<PAGE>

                                                                    Exhibit 10.4

                                    SUBLEASE

      THIS SUBLEASE (this "Sublease") is dated for reference purposes as of
April ___, 2004, and is made by and between Xenoport, Inc., a Delaware
corporation ("Sublandlord"), and ILYPSA, Inc., a Delaware corporation
("Subtenant"). Sublandlord and Subtenant hereby agree as follows:

      1. RECITALS: This Sublease is made with reference to the fact that Sobrato
Interests, as "Landlord," ("Master Landlord") and Sublandlord, as "Tenant," are
parties to that certain Lease dated September 24, 2001 (the "Master Lease") with
respect to those certain premises consisting of approximately 102,759 square
feet described therein (the "Master Premises") located at 3410 Central
Expressway, Santa Clara, California. A copy of the Master Lease is attached
hereto as Exhibit A. Capitalized terms used and not defined herein shall have
the meaning ascribed to them in the Master Lease. Sublandlord represents and
warrants to Subtenant that (i) the Master Lease attached hereto is a true and
correct copy of the Master Lease, has not been amended, and is in full force and
effect, and (ii) neither Sublandlord nor Master Landlord is in default thereof.

      2. SUBLEASED PREMISES: Subject to the terms and conditions of this
Sublease, Sublandlord hereby subleases to Subtenant, and Subtenant hereby
subleases from Sublandlord, a portion of the Master Premises consisting of
approximately 20,489 rentable square feet as more particularly shown on Exhibit
B attached hereto (the "Subleased Premises").

      3. TERM:

            A. TERM. The term (the "Term") of this Sublease shall be for the
period commencing on May 1, 2004 (the "Commencement Date") and ending April 30,
2006 unless this Sublease is sooner terminated pursuant to its terms or the
Master Lease is sooner terminated pursuant to its terms (the "Expiration Date").

            B. EARLY OCCUPANCY. Following the date by which Master Landlord
provides its written consent to this Sublease, provided Subtenant has provided
Sublandlord with the insurance certificates evidencing the insurance required
under Paragraph 21 of this Sublease, Subtenant shall be entitled to access the
Subleased Premises for the sole purpose of installing its furniture, equipment,
telecommunications systems and trade fixtures. Such occupancy shall be subject
to all of the terms of the Sublease except the obligation to pay Rent.

            C. NO OPTIONS TO EXTEND OR EXPAND. Except as specifically set forth
in Paragraph 30 of this Sublease, Subtenant shall not have any options to extend
or renew the term of the Sublease or any options to expand the Subleased
Premises.

      4. RENT.

            A. BASE RENT. Commencing on the Commencement Date and continuing
each month throughout the Term of this Sublease, Subtenant shall pay to
Sublandlord as base rent ("Base Rent") monthly installments as follows:

<TABLE>
<CAPTION>
          Months                      Base Rent per Month
--------------------------            -------------------
<S>                                   <C>
           1-12                           $52,000.00

           13-24                          $66,589.25

25-36 (if option exercised)               $66,589.25
</TABLE>

<PAGE>

Base Rent and Additional Rent, as defined in Paragraph 4.B below, (collectively,
hereinafter "Rent") shall be paid in advance on or before the first (1st) day of
each month. Rent for any period during the Term hereof which is for less than
one (1) month of the Term shall be a pro rata portion of the monthly installment
based on a thirty (30) day month. Rent shall be payable without notice or demand
and without any deduction, offset, or abatement, in lawful money of the United
States of America. Rent shall be paid directly to Sublandlord at the Master
Premises, Attention: Chief Financial Officer, or such other address as may be
designated in writing by Sublandlord.

            B. ADDITIONAL RENT. All monies other than Base Rent required to be
paid by Subtenant under this Sublease shall be deemed additional rent
("Additional Rent"). The parties acknowledge that Base Rent for the initial Term
of this Sublease already includes the Subleased Premises' share of the two
percent (2%) management fee, "Common Area Costs", Master Landlord insurance and
Building property taxes payable by the "Tenant" under the Master Lease.
Accordingly, Subtenant shall not be responsible for such costs. Subtenant shall,
however, be liable and shall pay prior to delinquency, all taxes and assessments
levied against Subtenant's personal property and trade or business fixtures.
Notwithstanding the foregoing, in the event any cost or expense is incurred by
Sublandlord as a result of Subtenant's request for certain services (such as
extra hours' charges, etc.), Subtenant shall pay the entire cost thereof.

      The parties further acknowledge that Subtenant is not responsible for any
additional charges for (i) building standard HVAC to the Subleased Premises
during regular business hours (i.e., Monday through Friday from 7:00 a.m. to
6:00 p.m. and excluding weekends) reasonably considered by Sublandlord to be
standard for the comfortable use and occupancy of the Subleased Premises for
general office purposes, (ii) general office and laboratory levels of
electricity and water, and (iii) use of general laboratory levels of the house
system (a) nitrogen, (b) DI water, (c) vacuum, (d) compressed dry air and (e)
carbon dioxide gas. Notwithstanding the foregoing, in the event Sublandlord
reasonably determines that Subtenant is using utilities to the Subleased
Premises in excess of that used by Sublandlord in the balance of the Master
Premises on a per square foot occupied basis, then Sublandlord may charge
Subtenant for such excess utilities as reasonably determined by Sublandlord.

            C. PREPAYMENT OF RENT. Upon execution hereof by Subtenant, Subtenant
shall pay to Sublandlord the sum of Fifty-Two Thousand Dollars ($52,000), which
shall constitute Base Rent for the first (1st) month of the Term.

      5. SECURITY DEPOSIT: Upon execution of this Sublease, Subtenant shall
deposit with Sublandlord Seventy Thousand Dollars ($70,000) in cash as security
for the performance by Subtenant of its obligations under this Sublease, and not
as a prepayment of rent (the "Security Deposit"). If Subtenant defaults under
this Sublease, Sublandlord may apply all or any part of the Security Deposit for
the payment of any rent or other sum in default, the repair of any damage to the
Subleased Premises caused by Subtenant or the payment of any other amount which
Sublandlord may spend or become obligated to spend by reason of Subtenant's
default or to compensate Sublandlord for any other loss or damage which
Sublandlord may suffer by reason of Subtenant's default to the full extent
permitted by law. Subtenant hereby waives any restriction on the use or
application of the Security Deposit by Sublandlord as set forth in California
Civil Code Section

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1950.7. To the extent any portion of the Security Deposit is used, Subtenant
shall within five (5) days after demand from Sublandlord restore the Security
Deposit to its full amount. Sublandlord may keep the Security Deposit in its
general funds and shall not be required to pay interest to Subtenant on the
deposit amount. If Subtenant shall perform all of its obligations under this
Sublease and return the Subleased Premises to Sublandlord at the end of the
Term, Sublandlord shall return all of the remaining Security Deposit to
Subtenant within thirty (30) days after the end of the Term. The Security
Deposit shall not serve as an advance payment of rent or a measure of
Sublandlord's damages for any default under this Sublease. Subtenant covenants
and agrees that it shall not assign or encumber or attempt to assign or encumber
the Security Deposit and neither Sublandlord nor its successors or assigns shall
be bound by any such agreement, encumbrance, attempted assignment or attempted
encumbrance.

      6. LATE CHARGE: If Subtenant fails to pay Sublandlord any amount due
hereunder on or before the fifth (5th) day after written notice from Sublandlord
that such amount is past due, Subtenant shall pay to Sublandlord upon demand a
late charge equal to five percent (5%) of the delinquent amount. The parties
agree that the foregoing late charge represents a reasonable estimate of the
cost and expense which Sublandlord will incur in processing each delinquent
payment. Sublandlord's acceptance of any interest or late charge shall not waive
Subtenant's default in failing to pay the delinquent amount.

      7. HOLDOVER: Subtenant acknowledges that it is critical that Subtenant
surrender the Subleased Premises on or before the expiration or earlier
termination of the Sublease in accordance with the terms of this Sublease.
Accordingly, Subtenant shall indemnify, defend and hold harmless Sublandlord
from and against all losses, costs, claims, liabilities and damages resulting
from Subtenant's failure to surrender the Subleased Premises on or before the
expiration or earlier termination of the Sublease in the condition required
under the terms of this Sublease (including, without limitation, any liability
or damages sustained by Sublandlord as a result of a holdover of the Master
Premises by Sublandlord occasioned by the holdover of the Subleased Premises by
Subtenant). In addition, Subtenant shall pay Sublandlord holdover rent equal to
one hundred fifty percent (150%) of Base Rent plus any Additional Rent payable
hereunder for any period from the Expiration Date through the date Subtenant
surrenders the Subleased Premises in the condition required hereunder.

      8. "AS IS" CONDITION: The parties acknowledge and agree that Subtenant is
subleasing the Subleased Premises on an "AS IS" basis, and that Sublandlord has
made no representations or warranties, express or implied, whatsoever (except as
otherwise specifically set forth herein), with respect to the Subleased
Premises, including, without limitation, any representation or warranty as to
the suitability of the Subleased Premises for Subtenant's intended use or any
representation or warranty made by Master Landlord under the Master Lease.
Except as specifically set forth in Paragraph 16 of this Sublease, Sublandlord
shall have no obligation whatsoever to make or pay the cost of any alterations,
improvements or repairs to the Subleased Premises, including, without
limitation, any improvement or repair required to comply with any law,
regulation, building code or ordinance (including the Americans with
Disabilities Act of 1990, as may be amended ("ADA")). Subtenant hereby expressly
waives the provisions of subsection 1 of Section 1932 and Sections 1941 and 1942
of the Civil Code of California and all rights to make repairs at the expense of
Sublandlord as provided in Section 1942 of said Civil Code. Section 17 of the
Master Lease, to the extent incorporated herein pursuant to Paragraph 28, shall
apply with respect to Subtenant's obligations to comply with laws or regulations
affecting the Subleased Premises. In addition, Subtenant shall not be
responsible for any noncompliance with law in the Subleased Premises resulting
from alterations and improvements constructed by Sublandlord in the Subleased
Premises nor shall Subtenant be responsible for remediation of Hazardous
Materials (as defined in the Master Lease) in the Subleased Premises except to
the extent of Hazardous Materials used or released by Subtenant. With respect to
ADA access to the Subleased Premises, when reasonably necessary (and only when
reasonably necessary), Sublandlord shall make available to

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Subtenant during normal business hours access through the main lobby and
elevators for the purposes of ingress and egress to and from the Subleased
Premises only, subject to Sublandlord's reasonable security measures.
Notwithstanding the foregoing, Sublandlord represents that to its current actual
knowledge, the building systems and fume hoods serving the Subleased Premises
are in operating condition. In the event, however, that the HVAC, air handlers
and fume hoods exclusively serving the Subleased Premises are not in operating
condition and a major repair is required to make such HVAC, air handlers and
fume hoods operational within thirty (30) days of Commencement Date, provided
Subtenant has provided Sublandlord written notice of such necessary major repair
prior to the expiration of such thirty (30)-day period, Sublandlord shall make
such repair or cause such repair to be made at no cost to Subtenant.

      9. MASTER LANDLORD'S OBLIGATIONS: Sublandlord shall have no obligation to
perform any repairs or any other obligation of Master Landlord required to be
performed by Master Landlord under the terms of the Master Lease (including,
without limitation, Master Landlord's obligations under Sections 11, 12, 17, 18,
28, 30 and 32 of the Master Lease and Master Landlord's obligation to comply
with laws and carry building insurance). Sublandlord shall, however, request
performance of the same in writing from Master Landlord promptly after being
requested to do so by Subtenant, and shall use Sublandlord's reasonable efforts
(not including the payment of monies, the incurring of any liabilities, or the
institution of legal proceedings) to obtain Master Landlord's performance.

      10. REPAIR AND MAINTENANCE: Subtenant shall, at its sole cost, be
responsible for all of "Tenant's" obligations under Section 11.E of the Master
Lease with respect to the Subleased Premises except that Subtenant shall not be
responsible for repairing the HVAC serving the Building in general, elevator and
roof membrane except to the extent of any damage caused by any act or omission
of Subtenant or its employees, agents, contractors or invitees. Subtenant shall,
however, be responsible for the maintenance of all HVAC and air handlers
exclusively serving the Subleased Premises. To the extent such HVAC and/or air
handlers are required to be replaced at Sublandlord's reasonable discretion,
except to the extent caused by Subtenant's or Subtenant's agents', employees',
contractors' or invitees' act or omission, Sublandlord shall complete or cause
Master Landlord to complete such replacement, and Subtenant shall pay that
portion of the cost equal to the product of such total cost multiplied by a
fraction, the numerator of which is the number of months remaining in the Term,
the denominator of which is the useful life (in months) of the replacement. In
the event Subtenant exercises the Extension Option, Subtenant shall at the time
of exercise pay an additional twelve (12) months' share of such cost.

      11. RIGHT TO CURE DEFAULTS: If Subtenant fails to pay any sum of money to
Sublandlord, or fails to perform any other act on its part to be performed
hereunder, then Sublandlord may, but shall not be obligated to, make such
payment or perform such act upon ten (10) days prior written notice to
Subtenant. All such sums paid, and all reasonable costs and expenses of
performing any such act, shall be deemed Additional Rent payable by Subtenant to
Sublandlord upon ten (10) days written demand, together with interest thereon at
the lesser of (i) ten percent (10%) per annum or (ii) the maximum rate allowable
under law (the "Interest Rate") from the date of the written demand until
repaid.

      12. ASSIGNMENT AND SUBLETTING: Subtenant may not assign any interest in
this Sublease (by operation of law or otherwise), sublet any of the Subleased
Premises, transfer any interest of Subtenant therein or permit any use of the
Subleased Premises by another party (collectively, "Transfer"), without the
prior written consent of Sublandlord and Master Landlord. Sublandlord's consent
shall not be unreasonably withheld, provided, however, Sublandlord's withholding
of consent shall in all events be deemed reasonable if for any reason Master
Landlord's consent is not obtained. A consent to one Transfer shall not be
deemed to be a consent to any subsequent Transfer. Any Transfer without such
consent shall be void and, at the option

                                      -4-
<PAGE>

of Sublandlord, shall be a material default under this Sublease. Sublandlord's
waiver or consent to any assignment or subletting shall be ineffective unless
set forth in writing, and Subtenant shall not be relieved from any of its
obligations under this Sublease. Notwithstanding the foregoing, so long as
Subtenant otherwise complies with the provisions of Section 29 of the Master
Lease, Subtenant may assign the Sublease, without Sublandlord's prior consent
(but subject to Master Landlord's consent to the extent required under the
Master Lease), to (i) any corporation which controls, is controlled by, or is
under common control with the original Subtenant to this Sublease by means of an
ownership interest of more than 50%; (ii) a corporation which results from a
merger, consolidation or other reorganization in which Subtenant is not the
surviving corporation, so long as the surviving corporation has a net worth at
the time of such assignment that is equal to or greater than the net worth of
Subtenant immediately prior to such transaction; and (iii) a corporation which
purchases or otherwise acquires all or substantially all of the assets of
Subtenant so long as such acquiring corporation has a net worth at the time of
such assignment that is equal to or greater than the net worth of Subtenant
immediately prior to such transaction.

      13. USE:

            A. Subtenant may use the Subleased Premises for general office and
laboratory research, development and testing, light manufacturing and related
legal uses (including vivarium use once constructed) and for no other purpose
whatsoever.

            B. Subtenant shall comply with all reasonable rules and regulations
promulgated from time to time by Master Landlord or Sublandlord.

      14. ENVIRONMENTAL MATTERS:

            A. Concurrently with the execution of this Sublease, Sublandlord and
Subtenant shall execute and deliver an Environmental Matters Agreement in the
form attached hereto as Exhibit C (the "Environmental Matters Agreement").
Sublandlord and Subtenant agree to be bound by and to comply with all of the
terms and conditions of the Environmental Matters Agreement and perform their
respective obligations thereunder.

            B. The provisions of this Paragraph 14 of the Sublease shall survive
the termination of the Sublease.

      15. EFFECT OF CONVEYANCE: As used in this Sublease, the term "Sublandlord"
means the holder of the "Tenant's" interest under the Master Lease. In the event
of any assignment or transfer of the Tenant's interest under the Master Lease,
which assignment or transfer may occur at any time during the Term hereof in
Sublandlord's sole discretion, Sublandlord shall be and hereby is entirely
relieved of all covenants and obligations of Sublandlord hereunder to the extent
the transferee has assumed all of such covenants and obligations hereunder, and
it shall be deemed and construed, without further agreement between the parties
hereto, that any transferee has assumed and shall carry out all covenants and
obligations thereafter to be performed by Sublandlord hereunder. Sublandlord
shall transfer and deliver any security of Subtenant to the transferee of the
Tenant's interest under the Master Lease, and thereupon Sublandlord shall be
discharged from any further liability with respect thereto.

                                      -5-
<PAGE>

      16. SUBLANDLORD WORK AND VIVARIUM:

            A. SUBLANDLORD WORK: Sublandlord shall construct at its sole cost
and expense (i) entry doors to the Sub1eased Premises as shown on Exhibit D
attached hereto and (ii) an access card reader for the entry to the Subleased
Premises (collectively, the "Sublandlord Work"). Sublandlord shall commence the
Sublandlord Work as soon as reasonably practicable after Master Landlord has
consented to this Sublease and shall use reasonable efforts to complete the
Sublandlord Work by the Commencement Date or as soon thereafter as reasonably
practicable without requiring overtime work. The Sublease shall not be void or
voidable, the Commencement Date shall not be delayed, nor shall Sublandlord be
liable to Subtenant for any loss or damage, by reason of delays in the
completion of the Sublandlord Work. Rent hereunder shall commence with respect
to the entire Subleased Premises on the Commencement Date notwithstanding any
delay in the construction of the Sublandlord Work.

            B. VIVARIUM:

                  (a) Sublandlord shall construct a vivarium (the "Vivarium") in
the portion of the Subleased Premises on the first floor of the Building in
accordance with the plans and specifications described on Exhibit E attached
hereto. Sublandlord's obligation to construct the Vivarium shall be subject to
receipt of Master Landlord's consent to the Vivarium and such plans and
specifications. If Sublandlord requests any changes to such plans, Subtenant
shall not unreasonably withhold its consent to such changes. In the event of a
disagreement in such changes, Sublandlord's good faith determination of such
changes shall control so long as the Vivarium is substantially similar in
quality to the vivarium currently existing in the Master Premises. Sublandlord
shall use reasonable efforts to complete construction of the Vivarium prior to
January 1, 2005. However, the Sublease shall not be void or voidable, the
Commencement Date shall not be delayed, Rent shall not abate, nor shall
Sublandlord be liable to Subtenant for any loss or damage, by reason of delays
in the completion of the Sublandlord Work.

                  (b) Subtenant shall be responsible for payment of one-third
(1/3) of the cost to design and construct the Vivarium. Subtenant shall pay its
portion of such cost on a monthly basis as such costs are incurred within twenty
(20) days after receiving Sublandlord's invoice therefor. The cost of the
Vivarium shall include, without limitation, all of the following: (i) all costs
of preliminary space planning and final architectural and engineering plans and
specifications, and architectural fees, engineering costs and fees, and other
costs associated with completion of said plans; (ii) all costs of obtaining
building permits and other necessary authorizations and approvals and other
applicable agencies and jurisdictions; (iii) all costs of interior design and
finish schedule plans and specifications including as-built drawings; (iv) all
direct and indirect costs of procuring, constructing and installing the
Vivarium, including, but not limited to, all labor and materials; and (v) all
fees payable to the general contractor and architect. If, prior to construction,
Sublandlord reasonably estimates that Subtenant's portion of the total cost of
the Vivarium shall exceed $175,000, then Subtenant shall have the right to
elect, prior to commencement of construction but no later than five (5) days
from the date of notice of such estimate, not to have the Vivarium constructed
in which event Subtenant shall reimburse Sublandlord for all costs incurred in
connection with the planning and designing of the Vivarium.

      17. SERVER ROOM: Subtenant shall be entitled to use a small portion of the
server room in the Master Premises (such portion to be designated by
Sublandlord) to place and operate minor computer server equipment. The scope of
Subtenant's use shall be subject to Sublandlord's prior approval, which shall
not be unreasonably withheld so long as such use does not adversely affect
Sublandlord's use of the server room for Sublandlord's operations. Subtenant's
access to the server room shall be subject to Sublandlord's reasonable

                                      -6-
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security measures and shall be subject to the following: (a) Subtenant shall be
limited to one (1) representative (to be designated by Subtenant) at a time
having such access to the server room; (b) Subtenant's access shall be limited
to regular business hours designated by Sublandlord; (c) Subtenant's access
after such hours shall be by appointment only made with an IT representative of
Sublandlord to be designated by Sublandlord.

      18. DELIVERY AND ACCEPTANCE: Subject to Paragraph 8 of this Sublease,
Sublandlord shall deliver the Subleased Premises in their "AS IS" condition.
This Sublease shall not be void or voidable, nor shall Sublandlord be liable to
Subtenant for any loss or damage, by reason of delays in the Commencement Date,
delays in the completion of the Sublandlord Work or delays in Sublandlord
delivering the Subleased Premises to Subtenant for any reason whatsoever;
provided, however, that Rent shall abate until Sublandlord delivers possession
of the Subleased Premises to Subtenant (which delivery may occur prior to the
substantial completion of the Sublandlord Work). The parties hereto acknowledge
that the construction of the Sublandlord Work may occur after the Commencement
Date and after the Subleased Premises are delivered to Subtenant and that such
construction or any delay in such construction shall not entitle Subtenant to
abate Rent or to terminate the Sublease.

      19. IMPROVEMENTS: Subtenant shall not make any alterations or improvements
to the Subleased Premises (i) without the prior written consent of both Master
Landlord and Sublandlord and (ii) except in accordance with the Master Lease.
Sublandlord's consent thereto shall not be unreasonably withheld; provided,
however, Sublandlord's withholding of consent shall in all events be deemed
reasonable if for any reason Master Landlord's consent to the same is not
obtained. Sublandlord may require that any such improvements so constructed by
Subtenant be removed by Subtenant (and the area restored in its condition and
configuration as of the Commencement Date), at Subtenant's expense, prior to the
Expiration Date, and Subtenant shall repair any damage or injury to the
Subleased Premises caused thereby. Sublandlord shall provide Subtenant with
notice of such removal requirement no later than March 1, 2006. Sublandlord may
instead at such time elect to require that Subtenant leave such improvements in
the Subleased Premises. Subject to Master Landlord's approval, Sublandlord
hereby approves of the described on Exhibit G hereto.

      20. RELEASE AND WAIVER OF SUBROGATION: Notwithstanding anything to the
contrary in this Sublease, the parties hereto release each other and their
respective agents, employees, successors and assigns from all liability for
damage to any property that is actually covered by property insurance in force
or which would normally be covered by full replacement value "Special Form"
property insurance, without regard to the negligence or willful misconduct of
the entity so released. Each party shall cause each insurance policy it obtains
to include a waiver of subrogation regarding the liabilities released hereby.
Sublandlord shall not be liable to Subtenant, nor shall Subtenant be entitled to
terminate this Sublease or to abate Rent for any reason, including, without
limitation, (i) failure or interruption of any utility system or service or (ii)
failure of Master Landlord to maintain the Subleased Premises as may be required
under the Master Lease. Failure by Sublandlord to perform any defined services,
or any cessation thereof, when such failure is caused by accident, breakage,
repairs, strikes, lockout or other labor disturbances or labor disputes of any
character, or by any other cause, similar or dissimilar, beyond the reasonable
control of Sublandlord, shall not render Sublandlord liable in any respect for
damages to either person or property, nor be construed as an eviction of
Subtenant, nor cause an abatement of rent nor relieve Subtenant from fulfillment
of any covenant or agreement hereof. In no event shall Sublandlord be liable to
Subtenant for any lost profit, damage to or loss of business or any form of
special, indirect or consequential damage.

      21. INSURANCE: Subtenant shall obtain and keep in full force and effect,
at Subtenant's sole cost and expense, during the Term the insurance required to
be carried by the "Tenant" under the Master Lease as incorporated herein, except
that reference to "$5,000,000.00" in Section 12.C of the Master Lease shall be

                                      -7-
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deemed to be "$2,000,000.00" for the purposes of this Paragraph so long as
Master Landlord approves of such reduced insurance requirement with respect to
Subtenant's insurance. Subtenant shall include Sublandlord and Master Landlord
as an additional insured in any policy of insurance carried by Subtenant in
connection with this Sublease and shall provide Sublandlord with certificates of
insurance upon Sublandlord's request.

      22. DEFAULT: Subtenant shall be in material default of its obligations
under this Sublease if any of the following events occur:

            A. Subtenant fails to pay any Rent within seven (7) days after
written notice of nonpayment;

            B. Subtenant fails to perform any term, covenant or condition of
this Sublease (except those requiring payment of Rent) and fails to cure such
breach within twenty (20) days after delivery of a written notice specifying the
nature of the breach; provided, however, that if the nature of such breach is
such that the same cannot reasonably be cured within such twenty (20) day
period, Subtenant shall not be deemed to be in default if Subtenant shall within
such period commence such cure and thereafter diligently prosecute the same to
completion;

            C. Subtenant fails to perform any term, covenant or condition of the
Environmental Matters Agreement and fails to cure such breach within ten (10)
days after delivery of a written notice specifying the nature of the breach;

            D. the bankruptcy or insolvency of Subtenant, transfer by Subtenant
in fraud of creditors, an assignment by Subtenant for the benefit of creditors,
or the commencement of any proceedings of any kind by or against Subtenant under
any provision of the Federal Bankruptcy Act or under any other insolvency,
bankruptcy or reorganization act unless, in the event any such proceedings are
involuntary, Subtenant is discharged from the same within thirty (30) days
thereafter;

            E. the appointment of a receiver for a substantial part of the
assets of Subtenant, which receiver is not discharged within thirty (30) days;

            F. the levy upon this Sublease or any estate of Subtenant hereunder
by any attachment or execution and the failure within thirty (30) days
thereafter to have such attachment or execution vacated or such other action
taken with respect thereto so as to put Sublandlord at no risk of having an
unconsented transfer of this Sublease;

            G. Subtenant abandons the Subleased Premises; or

            H. Subtenant commits any other act or omission which could
constitute a default under the Master Lease.

      23. REMEDIES: In the event of any default by Subtenant, Sublandlord shall
have all remedies provided to the "Landlord" under Sections 22.A, 22.B, 22.C and
22.D of the Master Lease as if a default and breach beyond applicable notice and
cure periods had occurred thereunder and all other rights and remedies otherwise
available at law and in equity. Sublandlord may resort to its remedies
cumulatively or in the alternative. Without limiting the generality of the
foregoing, Sublandlord shall have the remedy described in California Civil Code
Section 1951.4 (Sublandlord may continue the Sublease in effect after
Subtenant's

                                      -8-
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breach and abandonment and recover rent as it becomes due, if Subtenant has
right to sublet or assign, subject only to reasonable limitations).

      24. SURRENDER: On or before the Expiration Date or any sooner termination
of this Sublease, Subtenant shall remove all of its trade fixtures, personal
property and all alterations constructed by Subtenant in the Subleased Premises
which are required to be removed under the terms of this Sublease or the Master
Lease and shall surrender the Subleased Premises to Sublandlord in the same
condition as received as of the Commencement Date, reasonable wear and tear and
damage by casualty or condemnation excepted, with all of Subtenant's obligations
under Section 4(c) of the Environmental Matters Agreement performed and
completed. Subtenant shall repair any damage to the Subleased Premises caused by
Subtenant's removal of its personal property, furnishings and equipment. If the
Subleased Premises are not so surrendered, then Subtenant shall be liable to
Sublandlord for all costs incurred by Sublandlord in returning the Subleased
Premises to the required condition, plus interest thereon at the Interest Rate.

      25. BROKER: Sublandlord and Subtenant each represent to the other that
they have dealt with no real estate brokers, finders, agents or salesmen in
connection with this transaction other than CRESA Partners. Subtenant agrees to
indemnify and hold Sublandlord harmless from and against all claims for
brokerage commissions, finder's fees or other compensation made by any other
agent, broker, salesman or finder as a consequence of Subtenant's actions or
dealings with such other agent, broker, salesman, or finder.

      26. NOTICES: Unless at least five (5) days' prior written notice is given
in the manner set forth in this paragraph, the address of each party for all
purposes connected with this Sublease shall be that address set forth below
their signatures at the end of this Sublease. All notices, demands or
communications in connection with this Sublease shall be properly addressed and
delivered as follows: (a) personally delivered; or (b) submitted to an overnight
courier service, charges prepaid; or (c) deposited in the mail (certified,
return-receipt requested, and postage prepaid). Notices shall be deemed
delivered upon receipt, if personally delivered, one (1) business day after
being so submitted to an overnight courier service and two (2) business days
after deposit in the United States mail, if mailed as set forth above. All
notices given to Master Landlord under the Master Lease shall be considered
received only when delivered in accordance with the Master Lease.

      27. FURNITURE & EQUIPMENT. During the Term of the Sublease, Subtenant
shall have the right to use the furniture and equipment currently existing in
the Subleased Premises and outlined on Exhibit F attached hereto (the "Furniture
and Equipment"). Such Furniture and Equipment is provided by Sublandlord in
their "AS IS" condition, with all faults and defects, and Subtenant shall use
such Furniture at Subtenant's sole risk. No representations or warranties
whatsoever as to the Furniture and Equipment's condition or fitness for a
particular purpose, express or implied, are made by Sublandlord. Subtenant shall
maintain and repair the Furniture and Equipment, and shall surrender the
Furniture and Equipment at the expiration or earlier termination of the
Sublease, in the same condition as received by Subtenant subject to ordinary
wear and tear and free of any Hazardous Materials contamination caused by
Subtenant. If Subtenant shall use the phone system included in the Furniture and
Equipment, Subtenant shall arrange for and pay the costs of the phone services
directly to the current service provider. In such event, Subtenant shall utilize
the current vendor to upgrade the system for additional users.

      28. OTHER SUBLEASE TERMS:

            A. INCORPORATION BY REFERENCE. Except as set forth below and except
as otherwise provided in this Sublease, the terms and conditions of this
Sublease shall include all of the terms of the Master

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<PAGE>

Lease and such terms are incorporated into this Sublease as if fully set forth
herein, except that: (i) each reference in such incorporated sections to "Lease"
shall be deemed a reference to this "Sublease"; (ii) each reference to the
"Premises" shall be deemed a reference to the "Subleased Premises", and each
reference to "Base Monthly Rent" shall be deemed a reference to "Base Rent";
(iii) each reference to "Landlord" shall be deemed a reference to "Sublandlord"
and each reference to "Tenant" shall be deemed a reference to "Subtenant",
except as otherwise expressly set forth herein; (iv) with respect to work,
services, utilities, electricity, repairs (or damage caused by Master Landlord),
restoration, insurance, indemnities, reimbursements, representations, warranties
or the performance of any other obligation of "Landlord" under the Master Lease,
whether or not incorporated herein, the sole obligation of Sublandlord shall be
to request the same in writing from Master Landlord as and when requested to do
so by Subtenant, and to use Sublandlord's reasonable efforts (not including the
payment of money, the incurring of any liabilities, or the institution of legal
proceedings) to obtain Master Landlord's performance; (v) with respect to any
obligation of Subtenant to be performed under this Sublease, wherever the Master
Lease grants to "Tenant" a specified number of days to perform its obligations
under the Master Lease (including, without limitation, curing any defaults),
except as otherwise provided herein, Subtenant shall have three (3) fewer days
to perform the obligation or one-half the time period permitted under the Master
Lease, which ever allows Subtenant the greater amount of time; (vi) with respect
to any approval required to be obtained from the "Landlord" under the Master
Lease, such approval must be obtained from both Master Landlord and Sublandlord,
and Sublandlord's withholding of approval shall in all events be deemed
reasonable if for any reason Master Landlord's approval is not obtained; (vii)
in any case where the "Landlord" reserves or is granted the right to manage,
supervise, control, repair, alter, regulate the use of, enter or use the
Premises or any areas beneath, above or adjacent thereto, such reservation or
grant of right of entry shall be deemed to be for the benefit of both Master
Landlord and Sublandlord; (viii) in any case where "Tenant" is to indemnify,
release or waive claims against "Landlord", such indemnity, release or waiver
shall be deemed to run from Subtenant to both Master Landlord and Sublandlord;
(ix) in any case where "Tenant" is to execute and deliver certain documents or
notices to "Landlord", such obligation shall be deemed to run from Subtenant to
both Master Landlord and Sublandlord; and (x) the following modifications shall
be made to the Master Lease as incorporated herein:

                  (a) the following provisions of the Master Lease are not
incorporated herein: Sections 1, 2, 3, 4, 5, 6, 7, 8 (fifth sentence), 10
(except second through seventh sentences), 11, 12.B, 12.C, 13, 14, 17 (last
sentence), 18, 20, 22 (first paragraph), 26, 29.A (fifth and sixth sentences),
31, 32 (second paragraph), 34, 37, 38, 40, 41 (second sentence), 42.B, 43,
Exhibit A, Exhibit B, Exhibit C, and Schedule 1;

                  (b) reference to "Landlord" in the following provisions of the
Master Lease shall be deemed a reference to "Master Landlord" only: Sections
19.B (second sentence), 28.A (first, second, and fifth sentences) and 28.B;

                  (c) reference to "Permitted Alterations" in the Master Lease
shall be deleted for purposes of incorporation herein;

                  (d) With respect to the excess rent and other consideration
described in Section 29.B of the Master Lease incorporated herein, after Master
Landlord has received its share of such excess rent and other consideration from
Subtenant pursuant to Section 29.B of the Master Lease, Subtenant shall pay to
Sublandlord fifty percent (50%) of any remaining excess rent and other
consideration as calculated using the formula in Section 29.B of the Master
Lease as incorporated herein (except that references therein to "Base Monthly
Rent" shall be deemed a reference to "Base Rent" under this Sublease).

                                      -10-
<PAGE>

                  (e) the phrase "subject to the provisions of paragraph 31" in
Section 35 of the Master Lease shall be replaced with "subject to the provisions
of Paragraph 15 of this Sublease" for purposes of incorporation herein;

                  (f) the phrase "and all of the parties hereto shall be jointly
and severally liable hereunder" in Section 35 of the Master Lease shall be
deleted for purposes of incorporation herein; and

                  (g) any right to abate rent provided to Subtenant through
incorporation of the provisions of the Master Lease shall not exceed the rent
actually abated under the Master Lease with respect to the Subleased Premises.

            B. ASSUMPTION OF OBLIGATIONS. This Sublease is and at all times
shall be subject and subordinate to the Master Lease and the rights of Master
Landlord thereunder. Subtenant hereby expressly assumes and agrees: (i) to
comply with all provisions of the Master Lease (as incorporated herein or as
otherwise set forth in the Sublease); and (ii) to perform all the obligations on
the part of the "Tenant" to be performed under the terms of the Master Lease (as
incorporated herein or as otherwise set forth in the Sublease) with respect to
the Subleased Premises during the Term of this Sublease. In the event the Master
Lease is terminated for any reason whatsoever, this Sublease shall terminate
simultaneously with such termination without any liability of Sublandlord to
Subtenant. Sublandlord, however, shall not voluntarily terminate the Master
Lease (unless Subtenant receives nondisturbance from the Master Landlord) except
pursuant to Sublandlord's rights under the Master Lease or under law (e.g.,
casualty, condemnation or default by Master Landlord) or cause the same to be
terminated as a result of a default by Sublandlord under the Master Lease not
caused by Subtenant's default under the Sublease. In the event of a conflict
between the provisions of this Sublease and the Master Lease, as between
Sublandlord and Subtenant, the provisions of this Sublease shall control.

      29. RIGHT TO CONTEST: If Sublandlord does not have the right to contest
any matter in the Master Lease due to expiration of any time limit that may be
set forth therein or for any other reason, then notwithstanding any
incorporation of any such provision from the Master Lease in this Sublease,
Subtenant shall also not have the right to contest any such matter.

      30. OPTIONS TO EXTEND. Provided (1) Subtenant is not in default of any
term or provision of this Sublease and (2) Subtenant has not assigned this
Sublease or sublet any portion of the Subleased Premises, then Subtenant shall
have one (1) option (the "Extension Option") to extend the Term for an
additional one (1) year period commencing on the original Expiration Date of
this Sublease and ending the earlier of (i) April 30, 2007 or (ii) the date this
Sublease is sooner terminated pursuant to its terms or the Master Lease is
sooner terminated pursuant to its terms (the "Extension Period"), by giving
Sublandlord written notice of exercise of the Extension Option no later than
December 31, 2005. The Extension Period shall be on the same terms and
conditions of this Sublease, including Base Rent in the amount of Sixty-Six
Thousand Five Hundred Eighty-Nine and 25/100 Dollars ($66,589.25) per month,
except that Subtenant shall no longer have the Extension Option. The Extension
Option described in this Paragraph 30 is personal to ILYPSA, Inc. and are not
exercisable by or for any other party.

      31. SERVICES: Sublandlord shall provide reasonable cage-wash and
glass-wash services to Subtenant. Sublandlord shall invoice Subtenant monthly
for the cost of such services, and Subtenant shall pay such cost within ten (10)
days of such invoices. Sublandlord disclaims all warranties, express or implied,
including, but not limited to, the implied warranties of merchantability and
fitness for a particular purpose, with respect to such services. Sublandlord
makes no representations or warranties as to the quality, suitability

                                      -11-
<PAGE>

or adequacy of the services for any purpose or use, and Sublandlord shall not be
subject to any liability to Subtenant in connection with providing such
services.

      32. SIGNAGE: Subtenant shall not place or permit to be placed in, upon or
about the Subleased Premises signs, advertisements or notices without the
written consent of both Master Landlord and Sublandlord. Sublandlord's consent
may be withheld at Sublandlord's sole discretion. Any sign so placed on the
Subleased premises shall be removed by Subtenant, at its expense, prior to the
Expiration Date, and Subtenant shall repair any damage or injury to the
Subleased Premises caused thereby. To the extent permitted by Master Landlord
and subject to Sublandlord's and Master Landlord's approval of the location,
design and specifications of the following signage, Subtenant shall be entitled
to install, at its sole cost, (i) directional signage in the main lobby area of
the Subleased Premises, (ii) signage on the currently existing monument signs
identified on Exhibit H attached hereto, (iii) vinyl signage on the window of
the lobby of the Subleased Premises. Sublandlord's approval of the foregoing
shall not be unreasonably withheld; provided, however, Sublandlord's withholding
of approval shall in all events be deemed reasonable if for any reason Master
Landlord's permission and approval are not obtained. Any sign so installed by
Subtenant shall be removed by Subtenant, at its expense, prior to the Expiration
Date, and Subtenant shall repair any damage or injury to the Master Premises
caused thereby.

      33. SECURITY SYSTEMS: Sublandlord shall provide Subtenant with card keys
to access the Building and the Subleased Premises. Notwithstanding the
foregoing, Subtenant acknowledges that Sublandlord is not responsible for the
security of the Subleased Premises or the protection of Subtenant's property or
Subtenant's employees, invitees or contractors, and that to the extent Subtenant
determines that security or protection services are advisable or necessary,
Subtenant shall arrange for and pay the costs of providing the same.

      34. PARKING: Subtenant shall be entitled to the non-exclusive use of
sixty-four (64) unreserved parking spaces at no additional cost to Subtenant.

      35. CONDITIONS PRECEDENT: Notwithstanding anything to the contrary in this
Sublease, this Sublease and Sublandlord's obligations hereunder are conditioned
upon Sublandlord's receipt of the written consent of Master Landlord to this
Sublease. If Sublandlord does not receive such consent on or before May 15,
2004, then either Subtenant or Sublandlord may terminate this Sublease by giving
the other party written notice thereof prior to the date such consent is
obtained, and upon such termination, Sublandlord shall return to Subtenant all
prepaid rent and the Security Deposit.

      36. AMENDMENT: This Sublease may not be amended except by the written
agreement of all parties hereto.

      37. NO DRAFTING PRESUMPTION: The parties acknowledge that this Sublease
has been agreed to by both the parties, that both Sublandlord and Subtenant have
consulted with attorneys with respect to the terms of this Sublease and that no
presumption shall be created against Sublandlord because Sublandlord drafted
this Sublease.

      38. GOVERNING LAW: This Lease shall be governed by and construed in
accordance with California law.

      39. ATTORNEY'S FEES: If either Sublandlord or Subtenant shall bring any
action or legal proceeding for the possession of the Subleased Premises, for an
alleged breach of any provision of the

                                      -12-
<PAGE>

Sublease, to recover rent, to terminate the Sublease or otherwise to enforce,
protect or establish any term or covenant of the Sublease, the prevailing party
shall be entitled to recover reasonable attorneys' fees, court costs, and expert
fees.

      40. ENTIRE AGREEMENT: This Sublease constitutes the entire agreement
between the parties with respect to the subject matter herein, and there are no
binding agreements or representations between the parties except as expressed
herein. No subsequent change or addition to this Sublease shall be binding
unless in writing and signed by the parties hereto.

      41. AUTHORITY: Subtenant represents and warrants that each individual
executing this Sublease on behalf of Subtenant is duly authorized to execute and
deliver this Sublease on behalf of Subtenant, in accordance with a duly adopted
resolution of the Board of Directors of Subtenant or in accordance with the
by-laws of Subtenant, and that this Sublease is binding upon Subtenant in
accordance with its terms. Sublandlord represents and warrants that each
individual executing this Sublease on behalf of Sublandlord is duly authorized
to execute and deliver this Sublease on behalf of Sublandlord, in accordance
with a duly adopted resolution of the Board of Directors of Sublandlord or in
accordance with the by-laws of Sublandlord, and that this Sublease is binding
upon Sublandlord in accordance with its terms.

      42. COUNTERPARTS: This Sublease may be executed in one (1) or more
counterparts each of which shall be deemed an original but all of which together
shall constitute one (1) and the same instrument. Signature copies may be
detached from the counterparts and attached to a single copy of this Sublease
physically to form one (1) document.

                                      -13-
<PAGE>

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

SUBLANDLORD:                                 SUBTENANT:

Xenoport, Inc.                               ILYPSA, Inc.
a Delaware corporation                       a Delaware corporation

By: /s/ William G. Harris                    By: /s/ Scott Rocklage
    ---------------------------------            ------------------------------
Print Name: William G. Harris                Print Name: Scott Rocklage

Title: Senior Vice President and CFO         Title: Chairman and President

Address:                                     Address

Xenoport, Inc.,                              ILYPSA, Inc.,
3410 Central Expressway                      3410 Central Expressway
Santa Clara, California                      Santa Clara, California
Attention: Chief Financial Officer           Attention: _______________________

                                      -14-