<PAGE>

                                                                    EXHIBIT 10.4

                              SUBLEASE AGREEMENT
                              ------------------

     This SUBLEASE AGREEMENT ("Sublease") is made and entered into as of August
__, 1998 by and between GENSIA SICOR INC., a Delaware corporation
("Sublandlord") and ILLUMINA, INC., a__________ corporation ("Subtenant").

     WHEREAS, GENA PROPERTY COMPANY, a California general partnership, as
landlord ("Landlord"), and Sublandlord, as tenant, are parties to a certain
Lease Agreement dated as of December 21, 1993 ("Master Lease") whereby Landlord
leased to Sublandlord two (2) buildings (the "Buildings") located at 9360 (the
"9360 Building") and 9390 (the "9390 Building") Towne Centre Drive, San Diego,
CA 92121 (collectively, the "Master Premises") as more particularly described in
the Master Lease, upon the terms and conditions contained therein.  All
capitalized terms used herein shall have the same meaning ascribed to them in
the Master Lease unless otherwise defined herein.  A copy of those portions of
the Master Lease which are applicable to this Sublease is attached hereto as
Exhibit "A" and made a part hereof.  Hereinafter, the term "Master Lease" shall
refer to only those portions of the Master Lease which are intended to be
applicable to this Sublease, as attached hereto as Exhibit "A".

     WHEREAS, Sublandlord and Subtenant are desirous of entering into a sublease
of that portion of the 9390 Building crosshatched on the demising plan annexed
hereto as Exhibit "B" and made a part hereof ("Sublease Premises") on the terms
and conditions hereafter set forth.

     NOW, THEREFORE, in consideration of the mutual covenants herein contained,
and for other good and valuable consideration, the receipt and sufficiency of
which are hereby acknowledged, the parties hereto mutually covenant and agree as
follows:

     1.  Demise.  Sublandlord hereby subleases and demises to Subtenant and
         ------
Subtenant hereby hires and subleases from Sublandlord the Sublease Premises
(which, based on Sublandlord's measurement thereof in accordance with its
customary practice, the parties stipulate contain an aggregate of [*] rentable
square feet of laboratory space located in the 9390 Building), upon and subject
to the terms, covenants and conditions hereinafter set forth. Subject to any
existing rights in favor of other subtenants within the Buildings with respect
thereto, Sublandlord shall endeavor to notify Subtenant in the event space
comprising approximately 6000 rentable square feet becomes available for
subleasing on the first floor of the 9390 Building. Subtenant shall have five
(5) business days to respond to such notification with an offer to sublease such
additional space. The foregoing does not constitute an option with respect to
any such space in favor of Subtenant and Sublandlord shall not be required to
enter into exclusive negotiations with Subtenant with respect thereto.

     2.  Lease Term.
         ----------

         (a)  Lease Term.  The term of this Sublease ("Term") shall commence on
              ----------
August 21, 1998, or (ii) the date upon which Subtenant, or any person occupying
any of the Sublease Premises with Subtenant's permission, commences business
operations from the Sublease Premises ("Sublease Commencement Date") and end,
unless sooner terminated as provided herein, on August 20, 2000 ("Sublease
Expiration Date").

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____________________
[*] CERTAIN INFORMATION ON THIS PAGE HAS BEEN OMITTED AND FILED SEPARATELY WITH
THE COMMISSION. CONFIDENTIAL TREATMENT HAS BEEN REQUESTED WITH RESPECT TO THE
OMITTED PORTIONS.

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<PAGE>

         (b)  Option to Extend.  Notwithstanding the provisions of Section
              ----------------
2(a) to the contrary and provided Subtenant is not in default under this
Sublease at the time of the exercise thereof or at the time of its occupancy
pursuant thereto, Subtenant shall have one (1) option to extend this Sublease
("Option to Extend") as to the Sublease Premises for an additional one (1) year
period. The Option to Extend shall be exercisable by Subtenant upon delivery of
prior written notice (the "Exercise Notice") thereof to Sublandlord. Each
Exercise Notice shall be given not later than ninety (90) days prior to the
then-expiration of the Term. In the event Subtenant shall exercise its Option to
Extend pursuant to the provisions set forth herein, the Term of this Sublease
shall be extended by the period applicable to such Option to Extend and the
Sublease Expiration Date shall be deemed to be the expiration date of such
extended Term of this Sublease. Such extended Term shall be on all the terms and
conditions of this Sublease, as applicable, including the rental rate applicable
to the Sublease Premises for which occupancy is so extended.

     3.  Use.  The Sublease Premises shall be used and occupied by Subtenant
         ---
solely for research, development and laboratory uses in compliance with the
Master Lease and for no other purpose.

     4.  Subrental.
         ---------

         (a)  Base Rental. Beginning with the Sublease Commencement Date, and
              -----------
thereafter during the Term of this Sublease and ending on the Sublease
Expiration Date, Subtenant shall pay to Sublandlord monthly installments of base
rent in the amount of $_______ each ("Base Rental") calculated at the monthly
rate of [*] per rentable square foot of the Premises. On each anniversary of
the Sublease Commencement Date, the Base Rental shall increase by an amount
equal to [*] of the then-existing Base Rental.

     The first monthly installment of Base Rental shall be paid by Subtenant
concurrently with the execution of this Sublease by Subtenant.  Base Rental and
additional rent shall hereinafter be collectively referred to as "Rent."

         (b)  Prorations.  If the Sublease Commencement Date is not the first
              ----------
(1st) day of a month, or if the Sublease Expiration Date is not the last day of
a month, a prorated installment of monthly Base Rental based on a thirty (30)
day month shall be paid for the fractional month during which the Term commenced
or terminated.

         (c)  Normal Operating Expenses.  Beginning with the Sublease
              -------------------------
Commencement Date and continuing to the Sublease Expiration Date, Subtenant
shall pay to Sublandlord as additional rent for this subletting the cost of all
additional expenses, costs and charges payable to Landlord or to third party
providers by Sublandlord resulting from Subtenant's use of the Sublease
Premises, which are not Normal Operating Expenses (as defined below) for the
Building and the Sublease Premises. The term "Normal Operating Expenses" shall
mean the full cost of all operating expenses (including Building maintenance,
common area expenses, insurance premiums for casualty insurance maintained by
Sublandlord with respect to the Building, but excluding any insurance coverages
for Subtenant's personal property), security and janitorial services provided by
Sublandlord and real estate taxes, applicable to the Sublease

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____________________
[*] CERTAIN INFORMATION ON THIS PAGE HAS BEEN OMITTED AND FILED SEPARATELY WITH
THE COMMISSION. CONFIDENTIAL TREATMENT HAS BEEN REQUESTED WITH RESPECT TO THE
OMITTED PORTIONS.

                                       2
<PAGE>

Premises which are allocable to Subtenant's normal and customary use of the
Sublease Premises in accordance with this Sublease. Normal Operating Expenses
shall include Subtenant's utility charges for electricity usage to the extent
not separately metered to Subtenant and shall exclude other excess or non-
standard costs, expenses or charges incurred with respect to Subtenant's use or
occupancy of the Sublease Premises which are incurred or requested by Subtenant.
Subtenant shall not be responsible for payment of any Impositions (as defined in
Paragraph 9(a) of the Master Lease) which are part of the Normal Operating
Expenses or which are not otherwise made the responsibility of Subtenant
pursuant to this Sublease.

         (d)  Payment of Rent.  Except as otherwise specifically provided in
              ---------------
this Sublease, Rent shall be payable in lawful money without demand, and without
offset, counterclaim, or setoff in monthly installments, in advance, on the
first day of each and every month during the Term of this Sublease. All of said
Rent is to be paid to Sublandlord at its office at the address set forth in
Section 13 herein, or at such other place or to such agent and at such place as
Sublandlord may designate by notice to Subtenant. Any additional rent payable on
account of items which are not payable monthly by Sublandlord to Landlord under
the Master Lease is to be paid to Sublandlord as and when such items are payable
by Sublandlord to third parties or to Landlord under the Master Lease, unless a
different time for payment is elsewhere stated herein. Upon written request
therefor, Sublandlord agrees to provide Subtenant with copies of any statements
or invoices received by Sublandlord from Landlord pursuant to the terms of the
Master Lease.

         (e)  Late Charge.  Subtenant shall pay to Sublandlord an
              -----------
administrative charge at an annual interest rate equal to the Prime Rate plus
three percent (3%) ("Interest Rate") on all amounts of Rent payable hereunder
which are not paid within three (3) business days of the date on which such
payment is due, such charge to accrue from the date upon which such amount was
due until paid.

     5.  Security Deposit.  Concurrently with the execution of this Sublease,
         ----------------
Subtenant shall deposit with Sublandlord the sum of __________________________
Dollars ($_____) ("Deposit"), which shall be held by Sublandlord as security
for the full and faithful performance by Subtenant of its covenants and
obligations under this Sublease. The Deposit is not an advance Rent deposit, an
advance payment of any other kind, or a measure of Sublandlord's damage in case
of Subtenant's default. If Subtenant defaults in the full and timely performance
of any or all of Subtenant's covenants and obligations set forth in this
Sublease, then Sublandlord may, from time to time, without waiving any other
remedy available to Sublandlord, use the Deposit, or any portion of it, to the
extent necessary to cure or remedy the default or to compensate Sublandlord for
all or a part of the damages sustained by Sublandlord resulting from Subtenant's
default. Subtenant shall immediately pay to Sublandlord within five (5) days
following demand, the amount so applied in order to restore the Deposit to its
original amount, and Subtenant's failure to immediately do so shall constitute a
default under this Sublease. If Subtenant is not in default with respect to the
covenants and obligations set forth in this Sublease at the expiration or
earlier termination of the Sublease, Sublandlord shall return the Deposit to
Subtenant after the expiration or earlier termination of this Sublease.
Sublandlord's obligations with respect to the Deposit are those of a debtor and
not a trustee. Sublandlord shall not be required to maintain the Deposit
separate and apart from Sublandlord's general or other

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funds and Sublandlord may commingle the Deposit with any of Sublandlord's
general or other funds. Subtenant shall not at any time be entitled to interest
on the Deposit.

     6.  Signage.  Subtenant shall have no right to maintain Subtenant
         -------
identification signs in any location in, on, or about the Premises other than a
listing in the lobby directory for the Building and an identification sign
located at the entry to the Sublease Premises, the size, appearance and location
of such signs to be subject to Sublandlord's prior approval. The cost of such
signs, including the installation, maintenance and removal thereof, shall be at
Subtenant's sole cost and expense. If Subtenant fails to maintain its Sublease
Premises sign, or if Subtenant fails to remove same upon the expiration or
earlier termination of this Sublease and repair any damage caused by such
removal, Sublandlord may do so at Subtenant's expense and Subtenant shall
reimburse Sublandlord for all actual costs incurred by Sublandlord to effect
such removal.

     7.  Parking.  At no additional rent or charge, Subtenant shall have the
         -------
right, during the Term of this Sublease, to use on a non-reserved basis parking
spaces in the parking facilities of the Buildings in number equal to 3.6 spaces
per 1,000 square feet of rentable area of the Sublease Premises. All such
parking privileges shall be subject to the terms and conditions set forth in the
Master Lease.

     8.  Incorporation of Terms of Master Lease.
         --------------------------------------

         (a)  This Sublease is subject and subordinate to the Master Lease.
Subject to the modifications set forth in this Sublease, the terms of the Master
Lease are incorporated herein by reference, and shall, as between Sublandlord
and Subtenant (as if they were "Landlord" and "Tenant," respectively, under the
Master Lease) constitute the terms of this Sublease except to the extent that
they are inapplicable to, inconsistent with, or modified by, the terms of this
Sublease. Notwithstanding the foregoing, to the extent provisions of the Master
Lease are unique and personal to Sublandlord's interest in the Buildings
pursuant to the Master Lease or are indicated on the attached Exhibit "A" as
intentionally omitted from the Master Lease, Subtenant shall not be required to
comply with such provisions. Provisions which are personal and unique to
Sublandlord under the Master Lease include, but are not limited to, Paragraphs
17, 18 and 19 of the Master Lease. In the event of any inconsistencies between
the terms and provisions of the Master Lease and the terms and provisions of
this Sublease, the terms and provisions of this Sublease shall govern. Subtenant
acknowledges that it has reviewed the Master Lease and is familiar with the
terms and conditions thereof.

         (b)  For the purposes of incorporation herein, the terms of the
Master Lease are subject to the following additional modifications:

              (i)  In all provisions of the Master Lease (under the terms
     thereof and without regard to modifications thereof for purposes of
     incorporation into this Sublease) requiring the approval or consent of
     Landlord, Subtenant shall be required to obtain the approval or consent of
     both Sublandlord and Landlord.

              (ii) In all provisions of the Master Lease requiring Tenant to
     submit, exhibit to, supply or provide Landlord with evidence, certificates,
     or any other matter or thing, including, without limitation, the provisions
     of Sections 10(c) and 10(f) thereof,

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<PAGE>

     Subtenant shall be required to submit, exhibit to, supply or provide, as
     the case may be, the same to both Landlord and Sublandlord. In any such
     instance, Sublandlord shall determine if such evidence, certificate or
     other matter or thing shall be satisfactory.

              (iii) In the event of any taking by eminent domain or casualty to
     the Sublease Premises such that Subtenant is deprived of the use and
     occupancy of greater than fifty percent (50%) of the Sublease Premises for
     a period in excess of ninety (90) days, Subtenant and Sublandlord shall
     each have the right to terminate this Sublease upon not less than thirty
     (30) days written notice to the other. In the event of any such taking by
     eminent domain or casualty such that Subtenant is deprived of fifty percent
     (50%) or less of the use and occupancy of the Sublease Premises, or in the
     event Subtenant elects to continue occupancy of the remaining portion of
     the Sublease Premises after the occurrence of a taking or casualty giving
     Subtenant a right to terminate this Sublease, the Rent shall be
     proportionally reduced for the portion of the Term during which Subtenant
     is prevented from using and occupying the damaged or taken portion of the
     Sublease Premises. Sublandlord shall have no obligation to restore or
     rebuild any portion of the Sublease Premises after any destruction or
     taking by eminent domain, and Subtenant shall have no rights to any portion
     of the award in any eminent domain proceeding affecting the Sublease
     Premises.

         (c)  During the Term, Subtenant shall not be required to maintain
     casualty insurance policies and coverages with respect to the Sublease
     Premises and Subtenant shall be named as an additional insured under such
     policies maintained by Sublandlord (to the extent of Subtenant's interest
     in the Sublease Premises), evidence of such coverage to be in the form of a
     certificate of insurance provided by Sublandlord to Subtenant; provided,
                                                                    ---------
     however, such policies and coverages maintained by Sublandlord with respect
     -------
     to the Buildings and the Sublease Premises shall not include coverage for
     Subtenant's personal property and Subtenant, at its sole cost and expense,
     shall maintain such policies and coverages with respect to its personal
     property as it may elect.  During the Term, Subtenant shall maintain a
     policy of comprehensive general liability insurance with respect to its
     occupancy of, and activities on, the Sublease Premises and related common
     areas, which coverage shall be subject to any required waivers of
     subrogation as are described under Paragraph 16 of the Master Lease and
     shall have a minimum policy limit of $4,000,000 and shall otherwise meet
     the requirements of the Master Lease for such insurance coverage.  All such
     policies shall name Sublandlord, Landlord and any other party required to
     be so named under the Master Lease as additional insureds thereunder and
     shall be with carriers reasonably acceptable to Sublandlord and, in all
     events, in accordance with the requirements of the Master Lease except as
     otherwise provided hereinabove.  In the event Subtenant elects to carry its
     own policies of casualty insurance with respect to the Sublease Premises,
     all such policies shall name Sublandlord as an additional insured
     thereunder.

     9.  Subtenant's Obligations.  Subtenant covenants and agrees that all
         -----------------------
obligations of Sublandlord under the Master Lease shall be done or performed by
Subtenant with respect to the Sublease Premises, except as otherwise provided by
this Sublease, and Subtenant's obligations shall run to Sublandlord and Landlord
as Sublandlord may determine to be appropriate or be required by the respective
interests of Sublandlord and Landlord. Subtenant agrees to indemnify
Sublandlord, and hold it harmless, from and against any and all claims, damages,
losses, expenses and liabilities, except for special or consequential damages
(including reasonable

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attorneys' fees), incurred as a result of the non-performance, non-observance or
non-payment of any of Sublandlord's obligations under the Master Lease which, as
a result of this Sublease, became an obligation of Subtenant. If Subtenant makes
any payment to Sublandlord pursuant to this indemnity, Subtenant shall be
subrogated to the rights of Sublandlord concerning said payment. Subtenant shall
not do, nor permit to be done, any act or thing which is, or with notice or the
passage of time would be, a default under this Sublease or the Master Lease.

     10.  Sublandlord's Obligations.  Sublandlord covenants and agrees that all
          -------------------------
obligations of Sublandlord under the Master Lease, other than those which are to
be done or performed by Subtenant, with respect to the Sublease Premises shall
be done or performed by Sublandlord. Sublandlord agrees that Subtenant shall be
entitled to receive all services and repairs to be provided by Landlord to
Sublandlord under the Master Lease with respect to the Sublease Premises.
Subtenant shall look solely to Landlord for all such services and shall not,
under any circumstances, seek nor require Sublandlord to perform any of such
services, nor shall Subtenant make any claim upon Sublandlord for any damages
which may arise by reason of Landlord's default under the Master Lease;
provided, however, Sublandlord shall provide all necessary assistance and
cooperation to Subtenant (at no material cost or liability to Sublandlord) to
enforce Sublandlord's rights under the Master Lease to compel performance by
Landlord with respect to such services or repairs to which Subtenant is
entitled. Any condition resulting from a default by Landlord shall not
constitute as between Sublandlord and Subtenant an eviction, actual or
constructive, of Subtenant and no such default shall excuse Subtenant from the
performance or observance of any of its obligations to be performed or observed
under this Sublease, or entitle Subtenant to receive any reduction in or
abatement of the Rent provided for in this Sublease unless, and to the extent,
Sublandlord is excused from performance, or entitled to a reduction or abatement
of its rental obligations to Landlord under the Master Lease also. In
furtherance of the foregoing, Subtenant does hereby waive any cause of action
and any right to bring any action against Sublandlord by reason of any act or
omission of Landlord under the Master Lease, subject to the right of assistance
and cooperation from Sublandlord described above. Sublandlord covenants and
agrees with Subtenant that Sublandlord will pay all fixed rent and additional
rent payable by Sublandlord pursuant to the Master Lease to the extent that
failure to perform the same would adversely affect Subtenant's use or occupancy
of the Sublease Premises. Sublandlord shall extend all reasonable cooperation to
Subtenant (at no material cost or liability to Sublandlord) to enable Subtenant
to receive the benefits under this Sublease, as the same are dependent upon
performance under the Master Lease.

     11.  Default by Subtenant.  In the event Subtenant shall be in default of
          --------------------
any covenant of, or shall fail to honor any obligation under, this Sublease,
Sublandlord shall have available to it against Subtenant all of the remedies
available (a) to Landlord under the Master Lease in the event of a similar
default on the part of Sublandlord thereunder or (b) at law.

     12.  Quiet Enjoyment.  So long as Subtenant pays all of the Rent due
          ---------------
hereunder and performs all of Subtenant's other obligations hereunder,
Sublandlord shall do nothing to affect Subtenant's right to peaceably and
quietly have, hold and enjoy the Sublease Premises.

     13.  Notices.  Anything contained in any provision of this Sublease to the
          -------
contrary notwithstanding, Subtenant agrees, with respect to the Sublease
Premises, to comply with and remedy any default in this Sublease or the Master
Lease which is Subtenant's obligation to cure,

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<PAGE>

within the period allowed to Sublandlord under the Master Lease, even if such
time period is shorter than the period otherwise allowed therein due to the fact
that notice of default from Sublandlord to Subtenant is given after the
corresponding notice of default from Landlord to Sublandlord. Sublandlord agrees
to forward to Subtenant, promptly upon receipt thereof by Sublandlord, a copy of
each notice of default with respect to Subtenant's obligations under this
Sublease received by Sublandlord in its capacity as Tenant under the Master
Lease. Subtenant agrees to forward to Sublandlord, promptly upon receipt
thereof, copies of any notices received by Subtenant from Landlord or from any
governmental authorities. All notices, demands and requests shall be in writing
and shall be sent either by hand delivery or by a nationally recognized
overnight courier service (e.g., Federal Express), in either case return receipt
requested, to the address of the appropriate party. Notices, demands and
requests so sent shall be deemed given when the same are received.

     Notices to Sublandlord shall be sent to the attention of:

     Gensia Sicor, Inc.
     19 Hughes
     Irvine, CA  92628
     Attn: Chief Financial Officer

     Notices to Subtenant shall be sent to the attention of:

     Illumina, Inc.
     2187 Newcastle Avenue, Suite 101
     Cardiff, CA  92007
     Attn: President

     14.  Broker.  Sublandlord and Subtenant represent and warrant to each
          ------
other that no brokers were involved in connection with the negotiation or
consummation of this Sublease other than John Burnham & Company. Each party
agrees to indemnify the other, and hold it harmless, from and against any and
all claims, damages, losses, expenses and liabilities (including reasonable
attorneys' fees) incurred by said party as a result of a breach of this
representation and warranty by the other party.

     15.  Condition of Premises.  Subtenant acknowledges that it is subleasing
the Sublease Premises "as- is" in an unfurnished condition and that Sublandlord
is not making any representation or warranty concerning the condition of the
Sublease Premises and that Sublandlord is not obligated to perform any work to
prepare the Sublease Premises for Subtenant's occupancy. Subtenant acknowledges
that it is not authorized to make or do any alterations or improvements in or to
the Sublease Premises without Sublandlord's prior written consent, which consent
may not be unreasonably withheld and which may impose additional reasonable and
customary requirements applicable to the construction and completion of such
alterations or improvements in addition to requiring Subtenant's compliance with
requirements of the Master Lease. Sublandlord shall not be deemed to be
unreasonable in withholding its consent to any alteration or improvement which
does not conform with the use requirements under this Sublease or which is
materially different from alterations or improvements customarily seen in first
class laboratory space. Subtenant further acknowledges that it must

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<PAGE>

deliver the Sublease Premises to Sublandlord on the Sublease Expiration Date in
the condition substantially the same as that on the Sublease Commencement Date
subject to ordinary wear and tear and damage due to a taking or casualty (other
than arising from Subtenant's failure to maintain the Sublease Premises or due
to the negligence or intentional misconduct of Subtenant). Sublandlord may
require Subtenant to remove, and to repair all damage to the Sublease Premises
in connection therewith, any alterations made by Subtenant during the Term, at
Subtenant's sole cost and expense, in connection with any vacation of the
Sublease Premises by Subtenant under the terms of this Sublease.

     16.  Notice to Landlord.  Section 21(b) of the Master Lease requires
          ------------------
Sublandlord to provide thirty (30) days' written notice of this Sublease to
Landlord. Sublandlord shall provide such notice promptly following the execution
and delivery of this Sublease by Sublandlord and Subtenant. In the event
Landlord asserts that Landlord's written consent to this Sublease is required
under the Master Lease and such consent (without regard to the merit of
Landlord's assertion) has not been obtained within thirty (30) days of
Sublandlord's receipt of written notice from Landlord thereof, then this
Sublease may be terminated by either party hereto upon notice to the other, and
upon such termination neither party hereto shall have any further rights against
or obligations to the other party hereto. The Sublease Term shall not be deemed
to have commenced until such 30-day notice period has run and/or, if applicable,
Landlord's consent has been obtained. If Subtenant has commenced occupation of
the Sublease Premises pursuant to a right to do so under this Sublease prior to
the expiration of such notice period or receipt of such consent, such occupancy
shall be deemed to be pursuant to a revocable license which is otherwise on all
the terms and conditions of this Sublease, including payment of Rent, from
Sublandlord to Subtenant, which license Sublandlord may revoke at any time.

     17.  Termination of the Lease.  If for any reason the term of the Master
          ------------------------
Lease shall terminate prior to the Sublease Expiration Date, this Sublease shall
automatically be terminated. Sublandlord shall not be liable to Subtenant by
reason of Subtenant's loss of occupancy in the Sublease Premises due to such
termination unless (i) such termination shall have been caused by the default of
Sublandlord under the Master Lease, and said Sublandlord default was not as a
result of a Subtenant default hereunder, or (ii) Subtenant is not given at least
one (1) calendar month's prior written notice of the effective date of a
termination of the Master Lease if such termination is the result of any
election or exercise of a right or option held by Sublandlord under the Master
Lease to effect such termination, or is the result of Sublandlord's mutual
agreement with Landlord to terminate the Master Lease outside the parameters of
the Master Lease. In the event of any voluntary termination of the Master Lease
by Sublandlord, Sublandlord shall use reasonable efforts to endeavor to preserve
Subtenant's occupancy of the Sublease Premises, substantially on the terms and
provisions of this Sublease, for the remaining Sublease Term notwithstanding
such termination. Sublandlord shall not be required to incur any cost or
liability in connection with such endeavor and shall, in no event, be liable to
Subtenant for any failure on the part of Sublandlord to secure such continued
occupancy.

     18.  Assignment and Subletting.
          -------------------------

          (a) Independent of and in addition to any provisions of the Master
Lease, including without limitation the obligation to obtain Landlord's consent
to any assignment, it is understood and agreed that Subtenant shall have no
right to sublet the Sublease Premises or any

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<PAGE>

portion thereof or any right or privilege appurtenant thereto; provided,
however, that Subtenant shall have the right to assign this Sublease or any
interest therein, and to suffer or permit any other person (other than agents,
servants or associates of the Subtenant) to occupy or use the Sublease Premises,
only upon the prior written consent of Sublandlord and Landlord, which consent
shall not be unreasonably withheld. Any assignment by Subtenant without
Sublandlord's prior written consent shall be void and shall, at the option of
Sublandlord, terminate this Sublease.

          (b)  Subtenant shall advise Sublandlord by notice of (i) Subtenant's
intent to assign this Sublease, (ii) the name of the proposed assignee and
evidence reasonably satisfactory to Sublandlord that such proposed assignee is
comparable in reputation, stature and financial condition to tenants then
leasing comparable space in comparable buildings, and (iii) the terms of the
proposed assignment. Sublandlord shall, within twenty (20) days of receipt of
such notice, and any additional information requested by Landlord concerning the
proposed assignee's financial responsibility, elect one of the following:

               (i)  Consent to such proposed assignment; or

               (ii) Refuse such consent, which refusal shall be on reasonable
          grounds.

          (c)  In the event that Sublandlord shall consent to an assignment
under the provisions of this Section 18, Subtenant shall pay Sublandlord's
reasonable processing costs and reasonable attorneys' fees incurred in giving
such consent (not to exceed $3,000 in any one instance). Notwithstanding any
permitted assignment, Subtenant shall at all times remain directly, primarily
and fully responsible and liable for all payments owed by Subtenant under the
Sublease and for compliance with all obligations under the terms, provisions and
covenants of the Sublease. If for any proposed assignment, Subtenant receives
Rent or other consideration, either initially or over the term of the
assignment, in excess of the Rent required by this Sublease, after a deduction
for the following: (a) any brokerage commission paid by Subtenant in connection
therewith and (b) any reasonable attorneys' fees in connection with preparing
and negotiating an assignment document ("Profit"), Subtenant shall pay to
Sublandlord as additional Rent, fifty percent (50%) of such Profit or other
consideration received by Subtenant within five (5) days of its receipt by
Subtenant or, in the event the assignee makes payment directly to Sublandlord,
Sublandlord shall refund fifty percent (50%) of the Profit to Subtenant after
deducting (a) and (b) above.

          (d)  Occupancy of all or part of the Sublease Premises by parent,
subsidiary, or affiliated companies or a joint venture partnership of Subtenant
shall not be deemed an assignment or subletting provided that such parent,
subsidiary or affiliated companies or a joint venture partnership were not
formed as a subterfuge to avoid the obligation of this Section 18. If Subtenant
is a corporation, unincorporated association, trust or general or limited
partnership, then the sale, assignment, transfer or hypothecation of any shares,
partnership interest, or other ownership interest of such entity or the
dissolution, merger, consolidation, or other reorganization of such entity, or
the sale, assignment, transfer or hypothecation of the assets of such entity,
shall not be deemed an assignment or sublease subject to the provisions of this
Section 18.

                                                                    TOWNE CENTRE

                                       9
<PAGE>

     19.  Limitation of Estate.  Subtenant's estate shall in all respects be
          --------------------
limited to, and be construed in a fashion consistent with, the estate granted to
Sublandlord by Landlord. Subtenant shall stand in the place of Sublandlord and
shall defend, indemnify and hold Sublandlord harmless with respect to all
covenants, warranties, obligations, and payments made by Sublandlord under or
required of Sublandlord by the Master Lease with respect to the Subleased
Premises. In the event Sublandlord is prevented from performing any of its
obligations under this Sublease by a breach by Landlord of a term of the Master
Lease, then Sublandlord's sole obligation in regard to its obligation under this
Sublease shall be to use reasonable efforts in diligently pursuing the
correction or cure by Landlord of Landlord's breach.

     20.  Environmental Condition.
          -----------------------

          (a)  Base Line Study.  Subtenant shall conduct a Phase I
               ---------------
Environmental Assessment (the "Base Line Study") with respect to the Sublease
Premises in accordance with ASTM Standard E 1257-94 which, pursuant to such
Standard, shall not include any surface or subsurface testing on the Sublease
Premises. The Base Line Study shall assess the condition of the Sublease
Premises as it exists prior to any occupancy thereof by Subtenant and shall be
completed and approved by Subtenant as soon as possible. If the Base Line Study
is not completed and approved by Subtenant on or prior to the Sublease
Commencement Date, such completion and approval shall have occurred not later
than thirty (30) days following the Sublease Commencement Date. Subtenant's
failure to approve the results of such Base Line Study within five (5) days of
its completion shall permit Subtenant to terminate this Sublease, subject,
however, to Sublandlord's right (without any obligation of exercise) to cure
such disapproved matter to Subtenant's reasonable satisfaction within a
reasonable period of time after Sublandlord's receipt of notice of such
disapproval. Subtenant shall deliver a copy of the Base Line Study to
Sublandlord upon its completion. During the Term of the Sublease, Subtenant
shall deliver to Sublandlord, upon Sublandlord's request therefor, copies of all
notices, filings and permits delivered to, or received from, regulatory and
governmental entities having jurisdiction over Subtenant's operations on the
Sublease Premises with respect to the use, storage or disposal of Hazardous
Substances and a current inventory of all Hazardous Substances used and/or
stored on the Sublease Premises.

          (b)  Vacation.  Subtenant shall also conduct an exit environmental
               --------
assessment (the "Subtenant Exit Study") substantially the same in scope as the
Base Line Study (collectively, the "Studies"). The Subtenant Exit Study shall be
conducted not earlier than fifteen (15) days prior to Subtenant's vacation of
the Sublease Premises. In the event the Subtenant Exit Study reveals
contamination not described in the Base Line Study, then, to the extent such
contamination is the result of the act or omission of Subtenant, its agents,
employees, contractors, invitees or licensees, Subtenant shall promptly
remediate or remove such contamination in its entirety. Subtenant shall maintain
the results of the Base Line Study and the Subtenant Exit Study in strict
confidence and shall not, without Sublandlord's prior written consent, which may
be withheld in its sole discretion, disclose the results thereof, or any portion
thereof to any third party, excepting Subtenant's directors, officers,
employees, representatives and consultants on a need-to-know basis, unless
Subtenant is compelled under applicable law to disclose all or any portion of
said Studies. All such Studies shall be delivered to Sublandlord.

                                                                    TOWNE CENTRE

                                       10
<PAGE>

     21.  Sublandlord Entry and Inspection Rights.  In addition to all other
          ---------------------------------------
rights under the provisions of the Master Lease incorporated into this Sublease,
Sublandlord expressly reserves the right to enter onto the Sublease Premises to
inspect the Sublease Premises during the Term, which right shall include the
right to conduct the inspections and testing in the Sublease Premises during the
Term as described in Paragraph 10 of the Master Lease. Notwithstanding the
foregoing, Sublandlord shall use reasonable, good faith efforts to provide
Subtenant with at least twenty-four hours' prior notice (which may be
telephonic) of any entry onto the Sublease Premises and to provide the names of
the individuals who will be entering onto the Sublease Premises on Sublandlord's
behalf. Entry onto the Sublease Premises for the purpose of showing such space
to prospective subtenants or third party brokers shall be limited to the last
three (3) months of the Term unless Subtenant reasonably consents to each such
entry.

     22.  Entire Agreement.  It is understood and acknowledged that there are
          ----------------
no oral agreements between the parties hereto affecting this Sublease and this
Sublease supersedes and cancels any and all previous negotiations, arrangements,
brochures, agreements and understandings, if any, between the parties hereto or
displayed by Sublandlord to Subtenant with respect to the subject matter
thereof, and none thereof shall be used to interpret or construe this Sublease.
This Sublease, and the exhibits and schedules attached hereto, contain all of
the terms, covenants, conditions, warranties and agreements of the parties
relating in any manner to the rental, use and occupancy of the Sublease Premises
and shall be considered to be the only agreements between the parties hereto and
their representatives and agents. None of the terms, covenants, conditions or
provisions of this Sublease can be modified, deleted or added to except in
writing signed by the parties hereto. All negotiations and oral agreements
acceptable to both parties have been merged into and are included herein. There
are no other representations or warranties between the parties, and all reliance
with respect to representations is based totally upon the representations and
agreements contained in this Sublease. This Sublease may be executed in multiple
counterparts.

     IN WITNESS WHEREOF, the parties have entered into this Sublease as of the
date first written above.

<TABLE>
<CAPTION>
<S>                                              <C>

                                                 SUBLANDLORD:
                                                 -----------

                                                 GENSIA SICOR INC.,
                                                 a Delaware corporation

                                                 By:   _____________________________
                                                 Its:  _____________________________

                                                 SUBTENANT:
                                                 ---------
                                                 ILLUMINA, INC.,
                                                 a ______ corporation

                                                 By:   _____________________________
                                                 Its:  _____________________________
</TABLE>
                                                                    TOWNE CENTRE

                                       11
<PAGE>

                                  EXHIBIT "A"

                              COPY OF MASTER LEASE
                              --------------------

                                   [Attached]


                                                                    TOWNE CENTRE

                                       12
<PAGE>

                                  EXHIBIT "B"

                                 DEMISING PLAN
                                 -------------

                                   [Attached]



                                                                    TOWNE CENTRE

                                       13
<PAGE>

                     AMENDMENT NO. 1 TO SUBLEASE AGREEMENT
                     -------------------------------------

     This Amendment No. 1 to Sublease Agreement (this "Amendment") is made as of
March ___, 2000 ("Effective Date") by and between SICOR INC. (formerly known as
GENSIA SICOR INC.), a Delaware corporation ("Sublandlord") and ILLUMINA, INC., a
California corporation ("Subtenant").

                                    RECITALS
                                    --------

     A.  Sublandlord and Subtenant are parties to that certain Sublease
Agreement dated as of August 24, 1998 (the "Sublease") covering certain premises
("Sublease Premises") located at 9390 Towne Centre Drive, San Diego, California
92121, as more particularly described in the Sublease. All defined terms used in
this Amendment, unless otherwise indicated herein, shall have the meanings
ascribed to them in the Sublease.

     B.  The Sublease Premises originally consisted of approximately 9,876
rentable square feet of premises on the first floor of the Building ("Existing
Space"), as more particularly described in the Sublease. Subtenant desires to
expand into approximately 5,260 rentable square feet of additional space located
on the first floor of the Building ("Expansion Space"), as more particularly
described in Exhibit A attached hereto.
             ---------

     C.  Sublandlord and Subtenant wish to hereby modify certain terms and
provisions under the Sublease and are executing this Agreement to effectuate the
modification of the same.

                                   AGREEMENT
                                   ---------

     NOW, THEREFORE, in consideration of the foregoing Recitals, the mutual
covenants hereafter set forth, and other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties hereto
agree as follows:

     1.  Amendment to Sublease. Effective as of the "Expansion Space
         ---------------------
Commencement Date" (defined below), the Sublease is hereby amended as follows:

         a.  Sublease Premises. The Sublease Premises are hereby amended to
             -----------------
mean and refer to the Existing Space and the Expansion Space (collectively, the
"Sublease Premises"), which Sublease Premises shall be deemed by the parties to
equal 15,136 rentable square feet.

         b.  Condition of Expansion Space. Subtenant acknowledges (i) that it
             ----------------------------
is subleasing the Expansion Space "as-is" in an unfurnished condition, (ii) that
Sublandlord is not making any representation or warranty concerning the
condition of the Expansion Space, and (iii) that Sublandlord is not obligated to
perform any work to prepare the Expansion Space for Subtenant's occupancy other
than to deliver the same in broom-clean condition.

         c.  Demising Plan. The Demising Plan attached to the Sublease as
             -------------
Exhibit B is hereby deleted and replaced with the Demising Plan attached hereto
---------
as Exhibit B.
   ---------

         d.  Base Rental. Section 4(a) of the Sublease is hereby amended to
             -----------
provide that, beginning as of the Expansion Space Commencement Date, and
thereafter during the Term

                                      -1-
<PAGE>

of the Sublease and ending on the Sublease Expiration Date, unless extended
pursuant to Section 2(b) of the Sublease, Subtenant shall pay to Sublandlord
monthly installments of Base Rental in the amount of Three and 50/100 Dollars
($3.50) per rentable square foot of Sublease Premises each month (i.e.,
$52,976).

         e.  Expansion Space Commencement Date. The Expansion Space
             ---------------------------------
Commencement Date shall be the earlier of (i) the date the existing subtenant of
the Expansion Space vacates such Expansion Space and Sublandlord delivers the
same to Subtenant in the condition required hereunder or (ii) the date upon
which Subtenant, or any person occupying any of said Expansion Space with
Subtenant's permission, commences business operations from the Expansion Space
("Expansion Space Commencement Date") and end on the Sublease Expiration Date.

         f.  Security Deposit. On or before the Effective Date, Subtenant shall
             ----------------
deposit with Sublandlord, in immediately available funds, an additional Deposit
equal to Three and 50/100 Dollars per rentable square foot of the Expansion
Space (i.e., $18,410). Such additional sum, along with the Deposit described in
Section 5 of the Sublease shall be collectively referred to as the "Deposit" and
shall be held on the same terms and conditions set forth in Section 5 of the
Sublease.

     2.  Effect of Amendment. Except as expressly amended under this Amendment,
         -------------------
all provisions of the Sublease shall remain in full force and effect. In the
event of any conflict between this Amendment and the Sublease, this Amendment
shall control to the extent of such conflict.

     3.  Entire Agreement. This Amendment constitutes the entire agreement
         ----------------
between the parties pertaining to the subject matter hereof, and the final,
complete and exclusive expression of the terms and conditions thereof. All prior
agreements, representations, negotiations and understandings of the parties
hereto, oral or written, express or implied, are hereby superseded and merged
herein. This Amendment may be executed in one or more counterparts, each of
which shall be deemed an original, and all of which shall constitute one and the
same binding agreement.



                  [Remainder of page intentionally left blank]

                                      -2-
<PAGE>

     IN WITNESS WHEREOF, the undersigned have executed this Amendment No. 1 to
Sublease as of the date written below:

Dated: March __, 2000

"Subtenant"                                "Sublandlord"
ILLUMINA, INC.,                            SICOR INC.,
a California corporation                   a Delaware corporation

By:  _____________________                 By:  _____________________
Name:  ___________________                 Name:  ___________________
Its:  ____________________                 Its:  ____________________

                                      -3-
<PAGE>

                                   EXHIBIT A
                                   ---------

                                Expansion Space
                                ---------------

                                   [Attached]

                                      -4-
<PAGE>

                                   EXHIBIT B
                                   ---------

                                 Demising Plan
                                 -------------

                                   [Attached]

                                      -5-