EXHIBIT 10.56

                                FOURTH AMENDMENT

THIS FOURTH AMENDMENT (the "AMENDMENT") is made and entered into as of July 8,
2004, by and between EOP-INDUSTRIAL PORTFOLIO, L.L.C., A DELAWARE LIMITED
LIABILITY COMPANY ("LANDLORD") and LA JOLLA PHARMACEUTICAL COMPANY, A DELAWARE
CORPORATION ("TENANT").

                                    RECITALS

A.    Landlord (as successor in interest pursuant to merger with Spieker
      Properties, L.P., a California limited partnership, as successor in
      interest to BRE Properties, Inc., a Delaware corporation) and Tenant are
      parties to that certain lease dated July 27, 1992, which lease has been
      previously amended by the Addendum to Lease dated July 27, 1992, First
      Amendment to Lease dated March 15, 1993, Second Amendment to Lease dated
      July 18, 1994 and Third Amendment to Lease dated January 26, 1995
      (collectively, the "LEASE"). Pursuant to the Lease, Landlord has leased to
      Tenant space currently containing approximately 36,526 rentable square
      feet (the "PREMISES") in the building commonly known as Westridge I
      located at 6455 Nancy Ridge Drive, San Diego, California (the "BUILDING").

B.    Landlord and Tenant hereby acknowledge and agree that due to a scrivener
      error in paragraph A of the Recitals of that certain Third Amendment to
      Lease dated January 26, 1995, incorrectly stated that the Premises
      contained approximately "36,256" rentable square feet of space. Landlord
      and Tenant retroactively agree that from and after January 26, 1995, the
      Premises contains approximately "36,526" rentable square feet.

C.    The Lease by its terms shall expire on JULY 31, 2004 ("PRIOR EXTENDED
      TERMINATION DATE"), and the parties desire to extend the Lease Term, all
      on the following terms and conditions.

      NOW, THEREFORE, in consideration of the above recitals which by this
reference are incorporated herein, the mutual covenants and conditions contained
herein and other valuable consideration, the receipt and sufficiency of which
are hereby acknowledged, Landlord and Tenant agree as follows:

1.    EXTENSION. The Lease Term is hereby extended for a period of sixty (60)
      months and shall expire on JULY 31, 2009 ("SECOND EXTENDED TERMINATION
      DATE"), unless sooner terminated in accordance with the terms of the
      Lease. That portion of the Lease Term commencing the day immediately
      following the Prior Extended Termination Date ("SECOND EXTENSION DATE")
      and ending on the Second Extended Termination Date shall be referred to
      herein as the "SECOND EXTENDED TERM".

2.    BASE RENT. As of the Second Extension Date, the schedule of Base Rent
      payable with respect to the Premises during the Second Extended Term is
      the following:





                PERIOD                   ANNUAL RATE PER SQUARE FOOT   MONTHLY BASE RENT
                                                                 
August 1, 2004 through July 31, 2005               $13.80                  $42,004.90
August 1, 2005 through July 31, 2006               $14.35                  $43,679.01
August 1, 2006 through July 31, 2007               $14.93                  $45,444.43
August 1, 2007 through July 31, 2008               $15.52                  $47,240.29
August 1, 2008 through July 31, 2009               $16.14                  $49,127.47


      All such Base Rent shall be payable by Tenant in accordance with the terms
of the Lease.

3.    REAL PROPERTY TAXES. For the period commencing on the Second Extension
      Date and ending on the Second Extended Termination Date, Tenant shall pay
      for Tenant's pro rata share of the real property taxes and Tenant's pro
      rata share of all costs incurred by Landlord for the operation and
      maintenance of the Common Areas in accordance with the terms of the Lease.

4. IMPROVEMENTS TO PREMISES.

      4.01. CONDITION OF PREMISES. Tenant is in possession of the Premises and
            accepts the same "as is" without any agreements, representations,
            understandings or obligations on the part of Landlord to perform any
            alterations, repairs or improvements, except as may be expressly
            provided otherwise in the Lease or this Amendment.

      4.02. RESPONSIBILITY FOR IMPROVEMENTS TO PREMISES. Any construction,
            alterations or improvements to the Premises shall be performed by
            Tenant at its sole cost and expense using contractors selected by
            Tenant and reasonably approved by Landlord and shall be governed in
            all respects by the provisions of the Lease.

5.    OTHER PERTINENT PROVISIONS. Landlord and Tenant agree that, effective as
      of the date of this Amendment (unless different effective date(s) is/are
      specifically referenced in this Section), the Lease shall be amended in
      the following additional respects:

      5.01. PARKING. For the period commencing on the Second Extension Date and
            ending on the Second Extended Termination Date, Tenant shall retain
            its existing vehicle parking rights as set forth in the Lease.

      5.02. RIGHT OF FIRST REFUSAL TO LEASE 6465 NANCY RIDGE DRIVE AS SET FORTH
            IN THE ADDENDUM TO LEASE shall be deleted in its entirety and is of
            no further force and effect.

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      5.03. LIMITATION ON LANDLORD'S LIABILITY. The obligations of Landlord
            under the Lease (including any actual or alleged breach or default
            by Landlord) do not constitute personal obligations of the
            individual partners, directors, officers or shareholders of Landlord
            or Landlord's partners, and Tenant shall not seek recourse against
            the individual partners, directors, officers or shareholders of
            Landlord or Landlord's partners, or any of their personal assets for
            satisfaction of any liability with respect to the Lease. In
            addition, the liability of Landlord for its obligations under the
            Lease shall be limited solely to, and Tenant's sole and exclusive
            remedy shall be against, Landlord's interest in the Industrial
            Center, and no other assets of Landlord.

6. MISCELLANEOUS.

      6.01. This Amendment and the attached exhibits, which are hereby
            incorporated into and made a part of this Amendment, set forth the
            entire agreement between the parties with respect to the matters set
            forth herein. There have been no additional oral or written
            representations or agreements. Under no circumstances shall Tenant
            be entitled to any Rent abatement, improvement allowance, leasehold
            improvements, or other work to the Premises, or any similar economic
            incentives that may have been provided Tenant in connection with
            entering into the Lease, unless specifically set forth in this
            Amendment.

      6.02. Except as herein modified or amended, the provisions, conditions and
            terms of the Lease shall remain unchanged and in full force and
            effect.

      6.03. In the case of any inconsistency between the provisions of the Lease
            and this Amendment, the provisions of this Amendment shall govern
            and control.

      6.04. Submission of this Amendment by Landlord is not an offer to enter
            into this Amendment. Landlord shall not be bound by this Amendment
            until Landlord has executed and delivered the same to Tenant.

      6.05. The capitalized terms used in this Amendment shall have the same
            definitions as set forth in the Lease to the extent that such
            capitalized terms are defined therein and not redefined in this
            Amendment.

      6.06. Tenant hereby represents to Landlord that Tenant has dealt with no
            broker other than Irving Hughes in connection with this Amendment.
            Tenant agrees to indemnify and hold Landlord, its members,
            principals, beneficiaries, partners, officers, directors, employees,
            mortgagee(s) and agents, and the respective principals and members
            of any such agents (collectively, the "LANDLORD RELATED PARTIES")
            harmless from all claims of any brokers other than Irving Hughes
            claiming to have represented Tenant in connection with this
            Amendment. Landlord hereby represents to Tenant that Landlord has
            dealt with no broker in connection with this Amendment. Landlord
            agrees to indemnify and hold Tenant, its members, principals,
            beneficiaries, partners, officers, directors, employees, and agents,
            and the respective principals and members of any such agents

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            (collectively, the "TENANT RELATED Parties") harmless from all
            claims of any brokers claiming to have represented Landlord in
            connection with this Amendment.

      6.07. Landlord and Tenant each represent that each signatory of this
            Amendment has the authority to execute and deliver the same on
            behalf of the party hereto for which such signatory is acting.

      6.08. Equity Office Properties Management Corp. ("EOPMC") is an affiliate
            of Landlord and represents only the Landlord in this transaction.
            Any assistance rendered by any agent or employee of EOPMC in
            connection with this Lease or any subsequent amendment or
            modification hereto has been or will be made as an accommodation to
            Tenant solely in furtherance of consummating the transaction on
            behalf of Landlord, and not as agent for Tenant.

      6.09. CALIFORNIA WAIVERS. Notwithstanding anything to the contrary
            contained in the Lease, Tenant hereby waives any and all rights
            under and benefits of subsection 1 of Section 1932, Sections 1941
            and 1942 (Tenant's Repairs and Alterations), 1932(2) (Casualty
            Damage), and Section 1265.130 (Condemnation) of the California Code
            of Civil Procedure, or any similar or successor laws now or
            hereinafter in effect.

      6.10. NO EXTENSION OPTIONS DURING THE SECOND EXTENDED TERM. The parties
            hereto acknowledge and agree that during the Second Extended Term
            Tenant shall have no rights to extend the term of the Lease. The
            parties agree that any rights existing in the Lease to extend the
            term of the Lease shall be deleted in their entirety and are of no
            further force and effect.

      6.11. LEASE CANCELLATION RIGHT AND RIGHT OF FIRST OFFER TO PURCHASE THE
            PROJECT. The parties hereto acknowledge and agree that during the
            Second Extended Term, the Lease Cancellation Right as set forth in
            the Third Amendment to Lease and the Right of First Offer to
            Purchase the Project as set forth in the Addendum to Lease shall
            remain in full force and effect.

                       [SIGNATURES ARE ON FOLLOWING PAGE]

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      IN WITNESS WHEREOF, Landlord and Tenant have duly executed this Amendment
as of the day and year first above written.

                             LANDLORD:

                             EOP-INDUSTRIAL PORTFOLIO, L.L.C.,
\                            A DELAWARE LIMITED LIABILITY COMPANY

                             By: EOP Operating Limited Partnership, a
                                 Delaware limited partnership, its sole member

                                   By: Equity Office Properties Trust, a
                                       Maryland real estate investment trust,
                                       its general partner

                                       By: /s/ Robert E. Dezzutti
                                           ----------------------------
                                       Name:  Robert E. Dezzutti
                                       Title: Senior Vice President

                             TENANT:

                             LA JOLLA PHARMACEUTICAL COMPANY,
                             A DELAWARE CORPORATION

                             By: /s/ Steven B. Engle
                                 --------------------------------------
                             Name:  Steven B. Engle
                             Title: Chairman and CEO
                             Tenant's FEIN: 33-0361285

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