Document:

<PAGE>

                                                                   EXHIBIT 10.55

                              OFFICE SPACE LEASE
                              ------------------

                           Haseko Management, Inc.,
                                 as agent for

                              SHIN-EI CO., LTD.,
                            a Japanese corporation

                                  (Landlord)

                        CONCENTRIC NETWORK CORPORATION,
                            a Delaware corporation

                                   (Tenant)

                           Von Karman Business Park
                            16842 Von Karman Avenue
                              Irvine, California
                               Suite 400 and 450

                            (Building and Premises)

                                 May 26, 1999
<PAGE>

                               TABLE OF CONTENTS
                               -----------------

<TABLE>
<CAPTION>
                                                                          Page
                                                                          ----
<S>                                                                       <C>

BASIC LEASE INFORMATION.................................................     1
1.    PREMISES..........................................................     2
2.    TERM; COMPLETION OF IMPROVEMENTS..................................     2
3.    INTENTIONALLY OMITTED.............................................     3
4.    RENTAL PAYMENTS...................................................     4
5.    BASE MONTHLY RENT.................................................     4
6.    TENANT'S SHARE OF INCREASED COSTS.................................     4
7.    USE...............................................................     6
8.    SERVICES..........................................................     6
9.    TAXES PAYABLE BY TENANT...........................................     7
10.   IMPROVEMENTS, REPAIRS AND ALTERATIONS.............................     8
11.   LIENS.............................................................     8
12.   DAMAGE AND DESTRUCTION............................................     9
13.   WAIVER OF SUBROGATION.............................................     9
14.   INDEMNIFICATION...................................................     9
15.   COMPLIANCE WITH LAW...............................................    10
16.   INSURANCE.........................................................    10
17.   ASSIGNMENT AND SUBLETTING.........................................    11
18.   RULES.............................................................    12
19.   ENTRY BY LANDLORD.................................................    12
20.   EVENTS OF DEFAULT.................................................    12
21.   TERMINATION UPON DEFAULT..........................................    13
22.   CONTINUATION AFTER DEFAULT........................................    13
23.   OTHER RELIEF......................................................    13
24.   PARKING...........................................................    13
25.   INTENTIONALLY OMITTED.............................................    14
26.   TRADE FIXTURES....................................................    14
27.   SUCCESSORS AND ASSIGNS............................................    14
28.   TIME..............................................................    14
29.   LANDLORD'S DEFAULT................................................    14
30.   INTENTIONALLY OMITTED.............................................    15
31.   LANDLORD'S RIGHT TO CURE DEFAULTS.................................    15
32.   ATTORNEYS' FEES...................................................    15
33.   EMINENT DOMAIN....................................................    15
34.   SUBORDINATION.....................................................    15
35.   NO MERGER.........................................................    16
36.   CONVEYANCE BY LANDLORD............................................    16
37.   ESTOPPEL CERTIFICATE..............................................    16
38.   NO LIGHT, AIR OR VIEW EASEMENT....................................    16
39.   HOLDING OVER......................................................    16
40.   ABANDONMENT.......................................................    16
41.   SECURITY DEPOSIT..................................................    17
42.   WAIVER............................................................    17
43.   NOTICES...........................................................    17
44.   COMPLETE AGREEMENT................................................    17
45.   CORPORATE AUTHORITY...............................................    18
46.   HAZARDOUS MATERIALS...............................................    18
47.   ADDITIONAL PROVISIONS.............................................    18
48.   MISCELLANEOUS.....................................................    18
49.   EXHIBITS..........................................................    19
50.   SIGNAGE...........................................................    19
51.   ANTENNA/SATELLITE DISH............................................    19
52.   RIGHT OF FIRST NEGOTIATION........................................    19
</TABLE>
<PAGE>

                            BASIC LEASE INFORMATION
                            -----------------------

DATE:     May 26, 1999

BUILDING: Von Karman Business Park, 16842 Von Karman Avenue, Irvine

LANDLORD: SHIN-EI CO., LTD., a Japanese corporation

TENANT:   CONCENTRIC NETWORK CORPORATION, a Delaware corporation

LEASE SECTION
-------------

Section 1   Premises: Suite 400 on the first (1st) floor and Suite 450 located
            --------
            on the second (2nd) floor, as more particularly described on Exhibit
                                                                         -------
            "A" attached hereto
            ---

Section 2   Commencement Date: June 1, 1999 as to Suite 450; July 1,
            -----------------
            1999 as to Suite 400

Section 2   Term Expiration: June 30, 2004
            ---------------

Section 4   Base Monthly Rent: $31,562.15 (to be prorated from June 1, 1999 to
            -----------------
            June 30, 1999 to account for the inclusion of Suite 450 only)

Section 6   Tenant's Share of Increased Costs: 21.667% (based on 100,461
            ---------------------------------
            rentable square feet in the Building) (to be prorated from June 1,
            1999 to June 30, 1999 to account for the inclusion of Suite 450
            only)

Section 41  Security Deposit: $31,562.15 payable upon Lease execution
            ----------------

Section 43  Landlord's Address for Notices:
            ------------------------------

            SHIN-EI Co., Ltd.
            c/o HASEKO (California), Inc.
            Attn: John T. Troll
            350 South Figueroa Street, Suite 255
            Los Angeles, California 90071

            Tenant's Address for Notices;
            ----------------------------

            Concentric Network Corporation
            16842 Von Karman Avenue, Suite 400
            Irvine, California 92606

            with a copy to:
            Concentric Network Corporation
            1400 Parkmoor Drive
            San Jose, California 95126-3429

Section 49  Exhibits and Rider:
            ------------------

            EXHIBIT "A"  SITE PLAN OF PREMISES
            EXHIBIT "B"  IMPROVEMENTS TO PREMISES
            EXHIBIT "C"  INTENTIONALLY OMITTED
            EXHIBIT "D"  RULES AND REGULATIONS
<PAGE>

                              OFFICE SPACE LEASE
                              ------------------

          THIS OFFICE SPACE LEASE ("Lease"), dated May 26, 1999, is entered into
by and between SHIN-EI CO., LTD., a Japanese corporation, as Landlord, and
CONCENTRIC NETWORK CORPORATION, a Delaware corporation, as Tenant.

     1.   PREMISES.
          --------

          Landlord hereby leases to Tenant, and Tenant hereby hires from
Landlord, upon the terms and conditions hereinafter set forth, those certain
premises ("Premises") outlined on Exhibit "A" attached hereto. Suite 400 of the
                                  -----------
Premises is located on the first (1st) floor of the Building and Suite 450 of
the Premises is located on the second (2nd) floor of the Building. As used in
this Lease, the term "Building" shall mean the building described in the Basic
Lease Information attached hereto and all common areas, parking areas and
walkways serving said building and all areas adjacent to said building which are
owned by Landlord. Landlord and Tenant hereby irrevocably stipulate and agree
that the aggregate rentable area of the Premises is twenty-one thousand seven
hundred sixty-seven (21,767) square feet and the aggregate usable area of the
Premises is nineteen thousand four hundred thirty-five (19,435) square feet and
that there shall be no changes to the amount of Base Monthly Rent, the amount of
any other sums payable under this Lease, Tenant's Share of Increased Costs, the
amount of the tenant improvement allowance described in Paragraph 2.11 of
Exhibit "B" attached hereto or the amount of any other allowances based in whole
-----------
or in part upon any measurement or re-measurement by Landlord or Tenant of the
rentable or usable areas of the Premises.

          The Premises shall include the right to use, in common with others,
walkways, lobbies, entrances, stairs, elevators and other public portions of the
Building (collectively referred to as the "Common Areas"). All of the outside
walls and windows of the Premises and any space in the Premises used for shafts,
stacks, pipes, conduits, ducts, and electric or other Building facilities, and
the use thereof and access thereto through the Premises for the purposes of
operation, maintenance and repairs are reserved to Landlord.

          For purposes of this Lease, the term "rentable area" shall mean 112%
of the "usable area." The term "usable area" shall mean all floor area in the
Premises, measured to the inside glass surface of the outer building walls, to
the interior side of corridors and other permanent partitions, and to the center
of partitions that separate the Premises from adjoining tenant spaces, without
deduction for columns and projections necessary to the Building.

     2.   TERM: COMPLETION OF IMPROVEMENTS.
          --------------------------------

          The term ("Term") of this Lease shall commence on June 1, 1999
("Commencement Date") as to Suite 450 and on July 1, 1999 (also, "Commencement
Date") as to Suite 400 and shall expire on June 30, 2004. If Landlord, for any
reason whatsoever, cannot deliver possession of the Premises to Tenant following
execution hereof, this Lease shall not be voidable, nor shall Landlord or its
agents be liable to Tenant for any loss or damage resulting therefrom.

          Tenant shall accept the Premises in its "As-Is" condition upon
Landlord's delivery thereof to Tenant. Tenant acknowledges and agrees that
Landlord is not obligated to make any improvements to the Premises nor to
provide any allowance therefor, except as otherwise specifically provided in
Exhibit "B" attached hereto. Promptly after Landlord tenders possession of the
-----------
Premises to Tenant, Tenant shall construct the tenant improvements in the
Premises in accordance with Exhibit "B" attached hereto using Building standard
                            -----------
materials (the "Tenant Improvements") except as otherwise approved in writing by
Landlord. All of the terms of this Lease, except for terms requiring the payment
of rent, shall apply to Tenant's construction of the Tenant Improvements and
occupancy of the Premises prior to the Commencement Date. Tenant hereby
acknowledges Landlord's right to enter onto the Premises for the purposes of
reviewing the construction process, compliance with the approved plans and
specifications and completion of the Tenant Improvements as set forth in Exhibit
                                                                         -------
"B". Prior to commencing the Tenant improvement work, Tenant shall, at Tenant's
---
cost, have Tenant's contractor provide a completion bond in an amount equal to
one hundred percent (100%) of the cost of the work for which Tenant has
contracted as security for the faithful performance of the contract and also a
labor and material payment bond in
<PAGE>

an amount not less than one hundred percent (100%) of the cost of such work, as
security for the payment of persons performing labor and furnishing materials on
behalf of Tenant.

          Tenant shall have one (1) option to extend the Term of the Lease, for
a period of five (5) years (the "Extension Term"), provided that Tenant is not
then in default under any of the terms or provisions of the Lease and also
provided that Tenant has not been in default on three (3) or more separate
occasions during the Term of this Lease. Tenant may exercise the extension
option by giving written notice of Tenant's intent to exercise the option to
Landlord at least two hundred ten (210) days prior to the expiration of the then
current term, but no earlier than three hundred sixty-five (365) days prior to
the expiration of the then current term. At the commencement of the Extension
Term, the Base Rent shall be adjusted to be equal to ninety-five percent (95%)
of the then fair market rental value of the Premises, but no less than the rate
in effect immediately prior to the expiration of the Term, and said adjustment
may include future adjustments to Base Rent if such future adjustments are then
being included in office lease transactions for comparable buildings. If
Landlord and Tenant cannot agree upon the fair market rental value of the
Premises within sixty (60) days after Landlord's receipt of Tenant's notice
exercising the option contained herein, Landlord and Tenant shall each appoint a
"Qualified Arbitrator" (as defined below) within seven (7) days after the
expiration of the aforementioned sixty (60) day period. Such arbitrators shall
confer and select a third Qualified Arbitrator (the "Neutral Arbitrator"), who
alone shall determine the fair market rental value of the Premises. Should the
two (2) arbitrators fail to select a Third Qualified Arbitrator to act as the
Neutral Arbitrator within seven (7) days, the Neutral Arbitrator shall be
designated pursuant to California Code of Civil Procedure Section 1281.6, as
that Section may be amended or redesignated from time to time; provided,
however, that the Neutral Arbitrator so appointed must be a Qualified
Arbitrator. The determination of the Neutral Arbitrator shall be binding upon
Landlord and Tenant. Landlord and Tenant shall bear the cost of the arbitrator
appointed by such party and shall equally bear the cost of the Neutral
Arbitrator. As used herein, the term "Qualified Arbitrator" shall mean a person
who is an appraiser or real estate broker licensed by the State of California
and who has not less than five (5) years' experience in commercial leasing or
commercial real estate appraising.

     3.   INTENTIONALLY OMITTED

     4.   RENTAL PAYMENTS.
          ---------------

          Tenant shall pay base rent ("Base Rent") for the Premises to Landlord
throughout the Term on or before the first day of each calendar month during the
Term, without deduction or offset, in the amount(s) set forth in Section 5
hereof, as adjusted in accordance with Section 6, except that Tenant shall pay
its first twelve (12) monthly installments of Base Rent (i.e., $378,745.80)
concurrently with Tenant's execution hereof. If the Term commences on a day
other than the first day of a calendar month, then the Base Rent for the first
partial month shall be equitably prorated. All sums payable by Tenant to
Landlord hereunder shall be paid to Landlord, without deduction or offset, in
lawful money of the United States of America, addressed to Landlord c/o The Real
Estate Group, 9920 South La Cienega Boulevard, Suite 905, Inglewood, California
90301, or to such other person or at such other place as Landlord may from time
to time designate in writing. If any rent (including Base Rent, Tenant's Share
of Increased Costs and any other payment required to be made by Tenant) is not
received by Landlord within ten (10) days after the date such installment is
due, Tenant shall pay a late charge equal to eight percent (8 %) of such
installment and the installment and late charge shall bear interest (i) during
the initial Term at the lesser of twelve percent (12%) per annum or the highest
rate permitted by law and (ii) thereafter at the highest rate permitted by law.
Tenant recognizes and agrees that the late charge is intended to compensate
Landlord for and is a reasonable estimate of the administrative, legal,
bookkeeping and other expenses which will result from such delinquent rent
payment, which costs and expenses would be extremely difficult and impractical
to calculate.

          Any payment by Tenant or receipt by Landlord of a lesser amount than
stipulated herein for Base Rent, additional rent or any other charge hereunder
shall be deemed payment of the earliest stipulated rent, additional rent or
other charge then due. No endorsement or statement on a check and no letter
accompanying any check or payment shall be deemed an accord and satisfaction.
Landlord may accept any check or payment without prejudice to Landlord's rights
to recover the balance of rent, additional rent or other charges then due or to
pursue any other remedy set forth in this Lease or available at law or in
equity.
<PAGE>

     5.   BASE MONTHLY RENT.
          -----------------

<TABLE>
<CAPTION>
                               Rent Per Rentable
        Month                  Square Foot              Base Monthly Rent
        -----                  -----------------        -----------------
   <S>                         <C>                      <C>
   6/1/1999 - 5/31/2000              $1.45                  $31,562.15
   6/1/2000 - 5/31/2001              $1.51                  $32,868.17
   6/1/2001 - 5/31/2002              $1.57                  $34,174.19
   6/1/2002 - 5/31/2003              $1.63                  $35,480.21
   6/1/2003 - 6/30/2004              $1.70                  $37,003.90
</TABLE>

          Notwithstanding the foregoing, the Base Monthly Rent for June, 1999,
shall be prorated to include only Base Monthly Rent for Suite 450.

     6.   TENANT's SHARE OF INCREASED COSTS.
          ---------------------------------

          (a)  The Base Rent payable during each calendar year or part thereof
during the Term, after the calendar year 1999 (the calendar year 1999 being
hereinafter referred to as the "Base Year") shall be increased by Tenant's Share
of Increased Costs, as specified in the Basic Lease Information, of the total
dollar increase, if any, in Operating Expenses paid or incurred by Landlord in
the Base Year. As used herein "Operating Expenses" means all costs, expenses and
disbursements of any kind related to the administration, management, repair,
operation and maintenance of the Building or any portion thereof, including
without limitation, wages, salaries and other payroll costs and expenses,
janitorial maintenance, guard and other services, Building office rent or rental
value, power, water, waste disposal and other utilities, materials and supplies,
maintenance and repairs, insurance, and depreciation on personal property and
costs of making improvements to the Building or Common Areas that are required
by laws which come into effect after execution hereof, including, without
limitation, improvements required by the Americans With Disabilities Act (42
U.S.C. Section 12181 et seq.); provided, however, that Operating Expenses shall
                     -- ---
not include (i) taxes covered under paragraph (b) below; (ii) depreciation other
than depreciation on exterior window draperies and carpeting in public corridors
and Common Areas, if any; (iii) costs incurred for leasing, renovating,
improving or decorating vacant space or space for other tenants in the Building;
(iv) real estate brokers' commissions; (v) interest; (vi) except as set forth in
Section 6(f) below, capital items; (vii) costs arising as a result of a
violation of any law(s) applicable to the Building by Landlord, other tenants of
the Building or their respective agents, employees or contractors or costs to
bring the Building into compliance with any applicable laws which are in effect
as of execution hereof; (viii) costs incurred to correct any construction
defects in the Building or to comply with any conditions, covenants or
restrictions affecting the Building in effect as of execution hereof; (ix) costs
incurred in connection with negotiations or disputes with other tenants or
occupants of the Building and costs arising from the violation of any lease or
agreement by Landlord or any other tenant or occupant of the Building;(x)
without limitation on the provisions of Section 46 below, costs incurred in the
remediation of Hazardous Materials; and (xi) costs for which Landlord receives
reimbursement from a third party (except from other tenants in the Building as a
share of Operating Expenses in accordance with this provision or a similar
provision in such tenants' leases). The cost of premiums for earthquake or flood
insurance, if incurred by Landlord after the Base Year, shall be added to the
Base Year calculation and Tenant shall only be responsible for its share of the
amount exceeding the amount attributed to the Base Year. In the event that the
Building is less than ninety-five percent (95%) occupied, actual Operating
Expenses for both the Base Year and each subsequent calendar year shall be
adjusted to equal Landlord's reasonable estimate of Operating Expenses had
ninety-five percent (95%) of the total rentable area of the Building been
occupied and assessed.

          (b)  The Base Rent payable during each calendar year, or part thereof
during the Term, after the calendar year 1999 (the "Base Tax Year"), shall also
be increased by Tenant's Share of Increased Costs, as specified in the Basic
Lease Information, of the total dollar increase, if any, in real and personal
property taxes, rental tax, gross receipts tax and any tax, tax assessment,
special assessment, charges or other imposition of any nature whatsoever levied
wholly or partly in lieu thereof, whether or not such tax, tax assessment,
special assessment, charge or other imposition is presently within the
contemplation of the parties, levied against the Building and fixtures and other
property used in connection with the operation or maintenance of the Building
for such calendar year, over such taxes for the Base Tax Year. In the event that
the Building is less than ninety-five percent (95%) occupied, the actual amount
of said taxes and assessments for both the Base Tax Year and each subsequent
calendar year shall be adjusted to equal Landlord's reasonable estimate thereof
had ninety-five percent (95%) of the total rentable area of the Building been
occupied and assessed.
<PAGE>

          (c)  Prior to the start of each calendar year or as soon thereafter as
practicable, Landlord shall give Tenant written notice of its estimate of
amounts payable under paragraphs (a) and (b) above for the ensuing calendar
year. On or before the first day of each month during the ensuing calendar year,
Tenant shall pay to Landlord one-twelfth (1/12) of such estimated amounts,
provided that if such notice is not given in December, Tenant shall continue to
pay on the basis of the prior year's estimate until the month after such notice
is given. If at any time or times it appears to Landlord that the amounts
payable under either paragraph (a) and (b) above for the current calendar year
will vary from its estimate by more than five percent (5%), Landlord shall, by
written notice to Tenant, revise its estimate for such year, and subsequent
payments by Tenant for such year shall be based upon such revised estimate.

          (d)  Within a reasonable time after the close of each calendar year,
Landlord shall deliver to Tenant a statement of amounts payable under paragraphs
(a) and (b) above for such calendar year. If such statement shows an amount
owing by Tenant that is less than the estimated payments for such calendar year
previously made by Tenant, Tenant shall be given a credit towards future rents
owed in an amount equivalent to the overpayment. If such statement shows an
amount owing by Tenant that is more than the estimated payment for such calendar
year previously made by Tenant, Tenant shall pay the deficiency to Landlord
within thirty (30) days after delivery of the statement.

          (e)  If, for any reason, this Lease shall terminate on a day other
than the last day of a calendar year, the amount of increase (if any) in rent
payable by Tenant applicable to the calendar year in which such termination
shall occur shall be equitably prorated on the basis which the number of days
from the commencement of such calendar year to and including such termination
date bears to three hundred sixty-five (365).

          (f)  Tenant shall be charged for the amortization, with a market rate
of interest, of the cost of installation of capital investment items that are
for the purpose of reducing operating costs or which result in energy
conservation or that may be required by applicable law or governmental
authority. All such costs shall be amortized over the reasonable life of the
capital investment items, with the reasonable life and amortization schedule to
be determined in accordance with sound management accounting principles.

          (g)  All amounts payable under this Section 6 shall be considered
additional rent.

          (h)  Upon reasonable advance written notice by Tenant to Landlord,
given not more often than once per statement described above and within sixty
(60) days after Tenant's receipt of the statement described in Subsection 6(d)
above, Tenant shall be permitted to examine the books and records in Landlord's
possession which are pertinent to the Operating Expenses and Taxes described in
such statement. Such examination shall be conducted at Tenant's sole expense and
at Landlord's office or at such other place where such books and records are
commonly kept by Landlord, and shall be conducted so as not to interfere with
Landlord's normal business operations. If Tenant fails to conduct such
examination within sixty (60) days after its receipt of a statement as set forth
above, then Tenant's right to conduct such examination shall be deemed waived
with respect to such statement and such statement shall be final and binding
upon Landlord and Tenant. If such examination reveals an overpayment of
Operating Expenses or Taxes for the period covered-by such statement, then,
provided Landlord does not reasonably dispute the results thereof, Landlord
shall credit such overpayment against the next monthly rent payment of Tenant,
or if the Term hereof has expired, Landlord shall promptly refund the
overpayment to Tenant. If such examination reveals an underpayment of Operating
Expenses or Taxes for the period covered by such statement, then Tenant shall
pay the same with its next monthly rent payment, or if the Term hereof has
expired, Tenant shall pay the same within fifteen (15) days after receipt of the
examination results. If Tenant's examination reveals an overstatement of
Operating Expenses of five percent (5%) or more, then the reasonable costs and
expenses of Tenant's examination shall be paid by Landlord.

     7.   USE.
          ---

          (a)  The Premises shall be used for general office purposes and as a
computer server room containing fiber optic and telephone devices and electrical
switching devices (the "Data Center"), and for no other purpose without the
written consent of Landlord. Tenant shall not do or permit to be done in or
about the
<PAGE>

Premises, nor bring or keep or permit to be brought or kept therein, anything
which is prohibited by or will in any way conflict with any law, statute,
ordinance or governmental rule or regulation now in force or which may hereafter
be enacted or promulgated or which is prohibited by the standard form of fire
insurance policy, or will in any way increase the existing rate of or affect
any fire or other insurance upon the Building or any of its contents, or cause a
cancellation of any insurance policy covering the Building or any part thereof
or any of its contents. Tenant shall not do or permit anything to be done in or
about the Premises which will in any way obstruct or interfere with the rights
of other tenants of the Building, or injure or annoy them, or allow any
excessive noises, vibrations or odors to emit from the Premises, or use or allow
the Premises to be used for any improper, immoral, unlawful or objectionable
purpose, nor shall Tenant cause, maintain or permit any nuisance in, on or about
the Premises or commit or suffer to be committed any waste in, on or about the
Premises. Tenant shall keep the blinds closed on any first (1st) floor windows
through which telephone or computer equipment may be seen from outside the
Premises, as determined by Landlord.

          (b)  Tenant shall not use the name of the Building or any similar name
in connection with any business carried on by Tenant (except as Tenant's
address) without written consent of Landlord which Landlord may withhold in its
sole and absolute discretion.

          (c)  Tenant acknowledges that neither Landlord nor any agent of
Landlord has made any representation or warranty regarding the zoning of the
Building or the suitability of the Premises for the conduct of Tenant's
business, nor whether said business is permitted by law.

     8.   SERVICES.
          --------

          (a)  Landlord shall maintain the public and common areas of the
Building, such as lobbies, stairs, elevators, corridors and restrooms in
reasonably good order and condition except for damage occasioned by the act of
Tenant, which damage shall be repaired by Landlord at Tenant's expense.

          (b)  Landlord shall furnish the Premises with (i) electricity for
lighting and the operation of office machines consistent with normal general
office use, (ii) heat and air conditioning to the extent reasonably required in
Landlord's judgment for the comfortable occupation of the Premises for normal
general office use during the reasonable and usual business hours of 8:00 a.m.
to 6:00 p.m., Monday through Friday, and between the hours of 8:00 a.m. and 1:00
p.m. on Saturday (exclusive of Sundays and Holidays) or such shorter period
specified or prescribed by any applicable policies or regulations adopted by any
utility or government agency, (iii) elevator service (if an elevator currently
exists in the Building), (iv) lighting replacement (for building standard
lights), (v) restroom supplies, and (vi) daily janitor service based on normal
general office use five nights per week (exclusive of holidays) furnished in the
manner that such services are customarily furnished in comparable buildings in
the Irvine area. If Tenant requires any utilities or services during times other
than the business hours set forth in item (ii) above, then Tenant shall promptly
upon demand reimburse Landlord for all costs of providing the same, as
reasonably estimated by Landlord. Landlord shall not be in default hereunder or
be liable for any damages directly or indirectly resulting from, nor shall the
rental herein reserved be abated by reason of (1) the installation, use or
interruption of use of any equipment used for the furnishing of any of the
foregoing services or of any phone lines, (2) failure to furnish or delay in
furnishing any such services when such failure or delay is caused by repair,
accident or any condition beyond the reasonable control of Landlord or by the
making of necessary repairs or improvements to the Premises or to the Building,
or (3) the limitation, curtailment, rationing or restrictions on use of water,
electricity, gas or any other form of energy serving the Premises or the
Building. Landlord shall use reasonable efforts to remedy the interruption in
the furnishing of such services. Landlord shall be entitled to cooperate
voluntarily in a reasonable manner with the efforts of national, state or local
agencies or utilities suppliers in reducing energy or other resource
consumption. Landlord shall be under no obligation to provide additional or
after-hours heating or air conditioning, but if Landlord elects to provide such
services at Tenant's request, Tenant shall pay Landlord the then current
Building standard rate for such services as determined by Landlord.

          (c)  Whenever heat generating machines or equipment or lighting other
than Building standard lights are used in the Premises by Tenant which affect
the temperature otherwise maintained by the air conditioning system, unless
installed by Tenant pursuant to Section 2.13 of Exhibit "B", Landlord shall have
                                                -----------
the right to install
<PAGE>

supplementary air conditioning units in the Premises, and the cost thereof,
including the cost of installation and the cost of operation and maintenance
thereof, shall be paid by Tenant to Landlord upon billing by Landlord. In
addition, Tenant shall enter into and pay for a service contract with a licensed
air-conditioning contractor to service the supplementary air-conditioning units.
If Tenant installs lighting or equipment requiring power in excess of that
required for normal lighting or desk-top office equipment or normal copying
equipment, Tenant shall pay for the cost of such excess power as additional
rent, together with the cost of installing any additional risers or other
facilities that may be necessary to furnish such excess power to the Premises.

          (d)  In the event that Tenant has unusual needs with regard to the
services to be provided by Landlord set forth above, including but not limited
to, any unusual utility usage or installation, Tenant shall immediately notify
Landlord in writing of same. In the event of any of the above situations
requiring additional electricity, Landlord, at its option, may: (i) cause same
to be separately metered at Tenant's expense including the expense of
installation of such meters, in which case Tenant shall pay the cost of a
monthly meter reader to read the meter(s), or (ii) equitably estimate the cost
thereof to be charged directly to Tenant. If Tenant fails to give Landlord
written notice of Tenant's unusual needs for services, Landlord may back-charge
Tenant for an equitable amount to compensate Landlord for such extra electrical
usage; provided, however, Tenant's use of electric current shall never exceed
the capacity of the feeders to the Building in which the Premises is located or
the risers or wiring installation.

     9.   TAXES PAYABLE BY TENANT.
          -----------------------

          In addition to the monthly rental and other charges to be paid by
Tenant hereunder, Tenant shall reimburse Landlord upon demand for any and all
taxes payable by Landlord (other than net income taxes) whether or not now
customary or within the contemplation of the parties hereto: (a) upon, measured
by or reasonably attributable to the cost or value of Tenant's equipment,
furniture, fixtures and other personal property located in the Premises or by
the cost or value of any leasehold improvements made in or to the Premises by or
for Tenant, other than Landlord's work under Exhibit "B" regardless of whether
                                             ------------
title to such improvements shall be in Tenant or Landlord; (b) upon or measured
by the monthly rental payable hereunder, including, without limitation, any
gross income tax or excise tax levied by the City of Irvine, the State of
California, the Federal Government or any other governmental body with respect
to the receipt of such rental; (c) upon or with respect to the possession,
leasing, operation, management, maintenance, alteration, repair, use or
occupancy by Tenant of the Premises or any portion thereof; and (d) upon this
transaction or any document to which Tenant is a party creating or transferring
an interest or an estate in the Premises.

     10.  IMPROVEMENTS. REPAIRS AND ALTERATIONS.
          -------------------------------------

          Upon taking possession of the Premises as set forth herein, Tenant
shall, be deemed to have accepted the Premises as being in tenantable and good
condition. Upon delivery thereof, the Premises (and all Building systems
directly serving the Premises except those which Tenant is responsible for
installing in connection with the Tenant Improvements) shall be in good
condition, order and repair and the Premises roof shall be watertight. Tenant
shall, at Tenant's sole cost and expense, repair and maintain the Premises and
every part thereof in good order and condition and, except as expressly provided
in Section 15 below, in compliance with all applicable laws, ordinances and
regulations and, subject to the third sentence of this Section 10, Tenant shall,
at Tenant's sole cost and expense, make any change or alterations to the
Premises required thereby. Without limiting the foregoing, Tenant shall, at its
sole cost and expense, cause the Premises to comply at all times with the
requirements of Title III of the Americans With Disabilities Act (42 U.S.C.
Section 12181 et seq.), the regulations now or hereafter adopted pursuant
              -- ---
thereto, and any and all applicable laws, statutes, ordinances, rules and
regulations concerning public accommodations for disabled persons now or
hereafter in effect. Notwithstanding the foregoing, Tenant shall not alter or
change the Premises or any other portion of the Building without the prior
written consent of Landlord, which shall not be withheld for changes required by
law, except that such changes shall be subject to Landlord's reasonable approval
of plans therefor and Landlord may elect to have its own contractors perform any
such alterations that affect Building systems, utilities or structural portions
and Tenant shall reimburse Landlord for the reasonable costs thereof within five
(5) business days after written demand. Notwithstanding the immediately
preceding sentence, Tenant shall have the right (i) to make interior, non-
structural alterations which do not affect the Building systems (including,
without limitation; mechanical, electrical, HVAC, plumbing and life and safety
systems) and which do not cost more than $10,000 in the
<PAGE>

aggregate over the Term of the Lease and (ii) to install cables, computer lines
and telephone lines in the Premises subject to Landlord's approval as to size,
design, layout, location and method of installation. Tenant hereby waives the
provisions of Subdivision (1) of Section 1932 of the Civil Code of California,
and any successor or similar statute or law. All improvements, repairs and/or
alterations that may be required of or desired by Tenant shall be done by
Landlord's contractor but at the cost of Tenant. All improvements, repairs, and
alterations shall become the property of Landlord and shall remain upon and be
surrendered with the Premises; provided, however, that at Landlord's option,
Tenant shall, at Tenant's expense, when surrendering the Premises, restore the
same to their original condition. All damage or injury done to the Premises by
Tenant, or by any persons who may be in or upon the Premises with the consent of
Tenant, shall be paid for by Tenant. Tenant shall, at the termination of this
Lease by the expiration of time or otherwise, surrender and deliver up the
Premises to Landlord in as good condition as when received by Tenant from
Landlord, reasonable wear and tear excepted and subject to the following (to the
extent not caused or created by Tenant, its agents, employees or invitees): (i)
acts of God, (ii) casualty, (iii) condemnation, (iv) the presence of Hazardous
Materials not caused or created by Tenant, its agents employees or contractors,
and (v) improvements, repairs and/or alterations which Landlord has requested to
remain in the Premises. Tenant shall pay for all damage to the Building, as well
as all damage to tenants or occupants thereof, caused by Tenant's misuse or
neglect of the Premises or the appurtenances thereto.

     11.  LIENS.
          -----

          Tenant shall keep the Premises and the Building free from any
mechanic's and/or materialmen's liens or other liens arising out of any work
performed, materials furnished or obligations incurred by Tenant. Tenant shall
notify Landlord at least seventy-two (72) hours prior to the commencement of any
work or activity on the Premises which may give rise to such liens and Landlord
shall have the right to post and keep posted on the Premises any notices that
may be provided by law or which Landlord may deem to be proper for the
protection of Landlord, the Premises and the Building from such liens. If a
mechanic's lien is filed as a result of Tenant's activities, Tenant shall
promptly cause such lien to be removed, or if Tenant contests the correctness or
validity of any claim of lien, Tenant shall provide Landlord with evidence that
Tenant has recorded a statutory lien release bond pursuant to California Civil
Code Section 3143 and has given notice thereof pursuant to California Civil Code
Section 3144.5 or any successor statutes pertaining to those Sections. If Tenant
fails to do so, Landlord may, but need not (i) record the statutory lien release
bond, and charge Tenant the bond premium together with interest thereon as
additional rent hereunder, or (ii) Landlord may, at its option, pay the lien or
any portion of it without inquiry as to its validity. Any amounts paid by
Landlord to remove a mechanics' lien, including all expenses and reasonable
attorneys' fees incurred by Landlord, shall be due and payable by Tenant to
Landlord immediately upon demand, together with interest, until paid.

     12.  DAMAGE AND DESTRUCTION.
          ----------------------

          If the Premises or the Building are completely destroyed by any cause
insured against under a standard form fire and extended coverage policy of
insurance, or are so damaged thereby that they are untenantable within one
hundred eighty (180) days after the date of such destruction or damage, Landlord
or Tenant may terminate this Lease by written notice to the other given within
five (5) business days after the end of the one hundred eighty (180) day period.
Within forty-five (45) days after the date of such destruction or damage,
Landlord shall give written notice to Tenant as to whether or not the Premises
will be rendered tenantable within one hundred eighty (180) days after the date
of such destruction or damage. If this Lease is not terminated by Landlord or
Tenant as set forth above, Landlord shall with due diligence render the Premises
tenantable to the extent insurance proceeds are available therefor, and rent
allocable to the untenantable portion of the Premises shall be abated while such
portion remains untenantable. If the Premises or the Building are damaged or
destroyed by any cause other than a cause insured against under Landlord's
standard form fire and extended coverage policy of insurance or if more than
twenty-five percent (25%) of the replacement value of the Building is destroyed,
then Landlord may terminate this Lease by written notice to Tenant given within
thirty (30) days after such damage or destruction, which termination shall be
effective as of the date of the notice. Notwithstanding anything to the contrary
herein, if the Building or the Premises are damaged or destroyed within the last
twelve (12) months of the Term of this Lease, then Landlord may terminate this
Lease upon written notice to Tenant given within thirty (30) business days after
the damage or destruction occurs. Tenant hereby waives the provisions of
Subdivision 2 of Section 1932 of the California Civil Code and the
<PAGE>

provisions of Subdivision 4 of Section 1933 of the California Civil Code, and
all successor and similar statutes and laws and agrees that this Section 12 is
intended to govern damage and destruction to the Premises and the Building.

     13.  WAIVER OF SUBROGATION.
          ---------------------

          Prior to or immediately after the execution of this Lease, Tenant
shall procure from its insurers under all polices of property, liability,
workmen's compensation and other insurance now or hereafter existing during the
Term, and purchased by it insuring or covering the Premises or any portion
thereof or operations therein, a waiver of all rights of subrogation which the
insurer might otherwise have. Prior to or immediately after the execution of
this Lease, Landlord shall procure from its insurers under all polices of
property, liability, workmen's compensation and other insurance now or hereafter
existing during the Term, and purchased by Landlord insuring or covering the
Building or any portion thereof, or operations therein, a waiver of all rights
of subrogation which the insurer might otherwise have. The waiver of subrogation
under this Section 13 shall be applicable to Landlord's and Tenant's respective
agents, employees, contractors, successors, assigns and tenants or subtenants
and shall apply to all perils actually insured against by Landlord or Tenant
without regard to negligence or willful misconduct of the party so released.

     14.  INDEMNIFICATION.
          ---------------

          Tenant hereby waives all claims against Landlord, its agents,
employees and contractors for damage to Tenant's business or any of Tenant's or
any other person's or entity's property or injury to or death of any person in,
upon or about the Premises arising at any time and from any cause other than
solely by reason of the willful act or gross negligence of Landlord, its agents,
employees or contractors. Tenant shall defend (by counsel acceptable to
Landlord), indemnify and hold Landlord harmless from and against any and all
losses, claims, damages, liabilities and costs and expenses (including, without
limitation, reasonable attorneys' fees and expenses) arising directly or
indirectly from Tenant's (or any of Tenant's subtenants', assignees', agents',
contractors', employees', invitees', licensees' or guests') violation of any of
the terms, covenants or conditions of this Lease or from the use or occupancy of
the Premises, the Building, the Generator (as defined in Exhibit "B" attached
                                                         -----------
hereto) and/or the property upon which the Generator is located, except for
those losses, claims, damages, liabilities and costs and expenses caused solely
by the willful misconduct or gross negligence of Landlord, its agents, employees
or contractors. Tenant's obligations and Landlord's rights under this Section 14
shall survive the expiration or earlier termination of this Lease.

         Landlord shall indemnify, protect, defend (by counsel reasonably
satisfactory to Tenant), and hold Tenant harmless from and against any and all
claims, demands, actions, obligations, losses, liabilities, damages, costs, and
expenses (including, without limitation, reasonable attorneys' and other
professional fees), incurred by or asserted against Tenant in connection with
any claim, action, or demand for bodily injury or death or property damage
arising out of (i) any negligent act or omission or willful misconduct of
Landlord or of any of Landlord's employees, officers, agents, contractors, or
representatives occurring on or about the Common Areas to the extent the same is
covered Under a standard commercial general liability insurance policy, (ii) or
any construction defects in the Premises unless due to construction or
installation of improvements or alterations in the Premises by Tenant, its
agents employees or contractors, or (iii) in connection with any Hazardous
Materials present in the Building or the Premises not caused or created by
Tenant, its agents employees or contractors. Landlord's indemnity hereunder
shall exclude any claims for lost profits, loss in value, or other consequential
damages and shall not apply to the extent of any (a) negligence or willful
misconduct of Tenant or Tenant's agents, employees or contractors, or (b) breach
of any of Tenant's warranties or obligations hereunder. Landlord's obligations
and Tenant's rights under this Section 14 shall survive the expiration or
earlier termination of this Lease.

     15.  COMPLIANCE WITH LAW.
          -------------------

          Tenant shall, at its sole cost and expense, promptly comply with all
laws, statutes, ordinances and governmental rules, regulations or requirements
now in force or which may hereafter be in force, with the requirements of any
board of fire underwriters or other similar body now or hereafter constituted,
with any directions or occupancy certificates issued pursuant to any law by any
public officer or officers, as well as the provisions of all recorded documents
affecting the Premises, insofar as any thereof relate to or affect the
condition, use or occupancy of the Premises, or Tenant's business conducted
therein, excluding remediation of any Hazardous Materials not caused or created
<PAGE>

in any manner by Tenant and further excluding structural changes that are not
required due to improvements made by or for Tenant or due to Tenant's acts, but
including alterations to the Premises required by the Americans With
Disabilities Act that are required due to Tenant's alterations to the Premises.
Notwithstanding the foregoing, any cost to bring the Premises into compliance
with existing (i) applicable laws, (ii) conditions, covenants or restrictions,
or (iii) lender's requirements, which are in effect as of execution hereof for
the Premises based on normal general office use shall be at Landlord's cost.
Tenant shall be responsible for compliance with all applicable laws for the
Premises being used for other than normal general office use.

     16.  INSURANCE.
          ---------

          (a)  Tenant shall, at its sole cost and expense, during the Term of
this Lease, cause all improvements at any time located in the Premises (other
than the Building standard tenant improvements) and all equipment and fixtures
from time to time used or intended to be used in connection with the operation
and maintenance of the Premises, to be insured for the mutual benefit of
Landlord and Tenant against loss or damage by fire and against loss or damage by
other risks now or hereafter included in the All-Risk insurance policy, in an
amount equal to the full insurable value thereof. All proceeds from such
insurance shall be used for the repair or replacement of such improvements,
equipment and fixtures.

          (b)  Notwithstanding any other provisions of this Lease, Tenant, at
its own expense, shall also maintain the following insurance coverage. All
coverage shall be primary and non-contributory over any insurance the Landlord
may elect to provide on his behalf. Upon the commencement of the Term, and upon
renewal of such insurance coverage, Tenant shall deliver to the Landlord an
original certificate of such insurance from the insurer providing a minimum of
thirty (30) days' notice of cancellation or modification. All policies of
insurance required to be carried by Tenant under this Section 16 shall be in
form satisfactory to Landlord, shall name Landlord as an additional insured,
shall be issued by responsible insurance companies which are licensed to do
business in the State of California, and shall have a Best's rating of at least
"A" and a financial rating of not less than "X" and have been approved in
writing by Landlord. The policies shall contain cross-liability endorsements or
their equivalent, and shall be for the mutual and joint benefit and protection
of Landlord, Tenant and any other party designated by Landlord as an additional
insured.

               (1)  Worker's Compensation and Employer's Liability. Tenant shall
maintain Worker's Compensation insurance sufficient to comply with all
applicable State and/or Federal laws and an Employer's Liability policy with a
limit of not less than $1,000,000.

               (2)  Commercial General Liability. Tenant shall maintain a
Commercial General Liability policy with limits of liability not less than
$2,000,000 per occurrence and $3,000,000 general aggregate for Bodily Injury and
Property Damage and $2,000,000 aggregate products/completed operations coverage.
Such policy shall specifically name the Landlord as additional insured. Landlord
may, at its discretion, request evidence of products insurance.

               (3)  Business Interruption. Tenant shall also maintain a policy
of (or obtain an endorsement providing) business interruption insurance insuring
Tenant against losses from interruption of its use of the Premises for any
reason with coverage for a period of not less than one (1) year.

               (4)  Property Insurance. Tenant shall maintain an All-Risk
property insurance policy on all personal property and tenant improvements and
betterments for not less than ninety percent (90%) of the replacement cost of
the same. Tenant's property policy shall not provide for a deductible in excess
of $5,000 without prior written approval of Landlord.

     17.  ASSIGNMENT AND SUBLETTING.
          -------------------------

          Tenant shall not assign, mortgage, pledge or otherwise transfer this
Lease, or any interest therein, either voluntarily, involuntarily, or by
operation of law, and shall not sublet the Premises or any part thereof, or any
right or privilege appurtenant thereto, or suffer any other person (the agents
and employees of Tenant excepted) to occupy or use the Premises, or any portion
thereof, without the written consent of Landlord, which consent shall not be
unreasonably withheld. Notwithstanding the foregoing, Tenant may transfer its
interest in the Premises to (i) a parent company, subsidiary, or affiliate of
Tenant which controls or is controlled by or is under common control with
Tenant, (ii) a successor
<PAGE>

corporation related to Tenant by merger, consolidation, nonbankruptcy
reorganization or government action, or (iii) a purchaser of all or
substantially all of Tenant's assets (collectively "Affiliate"), without
Landlord's consent, but upon thirty (30) days prior written notice. If Tenant is
a corporation, then a change or changes in the ownership of Tenant, whether
voluntarily, involuntarily, or by operation of law, which aggregate(s) fifty
percent (50%) or more of total capital stock of Tenant or fifty percent (50%) or
more of voting capital stock of Tenant shall be deemed an assignment of this
Lease. Notwithstanding the immediately preceding sentence, so long as Tenant's
stock is sold on a nationally recognized public exchange, no sale of stock shall
be deemed an assignment or subletting. a consent to one assignment, mortgage,
pledge, subletting, occupation, or use by any other person shall not relieve
Tenant from any obligation under this Lease and shall not be deemed to be a
consent to any subsequent assignment, mortgage, pledge, subletting, occupation
or use by another person. Any assignment, mortgage, pledge, subletting,
occupation or use without such consent shall be void, and shall, at the option
of Landlord, terminate this Lease. Tenant's request for Landlord's consent
pursuant to this Section 17 shall be submitted in writing at least forty-five
(45) days prior to the date Tenant desires to secure such consent. Such request
shall be accompanied by all relevant information reasonably necessary for
Landlord to consider such request. Any request for Landlord's consent pursuant
to this Section 17 shall also be accompanied by a payment to Landlord of $500.00
for the review, evaluation, and/or preparation of any materials or documents;
provided, however, if Landlord elects to terminate pursuant to this Section 17,
the $500.00 shall be refunded to Tenant. In lieu of considering any such request
(other than a request to the mortgage or pledge of this Lease) following the
initial Term of this Lease, Landlord may, within fifteen (15) days after receipt
thereof from Tenant, notify Tenant of Landlord's election to terminate this
Lease (or if a subletting of only a part of the Premises is involved, terminate
this Lease only as to that part and reduce the rent and other monetary
obligations of Tenant proportionately), which election, if made, shall be
effective no less than sixty (60) nor more than ninety (90) days after the date
of such election. If such election is made by Landlord, Tenant shall surrender
the Premises (or if a subletting of only a part of the Premises is involved,
only that part) to Landlord on the effective date of such termination, and
Tenant shall thereafter incur no further liability under this Lease for the
Premises (or for that part of the Premises required to be surrendered).

          Tenant and Landlord shall equally divide any sums or other economic
consideration for which Tenant is entitled to as a result of an assignment,
sublease or transfer of Tenant's interest in and to the Premises, or any portion
thereof (other than (i) the rental or other payments received which are
attributable to the cost of leasehold improvements made to the assigned or
sublet portion of the Premises at the cost of Tenant, (ii) any brokerage
commission related to the assignment or sublet, and (iii) any reasonable
attorneys' fees related to the assignment or sublet, provided that each of the
foregoing costs are amortized over the term of the assignment or sublease, as
applicable), whether denominated rentals under the sublease or otherwise, which
exceed in the aggregate the total sums which Tenant is obligated to pay Landlord
under this Lease (prorated to reflect obligations allocable to that portion of
the Premises subject to such assignment or sublease) ("Net Proceeds"). Said Net
Proceeds shall be paid to Landlord (i) in the case of an assignment, in its
entirety promptly following the effective date of the assignment, or (ii) in the
case of a sublease, on a monthly basis, along with Tenant's payment of Base
Monthly Rent, without affecting or reducing any other obligation of Tenant
hereunder.

          Regardless of Landlord's consent, no subletting or assignment
(including subletting or assignment to an Affiliate) shall release Tenant of
Tenant's obligations hereunder or otherwise alter the primary liability of
Tenant hereunder. The acceptance of rent or any other sum by Landlord from any
person or entity shall not be deemed to be a waiver by Landlord of any provision
hereof. In the event of default by any assignee of Tenant or any successor of
Tenant in the performance of any of the terms hereof, Landlord may proceed
directly against Tenant without the necessity of exhausting remedies against
said assignee or successor. Landlord may consent to subsequent subletting or
assignments of this Lease by assignees of Tenant without notifying Tenant or any
successor of Tenant, and without obtaining its or their consent thereto and such
action shall not relieve Tenant of any liability under this Lease.

     18.  RULES.
          -----

          Tenant shall faithfully observe and comply with the rules and
regulations annexed to this Lease as Exhibit "D" and, after notice thereof, all
                                     -----------
reasonable modification thereof and additions thereto from time to time
promulgated in writing by Landlord. Landlord shall not be responsible to Tenant
for the nonperformance by any other tenant or occupant of the Building of any of
said rules and regulations.
<PAGE>

     19.  ENTRY BY LANDLORD.
          -----------------

          Landlord may enter the Premises at reasonable hours upon twenty-four
(24) hours prior notice (except (i) in the event of emergency or to provide
services pursuant to subsection (d) below in which case no notice shall be
necessary or (ii) only eight (8)hours prior notice shall be required with
respect to exhibiting the Premises to prospective tenants during the last seven
(7) months of the Term; provided, however, that Tenant shall use reasonable
efforts to cooperate with Landlord in the event Landlord provides fewer than
eight (8) hours notice) to: (a) inspect the same; (b) exhibit the same to
prospective purchasers, lenders or tenants; (c) determine whether Tenant is
complying with all of Tenant's obligations hereunder; (d) supply janitor service
and any other service to be provided by Landlord to Tenant hereunder, (e) post
notice of non-responsibility; and (f) make repairs required of Landlord under
the terms hereof or repairs to any adjoining space or utility service or make
repairs, alterations or improvements to any other portion of the Building,
provided, however, that all such work shall be done as promptly as reasonably
possible and so as to cause as little interference to Tenant as reasonably
possible. Tenant hereby waives any claim for damages for any injury or
inconvenience to or interference with Tenant's business, any loss of occupancy
or quiet enjoyment of the Premises or any other loss occasioned by such entry.
Landlord shall at all times have and retain a key with which to unlock all of
the doors in, on or about Premises (excluding Tenant's vaults, safes and similar
areas designated in writing by Tenant in advance) and Landlord shall have the
right to use any and all means which Landlord may deem proper to open said doors
in an emergency in order to obtain entry to the Premises. Any entry to the
Premises obtained by Landlord by any of said means, or otherwise, shall not be
construed or deemed to be a forcible or unlawful entry into or a detainer of the
Premises or an eviction, actual or constructive, of Tenant from the Premises, or
any portion thereof.

     20.  EVENTS OF DEFAULT.
          -----------------

          The occurrence of any one or more of the following events ("Events of
Default") shall constitute a breach of this Lease by Tenant: (a) if Tenant shall
fail to pay any rent (including Base Rent and Tenant's Share of Increased Costs)
within three (3) days after the date such rent becomes due and payable, or (b)
if Tenant shall fail to pay any other sum when and as the same becomes due and
payable and such failure shall continue for more than ten (10) business days
after receipt of written notice that such payment is overdue; or (c) if Tenant
shall fail to perform or observe any other term hereof or of the rules and
regulations described in Section 18 to be performed or observed by Tenant, such
failure shall continue for more than thirty (30) days after notice thereof from
Landlord and Tenant shall not within such period commence with due diligence and
dispatch the curing of such default, or, having so commenced, shall thereafter
fail or neglect to prosecute or complete with clue diligence and dispatch the
curing of such default; or (d) if Tenant shall make a general assignment for the
benefit of creditors, or shall admit in writing its inability to pay its debts
as they become due or shall file a petition in bankruptcy, or shall be
adjudicated as bankrupt or insolvent, or shall file a petition seeking any
reorganization, arrangement, composition, readjustment, liquidation, dissolution
or similar relief under any present or future statute, law or regulation, or
shall fail any answer admitting or shall fail timely to contest the material
allegations of a petition filed against it in any such proceeding, or shall seek
or consent to or acquiesce in the appointment of any trustee, receiver or
liquidator of Tenant or any material part of its properties; or (e) if within
thirty (30) days after the commencement of any proceeding against Tenant seeking
any reorganization, arrangement, composition, readjustment, liquidation,
dissolution or similar relief under any present or future statute, law or
regulation, such proceeding shall not have been dismissed, or if, within thirty
(30) days after the appointment without the consent or acquiescence of Tenant or
of any material part of its properties, such appointment shall not have been
vacated; or (f) if this Lease or any estate of Tenant hereunder shall be levied
upon under any attachment or execution and such attachment or execution is not
vacated within ten (10) days; or (g) if any other event occurs which is
described in this Lease as a material breach of, or default under, this Lease.

     21.  TERMINATION UPON DEFAULT.
          ------------------------

          If an Event of Default shall occur, Landlord at any time there after
may give a written termination notice to Tenant, and on the date specified in
such notice (which shall be not less than three (3) days after the giving of
such notice) Tenant's right to possession and this Lease shall terminate, unless
on or before such date all rent and other sums payable by Tenant under this
Lease (together with interest thereon at the maximum rate allowable by law) and
all costs have been paid by Tenant and all other breaches of this Lease by
Tenant at the time existing shall have been fully remedied. Upon such
termination, Landlord may recover from Tenant: (a) the worth at the time of
award of the unpaid rent which had been earned at the time of termination; (b)
the worth at the time of
<PAGE>

award of the amount by which the unpaid rent which would have been earned after
termination until the time of award exceeds the amount of such rental loss that
Tenant proves could have been reasonably avoided; (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; and (d) any other amount necessary to compensate
Landlord for all the detriment proximately caused by Tenant's failure to perform
its obligations under this Lease or which results therefrom. The "worth at the
time of award" of the amounts referred to in clauses (a) and (b) above shall be
computed by allowing interest at the rate of ten percent (10%) per annum. The
worth at the time of award of the amount referred to in clause (c) above shall
be computed by discounting such amount at the discount rate of the Federal
Reserve Bank of San Francisco at the time of award plus one percent (1%). For
the purposes of determining unpaid rent under clauses (a), (b) and (c) above,
the monthly rent reserved in this Lease shall be deemed to be the rent due under
Sections 4 and 5 above, as adjusted by Section 6.

     22.  CONTINUATION AFTER DEFAULT.
          --------------------------

          Landlord also has the remedy described in California Civil Code
Section 1951.4 (Lessor may continue Lease in effect after Lessee's breach and
abandonment and recover rent as it becomes due, if Lessee has the right to
sublet or assign, subject only to reasonable limitations). Acts of maintenance
or preservation or efforts to relet the Premises or the appointment of a
receiver upon application of Landlord to protect Landlord's interest under this
Lease shall not constitute a termination of Tenant's right to possession.

     23.  OTHER RELIEF.
          ------------

          The remedies provided for in this Lease are in addition to any other
remedies available to Landlord at law or in equity by statute or otherwise.

     24.  PARKING.
          -------

          Unless Tenant is in default under this Lease resulting in delivery of
a written termination notice pursuant to Section 21 above, Tenant shall be
entitled to fifty-four (54) unreserved vehicle parking spaces (based on (i) 3.8
spaces per 1,000 usable square feet in the Premises which is used as office
space, and (ii) 1 space per 750 usable square feet in the Premises which is used
as light industrial space (i.e., the Data Center)) in the Building parking
facility at no cost to Tenant during the initial Term of the Lease or the
Extension Term, if exercised. Thereafter, if applicable, parking spaces shall be
subject to a monthly parking fee for such spaces designated by Landlord for
parking, with Landlord reserving the right to set and increase monthly parking
fees for such spaces from time to time during the Term of this Lease. Upon
Tenant's completion of the Tenant Improvements, Tenant shall provide Landlord
with certification by Tenant's Space Planner (as defined in Exhibit "B" attached
                                                            -----------
hereto) of the usable square footage of the Data Center (which usable square
footage shall be subject to Landlord's verification), and the number of parking
spaces set forth above shall be adjusted accordingly (i.e., 19,435 [-] Data
Center usable square footage = office space usable square footage; [(office
space usable square footage/1,000) * 3.8] + [(Data Center usable square
footage/750] = total unreserved vehicle parking spaces). Landlord may assign any
unreserved and unassigned parking spaces and/or make all or a portion of such
spaces reserved, if it determines in its reasonable discretion that it is
necessary for orderly and efficient parking. Tenant shall not use more parking
than said number. If Landlord has not assigned specific spaces to Tenant, Tenant
shall not use any spaces which have been so specifically assigned by Landlord to
other tenants or for such other uses as visitor parking or which have been
designated by governmental entities with competent jurisdiction as being
restricted to certain uses. Tenant shall not permit or allow any vehicles that
belong to or are controlled by Tenant or Tenant's employees, suppliers,
shippers, customers, or invitees to be loaded, unloaded, or parking in areas
other than those designated by Landlord for such activities. If Tenant permits
or allows any of the prohibited activities described in this Section 24, then
Landlord shall have the right, without notice, in addition to such other rights
and remedies that it may have, to remove or tow away the vehicle involved and
charge the cost to Tenant, which cost shall be immediately payable upon demand
by Landlord. Landlord reserves the right at any time to relocate such spaces and
to substitute an equivalent number of parking spaces in a parking structure or
subterranean parking facility or in a surface parking area within a reasonable
distance of the Premises.

          If requested by Landlord, Tenant shall submit a written notice in a
form reasonably specified by Landlord containing the names and office addresses
and telephone numbers of those persons who are authorized by Tenant to use the
parking spaces on a
<PAGE>

monthly basis (the "Authorized Users") and shall use its best efforts to
identify each automobile by make, model and license number. Such notice, as
amended from time to time, is hereafter referred to as the "Parking Notice." No
person whose name, address, and phone numbers are not contained in the Parking
Notice shall have any right to park an automobile in the area of the parking
facilities designated for monthly parking and no person whether or not their
name is included in the Parking Notice shall have any right to park an
automobile not identified in the Parking Notice without (in either case) paying
the parking charge then applicable for daily parking in the parking facilities
for the Building and parking in the area designated for daily parking.

          Tenant and Authorized Users shall comply with all rules and
regulations as set forth in the Parking Rules and Regulations portion of the
rules and regulations adopted by Landlord from time to time. Landlord may refuse
to permit any person who violates the Parking Rules and Regulations to park in
the parking facility, and any violation of the rules shall subject the car to
removal. Tenant agrees to use its best efforts to acquaint all Authorized Users
and visitors with the Parking Rules and Regulations.

          All responsibility for damage to cars is assumed by Authorized Users.
Tenant shall repair or cause to be repaired at its sole cost and expense any and
all damage to the parking facility or any part thereof caused by Tenant or its
Authorized Users or resulting from vehicles of Authorized Users.

     25.  INTENTIONALLY OMITTED

     26.  TRADE FIXTURES.
          --------------

          Subject to the provisions of Sections 7 and 8 hereof, Tenant shall
install and maintain, its trade fixtures on the Premises, provided that such
fixtures, by reason of the manner in which they are affixed, do not become an
integral part of the Building or Premises. Tenant, if not in default hereunder,
may at any time or from time to time during the Term, or upon the expiration or
earlier termination of this Lease, alter or remove any such trade fixtures so
installed by Tenant. If not so removed by Tenant on or before the expiration or
earlier termination of this Lease, Tenant, upon the request of Landlord to do
so, shall thereupon remove the same. Any damage to the Premises caused by any
installation, alteration or removal of such trade fixtures shall be promptly
repaired at the expense of Tenant.

     27.  SUCCESSORS AND ASSIGNS.
          ----------------------

          Subject to the provisions hereof relating to assignment, mortgaging,
pledging and subletting, this Lease shall bind the heirs, executors,
administrators, successors and assigns of any and all the parties hereto.

     28.  TIME.
          ----

          Time is of the essence of this Lease.

     29.  LANDLORD's DEFAULT.
          ------------------

          If Landlord shall default in the performance of any of its obligations
under this Lease, Tenant shall have no right to pursue any remedies against
Landlord, including, without limitation, termination of this Lease, unless and
until Tenant shall have given Landlord written notice of the default and
Landlord shall not have commenced the cure of such default within thirty (30)
days after receipt of the notice, or thereafter shall not diligently prosecute
the cure to completion. Satisfaction of any money judgment obtained against
Landlord shall be satisfied only out of: (i) proceeds of sale or disposition of
Landlord's interest in the Building, whether by Landlord or by execution of
judgment; or (ii) rentals and other payments from tenants in the Building.

     30.  INTENTIONALLY OMITTED

     31.  LANDLORD's RIGHT TO CURE DEFAULTS.
          ---------------------------------

          All agreements and provisions to be performed by Tenant under any of
the terms of this Lease shall be performed at Tenant's sole cost and expense and
without any abatement or setoff against rent. If Tenant shall fail to pay any
sum of money, other than rent, required to be paid by it hereunder or shall fail
to perform any other act on its part to be performed hereunder and such failure
shall continue for thirty (30) days after notice thereof by Landlord, Landlord
may, but shall not be obligated to do so, and without waiving or releasing
Tenant from any obligations of Tenant, make any such payment or
<PAGE>

perform any such other act on Tenant's part to be made or performed as provided
in this Lease. All sums so paid by Landlord and all necessary incidental costs
shall be deemed additional rent payable hereunder and shall be payable to
Landlord on demand, and Landlord shall have (in addition to any other right or
remedy of Landlord) the same rights and remedies in the event of the nonpayment
thereof by Tenant as in the case of default by Tenant in the payment of rent.

     32.  ATTORNEYS' FEES.
          ---------------

          If as a result of any breach or default in the performance of any of
the provisions of this Lease, Landlord or Tenant shall use the services of any
attorney in order to secure compliance with such provisions or recover damages
therefore, or to enforce any judgment or to terminate this Lease or, in
Landlord's case, to evict Tenant, the non-prevailing party shall reimburse the
prevailing party upon demand for any and all reasonable attorneys' fees and
expenses so incurred by such prevailing party, including but not limited to,
fees and expenses incurred in connection with appellate proceedings, enforcement
proceedings and bankruptcy proceedings (and the obligation to pay such fees and
expenses shall survive and not be merged into any judgement).

     33.  EMINENT DOMAIN.
          --------------

          Should the whole or any part of the Premises be condemned and taken by
any competent authority for any public or quasi-public use or purpose, all
awards payable on account of such condemnation and taking shall be payable to
Landlord, and Tenant hereby waives all interest in or claim to said awards, or
any part thereof. If the whole of the Premises shall be so condemned and taken,
then this Lease shall terminate. If a part only of the Premises is condemned and
taken and the remaining portion thereof is not suitable for the purposes of
which Tenant had leased said Premises, Tenant shall have the right to terminate
this lease. If by such condemnation and taking a part only of the Premises is
taken, and the remaining part thereof is suitable for the purposes for which
Tenant has leased said Premises, this lease shall continue, but the rental shall
be reduced in an amount proportionate to the value of the portion taken as it
related to the total value of the Premises. a voluntary sale of the building by
Landlord to any public or quasi-public body, agency or person, corporate or
otherwise, having the power of eminent domain, either under threat of
condemnation or while condemnation proceedings are pending, shall be deemed to
be taking under the power of eminent domain for purposes of this Section 33.

     34.  SUBORDINATION.
          -------------

          This Lease, at Landlord's option, shall be subordinate to any ground
lease, mortgage, deed of trust, or any other hypothecation for security now or
hereafter placed upon the Building and to any and all advances made on the
security thereof and to all renewals, modification, consolidations, replacements
and extensions thereof. 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 the Lease, unless this Lease is otherwise terminated pursuant
to its terms. If at any time any mortgagee, trustee or ground landlord shall
elect to have this Lease prior to the lien of its mortgage, deed of trust or
ground lease, then this Lease shall be deemed prior to such mortgage, deed of
trust or ground lease, whether this Lease is dated prior or subsequent to the
date of said mortgage, deed of trust or ground lease or the date of recording
thereof. Tenant agrees to execute any documents required to effectuate such
subordination or to make this Lease prior to the lira of any mortgage, deed of
trust or ground lease, as the case may be, and failing to do so within ten (10)
days after demand, does hereby make, constitute and irrevocably appoint Landlord
as Tenant's attorney in fact and in Tenant's name, place and stead, to do so. If
Tenant fails to execute any documents required to be executed by Tenant under
this Section within fifteen (15) days after written demand by Landlord, then
such failure shall constitute an Event of Default under this Lease.

     35.  NO MERGER.
          ---------

          The voluntary or other surrender of this Lease by Tenant, or a mutual
cancellation thereof, shall not work at merger, and shall, at the option of
Landlord, terminate all or any existing subleases or subtenancies, or may, at
the option of Landlord, operate as an assignment to it of any or all such
subleases or subtenancies.
<PAGE>

     Delivery Dock Hours:                   Monday-Friday 7:00 A.M. to 5:00 P.M.
     Freight Elevator Hours:                Monday-Friday 6:00 A.M. to 6:00 P.M.

     Note:  Other hours of access are available with prior arrangement.

8.   Building access hours:

         Monday-Friday:  6:00 AM to 10:00 PM
         Saturday:       8:00 AM to 6:00 PM
         Sunday:         10:00 AM to 6:00 PM

         Note:  Other hours of access are available with prior arrangement.

9.   Contractor, subcontractors and materialsmen are responsible for maintaining
     the condition of docks, elevators and corridors used. Contractor is
     responsible to protect floor and walls in corridors leading from the
     freight elevator to the entrance of the construction sight, as well as
     freight door jams.

10.  All materials are to be stored at the Job Site or in designated storage
     areas. No materials are to be stored in corridors or in public areas. The
     Landlord's Agent may provide minimum secured storage for materials with
     prior arrangement.

11.  Contractor, subcontractors and materialsmen must arrange access to areas
     other than Job Site at a minimum of 48 hours in advance.

12.  All work areas are to be visually and materially protected from the tenants
     and general public. Radios or other excessive noise are not permitted. All
     Contractors will be held responsible for compliance with O.S.H.A. Rules and
     Regulations.

13.  Toxic materials or odor-causing liquids are not to be used without prior
     scheduling with the Landlord's Agent, and prior notice to the tenants in
     suites adjacent to the Job Site.

14.  All non-Job Site areas of the building are to be kept clean; dust, debris
     and materials are to be cleaned immediately. There is to be no tracking of
     material residue through corridors or public areas.

15.  The Contractor and subcontractors are to ensure the Job Site is left broom
     clean at the completion of each scheduled work day. No trash or excess
     materials are
<PAGE>

     permitted to remain on, in, or at the Job Site. Materials are to be
     disposed of in bins or by truck promptly, not staged or stored at the Job
     Site in any public or adjacent areas, nor disposed of in the building's
                                           ---------------------------------
     trash receptacles.
     -----------------

16.  Tool clean-up is permitted in janitorial/utility closets only; no clean-up
     is permitted in rest rooms.

17.  Contractor is to furnish adequate protection against personal injury to
     employees and public while work is in progress. In addition, all equipment,
     furniture and supplies shall be protected from damage.

18.  The work area may be occupied during construction, which may require the
     Contractor to move and relocate furniture, files, machinery and equipment
     during construction. Upon the completion of the work, the contractor is to
     return all items relocated during the work to their original location.

19.  All salvageable items removed during the course of the work that are to be
     reused in the job, whenever possible, are to be stored and maintained by
     the Contractor. All salvageable materials and items of value, as determined
     by Landlord's Agent, that are removed from the site, that are not to be
     reused in the work, shall remain the property of the Landlord's Agent, and
     shall be stored or disposed of as directed by the Landlord's Agent.

20.  All work includes replacing, patching and finishing all adjacent surfaces
     or features displaced or disturbed in the performance of the work such as,
     but not limited to: acoustical tile, topset base, cove base, floor
     coverings, paint, etc. Upon completion of the work, there shall be no
     discrepancy between the new work and the existing work.

21.  The Contractor shall not disable, interrupt or test any building utilities
     or systems without prior arrangement with the Agent, nor without the
     presence of Building Engineering personnel.

22.  The Contractor shall be responsible for any stoppage, interruptions or
     failures to building services, utilities or incidental damages to the
     building during the course of the work being performed as a result of his
     performance of the work.
<PAGE>

23.  All Contractors are responsible for supplying the following tools or
     materials to the Job Site:

         a.  Ladders
         b.  Industrial vacuum cleaner
         c.  Protection for corridor floor coverings, walls and ceilings from
             the Job Site to the elevators
         d.  Protection for the elevators and the Job Site

24.  All anchoring of studs, drilling or coring of holes in concrete, applying
     carpet tack, and applying noxious materials (stains, fire-sealers, etc.)
     should be done after hours.

25.  The Landlord's Agent is not responsible for providing any tools, equipment,
     materials or labor for the work.

26.  The Contractor is responsible for the compliance to these rules and
     regulations by all his own personnel and those of his subcontractors,
     materialsmen and any other parties who may be employed for the performance
     and completion of the work.
<PAGE>

                                  EXHIBIT B-1
                                  -----------

         SECTION II: LANDLORD's REQUIREMENTS FOR TENANT IMPROVEMENTS OR
                     --------------------------------------------------
                     ALTERATIONS TO LEASED SPACE BY TENANT OR CONTRACTOR(S)
                     ------------------------------------------------------
                     HIRED BY TENANT
                     ---------------

The Tenant has certain requirements to provide information to the Landlord's
Agent regarding any alteration to be performed in the leased premises by Tenant.
Said information is to be submitted for approval by Landlord's Agent, which
approval shall not be unreasonably withheld. Below is a listing of those
requirements:

     1.   Two sets of plans (a.k.a. working drawings) of the work to be
          performed, including details of connections to any building system
          (i.e., electrical, life-safety, plumbing, HVAC, etc.). One set will be
          retained by Landlord's Agent. One set will be returned to Tenant,
          signed by Landlord's Agent, as the approval set of record.

     2.   List of all Contractors, sub-contractors and material suppliers.

     3.   A copy of the Contractor's and sub-contractors' current construction
          licenses including expiration date and type.

     4.   Certificates of Insurance from the Contractor, naming Master Landlord,
          Landlord, Landlord's Agent and Tenant as Additional Insureds, and an
          adequate amount of liability coverage, specifically:

          a.   General & Public Liability, no less than $1,000,000.

          b.   Workers' Compensation not less than statutory requirements.

          c.   Contractor's Business Liability (Umbrella) coverage of no less
               than $1,000,000.

Upon submittal to Landlord's Agent of the above items, Landlord's Agent shall
review the plans, list of project participants and other documentation, and make
recommendations, if any, for modifications and compliance with building
standards, including materials, as well as proper connections to the building
systems.
<PAGE>

After obtaining approval from the Landlord's Agent, and prior to the
commencement of work, the Tenant shall provide:

     1.   Hold Harmless Agreements signed by the Tenant and the Tenant's
          Contractor for the purpose of indemnifying the Master Landlord,
          Landlord, and Landlord's Agent from any liabilities, including but not
          limited to, liens filed against the property by any and all General
          Contractors, sub- contractors and sub-sub-Contractors, material
          suppliers and laborers.

     2.   A copy of the fully executed Contract for Work between Tenant and
          Contractor.

     3.   A copy of all required Municipal Building Permits.

The Tenant shall be responsible for instructing the Contractor and sub-
contractors to follow the building's Rules and Regulations provided herewith.
The Tenant will then advise the Landlord's Agent of the commencement date of
work, upon which notification the Landlord's Agent shall complete a Notice of
Non-Responsibility for filing with the County Recorder's Office and posting on
the job site. The Tenant shall provide Landlord with an anticipated payment
schedule prior to the commencement of work.

During the performance of the work, if there is a change or addition of
contractors, sub-contractors or material suppliers, the Tenant shall immediately
notify the Landlord's Agent, in writing, of the change or addition. All the same
qualifications shall apply to the changed or added parties.

In the event a Preliminary Lien Notice or Lien Notice is received by the Tenant,
Tenant shall immediately provide a copy of same to Landlord's Agent.

Landlord's Agent may, at its option, inspect the work in progress to insure that
the building's minimum standards of quality of craftsmanship are maintained.

The Tenant is responsible for coordinating with the office of the building, any
access requirements for the contractor for the purpose of stocking the job, work
to be performed in adjacent space, or connecting to or testing of base building
systems which may disturb the normal operation of the building.

After completion of the alteration, Tenant shall obtain the completed Permit Job
Card and a Temporary Certificate of
<PAGE>

Occupancy clearly indicating the City's final Inspection by signature and date.
Tenant shall submit a copy of same to Landlord's Agent as evidence of the
completed alteration.

Tenant shall, at the conclusion of all work, provide original Unconditional
Lien Release documents to the Landlord's Agent demonstrating the payment of all
outstanding invoices for the work.

Upon completion of the work, Contractor is to provide Landlord's Agent with a
set of "as-built" plans, cut sheets and specifications on all installed
equipment, all warranties, and the stamped plancheck approved drawings with the
permit signature card. These plans would include, but not be limited to:
architectural, structural, electrical, plumbing and mechanical drawings as
applicable.

If any reimbursement from Landlord's Agent is due Tenant, copies of all paid
invoices to all Contractors, sub-contractors and material suppliers must
accompany above said original Unconditional Lien Releases from each. Landlord's
Agent shall then reimburse Tenant's costs up to the agreed upon Tenant
Improvement Allowance, less any costs Landlord or Landlord's Agent may have
incurred in association with the performance of the work.

These requirements neither supersede or subjugate any of the terms and
conditions of the Lease for the leased space.
<PAGE>

                                  EXHIBIT B-2

                                 [FLOOR PLAN]
<PAGE>

                                  EXHIBIT "C"
                                  -----------

                             INTENTIONALLY OMITTED
<PAGE>

                                  EXHIBIT "D"
                                  -----------

                             RULES AND REGULATIONS
                             ---------------------

     The following Rules and regulations shall be in effect at the Building.
Landlord reserves the right to adopt reasonable modifications and additions
hereto.

     (1)  The sidewalks, entrances, passages, courts, elevators, vestibules,
stairways, corridors or halls of the Building shall not be obstructed by any
tenant or used for any purpose other than ingress and egress from the respective
premises. The halls, passages, entrances, elevators, stairways, balconies and
roof are not for the use of the general public, and Landlord shall in all cases
retain the right to control and prevent access thereto of all persons whose
presence in the judgment of Landlord shall be prejudicial to the safety,
character, reputation and interests of the Building and its tenants, provided
that nothing herein contained shall be construed to prevent such access to
persons with whom Tenant normally deals only for the purpose of conducting its
business on the Premises (such as clients, customers, office suppliers and
equipment vendors, and the like) unless such persons are engaged in illegal
activities. No tenant and no employees of any tenant shall go upon the roof of
the Building without the written consent of Landlord.

     (2)  No awnings or other projection shall be attached to the outside walls
of the Building or to balconies without the prior written consent of Landlord.
No hanging planters, television sets or other objects shall be attached to or
suspended from ceilings without the prior written consent of Landlord. No
curtains, blinds, shades or screens shall be attached to or hung in, or used in
connection with, any window or door of the Premises without the prior written
consent of Landlord. All electrical ceiling fixtures hung in offices or spaces
along the perimeter of the Building must be of a quality, type, design and bulb
color approved by Landlord. No awnings, furniture, trees or plants or other
personal property shall be placed upon any balcony or patio, without Landlord's
prior written approval.

     (3)  No sign, advertisement or notice shall be exhibited, painted or
affixed by any tenant on any part of, or so as to be seen from the outside of,
the Premises or the Building without the prior written consent of Landlord. In
the event of the violation of the foregoing by any tenant, Landlord may remove
such sign, advertisement or notice without any liability and may charge the
expense incurred in such removal to the tenant violating this rule. Interior
signs on doors and director tablet shall be inscribed, painted or affixed for
each tenant by Landlord at the expense of such tenant, and shall be of a size,
color and style acceptable to Landlord.

     (4)  The sashes, sash doors, skylights, windows and doors that reflect or
admit light and air into the halls, passageways or other public places in the
Building shall not be covered or obstructed by any tenant, nor shall any
bottles, parcels or other articles be placed in the windowsills, balcony or
patio railings.

     (5)  The water and wash closets and other plumbing fixtures shall not be
used for any purpose other than those for which they were constructed, and no
foreign substance of any kind shall be thrown herein. All damages resulting from
any misuse of the fixtures shall be borne by the tenant who, or whose servants,
employees, agents, visitors or licensees shall have caused the same.

     (6)  No tenant shall mark, paint, drill into, or in any way deface any part
of the Premises or the Building. No boring, cutting or stringing of wires or
laying of linoleum or other floor coverings shall be permitted, except with the
prior written consent of Landlord, and as Landlord may direct or as specifically
permitted under the Lease. Any tenant permitted by Landlord to lay linoleum or
other similar floor covering shall not affix the same to the floor of the
Premises in any manner except by a paste, or other material which may easily be
removed with water, the use of cement or other similar adhesive materials being
expressly prohibited. The method of affixing any such linoleum or other similar
floor covering to the floor, as well as the method of affixing carpets or rugs
to the Premises, shall be subject to approval by Landlord. The expense of
repairing any damage resulting from a violation of this rule shall be borne by
the tenant by whom, or by those agents, clerks, employees or visitors, the
damage shall have been caused.

     (7)  If Tenant desires telephone, cable TV, computer or telegraph
connections, other than for the Data Center which shall be governed by the
provisions of Exhibit "B"
<PAGE>

of the Lease, Landlord will direct electricians as to where and how the wires
are to be introduced.

     (8)  No bicycles, vehicles or animals of any kind shall be brought into or
kept in or about the Premises, and no cooking shall be done or permitted by any
tenant in the Premises, except for items customarily cooked in standard
household microwave ovens and preparation of coffee, tea, hot chocolate and
similar items for tenants, their employees and visitors shall be permitted. No
tenant shall cause or permit any unusual or objectionable odors to be produced
in or permeate from or throughout the Premises.

     (9)  No portion of the Building shall be used for manufacturing or for the
storage of merchandise except as expressly permitted under the use provisions of
the Lease and except as such storage may be incidental to the use of the
Premises for general office purposes without Landlord's prior written approval.
No tenant shall, without the prior written consent of the Landlord, occupy or
permit any portion of this premises to be occupied or used for the manufacture
or sale of liquor, narcotics, or tobacco in any form, as a medical office,
chiropractor's office, as a barber or manicure shop, or as an employment bureau
or any business other than that specifically provided for in the Lease. No
tenant shall engage or pay any employees on its premises except those actually
working for such tenant on its premises nor advertise for laborers giving an
address at its premises. The Building shall not be used for lodging or sleeping
or for any immoral or illegal purposes.

     (10) Except with the prior written consent of the Landlord, no tenant shall
sell, or permit the sale at retail or otherwise of newspapers, magazines,
periodicals, or theatre tickets, in or from the Building, nor shall any tenant
carry on, or permit or allow any employee or other person to carry on, the
business of stenography, typewriting or any similar business in or from the
Building for the service or accommodation of occupants of any other portion of
the Building.

     (11) Landlord reserves the right to prohibit personal goods and services
vendors (as such term is defined below) from access to the Building. To the
extent that Landlord permits such vendors access to the Building, such access
shall be upon such reasonable terms and conditions, including but not limited to
the payment of a reasonable fee and provision for insurance coverage, as are
related to the safety, care and cleanliness of the Building, the preservation of
good order thereon, and the relief of any financial or other burden on Landlord
occasioned by the presence of such vendors or the sale by them of personal goods
or services (as such term is defined below) to a tenant or its employees. If
reasonably necessary for the accomplishment of the aforementioned purposes,
Landlord may exclude a particular vendor entirely or limit the number of vendors
who may be present at any one time in the Building. The term "personal goods or
services vendors" means persons who periodically enter the Building for the
purpose of selling goods or services to a tenant, other than goods or services
which are used by a tenant only for the purpose of conducting its business on
its premises. "Personal goods or services" include, but are not limited to,
barbering services and shoe shining services. "Personal goods or services" shall
not include vendors delivering bottled water, soft drinks, pizza, sandwiches and
the like when doing so at the express request of Tenant or Tenant's employees
for purposes other than resale.

     (12) No tenant shall make, or permit to be made, any unseemly or disturbing
noises or disturb or interfere with occupants of this or neighboring buildings
or premises or those having business with them by the use of any musical
instrument, radio, phonograph or unusual noise, or in any other way.

     (13) No tenant shall throw anything out of doors, windows or skylights or
down the passageways.

     (14) No tenant, nor any of a tenant's servants, employees, agents, visitors
or licensees, shall at any time bring, keep or use on the Building any kerosene,
gasoline, or inflammable, combustible, explosive, or corrosive fluid, or any
other illuminating material, or use any method of heating other than that
supplied by Landlord.

     (15) No tenant shall sweep or throw or permit to be swept or thrown from
the Premises any dirt or other substance into any of the corridors or halls or
elevators, or out of the doors, windows, stairways, patios or balconies of the
Building, and Tenant shall not use, keep or permit to be used or kept any foul
or noxious gas or substance in the Premises, or Permit or suffer the Premises to
be occupied or used in a manner offensive or objectionable to Landlord or other
occupants of the Building by reason of noise, odors and/or vibrations, or
interfere in any way with other tenants or those
<PAGE>

having business therein, nor shall any animals or birds be kept in or about the
Building. Smoking or carrying lighted cigars, cigarettes, pipes, or other
lighted smoking materials, in the elevators and all other common and/or public
areas of the Building is prohibited.

     (16) No additional locks or bolts of any kind shall be placed upon any of
the doors or windows by any tenant, or shall any changes be made in existing
locks or the mechanisms thereof unless Landlord is first notified thereof and
gives written approval. Each tenant must, upon termination of his tenancy, give
to Landlord all keys of stores, offices, or toilets and toilet rooms, either
furnished to, or otherwise procured by, such tenant, and in the event of the
loss of any keys so furnished, such tenant shall pay Landlord the cost of
replacing the same or of changing the lock or locks opened by such lost key if
Landlord shall deem it necessary to make such change.

     (17) All removals, or the carrying in or out of any safes, freight,
furniture, or bulky matter of any description must take place during the hours
which Landlord may determine from time to time. The moving of safes or other
fixtures or bulky matter of any kind must be made upon previous notice to the
manager of the Building and under his/her supervision, and the persons employed
by any tenant for such work must be acceptable to Landlord. Landlord reserves
the right to inspect all safes, freight or other bulky articles to be brought
into the Building and to exclude from the Building and all such bulky articles
which violate any of the Rules and Regulations or the Lease of which these Rules
and Regulations are a part. Landlord reserves the right to prescribe the weight
and position of all safes, which must be placed upon supports approved by
Landlord to distribute the weight.

     (18) No tenant shall purchase janitorial, maintenance or other services
from any company or persons not approved by Landlord, which approval shall not
be unreasonably withheld. Any person employed by any tenant to do janitorial
work shall, while in the Building and outside of the Premises, be subject to and
under the control and direction of the office or management of the Building (but
not as an agent or servant of Landlord, and the tenant shall be responsible for
all acts of such persons). Except with Landlord's prior written approval, no
tenant shall permit janitorial services to be performed during the hours of 7:00
a.m. to 6:00 p.m. Monday through Friday.

     (19) Should the Building have retail tenants, Landlord shall have the right
to prohibit any advertising by any tenant which, in Landlord's opinion, tends to
impair the reputation of the Building or its desirability as an office/retail
building and upon written notice from Landlord any tenant shall refrain from and
discontinue such advertising.

     (20) On Saturdays from 1:00 p.m. to 8:00 a.m., Sundays, those legal
holidays designated by Landlord, and on other days between the hours of 7:00
p.m. and 7:00 a.m., access to the Building or to the halls, corridors, elevators
or stairways in the Building, or to the Premises may be refused unless the
person seeking access is pre-approved by Landlord. Any list of employees of
Tenant submitted to Landlord shall be deemed pre-approved. Landlord shall in no
case be liable for damages for admission to or exclusion from the Building of
any person whom Landlord has the right to exclude. Each tenant shall be
responsible for all persons for whom he requests after hours access and shall be
liable to Landlord for all acts of such persons. In case of invasion, mob, riot,
public excitement, or other commotion, Landlord reserves the right but shall not
be obligated to prevent access to the Building during the continuance of the
same by closing the doors or otherwise, for the safety of the tenants and
protection of property in the Building.

     (21) All doors opening into public corridors shall be kept closed, except
when in use for ingress and egress. Tenants shall see that the windows, transoms
and doors of their premises are closed and securely locked before leaving the
Building.

     (22) The requirements of tenants will be attended to by the manager of the
Building upon formal written or oral request of Tenant.

     (23) Canvassing, soliciting and peddling in the Building are prohibited and
each tenant shall cooperate to prevent the same.

     (24) There shall not be used in any space, or in the public halls of the
Building, either by any tenant or others, any hand trucks except those equipped
with rubber tires and side guards.
<PAGE>

     (25) No vending or coin operated machines shall be placed by any tenant
within his premises without the prior written consent of Landlord, not to be
unreasonably withheld.

     (26) Tenant shall fully abide by and comply with any Covenants, Conditions
and Restrictions or similar instrument or document imposed against or
encumbering the Building or Project.

     (27) These Rules and Regulations are in addition to, and shall not be
construed to in any way modify or amend, in whole or in part, the terms,
covenants, agreements and conditions or any lease of premises in the Building.<PAGE>

                                                                   EXHIBIT 10.56

                                   SUBLEASE

     THIS SUBLEASE AGREEMENT ("Sublease"), made and entered on the 22nd day
December 1999, by and between WILLIAMS COMMUNICATIONS, INC., a Delaware
corporation formerly known as CRITICAL TECHNOLOGIES, INC., a Missouri
corporation ("Sub-Landlord") and CONCENTRIC NETWORK CORPORATION, a Delaware
corporation ("Sub-Tenant") (collectively the "parties").

                                  WITNESSETH:

     WHEREAS, an office building lease with an effective date of February 26,
1997, was entered into by and between Sub-Landlord as Tenant and Armstrong
Properties, LTC as Landlord (the "Lease");

     WHEREAS, the Premises covered by the Lease is an approximately 23,500
square foot office building and adjoining parking areas located at 944 Anglum
Drive, Hazelwood, Missouri 63042 (the "Premises"). Sub-Landlord desires to
sublet the entire Premises (hereinafter the "Sublease Premises") to Sub-Tenant,
and Sub-Tenant desires to Rent from Sub-Landlord the Sublease Premises.

     WHEREAS, the parties have reached an agreement by which Sub-Tenant would
sublease the Sublease Premises from Sub-Landlord; and

     WHEREAS, the parties desire to set forth the terms and conditions of the
sublease of the Sublease Premises.

     NOW, THEREFORE, in consideration of the premises and the following mutual
covenants, the parties hereby agree:

1.   Recitals: The above recitals are incorporated herein as terms of this
     Sublease.

2.   Sublease: Sub-Landlord hereby subleases to Sub-Tenant and Sub-Tenant hereby
     subleases from Sub-Landlord the Sublease Premises, subject to and
     conditioned upon obtaining the consent of Landlord to this Sublease.

3.   Lease: Sub-Tenant represents and warrants that it has received a conformed
     copy of the Lease, that it has reviewed the same, and that it agrees to
     comply with the terms thereof the same as if it were the Tenant
<PAGE>

     thereunder, except as otherwise provided herein. This Sublease is and shall
     remain subordinate to the terms and conditions of the Lease. To the extent
     that Sub-Landlord has rights or obligations under the Lease as Tenant, Sub-
     Tenant has the same rights or obligations with respect to the Sublease
     Premises. This Sublease shall not increase any obligation of Sub-Landlord
     beyond its obligations as a Tenant under the Lease. A copy of the Lease is
     attached hereto as Exhibit "A" and made a part hereof by reference.

4.   Term: The Sublease shall commence on November 1, 1999, (the "Commencement
     Date") subject to Landlord's consent to the Sublease, and terminate on
     March 31, 2002 (the "Termination Date"), unless sooner terminated as
     hereinafter provided (the "Sublease Term"). If Landlord's consent has not
     occurred for any reason whatsoever on or before December 15, 1999, then
     either party may terminate the Sublease by written notice to the other and
     Sub-Tenant shall promptly vacate the Sublease Premises.

5.   Basic Rent: Sub-Tenant shall pay Sub-Landlord as Rent for the Sublease
     Premises the sum Fourteen Thousand Six Hundred Eighty Seven and 00/100
     Dollars ($14,687.00) per month from November 1, 1999, through March 31,
     2000; and, commencing April 1, 2000, through March 31, 2002, Sub-Tenant
     shall pay Sub-Landlord as Rent for the Sublease Premises the sum Sixteen
     Thousand Six Hundred Forty Five and 00/100 Dollars ($16,645.00) per month.
     Rent shall be payable in advance without demand on the first day of each
     and every month during the remaining term of the Lease. Any Rent accrued
     prior to obtaining Landlord's consent to the Sublease shall be due and
     payable on obtaining Landlord's consent. A late charge of five percent (5%)
     of any monthly payment will be added after fifteen (15) days from the due
     date and paid by Sub-Tenant. Sub-Tenant's failure to pay any monthly rental
     within ten (10) days after the due date shall be deemed an event of default
     under this Sublease.

6.   Operating Expenses: Sub-Tenant shall, from the Commencement Date, pay Sub-
     Landlord for all gas, electricity, water, air conditioning, sewer and
     telephone service and all other utilities used in and upon the Sublease
     Premises. Sub-Tenant shall pay for its own trash removal.
<PAGE>

7.   Real Estate Taxes: Sub-Tenant shall pay all real estate and occupancy
     taxes, assessments, and/or installments thereon (collectively, "Taxes") on
     or before the date the same shall become due, whether general or special,
     foreseen and unforeseen, and shall furnish Landlord and Sub-Landlord a copy
     of the paid receipts therefor. Taxes shall be pro-rated between Sub-
     Landlord and Sub-Tenant for the year 1999, according to the Commencement
     Date.

8.   Use of Sublease Premises:

     8.1  The Sublease Premises are subleased to Sub-Tenant in "as is" condition
          with all faults as of the Commencement Date of the Sublease Term and
          Sub-Landlord has made no representation or warranty, express or
          implied, with respect to the condition of the Sublease Premises, or
          appurtenant grounds or facilities or with respect to their suitability
          for the conduct of Sub-Tenant's business or other intended use. Prior
          to the Commencement Date, Sub-Landlord shall have cleared all debris
          from the Sublease Premises and shall deliver the Sublease Premises to
          Sub-Tenant in vacant, good, "broom-clean" condition, with all systems
          that were Tenant's responsibility under the Lease in good working
          order. Sub-Tenant's acceptance of the Sublease Premises shall not be
          deemed a waiver of the above representations. Subject to Landlord's
          consent, Sub-Landlord hereby approves Sub-Tenant's installation of the
          alterations described in Exhibit "B", attached hereto, and subject to
          Landlord's consent agrees the Sub-Tenant may surrender such
          alterations on the termination of the Sublease.

     8.2  The Sublease Premises are to be used only for the purposes allowed by
          the Lease, including a data center, and must be continuously occupied
          by Sub-Tenant.

     8.3  Upon the termination of the Sublease, Sub-Tenant will return the
          Sublease Premises to Sub-Landlord in the same condition as the
          Sublease Premises were in as of the Commencement Date of this
          Sublease,
<PAGE>

          reasonable wear and tear, casualty and condemnation damage, and
          approved alterations excepted.

9.   Assignment and Subletting: Sub-Tenant will not assign this Sublease or
     sublet the Sublease Premises without the prior written consent of Landlord
     and Sub-Landlord. Sub-Landlord shall not unreasonably withhold or delay its
     consent. Provided, Sub-Tenant may, without Sub-Landlord's prior written
     consent (but subject to Landlord's consent to the extent required under the
     Lease), sublet the Sublease Premises or assign the Sublease to (i) an
     entity controlling, controlled by or under common control with Sub-Tenant;
     (ii) a successor entity related to Sub-Tenant by merger, consolidation,
     nonbankruptcy reorganization, or government action; or (iii) a purchaser of
     substantially all of Sub-Tenant's assets located in the Sublease Premises.
     In the event of any sublease or assignment pursuant to (i), (ii), or (iii)
     above, Sub-Tenant shall remain liable under this Sublease.    A transfer of
     Sub-Tenant's capital stock shall not be deemed an assignment, subletting or
     any other transfer of the Sublease or the Sublease Premises.

10.  No Real Estate Broker: Each of the parties represents that no real estate
     broker was used in connection with this Sublease.

11.  No Security Deposit: Sub-Tenant acknowledges that Sub-Landlord has
     deposited with Landlord the sum Sixteen Thousand Six Hundred Forty Five and
     00/100 Dollars ($16,645.00) as a Security Deposit pursuant to paragraph 6
     of the Lease, and agrees to make no claim to or against said Security
     Deposit or any portion thereof on termination of this Sublease, or
     otherwise. Sub-Landlord will not require any security deposit from Sub-
     Tenant under this Sublease.

12.  No Option to Renew: Sub-Tenant may not exercise the Option to Renew granted
     to Sub-Landlord under paragraph 31 of the Lease unless Landlord shall first
     have agreed in writing with Sub-Landlord and Sub-Tenant that Sub-Landlord
     shall have no further liability under the Lease or Sublease whatsoever with
     respect to the extension period, and that Sub-Landlord shall receive full
     refund of the Security Deposit on termination of the Lease. Sub-Landlord
     shall not exercise the Option to Renew
<PAGE>

     unless first obtaining Sub-Tenant's prior written consent.

13.  Notice and Payment Addresses: Notices shall be delivered in the manner set
     forth in Section 22 of the Lease to the addresses set forth below:

     Sub-Landlord:

          Williams Communications, Inc.
          One Williams Center
          Suite 2200
          Tulsa, Oklahoma 74172
          Attn: Director of Facilities Management

     Sub-Tenant:

          Concentric Network Corporation
          944 Anglum Drive
          Hazelwood, Missouri 63042
          Attn: Office Manager

          Concentric Network Corporation
          10590 North Tantau Avenue
          Cupertino, California 95014
          Attn: Director of Administration

     Landlord:

          Armstrong Properties, LTC
          31 Fordyce
          St. Louis, MO 63124
          Attn: Mr. William H. Armstrong

14.  Termination of Lease: The parties hereto agree that in the event the Lease
     terminates, then this Sublease shall also terminate on that same date.

15.  Insurance: Sub-Tenant agrees, at its sole cost and expense, during the term
     of this Sublease to maintain in full force and effect insurance coverages
     in form and substance as required of Tenant under the Lease, and to name
     Sub-Landlord as an additional insured in each case in which Landlord must
     be named an additional insured as provided by the Lease.

16.  Sub-Landlord Warranties:
<PAGE>

     16.1  Sub-Landlord represents and warrants the following to Sub-Tenant:

          16.1.1 The Lease is in full force and effect and that there is no
          default thereunder or to Sub-Landlord's knowledge no event which, with
          the passage of time and giving of notice or both, would constitute a
          default thereunder.

          16.1.2 Sub-Landlord has corporate authority to enter into this
          Sublease and perform its obligations hereunder.

          16.1.3 This Sublease evidences a valid and binding contractual
          obligation of Sub-Landlord enforceable in accordance with its terms.

          16.1.4 The copy of the Lease attached hereto as Exhibit A is a true,
          correct and complete copy of the Lease.

17.  Sub-Tenant's Authority:

     17.1  Sub-Tenant represents and warrants the following to Sub-Landlord:

          17.1.1  Sub-Tenant has corporate authority to enter into this Sublease
          and perform its obligations hereunder.

          17.1.2  This Sublease evidences a valid and binding contractual
          obligation of Sub-Tenant.

18.  Indemnification: The following indemnification provisions shall apply.

          (a) By Sub-Landlord. Sub-Landlord will indemnify, defend, protect, and
              ---------------
          hold Sub-Tenant, its officers, directors, employees, and agents
          (collectively, the "Sub-Tenant Indemnitees") harmless from and against
          any and all demands, actions or causes of action, assessments,
          judgments, damages, obligations, liabilities and claims (collectively,
          "Claims") of every type and nature whatsoever (including, without
          limitation, injury to or death of any person or persons, or
<PAGE>

          damage to or loss of any property) and shall reimburse the Sub-Tenant
          Indemnitees for any and all financial expenditures, costs and expenses
          (including, without limitation, interest, penalties and reasonable
          attorneys' fees, reasonable consultants' fees, expenses and court
          costs incurred in connection therewith and all reasonable costs and
          expenses of investigating and defending any claim or any order,
          directive, final judgment, compromise, settlement, fine, penalty,
          court costs or proceeding) in consequence of such Claims arising from
          or related to:

               (i)   any inaccuracy in or breach by Sub-Landlord of any
               representation or warranty made by it herein; or

               (ii)  any claim or demand for commission or other compensation by
               any broker, finder, agent or similar intermediary claiming to
               have been employed by or on behalf of Sub-Landlord, in connection
               with this transaction; or

               (iii) any contamination at, on, in, above or beneath the Sublease
               Premises during the term of the Lease and preceding the term of
               the Sublease; or

               (iv)  any negligent acts or omissions, or willful misconduct, by
               Sub-Landlord, its employees or agents, which result in or cause
               harm or damage to any person or property, in, upon, or about the
               Sublease Premises; or

               (v)   any event of default by Sub-Landlord under the Lease or
               this Sublease.

          (b)  By Sub-Tenant. Sub-Tenant will indemnify, defend, protect, and
               -------------
          hold Sub-Landlord and Landlord and any affiliated company thereto,
          their respective officers, directors, stockholders, managers, members,
          employees, and agents (the "Sub-Landlord Indemnitees") harmless from
          and against any and all demands, actions or
<PAGE>

          causes of action, assessments, judgments, damages, obligations,
          liabilities and claims (collectively, "Claims") of every type and
          nature whatsoever (including, without limitation, injury to or death
          of any person or persons, or damage to or loss of any property) and
          shall reimburse the Sub-Landlord Indemnitees for any and all financial
          expenditures, costs and expenses (including, without limitation,
          interest, penalties and reasonable attorneys' fees, reasonable
          consultants' fees, expenses and court costs incurred in connection
          therewith and all reasonable costs and expenses of investigating and
          defending any claim or any order, directive, final judgment,
          compromise, settlement, fine, penalty, court costs or proceeding) in
          consequence of such Claims, and arising from or pursuant to:

               (i)   any inaccuracy in or breach by Sub-Tenant of any
               representation or warranty made by it herein;

               (ii)  any claim or demand for commission or other compensation by
               any broker, finder, agent or similar intermediary claiming to
               have been employed by or on behalf of Sub-Tenant in connection
               with this transaction;

               (iii) any contamination at, on, in, above or beneath the Sublease
               Premises during the term of this Sublease caused or created by
               Sub-Tenant or its agents, employees, or contractors; or

               (iv)  any negligent acts or omissions, or willful misconduct, by
               Sub-Tenant, its employees or agents, which result in or cause
               harm or damage to any person or property, in, upon, or about the
               Sublease Premises; or

               (v)   any event of default by Sub-Tenant under this Sublease.

19.  Applicable Law: This Sublease shall be construed according to the laws of
     the State of Missouri.
<PAGE>

20.  Headings: The headings in this Sublease are for reference only and do not
     expand or limit the terms agreed to by the parties.

21.  Entire Agreement: This Sublease represents the entire agreement between the
     parties and no modification hereof shall be effective unless first reduced
     to writing and signed by both parties.

22.  Incorporation of Lease. All of the provisions of the Lease are incorporated
     herein as if set forth in their entirety herein, except (a) the following
     provisions shall not be incorporated herein: Sections 4 (the first sentence
     only), 5, 6, 22, 31, and 32; and (b) references to "Landlord" in the
     following provisions shall mean "Landlord" only: Sections 10 (except the
     fourth paragraph), 11 (except the first sentence), 14, 17 (the third
     through seventh sentences only) and 19 (except the last sentence of subpart
     (a)). References in the Lease as incorporated herein to "Landlord",
     "Tenant", "Lease" and "Leased Premises" shall be deemed to refer to "Sub-
     Landlord", "Sub-Tenant", "Sublease" and "Sublease Premises", respectively;
     provided, however, that (i) with respect to work, services, repairs,
     restoration, insurance or any other similar obligation of Landlord under
     the Lease, the sole obligation of Sub-Landlord shall be to use Sub-
     Landlord's reasonable efforts to obtain Landlord's performance as set forth
     below; and (ii) with respect to any consent or approval required to be
     obtained from the "Landlord" under the Lease, such consent must be obtained
     from both Landlord and Sub-Landlord, and the approval of Sub-Landlord may
     be withheld if Landlord's consent is not obtained.

23.  Quiet Enjoyment. In the event that Sub-Landlord defaults in the performance
     or observance of any of Sub-Landlord's remaining obligations under the
     Lease or fails to perform Sub-Landlord's stated obligations under the
     Sublease, then Sub-Tenant shall give Sub-Landlord notice specifying in what
     manner Sub-Landlord has defaulted, and if such default shall not be cured
     by Sub-Landlord within thirty (30) days thereafter (except that if such
     default cannot be cured within said thirty (30) day period, this period
     shall be extended for an additional reasonable time, provided
<PAGE>

     that Sub-Landlord commences to cure such default within such thirty (30)
     day period and proceeds diligently thereafter to effect such cure as
     quickly as possible), then Sub-Tenant shall be entitled to cure such
     default and promptly collect from Sub-Landlord Sub-Tenant's reasonable
     expenses in so doing (including, without limitation, reasonable attorneys'
     fees). Sub-Tenant shall not be required, however, to wait the entire cure
     period described herein if earlier action is required to comply with the
     Lease or with any applicable governmental law, regulation or order.

24.  Sub-Landlord's Obligations. Sub-Landlord shall fully perform all of its
     obligations under the Lease to the extent Sub-Tenant has not agreed to
     perform such obligations under the Sublease. Sub-Landlord shall not
     terminate or take any action under the Lease that could give rise to the
     termination of the Lease, amend or waive any provisions under the Lease or
     make any elections, exercise any right or remedy or give any consent or
     approval under the Lease without, in each instance, Sub-Tenant's prior
     written consent if any of the foregoing would materially adversely affect
     Sub-Tenant's rights or obligations hereunder. Sub-Landlord, with respect to
     the obligations of Landlord under the Lease, shall use Sub-Landlord's
     diligent good faith efforts to cause Landlord to perform such obligations
     for the benefit of Sub-Tenant. Such diligent good faith efforts shall
     include, without limitation: (a) upon Sub-Tenant's written request,
     immediately notifying Landlord of its nonperformance under the Lease, and
     requesting that Landlord perform its obligations under the Lease; and (b)
     to commence litigation against Landlord to obtain the performance required
     from Landlord under the Lease.

25.  Authorization to Direct Sublease Payments. Sub-Tenant shall have the right
     to pay all rent and other sums owing by Sub-Tenant to Sub-Landlord
     hereunder for those items which also are owed by Sub-Landlord to Landlord
     under the Lease directly to Landlord if Sub-Tenant reasonably believes that
     Sub-Landlord has failed to make any payment required to be made by Sub-
     Landlord to Landlord under the Lease and Sub-Landlord fails to provide
     adequate proof of payment within two (2) business days after Sub-Tenant's
     written
<PAGE>

     demand requesting such proof. Any sums paid directly by Sub-Tenant to
     Landlord in accordance with this paragraph shall be credited toward the
     amounts payable by Sub-Tenant to Sub-Landlord under the Sublease. In the
     event Sub-Tenant tenders payment directly to Landlord in accordance with
     this paragraph and Landlord refuses to accept such payment, Sub-Tenant
     shall have the right to deposit such funds in an account with a national
     bank for the benefit of Landlord and Sub-Landlord, and the deposit of said
     funds in such account shall discharge Sub-Tenant's obligation under the
     Sublease to make the payment in question.

26.  Assignment of Rights. Sub-Landlord hereby assigns to Sub-Tenant all
     warranties given and indemnities made by Landlord to Sub-Landlord under the
     Lease which would reduce Sub-Tenant's obligations hereunder, and shall
     cooperate with Sub-Tenant to enforce all such warranties and indemnities.

27.  Subordination. Sub-Landlord shall reasonable efforts to obtain from any
     lenders or ground lessors of the Sublease Premises a written agreement in
     form reasonably satisfactory to Sub-Tenant providing for recognition of
     Sub-Tenant's interests under the Sublease in the event of foreclosure of
     the lender's security interest or termination of the ground lease.

28.  Hazardous Materials. To the best knowledge of Sub-Landlord, no Hazardous
     Materials are present in or about the Sublease Premises and no action,
     proceeding, or claim is pending or threatened concerning any Hazardous
     Materials or pursuant to any laws. Sub-Landlord shall indemnify, defend,
     protect and hold Sub-Tenant, its agents, officers, directors and
     shareholders, harmless from and against all claims, losses, costs, damages,
     liabilities, (including, without limitation, sums paid in settlement of
     claims), and expenses (including, without limitation, reasonable attorneys'
     and consultant's fees and litigation expenses), arising out of or based
     upon the presence of any Hazardous Materials on, under, in or about the
     Sublease Premises, except to the extent the same results from Sub-Tenant's,
     or any other person or entity's, release or emission of Hazardous Materials
     in or about the Sublease Premises.
<PAGE>

29.  Approvals. Whenever the Sublease requires an approval, consent,
     designation, determination, selection or judgment by either Sub-Landlord or
     Sub-Tenant, 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 and, in exercising any right or remedy
     hereunder, each party shall at all times act reasonably and in good faith.

30.  Landlord Consent. The Sublease shall be conditioned upon receipt of consent
     thereto by Landlord in a form reasonably acceptable to Sub-Tenant, which
     consent shall, at Sub-Tenant's election, include the terms set forth in
     Exhibit "C" hereto. Sub-Landlord shall use commercially reasonable efforts
     to obtain such consent. In the event Landlord fails to so consent within
     thirty (30) days for the date Sub-Tenant executes the Sublease, either Sub-
     Landlord or Sub-Tenant shall have the right to terminate the Sublease at
     any time before such consent is received by delivering written notice
     thereof to the other party.

     IN WITNESS WHEREOF, the parties hereto have caused this Sublease to be
executed and sealed by their respective representatives, thereunto duly
authorized, as of the date first above written.

                         Sub-Landlord:

                         Williams Communications Inc.,

                         By:  /s/ James A. Wootten
                              --------------------

                         Printed: James A. Wootten
                                  ----------------

                         Title:  Vice President
                                 -----------------

ATTEST:

-----------------
Secretary [Seal]
<PAGE>

                         Sub-Tenant:

                         Concentric Network Corporation

                         By:  /s/ Henry R. Nothhaft
                              ---------------------------

                         Printed:  Henry R. Nothhaft
                                   ----------------------

                         Title: Chairman, President & CEO
                               --------------------------

ATTEST:

--------------------
Secretary [Seal]
<PAGE>

                                   EXHIBIT B

                         Williams Technology Solutions
                         Anglum Leasehold Improvements
                                1997 Relocation

                                          Net Book Value
     Phase I
          Office Buildout                    $ 76,829.22
          Electrical                         $ 63,941.84
          Kitchen-New Cabinets/Counter       $    630.63
          Net Ops/Computer Room              $ 31,966.17
          Security/Fire Protection           $ 16,713.87
                                             -----------
                    Sub-total                $190,081.73

     Phase II
          Construction                       $ 58,102.50
          Floor Covering                     $ 16,288.64
          Electrical                         $ 50,471.02
          HVAC                               $  4,383.86
          Signage                            $  5,579.46
          Misc.                              $  1,092.78
                                             -----------
                    Sub-total                $135,918.27
                                             -----------

                    Total                    $326,000.00
                                             ===========
<PAGE>

                                   Exhibit B

5 ton Liebert cooling system w/Humidification

30 KVA UPS
<PAGE>

                                     LEASE

THIS LEASE, made and entered into the 26 day of February, 1997, by and between
ARMSTRONG PROPERTIES, LTC, a Missouri Limited Partnership ("Landlord"), and
CRITICAL TECHNOLOGIES, INC., a Missouri corporation ("Tenant"),

                                  WITNESSETH:

1.   PREMISES: Landlord, for and in consideration of the rents, covenants and
     --------
     agreements hereinafter mentioned and hereby agreed to be paid, kept and
     performed by Tenant, does hereby lease with covenant for quiet enjoyment to
     Tenant, and Tenant hereby hires from the Landlord, the following described
     premises (the "Leased Premises") located in the city of Hazelwood, in the
     County of St. Louis, State of Missouri, and more particularly described as
     follows:

          A 23,500 square foot office building and adjoining parking areas known
          and numbered as 944 Anglum Drive, Hazelwood, Missouri 63042.

2.   USE OF PREMISES: The Leased Premises may be used and occupied by Tenant
     ---------------
     during the term hereof, subject to the conditions herein contained and
     subject to applicable zoning regulations, for parking, office and warehouse
     activities. In no event shall the leased Premises be used for any purpose
     contrary to law, zoning regulations, or recorded restrictions, if any.

3.   IMPROVEMENTS TO PROPERTY: Landlord agrees that prior to the commencement of
     ------------------------
     the term of this Lease it will, at its expense, inspect and repair all of
     the mechanical (heating, cooling and ventilating) units, lighting,
     electrical, plumbing, and windows, in order to place same in good working
     order. Landlord shall not be obligated to make any other repairs or
     improvements to accommodate Tenant's use. Tenant shall have the right to
     install in the Leased Premises additional heating ventilating and air
     conditioning equipment, loading facilities, interior furnishes and shall
     have the right to instill a free-standing electrical generator outside of
     the building, provided all of the following conditions have been met: (a)
     plans and specifications for any such improvement shall have been submitted
     to Landlord and Landlord shall have specifically approved same in writing
     (which approval Landlord agrees shall not be unreasonably withheld) and (b)
     all work is done in a good and workmanlike manner in accordance with the
     plans and specifications approved by Landlord, (c) all work is done in
     full compliance with all building codes, City of Hazelwood ordinances and
     other laws applicable thereto, and (d) Tenant shall pay for all cost and
     expense involved in such work, including and professional fees incurred by
     Landlord to review such plans and specifications, and (e) Tenant shall
     obtain Lien Waivers from all mechanics and material suppliers for such
     improvements.

4.   TERM: The term of this Lease shall commence on the 26th day of February,
     ----
     1997, and end on the 31st day of March, 2002, both dates inclusive. If by
     mutual consent of the parties, Tenant shall remain in possession of the
     Leased Premises after the expiration of the term of this Lease, such
     possession shall be as a month-to-month tenant, during which the rent shall
     be payable at the same rate as that in effect during the last month of the
     term, and provisions of this Lease shall be applicable.

5.   RENT: Tenant shall, without deduction, abatement or set-off of any nature
     ----
     whatsoever, pay to Landlord as fixed rent for the Leased Premises, as
     follows. There shall be no rent paid for the period of February 26, 1997
     to March 31, 1997.

          Commencing April 1, 1997 to March 31, 1998 = $11,750.00 per month
          Commencing April 1, 1998 to March 31, 1999 = $12,729.00 per month
          Commencing April 1, 1999 to March 31, 2000 = $14,687.00 per month
          Commencing April 1, 2000 to March 31, 2002 = $16,645.00 per month

                                  Page 1 of 8
<PAGE>

     payable in advance without demand on the first day of each and every month
     during the term of this Lease, commencing April 1, 1997. Tenant shall pay
     the fixed rent for April, 1997 upon the execution hereof.

     A late charge of five percent (5%) of any monthly rental payment will be
     added after fifteen (15) days from the due date. Failure to pay any monthly
     rental within ten (10) days after the due date shall be deemed to be an
     event of default by Tenant under this Lease.

6.   SECURITY DEPOSIT: Upon the execution of this Lease, Tenant shall deposit
     ----------------
     with Landlord the sum equal to $28,395.00 of which $11,750.00 shall be
     credited against the first month's rent payable hereunder and the balance
     of $16,645.00 shall be held by Landlord as security for the faithful
     performance and observance by Tenant of all the terms, covenants and
     conditions of this Lease. Landlord shall retain said funds, as its own,
     (without being liable for interest thereon) and may use, apply or retain
     the whole or any part of the funds so deposited to the extent required for
     the payment of any rent, additional rent or other sums as to which Tenant
     is in default, or for the payment of any amount which Lessor may be
     required to expend by reason of Tenant's default in respect of any of the
     terms of this Lease. Landlord shall give Tenant five (5) days' written
     notice before applying the deposit to any default. Should Tenant comply
     with all of the terms of this Lease, so much of said security deposit not
     spent or applied pursuant to the provisions of this paragraph shall be
     returned to Tenant within thirty (30) days after the termination of this
     Lease. If any portion of said deposit is so used or applied, Tenant shall,
     within ten (10) days after the demand therefor, deposit cash with Landlord
     in an amount sufficient to restore the security deposit to its original
     amount and Tenant's failure to do so shall be a material breach of this
     Lease. Should Landlord sell its interest in the Premises during the term
     hereof and if Landlord delivers to the purchaser thereof the then
     unappropriated funds deposited by Tenant as aforesaid, thereupon Landlord
     shall be discharged from any and all liability, with respect to said
     security deposit. The security deposit may not be used to pay the last
     month's rent.

7.   TAXES: Tenant shall pay all real estate and occupancy taxes, assessments
     -----
     and/or installments thereof on or before the date the same become due,
     whether general or special, foreseen and unforseen, and shall furnish
     Landlord a copy of the paid receipts therefor. Taxes shall be prorated for
     1997 and 2002 for the period of the Lease.

     Tenant reserves the right and privilege to contest the validity and amount
     of any tax or assessment payable by it to any governmental body or agency,
     whether assessed in its name or in the name of the Landlord. Landlord
     grants Tenant the right to contest the validity and amount of any such tax
     or assessment provided Tenant pays all costs and fees incurred in
     proceedings before any agency or court; and, provided further, that Tenant
     shall make proper provision to prevent any such tax or assessment from
     becoming delinquent by reason of any contest thereof.

8.   ASSIGNMENT AND SUBLETTING: Tenant shall not assign this Lease nor sublet
     -------------------------
     all or any part of the Leased Premises without the prior written consent of
     Landlord, which consent shall not be unreasonably withheld. Landlord's
     consent to one assignment or subletting shall not be deemed a consent to
     any other or further assignment or subletting. No assignment of this Lease
     or subletting thereunder and no acceptance by Landlord of any rent or any
     other sum of money from any assignee or sublessees shall release Tenant
     from any of its obligations under this Lease; and in any event Tenant shall
     remain primarily liable on this Lease for the entire term hereof and shall
     in no way be released from the full and complete performance of all the
     terms, conditions, covenants and agreements herein contained.

9.   PARKING: Tenant shall during the Lease term have exclusive right to use all
     -------
     of the parking spaces.

10.  REPAIRS AND MAINTENANCE: Landlord shall, at its cost, during the term of
     -----------------------
     this Lease keep in good repair the foundations, exterior walls, roofs,
     gutters, and down spouts forming a part of the Leased Premises.

     Landlord will be responsible for making major repairs or replacement of the
     HVAC system until March 31, 1999, at which time Tenant will be responsible
     for HVAC repairs or

                                  Page 2 of 8
<PAGE>

     replacement throughout the remainder of the Lease, as required. Tenant
     shall, at its cost, keep in good repair the parking lot drives, sidewalks,
     and common areas forming a part of the Leased Premises and shall maintain
     in good and first-class condition the lawn, sidewalks, drives, common
     areas, and shrubbery, including watering same, cutting the grass, and the
     replacing of any dead trees, bushes or other ornamental plants.

     Tenant also, at its own cost and expense, keep all other parts of the
     Leased Premises in good repair (including, but not limited to, repair and
     replacement of the mechanical equipment, plumbing system, electrical
     system, sprinkler system, exterior doors and interior doors and partitions)
     and shall keep the Leased Premises in good order to the standards of a
     first-class office building, including, but in no way limited to, keeping
     the Leased Premises free of trash; and maintaining, and replacing all
     broken glass, plate glass and skylights, in the Leased Premises.

     In the event that Tenant shall be in default under this Paragraph 10, then
     Landlord may cure such default on behalf of Tenant after providing 10 days
     prior written notice, in which event Tenant on demand shall reimburse
     Landlord for all sums paid to effect such cure, plus twelve percent (12%)
     thereof to cover Landlord's overhead expenses and plus reasonable
     attorneys' fees. In order to collect such reimbursement, Landlord shall
     have all the remedies available under this Lease for a default in the
     payment of rent.

11.  ALTERATIONS: No substantial alteration, addition or improvement to the
     -----------
     Leased Premises shall be made by Tenant without the written consent of
     Landlord, such consent not to be unreasonably withheld. Any alteration,
     addition, or improvement made by Tenant after such consent shall have been
     given, and any non-movable fixtures installed as a part thereof, shall at
     Landlord's option become the property of Landlord upon the expiration or
     sooner termination of this Lease; provided, however, that Landlord shall
     have the right to require Tenant to remove such fixtures including all
     phone, computer and telecommunications cabling, at Tenant's cost upon such
     termination of this Lease. It is expressly understood and agreed, however,
     that Tenant shall retain ownership of, and shall upon termination of this
     Lease be permitted to remove from the Leased Premises, those items of
     equipment and personal property described on Exhibit A attached hereto,
                                                  ---------
     provided that such removal does not adversely affect or impair the
     structure of the Leased Premises or mechanical or working systems serving
     the Leased Premises, and further provided that Tenant shall be responsible
     at its sole cost for repairing all damage to the Leased Premises caused by
     such removal.

12.  WASTE: Tenant covenants not to do or suffer any waste to the Leased
     -----
     Premises.

13.  MECHANICS' LIENS: Tenant shall not permit mechanics' liens to be filed
     ----------------
     against the fee of the Leased Premises or against Tenant's leasehold
     interest in the Premises by reason of work, labor, services or materials
     supplied or claimed to have been supplied to Tenant or anyone holding the
     Leased Premises through or under Tenant, whether prior or subsequent to the
     commencement of the term hereof. If any such mechanics' lien shall at any
     time be filed, against the Leased Premises and Tenant shall fail to remove
     same within thirty (30) days thereafter, it shall constitute a default
     under the provisions of this Lease.

14.  RESTRICTIONS OF USE: Tenant shall not allow, permit or suffer any noise,
     -------------------
     smoke or odor to escape from the Leased Premises, or occupy the Leased
     Premises in such manner as to constitute a public nuisance or environmental
     hazard. No sign, fixture, advertisement or notice shall be displayed,
     inscribed, painted, or affixed by Tenant on any part of the outside of the
     Leased Premises or on the parking lot or on any part of the Leased
     Premises' without the prior written consent of Landlord. At the expiration
     of the Lease term, Tenant shall remove all such signs or advertisement
     matter at its cost and shall repair any damage resulting from such removal.
     Nor shall Tenant allow or permit any goods, materials or equipment to be
     stored outside of the buildings without the prior written consent of
     Landlord. Such consent may not be unreasonably withheld.

15.  UTILITIES: Tenant shall pay for all gas, electricity, water, air
     ---------
     conditioning, sewer and telephone service and all other utilities used in
     and upon the Leased Premises. Tenant shall be responsible for its own trash
     removal.

                                  Page 3 of 8
<PAGE>

16.  ACCESS: Landlord, and its duly authorized agents, employees and
     ------
     contractors, shall have access to the Leased Premises at all reasonable
     times for the purpose of inspecting the same and making necessary repairs
     or replacements as described under Paragraph 10.

17.  INSURANCE: Prior to commencement of occupancy by Tenant, Tenant at its
     ---------
     expense shall obtain a policy of insurance insuring the Leased Premises
     against losses for fire and extended coverage for the full replacement
     value of the building on the Leased Premises including earthquake, coverage
     and shall also obtain a policy of public liability insurance in at least
     the amount of $1,000,000.00. Landlord shall be named as an insured under
     such policies. In the event the building and improvements on the Leased
     Premises are damaged or destroyed by fire or other casualty, rent shall not
     abate and Landlord shall restore the said premises to substantially the
     same condition in which they existed prior to such damage, and with all
     reasonable speed and promptness, not to exceed one hundred eighty (180)
     days. Landlord shall use the proceeds of such insurance and repairs in
     rebuilding the Leased Premises. In determining what constitutes reasonable
     speed and promptness, considerations shall be given to delays caused, by
     strikes, adjustment of insurance, and other causes beyond Landlord's
     control. In no event shall Landlord be required to restore any alteration,
     additions, or improvement made by or for Tenant, nor any trade fixtures,
     equipment or other property belonging to Tenant. In the event that the
     Leased Premises have not been restored within one hundred eighty (180) days
     of the casualty, either Tenant or Landlord may thereafter elect to
     terminate this Lease by serving written notice of termination on the other
     party, provided that the Leased Premises have not been restored prior to
     the date on which the notice of termination has been given hereunder.
     Tenant shall have the right to provide the insurance policies required
     above pursuant to blanket policies obtained by Tenant, provided such
     blanket policies expressly afford coverage to the Premises and Landlord
     required by this Lease. Landlord and Tenant hereby waive the right each
     may have against the other on account of any loss or damage occasioned to
     Landlord or Tenant, as the case may be, their respective property, the
     Leased Premises or its contents arising from any risk insured against by
     Landlord or Tenant; and the parties each, on behalf of their respective
     insurance companies insuring the property of either Landlord or Tenant
     against any such loss, waive any right of subrogation that it may have
     against Landlord or Tenant, as the case may be. This release shall apply
     only to the extent that such loss or damage is covered by insurance and
     only so long as the applicable insurance policies contain a clause or
     otherwise provide that this release shall not affect the right of the
     injured to recover under such policies.

18.  LIABILITY: Landlord shall not be liable for any failure of water supply,
     ---------
     gas, or electric current; nor for any injury or damage to person or
     property caused by gasoline, oil, steam, gas electricity, ice/snow,
     tornado, flood, wind, or similar storms and disturbances; nor water or rain
     which may leak or flow from the street, sewer, gas mains or any subsurface
     area from any part of the buildings or improvements on the Leased Premises
     occurring from such causes or at no fault of Landlord; nor for any
     interference with light or air. Landlord shall not be liable for any
     personal injury to Tenant, its officers, agents, employees and invitees,
     nor for any damages to any property of Tenant, irrespective of how much
     such injury or damage may be caused.

     Tenant shall indemnify and hold Landlord harmless from any loss, damages,
     and expenses incident thereto, including attorneys' fees, arising out of
     the liability to any person on account of loss of or damage to property or
     injury persona resulting item the use and occupancy of the Leased Premises
     or the parking lot, sidewalks, XXX, or common areas by Tenant; except,
     however, Tenant shall not indemnify Landlord for its own acts of
     negligence.

19.  CONDEMNATION
     ------------

     (a)  If the whole of the Leased Premises shall be taken for any public or
          any quasi-public use under any statute or by right of eminent domain,
          or by purchase under threat of condemnation, then this Lease shall
          automatically terminate as of the date that title shall be taken. If
          any part of the Leased Premises shall be so taken as to render the
          remainder thereof unusable for the purposes for which the Leased
          Premises were leased in either parties' discretion, then Landlord and
          Tenant shall each have the right to terminate this Lease on thirty
          (30) days' notice to the other given within ninety (90) days after the
          date of such taking. In the event that this Lease shall terminate or
          be

                                  Page 4 of 8
<PAGE>

          terminated, the rental shall, if and as necessary, be prorated between
          Landlord and Tenant as of the date of such termination;

     (b)  If any part of the Leased Premises shall be so taken and this Lease
          shall not terminate or be terminated under the provisions of
          Subparagraph (a) above, then the rental shall be equitably apportioned
          according to the area so taken, and Landlord shall, at its own cost
          and expense, restore the remaining portion of the Leased Premises to
          the extent necessary to render them reasonably suitable for the
          purposes for which they were leased, and shall make all repairs to the
          building in which the Leased Premises are located to the extent
          necessary to constitute the building a complete architectural unit;
          and

     (c)  All compensation awarded or paid upon such a total or partial taking
          of the Leased Premises shall belong to and be the property of Landlord
          without any participation by Tenant; provided, however, that nothing
          contained herein shall be construed to preclude Tenant from
          prosecuting any claim directly against the condemning authority in
          such condemnation proceeding for loss of business, depreciation to,
          damage to, or cost of removal of, or the value of stock, trade
          fixtures, furniture, and other personal property belonging to Tenant;
          provided, however, that no such claim shall diminish or otherwise
          adversely affect Landlord's award.

20.  DEFAULT: The following events shall be deemed to be events of default by
     -------
     Tenant under this Lease: (i) if Tenant shall fail to pay any fixed or
     additional rent hereby reserved within ten (10) days after due date; (ii)
     if Tenant shall fail to comply with any term, or provision, or covenant of
     this Lease, other than the payment of rent, and shall not cure such failure
     within thirty (30) days after written notice thereof to Tenant; (iii) if
     Tenant shall become insolvent, or shall make a transfer with intent to
     defraud its creditors, or shall make an assignment for the benefit of its
     creditors; (iv) if Tenant shall file a petition under any section or
     chapter of the National Bankruptcy Act; as amended, or under any similar
     law or statute of the United States or any state thereof; or Tenant shall
     be adjudicated bankrupt or insolvent in proceedings filed thereunder; (v)
     if a receiver or trustee shall be appointed for all or substantially all of
     the assets of Tenant; or (vi) if Tenant shall desert or vacate any
     substantial portion of the Leased Premises.

     Upon the occurrence of any such event of default, Landlord shall have the
     option to pursue any one or more of the following remedies (as well as any
     other remedies provided by law) without any further notice or demand
     whatsoever:

     (a)  Declare immediately due and payable the entire amount of the rent then
          remaining to be paid under this Lease for the balance of the Lease
          term;

     (b)  Enter upon and take possession of the Leased Premises by any lawful
          means, and dispossess, expel, and remove Tenant and any other persons
          who may be occupying the Leased Premises or any part thereof
          (including changing or altering the locks and other security devices)
          and remove and expel any personal property or trade fixtures located
          therein, all without being liable to any prosecution thereof or for
          any damages resulting therefrom. Such re-entry and/or repossession by
          Landlord shall not terminate this Lease nor relieve Tenant of its
          obligations under this Lease, including its obligation to pay rent
          (whether or not the time for payment of rent has been accelerated). In
          the event of such re-entry or repossession by Landlord, Landlord shall
          also have the option to re-let the Leased Premises as agent for Tenant
          (in the name of Landlord or in the name of Tenant), at any rent and
          for any term readily obtainable and receive the rent therefor, in
          which event Tenant shall be given credit for any rents that may arise
          by reason, of such re-letting (after first deducting all repossession
          costs, brokerage commissions, legal expenses, attorneys' fees, and all
          other expenses in cleaning, repairing and altering the premises for
          re-letting); and

     (c)  Forfeit and terminate this Lease forthwith. In the event of such
          termination, Tenant shall immediately surrender the Leased Premises to
          Landlord and if Tenant fails to do so, Landlord may enter upon and
          take possession of the Leased Premises by any lawful means and
          expel or remove Tenant and any other person who may be

                                  Page 5 of 8
<PAGE>

          occupying said premises or any part thereof, and any personal property
          or trade fixtures located therein. In the event of the forfeiture of
          this Lease as herein provided, Tenant agrees that any security deposit
          being held by Landlord hereunder shall be retained by Landlord and
          applied against all damages incurred with respect to Tenant's default,
          which damages shall include all unpaid rent and any other damages
          accruing to Landlord by reason of the violation by Tenant of any of
          the terms, provisions and covenants of this Lease.

     Tenant hereby waives demand for rent, demand for possession, notice for
     forfeiture, notice of termination and any and all other demands or notices
     required by law.

     Pursuit by Landlord of any of the foregoing remedies or any other remedy
     provided by law shall not constitute a forfeiture or waiver of any rent due
     to Landlord hereunder or of any damages accruing to Landlord by reason of
     the violation by Tenant of any of the terms, provisions and covenants of
     this Lease. In no event shall Tenant be relieved from its obligation to pay
     the rentals specified in this Lease by reason of a surrender of possession,
     termination of this Lease or in any other manner whatsoever, unless
     specifically agreed to in writing by Landlord.

     No waiver by Landlord of any violation or breach of any of the terms,
     provisions and covenants of this Lease shall be deemed or construed to
     constitute a waiver of any other violation or breach of any of the terms,
     provisions and covenants herein contained. Forbearance by Landlord to
     enforce one or more of the remedies herein provided upon an event of
     default shall not be deemed or construed to constitute a waiver of such
     default.

     If Landlord incurs any expenses, including court costs and attorneys' fees,
     as a result of a default by Tenant under this lease, then such expenses
     shall be reimbursed by Tenant as additional rent, whether or not such
     default is subsequently cured.

     Tenant's delinquent payments shall bear interest at the rate of twelve
     percent (12%) per annum from the date of delinquency until paid.

21.  SURRENDER AND TERMINATION: At the expiration of the Lease term, Tenant
     -------------------------
     shall surrender the Leased Premises in as good condition as they were in at
     the beginning of the term, reasonable use and wear and damage by the
     elements excepted.

     Notwithstanding and provisions of law or any judicial decision to the
     contrary, no notice shall be required to terminate the term of this Lease
     as herein provided, and the term of this Lease shall expire on this
     termination date herein mentioned without notice being required from either
     party. In the event that Tenant or any party holding under Tenant shall
     remain in possession of the Leased Premises beyond the expiration of the
     term of this Lease, whether by limitation or forfeiture, such party shall
     pay double rent hereunder during such hold-over period, except if such
     hold-over is with Landlord's consent as provided in Paragraph 4.

22.  NOTICES: Any notice required to be given by either party to the other party
     -------
     under the terms of this Lease shall be personally served upon it or mailed
     by United Stated certified mail to said party at its last known address.
     The current addresses of the parties are as follows:

          LANDLORD                                   TENANT
          --------                                   ------
          Mr. William H. Armstrong, Jr.              Mr. Mike Fallon, Treasurer
          Armstrong Properties, LTC                  Critical Technologies, Inc.
          31 Fordyce                                 3324 Hollenberg Drive
          St. Louis, Missouri 63124                  Bridgeton, Missouri 63044

23.  HEADINGS AND DEFINITIONS:
     ------------------------

     (a)  It is agreed that the headings and phrases as to the contents of
          particular paragraphs of this Lease are inserted a matter of
          convenience and for reference, and in no way are or are intended to be
          a part of this Lease or in any way to define, limit or describe the
          scope or intent of the paragraph to which they refer; and

                                  Page 6 of 8
<PAGE>

     (b)  Where in this instrument pronouns appear, or words indicating the
          singular number, such words shall be considered as masculine,
          feminine, or neuter pronouns or words indicating the plural number,
          and vice versa, where the context indicates the propriety of such use.

24.  MODIFICATIONS: Landlord and Tenant agree that this Lease contains the
     -------------
     entire agreement between them and shall not be modified in any manner
     except by an instrument in writing signed by each of them.

25.  BENEFIT: This Lease shall inure to the benefit of and be binding upon
     -------
     Landlord and Tenant and their respective heirs, executors, personal
     representatives, administrators, successors and assigns, as the case may
     be.

26.  SUBORDINATION: Tenant agrees that upon delivery to it by any mortgagee of
     -------------
     the Leased Premises of a "non-disturbance letter," as same is defined
     below, that this Lease and Tenant's interest in this Lease shall be
     subordinated to any mortgage, deed of trust or other method of financing or
     refinancing now or hereafter encumbering the Leased Premises, the land
     underlying the Leased Premises, and/or the building of which the Leased
     Premises comprise a part; and to all renewals, modifications, replacements,
     consolidations and extensions thereof. Tenant further agrees that in such
     event it will execute and deliver any and all documents necessary to
     evidence the subordination of its rights under this Lease as aforesaid. The
     "non- disturbance letter" referred to above shall be any letter from the
     holder of such mortgage, deed of trust or other security instrument to the
     effect that in the event of a foreclosure or other action taken under any
     such security instrument that this Lease and the rights of Tenant hereunder
     shall not be disturbed, diminished or interfered with, but shall continue
     in full force and effect so long as Tenant shall not be in default
     hereunder.

     In any event, if any such mortgage, deed of trust or other security
     instrument encumbering the Leased Premises is foreclosed for any reason,
     and the holder of such mortgage, deed of trust or other security instrument
     succeeds to the interest of Landlord under this Lease, Tenant shall be
     bound to such mortgage, deed of trust or security holders under all of the
     terms of this Lease for the balance of the term thereof remaining, with the
     same force and effect as if said mortgagee were the Landlord under this
     Lease; and Tenant hereby attorns to the mortgagee as its Landlord, such
     attornment to be effective and self-operative, without the execution of any
     further instrument on the part of either of the parties hereto, immediately
     upon the mortgage succeeding to the interest of Landlord under this Lease.

27.  ESTOPPEL CERTIFICATE: Tenant agrees, at any time, and from time to time,
     --------------------
     upon not less than ten (10) days' prior notice by Landlord, to execute,
     acknowledge and deliver to Landlord, a statement in writing addressed to
     Landlord certifying that this Lease is unmodified and in full force and
     effect (or, if there have been modifications, that the same is in full
     force and effect as modified and stating the modifications), stating the
     dates to which the fixed minimum rent, additional rental and other charges
     have been paid, and stating whether or not to the best knowledge of the
     signer of such certificate, agreement, term, provision or condition
     contained in this Lease, and, if so, specifying each such default of which
     the signer may have knowledge, it being intended that any such statement
     delivered pursuant hereto may be relied upon by Landlord and by any
     mortgagee or prospective mortgagee of any mortgage affecting the building
     or the building and the land, and by prospective purchaser of the Property.

28.  SEVERABILITY: This Lease and its provisions are to be construed as a whole,
     ------------
     but should any provision be held or be void or illegal, then such clause or
     provision shall be deemed severable from the Lease and shall be considered
     stricken herefrom, but the Lease shall not be deemed void or otherwise
     modified or affected.

29.  QUIET ENJOYMENT: Tenant shall at all times during the term hereof and all
     ---------------
     extensions or renewals, subject only to its payment of the rental and
     performance of the agreements on its part to be performed, peacefully and
     quietly have, hold and enjoy the premises without any manner of suit,
     trouble, hindrance or from Landlord, its successors or assigns, or any
     other person.

                                  Page 7 of 8
<PAGE>

30.  ENVIRONMENTAL: Tenant shall not use, store, manufacture, dispose of or
     -------------
     discharge any pollutants, contaminants, or harmful or hazardous substances
     from or on the Leased Premises or otherwise occupy or permit the Leased
     Premises to be occupied or used in a manner which (i) violates any law,
     regulation, rules or other governmental requirement, (ii) impairs the
     health, safety or condition of any person or property or (iii) adversely
     affects the use, enjoyment or value of the Leased Premises or the
     surrounding property. Tenant shall promptly notify Landlord of the breach,
     or the potential or threatened breach, of any of the provisions of this
     paragraph. Tenant shall indemnify and hold Landlord and its officers,
     shareholders, partners, employees, and agents, harmless from any loss,
     claim, liability or expense (including, without limitation, attorneys'
     fees, court costs, consultant fees, expert fees, penalties, fines, removal,
     clean-up, transportation, disposal and restoration expenses) arising in
     connection with Tenant's failure to comply with the provisions of this
     paragraph. A breach of the provisions of this paragraph shall be a material
     default enabling Landlord to exercise any of the remedies set forth in this
     Lease. Tenant's obligation hereunder shall survive the termination of this
     Lease.

31.  RENEWAL OPTION: Tenant shall have the right to extend the term of the Lease
     --------------
     for an additional period of three (3) years, commencing on the expiration
     of the original term of the Lease. Such renewal option shall be deemed
     effectively exercised only if Tenant has given Landlord written notice
     thereof at least one hundred eighty (180) days prior to the expiration of
     the original term and only if Tenant is not in default under this Lease
     both at the time of such exercise and at the time of the commencement of
     the renewal term. All terms and provisions of the Lease shall be applicable
     during such renewal term, except the fixed rent payable pursuant to
     paragraph 5 shall equal $223,250.00 annually, with equal monthly payments
     of $18,604.17. Such rent shall be payable without deductions, abatements or
     set-offs of any nature whatsoever. It is expressly understood that the
     renewal option granted in this paragraph is personal to the entity
     expressly named as Tenant in this Lease and to any assignee and subtenant
     which has been approved by Landlord, and that said option shall terminate
     upon an assignment or subletting of Tenant's interest hereunder and shall
     not inure to the benefit of any assignee or subtenant of Tenant which has
     not been approved by Landlord.

32.  CANCELLATION OPTION: Upon six months prior written notification, Leasee
     -------------------
     will have the right to terminate this Lease at the end of the 36th month.
     Anytime after 36 months Leasee can terminate this Lease with three months
     prior written notice. As consideration, Leasee will pay Lessor, an amount
     equal to 50% of the remaining fixed rent obligation under the Lease as of
     the effective date of the Lease termination, which amount will accompany
     and be a requirement of the notice to terminate.

This Lease consists of thirty-two (32) paragraphs numbered consecutively.

IN WITNESS WHEREOF, the parties hereto have hereunto set their hands the day and
year first above mentioned.

TENANT:                             LANDLORD:

CRITICAL TECHNOLOGIES, INC.         ARMSTRONG PROPERTIES, LTC

By: /s/ [ILLEGIBLE]^^               By: /s/ William H Armstrong, Jr.
    --------------------                ----------------------------------------
                                        Wm. H. Armstrong, Jr., General Partner

Date:   2/27/97                     Date:  2/27/97
      ------------------                   -------------------------------------

Time:   12:00 pm                    Time:  1:30 pm
      ------------------                   -------------------------------------

                                  Page 8 of 8

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