"), all terms of which are
            incorporated herein by this reference."

      3.    In consideration of the changes set forth herein and as a condition
to the effectiveness hereof, immediately upon signing this Amendment Borrower
shall pay to Bank a non-refundable fee of $7,500.00 per annum.

      4.    Except as specifically provided herein, all terms and conditions of
the Credit Agreement remain in full force and effect, without waiver or
modification. All terms defined in the Credit Agreement shall have the same
meaning when used in this Amendment. This Amendment and the Credit Agreement
shall be read together, as one document.

      5.    Borrower hereby remakes all representations and warranties contained
in the Credit Agreement and reaffirms all covenants set forth therein. Borrower
further certifies that as of the date of this Amendment there exists no Event of
Default as defined in the Credit Agreement, nor any condition, act or event
which with the giving of notice or the passage of time or both would constitute
any such Event of Default.

      IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed as of the day and year first written above.

                                          WELLS FARGO BANK,
FAIR ISAAC CORPORATION                      NATIONAL ASSOCIATION

By:  /s/ KENNETH J. SAUNDERS             By: /s/ LAURA KAY MATHERLY
     -----------------------                 ----------------------
                                             Laura Kay Matherly
Title:  CHIEF FINANCIAL OFFICER           Vice President
       ---------------------------

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                                                                   EXHIBIT 10.53

February 23, 2004

Gail Sloan
6455 Nancy Ridge Drive
San Diego, CA  92121

Re:  Severance Agreement

Dear Gail,

      As a supplement to the offer letter and agreement dated March 20, 1996
between La Jolla Pharmaceutical Company ("LJP") and Gail Sloan ("Sloan") related
to Sloan's employment by LJP, Sloan and LJP hereby agree as follows:

      In connection with her employment with LJP, Sloan's new title will be Vice
President of Finance and Controller.

      If Sloan's employment is terminated by LJP without cause (as defined
below), or if a Change in Control of LJP (as defined below) occurs and Sloan's
employment with LJP or its successor "terminates in connection with" (as defined
below) that Change in Control and in the absence of any event or circumstance
constituting Cause, then:

            (i)   Sloan will be entitled to receive from LJP a severance payment
                  equal to her then-current base salary for a period of six full
                  calendar months from the date of termination and an additional
                  three full calendar months if and when after the first six
                  months she has not found suitable employment, payable
                  consistent with LJP's normal payroll practices, provided that
                  such payment will be contingent upon execution and delivery by
                  Sloan and LJP of a mutual release, in form satisfactory to
                  LJP, of all claims arising in connection with Sloan's
                  employment with LJP and termination thereof, and

            (ii)  Sloan will be entitled to receive for a period of six full
                  calendar months from the date of termination and an additional
                  three full calendar months if and when after the first six
                  months she has not found suitable employment, medical and
                  dental benefits coverage for Sloan and/or her dependents
                  through the Company's available plans at the time and LJP will
                  be responsible to continue payment of all applicable
                  deductions for premium costs. After the Company's obligation
                  to pay the premiums for health and dental coverage Sloan
                  and/or her dependents will be eligible to continue plan
                  participation under COBRA.

            (iii) Notwithstanding anything to the contrary in the option plan
                  (the "PLAN") pursuant to which all of Sloan's existing options
                  were granted, the Options shall automatically vest and become
                  fully exercisable as of the date of termination of Executive's
                  employment (the TERMINATION DATE"),

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                  notwithstanding any vesting or performance conditions
                  applicable thereto, and shall remain exercisable for a period
                  of one year following the Termination Date or such longer
                  period as is provided by the Plan or grant pursuant to which
                  the Options were granted. However, notwithstanding the
                  foregoing, in no case will the Options be exercisable beyond
                  the duration of the original term thereof, and if the Options
                  qualify as an incentive stock option under the Internal
                  Revenue Code and applicable regulations thereunder, the
                  exercise period thereof shall not be extended in such a manner
                  as to cause the Options to cease to qualify as an incentive
                  stock option unless Executive elects to forego incentive stock
                  option treatment and extend the exercise period thereof as
                  provided herein.

           For purposes hereof, "CHANGE IN CONTROL" of LJP has the meaning set
           forth in the Plan in its form as the date of grant of the Options.

           For purposes hereof, "CAUSE" means Sloan has (i) engaged in serious
           criminal activity or other wrongful conduct that has an adverse
           impact on LJP, (ii) disregarded instructions given to her under the
           authority of LJP's Board of Directors, (iii) performed services for
           any person or entity other than LJP and appropriate civic
           organizations, or (iv) otherwise materially breached her employment
           or fiduciary responsibilities to LJP.

           For purposes hereof, Sloan's employment with LJP or its successor
           will be deemed to "TERMINATE IN CONNECTION WITH" a Change in Control
           if, within 180 days after the consummation of the Change of Control,
           (i) Sloan is removed from Sloan's employment by, or resigns her
           employment upon the request of, a person exercising practical voting
           control over LJP or its successor following the Change in Control or
           a person acting upon authority or at the instruction of such person;
           or (ii) Sloan's position is eliminated as a result of a reduction in
           force made to reduce over-capacity or unnecessary duplication of
           personnel and Sloan is not offered a replacement position with LJP or
           its successor as a Vice President with compensation and functional
           duties substantially similar to the compensation and duties in effect
           immediately before the Change in Control; or (iii) Sloan resigns her
           employment with the Company or its successor rather than comply with
           a relocation of her primary work site more than 50 miles from LJP's
           headquarters.

           In Witness Whereof, LJP and Sloan have entered into this agreement
           as of ___April 23________ 2004.

           LA JOLLA PHARMACEUTICAL COMPANY

           By: /s/ Steven B. Engle                  /s/ Gail A. Sloan
               --------------------                 -------------------
                Steven B. Engle                     Gail Sloan
                Chairman & CEO                      Vice President of Finance
                                                    and Controller

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