EXHIBIT 10.20
                            FIRST AMENDMENT TO LEASE


This First Amendment to Lease Agreement (the "First Amendment") is made and
entered into as of April l4, 2000 by and between BioMarin Pharmaceutical, Inc.,
a Delaware corporation ("Tenant") and Limar Realty Corp. #18, a California
corporation ("Landlord"), with reference to the following facts:

                                    RECITALS

A.       Landlord and Tenant entered into that certain Lease Agreement dated
         June 25, 1998 (the "Lease") whereby Tenant is leasing from Landlord and
         Landlord is leasing to Tenant that certain real property located at 46
         Galli Drive, South Building, Novato, California containing 31,056
         rentable square feet (the "Existing Premises"), as such premises are
         more fully described in the Lease.

B.       Tenant and Landlord wish to modify some of the provisions of the Lease
         to permit Tenant to extend the Term of the Lease for the Existing
         Premises and lease additional area containing 38,793 rentable square
         feet known as 46 Galli Drive, North Building (the "Additional
         Premises") so that the total area shall become 69,849 rentable square
         feet (the "Expanded Premises") comprised of the Existing Premises and
         the Additional Premises.

C.       Landlord and Tenant desire to modify the Lease on terms and conditions
         set forth in this First Amendment.

NOW, THEREFORE, in consideration of the mutual covenants, representations and
warrants contained in the Lease and this First Amendment, Landlord and Tenant
hereto agree as follows:

         1.    Recitals: Landlord and Tenant agree that the above recitals are
               true and correct.

         2.    Expanded Premises: Commencing on the Additional Premises
               Commencement Date (as defined below), Landlord hereby leases to
               Tenant and Tenant hereby leases from Landlord, that certain real
               property located at 46 Galli Drive, Novato, California containing
               69,849 rentable square feet (i.e., the Expanded Premises( upon
               all of the terms and conditions set forth in the Lease, as the
               same are amended by this First Amendment.

         3.    Term:

               A.     Lease Commencement. This First Amendment shall be
                      effective as to the Additional Premises on the earliest
                      to occur of: (i) substantial completion of the Approved
                      Work (as defined below) in the Additional Premises;
                      (ii) Tenant's commencement of occupancy of the
                      Additional Premises; or (iii) one hundred twenty (120)
                      days following execution of this First Amendment (the
                      "Additional Premises Commencement Date").

               B.     Lease Expiration. The Term of the Lease as to the
                      Expanded Premises shall expire at 11:59 p.m. on August
                      31, 2010.

         4.    Monthly Base Rent: The Monthly Base Rent to be paid by Tenant to
               Landlord shall be as follows:

               A.     Existing Premises. The monthly Base Rent for the Existing
                      Premises will remain as scheduled in the Lease and shall
                      continue forward with the annual CPI adjustment pursuant
                      to Paragraphs 1.n. and 4.(b) of the Lease on September 1,
                      2003 and every September 1 thereafter.

               B.     Additional Premises. The initial monthly Base Rent for the
                      Additional Premises shall be Forty-Three Thousand Nine
                      Hundred Eighty-Six and 71/100 Dollars ($43,986.71).
                      Commencing September 1, 2001 and each September 1
                      thereafter, the monthly Base Rent for the Additional
                      Premises shall be increased in accordance with the annual
                      Cost of Living Adjustment as set forth in Paragraph 4.b.
                      of the Lease provided, however, the annual floor limit as
                      set forth in Paragraph 1.n. of the Lease for the
                      Additional Premises (the "Additional Premises Floor
                      Limit") shall be an increase of four percent (4%) and the
                      annual ceiling limit for the Additional Premises (the
                      "Additional Premises Ceiling Limit") shall be an increase
                      of six percent (6%).



         5.    Tenant's Pro Rata Share: Commencing on the Additional Premises
               Commencement Date, Tenant's Share of Building pursuant to
               Paragraph 1.j. of the Lease and Tenant's Share of Property
               pursuant to Paragraph 1.k. of the Lease shall be increased to one
               hundred percent (100%).

         6.    Condition of the Premises: Tenant hereby accepts and agrees to
               occupy the Additional Premises in its current "as is" condition
               with the roof water tight. The elevator serving the production
               space portion of the Additional Premises shall be fully
               operational and certified by the State of California as of the
               Additional Premises Commencement Date. Within twelve (12) months
               after the Additional Premises Commencement Date, Landlord shall
               repaint the exterior of the Building and upgrade the exterior
               landscaping. Landlord hereby grants Tenant a one-time
               construction allowance of up to Three Hundred Eighty-Seven
               Thousand Nine Hundred Thirty Dollars ($387,930.00) ("Tenant's
               Construction Allowance") for the cost of generic tenant
               improvements to be installed in the Additional Premises by Tenant
               including all associated architectural, engineering and
               professional fees and costs (exclusive of any overhead costs of
               Landlord). If requested by Tenant no later than September 1,
               2001, Landlord shall provide an additional allowance ("Tenant's
               Improvement Allowance") of up to $193,965 to reimburse Tenant for
               additional Approved Work. The amount of Tenant's Improvement
               Allowance that is actually used shall be fully amortized
               (inclusive of 10% per annum interest) over the Term of the Lease
               payable monthly as additional Rent. Tenant shall submit its plans
               for the tenant improvements for Landlord's written approval (the
               "Approved Work") prior to Tenant's commencement of construction
               of the Approved Work, and Landlord shall respond within five (5)
               business days of the date Tenant provides Landlord any specific
               set of complete preliminary or complete final plans required by
               Landlord's approval. All work performed by Tenant shall be
               performed in strict compliance with the plans submitted for the
               Approved Work and no modification shall be made in such plans
               without the prior written approval of Landlord. Landlord shall
               pay Tenant's outside vendors or contractors for materials and
               services constituting the Approved Work, up to the maximum
               Tenant's Construction Allowance set forth above, within thirty
               (30) days following Landlord's receipt of Tenant's submittal to
               Landlord of approved invoices and conditional lien releases for
               payment. Tenant shall also be reimbursed from Tenant's
               Construction Allowance for the reasonable cost of all preliminary
               and final plans and specifications and all permits relating to
               the installation of the Approved Work. All of the Approved Work
               to be done by Tenant shall be done in accordance with the
               provisions of Paragraph 14. of the Lease, and Tenant shall be
               required to follow Landlord's reasonable rules and regulations
               relating to contractors working in the Project. Landlord shall
               have the right to reasonably approve all of Tenant's proposed
               contractors and subcontractors related to the installation of the
               Approved Work. Landlord shall not charge an administrative fee
               relating to the installation of the Approved Work. Tenant shall
               have the right to access the Additional Premises upon full
               execution of this First Amendment and vacation of the Additional
               Premises by the existing tenant for the purpose of installing the
               Approved Work (the "Construction Period"), provided, however,
               Tenant shall be bound by the terms and conditions of the Lease
               and this First Amendment during the Construction Period except
               for Tenant's obligation to pay Base Rent or Operating Expenses.

         7.    Option(s) to Renew: Tenant's Option(s) to Renew as set forth in
               Paragraph 32. of the Lease shall be deleted in its entirety and
               replaced with the following:

               "OPTIONS TO RENEW:

               a.     Grant of Option(s). Tenant shall have the right, at its
                      option, to expand the Lease for the Extended Premises
                      for two (2) period(s) of five (5) years each ("Extended
                      Term(s)") on an "as is" basis commencing at the
                      expiration of the previous Term, provided that at the
                      time of exercise and at the time of commencement of
                      each Extended Term, Tenant is not in default beyond any
                      applicable cure period under this Lease.

               b.     Exercise of Option(s). If Tenant decides to extend the
                      Lease for an Extended Term, Tenant shall give written
                      notice to Landlord of its election to extend not less
                      than nine (9) months prior to the expiration of the
                      previous Term. Tenant's failure to give timely notice
                      to Landlord of Tenant's election to extend shall be
                      deemed a waiver of Tenant's right to extend. The terms
                      and conditions



                      applicable to each Extended Term shall be the same
                      terms and conditions contained in this Lease except
                      that Tenant shall not be entitled to any further
                      option to extend beyond the second Extended Term. The
                      Base Rent for each Extended Term shall be as
                      determined in accordance with Paragraph c, below.

               c.     Determination of Base Rent During Extended Term(s).

                       1)  Agreement on Initial Base Rent. Landlord shall not
                           be obligated to provide Tenant with the proposed
                           fair market rental value until six (6) months
                           prior to the expiration of the previous Term.
                           Landlord and Tenant shall have thirty (30) days
                           after Landlord provides the proposed fair market
                           rental value in which to agree on the Base Rent
                           during each Extended Term, which shall be the fair
                           market rental value of the Premises during said
                           Extended Term. The initial fair market rental
                           value of the Premises during said Extended Term
                           shall be based on the uses of the Premises
                           permitted under this Lease, and quality, size,
                           design and location of the Premises, and the
                           rental value for lease renewals or extensions of
                           comparable size, quality and location, provided,
                           however, the initial Fair Market Rental Value
                           shall be subject to a 4% annual rental increase.
                           If Landlord and Tenant agree on the Base Rent for
                           each Extended Term during the thirty (30) day
                           period, they shall immediately execute an
                           amendment to this Lease stating the new Base Rent.

                       2)  Selection of Appraisers. If Landlord and Tenant
                           are unable to agree on the Base Rent (including
                           any periodic adjustments) for the subject Extended
                           Term within the thirty (30) day period, then
                           within ten (10) days after the expiration of the
                           thirty (30) day period and provided that Tenant
                           has timely exercised the subject renewal option as
                           set forth above, Landlord and Tenant each at its
                           own cost and by giving notice to the other party,
                           shall appoint a competent and disinterested real
                           estate appraiser with at least five (5) years
                           full-time commercial appraisal experience in the
                           Marin County market area to appraise the fair
                           market rental value of the Premises and set the
                           initial Base Rent during said Extended Term. If
                           either Landlord or Tenant does not appoint an
                           appraiser within said ten (20) days, the single
                           appraiser appointed shall be the sole appraiser
                           and shall set the Initial Base Rent during said
                           Extended Term. If two (2) appraisers are appointed
                           by Landlord and Tenant as stated herein, they
                           shall meet promptly and attempt to set the Initial
                           Base Rent for said Extended Term. If the two (2)
                           appraisers are unable to agree within thirty (30)
                           days after the second appraiser has been
                           appointed, they shall attempt to select a third
                           appraiser meeting the same qualifications within
                           ten (20) days after the last day the two (2)
                           appraisers are given to set the Initial Base Rent.
                           If they are unable to agree on the third
                           appraiser, either Landlord or Tenant, by giving
                           ten (10) days' notice to the other party, can
                           apply to the then President of the Real Estate
                           Board or to the Presiding Judge of the Superior
                           Court of the county in which the Premises are
                           located, for the selection of a third appraiser
                           who meets the qualifications stated herein.
                           Landlord and Tenant each shall bear one-half (1/2)
                           of the cost of appointing the third appraiser and
                           of paying the third appraiser's fee. The third
                           appraiser, however selected, shall be a person who
                           has not previously acted in any capacity for
                           either Landlord or Tenant, or their affiliates.

                       3)  Value Determined by Three (3) Appraisers. Within
                           thirty (30) days after the selection of the third
                           appraiser, a majority of the appraisers shall set
                           the Initial Base Rent for each Extended Term. If a
                           majority of the appraisers are unable to set the
                           Initial Base Rent within the stipulated period of
                           time, Landlord's appraiser shall arrange for
                           simultaneous exchange eof written appraisals from
                           each of the appraisers and the three (3)
                           appraisals shall be added together and their total
                           divided by three (3); the resulting quotient shall
                           be the Initial Base Rent for the Premises during
                           each Extended Term. If, however, the low appraisal
                           and/or the high appraisal are/is more than fifteen
                           percent (15%) lower and/or higher than the middle
                           appraisal, such low appraisal and/or high
                           appraisal shall be disregarded. If only one (1)
                           appraisal is disregarded, the remaining



                           two (2) appraisals shall be added together
                           and their total divided by two (2); the
                           resulting quotient shall be the Initial Base
                           Rent for the Premises during each Extended
                           Term. If both the low appraisal and the high
                           appraisal are disregarded as stated in this
                           Paragraph c3, the middle appraisal shall be the
                           Initial Base Rent for the Premises during
                           each Extended Term.

                       4)  Minimum Base Rent Level. Notwithstanding any other
                           provision of this Lease, in no event shall the
                           Initial Base Rent for the subject Extended Term be
                           less than the Base Rent prevailing immediately
                           prior to the expiration of the previous Term.

8.       Parking:  Commencing on the Additional Premises Commencement Date,
         Tenant's parking shall be increased to include all of the parking
         spaces included with the Property.

9.       Security Deposit: Landlord acknowledges that Tenant has previous
         deposited with Landlord a Security Deposit in the amount of $114,000.00
         (the "Existing Security Deposit"). Upon execution of this First
         Amendment, Tenant shall deposit with Landlord an additional security
         deposit (the "Additional Security Deposit") in the amount of $87,973.42
         so that the Existing Security Deposit combined with the Additional
         Security Deposit shall collectively provide for an Expanded Premises
         Security Deposit of $201,973.42 to be held by Landlord in accordance
         with Paragraph 6 of the Lease.

10.      Effect of Amendment: Except as modified herein, the terms and
         conditions of the Lease shall remain unmodified and continue in full
         force and effect as to the Expanded Premises. In the event of any
         conflict between the terms and conditions of the Lease and this First
         Amendment, the terms and conditions of this First Amendment shall
         prevail.

11.      Definitions:  Unless otherwise defined in this First Amendment, all
         terms not defined in this First Amendment shall have the meaning set
         forth in the Lease.

12.      Authority: Subject to the provisions of the Lease, this First Amendment
         shall be binding upon and inure to the benefit of the parties hereto,
         their respective heirs, legal representatives, successors and assigns.
         Each party hereto and the persons signing below warrant that the person
         signing below on such party's behalf is authorized to do so and to bind
         such party to the terms of this First Amendment.

IN WITNESS WHEREOF, the parties hereto have executed this First Amendment as of
the first date set forth hereinabove.

TENANT:                                          LANDLORD:
BioMarin Pharmaceutical, Inc.,                   Limar Realty Corp. #10,
a Delaware corporation                           a California corporation

By:  /s/ R. W. Anderson                          By:  /s/ Thomas Numainville
Name:  R. W. Anderson                            Name:  Thomas A. Numainville
Title:  V.P. Fin. and Admin.                     Title:  Sr. V.P.
Date:  April 19, 2000                            Date:  4-28-00

By:  /s/Christopher M. Stein                     By:  /s/ Thomas A. Numainville
Name:  Christopher M. Stein                      Name:  Thomas A. Numainville
Title:  V.P. Research & Development              Title:  Asst. Secretary
Date:  4/28/00                                   Date:  4/28/00