<PAGE>

                                                                 EXHIBIT 10.54
                                   SUBLEASE
                                   --------

     THIS SUBLEASE (this "Sublease") is made and entered into this _____ day of
September, 1999, by and between Raytheon Company, a Delaware corporation
("Sublessor"), and Concentric Network Corporation, a Delaware corporation
("Sublessee").

                                R E C I T A L S
                                - - - - - - - -

     A.  Tiburon Systems, Inc. ("Tiburon") entered into that certain Lease dated
May 23, 1991, an option agreement dated September 18, 1991 and amendments dated
April 7, 1992 and July 28, 1992 (collectively, "Master Lease"), with The Sobrato
Group, a California limited partnership ("Master Lessor"), for the lease of that
certain real property commonly known as 1290 Parkmoor Avenue, San Jose, CA,
consisting of approximately 66,479 square feet (the "Master Premises"). A copy
of the Master Lease is attached as Exhibit "A" hereto.

     B.  Texas Instruments Incorporated ("TI") purchased the stock of Tiburon on
September 22, 1995 and assignment of the lease to TI was approved by the Master
Lessor on October 31, 1995.

     C.  TI assigned the Master Lease to Raytheon TI Systems Inc., a wholly
owned subsidiary of Sublessor and said assignment was consented to by Master
Lessor on May 27, 1997.

  D. Raytheon TI Systems was merged into Sublessor on December 28, 1998.

     E.  Sublessor and Sublessee desire to provide for a sublease of the Master
Premises consisting of approximately 66,479 rentable square feet, (the
"Premises") pursuant to the provisions hereof.

  NOW, THEREFORE, the parties agree as follows:

     1.  SUBLEASE. Subject and pursuant to the provisions hereof, Sublessor
         --------
subleases to Sublessee, and Sublessee subleases from Sublessor, the Premises.

     2.  TERM. The term of this Sublease shall be for approximately Twenty Nine
         ----
(29) months (the "Term") commencing on the latter of November 1, 1999 or the
date on which Sublessor has delivered legal possession of the Premises to
Sublessee in the condition required hereunder (the "Commencement Date") and
ending on March 22, 2002, unless sooner terminated hereunder. If the
Commencement Date has not occurred for any reason whatsoever (other than delay
on the part of Sublessee) on or before February 28, 2000, then, Sublessee may
terminate the Sublease by written notice to Sublessor, whereupon any monies
previously paid by Sublessee to Sublessor shall be reimbursed to Sublessee or,
at Sublessee's election, the date Sublessee is otherwise obliged to commence
payment of Rent shall be delayed by one day for each day that the Commencement
Date is delayed beyond such date.

                                       1
<PAGE>

  3. RENT. During the term of this Sublease, Sublessee shall pay as rent
     ----
("Rent") for the Premises an amount equal to the monthly Rent under the Master
Lease, which at the commencement of this sublease is $84,999.99. The Rent shall
increase periodically during the term pursuant to the same terms and conditions
by which Rent shall increase under the Master Lease.

Rent shall be paid to Sublessor without demand, deduction, set-off or
counterclaim, in advance on the first day of each calendar month during the term
of this Sublease, and in the event of a partial rental month, rent shall be
prorated on the basis of the number of days in the month. Sublessee shall pay to
Sublessor upon the execution hereof the first full monthly installment of Rent.

In addition to the above Sublessee shall pay to Sublessor on a monthly basis as
Additional Rent all costs and expenses attributable to the Premises payable
under the Master Lease, as incorporated herein, including but not limited to
utilities, real estate taxes, insurance and other operating expenses which
Sublessor is required to pay under the Master Lease. In no event shall
Sublessee's obligation to pay Additional Rent exceed the amount attributable to
the Premises due and payable by Sublessor under the Master Lease. To the extent
paid by Sublessee, Sublessee shall be entitled to all credits, if any, given by
Master Lessor to Sublessor for Sublessor's overpayments of Additional Rent.

Payment of all Rent Additional Rent and other amounts due and payable from
Sublessee to Sublessor, shall paid in accordance with this Lease at the
following address, or such other address as the Sublessor shall instruct the
Sublessee in writing:

     Raytheon Company
     7700 Arlington Boulevard
     Falls Church, VA 22042-2900
     ATTN: Angie Rickett

     4.  SECURITY DEPOSIT. Sublessee shall deposit with Sublessor upon
         ----------------
Sublessee's execution hereof Eighty-five Thousand dollars ($85,000.00)
("Deposit") as security for Sublessee's faithful performance of Sublessee's
obligations hereunder. If Sublessee fails to pay rent or other charges due
hereunder, or otherwise defaults with respect to any provision of this Sublease,
in each case after expiration of applicable notice and cure periods Sublessor
may use, apply or retain all or any portion of the Deposit for the payment of
any rent or other charge in default or for the payment of any other sum to which
Sublessor may become obligated by reason of Sublessee's default, or to
compensate Sublessor for any loss or damage which Sublessor may suffer thereby
to the extent permitted by law. If Sublessor so uses or applies all or any
portion of the Deposit, Sublessee shall within ten (10) days after written
demand therefor deposit cash with Sublessor in an amount sufficient to restore
the Deposit to its full amount and Sublessee's failure to do so shall be a
material breach of this Sublease. Sublessor shall not be required to keep the
Deposit separate from its general accounts. If Sublessee performs all of
Sublessee's obligations hereunder, the Deposit, or so much thereof as has not
theretofore been applied by Sublessor, shall be returned, without payment of
interest or other increment for its use to Sublessee (or at Sublessor's option,
to the last assignee, if any, of Sublessee's interest

                                       2
<PAGE>

hereunder) at the expiration of the term hereof, and after Sublessee has vacated
the Premises. No trust relationship is created herein between Sublessor and
Sublessee with respect to the Deposit. Any deposit under the Master Lease which
may be returned by the Master Lessor shall be the property of Sublessor.

     5.  USE. Sublessee shall use and occupy the Premises only for the purposes
         ---
described in Section 3 of the Master Lease and for no other purpose without the
Sublessor's and Master Lessor's prior written consent.

     6.  MASTER LEASE.
         ------------

       6.01  COMPLIANCE WITH MASTER LEASE.
             ----------------------------

               (a) Definitions. Except as otherwise expressly provided herein,
                   -----------
during the Term and for all subsequent periods with respect to obligations
arising prior to the termination of the Sublease, Sublessee shall comply with
and perform, for the benefit of Master Lessor and Sublessor, all of the terms,
covenants, conditions and obligations of the "tenant" or "lessee" under the
Master Lease allocable or applicable to the Premises. Such terms, covenants,
conditions and obligations shall, unless the context of the Master Lease
indicates otherwise, be applied with the terms "Sublessor" and "Sublessee"
substituted respectively for "Landlord" (or "Lessor") and "Tenant" (or "Lessee")
and with the term "Premises" under the Master Lease meaning the Premises demised
hereunder. Sublessee acknowledges that it has read the attached copy of the
Master Lease and agrees that this Sublease shall be subject and subordinate to
the provisions thereof Sublessee shall not do, permit or suffer any act,
occurrence or omission which if done, permitted or suffered by Sublessor would
be (with notice, the passage of time or both) in violation of or default by the
tenant under the Master Lease, or could lead in any respect to the termination
of the Master Lease.

               (b) Consents. Sublessor shall use reasonable efforts to obtain
                   --------
from the Master Lessor any approvals or consents reasonably requested by
Sublessee and any work, services, repairs or other performance to be performed
by the Master Lessor under the Master Lease; provided, however, in the case of
legal proceedings requested by Sublessee to be instituted, Sublessee shall
indemnify, defend, protect and hold Sublessor harmless from and against any
legal fees and disbursements and all other costs, expenses, liabilities, claims
and obligations incurred by or asserted against Sublessor in connection with any
such proceedings.

       6.02  INCORPORATION BY REFERENCE.
             --------------------------

               (a) Incorporation. Subject to the provisions of Section 6.01 and
                   -------------
this Section 6.02 and this Sublease, the provisions of the Master Lease are
hereby incorporated by this reference; provided, however, that in the event that
any provision of the Master Lease shall explicitly conflict with the provisions
of this Sublease, the provisions of this Sublease shall prevail.

               (b) Deletions. Notwithstanding any provision of this Sublease
                   ---------
to the contrary, Sublessee shall not be responsible, and does not expressly
assume, the following

                                       3
<PAGE>

provisions of the Master Lease: Option to Lease document dated September 18,
1991, Article 5, 7, 37, 37(a), 40, 42 Exhibits B-F. References in the following
provisions to "Landlord" shall mean "Master Lessor": Articles 13, 28, 30, 31
(the first sentence only) and 43. The first reference to "Landlord" in the fifth
line of Section 19 shall mean Master Lessor. In addition, (a) Sublessor shall
not exercise its "recapture" right under Section 29 (i) unless Master Lessor
exercises such right under the Master Lease, (b) Sublessor shall not withhold
its consent to a sublease due to Section 29(d) unless Master Lessor withholds
its consent and (c) the limitation on liability in Section 41 shall apply to
Master Lessor only. Sublessor agrees that it will not extend the term of the
Master Lease, including any exercise of the option to extend in Section 37 of
the Master Lease.

As to the aforesaid provisions, Sublessor shall agree to perform and be
responsible for the same.

     6.03 NO ASUMPTION BY SUBLESSOR. Sublessor does not assume the obligations
          -------------------------
of the Master Lessor under the Master Lease. Sublessee acknowledges that
Sublessor's obligation to perform services, provide utilities, make repairs and
carry insurance shall be satisfied only to the extent that the Master Lessor
under the Master lease satisfies those same obligations. With respect to the
performance by Master Lessor of its obligations under the Master Lease,
Sublessor's sole obligation with respect thereto will be to request the same, on
request in writing from Sublessee, and to use reasonable efforts to obtain the
same from Landlord; provided, however, Sublessor will have no obligation to
institute legal action against Master landlord.

     6.04 PERFORMANCE DIRECTLY TO LANDLORD. At any time and on reasonable prior
          --------------------------------
notice to Sublessee, Sublessor may elect to require Sublessee to perform its
obligations under this Sublease directly to the Master Lessor, in which event
Sublessee will send to Sublessor from time to time copies of all notices and
other communications it will send to and receive from Master Lessor.

     6.05 TERMINATION OF MASER LEASE. If the Master Lease terminates under the
          --------------------------
specific provisions of the Master Lease, this Sublease will terminate, unless
the Master Lessor elects to accept this Sublease as a direct lease between the
Master Lessor and Subtenant, and the parties will be relieved from all
liabilities and obligations under this Sublease excepting obligations which have
accrued as of the date of the termination.


     7.   MODIFICATIONS TO CERTAIN INCORPORATED PROVISIONS. Notwithstanding the
          ------------------------------------------------
incorporation of the provisions of the Master Lease above provided in Paragraph
6, certain of those provisions as the same apply to this Sublease are modified
as follows:

       7.01 NOTICES. In the event that Sublessor shall receive any notice from
            -------
 Master Lessor for any reason pertaining to the Master Lease, then, within three
(3) days from the date of such receipt, Sublessor shall send a copy of such
notice to Sublessee.

                                       4
<PAGE>

          The provisions of the Master Lease regarding the giving of notices
shall apply to the Sublease, and notices to Sublessor and Sublessee shall be
sent to the following address::

     Notices To Sublessor:    Raytheon Company
                              Office of General Counsel
                              141 Spring Street
                              Lexington, MA 02421
                              Attention: Robert Moore

     Notices To Sublessee:    Concentric Network Corporation
                              1400 Parkmoor Avenue
                              San Jose, CA 95126
                              Attention: Peter Bergeron


          7.02 CONDITION OF PREMISES. Sublessee has inspected the Premises and
               ---------------------
all improvements located thereon, and has agreed to accept the Premises in an
"AS-IS" condition, in its condition existing as of the date of this Sublease
subject to all applicable municipal, county, state and federal laws, ordinances
and regulations governing and regulating the use and occupancy of the Premises,
and accepts the Sublease subject thereto and to all matters disclosed thereby,
without warranty or representation concerning the same. Sublessor hereby
acknowledges that the Premises are to be delivered to Sublessee at the
commencement of the term of the Sublease, unoccupied, and in a broom-swept
condition. Sublessee acknowledges that the taking of possession of the Premises
by Sublessee will be conclusive evidence that the Premises were in good and
satisfactory condition at the time possession was taken. Sublessee specifically
agrees that, except as specifically provided by laws in force as of the date
hereof, Sublessor has no duty to make any disclosures concerning the condition
of the Buildings or Premises and/or the fitness of the Buildings or Premises for
Sublessee's intended use.

          7.03 ASSIGNMENT, SUBLETTING AND ENCUMBRANCE. Sublessee shall not
               --------------------------------------
voluntarily or involuntarily assign, sublet, mortgage or otherwise encumber all
or any portion of its interest in this Sublease or in the Premises, without
obtaining the prior written consent of Sublessor thereto, which Sublessor may
grant or withhold in Sublessor's reasonable discretion. Any assignment,
subletting, mortgage or other encumbrance attempted by Sublessee to which
Sublessor has not consented in writing shall be null and void and of no effect.

          7.04  ALTERATIONS.
                -----------

                    (a) Alterations and Improvements By Sublessee. Sublessee
                        -----------------------------------------
shall not make any alterations, additions or improvements to the Premises
(collectively "Alterations") without obtaining the prior written consent of
Sublessor thereto, which Sublessor may grant or withhold, and to which Sublessor
may impose any conditions in Sublessor's reasonable discretion. All such
Alterations shall be constructed only after necessary permits, licenses and
approvals have been obtained from appropriate governmental agencies and all
improvements shall be constructed as to conform to all relevant codes,
regulations, and ordinances. All such Alterations shall be made at Sublessee's
sole cost and shall be diligently prosecuted to

                                       5
<PAGE>

completion. All such alterations shall be subject to all of the terms and
conditions imposed under the Master Lease. In addition to consent of the
Sublessor, consent of the Master Lessor, if required under the Master lease
shall also be a precondition to Sublessee commencing any improvements to the
Premises.

Any contractor or person making such Alterations shall first be approved in
writing by Sublessor. Upon the expiration or earlier termination of this
Sublease, Sublessor may elect to have Sublessee either (i) surrender with the
Premises any or all of such Alterations as Sublessor shall determine (except
personal property Sublessee's equipment and trade fixtures as provided in
Subsection (b) below), in which case, such Alterations shall become the property
of Sublessor, or (ii) in the event Master Lessor requires Sublessor to remove
the Alterations under the Master Lease, Sublessee shall promptly remove any or
all of such Alterations designated by Master Lessor or Sublessor to be removed,
in which case, Sublessee shall repair and restore the Premises to its original
condition as of the Commencement Date, reasonable wear and tear, casualty and
condemnation excepted. Sublessee shall permit no mechanic's or other liens to be
recorded against the Premises. Should a lien be made or filed against the
Premises Master Premises or real property on which the Premises are situated,
Sublessee at its sole cost, shall bond against or discharge said lien within 10
days after Sublessor's or Master Lessor's request to do so. Notwithstanding
anything to the contrary herein, Sublessor shall not require Sublessee to remove
or restore any Alterations unless Master Lessor requires Sublessor to remove,
restore or pay the cost of removing or restoring such Alterations.

          (b) Removal of Personal Property. All articles of personal property,
              ----------------------------
and all business and trade fixtures, machinery and equipment, cabinet work,
furniture and movable partitions, if any, owned or installed by Sublessee at its
expense in the Premises shall be and remain the property of Sublessee and may be
removed by Sublessee at any time, provided that Sublessee, at its expense, shall
repair any damage to the Premises caused by such removal or by the original
installation. Sublessor may elect to require Sublessee to remove all or any part
of the aforementioned property at the expiration or sooner termination of the
Sublease, in which event such removal shall be done at Sublessee's expense, and
Sublessee shall at its own expense repair any damage to the Premises caused by
such removal prior to the termination of this Sublease.

          (c) At the end of the Sublease Term, Sublessee shall restore the
Premises in accordance with the Terms of Article 8 of the Master Lease to the
condition required under the Master Lease as if the Sublessee were tenant under
the Master Lease.

       7.05 HOLDING OVER. If Sublessee holds over after the expiration or
            ------------
earlier termination of this Sublease, with or without the express or implied
consent of Sublessor, then at the option of Sublessor Sublessee shall become and
be only a holdover tenancy at a rent equal to the greater of(a) one hundred
fifty percent (150%) of the Rent payable by Sublessee immediately prior to such
expiration or termination or (b) one hundred and fifty (150%) percent of the
Fair Market Rental (as defined in the master lease), pro rated on a daily basis
and otherwise upon the terms, covenants and conditions herein specified.
Notwithstanding any provision to the contrary contained herein, (i) Sublessor
expressly reserves the right to require Sublessee to surrender possession of the
Premises upon the expiration of the Term or upon the

                                       6
<PAGE>

earlier termination hereof and the right to assert any remedy at law or in
equity to evict Sublessee and/or collect damages in connection with any such
holding over, and (ii) Sublessee shall indemnify, defend and hold Sublessor
harmless from and against any and all claims, demands, actions, losses, damages,
obligations, costs and expenses, including, without limitation, attorneys' fees
incurred or suffered by Sublessor by reason of Sublessee's failure to surrender
the Premises on the expiration or earlier termination of this Sublease in
accordance with the provisions of this Sublease.

     8.  ENVIRONMENTAL MATTERS.
         ---------------------

       8.01 HAZARDOUS MATERIAL. As used herein, the term "Hazardous Material"
            ------------------
means any hazardous, toxic, explosive or radioactive substance, material or
waste which is or becomes regulated by any local governmental authority, the
State of California or the United States Government, including, without
limitation, any material or substance which is (i) defined or listed as a
"hazardous waste," "extremely hazardous waste," "restricted hazardous waste,"
"hazardous substance," "hazardous material," "pollutant" or "contaminant" under
any applicable federal, state or local law or administrative code promulgated
thereunder, (ii) petroleum, (iii) asbestos, (iv) flammable explosives, (v)
radioactive materials or (vi) polychlorinated biphenyls.

       8.02 SUBLESSEE'S USE OF PREMISES. Sublessee hereby agrees, represents,
            ---------------------------
covenants, and warrants that neither it nor its employees, agents, contractors,
sublessees, assignees, licensees and invitees, shall engage in or permit to
exist anywhere in, on, under above or about the Premises any Hazardous Material
without Sublessor's prior written consent. Notwithstanding the foregoing,
Sublessee may, but in strict compliance with all Environmental Laws, use
deminimus amounts of ordinary and customary materials such as office supplies
reasonably required in the normal course of Sublessee's use of the Premises for
general office purposes, so long as Sublessee's use of such materials does not
expose the Premises or any other adjacent property to any risk of contamination
by a Hazardous Material or expose the Landlord to any liability therefore.

       8.03 INDEMNIFICATION OF SUBLESSOR. Sublessee shall indemnify, defend,
            ----------------------------
protect and hold Sublessor and its partners, officers, directors, employees,
trustees, successors, assigns, agents, servants, affiliates, representatives and
contractors (collectively, herein "Sublessor Affiliates") harmless from any and
all claims, actions, administrative proceedings (including informal
proceedings), judgments, damages, punitive and consequential damages, penalties,
fines, costs, liabilities, interest or losses, including reasonable attorneys'
fees and expenses, consultant fees, and expert fees, together with all other
costs and expenses of any kind or nature that arise during or after the term of
this Sublease directly or indirectly from, attributable to or in connection with
the presence, suspected presence, release or suspected release of any Hazardous
Material in or into the air, soil, surface, surface water or groundwater at, on,
about, under or within the Premises or the Master Premises, or any portion
thereof, by Sublessee, Sublessee Affiliates, or any invitee of Sublessee.

       8.04 MASTER LEASE. In addition to the obligations of this Section 8,
            ------------
Sublessee agrees to be bound and fulfill all environmental provisions of the
Master Lease and those provisions are hereby incorporated and restated.

                                       7
<PAGE>

          8.05 SURVIVABILITY. Each of the covenants and agreements of Sublessee
               -------------
set forth in this Section 8 shall survive the expiration or earlier termination
of this Sublease.

     9.  REPRESENTATIONS AND WARRANTIES BY SUBLESSOR. Sublessor represents and
         -------------------------------------------
warrants, to the best of Sublessor's knowledge, as follows:

          a.  Sublessor is the "Tenant" or "Lessee" under the Master Lease, and
that no portion of the Premises have been assigned or sublet to any other person
or entity other than Sublessee;

          b.  The Master Lease is in full force and effect and has not been
modified, altered or amended except as herein identified and the copy of the
Master Lease attached hereto is a true, correct and complete copy of the Master
Lease;

          c.  Sublessor has not received any written notice of default under the
Master Lease or notice of termination of the Master Lease from Master Lessor,
nor has Sublessor received any written notice of violation or condemnation from
any federal, state, municipal or local governmental authority relating to the
Premises; and

          d.  Sublessor has not received a Notice of Default from Master Lessor
that remains uncured, and to the best of the actual knowledge of Sublessor,
there exists under the Master Lease no default by either Master Lessor or
Sublessor.

     10.  INDEMNIFICATION: EXCULPATION
          ----------------------------

         10.01  NON-LIABILITY OF SUBLESSOR. Sublessor shall not be liable to
                --------------------------
Sublessee and Sublessee hereby waives and releases all claims against Sublessor
and Sublessor Affiliates (as defined in Section 8.03 above) for injury or damage
to any person or property occurring or incurred in connection with or in any way
relating to the Premises or the Master Premises. Without limiting the foregoing,
neither Sublessor nor any of the Sublessor Affiliates shall be liable for and
there shall be no abatement of Rent for (i) any damage to Sublessee's property
stored with or entrusted to Sublessor or Sublessor Affiliates, (ii) loss of or
damage to any property by theft or any other wrongful or illegal act, or (iii)
any injury or damage to persons or property resulting from fire, explosion,
falling plaster, steam, gas, electricity, water or rain which may leak from
pipes, appliances, appurtenances or plumbing works therein or from the roof,
street or sub-surface or from any other place or resulting from dampness or any
other cause whatsoever or from the acts or omissions of other sublessees,
occupants or other visitors to the Premises or the Master Premises or from any
other cause whatsoever, or (iv) any latent or other defect in the Premises or
the Master Premises. Notwithstanding anything to the contrary herein, Sublessor
shall not be released or indemnified from any losses, damages, liabilities,
claims, attorneys' fees, costs and expenses arising from the gross negligence or
willful misconduct of Sublessor or Sublessor's Affiliates, Sublessor's violation
of any law, order or regulation, or breach of Sublessor's obligations or
representations under the Sublease.

                                       8
<PAGE>

          10.02  INDEMNIFICATION OF SUBLESSOR. Sublessee shall indemnify,
                 ----------------------------
defend, protect and hold Sublessor harmless from and against any and all claims,
suits, judgments, losses, costs, obligations, damages, expenses, interest and
liabilities, including, without limitation, actual attorneys' fees and costs,
incurred or asserted in connection with (i) injury or damage to any person or
property whatsoever arising out of or in connection with this Sublease, the
Premises or Sublessee's activities in or about the Premises including, without
limitation, when such injury or damage has been caused in whole or in part by
the act, negligence, fault or omission of Sublessee, its agents, servants,
contractors, employees, representatives, licensees or invitees, or (ii) any
breach or default by Sublessee of its obligations under this Sublease. The
provisions of this Section 10.02 shall survive the expiration or earlier
termination of this Sublease.

          10.03  MASTER LESSOR DEFAULT; CONSENTS. Notwithstanding any provision
                 -------------------------------
of this Sublease to the contrary, provided Sublessor performs its obligations
hereunder, (a) Sublessor shall not be liable or responsible in any way for any
loss, damage, cost, expense, obligation or liability suffered by Sublessee by
reason or as the result of any breach, default or failure to perform by the
Master Lessor under the Master Lease and (b) whenever the consent or approval of
Sublessor and Master Lessor is required for a particular act, event or
transaction (i) any such consent or approval by Sublessor shall be subject to
the consent or approval of Master Lessor and (ii) should Master Lessor refuse to
grant such consent or approval, under all circumstances, Sublessor shall be
released from any obligation to grant its consent or approval.


     11.    INSURANCE. Sublessee shall procure and maintain, at its own cost and
            ---------
expense, such insurance as is required to be carried by Sublessor under the
Master Lease as incorporated herein, naming Sublessor, as well as Master Lessor,
in the manner required therein.

     12.    MISCELLANEOUS.
            -------------

        12.01  COUNTERPARTS. This Sublease may be executed in one or more
                ------------
counterparts by the parties hereto. All counterparts shall be construed together
and shall constitute one agreement.

        12.02  SOLE AGREEMENT. This Agreement contains all of the
               --------------
understandings of the parties and all representations made by either party to
the other are merged herein.

        12.03  MODIFICATION. This Agreement may not be modified in any respect
               ------------
except by a document in writing executed by both parties hereto or their
respective successors.

        12.04  ATTORNEYS' FEES. If any party commences an action against the
               ---------------
other, the prevailing party shall be entitled to recover from the losing party
reasonable attorneys' fees and costs.

        12.05  BINDING EFFECT. This Agreement shall be binding on and inure to
               --------------
the benefit of the parties and their respective heirs, successors and assigns.

                                       9
<PAGE>

        12.06  BROKER COMMISSION. Sublessee acknowledges that Cushman &
               -----------------
Wakefield of California and Spallino Reid Corporate Real Estate Services (the
"Brokers") are the only real estate brokers responsible for bringing about or
negotiating this Lease and are the only Brokers with whom Sublessee has dealt
with regarding this Lease. In addition to any other Rent or Additional Rent,
Sublessee agrees to pay Sublessor $5,659.71 per month for each month during the
term of this sublease. This payment is to reimburse Sublessor for the brokerage
commission amortized over the term of the Sublease at 8.5%. In the event that
the Sublease terminates before March 31, 2002, due in any part to a default by
Sublessee, Sublessee shall immediately pay, in additional to any other amounts
which may then be due and payable, a payment which equals the number of months
remaining from the date of termination to March 31, 2002 times $5,659.71.

        12.07  SUBLESSORS OBLIGATIONS. Provided Sublessee is not in default,
               ----------------------
Sublessor shall not terminate or take any actions which could give rise to the
termination of the Master Lease, amend or waive any provisions under the Master
Lease or make any elections, exercise any right or remedy or give any consent or
approval under the master Lease to the extent the foregoing would have a
material adverse effect on Sublessee's rights or obligations hereunder without
in each instance, Sublessee's prior written consent not unreasonably withheld.
Sublessor, with respect to the obligations of Master Lessor under the Master
Lease, shall use Sublessor's good faith efforts to cause Master Lessor to
perform such obligations for the benefit of Sublessee, however, nothing herein
shall require Sublessor to incur any costs or expenses. Such good faith efforts
shall include: (a) upon Sublessee's written request, promptly notifying Master
Lessor of its nonperformance under the Master Lease, and requesting that Master
Lessor perform its obligations under the Master Lease; and (b) permitting
Sublessee to commence a lawsuit or other action in Sublessor's name to obtain
the performance required from Master Lessor under the Master Lease; provided,
however, that if Sublessee commences a lawsuit or other action, Sublessee shall
pay all costs and expenses incurred in connection therewith, and Sublessee shall
indemnify Sublessor against, and hold Sublessor harmless from, all costs and
expenses incurred by Sublessor in connection therewith.

        12.08  ASSIGNMENT OF RIGHTS. To the extent assignable and at no cost and
               --------------------
expense to Sublessor, Sublessor hereby assigns to Sublessee all warranties and
indemnities made by Master Lessor to Sublessor under the Master Lease which
would reduce Sublessee's obligations hereunder, and shall cooperate with
Sublessee to enforce all such warranties and indemnities.

        12.09  SUBORDINATION. Sublessor shall use its best efforts, without
               -------------
incurring any cost or expense, to obtain from any lenders or ground Sublessor of
the Premises or the building in which the Premises are located a written
agreement providing for recognition of Sublessee's interests under the Sublease
in the event of a foreclosure of the lender's security interest or termination
of the ground lease. Further, prior to Sublessor's subordination of its
leasehold interest to a ground lease or instrument of security, Sublessor shall,
without being required to incur any costs or expenses, use reasonable efforts to
obtain from any such ground lessor or lenders such a recognition agreement. The
inability of Sublessor to obtain such recognition of the Sublessee shall not
constitute a default under this Sublease.

                                       10
<PAGE>

        12.10  AUTHORIZATION TO DIRECT SUBLEASE PAYMENTS. Sublessee shall have
               -----------------------------------------
the right to pay all rent and other sums owing by Sublessee to Sublessor
hereunder for those items which also are owed by Sublessor to Master Lessor
under the Master Lease directly to Master Lessor if Sublessor fails to make any
payment required to be made by Sublessor to Master Lessor under the Master
Lease. Sublessee shall provide to Sublessor concurrently with any payment to
Master Lessor reasonable evidence of such payment. Any sums paid directly by
Sublessee to Master Lessor in accordance with this paragraph shall be credited
toward the amounts payable by Sublessee to Sublessor under the Sublease.

        12.11  APPROVALS. Whenever the Sublease requires an approval, consent,
               ---------
designation, determination, selection or judgment by either Sublessor or
Sublessee, unless another standard is expressly set forth, such approval,
consent, designation, determination, selection or judgment and any conditions
imposed thereby shall be reasonable and shall not be unreasonably withheld or
delayed.

        12.12  MASTER LESSOR CONSENT. The Sublease and the obligations of the
               ---------------------
parties thereto are conditioned upon receipt of Master Lessor's consent to the
Sublease. In the event that Master Lessor fails to consent to the Sublease as
provided in the Master Lease, and within the time period specified under the
Master Lease, either party shall have the right to terminate the Sublease.

        12.13  CORPORATE AUTHORITY. If Tenant is a corporation, Tenant
               -------------------
represents and warrants that each individual executing this Sublease on its
behalf is duly authorized to execute and deliver this Sublease on behalf of said
corporation, in accordance with a duly adopted resolution of the Board of
Directors of said corporation or in accordance with the by-laws of said
corporation, and that this Sublease is binding upon said corporation in
accordance with its terms.



        IN WITNESS WHEREOF, the parties hereto have hereunto set their hand on
the date first above written.


SUBLESSOR:                                SUBLESSEE:


RAYTHEON COMPANY                        CONCENTRIC NETWORK CORPORATION
a Delaware corporation                    a Delaware corporation



By: /s/ Thomas D. Hyde                    By: /s/ Henry R. Nothhaft
    --------------------------                -------------------------


Name:   Thomas D. Hyde                    Name:   Henry R. Nothhaft
      ------------------------
Title:  Senior Vice President             Title:  Chairman, President & CEO
      ------------------------
        Secretary & General Counsel

                                       11
<PAGE>

                                                                          [LOGO]
                                                                         SOBRATO
                                                           DEVELOPMENT COMPANIES

                        LANDLORD'S CONSENT TO SUBLEASE

The Sobrato Group ("Landlord"), as Landlord under that certain Lease (the
"Lease") dated May 23, 1991 as amended by First Amendment to Lease dated April
7, 1992, and by Second Amendment to Lease dated July 28, 1992, by and between
Landlord and Raytheon TI Systems, Inc., as successor in interest to Texas
Instruments Inc., as successor in interest to Tiburon Ssytems, Inc. ("Tenant"),
as Tenant, subject to and specifically conditioned upon the following terms and
conditions hereby grants its consent to the Sublease dated October 25, 1999 made
by and between the Tenant, as sublandlord, and Concentric Network Corporation
("Subtenant"), as subtenant, a copy of which is attached as Exhibit B ("the
Sublease"), covering that certain premises (the "Premises") commonly known as
1290 Parkmoor Avenue, San Jose, California.

As conditions to the consent of Landlord to the Sublease, it is understood and
agreed as follows:

1. No Release. This Consent to Sublease shall in no way release the Tenant or
any person or entity claiming by, through or under Tenant, including Subtenant,
from any of its covenants, agreements, liabilities and duties under the Lease,
as the same may be amended from time to time, without respect to any provision
to the contrary in the Sublease.

2. Specific Provisions of Lease and Sublease. This Consent to Sublease
consenting to a sublease to Subtenant does not constitute approval by Landlord
of any of the provisions of the Sublease document or agreement thereto or
therewith; nor shall the same be construed to amend the Lease in any respect,
any purported modifications being solely for the purpose of setting forth the
rights and obligations as between Tenant and Subtenant, but not binding
Landlord. The Sublease is, in all respects, subject and subordinate to the
Lease, as the same may be amended. Furthermore, in the case of any conflict
between the provisions of this Consent to Sublease or the Lease and the
provisions of the Sublease, the provisions of this Consent to Sublease or (as
between Landlord and Tenant) the Lease, as the case may be, shall prevail
unaffected by the Sublease.

3. Limited Consent. This Consent to Sublease does not and shall not be construed
or implied to be a consent to any other matter for which Landlord's consent is
required under the Lease, including, without limitation, any Alterations under
the Lease.

4. Tenant's Continuing Liability. Tenant shall be liable to Landlord for any
default under the Lease, whether such default is caused by Tenant or Subtenant
or anyone claiming by or through either Tenant or Subtenant, but the foregoing
shall not be deemed to restrict or diminish any right which Landlord may have
against Subtenant pursuant to the Lease, in law or in equity for violation of
the Lease or otherwise,
<PAGE>

including, without limitation, the right to enjoin or otherwise restrain any
violation of the Lease by Subtenant.

5. Default by Tenant under the Lease. If Tenant defaults under the Lease,
Landlord may elect to receive directly from Subtenant all sums due or payable to
Tenant by Subtenant pursuant to the Sublease. Upon written notice from Landlord,
Subtenant shall thereafter pay to Landlord any and all sums due or payable under
the Sublease. In such event, Tenant shall receive from Landlord a corresponding
credit for such sums against any payments then due or thereafter becoming due
from Tenant.

6. Termination of Lease. If at any time prior to the expiration of the term of
the Sublease the Lease shall terminate or be terminated for any reason, the
Sublease shall simultaneously terminate. However, Subtenant agrees, at the
election and upon written demand of Landlord, and not otherwise, to attorn to
Landlord for the remainder of the term of the Sublease, such attornment to be
upon all of the terms and conditions of the Lease, except that the Base Rent set
forth in the Sublease shall be substituted for the Base Rent set forth in the
Lease and the computation of Additional Rent as provided in the Lease shall be
modified as set forth in the Sublease. The foregoing provisions of this
paragraph shall apply notwithstanding that, as a matter of law, the Sublease may
otherwise terminate upon the termination of the Lease and shall be self-
operative upon such written demand of the Landlord, and no further instrument
shall be required to give effect to said provisions. Upon the demand of
Landlord, however, Subtenant agrees to execute, from time to time, documents in
confirmation of the foregoing provisions of this paragraph satisfactory to
Landlord in which Subtenant shall acknowledge such attornment and shall set
forth the terms and conditions of its tenancy.

7. Sublease Profits. Landlord and Tenant agree that no consideration is due in
excess of base monthly rent pursuant to section 29 of the Lease Agreement.

8. No Waiver; No Privity. Nothing herein contained shall be deemed a waiver of
any of the Landlord's rights under the Lease. In no event, however, shall
Landlord be deemed to be in privity of contract with Subtenant or owe any
obligation or duty to Subtenant under the Lease or otherwise, any duties of
Landlord under the Lease being in favor of, for the benefit of and enforceable
solely by Tenant.

9. Notices. Subtenant agrees to promptly deliver a copy to Landlord of all
notices of default and all other notices sent to Tenant under the Sublease, and
Tenant agrees to promptly deliver a copy to Landlord of all such notices sent to
Subtenant under the Sublease. All copies of any such notices shall be delivered
personally or sent by United States registered or certified mail, postage
prepaid, return receipt requested, to Landlord.

10. Additional Provisions. Landlord and Subtenant further agree as follows:

     (a)    In the event that the Lease terminates prior to the expiration of
            the term thereof for any reason other than as a result of an event
            of default by Subtenant under the Sublease shall continue in full
            force and effect as a direct lease between Landlord and Subtenant
            upon all of the terms,

                                    Page 2
<PAGE>

            covenants and conditions of the Sublease; provided, however, that
            the rental rate thereunder shall be increased to the same per square
            foot rental rate schedule as in the Lease between Landlord and
            Subtenant dated May 15, 1998 for the building located at 1400
            Parkmoor Avenue, San Jose, California.

     (b)    Notwithstanding anything to the contrary herein, the release and
            waiver of subrogation in Section 12 of the Lease shall apply as
            between Landlord and Subtenant.

     (c)    Landlord shall not exercise any recapture right it may have under
            the Lease in the event Subtenant sublets the Premises or assigns the
            Sublease to an entity controlling, controlled by or under common
            control with Subtenant, a successor entity related to Subtenant by
            merger or consolidation, or a purchaser of substantially all of
            Subtenant's assets or stock. Landlord acknowledges that Subtenant
            intends to sublease portions of the Premises and agrees not to
            exercise any recapture right that it may have with respect to such
            subletting portions of the premises in the first year of the
            Sublease term.


Landlord
The Sobrato Group, a California limited Partnership

by   /s/ ["ILLEGIBLE"]
     ------------------
its   GP.
      -----------------

Tenant
Raytheon TI Systems, Inc., a Delaware corporation

by_____________________

its____________________

Subtenant
Concentric Network Corporation, a Delaware corporation

by   /s/ ["ILLEGIBLE"]
     --------------------

its   Corporate Secretary
      -------------------

                                    Page 3
<PAGE>

          covenants and conditions of the Sublease; provided, however, that the
          rental rate thereunder shall be increased to the same per square foot
          rental rate schedule as in the Lease between Landlord and Subtenant
          dated May 15, 1998 for the building located at 1400 Parkmoor Avenue,
          San Jose, California.

     (b)  Notwithstanding anything to the contrary herein, the release and
          waiver of subrogation in Section 12 of the Lease shall apply as
          between Landlord and Subtenant.

     (c)  Landlord shall not exercise any recapture right it may have under the
          Lease in the event Subtenant sublets the Premises or assigns the
          Sublease to an entity controlling, controlled by or under common
          control with Subtenant, a successor entity related to Subtenant by
          merger or consolidation, or a purchaser of substantially all of
          Subtenant's assets or stock. Landlord acknowledges that Subtenant
          intends to sublease portions of the Premises and agrees not to
          exercise any recapture right that it may have with respect to such
          subletting portions of the premises in the first year of the Sublease
          term.


Landlord
The Sobrato Group, a California limited Partnership

by________________________

its_______________________

Tenant Raytheon Company, successor by merger to
Raytheon TI Systems, Inc, a Delaware corporation

by /s/ Thomas D. Hyde
   -------------------------
       Thomas D. Hyde
its    Senior Vice President
       ---------------------
       Secretary and General Counsel

Subtenant
Concentric Network Corporation, a Delaware corporation

by________________________

its_______________________

                                    Page 3
<PAGE>

                           [LETTERHEAD APPEARS HERE]


                           SECOND AMENDMENT TO LEASE

     This Amendment is made this 28th day of July 1992 by and between The
     Sobrato Group having an address at 10600 N. De Anza Blvd., Suite 200,
     Cupertino, California 95014 ("Landlord") and Tiburon Systems, Inc., a
     California corporation ("Tenant").

                                   WITNESSETH

     WHEREAS Landlord and Tenant entered into a lease ("Lease") dated May 23,
     1991 for the premises ("Premises") located at 1290 Parkmoor Avenue, San
     Jose, California.

     WHEREAS effective July 28, 1992, Landlord and Tenant wish to modify the
     Lease to reflect the increase in rent by acceptance of the Tenant
     Improvement costs to Tenant in the amount of $897,219.33 totaling
     $232,429.33 more than the Tenant Interior Improvement Allowance of
     $664,790.00 as defined in paragraph 7 of the Lease; and

     WHEREAS effective July 28, 1992, Landlord and Tenant wish to document the
     elimination of the Option to Lease dated September 18, 1991 by and between
     The Sobraro Group and Tiburon Systems, Inc., for the Option Building;

     NOW, THEREFORE, in order to effect the intent of the parties as set forth
     above and for good and valuable consideration exchanged between the
     pasties, the Lease is amended effective July 28, 1992 as follows:

          1.   The initial monthly rent shall be increased by $3,486.44 per
               month to a total of $71,959.81 per month;

          2.   The Option to Lease dated September 18, 1991 is hereby eliminated
               and a rental credit of $35,000.00 given to Tenant;

          3.   Except as hereby amended, the Lease and all of the terms,
               covenants and conditions thereof are ratified and confirmed.

     IN WITNESS WHEREOF, the parties hereto have set their hands to this
     Amendment as of the day and date first above written.

       LANDLORD                     TENANT
       The Sobrato Group            Tiburon Systems, Inc.,
                                    a California corporation



BY:   /s/ ["ILLEGIBLE"]             BY:   /s/ ["ILLEGIBLE"]
      -----------------                  ------------------

ITS:  Trustee                       ITS:    President
                                          -----------------
<PAGE>

                           [LETTERHEAD APPEARS HERE]


                           FIRST AMENDMENT TO LEASE

This Amendment is made this 7/th/,day of April 1992 by and between The Sobrato
Group having an address at 10600 N. De Anza Blvd., Suite 200, Cupertino,
California 95014 ("Landlord") and Tiburon Systems, Inc., a California
corporation ("Tenant").

                                  WITNESSETH

WHEREAS Landlord and Tenant entered into a lease ("Lease") dated May 23, 1991
for the premises ("Premises") located at 1290 Parkmoor Avenue, San Jose,
California; and

WHEREAS effective March 23, 1992, Landlord and Tenant wish to modify the Lease
to document the Commencement Date based on Substantial Completion of the Tenant
Improvements which occurred on March 23, 1992;

NOW, THEREFORE, in order to effect the intent of the parties as set forth above
and for good and valuable consideration exchanged between the parties, the Lease
is amended effective March 23, 1992 as follows:

  1.   The Commencement Date of the Lease shall be March 23, 1992.

  2.   Except as hereby amended, the Lease and all of the terms, covenants and
       conditions thereof are ratified and confirmed.

IN WITNESS WHEREOF, the parries hereto have set their hands to this Amendment as
of the day and date first above written.

LANDLORD                                     TENANT
The Sobrato Group                            Tiburon Systems, Inc.,


BY: /s/ [ILLEGIBLE]^^                        BY: /s/ [ILLEGIBLE]^^
    ---------------------                       -----------------------

ITS:  Trustee                                ITS: Facilities Mgr.
                                                  ---------------------
<PAGE>

                                OPTION TO LEASE

     THIS AGREEMENT is entered as of the 18th  day of September, 1991, by and
between THE SOBRATO GROUP, a California Limited partnership (hereinafter
collectively called "Landlord"), and TIBURON SYSTEMS, INC. (hereinafter called
"Tenant"), a California corporation.

                                   Recitals:

     A.   Concurrently with the execution of this Agreement, Landlord and Tenant
are entering into a lease (" 1290 Parkmoor Lease") respecting premises (the
"Premises") located at 1290 Parkmoor, San Jose, California.

     B.   As part of the consideration for Tenant entering into the 1290
Parkmoor Lease, Landlord is willing to grant to Tenant an option to lease a
building on adjacent land on which Landlord has an option to purchase outlined
on Exhibit A (the "Property").  Such building currently does not exist, but
Landlord agrees to exercise its option to purchase the Property and construct
the building if Tenant exercises such option to lease. Such building and
Property is herein referred to as the "Option Building".

     C.   The parties now wish to document the terms of such option to lease the
Option Building.

     NOW, THEREFORE, in consideration of the execution of the 1290 Parkmoor
Lease by both parties, and in consideration of the mutual covenants set forth
below, the parties agree as follows:

     1.   Grant of Option. Landlord hereby grants to Tenant an option to lease
the Option Building (the "Option") subject to the terms and conditions set forth
in this Agreement.

     2.   Term of Option. Tenant shall be entitled to exercise the Option at any
time during the period commencing on the Commencement Date of the 1290 Parkmoor
Lease (as the Commencement Date is therein defined) and ending at 5:00 p.m. June
26, 1992. Such period shall herein be referred to as the "Option Period".

     3.   Exercise of Option. Tenant shall exercise the Option by delivery of
written notice to Landlord within the option Period of such exercise. Tenant
shall be entitled to exercise the option only if (i) Tenant has not been in
default under the terms of the 1290 Parkmoor Lease, and (ii) Tenant's financial
condition is such that an institutional lender is willing to commit to make a
non-recourse loan to Landlord in a minimum amount equal to seventy five percent
(75%) of the value of the Option Building.

     4.   Lease of the Option Building. Within thirty (30) days after Tenant's
exercise of the Option, Landlord and Tenant shall enter into a written lease of
the Option Building (the "Option Building Lease"). The Option Building Lease
shall be on the same terms as the 1290 Parkmoor Lease, except as follows:

          (a)  The Premises shall be Option Building. References in the 1290
Parkmoor Lease format shall be changed in the Option Building Lease to refer to
Option Building.

          (b)  Landlord shall provide 3.4 parking spaces per 1,000 square feet
of leasable space within the option Building.

          (c)  The term shall commence upon the date of Substantial Completion
of Tenant Improvements for the Option Building ("Commencement Date"), and end on
the tenth (10th)

                                    Page 1
<PAGE>

anniversary thereof, subject to two (2) options to extend the term for five (5)
years each.

          (d)  Rent shall be payable beginning on the Commencement Date referred
to in paragraph 2 hereinabove. The monthly rent for the Option Building shall be
the total achieved by multiplying the same per square foot rent each month as is
applicable for the 1290 Parkmoor Lease by the number of leasable square feet for
the Option Building. Monthly rent for the Option Building shall be subject to
adjustment on the same dates as the rent under the 1290 Parkmoor Lease.

          (e)  The security deposit shall be equal to the rent amount for the
Option Building for the first month of the term.

          (f)  The Tenant Improvement Allowance shall be modified to (i) reflect
a Tenant Improvement Allowance of Twenty Five Dollars ($25.00) times the number
of leasable square feet of space in the Option Building, and (ii) require
Tenant's submission to Landlord of its Working Drawings as set forth below in
this Agreement.

          (g)  A default under the 1290 Parkmoor Lease shall be deemed a default
under the Option Building Lease; and a default under the Option Building Lease
shall be deemed a default under the 1290 Parkmoor Lease.

          (h)  Tenant may elect, prior to the Commencement Date of the Option
Building Lease, to extend the term of the 1290 Parkmoor Lease so as to be co-
terminous with the Option Building Lease. If said election is made by Tenant,
the rent for the Premises during said extension period under the 1290 Parkmoor
Lease shall be at Fair Market Value (as the term is therein defined.)

     5.   Construction of Shell and Tenant Improvements.

          (a)  Within thirty (30) days after Tenant's exercise of the Option,
Landlord shall deliver to Tenant plans and specifications for construction of
the shell of Option Building (together called the "Shell Plans"). The Shell
Plans shall contemplate construction of a building containing approximately
26,000 square feet of leasable square feet in a single story building with
parking sufficient to provide at least 3.4 parking spaces per 1,000 square feet
of leasable space in the building. "Leasable Square Feet" shall include all
square footage within the Option Building measuring from the exterior surface of
exterior building walls as to each such floor, including any covered loading
docks. The Shell Plans shall contemplate construction of a building of a design
and quality comparable to the Premises and shall include a covered walkway
connecting the Premises with the Option Building.

          (b)  Within ninety (90) days after Tenant's receipt of the Shell
Plans, Tenant shall submit to Landlord Working Drawings respecting Tenant
Improvements that Tenant desires Landlord to construct in the Option Building.
The respective rights and obligations of Landlord and Tenant regarding the
Tenant Improvements shall be as otherwise set forth in the 1290 Parkmoor lease.

          (c)  Landlord shall commence construction of Option Building as soon
as reasonably possible after Tenant's exercise of the Option, and continue
diligently to construct the same until completion thereof in accordance with the
Shell Plans. All costs of construction of the shell of Option Building shall be
borne solely by Landlord. The costs included within the shell construction shall
be as set forth on Exhibit B hereto. The costs of the Tenant Improvements
constructed therein shall be borne as set forth in the 1290 Parkmoor Lease.

     6.   Failure by Landlord to Purchase the Property. Tenant acknowledges that
Landlord does not own the Property as of the date of this Agreement In the event
that Tenant

                                    Page 2
<PAGE>

exercises the Option and Landlord is unable to purchase the Property through no
fault of Landlord, the Option shall be of no further force and effect, and
Landlord shall have no further liability to Tenant hereunder.

     7.   Memorandum of Option. The parties shall record within ten (10) days
after execution of this Agreement by both parties hereto a short form memorandum
of this Agreement in form reasonably satisfactory to both parties against title
to the Property.

     8.   Notices. All notices, consents, approvals, or other communications
desired or required to be given under this Agreement to either party shall be
given in writing personally (including by courier), or by depositing the same in
the United States mail, postage prepaid, registered or certified mail, return
receipt requested, and addressed to the parties as follows:

    If to Tenant    Tiburon Systems, Inc
                    2085 Hamilton Avenue
                    San Jose, CA 95125
                    Attention: Lynn Canda

    If to Landlord: The Sobrato Group
                    10600 N. De Anza Blvd., Suite 200
                    Cupertino, CA. 95014-2031
                    Attn: John Michael Sobrato

     All notices shall be deemed received upon actual receipt thereof; or if
given by U.S. mail, then three (3) days after the posted date of mailing. Either
party may change its address by written notice to the other party in accordance
with the provisions of this paragraph.

     9.   Entire Agreement. This Agreement and the 1290 Parkmoor Lease contain
all representations and the entire understanding between the parties hereto with
respect to the subject matter hereof. Any prior correspondence, memoranda or
agreements are replaced in total by this Agreement.

     10.  Time. Time is of the essence in the performance of the parties'
respective obligations herein contained.

     11.  Attorneys' Fees. In the event any dispute between the parties hereto
should result in litigation, the prevailing party shall be reimbursed for all
reasonable costs, including, but not limited to, reasonable attorney's fees.

     12.  Severability. If any provision of this Agreement as applied to either
party or to any circumstances shall be adjudged by a court of competent
jurisdiction to be void or unenforceable for any reason, the same shall in no
way affect (to the maximum extent permissible by law) any other provision under
circumstances different from those adjudicated by the court, or the validity or
enforceability of the Agreement as a whole.

     13.  Amendments. No addition to or modification of any provisions contained
in the Agreement shall be effective unless fully set forth in writing by both
Landlord and Tenant.

     14.  Successors. The terms and provisions hereof shall be binding upon and
inure to the benefit of the successors and assigns of the parties hereto.
However, Tenant shall not assign its interest, or any portion thereof, in this
Agreement, unless such assignment is in conjunction with and effective
concurrently with an assignment of Tenant's interest in the 1290 Parkmoor Lease.
Furthermore, Landlord shall not assign its interest under this Agreement, or
delegate any obligations hereunder, without Tenant's prior written consent,
which shall not unreasonably be withheld.

                                    Page 3
<PAGE>

     15.  Quitclaim Deed. In the event Tenant does not exercise the Option
within the Option Period, then upon request to do so by Landlord, Tenant shall
execute a quitclaim deed transferring any right, rifle, or interest it may have
under this Agreement to Landlord. Such quitclaim deed shall be in form
reasonably designed to effectuate the foregoing.

     16.  Captions. The marginal headings or rifles to the paragraphs of this
Agreement are not a part of this Agreement and shall have no effect upon the
construction or interpretation of any part thereof.

     17.  Governing Law. This Agreement shall be construed and enforced in
accordance with the laws of State of California.

     IN WITNESS WHEREOF, Landlord and Tenant have executed these presents, the
day and year first above written.

LANDLORD: THE SOBRATO GROUP                  TENANT: TIBURON SYSTEMS

a California Limited Partnership             a California Corporation


BY: /s/ [ILLEGIBLE]^^                        BY: /s/ [ILLEGIBLE]^^
   ------------------------------               ---------------------------

ITS: General Partner                         ITS: _________________________
    -----------------------------

                                    Page 4
<PAGE>

                                  EXHIBIT "A"
                                   Property

                                    Page 5
<PAGE>

                                  EXHIBIT "B"
                               Shell Definition

Building Shell Definition

The Building Shell includes the following items:

1.   Site Work

     a.   Asphalt concrete paving, wheel stops, and striping.

     b.   concrete sidewalks, curbs, gutter, driveway, approaches, and planter
          walls.

     c.   Landscaping, landscape lighting, waterscape, and irrigation.

     d.   Underground utilities - water, gas, fire line, sanitary line, site
          storm drainage system and primary and secondary electrical line
          stubbed into building.

2.   Building Structure

Includes all elements necessary to provide for a completely waterproof Building
Shell including but not limited to:

     a.   Concrete foundation and slab on grade including all reinforcing steel
          and ire mesh including loading dock if applicable.

     b.   Structural steel, columns and beams.

     c.   Wood panelized gluelam roof structure with fiberglass built-up roofing
          including roof drainage plumbing.

     d.   Glass, glazing and perimeter roll up or hollow metal doors including
          normal passage hardware.

     e.   Concrete tilt up or plaster on metal stud framed exterior walls.

     f.   Exterior painting.

Other than those items delineated above, all other costs associated with
building construction shall be included as part of the interior improvement
allowance.
<PAGE>

                                                                         Annex 1

                                    (LOGO)

                                 Lease between
                  Tiburon Systems, Inc. and The Sobrato Group

<TABLE>
<S>                                                            <C>
Parties......................................................   1
Premises.....................................................   1
Use..........................................................   1
Term and Rental..............................................   1
   Rental Adjustment.........................................   1
Security Deposit.............................................   1
Late Charges.................................................   2
Construction and Possession..................................   2
Acceptance of Possession and Covenants to Surrender..........   3
Uses Prohibited..............................................   4
Alterations and Additions....................................   4
Maintenance of Premises......................................   4
Hazard Insurance.............................................   5
Taxes........................................................   5
Utilities....................................................   6
Abandonment..................................................   6
Free From Liens..............................................   6
Compliance With Governmental Regulations.....................   6
Toxic Waste and Environmental Damage.........................   6
Indemnity....................................................   7
Advertisements and Signs.....................................   7
Attorney's Fees..............................................   7
Tenant's Default.............................................   7
   Remedies..................................................   8
   Right to Re-enter.........................................   8
   Abandonment...............................................   8
   No Termination............................................   8
Surrender of Lease...........................................   9
Habitual Default.............................................   9
Landlord's Default...........................................   9
Notices......................................................   9
Entry by Landlord............................................   9
Destruction of Premises......................................   9
Assignment or Sublease.......................................  10
Condemnation.................................................  11
Effects of Conveyance........................................  11
Subordination................................................  11
Waiver.......................................................  12
Holding Over.................................................  12
Successors and Assigns.......................................  12
Estoppel Certificates........................................  12
Option to Extend the Term....................................  12
   Resolution of a Disagreement over the Fair Market Rental..  13
Options......................................................  14
Quiet Enjoyment..............................................  14
Brokers......................................................  14
Landlord's Liability.........................................  14
Authority of Parties.........................................  14
   Corporate Authority.......................................  14
   Limited Partnerships......................................  14
Transportation Demand Management Programs....................  14
Miscellaneous Provisions.....................................  14
</TABLE>

                                    Page i
<PAGE>

<TABLE>
<S>                                                                 <C>
Exhibit "A".......................................................  16
Exhibit "B".......................................................  17
Exhibit "C".......................................................  18
Exhibit "D".......................................................  19
Exhibit "E".......................................................  20
Exhibit "F".......................................................  21
</TABLE>

                                    Page ii
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1.   PARTIES:  THIS LEASE, is entered into on this 23/RD/ day of May, 1991,
between THE SOBRATO GROUP, a California Limited Partnership, and TIBURON
SYSTEMS, INC., a California Corporation, hereinafter called respectively
Landlord and Tenant.

2.   PREMISES:  Landlord hereby leases to Tenant, and Tenant hires from Landlord
those certain Premises with the appurtenances, more particularly described as
follows, to-wit:

That certain real property commonly known and designated as 1290 Parkmoor
Avenue, San Jose, California, consisting of 66,479 square feet ("Building") as
outlined in red on Exhibit "A".

3.   USE:  Tenant shall use the Premises only for the following purposes and
shall not change the use of the Premises without the prior written consent of
Landlord: Office, research, development, testing, light manufacturing, ancillary
warehouse, and related legal uses.

4.   TERM AND RENTAL: The term shall be for One Hundred Twenty (120) months,
commencing, as adjusted pursuant to paragraph 7, on the first day of April, 1992
("Commencement Date"), and ending on the 30th day of March, 2002, at the total
rent or sum, as adjusted pursuant to paragraph 4(a), of Eight Million Two
Hundred Sixteen Thousand Eight Hundred Four and 40/100 Dollars ($8,216,804.40),
payable, without deduction or offset, in monthly installments of Sixty Eight
Thousand Four Hundred Seventy Three and 37/100 Dollars ($68,473.37), due on or
before the first day of each calendar month during the term hereof. Said rental
shall be paid in lawful money of the United States of America, without offset or
deduction, and shall be paid to Landlord at such place or places as may be
designated from time to time by Landlord. Rent for any period less than a
calendar month shall be a pro rata portion of the monthly installment.

4. (a)      Rental Adjustment: Beginning thirty (30) months after the
Commencement Date, and every thirty (30) months thereafter, the then payable
monthly rent shall be subject to adjustment based on the increase, if any, in
the Consumer Price Index ("Adjustment Date"). The basis for computing the
adjustment shall be the U.S. Department of Labor, Bureau of Labor Statistic's
Consumer Price Index for All Urban Consumers, All Items, 1982-84=100, for the
San Francisco-Oakland - San Jose area, ("Index"). The Index most recently
published preceding the commencement of the Lease (or previous Adjustment Date,
as applicable), shall be considered the "Base Index". If the Index most recently
published preceding the Adjustment Date ("Comparison Index") is greater than the
Base Index, the then payable monthly rent shall be increased by multiplying the
monthly rent by a fraction, the numerator of which is the Comparison Index and
the denominator of which is the Base Index. Notwithstanding any subsequent
decrease in the Index, the increase in the CPI for any calendar year shall never
be less than four percent (4%) per year compounded annually nor more than eight
percent (8%) per year compounded annually. Landlord's calculation of the rent
escalation shall be conclusive and binding unless Tenant objects to said
calculation within a thirty (30) day period. On adjustment of the monthly rent
Landlord shall notify Tenant by letter stating the new monthly rent. If the
Index base year is changed so that it differs from 1982-84=100, the Index shall
be converted in accordance with the conversion factor published by the United
States Department of Labor, Bureau of Labor Statistics. If the Index is
discontinued or revised during the term, such other government index or
computation with which it is replaced shall be used in order to obtain
substantially the same result as would be obtained if the index had not been
discontinued or revised.

5.   SECURITY DEPOSIT:   On or before December 20th, 1991, Tenant shall deposit
with Landlord the sum of Seventy Thousand and No/100 Dollars ($70,000.00) as a
security deposit. If Tenant defaults with respect to any provisions of this
Lease, including but not limited to the provisions relating to payment of rent
or other charges. Landlord may, to the extent reasonably necessary to remedy
Tenant's default, use all or any part of said deposit for the payment of rent or
other charges in default or the payment of any other payment of any other amount
which Landlord may spend or become obligated to spend by reason of Tenant's
default or to compensate Landlord

                                    Page 1
<PAGE>

for any other loss or damage which Landlord may suffer by reason of Tenant's
default. If any portion of said deposit is so used or applied, Tenant shall,
within ten (10) days after written demand therefor, deposit cash with Landlord
in an amount sufficient to restore said deposit to the full amount hereinabove
stated and shall pay to Landlord such other sums as shall be necessary to
reimburse Landlord for any sums paid by Landlord. Said deposit shall be returned
to Tenant within thirty (30) days after the expiration of the term hereof less
any amount deducted in accordance with this paragraph, together with Landlord's
written notice itemizing the amounts and purposes for such retention. In the
event of termination of Landlord's interest in this Lease, Landlord shall
transfer said deposit to Landlord's successor in interest.

Notwithstanding the foregoing provisions of this paragraph 5, Landlord agrees
that in lieu of a cash security deposit in the amounts specified above, Tenant
may deposit an irrevocable letter of credit in favor of Landlord in the initial
sum of Seventy Thousand and No/100 Dollars ($70,000.00), in a form reasonably
acceptable to Landlord. Landlord shall be entitled to draw against the letter of
credit in accordance with the preceding paragraph, provided that Landlord
certifies to the issuer of the letter of credit under penalty of perjury that
Tenant is in default under the Lease (as defined in paragraph 22 hereof). Tenant
shall keep the letter of credit in effect during the entire Lease Term, as the
same may be extended, plus a period of eight (8) weeks thereafter. At least
sixty (60) days prior to expiration of any letter of credit, the term thereof
shall be renewed or extended. Tenant's failure to so renew or extend the letter
of credit shall be a material default of this Lease by Tenant. If Landlord draws
against the letter of credit, Tenant shall replenish the existing letter of
credit or cause a new letter of credit to be issued such that the aggregate
amount of letters of credit available to Landlord at all times during the Lease
Term is the amount of the security deposit required herein

6.   LATE CHARGES:   Tenant hereby acknowledges that late payment by Tenant to
Landlord of rent and other sums due hereunder will cause Landlord to incur costs
not contemplated by this Lease, the exact amount of which will be extremely
difficult to ascertain. Such costs include, but are not limited to,
administrative, processing, accounting charges, and late charges, which may be
imposed on Landlord by the terms of any contract, revolving credit, mortgage or
trust deed covering the Premises. Accordingly, if any installment of rent or any
other sum due from Tenant shall not be received by Landlord or Landlord's
designee within ten (10) days after written notice from Landlord that such
amount is due, Tenant shall pay to Landlord a late charge equal to five (5%)
percent of such overdue amount which shall be due and payable with the payment
then delinquent. The parties hereby agree that such late charge represents a
fair and reasonable estimate of the costs Landlord will incur by reason of late
payment by Tenant. Acceptance of such late charge by Landlord shall in no event
constitute a waiver of Tenant's default with respect to such overdue amount, nor
prevent Landlord from exercising any of the other rights and remedies granted
hereunder. In the event that a late charge is payable hereunder, whether or not
collected, for three (3) consecutive installments of rent, then rent shall
automatically become due and payable quarterly in advance, rather than monthly,
notwithstanding any provision of this Lease to the contrary.

IT IS FURTHER MUTUALLY AGREED BETWEEN THE PARTIES AS FOLLOWS:

7.   CONSTRUCTION AND POSSESSION:   The Tenant Improvements shall be constructed
by independent contractors to be employed by and under the supervision of
Landlord, as general contractor, in accordance with plans prepared by Dennis
Kobza & Associates, Inc. Landlord shall construct the Tenant Improvements in
accordance with all existing applicable municipal, local, state and federal
laws, statutes, rules, regulations and ordinances.

Landlord shall be responsible for and shall pay the cost of the Tenant
Improvements up to the amount of Six Hundred Sixty Four Thousand Seven Hundred
Ninety and No/100 Dollars ($664,790.00) ("Tenant Improvement Allowance"). In the
event the cost of Tenant Improvements is more than the Tenant Improvement
Allowance, the monthly rental under the Lease shall be increased at the rate of
Fifteen Dollars ($15.00) per month for each One Thousand Dollars ($1,000.00) of
the increase in the Tenant Improvement Allowance up to a maximum increase in the
Tenant Improvement Allowance of Three Hundred Thirty Two Thousand Three Hundred
Ninety Five and No/100 Dollars ($332,395.00). In the event the cost of Tenant
Improvements is less than

                                    Page 2
<PAGE>

the Tenant Improvement Allowance, the monthly rental under the Lease shall be
reduced at the rate of Ten Dollars ($10.00) per month for each One Thousand
Dollars ($1,000.00) of the Tenant Improvement Allowance not used. The cost of
the Tenant Improvements including fit-up of special areas shall include a fee of
Nine percent (9%) to cover all of the following: a field superintendent,
temporary on-site facilities; home office administration, supervision, and
coordination; financing fees, and construction interest. Costs in excess of said
Tenant Improvement Allowance, if any, shall be paid for by Tenant in cash within
ten (10) days after Landlord has provided Tenant with evidence that Landlord's
progress payments to sub-contractors has exceeded said Tenant Improvement
budget. All costs for Tenant Improvements shall be fully documented to and
verified by Tenant.

Landlord and Tenant have approved the preliminary working drawings ("Preliminary
Working Drawings") attached as Exhibit "B" and the preliminary budget for the
Tenant Improvement costs ("Preliminary Budget") attached as Exhibit "C". Based
on this information, Landlord shall prepare the final working drawings ("Final
Working Drawings") attached as Exhibit "D" and final budget for the Tenant
Improvement costs ("Final Budget") attached as Exhibit "E". In the event the
Final Budget exceeds the Tenant Improvement Allowance, Landlord shall have the
right to require Tenant to post a letter to credit to secure Tenant's
reimbursement obligation for the difference between the Final Budget and the
Tenant Improvement Allowance. In the event Tenant makes any changes to the Final
Working Drawings which cause Landlord's construction schedule to be delayed, the
Commencement Date shall occur one (1) day in advance of Substantial Completion
as defined below for each day of delay.

If Landlord, for any reason whatsoever, cannot deliver possession of the said
Premises to Tenant by the Commencement Date, this Lease shall not be void or
voidable, nor shall Landlord be liable to Tenant for any loss or damage
resulting therefrom; but in that event the Commencement Date and termination
date of the Lease and all other dates affected thereby shall be revised to
conform to the date of Landlord's delivery of possession. The term of the Lease
shall not commence until substantial completion of the Premises occurs.
"Substantial Completion" shall mean that: (i) all necessary governmental
approvals, permits, consents, and certificates have been obtained by or for
Landlord for the lawful construction by Landlord, and occupancy by Tenant, or
said Premises, excluding work attributable to any special fit-up requested or
required by Tenant, (ii) all of the Premises interior fully meet all of the
Final Working Drawings, excluding Tenant's special fit-up, (iii) all of the
Premises exterior substantially meets the applicable Final Working Drawings,
including paved parking areas, and (iv) said interior is in a "broom clean"
finished condition. If necessary, Landlord reserves the right to post a bond for
the uncompleted portion of the landscaping.

8.   ACCEPTANCE OF POSSESSION AND COVENANTS TO SURRENDER: By entry hereunder,
Tenant accepts the Premises as being in good and sanitary order, condition and
repair and accepts the Building and the other improvements in their present
condition, except for the "punch list" as set forth on Exhibit "F", attached
hereto. The Tenant agrees on the last day of the term hereof, or on the sooner
termination of this Lease, to surrender the Premises to Landlord in good
condition and repair, reasonable wear and tear excepted. "Good condition" shall
mean that the interior walls, floors, suspended ceilings, and carpeting within
the Premises will be cleaned to the same condition as existed at the
commencement of the Lease, normal wear and tear excepted. Tenant agrees to
remove all phone and data cabling from the suspended ceiling and repair any
damage to the ceiling caused by such cabling. Tenant shall ascertain from
Landlord within thirty (30) days before the end of the term of this Lease
whether Landlord desires to have the Premises or any part or parts thereof
restored to their condition as of the commencement of this Lease or to cause
Tenant to surrender all post-commencement alterations, additions, and
improvements in place to Landlord. If Landlord shall so desire, then Tenant
shall remove such post-commencement alterations, additions, and improvements as
Landlord may require and shall repair and restore said Premises or such part or
parts thereof before the termination of this Lease at Tenant's sole cost and
expense. Tenant on or before the end of the term or sooner termination of this
Lease, shall remove all its personal property and trade fixtures from the
Premises, and all property not so removed shall be deemed to be abandoned by
Tenant. If the Premises are not surrendered at the end of the term or sooner
termination of this Lease, Tenant shall indemnify Landlord against loss or
liability resulting from delay by Tenant in so surrendering the Premises
including, without limitation, any claims made by any succeeding tenant founded
on such delay.

                                    Page 3
<PAGE>

9.   USES PROHIBITED:   Tenant shall not commit, or suffer to be committed, any
waste upon the said Premises, or any nuisance, or other act or thing which may
disturb the quiet enjoyment of any other tenant in or around the Building or
allow any sale by auction upon the Premises, or allow the Premises to be used
for any unlawful or objectionable purpose, or place any loads upon the floor,
walls, or ceiling which endanger the structure, or use any machinery or
apparatus which will in any manner vibrate or shake the Building, or place any
harmful liquids, waste materials, or hazardous materials in the drainage system
of, or upon or in the soils surrounding the Building. No materials, supplies,
equipment, finished products or semi-finished products, raw materials or
articles of any nature or any waste materials, refuse, scrap or debris shall be
stored upon or permitted to remain on any portion of the Premises outside of the
Building proper without Landlord's prior approval, which approval may be
withheld in its sole discretion.

10.  ALTERATIONS AND ADDITIONS:  Tenant shall not make, or suffer to be made,
any alteration or addition to the said Premises, or any part thereof, without
(i) the written consent of Landlord first had and obtained, and (ii) delivering
to Landlord the proposed architectural and structural plans for all such
alterations. Any addition or alteration to the Premises, except movable
furniture and trade fixtures, shall become at once a part of the realty and
belong to Landlord. Alterations and additions which are not to be deemed as
trade fixtures shall include heating, lighting, electrical systems, air
conditioning, partitioning, carpeting, or any other installation which has
become an integral part of the Premises. After having obtained Landlord's
consent, Tenant agrees that prior to the commencement of any alterations and
additions, Tenant shall cause to be provided to Landlord, payment and
performance bonds satisfactory to Landlord, to assure timely completion of such
work and payment of all costs of such work. Tenant will at all times permit such
notices to be posted and to remain posted until the completion of work. Tenant
acknowledges Landlord's right to and hereby consents to construction of
additional building(s) on the land where the Premises are located or on adjacent
land owned by Landlord.

11.  MAINTENANCE OF PREMISES: Landlord warrants that as of the date of this
Lease, the roof and the roof membrane, exterior walls, glazing, plumbing,
electrical and HVAC systems, sidewalks and parking areas, of the Premises are in
good and sanitary order, condition, and repair. Tenant shall, at its sole cost,
keep and maintain, repair and replace, said Premises and appurtenances and every
part hereof, including but not limited to, the roof membrane, glazing,
sidewalks, parking areas, plumbing, electrical and HVAC systems, and all the
Tenant Interior Improvements in good and sanitary order, condition, and repair.
Notwithstanding the foregoing, Landlord at its sole cost and expense, shall
maintain in good condition, order, and repair, and replace as and when
necessary, the foundation, exterior walls, structure and structural members, and
roof structure of the Building. Subject to the obligations of Tenant to provide
periodic routine maintenance of the Premises in accordance with the provisions
set forth in Paragraph 11 above, Landlord shall also provide a contractor's
warranty on the Tenant Improvements for a period of one (1) year from the
Commencement Date. Tenant shall provide Landlord with a copy of a service
contract between Tenant and a licensed air-conditioning and heating contractor
which contract shall provide for bimonthly maintenance of all air conditioning
and heating equipment at the Premises. Tenant shall pay the cost of all air-
conditioning and heating equipment repairs or replacements which are either
excluded from such service contract or any existing equipment warranties. Tenant
shall be responsible for the preventive maintenance of the membrane of the roof,
which responsibility shall be deemed properly discharged if (i) Tenant contracts
with a licensed roof contractor who is reasonably satisfactory to both Tenant
and Landlord, at Tenant's sole cost, to inspect the roof membrane at least every
six (6) months, with the first inspection due the sixth (6th) month after the
Commencement Date, and (ii) Tenant performs, at Tenant's sole cost, all
preventive maintenance recommendations made by such contractor within a
reasonable time after such recommendations are made. Such preventive maintenance
might include acts such as clearing storm gutters and drains, removing debris
from the roof membrane, trimming trees overhanging the roof membrane, applying
coating materials to seal roof penetrations, repairing blisters, and other
routine measures. Tenant shall provide to Landlord a copy of such preventive
maintenance contract and paid invoices for the recommended work. All vinyl wall
surfaces and floor tile are to be maintained in an as good a condition as when
Tenant took possession free of holes, gouges, or defacements. Tenant agrees to
limit attachments to vinyl wall surfaces exclusively to V-joints. Tenant agrees
to water, maintain and replace, when necessary, any shrubbery and landscaping.

                                    Page 4
<PAGE>

Notwithstanding anything to the contrary in this Lease, if Tenant's maintenance
or repair obligations as set forth in this Lease would require Tenant to perform
or pay for any item which (i) would be properly be capitalized under generally
accepted accounting principles, and (ii) costs in excess of $25,000.00 per
occurrence, then Landlord shall perform such repair or make such replacement
promptly following written notice by Tenant of the need therefor and the cost of
such item or improvement shall be allocated as follows: Tenant shall pay to
Landlord within ten (10) days after receipt of Landlord's written demand and
supporting documentation a proportion of the cost equal to the actual cost of
such improvement or item as paid by landlord to third parties times a fraction,
the numerator of which is the number of months remaining in the initial Lease
Term, and the denominator of which is the useful life of the improvement in
months, and Landlord shall pay the balance of such cost.

12.  HAZARD INSURANCE:  Tenant shall not use, or permit said Premises, or any
part thereof, to be used, for any purpose other than that for which the said
Premises am hereby leased; and no use shall be made or permitted to be made of
the said Premises, nor acts done, which will cause an increase in premiums or a
cancellation of any insurance policy covering said Building, or any part
thereof, nor shall Tenant sell or permit to be kept, used or sold, in or about
said Premises, any article which may be prohibited by the standard form of fire
insurance policies. Tenant shall, at its sole cost and expense, comply with any
and all requirements, pertaining to said Premises, of any insurance organization
or company, necessary for the maintenance of reasonable fire and public
liability insurance, covering said Building and appurtenances. The Landlord
agrees to purchase and keep in force fire, earthquake (at Landlord's election),
and extended coverage insurance covering the Premises in amounts not to exceed
the actual insurable value of the Building as determined by Landlord's insurance
company's appraisers. The Tenant agrees to pay to the Landlord as additional
rent, on demand, the full cost of said insurance as evidenced by insurance
billings to the Landlord, and in the event of damage covered by said insurance,
the amount of any deductible under such policy. Tenant shall have the  to
specify the amount of any insurance policy to be carried by Landlord under this
Lease and shall reimburse Landlord for the premiums payable with respect to
insurance policies for which Tenant is responsible containing the deductible so
specified by Tenant or on insurance policies for which Tenant fails to specify a
deductible amount within ten (10) days following Landlord's written demand for
such deductible specification. In the event of damage to the Premises covered by
Landlord's "all risk" casualty policy (and not caused by the negligence or
willful misconduct of Landlord or Landlord's employees, agents, contractors,
subcontractors, or invitees), Tenant shall pay the amount of any deductible
under such policy if this Lease is not terminated in connection with such
casualty as provided in paragraph 28. Payment shall be due to Landlord within
ten (10) days after written invoice to Tenant. Notwithstanding the foregoing,
Tenant's obligation to pay for the cost of any earthquake insurance premiums
shall be limited to an amount equal or less than four (4) times the cost of the
fire and extended coverage premiums.

In addition, Tenant agrees to insure its personal property, additions,
alterations, and improvements for their full replacement value (without
depreciation) and to obtain worker's compensation and public liability and
property damage insurance for occurrences within the Premises of $5,000,000.00
combined single limit for bodily injury and property damage. Tenant shall name
Landlord and Landlord's lender as an additional insured, shall deliver a copy of
the policies and renewal certificate to Landlord. All such policies shall
provide for thirty (30) days' prior written notice to Landlord of any
cancellation or termination. Notwithstanding the above, Landlord retains the
right to have Tenant provide other forms of insurance which may be reasonably
required to cover future risks.

It is understood and agreed that Tenant's obligation under this paragraph will
be prorated to reflect the commencement and termination dates of this Lease.
Landlord and Tenant hereby waive any rights each may have against the other on
account of any loss or damage occasioned to the Landlord or the Tenant as the
case may be, or to the Premises or its contents, and which may arise from any
risk covered by their respective insurance policies, as set forth above. The
parties shall use their best efforts to obtain from their respective insurance
companies a waiver of any right of subrogation which said insurance company may
have against the Landlord or the Tenant, as the case may be.

13.  TAXES: Tenant shall be liable for all taxes levied against personal
property and trade or business fixtures, and agrees to pay, as additional
rental, all real estate taxes and special

Page 5
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assessment installments levied on the Premises, upon the occupancy of the
Premises and including any substitute or additional charges which may be imposed
during, or applicable to the Lease term including real estate tax increases due
to a sale or other transfer of the Premises, as they appear on the City and
County tax bills during the Lease term, and as they be, come due. It is
understood and agreed that Tenant's obligation under this paragraph will be
prorated to reflect the commencement and termination dates of this Lease. In any
time during the term of this Lease a tax, excise on rents, business license tax,
or any other tax, however described, is levied or assessed against Landlord, as
a substitute or addition in whole or in part for taxes assessed or imposed on
land or Buildings, Tenant shall pay and discharge his pro rata share of such tax
or excise on rents or other tax before it becomes delinquent, except that this
provision is not intended to cover income taxes, inheritance, gift or estate tax
imposed upon the Landlord. In the event that a tax is placed, levied, or
assessed against Landlord and the taxing authority takes the position that
Tenant cannot pay and discharge his pro rata share of such tax on behalf of the
Landlord, then at the sole election of the Landlord, the Landlord may increase
the rental charged hereunder by the exact amount of such tax.

14.  UTILITIES: Tenant shall pay directly to the providing utility all water,
gas, heat, light, power, telephone and other utilities supplied to the Premises.
Landlord shall not be liable for a loss of or injury to property, however
occurring, through or in connection with or incidental to furnishing or failure
to furnish any of utilities to the Premises and Tenant shall not be entitled to
abatement or reduction of any portion of the rent so long as any failure to
provide and furnish the utilities to the Premises due to any cause beyond the
Landlord's reasonable control.

15.  ABANDONMENT: Tenant shall not vacate or abandon the Premises at any time
during the term; and if Tenant shall abandon, vacate or surrender said Premises,
or be dispossessed by process of law, or otherwise, any personal property
belonging to Tenant and left on the Premises shall be deemed to be abandoned, at
the option of Landlord, except such property as may be mortgaged to Landlord.

16.  FREE FROM LIENS: Tenant shall keep the Premises and the Building free from
any liens arising out of any work performed, materials furnished, or obligations
incurred by Tenant.

17.  COMPLIANCE WITH GOVERNMENTAL REGULATIONS: Tenant shall, at its sole cost
and expense, comply with all of the requirements of all Municipal, State and
Federal authorities now in force, or which may hereafter be in force, pertaining
to the said Premises, and shall faithfully observe in the uses of the Premises
all Municipal ordinances and State and Federal statutes now in force or which
may hereafter be in force. The judgement of any court of competent jurisdiction,
or the admission of Tenant in any action or proceeding against Tenant, whether
Landlord be a party thereto or not, that Tenant has violated any such ordinance
or statute in the use of the Premises, shall be conclusive of that fact as
between Landlord and Tenant.

18.  TOXIC WASTE AND ENVIRONMENTAL DAMAGE:   Without the prior written consent
of Landlord, Tenant shall not bring, use, or permit upon the Premises, or
generate, emit, or dispose from the Premises any chemicals, toxic or hazardous
gaseous, liquid or solid materials or waste, including without limitation,
material or substance having characteristics of ignitability, corrosivity,
reactivity, or toxicity or substances or materials which are listed on any of
the Environmental Protection Agency's lists of hazardous wastes or which am
identified in Sections 66680 through 66685 of Title 22 of the California
Administrative Code as the same may be amended from time to time ("Hazardous
Materials"). Tenant shall comply, at its sole cost, with all laws pertaining to,
and shall indemnify and hold Landlord harmless from any claims, liabilities,
costs or expenses incurred or suffered by Landlord arising from such bringing,
using, permitting, generating, emitting or disposing of Hazardous Materials.
Tenant's indemnification and hold harmless obligations include, without
limitation, (i) claims, liability, costs or expenses resulting from or based
upon administrative, judicial (civil or criminal) or other action, legal or
equitable, brought by any private or public person under common law or under the
Comprehensive Environmental Response. Compensation and Liability Act of 1980
("CERCLA"), the Resource Conservation and Recovery Act of 1980 ("RCRA") or any
other Federal, State, County or Municipal law, ordinance or regulation, (ii)
claims, liabilities, costs or expenses pertaining to the identification,
monitoring, cleanup, containment, or removal of Hazardous Materials from soils,
riverbeds or aquifers including the provision of an alternative public drinking
water source, and (iii) all costs of defending such claims.

                                    Page 6
<PAGE>

In order to obtain consent, Tenant shall deliver to Landlord its written
proposal describing the toxic material to be brought onto the Premises, measures
to be taken for storage and disposal thereof, safety measures to be employed to
prevent pollution of the air, ground, surface and ground water. Landlord's
approval may be withheld in its reasonable judgement. In the event Landlord
consents to Tenant's use of Hazardous Materials on the Premises. Tenant
represents and warrants that Tenant will (i) adhere to all reporting and
inspection requirements imposed by Federal, State, County or Municipal laws,
ordinances or regulations and will provide Landlord a copy of any such reports
or agency inspections, (ii) obtain and provide Landlord copies of all necessary
permits required for the use and handling Hazardous Materials on the Premises,
(iii) enforce Hazardous Materials handling and disposal practices consistent
with industry standards, and (iv) properly close the facility with regard to
Hazardous Materials including the removal or decontamination of any process
piping, mechanical ducting,  storage tanks, containers, or trenches which have
come into contact with Hazardous Materials and obtain a closure certificate from
the local administering agency. Tenant shall have the right to approve the
selection of Landlord's attorneys and the attorney's fee schedule prior to the
engagement by Landlord of any attorneys pursuant to this paragraph 18.

19.  INDEMNITY:   As a material part of the consideration to be rendered to
Landlord, Tenant hereby waives all claims against Landlord for damages to goods,
wares and merchandise, and all other personal property in, upon or about said
Premises and for injuries to persons in or about said Premises, from any cause
arising at any time except due to the negligence or willful misconduct of
Landlord, and Tenant will hold Landlord exempt and harmless from any damage or
injury to any person, or to the goods, wares and merchandise and all other
personal property of any person, arising from the use of the Premises by Tenant,
or from the failure of Tenant to keep the Premises in good condition and repair,
as herein provided. Further, in the event Landlord is made party to any
litigation due to the acts or omission of Tenant, Tenant will indemnify and hold
Landlord harmless from any such claim or liability including Landlord's costs
and expenses and reasonable attorney's fees incurred in defending such claims.
Tenant shall have the right to approve the selection of Landlord's attorneys and
the attorney's fee schedule prior to the engagement by Landlord of any attorneys
pursuant to this paragraph 19.

20.  ADVERTISEMENTS AND SIGNS:    Tenant will not place or permit to be placed,
in, upon or about the said Premises any unusual or extraordinary signs, or any
signs not approved by the city or other governing authority. The Tenant will not
place, or permit to be placed, upon the Premises, any signs, advertisements or
notices without the written consent of the Landlord as to type, size, design,
lettering, coloring and location, and such consent will not be unreasonably
withheld. Any sign so placed on the Premises shall be so placed upon the
understanding and agreement that Tenant will remove same at the termination of
the Lease and repair any damage or injury to the Premises caused thereby, and if
not so removed by Tenant then Landlord may have same so removed at Tenant's
expense.

21.  ATTORNEY'S FEES:    In case suit should be brought for the possession of
the Premises, for the recovery of any sum due hereunder, or because of the
breach of any other covenant herein, the losing party shall pay to the
prevailing party a reasonable attorney's fee as part of its costs which shall be
deemed to have accrued on the commencement of such action.

22.  TENANT'S DEFAULT:   The occurrence of any of the following shall
constitute a material default and breach of this Lease by Tenant: a) Any failure
by Tenant to pay the rental or to make any other payment required to be made by
Tenant hereunder, where such failure continues for ten (10) days after written
notice thereof by Landlord to Tenant; b) The abandonment or vacation of the
Premises by Tenant; c) A failure by Tenant to observe and perform any other
provision of this Lease to be observed or performed by Tenant, where such
failure continues for thirty (30) days after written notice thereof by Landlord
to Tenant; provided, however, that if the nature of such default is such that
the same cannot reasonably be cured within such thirty (30) day period Tenant
shall not be deemed to be in default if Tenant shall within such period commence
such cure and thereafter diligently prosecute the same to completion; d) The
making by Tenant of any general assignment for the benefit of creditors; the
filing by or against Tenant of a petition to have Tenant adjudged a bankrupt or
of a petition for reorganization or arrangement under any law relating to
bankruptcy (unless, in the case era petition fried against Tenant, the same is
dismissed after the filing); the appointment of a trustee or receiver to take
possession of substantially all of Tenant's assets located at the Premises or of
Tenant's interest in this Lease, where possession is

                                    Page 7
<PAGE>

not restored to Tenant within thirty (30) days; or the attachment, execution or
other judicial seizure of substantially all of Tenant's assets located at the
Premises or of Tenant's interest in this Lease, where such seizure is not
discharged within thirty (30) days. The notice requirements set forth herein are
in lieu of and not in addition to the notices required by California Code of
Civil Procedure Section 1161.

22.(a)   Remedies:   In the event of any such default by Tenant, then in
addition to any other remedies available to Landlord at law or in equity,
Landlord shall have the immediate option to terminate this Lease and all rights
of Tenant hereunder by giving written notice of such intention to terminate. In
the event Landlord shall elect to so terminate this Lease, Landlord may recover
from Tenant: a) the worth at the time of award of any unpaid rent which had been
earned at the time of such termination; plus b) the worth at the time of award
of the amount by which the unpaid rent would have been earned after termination
until the rime of award exceeds the amount of such rental loss Tenant proven
could have been reasonably avoided; plus c) the worth at the time of award of
the amount by which the unpaid rent for the balance of the term after the time
of award exceeds the amount of such rental loss that Tenant proves could Be
reasonably avoided; plus d) any other amount necessary to compensate Landlord
for all the detriment proximately caused by Tenant's failure to perform his
obligations under this Lease or which in the ordinary come of things would be
likely to result therefrom, and c) at Landlord's election, such other amounts in
addition to or in lieu of the foregoing as may be permitted from time to time by
applicable California law. The term "rent", as used herein, shall be deemed to
be and to mean the minimum monthly installments of rent and all other sums
required to be paid by Tenant pursuant to the terms of this Lease, all other
such sums being deemed to be additional rent due hereunder. As used in (a) and
(b) above, the "worth at the time of award" is computed by allowing interest at
the rate of the discount rate of the Federal Reserve Bank of San Francisco plus
five (5%) percent per annum. As used in (c) above, "worth at the time of award
is computed by discounting such amount at the discount rate of the Federal
Reserve Bank of San Francisco at the time of award plus one (1%) percent.

22.(b)   Right to Re-enter:   In the event of any such default by Tenant,
Landlord shall also have the right, with or without terminating this Lease, to
re-enter the Premises and remove all persons and property from the Premises;
such property may be removed and stored in a public warehouse or elsewhere at
the cost of and for the account of Tenant.

22.(c)   Abandonment:   In the event of the vacation or abandonment of the
Promises by Tenant or in the event that Landlord shall elect to re-enter as
provided in paragraph 22.(b) above or shall take possession of the Premises
pursuant to legal proceeding or pursuant to any notice provided by law, then if
Landlord does not elect to terminate this Lease as provided in paragraph 22.(a)
above, then the provisions of California Civil Coda Section 1951.4, as amended
from time to time, shall apply and Landlord may from time to time, without
terminating this Lease, either recover all rental as it becomes due or relet the
Promises or any part thereof for such term or terms and at such rental or
rentals and upon such other terms and conditions as Landlord in its sole
discretion may deem advisable with the right to make alterations and repairs to
the Premises. In the event that Landlord shall elect to so relet, then rentals
received by Landlord from such reletting shall be applied: first, to the payment
of any indebtedness other than rent due hereunder from Tenant to Landlord;
second, to the payment of any cost of such reletting; third, to the payment of
the cost of any alterations and repairs to the Premises; fourth, to the payment
of rent due and unpaid hereunder; and the residue, if any, shall be held by
Landlord and applied in payment of future rent as same may become due and
payable hereunder. Should that portion of such rentals received from such
reletting during any month, which is applied by payment of rent hereunder, be
less than the rent payable during that month by Tenant hereunder, then Tenant
shall pay such deficiency to Landlord immediately upon demand therefor by
Landlord. Such deficiency shall be calculated and paid monthly. Tenant shall
also pay to Landlord, as soon as ascertained, any costs and expenses incurred by
Landlord in such reletting or in making such alterations and repairs not covered
by the rentals received from such reletting.

22.(d)   No Termination:   No re-entry or taking possession of the Premises by
Landlord pursuant to 22.(a) or 22.(c) of this Article 22 shall be construed as
an election to terminate this Lease unless a written notice of such intention be
given to Tenant or unless the termination thereof be decreed by a court of
competent jurisdiction. Notwithstanding any reletting without termination by
Landlord because of any default by Tenant, Landlord may at any time after such
reletting elect to terminate this Lease for any such default.

                                    Page 8
<PAGE>

23.  SURRENDER OF LEASE:   The voluntary or other surrender of this Lease by
Tenant, or a mutual cancellation thereof, shall not automatically effect a
merger of the Lease with Landlord's ownership of the Building or Premises.
Instead, at the option of Landlord, Tenant's surrender may terminate all or any
existing sublease or subtenancies, or may operate as an assignment to Landlord
of any or all such subleases or subtenancies, thereby creating a direct
Landlord-Tenant relationship between Landlord and any subtenants.

24.  HABITUAL DEFAULT:   Notwithstanding anything to the contrary contained in
paragraph 22, 22 (a) (b) (c) and (d), the parties hereto agree that if the
Tenant shall have defaulted in the performance of any (but not necessarily the
same) term or condition of this Lease for three or more times during any twelve
month period during the term hereof, then such conduct shall, at the election of
the Landlord, represent a separate event of default which cannot be cured by the
Tenant. Tenant acknowledges that the purpose of this provision is to prevent
repetitive defaults by the Tenant under the Lease, which work a hardship upon
the Landlord, and deprive the Landlord of the timely performance by the Tenant
hereunder.

25.  LANDLORD'S DEFAULT:   In the event of Landlord's failure to perform any of
its covenants or agreements under this Lease, Tenant shall give Landlord written
notice of such failure and shall give Landlord thirty (30) days or such other
reasonable opportunity to cure such failure prior to any claim for breach or for
damages resulting from such failure.

26.  NOTICES:   All notices required to be given under this Lease shall be sent
by U.S. certified mail, return receipt requested, or by personal delivery
addressed to the party to be notified at the address for such party specified in
paragraph 1 of this Lease, or to such other place as the party to be notified
may from time to time designate by at least fifteen (15) days notice to the
notifying party.

27.  ENTRY BY LANDLORD:   Tenant shall permit Landlord and his agents to enter
into and upon said Premises at all reasonable times subject to any security
regulations of Tenant for the purpose of inspecting the same or for the purpose
of maintaining the Premises or for the purpose of making repairs, alterations or
additions to any other portion of said Premises or for the purpose of erecting
additional building(s) and improvements on the land where the Premises are
situated, or on adjacent land owned by Landlord, including the erection and
maintenance of such scaffolding, canopies, fences and props as may be required
without any rebate of rent or without any liability to Tenant for any loss of
occupation or quiet enjoyment of the Premises thereby occasioned; and Tenant
shall permit Landlord and his agents, at any time within one hundred eighty
(180) days prior to the expiration of this Lease, to place upon the Premises any
"For Sale" or "For Lease" signs and exhibit the Premises to prospective tenants
at reasonable hours.

28.  DESTRUCTION OF PREMISES:   In the event of a partial destruction of the
Premises by an insured causality during the term from any cause, Landlord shall
forthwith repair the same, provided such repairs can be made within one hundred
eighty (180) days from the date of receipt of all necessary governmental
approvals necessary under the laws and regulations of State, Federal, County or
Municipal authorities, such partial destruction shall in no way annul or void
this Lease, except that Tenant shall be entitled to a proportionate reduction of
rent while such repairs are being made, such proportionate reduction to be based
upon the extent to which the making of such repairs shall interfere with the
business carried on by Tenant in the Premises, in the reasonable judgement of
Landlord. For purposes of this paragraph "partial destruction" shall mean
destruction of no greater than one-third (1/3) of the replacement cost of the
Premises, including the replacement cost of the Tenant Improvements paid for by
Landlord. In the event the Premises are more than partially destroyed, or in the
event the repairs cannot be made in one hundred eighty  (180) days, Landlord or
Tenant may elect to terminate this Lease. Landlord shall not be required to
restore additions, alterations or improvements made by Tenant or replace
Tenant's fixtures or personal property. In respect to any partial destruction
which Landlord is obligated to repair or may elect to repair under the terms of
this paragraph, the provision of Section 1932, Subdivision 2, and of Section
1933, Subdivision 4, of the Civil Code of the State of California am waived by
Tenant.

In the event of a total or partial destruction of the Premises by an uninsured
casualty, the Lease shall automatically terminate, unless (i) Landlord elects to
rebuild, and (ii) the damage can be repaired within one hundred eighty (180)
days.

                                    Page 9
<PAGE>

29. ASSIGNMENT OR SUBLEASE: In the event Tenant desires to assign this Lease or
any interest therein including, without limitation, a pledge, mortgage or other
hypothecation, or sublet the Premises or any part thereof, Tenant shall deliver
to Landlord executed counterparts of any such agreement and of all ancillary
agreements with the proposed assignee or subtenant, financial statements, and
any additional information as reasonably required to determine whether it will
consent to the proposed assignment or sublease. The notice shall give the name
and current address of the proposed assignee/subtenant, proposed use of the
Premises, rental rate and current financial statement and upon request to
Tenant, Landlord shall be given additional information as reasonably required to
determine whether it will consent to the proposed assignment or sublease.
Landlord shall then have a period of thirty (30) days following receipt of such
notice within which to notify Tenant in writing that Landlord elects (i) to
terminate this Lease as to the space to affected as of the date so specified by
Tenant in which event Tenant will be relieved of all further obligations
hereunder as to such space, (ii) to permit Tenant to assign or sublet such space
to the named assignee/subtenant on the terms and conditions set forth in the
notice, or (iii) to refuse consent. If Landlord should fail to notify Tenant in
writing of such election within said thirty (30) day period, Landlord shall be
deemed to have elected option (ii) above. Any rent or other economic
consideration realized by Tenant under any such sublease and assignment in
excess of the rent payable hereunder (including an allocation of the purchase
price attributable to Tenant's leasehold interest in the event of a sale of the
Tenant's business), after the net unamortized cost of the Tenant Improvements
for which Tenant has itself paid, and reasonable subletting and assignment
costs, shall be divided and paid sixty-seven percent (67%) to Landlord and
thirty-three percent (33%) to Tenant. Tenant's obligation to pay over Landlord's
portion of the consideration shall constitute an obligation for additional rent
hereunder. The above provisions relating to Landlord's right to terminate the
Lease and relating to the allocation of bonus rent are independently negotiated
terms of the Lease, constitute a material inducement for the Landlord to enter
into the Lease, and are agreed as between the parties to be commercially
reasonable. No assignment or subletting by Tenant shall relieve Tenant of any
obligation under this Lease. Any assignment or subletting which conflicts with
the provisions hereof shall be void.

If Landlord exercises its option to terminate this Lease in part in the event
Tenant desires to sublet or assign part of the Premises, then (a) this Lease
shall end and expire, with respect to such part of the Premises, on the date
upon which the proposed sublease was to commence, and (b) from and after such
date, the rent and Tenant's allocable share of all other costs and charges shall
be adjusted, based upon the proportion that the rentable area of the Premises
remaining bears to the total rentable area of the Premises.

If Landlord does not exercise its option to terminate this Lease, Landlord's
consent (which must be in writing and in form reasonably satisfactory to
Landlord) to the proposed assignment or sublease shall not be unreasonably
withheld or delayed, provided and upon condition that:

(a) The proposed assignee or subtenant is engaged in a business that is limited
to the use expressly permitted under this Lease;

(b) The proposed assignee or subtenant is a company with sufficient financial
worth and management ability to undertake the financial obligation of this
Lease, and Landlord has been furnished with reasonable proof thereof;

(c) The proposed sublease shall be in form reasonably satisfactory to Landlord;

(d) The amount of the aggregate rent to be paid by the proposed subtenant is not
less than the then current "Fair Market Value" as defined in paragraph 38 below;

(e) Tenant shall reimburse Landlord on demand for any costs that may be incurred
by Landlord in connection with said assignment or sublease, including the costs
of making investigations as to the acceptability of the proposed assignee or
subtenant and legal costs incurred in connection with the granting of any
requested consent; and

(f) Tenant shall not have advertised or publicized in any way the availability
of the Premises without prior notice to, and approval by Landlord.

                                    Page 10
<PAGE>

Any assignment or transfer shall be made only if and shall not be effective
until the assignee shall execute, acknowledge and deliver to Landlord an
agreement, in form and substance satisfactory to Landlord, whereby the assignee
shall assume all of the obligations of this Lease on the part of Tenant to be
performed or observed and shall be subject to all of the covenants, agreements,
terms, provisions and conditions contained in this Lease. Notwithstanding any
such sublease or assignment and the acceptance of rent or additional rent by
Landlord from any subtenant or assignee, Tenant shall and will remain fully
liable for the payment of the rent and additional rent due, and to become due
hereunder, for the performance of all of the covenants, agreements, terms,
provisions and conditions contained in this Lease on the part of Tenant to be
performed and for all acts and omissions of any licensee, subtenant, assignee or
any other person claiming under or through any subtenant that shall be in
violation of any of the obligations of this Lease, and any such violation shall
be deemed to be a violation by Tenant. Tenant shall further indemnify, defend
and hold Landlord harmless from and against any and all losses, liabilities,
damages, costs and expenses (including reasonable attorney fees) resulting from
any claims that may be made against Landlord by the proposed assignee or
subtenant or by any real estate brokers or other persons claiming a commission
or similar compensation in connection with the proposed assignment or sublease.

In the event of Tenant's default, Tenant hereby assigns all rents due from any
assignment or subletting to Landlord as security for performance of its
obligations under this Lease and Landlord may collect such rents as Tenant's
Attorney-in-Fact, except that Tenant may collect such rents unless a default
occurs as described in paragraph 22 above. The termination of this Lease due to
Tenant's default shall not automatically terminate any assignment or sublease
then in existence.  At the election of Landlord, the assignee or subtenant shall
attorn to Landlord and Landlord shall undertake the obligations of the Tenant
under the sublease or assignment; provided the landlord shall not be liable for
prepaid rent, security deposits or other defaults of the Tenant to the subtenant
or assignee.

If Tenant is a corporation or partnership, all the above provisions shall apply
to a transfer (by one or more transfers) of a majority of the stock of the
corporation or the majority of ownership or control of the partnership, as if
such transfer were an assignment of this Lease.

30. CONDEMNATION: If any part of the Premises shall be taken for any public or
quasi-public use, under any statute or by right of eminent domain or private
purchase in lieu thereof, and a part thereof remains which is susceptible of
occupation hereunder, this Lease shall as to the part so taken, terminate as of
the date title shall vest in the condemnor or purchaser, and the rent payable
hereunder shall be adjusted so that the Tenant shall be required to pay for the
remainder of the term only such portion of such rent as the value of the part
remaining after such taking bears to the value of the entire Premises prior to
such taking;, but in such event Landlord shall have the option to terminate this
Lease as of the date when title to the part so taken vests in the condemnor or
purchaser. If all of the Premises, or such part thereof be taken so that there
does not remain a portion susceptible for occupation hereunder, this Lease shall
thereupon terminate. If a part or all of the Premises be taken, all compensation
awarded upon such taking shall go to the Landlord and the Tenant shall have no
claim thereto but Landlord shall cooperate with Tenant to mover compensation for
damage to or taking of any alterations, additions or improvements made by Tenant
or Tenant's moving costs. Tenant hereby waives the provisions of California Code
of Civil Procedures Section 1265.130.

31. EFFECTS OF CONVEYANCE: The term Landlord as used in this Lease, means only
the owner for the time being of the land and Building, containing the Premises,
so that, in the event of any sale of said land or Building, or in the event of a
master Lease of the Building, the Landlord shall be and hereby is entirely freed
and relieved of all covenants and obligations of the Landlord hereunder, and it
shall be deemed and construed, without further agreement between the parties and
the purchaser at any such sale, or the master tenant of the Building, that the
purchaser or master tenant of the Building has assumed and agreed to carry out
any and all covenants and obligations of the Landlord hereunder. Landlord shall
transfer and deliver Tenant's security deposit, to the purchaser at any such
sale or the master tenant of the Building, and thereupon the Landlord shall be
discharged from any further liability in reference thereto.

32. SUBORDINATION: In the event Landlord notifies Tenant in writing, this Lease
shall be subordinate to any ground Lease, deed of trust, or other hypothecation
for security now or

                                    Page 11
<PAGE>

hereafter placed upon the real property of which the Premises are a part and to
any and all advances made on the security the, roof and to renewals,
modifications, replacements and extensions thereof. Tenant agrees to promptly
execute any documents which may be required to effectuate such subordination.
Notwithstanding such subordination, Tenant's right to quiet possession of the
Premises shall not be disturbed if Tenant is not in default and so long as
Tenant shall pay the rent and observe and perform all of the provisions of this
Lease. At the request of any lender, Tenant agrees to execute and deliver any
reasonable modifications of this Lease which do not materially adversely affect
Tenant's s hereunder.

33. WAIVER: The waiver by Landlord of any breach of any term, covenant or
condition, herein contained shall not be deemed to be a waiver of such term,
covenant or condition or any subsequent breach of the same or any other term,
covenant or condition herein contained. The subsequent acceptance of rent
hereunder by Landlord shall not be deemed to be a waiver of any preceding breach
by Tenant of any term, covenant or condition of this Lease, other than the
failure of Tenant to pay the particular rental so accepted, regardless of
Landlord's knowledge of such preceding breach at the time of acceptance of such
rent.

34. HOLDING OVER: Any holding over after the termination or expiration of
the said term, shall be construed to be a hold over tenancy and Tenant shall pay
rent to Landlord at a rate equal to the greater of (i) one hundred fifty percent
(150%) of the monthly rental installment due in the month preceding the
termination or expiration of the Lease, pro rated on a daily basis or (ii) one
hundred fifty percent (150%) of the Fair Market Rental (as defined in paragraph
37), pro rated on a daily basis. Any holding over shall otherwise be on the
terms and conditions herein specified, except those provisions relating to the
term and any options to extend or renew, which terms are expressly waived during
any hold over. Furthermore, no holding over shall be deemed or construed to
exercise any option to extend or renew this Lease in lieu of full and timely
exercise of any such option as required hereunder.

35. SUCCESSORS AND ASSIGNS: The covenants and conditions herein contained
shall, subject to the provisions as to assignment, apply to and bind the heirs,
successors, executors, administrators and assigns of all the parties hereto; and
all of the parties hereto shall be jointly and severally liable hereunder.

36. ESTOPPEL CERTIFICATES: Tenant shall at any time during the term of this
Lease, upon not less than ten (10) days prior written notice from Landlord,
execute and deliver to Landlord a statement in writing certifying that this
Lease is unmodified and in full force and effect (or, if modified, stating the
nature of such modification) and the date to which the rent and other charges
are paid in advance, if any, and acknowledging that there are not, to Tenant's
knowledge, any uncured defaults on the part of Landlord hereunder or specifying
such defaults if they are claimed. Any such statement may be conclusively relied
upon by any prospective purchaser or encumbrancer of the Premises. Tenant's
failure to deliver such statement within such time shall be conclusive upon the
Tenant that: (a) this Lease is in full force and effect, without modification
except as may be represented by Landlord; (b) there are not uncured defaults in
Landlord's performance. Tenant also agrees to provide thee (3) years of audited
financial statements within five (5) days of a request by Landlord for
Landlord's use in financing the Premises with commercial lenders.

37. OPTION TO EXTEND THE TERM: Landlord hereby grants to Tenant, upon and
subject to the terms and conditions set forth in this paragraph, the option (the
"Option") to extend the term of this Lease for an additional term (the "Option
Term"), which option Term shall be a period of Sixty (60) months. The Option
Term shall be exercised, if at all, by written notice to Landlord on or before
the date that is six (6) months prior to the expiration date of the initial term
of the Lease. If Tenant exercises the Option, each of the terms, covenants and
conditions of this Lease except this paragraph shall apply during the Option
Term as though the expiration date of the Option Term was the date originally
set forth herein as the expiration date of the initial term, provided that the
rent to be paid shall be the greater of (i) the rent applicable to the period
immediately prior to the commencement of the Option Term, or (ii) the Fair
Market Rental, as hereinafter defined, for the Premises for the Option Term.
Anything contained herein to the contrary notwithstanding, if Tenant is in
monetary or material non-monetary default under any of the terms, covenants or
conditions of this Lease either at the time Tenant exercises the Option or at
any time thereafter prior to the commencement date of the Option Term, Landlord
shall have, in

                                    Page 12
<PAGE>

addition to all of Landlord's other rights and remedies provided in this Lease,
the right to terminate the Option upon notice to Tenant, in which event the
expiration date of this Lease shall be and remain the expiration date of the
initial term. As used herein, the term "Fair Market Rental" for the Premises
shall mean the base rent that Landlord could obtain during the Option Term from
a third party desiring to lease the Premises for the Option Term, taking into
account concessions being offered on the market at that time, the age of the
Building, the quality of construction of the Building and the Premises, the
services provided under the terms of this Lease, the rental and other monetary
payments, any escalations and adjustments thereto (including without limitation
Consumer Price Indexing) then being obtained for new leases of space comparable
to the Premises in the locality of the Building, and all other factors that
would be relevant to a third party desiring to lease the Premises for the Option
Term in determining the rental such party would be willing to pay therefor. The
determination of Fair Market Value shall also take into account that (i) Tenant
is in occupancy and making functional use of the space in its then existing
condition, and (ii) no brokerage commission is payable.

If Tenant exercises the Option, Landlord shall send to Tenant a notice setting
forth the Fair Market Rental for the Premises for the Option Term, on or before
the date that is one hundred fifty (150) days prior to the expiration date of
the initial terra. If Tenant disputes Landlord's determination of the Fair
Market Rental for the Option Term, Tenant shall, within thirty (30) days after
the date of Landlord's notice setting forth the Fair Market Rental for the
Option Term, send to Landlord a notice stating that Tenant either (x) elects to
terminate its exercise of the Option, in which event the Option shall lapse and
this Lease shall terminate on the expiration date of the initial term in the
manner provided herein, or (y) disagrees with Landlord's determination of Fair
Market Rental for the Option Term and elects to resolve the disagreement as
provided in paragraph 37(a) below, If Tenant does not send to Landlord a notice
as provided in the previous sentence, Landlord's determination of the Fair
Market Rental shall be the basis for determining the rent to be paid by Tenant
hereunder during the Option Term. If Tenant elects to resolve the disagreement
as provided in paragraph 37(a) below and such procedures shall not have been
concluded prior to the commencement date of the Option Term, Tenant shall pay
rent to Landlord hereunder adjusted to reflect the Fair Market Rental as
determined by Landlord in the manner provided above. If the amount of Fair
Market Rental as finally determined pursuant to in paragraph 37(a) below is
greater than Landlord's determination, Tenant shall pay to Landlord the
difference between the amount paid by Tenant and the Fair Market Rental as so
determined in paragraph 37(a) below within thirty (30) days after the
determination. If the Fair Market Rental as finally determined in paragraph
37(a) below is less than Landlord's determination, the difference between the
amount paid by Tenant and the Fair Market Rental as so determined in paragraph
37(a) below shall be credited against the next installments of rent due from
Tenant to Landlord hereunder.

37(a). Resolution of a Disagreement over the Fair Market Rental:   Any
disagreement regarding the Fair Market Rental shall be resolved as follows:

(i)   Within thirty (30) days after Tenant's response to Landlord's notice to
Tenant of the Fair Market Rental, Landlord and Tenant shall meet no less than
two (2) times, at a mutually agreeable time and place, to attempt to resolve any
such disagreement.

(ii)  If within the thirty (30) day period referred to in (i) above, Landlord
and Tenant can not reach agreement as to the Fair Market Rental, they shall each
select one appraiser determine the Fair Market Rental. Each such appraiser shall
arrive at a determination of the Fair Market Rental and submit their conclusions
to Landlord and Tenant within thirty (30) days after the expiration of the
thirty (30) day consultation period described in (i) above.

(iii) If only one appraisal is submitted within the requisite time period, it
shall be deemed to be the Fair Market Rental. If both appraisals are submitted
within such time period and the two appraisals so submitted differ by less than
ten percent (10%) of the higher of the two, the average of the two shall be the
Fair Market Rental. If the two appraisals differ by more than ten percent (10%)
of the higher of the two, then the two appraisers shall immediately select a
third appraiser who shall within thirty (30) days after his or her selection
make a determination of the Fair Market Rental and submit such determination to
Landlord and Tenant. This third appraisal will then be averaged with the closer
of the two previous appraisals and the result shall be the Fair Market Rental.

                                    Page 13
<PAGE>

(iv)  All appraisers specified pursuant to this paragraph shall be members of
the American Institute of Real Estate Appraisers with not less than ten (10)
years experience appraising commercial properties in the Santa Clara Valley.
Each party shall pay the cost of the appraiser selected by such party and one-
half of the cost of the third appraiser plus one-half of any other costs
incurred in resolving the dispute pursuant to this paragraph.

38. OPTIONS: All Options provided Tenant in this Lease are personal and granted
to original Tenant and arc not exercisable by any third party should Tenant
assign or sublet all or a portion of its rights under this Lease, unless
Landlord consents to permit exercise of any option by any assignee or subtenant,
in Landlord's sole discretion. In the event that Tenant hereunder has any
multiple options to extend this Lease, a later option to extend the Lease cannot
be exercised unless the prior option has been so exercised. Notwithstanding the
foregoing, the option shall be transferable or assignable to any entity that
acquires either a majority of the shares of stock of Tenant or a majority of the
assets of Tenant.

39. QUIET ENJOYMENT:  Upon Tenant's faithful and timely performance of all the
terms and covenants of the Lease, Tenant shall quietly have and hold the
Premises for the term and any extensions thereof.

40. BROKERS: Tenant represents it has not utilized or contacted a real estate
broker or finder with respect to this Lease other than Cornish & Carey
Commercial and McMillan, Moore, Buchanan, and Tenant agrees to indemnify and
hold Landlord harmless against any claim, cost, liability or cause of action
asserted by any other broker or finder claiming through Tenant.

41. LANDLORD'S LIABILITY:  If Tenant should recover a money judgment against
Landlord arising in connection with this Lease, the judgment shall be satisfied
only out of Landlord's interest in the Premises including the improvements and
real property and neither Landlord or any of its partners shall be liable
personally for any deficiency.

42.  AUTHORITY OF PARTIES:

42.(a)  Corporate Authority: If Tenant is a corporation, each individual
executing this Lease on behalf of said corporation represents and warrants that
he is duly authorized to execute and deliver this Lease on behalf of said
corporation, in accordance with a duly adopted resolution of the Board of
Directors of said corporation or in accordance with the by-laws of said
corporation, and that this Lease is binding upon said corporation in accordance
with its terms.

42.(b)  Limited Partnerships: If the Landlord herein is a limited partnership,
it is understood and agreed that any claims by Tenant on Landlord shall be
limited to the assets of the limited partnership. And furthermore, Tenant
expressly waives any and all rights to proceed against the individual partners
or the officers, directors or shareholders of any corporate partner, except to
the extent of their interest in said limited partnership.

43.  TRANSPORTATION DEMAND MANAGEMENT PROGRAMS Should a government agency or
municipality require Landlord to institute TDM (Transportation Demand
Management) facilities and/or program, Tenant hereby agrees that the cost of TDM
imposed facilities required on the Premises, including but not limited to
employee showers, lockers, cafeteria, or lunchroom facilities, shall be included
as Tenant Improvement Costs and any ongoing costs or expenses associated with a
TDM program, such as an on-site TDM coordinator, which arc required for the
Premises and not provided by Tenant shall be provided by Landlord with such
costs being included as additional rent and reimbursed to Landlord by Tenant.

44.  MISCELLANEOUS PROVISIONS:
All monetary sums due from Tenant to Landlord under this Lease shall be deemed
to be rent.

Subject to the written notice and aim opportunity requirements of Paragraph 22
of this Lease, if after said notice and at the expiration of said cure period,
Tenant has failed to perform any obligation required under this Lease or by law
or governmental regulation, Landlord may in its sole discretion without notice
perform such obligation, in which event Tenant shall pay Landlord as additional
rent all sums paid by Landlord in connection with such substitute performance
within ten (10) days following Landlord's written notice for such payment.

                                    Page 14
<PAGE>

All sums due hereunder, including rent and additional rent, if not paid when
due, shall bear interest at the maximum rate permitted under California law
accruing from the date due until the date paid to Landlord.

All rights and remedies hereunder are cumulative and not alternative to the
extent permitted by law and are in addition to all other rights and remedies in
law and in equity.

If any term or provision of this Lease is held unenforceable or invalid by a
court of competent jurisdiction, the remainder of the Lease shall not be
invalidated thereby but shall be enforceable in accordance with its terms,
omitting the invalid or unenforceable term.

This Lease shall be governed by and construed in accordance with California law.

Time is of the essence hereunder.

This instrument contains all of the agreements and conditions made between the
parties hereto and may not be modified orally or in any other manner than by an
agreement in writing signed by all of the parties hereto or their respective
successors in interest.

Tenant acknowledges that neither Landlord or its affiliates or agents have made
any agreements, representations, warranties or promises with respect to the
demised Premises or the Building of which they are a part, or with respect to
present or future rents, expenses, operations, tenancies or any other matter.
Except as herein expressly set forth herein, Tenant relied on no statement of
Landlord or its agents for that purpose.

The headings or titles to the paragraphs of this Lease are not a part of this
Lease and shall have no effect upon the construction or interpretation of any
part thereof.

IN WITNESS WHEREOF, Landlord and Tenant have executed these presents, the day
and year first above written.

LANDLORD: THE SOBRATO GROUP                  TENANT: TIBURON SYSTEMS, INC.

a California Limited Partnership             a California Corporation


BY: /s/ [ILLEGIBLE]^^                        BY:  /s/ [ILLEGIBLE]^^
   ----------------------------                 ----------------------------

ITS:___________________________              ITS:___________________________

                                    Page 15
<PAGE>

                                  EXHIBIT "A"
                                   Premises


                                    [Image]


                                    Page 16
<PAGE>

                                  EXHIBIT "B"
                     Approved Preliminary Working Drawings

                                    Page 17
<PAGE>

                                  EXHIBIT "C"
                          Approved Preliminary Budget



                      Tiburon Preliminary Budget 5/14/91


This budget is per Kobza's drawings, sheets T-l, T-3 and T-5, dated 5/3/91.

Total square feet:                                                      66,479

<TABLE>
<CAPTION>
--------------------------------------------------------------------------------
  COST
  CODE                   DESCRIPTION                        VALUE       PSF
--------------------------------------------------------------------------------
<S>      <C>                                                <C>         <C>
  40200  Demolition                                         $ 12,500    $ 0.19
  42200  HVAC                                               $ 60,000    $ 0.90
  42600  Fire Sprinklers                                    $  9,500    $ 0.14
  43600  Fire Extinguishers                                 $  1,000    $ 0.02
  43900  Electrical                                         $183,000    $ 2.75
  44600  Plumbing                                           $  5,000    $ 0.08
  45400  Acoustical Ceiling                                 $ 10,000    $ 0.15
  46100  Drywall                                            $ 48,000    $ 0.72
  47200  Doors, Frames & Hardware                           $ 39,600    $ 0.60
  47600  Insulation                                         $  2,000    $ 0.03
  48300  Glass                                              $  4,700    $ 0.07
  49100  Ceramic Tide                                       $  2,000    $ 0.03
  50800  Cabinets & Tops                                    $ 14,000    $ 0.21
  51300  Paint                                              $ 32,000    $ 0.48
  53900  Carpet Removal, New Carpet & Base, Wt Room Floor   $125,000    $ 1.88
  54500  Window Coating                                     $  4,000    $ 0.06
  55100  Computer Floor                                     $ 45,000    $ 0.68
  58500  Fencing (Chain Link)                               $  7,500    $ 0.11
  60800  Plan Check Fee (allowance)                         $  2,000    $ 0.03
  60900  Permit & Construction Tax @ 5% (allowance)         $ 30,500    $ 0.46
  62500  Blueprinting (allowance)                           $  3,000    $ 0.05
  64900  Architect Fee (Kobza)                              $39,4501    $ 0.59
  65200  Construction Clean-up                              $ 10,000    $ 0.15
--------------------------------------------------------------------------------
                              Subtotal:                     $689,750    $10.38
  61000  Contingency @ 5%                                   $ 34,488    $ 0.52
         Contractor's Fee @ 10%                             $ 72,424    $ 1.09
--------------------------------------------------------------------------------
                                               TOTAL:       $796,661    $11.98
--------------------------------------------------------------------------------
</TABLE>

Qualifications:
               Painting of door frames excluded
               24 gauge sheetmetal at SCIF room roof

                                    Page 18
<PAGE>

                                  EXHIBIT "D"
                        Approved Final Working Drawings

                                    Page 19
<PAGE>

                                  EXHIBIT "E"
                             Approved Final Budget

                                    Page 20
<PAGE>

                                  EXHIBIT "F"
                                  Punch List

                                    Page 21
<PAGE>

[LOGO OF THERMA INC.]                                                  Quotation

                                                           Date    May 13,  1991
                                                               ----------     --

--------------------------------------------------------------------------------
     TO:
         Sobrato Dev. Cos.
     -----------------------------------------------------------------
         10600 N. DeAnza Blvd. #200
     -----------------------------------------------------------------
         Cupertino, CA 95014
     -----------------------------------------------------------------
         Attention: Mr. Don Jones
     -----------------------------------------------------------------

     We propose to furnish you with the following material and/or service under
 conditions herein stipulated

     Subject: Tiburon Systems
              1290 Parkmoor Ave.

     Please find below, cost breakdown for the subject project.

     1st Floor
        Warehouse  (11'-0" clear, no ceiling)
        - Remove and replace 4 zones with galvanized spiral pipe (#'s 101, 102,
          103, 104)
        - Remove and replace half the duct of 3 zones with galvanized spiral
          pipe ( #'s 109, 110, 111)
        - Replace heating duct with spiral pipe an insulate

     Office #132 and #133
          Sput one zone into 2-offices

     Office #121
          Add cooling only VAV zone

                                          FOR THE SUM OF ............ $11,000.00

     Page 1 of 2
--------------------------------------------------------------------------------
     2051 Ringwood Avenue   San Jose, CA 95131  (408) 433-5577  FAX: 434-0773

                     Contractor's State License No. 270648
               TERMS OF PAYMENT: NET DUE UPON RECEIPT OF INVOICE
    Sales tax, use or similar State or Federal Tax to be paid by purchaser.

     We hereby accept the proposal.     Respectfully Submitted for the Company.

     ________________________________   By____________________________
                                          Howard Hakamura

     ________________________________   Approved

     Dated at________________________   By____________________________

     _________________ 19____________   Dated at___________ 19________
     HN/tdp,to911.quo

     ________________________________   ________________________________
<PAGE>

                                               May 13, 1991
Don Jones
                                               Page 2 of 2

2nd Floor
  -  Office #21, 232, 233
     Add cooling only VAV zone

  -  Office #228, 229, 230
     Add cooling only VAV zone

  -  Office #225
     Tie into existing VAV zone #215

  -  Office #221 and 222
     Revise existing duct

  -  Office #218
     Tie into existing zone #228

  -  Office #214 and 215
     Add cooling only VAV zone

  -  Office #210, 211, 212
     Add cooling only VAV zone

  -  Office #208 and 209
     Add cooling only VAV zone
                                            FOR THE SUM OF ........... $9,400.00
3rd Floor
  -  Add 3 ton split system AC-unit for SCIF area

  -  Add switched main for pneumatic controls around classified area.

  -  Add duct to AC unit #1 in shaft to supply air to 3/rd/ floor

  -  Office #326
     Add cooling only VAV zone

  -  Office #327
     Add one each cooling only and heating/cooling zone

  -  Office #328
     Add cooling only VAV zone

<TABLE>
<CAPTION>
<S>                                         <C>
                                            FOR THE SUM OF............$20,450.00
                                                      XXX.............    800.00

Miscellaneous Work
  Replace Exhaust Fans ...........................................    $ 2,150.00
  24 gauge metal over SCIF........................................    $   980.00
  Air balance.....................................................    $15,000.00
  Misc. plumbing allow............................................    $ 5,000.00

                                             TOTAL................    $63,980.00
</TABLE>

Respectfully Submitted,
 /s/ Howard Hakamura
Howard Hakamura

<PAGE>

Cupertino, CA 95014

ATTN: Mr. Don Jones

RE: Tiburon Systems
    WSJCC Bldg. #5
    San Jose, CA

Gentlemen,

     We are pleased to quote you for the electrical work required on the above
ref. Protect as follows. Our quote is based on out meeting with Tiburon on
Monday May 6, our walk thru the bldg. With you and the new floor plan by Dennis
Kobza & Assoc. dated 5/3/91.

Lighting:
     Remove:
            8 - 2'x2' T- bar Fixtures
          100 - 2'x4' T-bar Fixtures
           28 - 4' Fluorescent Strips
            5 - Exit Lights
           12 - Twin Head Battery Packs
           10 - Double Switches
            4 - 4 Gang Switches
           12 - Down Lights in T-bar

     Reinstall Existing Features:
            8 - 2'x2' T-bar Fixtures
           72 - 2'x4' T-bar Fixtures
            5 - Exit Lights

     New Fixtures:
            2 - 2'x2' T-bar Fixtures
           24 - 8', 2-Lamp Industrial Fluorescent Fixtures
            9 - Exit Lights
            7 - New Batt. Packs
<PAGE>

          XXX - 8' Lite Track
           20 - 75 Watt Lite Track Fixtures
            5 - Single Switches
           41 - Double Switches
            4 - 4 Gang Switches
            2 - Dimmers
          Lot - Replace burn out fluorescent and incandell lamps and ballasts
          Lot - Replace broken and missing lenses

Power:
     Remove:
          230'- of existing 2000 wiremold
           12 - Cord Drops
           27 - Duplex Receptacles in walls
            3 - 30amp Receptacles in walls
            5 - Surface Mtd. Receptacles
            7 - Power Poles
           22 - Remove Floor Boxes

New:
           73 - Duplex Receptacles
            5 - Dedicated Receptacles
           48 - 4 Plex Receptacles
            5 - 30A, 209V, 10 Receptacles
            1 - 50A, 209V, 10 Receptacles
           12 - J.B.'s in Ceiling for Security Power
           17 - Floor Fees for Partitions with 3-Circuits each
           14 - Wall or Column Feeds for Partitions w/ 3-Circuits each
            2 - Electric Screens
           44 - Telephone Ring and Pull String
            1 - Replace Noisey 75KVA Transformer in 3/rd/ Floor

Depot Repair:
            1 - new 75 KVA Transformer and Feeder from MSB
            1 - new 2- section panel w/ main and feeder from tansf.
           60'- 4000 wiremold w/ 6 - 30A, 280V, 30 outlets, 3 -30A,
                208V, 10 outlets, 3 -20A, 208V, 14 outlets,
                  6 - dedicated duplex, & 12 - STD. Duplex
<PAGE>

           12  - Plex Cord Drops for work benches
            1  - E.P.O Switch

1/st/ Floor Computer Room:
            1  - new 42 circuit panel fed from exist. Panel
           30' - 6000 wiremold under (E) computer floor of
                   3  - 30A, 208V, 30 outlets on 10' S.T. Flex
                   6  - 20A, 208V, 14 "  "  "
                  20  - 4 Plex            "  "  "
            1  - Rolm Tel. Equip. power and connection

3/rd/ Floor Computer Room:
            1  - new 112 1/2 KVA Transformer, 1 -175A fused switch in MSB w/
                 feeder from MSB
            1  - new 3 - section 400A panel w/ main breaker
            2  - E.P.O. switches
          400' - 40000 wiremold under computer floor w/
                  19  - 30A, 208V, 30 outlets on 10' S.T. Flex
                   5  - 30A, 208V, 10    "  "
                  10  - 20A, 208V, 10   "  "
                  84  - 4-Plex outlets in 10' S.T. Flex
            1  - New 100AMP loadcenter for screen room w/ feeder from 3/rd/
                 floor computer panel
           12  - connect lights in screen room

Misc:
            1  - Feeder, Connection and Combo Starter for new condensing unit on
                 roof
            1  - Feeder, Connection and Combo Starter for new fan coil in SCIF
                 room
            1  - Feeder, Connection and Disconnet for condensate drain pump
          Lot  - Control wire to stat.
          Lot  - Replace all painted switch and receptacle plates with ivory
                 plates
          Lot  - Cut and patch concrete floor for new feeds to (E) floor boxes
                 in rooms 127 & 128
          Lot  - Core floors for partition floor feeds
<PAGE>

          Our quote for the above electrical work, $183,000.00

Exclusions:
            1  - Disconnection and moving of Tiburons equipment at their
                 existing location.

     If you should have any questions please feel free to contact us.

                                                       Sinc
                                                       /s/ [ILLEGIBLE]^^