Document:

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                                                                   EXHIBIT 10.67

                                     LEASE
                                     -----

                                 BY AND BETWEEN

                         ARE-50 WEST WATKINS MILL, LLC

                                      AND

                                GENE LOGIC INC.

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<TABLE>
<CAPTION>
                               TABLE OF CONTENTS
                               -----------------

                                                                           PAGE
                                                                           ----

<S>                                                                        <C>
1.     Lease of Premises.                                                     1
2.     Basic Lease Provisions.                                                1
3.     Term.                                                                  3
4.     Possession and Commencement Date.                                      3
5.     Rent.                                                                  4
6.     Rent Adjustments.                                                      5
7.     Operating Expenses.                                                    5
8.     Intentionally omitted.                                                 9
9.     Security Deposit.                                                     10
10.    Use.                                                                  11
11.    Brokers.                                                              14
12.    Holding Over.                                                         15
13.    Taxes on Tenant's Property.                                           15
14.    Condition of Demised Premises.                                        16
15.    Common Areas and Parking Facilities.                                  16
16.    Utilities and Services.                                               16
17.    Alterations.                                                          18
18.    Repairs and Maintenance.                                              20
19.    Liens.                                                                21
20.    Indemnification and Exculpation.                                      22
21.    Insurance - Waiver of Subrogation.                                    23
22.    Damage or Destruction.                                                24
23.    Eminent Domain.                                                       26
24.    Tenant's Default and Landlord's Remedies.                             27
25.    Assignment or Subletting.                                             30
26.    Intentionally omitted.                                                34
27.    Bankruptcy.                                                           34
28.    Definition of Landlord.                                               34
29.    Estoppel Certificate.                                                 35
30.    Intentionally omitted.                                                35
31.    Limitation of Landlord's Liability.                                   35
32.    Project Control by Landlord.                                          36
33.    Quiet Enjoyment.                                                      37
34.    Intentionally Omitted.                                                37
35.    Subordination and Attornment.                                         37
36.    Surrender.                                                            38
37.    Waiver and Modification.                                              38
38.    Intentionally omitted.                                                38
39.    Intentionally omitted.                                                38
40.    Hazardous Materials.                                                  38
41.    Intentionally omitted.                                                41
42.    Options to Extend Term.                                               41
43.    Miscellaneous.                                                        42
</TABLE>

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<TABLE>
<CAPTION>
EXHIBITS
--------
<S>    <C>
A      Legal Description and Site Plan
B      Work Letter
C      Rules and Regulations
D      Estoppel Certificate
E      Form of Acknowledgement
F      Form of Non-Disturbance Agreement
G      Parking
</TABLE>

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                                     LEASE

       THIS LEASE is made as of July 21, 2000, by and between ARE-50 WEST
WATKINS MILL, LLC, a Delaware limited liability company (hereinafter called
"LANDLORD") and GENE LOGIC INC., a Delaware corporation (hereinafter called
"TENANT").

       1.     Lease of Premises.

              1.1    Landlord hereby leases to Tenant and Tenant hereby leases
from Landlord, that certain building located at the address set forth below
(hereinafter called the "Demised Premises" or the "Building"). The real property
upon which the Building is located, and all landscaping, parking facilities, and
other improvements and appurtenances related thereto, are hereinafter
collectively referred to as the "Project", the site plan and legal description
for which are attached hereto as Exhibit "A." All portions of the Project which
are for the non-exclusive use of tenants of the Building, including, without
limitation, driveways, sidewalks, parking areas, landscaped areas, service
corridors, stairways, elevators, public restrooms and Building lobbies, are
hereinafter referred to as "Common Area". Promptly following the execution
hereof, Landlord shall cause its architect to field measure the rentable square
footage of the Building, such measurement to be certified in accordance with, at
Landlord's option, either (a) the Building Owners and Managers Association
method of measurement (ANSI 265.1 1996) or (b) GWCAR. In the event that the
field measurement discloses that the rentable square footage of the Building is
more than two percent (2%) larger or smaller than 57,410, appropriate rental
adjustments shall be made by way of an amendment to this Lease. Landlord shall
furnish to Tenant a copy of Landlord's architect's field measurement report.

       2.     Basic Lease Provisions.

              2.1    For convenience of the parties, certain basic provisions of
this Lease are set forth herein. The provisions set forth herein are subject to
the remaining terms and conditions of this Lease and are to be interpreted in
light of such remaining terms and conditions.

                     2.1.1  Address of the Building: 50 West Watkins Mill Road
                            Gaithersburg, MD 20878

                     2.1.2  Designation of Tenant's Demised Premises 100% of the
                            Building as shown on Exhibit "A"

                     2.1.3  (a)    Rentable Area of Demised Premises: 57,410 sq.
                                   ft.

                            (b)    Rentable Area of Building/Project: 57,410 sq.
                                   ft.

                     2.1.4  Initial Basic Annual Rent: 57,410 sq. ft. x $14.50
per sq. ft. = $832,445, plus any additional Basic Annual Rent pursuant to
Section 8 of Exhibit "B" attached hereto; subject to the rental abatement set
forth in Section 5.1 hereof.

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                     2.1.5  Initial Monthly Rental Installments of Basic Annual
Rent: $69,370.42, plus any additional Basic Annual Rent pursuant to Section 8 of
Exhibit "B" attached hereto.

                     2.1.6  Tenant's Pro Rata Share: 100.00% of the Building

                     2.1.7  (a)    Term Commencement Date: The date hereof

                            (b)    Term Expiration Date: 120 months from the
                                   first day of the month following the month in
                                   which the Rent Commencement Date occurs

                     2.1.8  Security Deposit and Rent Deposit:

                            (a)    $208,111.30 and

                            (b)    $69,370.42

subject to application in accordance with Section 9.5 hereof.

                     2.1.9  Permitted Use: General office use,
bio-medical/bio-chemical laboratory use, storage and other incidental uses
consistent with the foregoing named uses.

                     2.1.10 Address for Rent Payment:

                            Alexandria Real Estate Equities, Inc.
                            135 N. Los Robles Avenue, Suite 250
                            Pasadena, CA 91101
                            Attention: Accounts Receivable

                            Address for Notices to Landlord:

                            Alexandria Real Estate Equities, Inc.
                            135 N. Los Robles Avenue, Suite 250
                            Pasadena, CA 91101
                            Attention: General Counsel

                            Address for Notices to Tenant:

                            Gene Logic Inc.
                            708 Quince Orchard Road
                            Gaithersburg, Maryland 20878
                            Attention: Chief Financial Officer

                            With, in each case, a copy to:

                            Silverstein and Mullins, P.L.L.C.
                            a division of Buchanan Ingersoll, P.C.

                                       2
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                            1776 K Street, N.W.
                            Washington, D.C. 20006
                            Attention: Gary K. Bahena, Esq.

                     2.1.11 Guarantor of Lease: N/A

                     2.1.12 Space Plan Approval Date: N/A

                     2.1.13 The following Exhibits are attached hereto and
incorporated herein: A, B, C, D, E, F and G.

       3.     Term.

              3.1    This Lease shall take effect upon the date of execution and
delivery hereof by all parties hereto and, except as specifically otherwise
provided within this Lease, each of the provisions hereof shall be binding upon
and inure to the benefit of Landlord and Tenant from the date of execution and
delivery hereof by all parties hereto.

              3.2    The term of this Lease (the "TERM") shall commence on the
Term Commencement Date and shall expire on the Term Expiration Date subject to
earlier termination of this Lease as provided herein.

       4.     Possession and Commencement Date.

              4.1    Landlord shall deliver two fully executed copies of the
Lease and tender to Tenant possession of the Demised Premises no later than the
fourth business day following the later of (i) the date of receipt by Landlord
from Tenant of four (4) copies of this Lease executed by Tenant and (ii) the
date the existing tenant of the Building vacates or surrenders same (the
"DELIVERY DATE"). In the event that the Demised Premises have not been delivered
to Tenant by August 4, 2000, then Tenant shall have the right to terminate this
Lease by written notice received by Landlord within ten (10) business days
thereafter.

              4.2    Notwithstanding anything to the contrary set forth
elsewhere in this Lease, Tenant shall not have any obligation to pay to Landlord
Basic Annual Rent in respect of the Demised Premises until the earlier of (the
"RENT COMMENCEMENT DATE") (i) Tenant's occupancy and commencement of regular
business operations within the Demised Premises or (ii) January 1, 2001 (such
date, however, being extended by one day for each day following August 4, 2000
that Landlord has failed to make the Demised Premises available to Tenant for
Tenant's work under the Work Letter and such date to be further extended by one
day for each day of Landlord delay pursuant to Section 4.4 hereof).

              4.3    From and after the date hereof Tenant shall be permitted to
enter upon the Demised Premises for the purposes of measurement and inspection.
The terms of this Section 4.3 shall no longer be applicable following delivery
of possession pursuant to Section 4.1 hereof.

              4.4    Notwithstanding anything to the contrary set forth
elsewhere in this Lease, the Rent Commencement Date shall be extended by one day
for each day that substantial completion of Tenant's Work and/or Tenant
Performed Landlord Work (as

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such terms are defined in Exhibit "B") are delayed solely by the failure of
Landlord to respond in a timely fashion to Tenant's requests for review and
approval or to complete the Landlord Work (or coordinate same with Tenant) so as
to avoid delaying Tenant's timely performance of the Tenant's Work and/or the
Tenant Performed Landlord Work. Landlord shall have five (5) business days
following receipt of Tenant's request for review and approval to review and
approve or disapprove such request. Landlord and Tenant shall execute and
deliver written acknowledgment of the actual Rent Commencement Date in the form
of Exhibit "E." Further notwithstanding anything to the contrary contained in
this Lease, the Rent Commencement Date shall be extended by 1 day for each day
that the Landlord Work is not completed by January 1, 2001, or for Landlord
Delay pursuant to Schedule 1-A.

              4.5    There shall be no charge to Tenant for Landlord's personnel
or engineer in connection with Tenant moving in and moving out of the Building.

              4.6    The provisions governing the preparation of plans and the
performance of Tenant's Work are set forth in Exhibit "B" attached hereto and
made a part hereof.

       5.     Rent.

              5.1    Tenant agrees, commencing on the Rent Commencement Date, to
pay Landlord as Basic Annual Rent for the Demised Premises the sum set forth in
Section 2.1.4 subject to the rental adjustments provided in Article 6 hereof.
Basic Annual Rent shall be paid in the equal monthly installments set forth in
Section 2.1.5, subject to the adjustments to Basic Annual Rent provided in
Article 6 hereof and in Section 8 of the Work Letter, each in advance on the
first day of each and every calendar month during the Term. Notwithstanding the
foregoing, but subject to one additional day of abatement for each day of
Landlord delay pursuant to Sections 4.2 and/or 4.4, monthly installments of the
Basic Annual Rent set forth in Section 2.1.4 shall be abated for January,
February and March and the rent due for April, 2001 shall be $45,638.75.
Commencing with May 2001 and each month thereafter, subject to adjustment as
herein provided, monthly installments of Basic Annual Rent shall be due and
payable in the full amount of $69,370.42 as increased pursuant to Section 8 of
the Work Letter. No Basic Annual Rent due in connection with the amortization of
any portion of the $4,592,800 additional Allowance which may be used by Tenant
pursuant to Section 8 of the Work Letter shall be abated pursuant any provision
of this Lease, including this Section 5.1.

              5.2    In addition to Basic Annual Rent, Tenant agrees to pay to
Landlord as additional rent ("ADDITIONAL RENT") at times hereinafter specified
in this Lease (i) Tenant's pro rata share, as set forth in Section 2.1.6
("TENANT'S PRO RATA SHARE") of Operating Expenses as provided in Article 7 and
(ii) any other amounts that Tenant assumes or agrees to pay under the provisions
of this Lease that are owed to Landlord, including, without limitation, any and
all other sums that may become due by reason of any default of Tenant or failure
on Tenant's part to comply with the agreements, terms, covenants and conditions
of this Lease to be performed by Tenant, after notice and lapse of applicable
cure period.

              5.3    Basic Annual Rent and Additional Rent shall together be
denominated "RENT". Rent shall be paid to Landlord, without abatement, deduction
or offset in lawful money of the United States of America, at the office of
Landlord as set forth

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in Section 2.1.10 or to such other person or at such other place as Landlord may
from time designate in writing. In the event the Term commences or ends on a day
other than the first day of a calendar month, then the Rent for such fraction of
a month shall be prorated for such period on the basis of a thirty (30) day
month and shall be paid at the then current rate for such fractional month.

       6.     Rent Adjustments.

              6.1    Commencing with the monthly installment of Basic Annual
Rent which is due on or after the first anniversary of the first day of the
first full month following the Rent Commencement Date, and on the same day of
every calendar year thereafter for so long as this Lease continues in effect,
the Basic Annual Rent shall be increased by an amount equal to the greater of
2.5% or the CPI Adjustment Percentage multiplied by the Basic Annual Rent then
in effect; provided, however, that such adjustment shall not exceed 4.5% of the
Basic Annual Rent then in effect. Basic Annual Rent adjustments for any
fractional calendar month shall be prorated. "CPI ADJUSTMENT PERCENTAGE" means a
fraction, stated as a percentage, the numerator of which shall be the Index (as
defined below) for the calendar month 3 months before the month in which the
Basic Annual Rent adjustment is to be made, and the denominator of which shall
be the Index for the calendar month 3 months before the last Basic Annual Rent
adjustment or, if no prior Basic Annual Rent adjustment has been made, 3 months
before the first day of the first full month following the Rent Commencement
Date. Landlord shall give Tenant written notice indicating the Basic Annual
Rent, as adjusted pursuant to this Section, and the method of computation, and
Tenant shall pay to Landlord an amount equal to any underpayment of Basic Annual
Rent by Tenant within 30 days of Landlord's notice to Tenant. "INDEX" means the
"Consumer Price Index- All Urban Consumers-Washington-Baltimore Metropolitan
Area" compiled by the U.S. Department of Labor, Bureau of Labor Statistics,
(1987 = 100). If a substantial change is made in the Index, the revised Index
shall be used, subject to such adjustments as Landlord may reasonably deem
appropriate in order to make the revised Index comparable to the prior Index. If
the Bureau of Labor Statistics ceases to publish the Index, then the successor
or most nearly comparable index, as reasonably determined by Landlord, shall be
used, subject to such adjustments as Landlord may reasonably deem appropriate in
order to make the new index comparable to the Index.

       7.     Operating Expenses.

              7.1    As used herein, the term "OPERATING EXPENSES" shall
include:

                     (a)    Government impositions including, without
limitation, property tax costs consisting of real and personal property taxes
and assessments constituting a lien upon the Project, including amounts due
under any improvement bond upon the Building and/or Project including the parcel
or parcels of real property upon which the Building and areas serving such
Building are located or assessments levied in lieu thereof imposed by any
governmental authority or agency, any tax on or measured by gross rentals
received from the rental of space in the Building (i.e., made without regard to
or allowance for any expense or other deductions, allowances or the like), or
tax based on the square footage of the Demised Premises, Building, or Project as
well as any parking charges, utilities. surcharges, or any other costs levied,
assessed or imposed by, or at the direction of, or resulting from statutes or
regulations, or interpretations thereof,

<PAGE>   9

promulgated by any federal, state, regional, municipal or local government
authority in connection with the use or occupancy of the Building or the parking
facilities serving the Building, any tax on this transaction or any document to
which Tenant is a party creating or transferring an interest in the Demised
Premises, any fee for a business license to operate an office building, and any
expenses, including the reasonable cost of attorneys or experts, reasonably
incurred by Landlord in seeking reduction by the taxing authority of the
applicable taxes, less tax refunds obtained as a result of an application for
review thereof. Operating Expenses shall not include any net income, franchise,
capital stock, estate or inheritance taxes, or taxes which are the personal
obligation of Landlord or of another tenant of the Project, or taxes on or in
respect of personal property (or the value or cost thereof) not permanently
located at and used in connection with the Building or Project, or any "rent" or
similar tax unless applicable solely to landlords of real property or to real
property rental receipts, or any "gross receipts", "receipts" or other similar
tax unless measured, assessed and paid without regard to any deductions or
offsets against receipts, including without deduction for operating expenses, or
any income, transfer, business, unincorporated business or gains tax or any real
estate tax or other sum, charge, levy or tax attributable to any land or
improvements other than the Building and the land described in Exhibit "A". If
any assessments are payable in installments, then for the purpose hereof
(regardless of whether Landlord elects to pay same in installments) Operating
Expenses for any calendar year occurring during the Term shall include only
those installments, together with interest, that would have become due if
Landlord opted to pay same in the maximum number of installments permitted. All
real estate taxes and similar charges includable in Operating Expenses pursuant
to this Section 7.1(a) shall be computed as if the Building and Project were the
only asset of Landlord. Upon request by Tenant, Landlord shall furnish Tenant
with copies of all proposed assessments, assessments, real estate tax bills and
the like. Landlord shall also notify Tenant promptly following the filing or
commencement of, and again following any decision in or conclusion or settlement
of, any tax or assessment appeal, contest, reduction or challenge. On or before
the 40th day before the last day to file an application to contest any such tax
or assessment, Tenant may request Landlord to notify Tenant whether Landlord
intends to file such application and within ten (10) days after such request
Landlord shall notify Tenant whether or not Landlord will do so. If within such
ten (10) day period Landlord either does not so notify Tenant or notifies Tenant
that Landlord does not intend to file such an application, Tenant, at its sole
cost and expense, shall have the right (and Landlord hereby constitutes Tenant
as Landlord's attorney-in-fact to the extent required by law to enable Tenant)
to challenge and/or appeal any tax, assessment or other item includable in
Operating Expenses pursuant to this Section 7. 1 (a), and Landlord shall
cooperate with Tenant as requested by Tenant in any such challenge and/or
appeal. Tenant hereby agrees to save Landlord harmless from and against all
costs, expenses, loss or damage resulting from any such contest or appeal.

                     (b)    All other reasonable costs of any kind paid or
incurred by Landlord in connection with the operation and maintenance of the
Building and the Project including, by way of examples and not as a limitation
upon the generality of the foregoing, costs of repairs and replacements to
improvements within the Project as appropriate to maintain the Project as
required hereunder, including cost of funding such reasonable reserves as
Landlord, consistent with good business practice, may establish (but in no event
in excess of Twenty Thousand Dollars ($20,000) per annum) to provide for future
repairs and replacements, costs of utilities furnished to the Common Areas,
sewer fees, cable T.V., when applicable, trash collection, cleaning, including
windows, heating, ventilation, air-conditioning, maintenance of landscape and
grounds, maintenance

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of drives and parking areas, security services and devices, building supplies,
maintenance and replacement to equipment utilized for operation and maintenance
of the Project, license, permit and inspection fees, sales, use and excise taxes
on goods and services purchased by Landlord in connection with the operation,
maintenance or repair of the Project and Building systems and equipment,
telephone, postage, stationary supplies and other expenses incurred in
connection with the operation, maintenance, or repair of the Project,
accounting, legal and other professional fees and expenses incurred in
connection with the Project, capital expenditures, costs of complying with any
applicable laws, hazardous waste remediation, rules or regulations, insurance
premiums including premiums for public liability, property casualty, earthquake
and environmental coverages, portions of insured losses paid by Landlord as part
of deductible portion of loss (not to exceed $50,000.00 for any single loss) by
reason of insurance policy terms, service contracts, costs of services of
independent contractors retained to do work of the nature before referenced, and
costs of compensation (including employment taxes and fringe benefits) of all
persons who perform regular and recurring on-site duties connected with the
day-to-day operation and maintenance of the Project, its equipment, the adjacent
walks, landscaped areas, drives, and parking areas, including without
limitation, janitors, floor waxers, window-washers, watchmen, gardeners,
sweepers, and handymen and costs of management services, which costs of
management services shall not exceed four percent (4%) of the Basic Annual Rent.
In the event that any capital expenditure by Landlord is in excess of
Seventy-Five Thousand Dollars ($75,000) there shall be included each calendar
year as an Operating Expense in respect of such expenditure only the amortized
cost of such item for that year (using the shorter of seven (7) years or the
useful life determined in accordance with the U.S. Internal Revenue Code
regulations in effect at the time the expenditure was made). Notwithstanding
anything to the contrary set forth elsewhere in this Lease, (i) in no event
shall Landlord establish reserves for the Building in excess of $100,000.00 and
(ii) in the event that a reserve is in existence and a capital expenditure is
required Landlord shall first use funds in reserve to pay for such capital
expenditure, in which event Landlord shall thereafter replenish the reserve
(subject to the $100,000.00 limitation).

                     (c)    The foregoing notwithstanding, term "OPERATING
EXPENSES" shall not include (1) depreciation; (2) interest on and amortization
of debts; (3) leasehold improvements, alterations, decorations and painting done
for particular tenants or occupants of the Building; (4) leasing and brokerage
commissions; (5) refinancing costs; (6) the cost or repairs or replacements
incurred by reason of fire or other casualty to the extent covered by insurance
proceeds; (7) the cost of items, work, services or overtime heating, ventilation
or air conditioning for which Landlord is or may be entitled to be compensated
by payments by tenants or occupants, including Tenant which are not fixed annual
rent; (8) amounts received by Landlord through proceeds of insurance, to the
extent the proceeds are compensation for expenses which would be includable in
Operating Expenses; (9) advertising and promotional expenditures; (10) ground
rents; (11) legal fees (provided, however, that Landlord may be entitled to
collect legal fees pursuant to Section 24.2.5 hereof); (12) auditing or
accounting fees other than those reasonably incurred in the preparation of
statements and calculations pursuant to this Section 7.1; (13) wages, benefits
or other compensation or payments to or in respect of employees or other persons
not providing on-site services to the Project or to executives or other persons
above (or performing functions typically assigned to or performed by persons
above) the grade of building manager; (14) wages, benefits or other compensation
or payments to or in respect of any person owning or controlling, directly or
indirectly, any right, title, interest or estate, legal, beneficial, equitable
or otherwise, in or to all or any part

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of Landlord, the Building and/or the Project and/or in or to any management
agent or company for either or both of the same; (15) management fees or other
markups of any kind or description other than for the management fee expressly
provided for in Section 7.1(b) above; (16) costs of Landlord's general overhead
and general administrative expenses (individual, partnership or corporate, as
the case may be); (17) charitable contributions; (18) any wages, benefits or
other compensation or payments paid clerks, attendants or other persons in
commercial concessions (such as snack bar or restaurant), if any, operated by
Landlord or in the Building; (19) costs attributable to the gross negligence of
Landlord, its agents, contractors or employees; (20) costs and expenses paid to
non-arms length contractors in excess of fair market value; (21) when operated
as a commercial concession or by a commercial parking operator, parking lot
garage maintenance or other costs in connection with any parking lot or garage;
(22) costs (including, but not limited to, rent) incurred in connection with or
otherwise attributable to office or other space used for or in connection with
the Building (including any management office space, but excluding any ordinary,
customary and reasonable amounts of space or area used solely for Building
mechanical, electrical, telephone, storage and/or engineering rooms); and (23)
costs or expenses associated with leasing other space in the Building and/or in
connection with any sale, financing and/or refinancing of the Building, the
Project or any interest of Landlord. In addition, Operating Expenses shall not
include any costs incurred by Landlord to test, survey, clean-up, contain,
abate, remove or otherwise remediate Hazardous Materials (as hereinafter
defined) in the Project unless such costs were incurred as a result of the acts
or omissions of Tenant.

              7.2    Tenant shall pay to Landlord on the first day of each
calendar month of the Term, as Additional Rent, Landlord's reasonable estimate
of Tenant's Pro Rata Share (as set forth in Section 2.1.6) of Operating Expenses
with respect to the Project for such month. On or before December 15th of each
year, Landlord shall submit to Tenant Landlord's good faith estimate of the
Operating Expenses for the succeeding calendar year. Landlord shall be permitted
to submit revised estimates at any time and from time to time. In the event that
Landlord revises its estimate of Operating Expenses, payments by Tenant in
respect of Operating Expenses pursuant to the revised estimate shall commence on
the first payment data that is at least thirty (30) days following Tenant's
receipt of such estimate.

                     (a)    Within ninety (90) days after the conclusion of each
calendar year (or such longer period as may be reasonably required), Landlord
shall furnish to Tenant a statement showing in reasonable detail the actual
Operating Expenses and Tenant's Pro Rata Share of Operating Expenses for the
previous calendar year. Any additional sum due from Tenant to Landlord shall be
due and payable within thirty (30) days following delivery of such written
statement. If the aggregate amount paid by Tenant pursuant to Section 7.2
exceeds Tenant's Pro Rata Share of Operating Expenses for the previous calendar
year, the difference shall be credited by Landlord against the Rent next due and
owing from Tenant; provided that if the Lease term has expired, Landlord shall
accompany said statement with payment for the amount of such difference.

                     (b)    Any amount due under Section 7.2 for any period
which is less than a full month shall be prorated (based on a 30-day month) for
such fractional month.

                     (c)    Landlord's annual statement, except as otherwise
provided in Section 7.3 below, shall constitute a final statement as to such
year, Anything

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to the contrary contained herein notwithstanding, in the event that such
statement is not received by Tenant on or prior to August 31 of any calendar
year for the immediately preceding calendar year then Landlord may not
thereafter request payment of any deficiency on account of such prior year.
Landlord shall keep true and accurate books and records with respect to all
Operating Expenses in accordance with generally accepted accounting principals
consistently applied.

              7.3    Landlord's annual statement shall be final and binding upon
Tenant unless Tenant, within ninety (90) days after Tenant's receipt thereof,
shall contest any item therein by giving written notice to Landlord, specifying
each item contested and the reason therefor. If, during such 90 day period,
Tenant reasonably and in good faith questions or contests the correctness of
Landlord's statement of Tenant's Pro Rata Share of Operating Expenses, (provided
that Tenant shall have paid to Landlord any additional sum due pursuant to
Section 7.2(a)) Landlord will provide Tenant and/or Tenant's designated
representative with access to Landlord's books and records and such information
as Landlord reasonably determines to be responsive to Tenant's questions.
Tenant's designated representative shall be an independent public accounting
firm working pursuant to a fee arrangement other than a contingent fee basis. In
the event that after Tenant's review of such information, Landlord and Tenant
cannot agree upon the amount of Tenant's Pro Rata Share of Operating Expenses,
then Tenant shall have the right to have an independent public accounting firm
working pursuant to a fee arrangement other than a contingent fee basis hired by
Tenant (at Tenant's sole cost and expense) and approved by Landlord (which
approval shall not be unreasonably withheld or delayed) audit and/or review such
Landlord's books and records for the year in question (the "INDEPENDENT
REVIEW"). The results of any such Independent Review shall be binding on
Landlord and Tenant. If the Independent Review shows that Tenant s Pro Rata
Share of Operating Expenses actually paid for the calendar year in question
exceeded Tenant's obligations for such calendar year, Landlord shall at Tenant's
option either (1) credit the excess to the next succeeding installments of
estimated Additional Rent or (2) pay the excess to Tenant within thirty (30)
days after delivery of such statement (provided, however, that in the event that
the Independent Review indicates that the amount of Operating Expenses paid by
Tenant with respect to a calendar year exceeded by more than five percent (5%)
the amount actually due from Tenant (exclusive of any difference between the
amount included in Operating Expenses in respect of insurance premiums and the
amount that should have been included in Operating Expenses in respect of
insurance premiums), then Landlord shall reimburse Tenant for the cost of such
Independent Review). If the Independent Review shows that Tenant's payments of
Tenant's Pro Rata Share of Operating Expenses for such calendar year were less
than Tenant's obligation for the calendar year, Tenant shall pay the deficiency
to the Landlord within thirty (30) days after delivery of such statement.

              7.4    Tenant shall not be responsible for Operating Expenses
attributable to the time period prior to the Rent Commencement Date. The
responsibility of Tenant for Tenant's Pro Rata Share of Operating Expenses shall
continue to the later of (i) the date of termination of the Lease, or (ii) the
date Tenant has fully vacated the Demised Premises. Tenant shall not be deemed
to have fully vacated the Demised Premises until Tenant shall have removed all
items required to be removed and shall have completed all procedures necessary
to fully release and terminate any permits or licenses restricting the use of
the Demised Premises in any manner.

                                       9
<PAGE>   13

              7.5    Operating Expenses for the calendar year in which Tenant's
obligation to share therein commences and in the calendar year in which such
obligation ceases, shall be prorated on the basis of the number of days in such
calendar year as are included within the Term over 360. Expenses such as taxes,
assessments and insurance premiums which are incurred for an extended time
period shall be prorated based upon time periods to which applicable so that the
amounts attributed to the Demised Premises relate in a reasonable manner to the
time period wherein Tenant has an obligation to share in operating Expenses.

       8.     Intentionally omitted.

       9.     Security Deposit.

              9.1    On the date of delivery of the Demised Premises by Landlord
to Tenant, Tenant shall deposit with Landlord the sum set forth in Section
2.1.8(a) (the "SECURITY DEPOSIT") which sum shall be held by Landlord as
security for the faithful performance by Tenant of all of the terms, covenants,
and conditions of this Lease to be kept and performed by Tenant during the Term.
If an Event of Default shall occur, Landlord may (but shall not be required to)
use, apply or retain all or any part of the Security Deposit to the extent
necessary to remedy such Event of Default and/or to compensate Landlord for any
other loss or damage which Landlord may suffer by reason of such Event of
Default. If any portion of the Security Deposit is so used or applied, Tenant
shall, within ten (10) days following 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.
The term "SECURITY DEPOSIT" includes any interest to which Tenant is entitled
pursuant hereto on any cash portion of such Security Deposit. Landlord shall
deposit the cash portion of the Security Deposit in a segregated
interest-bearing account of its choice and Tenant shall be entitled to the
interest earned thereon. The Security Deposit may, at Tenant's election, and at
any time, be or be changed to be in the form of a letter of credit (the "LETTER
OF CREDIT"). Any Letter of Credit tendered as and for the Security Deposit shall
be (i) unconditional (except for standard conditions relating to presentation);
(ii) irrevocable; (iii) issued by a financial institution reasonably approved by
Landlord in Landlord's reasonable discretion; (iv) in a form reasonably approved
by Landlord, assignable (in accordance with the issuer's standard requirements)
and permitting partial and multiple drawings; (v) for either multiple terms of
one (1) year each in duration, renewed (unless automatically renewing) at least
sixty (60) days prior to the expiration thereof, the entire term extending until
the date which is ninety (90) days after the expiration of the Term, as such
Term may be extended pursuant to the provisions of this Lease, or at Tenant's
option for a single term extending until the date which is ninety (90) days
after the expiration of the Term, as such Term may be extended pursuant to the
provisions of this Lease; and (vi) be in form and substance acceptable to the
Landlord, in its reasonable discretion. Unless automatically renewing, Tenant
shall provide Landlord with a replacement Letter of Credit at least sixty (60)
days prior to the expiration of the immediately preceding Letter of Credit. If a
partial drawing occurs under the Letter of Credit, Tenant shall, upon demand but
not more than five (5) days after such partial drawing, cause the financial
institution to reissue the Letter of Credit in the amount then currently
required under the terms of this Lease. Notwithstanding the foregoing, Landlord
shall be entitled to draw down on the Letter of Credit, without any notice, at
any time on or after the earlier of (i) the, occurrence and continuance of an
Event of Default by Tenant under this Lease; or (ii) the thirtieth (30th) day
preceding the expiration date of the Letter of Credit in the event Tenant is
required to and fails to timely

                                       10
<PAGE>   14

replace the Letter of Credit. Landlord shall provide Tenant with written notice
of any draws made on the Letter of Credit.

              9.2    In the event of bankruptcy or other debtor-creditor
proceedings against Tenant, the Security Deposit shall be deemed to be applied
first to the payment of Rent and other charges due Landlord for all periods
prior to the filing of such proceedings.

              9.3    Landlord shall deliver the funds deposited hereunder by
Tenant to any purchaser of Landlord's interest in the Demised Premises and
thereupon Landlord shall be discharged from any further liability with respect
to such Security Deposit. This provision shall also apply to any subsequent
transfers.

              9.4    To the extent the Security Deposit has not been applied
pursuant to this Article 9, the Security Deposit or any balance thereof, shall
be returned to Tenant (or, at Landlord's option, to the last assignee of
Tenant's interest hereunder) within thirty (30) days after the expiration or
earlier termination of this Lease.

              9.5    Tenant shall, at the time it delivers the Security Deposit
to Landlord, deposit with Landlord the sum set forth in Section 2.1.8(b) (the
"RENT DEPOSIT") which sum shall be held by Landlord and applied against the
first full monthly payment of Basic Annual Rent.

              9.6    If on the three year anniversary of the Rent Commencement
Date there is then no uncured Event of Default, the Security Deposit shall be
reduced to an amount equal to one month's then applicable monthly Basic Annual
Rent (the "REDUCED SECURITY DEPOSIT"). If Tenant qualifies for such reduction of
the Security Deposit, Tenant shall provide Landlord with written notice
requesting that Landlord reduce the Security Deposit as described above. If
Landlord agrees that the condition described above is met, Landlord shall return
the unapplied portion of the Security Deposit then held by Landlord, less the
Reduced Security Deposit, to Tenant within thirty (30) days of Tenant's delivery
of such written request. If the Security Deposit is then held in the form of a
Letter of Credit Landlord shall either draw the Letter of Credit and return to
Tenant any excess portion of the Security Deposit in accordance with this
Section, or Tenant shall supply Landlord with a replacement Letter of Credit in
the amount of the Reduced Security Deposit, in which case Landlord shall return
the original Letter of Credit to Tenant. From and after the date such monies are
returned to Tenant, the "Security Deposit" shall be deemed to be the Reduced
Security Deposit for all purposes of this Lease.

       If thereafter there occurs an Event of Default hereunder resulting from
Tenant's failure to pay any Rent in an amount of $50,000 or more, the Reduced
Security Deposit shall be increased to an amount equal to the original amount of
the Security Deposit hereunder. Such increased Security Deposit shall be paid to
Landlord within 10 days of Landlord's written demand, in the case of an Event of
Default under the Lease. If Tenant is required to increase the Reduced Security
Deposit in accordance with this Section, then from and after the date such
monies are deposited with Landlord, the "Security Deposit" shall be deemed to be
the amount then held by Landlord hereunder.

       10.    Use.

                                       11
<PAGE>   15

              10.1   Tenant shall use the Demised Premises for the purpose set
forth in Section 2.1.9 and shall not use the Demised Premises, or permit or
suffer the Demised Premises to be used, for any other purpose without the prior
written consent of Landlord which may be withheld in Landlord's sole discretion,
(provided, however, that Landlord's approval of a change in use shall not be
unreasonably withheld, conditioned or delayed in the case of a change proposed
in connection with an assignment or subletting of the Lease and/or the Demised
Premises under circumstances where, pursuant to the terms of Section 25 below,
Landlord's consent to such assignment or subletting may not be unreasonably
withheld, conditioned or delayed). In no event shall Landlord be deemed to have
acted unreasonably in the event that Landlord does not approve a change in use
which would reduce the number of square feet of the Demised Premises maintained
as laboratories constructed in whole or in part using the Allowance under the
Work Letter unless Tenant as a condition to Landlord's consent agrees, upon
expiration or earlier termination of this Lease, either (i) to restore such
laboratory space or (ii) to pay Landlord the amount Landlord reasonably
estimates it will cost to cause such restoration and, in either case, provides
such security for such restoration obligation as Landlord shall reasonably
require.

              10.2   Tenant shall not use or occupy the Demised Premises in
violation of any federal, state and local laws and regulations, zoning
ordinances, or of the certificate of occupancy issued for the Building, and
shall, upon five (5) days' written notice from Landlord, discontinue any use of
the Demised Premises which is declared or claimed by any governmental authority
having jurisdiction to be a violation of law, regulation or zoning ordinance or
of said certificate of occupancy. Tenant shall comply with any direction of any
governmental authority having jurisdiction which shall, by reason of the nature
of Tenant's use or occupancy of the Demised Premises, impose any duty upon
Tenant or Landlord with respect to the Demised Premises or with respect to the
use or occupation thereof. Provided non-compliance therewith shall not
constitute a crime or an offense punishable by imprisonment of Landlord and
provided non-compliance will not endanger the Demised Premises, Tenant may, at
its sole cost and expense, contest the application or validity of any such law
and such non-compliance shall not be deemed a breach of this Lease during such
contest provided such contest shall be diligently prosecuted.

              10.3   Tenant shall not do or permit to be done anything which
will invalidate or increase the cost of any fire, environmental, extended
coverage or any other insurance policy covering the Building and Project and
shall comply with all rules, orders, regulations, and requirements of the
insurers of the Building and Project and Tenant shall within thirty (30) days
following written demand reimburse Landlord for any additional premium charged
for such policy by reason of Tenant's failure to comply with the provisions of
this Section.

              10.4   Intentionally omitted.

              10.5   No additional locks or bolts of any kind shall be placed
upon any of the doors or windows by Tenant nor shall any changes be made in
existing locks or the mechanism thereof without the prior written consent of
Landlord (or, alternatively, without furnishing to Landlord one or more master
keys therefor). Tenant must, upon termination of this Lease return to Landlord
all keys to offices and restrooms, either furnished to, or otherwise procured by
Tenant. The foregoing notwithstanding, Tenant shall have the right to designate
certain areas as "secure" areas and, subject to the

                                       12
<PAGE>   16

provisions of Section 32.3 hereof, to limit access thereto (including, but not
limited to, by installing locks or other apparatus to which Landlord is not
provided keys or other means of entry).

              10.6   No awnings or other projection shall be attached to any
outside wall of the building. Neither the interior nor exterior of any windows
shall be coated or otherwise sunscreened without the express written consent of
Landlord.

              10.7   No sign, advertisement or notice shall be exhibited,
painted or affixed by Tenant on the exterior of the Building without the prior
written consent of Landlord. Notwithstanding anything to the contrary contained
elsewhere in this Lease so long as Tenant occupies more than fifty percent (50%)
of the Building, Tenant shall have the right, at its sole cost and expense, to
install and maintain an illuminated exterior sign (if permitted by law and
matters currently of record affecting the Project) on the Building upon and
subject to the following terms and conditions:

                     (i)    Tenant shall have submitted to Landlord for its
approval plans and specifications for such installation, including without
limitation, the size, weight, location, design and manner of affixation to the
Building;

                     (ii)   Tenant shall have obtained all required governmental
approvals and permits and delivered copies of the same to Landlord prior to the
commencement of any such installation;

                     (iii)  Tenant's installation shall be performed in
accordance with all applicable laws, applicable provisions of this Lease and
Landlord's reasonable requirements; and

                     (iv)   If requested by Landlord, prior to the expiration or
earlier termination of this Lease, Tenant shall remove such sign and restore the
affected area of the Building to its condition prior to such installation.

Tenant's right to install signage on the exterior of the Building shall be
exclusive to Tenant so long as Tenant occupies more than fifty percent (50%) of
the Building, Notwithstanding the foregoing, Landlord (or if Landlord shall fail
to do so then Tenant, in addition to any Building mounted sign) may install and
maintain one or more monument signs for the Building or the Project and Tenant,
in common with other tenants of the Building and the Project shall have the
right to non-exclusive signage on such monument, subject to all applicable legal
requirements and Landlord's reasonable approval.

              10.8   Tenant shall cause any office equipment or machinery to be
installed in the Demised Premises so as to reasonably prevent sounds or
vibrations therefrom from extending outside of the Building or, if other tenants
are occupying any part of the Building, from extending into Common Areas as
defined in Section 1.1 or other tenant offices in the Building. Tenant shall not
place a load on any floor of the Demised Premises exceeding a floor load of one
hundred (100) pounds per square foot (one hundred twenty five (125) pounds per

                                       13
<PAGE>   17

square foot with respect to the loading docks) without advance notice to and
reasonable approval by Landlord.

              10.9   Tenant shall not do or permit anything to be done in or
about the Demised Premises which shall in any way obstruct or interfere with the
rights of other tenants or occupants of the Building, or injure or annoy them,
or use or allow the Demised Premises to be used for immoral or unlawful
purposes, nor shall Tenant knowingly cause, maintain or permit any nuisance or
waste in, on, or about the Demised Premises, Building or Project.

              10.10  Notwithstanding any other provision herein to the contrary
except for the Landlord Work and the Tenant Performed Landlord Work, Tenant
shall be responsible for all liabilities, costs and expense arising out of or in
connection with the compliance of the Demised Premises with the Americans With
Disabilities Act, 42 U.S.C. Section 12101, et seq. (together with regulations
promulgated pursuant thereto, "ADA") and Tenant shall indemnify, defend and hold
harmless from and against any loss, cost, liability or expense (including
reasonable attorneys' fees and disbursements) arising out of any failure of the
Demised Premises to comply with the ADA.

              10.11  Notwithstanding anything to the contrary contained
elsewhere in this Lease, Tenant shall have the non-exclusive right, at its sole
cost and expense but without charge by Landlord, to install and maintain
air-conditioning and communications equipment on the roof of the Building (if
permitted by law and matters currently of record affecting the Project) upon and
subject to the following terms and conditions:

                     (i)    Tenant shall have submitted to Landlord for its
reasonable approval plans and specifications for such installation, including,
without limitation, the size, weight, location, design and manner of penetration
of the roof of the Building;

                     (ii)   All equipment installed on the roof of the Building
shall be tastefully screened if required by applicable law (Landlord agreeing to
reasonably cooperate with Tenant, at no out-of-pocket cost to Landlord, in
seeking to obtain a waiver of any such requirement);

                     (iii)  Tenant shall have obtained all required governmental
approvals and permits and delivered copies of the same to Landlord prior to the
commencement of any such installation;

                     (iv)   Tenant's installation shall be performed in
accordance with all applicable laws, applicable provisions of this Lease and
Landlord's reasonable requirements; and

                     (v)    If requested by Landlord, prior to the expiration or
earlier termination of this Lease, Tenant shall remove such installations and
restore the affected areas of the roof to a leak-free state.

                                       14
<PAGE>   18

              10.12  If the Project is annexed to any business or similar park,
then (a) Tenant shall not be liable for any costs or expenses associated with
such annexation, (b) Tenant shall not be required to pay any common area or
similar costs ("COMMON AREA COSTS") imposed on occupants of such business park,
except to the extent Landlord reasonably determines that the Project benefits
from the service or improvement paid for by such Common Area Cost, provided that
Tenant shall not be liable under any circumstances for any costs associated with
(i) undeveloped land in any such park, (ii) storm water management in any such
park, (iii) the initial cost of park improvements, or (iv) driveways or roads
which serve solely a single parcel or lot, and (c) neither Tenant nor this Lease
shall be subject to any covenants, conditions or restrictions affecting any such
park.

       11.    Brokers.

              11.1   Landlord and Tenant represent and warrant that they have
had no dealings with any real estate broker or agent in connection with the
negotiation of this Lease other than Scheer Partners and that they know of no
other real estate broker or agent who is or might be entitled to a commission in
connection with this Lease.

              11.2   Tenant represents and warrants that no broker or agent has
made any representation or warranty relied upon by Tenant in Tenant's decision
to enter into this Lease other than as contained in this Lease.

              11.3   Tenant acknowledges and agrees that the employment of
brokers by Landlord is for the purpose of solicitation of offers of lease from
prospective tenants and no authority is granted to any broker to furnish any
representation (written or oral) or warranty from Landlord unless expressly
contained within this Lease. Landlord in executing this Lease does so in
reliance upon Tenant's representations and warranties contained within Sections
11.1 and 11.2 herein.

       12.    Holding Over.

              12.1   If, with Landlord's express written consent, Tenant holds
possession of all or any part of the Demised Premises after the Term, Tenant
shall become a tenant from month-to- month upon the date of such expiration or
earlier termination, and in such case Tenant shall continue to pay in accordance
with Article 5 the Basic Annual Rent as adjusted from the Rent Commencement Date
in accordance with Article 6, and Tenant's Pro Rata Share of Operating Expenses,
and such month-to-month tenancy shall be subject to every other term, covenant
and agreement contained herein.

              12.2   Notwithstanding the foregoing, if Tenant remains in
possession of the Demised Premises after the expiration or earlier termination
of the Term without the express written consent of Landlord, Tenant shall become
a tenant at sufferance upon the terms of this Lease except that the monthly
Basic Annual Rent shall be equal to one hundred fifty percent (150%) of the
Basic Annual Rent in effect during the last thirty (30) days of the Term.

                                       15
<PAGE>   19

              12.3   Acceptance by Landlord of Rent after such expiration or
earlier termination shall not result in a renewal or reinstatement of this
Lease.

              12.4   The foregoing provisions of this Article 12 are in addition
to and do not affect Landlord's right to re-entry or any other rights of
Landlord hereunder or as otherwise provided by law.

              12.5   If pursuant to the operation of Section 40.5 or the last
sentence of Section 7.4 Tenant shall not be deemed to have fully vacated the
Demised Premises, Tenant shall continue to pay in accordance with Article 5 the
Basic Annual Rent as adjusted in accordance with Article 6 and Tenant's Pro Rata
Share of Operating Expenses until such time as Tenant shall have complied with
its obligations pursuant to Section 40.5 or the last sentence of 7.4, as
applicable.

       13.    Taxes on Tenant's Property.

              13.1   Tenant shall pay, prior to delinquency, any and all taxes
levied against any personal property or trade fixtures placed by Tenant in or
about the Demised Premises.

              13.2   If any such taxes on Tenant's personal property or trade
fixtures are levied against Landlord or Landlord's property or, if the assessed
valuation of the Building is increased by the inclusion therein of a value
attributable to Tenant's personal property or trade fixtures, and if Landlord
after written notice to Tenant pays the taxes based upon such increase in the
assessed valued, then Tenant shall within thirty (30) days following Tenant's
receipt of written demand by Landlord repay to Landlord the taxes so levied
against Landlord (Landlord, however, agreeing to give Tenant written notice upon
first learning of any such tax or other charge and Tenant reserving the right to
contest same whether in the name of Landlord or Tenant).

       14.    Condition of Demised Premises.

              14.1   Tenant acknowledges that neither Landlord nor any agent of
Landlord has made any representation or warranty with respect to the condition
of the Demised Premises or the Building or Project, or with respect to the
suitability for the conduct of Tenant's business. Except for Landlord Work, the
Landlord Payment and the Allowance, Tenant agrees to take possession of the
Demised Premises in its current "as-is" condition.

       15.    Common Areas and Parking Facilities.

              15.1   Tenant shall have the non-exclusive right , in common with
other Building tenants, if any, to use the Common Areas, subject to the rules
and regulations adopted by Landlord and attached hereto as Exhibit "C" together
with such other reasonable and nondiscriminatory modifications thereof and
additions thereto as are hereafter promulgated by Landlord in its reasonable
discretion (the "RULES AND REGULATIONS"). Tenant shall observe and comply with
the Rules and Regulations. In the event of any conflict or inconsistency between
any Rule or Regulation and any other term or provision of this Lease, such other

                                       16
<PAGE>   20

term or provision of this Lease shall control. Tenant shall be entitled to use
all of the parking.

              15.2   Parking spaces shall be allocated to tenants of the
Building on a pro-rata basis.

              15.3   Landlord reserves the right to modify Common Areas
including the right to add or remove exterior and interior landscaping provided
that the same shall not unreasonably interfere with Tenant's use and enjoyment
of the Demised Premises, of the Building and/or of the Project (including, but
not limited to, the Common Areas) or reduce the amount of parking except by
reason of any taking in eminent domain or similar governmental or
quasi-governmental action.

              15.4   The parking for the Building shall include all of the area
depicted on Exhibit "G-1" attached hereto, subject to any reduction in such area
by reason of any taking of any portion of such area by exercise of the right of
eminent domain or any conveyance under the threat of such exercise. The parking
area described on Exhibit "G-1" shall be for the exclusive use of tenants of the
Building.

       16.    Utilities and Services.

              16.1   Tenant shall pay for all water (including the cost to
service, repair and replace reverse osmosis, deionized and other treated water
facilities serving only the Demised Premises, gas, heat, light, power, telephone
and other utilities supplied to the Demised Premises, together with any fees,
surcharges and taxes thereon. If any such utility is not separately metered to
Tenant, Tenant shall pay a reasonable proportion to be determined by Landlord of
all charges jointly metered with other premises as part of Tenant's Pro Rata
Share of Operating Expenses.

              16.2   Landlord shall not be liable for nor shall any eviction of
Tenant result from the failure to furnish any such utility or service whether or
not such failure is caused by accident, breakage, repairs, strikes, lockouts or
other labor disturbances or labor disputes of any character, governmental
regulation, moratorium or other governmental action, inability despite the
exercise of reasonable diligence or by any other cause, including the negligence
of Landlord. In the event of such failure, Tenant shall not be entitled to any
abatement or reduction of Rent, nor be relieved from the operation of any
covenant or agreement of this Lease. In the event that Landlord fails to make a
repair that Landlord is obligated to make pursuant to the terms of this Lease
and as a result Tenant is substantially interfered with or interrupted in
conducting its business in the Demised Premises, Tenant, at its sole cost and
expense (unless such repair was an obligation of Landlord pursuant to Section
18.1 that was not includable as an Operating Expense, or unless such repair was
a capital expenditure in excess of $75,000.00 that would have been amortized as
an Operating Expense pursuant to Section 7.1(b), in either of which events
Landlord shall reimburse Tenant in an amount equal to the reasonable costs paid
by Tenant to make such repair promptly following a request by Tenant for
reimbursement accompanied by copies of all invoices paid by Tenant), shall have
the right to make such repair. In the event that Tenant makes any such repair
Tenant shall give Landlord prompt notice of

                                       17
<PAGE>   21

Tenant's repair and Tenant shall deliver to Landlord copies of all invoices paid
by Tenant to effect any such repair.

              16.3   Tenant shall pay for, prior to delinquency, any utilities
and services which may be furnished to the Demised Premises during the Term.

              16.4   Tenant shall not, without the prior written consent of
Landlord, use any device in the Demised Premises, including, but without
limitation, data processing machines, which will in any way increase the amount
of ventilation, air exchange, gas, steam, electricity or water beyond the
existing capacity of the Building (as such capacity may be increased based upon
improvements by Landlord or Tenant).

              16.5   Intentionally omitted.

              16.6   Utilities and services which are separately metered to the
Demised Premises shall be paid by Tenant directly to the supplier of such
utility or service.

              16.7   Intentionally omitted.

              16.8   Subject in all cases to the terms of Section 16.2 hereof,
Landlord reserves the right to stop service of the elevator, plumbing,
ventilation, air conditioning and electric systems, when necessary, by reason of
accident or emergency or for repairs, alterations or improvements, in the
judgment of Landlord desirable or necessary to be made, until said repairs,
alterations or improvements shall have been completed, and Landlord shall
further have no responsibility or liability for failure to supply elevator
facilities, plumbing, ventilation, air conditioning or electric service, when
prevented from doing so by strike or accident, or by laws, rules, order,
ordinances, directions, regulations or requirements of any federal, state,
country or municipal authority or failure to deliver gas, oil or other suitable
fuel supply or inability by exercise of reasonable diligence to obtain gas, oil
or other suitable fuel. It is expressly understood and agreed that any covenants
on Landlord's part to furnish any service pursuant to any of the terms,
covenants, conditions, provisions or agreements of this Lease, or to perform any
act or thing for the benefit of Tenant, shall not be deemed breached if Landlord
is unable to finish or perform the same by virtue of a strike or labor trouble
or any other cause whatsoever. The foregoing notwithstanding, Landlord shall use
its best efforts to minimize any interference with Tenant's use and enjoyment of
the Demised Premises in connection with any action by Landlord under this
Section 16.8 and, in particular, shall coordinate and schedule all such
activities (except in case of emergency) with Tenant.

              16.9   Landlord shall have no responsibility to provide an
emergency power generator.

       17.    Alterations.

              17.1   Except as otherwise specifically provided herein, Tenant
shall make no alterations, additions or improvements in or to the Demised
Promises without Landlord's prior written consent, which approval shall not be

                                       18
<PAGE>   22

unreasonably withheld, conditioned or delayed (provided, however, that in the
event any proposed alteration, addition or improvement (i) affects any
structural portions of the Building including exterior walls, roof, foundation
and core of the Building, (ii) affects the exterior of the Building or (iii)
materially and adversely affects any Building systems, including elevator,
plumbing, air conditioning, heating, electrical, security, life safety and
power, then, except as otherwise specifically provided in this Lease, Landlord
may withhold its consent with respect thereto in its sole and absolute
discretion), and then only by architects, contractors, suppliers or mechanics
reasonably approved by Landlord. In seeking Landlord's approval, Tenant shall
provide Landlord, at least five (5) business days in advance of any proposed
construction, with plans, specifications, bid proposals, work contracts and such
other information concerning the nature and cost of the alterations as may be
reasonably requested by Landlord (to the extent the same exist). The foregoing
notwithstanding, Tenant shall have the right without Landlord's prior written
consent or approval to make interior, non-structural alterations, additions
and/or improvements not materially and adversely affecting the Building systems
or the Common Areas and not, as to any particular project, exceeding $30,000,00
in hard costs in the event that the subject project is undertaken prior to the
fifth anniversary of the Rent Commencement Date and not exceeding $50,000.00 in
hard costs in the event that the subject project is undertaken thereafter;
provided, however, that Tenant shall nevertheless furnish Landlord with prior
written notice thereof in accordance with Section 17.5 below and with a copy of
any preliminary plans and specifications, working drawings and final "as-built"
drawings obtained therefor. In all events Tenant shall deliver to Landlord a
copy of all documents, plans and drawings submitted to governmental authorities
in connection with any alteration, addition or improvement.

              17.2   Tenant agrees that there shall be no construction of
partitions or other obstructions which might interfere with free access to
mechanical installation or service facilities of the Building or interfere with
the moving of Landlord's equipment to or from the enclosures containing said
installations or facilities. The foregoing shall not prohibit Tenant from
constructing corridors or other internal security partitions closing off such
areas from general public access, provided, however, that in such event Tenant
shall ensure that Landlord is given a copy of all keys and the like needed for
Landlord to have access to all Building mechanical systems and service
facilities and provided, further, however, that in no event shall any such
construction interfere with the moving of Landlord's equipment to and from the
subject enclosures.

              17.3   Tenant agrees to use its best efforts to ensure that any
work by Tenant shall be accomplished in such a manner as to permit any fire
sprinkler system and fire water supply lines to remain fully operable at all
times.

              17.4   If at the time such work is to be performed Tenant is not
the only tenant in the Building, all such work shall be done at such times and
in such manner as Landlord may from time to time reasonably designate. Tenant
covenants and agrees that all work done by Tenant shall be performed in full
compliance with all laws, rules, orders, ordinances, directions, regulations,
and requirements of all governmental agencies, offices, departments, bureaus and
boards having jurisdiction, and in full compliance with the rules, orders,
directions, regulations, and requirements of any applicable fire rating bureau.
Tenant shall

                                       19
<PAGE>   23

provide Landlord with copies of "as-built" plans, if obtained, showing any
change in the Demised Premises. In all events Tenant shall deliver to Landlord a
copy of all documents, plans and drawings submitted to governmental authorities
in connection with any alteration, addition or improvement.

              17.5   Before commencing any work, Tenant shall give Landlord
prior written notice of the proposed commencement of such work and shall, if
required by Landlord (in the event that the total projected hard costs of such
work exceed $100,000,00), secure at Tenant's own cost and expense a completion
and lien indemnity bond (in industry standard form) for said work. Such notice
shall be received by Landlord at least five (5) business days prior to the
commencement of such work.

              17.6   All alterations, attached equipment, decorations, fixtures,
trade fixtures, additions and improvements, subject to Section 17.8, attached to
or built into the Demised Premises, made by either of the parties, including
(without limiting the generality of the foregoing) all floor and wall covering,
built-in cabinet work and paneling, sinks and related plumbing fixtures,
exterior venting fume hoods and non-modular walk-in-freezers and refrigerators,
ductwork, conduits, electrical panels and circuits, shall, unless prior to such
construction or installation, Landlord elects otherwise, become the property of
Landlord upon the expiration or earlier termination of the term of this Lease,
and shall remain upon and be surrendered with the Demised Premises as a part
thereof.

              17.7   Tenant shall repair any damage to the Demised Premises
caused by Tenant's removal of any property from the Demised Premises. During any
such restoration period, Tenant shall pay Rent to Landlord as provided herein as
if said space were otherwise occupied by Tenant.

              17.8   Notwithstanding anything to the contrary set forth
elsewhere in this Lease, (a) to extent no part of any such item was paid for in
whole or in part from the Allowance under the Work Letter, Tenant shall have the
right to remove the following items: modular chillers, modular walk-in freezers,
modular refrigerators, emergency/uninterrupted power generators/systems
(including related electrical panels and transfer switches), modular casework,
countertops for modular casework, wireless LAN, audiovisual equipment not built
into the Demised Premises, modular furniture and equipment, security systems not
built into the Demised Premises and self-contained air conditioning units and
/or fire suppression units not built into the Demised Premises, autoclaves, fume
hoods that are not exterior venting, robotic equipment, glass washer and dryer,
phone systems, film processors, and other Tenant equipment; provided, however,
that Tenant shall repair any damage caused by the removal thereof and (b) Tenant
shall not have the right to remove piping, ductwork, exhaust vents, wiring,
cabling, electrical panels or transfer switches (except as provided above),
transformers, circuits, conduits, gas and vacuum distribution systems,
specialized water systems (reverse osmosis and deionized), exterior exhausting
fume hoods and air conditioners, non-modular casework and bench tops, built- in
cabinets, wall and floor coverings, pumps, Building boilers, air-handlers, steam
coils, heat exchangers, non-modular chillers, waste disposal systems, steam
generators, light fixtures, life and safety systems (i.e., fire alarms, eye wash
stations and fire sprinklers), drop ceiling structure and tiles, sinks and hot
water heaters. In any

                                       20
<PAGE>   24

event Tenant shall not be permitted to remove (i) any part of the Building's
basic operating systems (as distinguished from specialized laboratory items
permitted to be removed pursuant to clause (a) above), (ii) anything purchased
or paid for by Landlord directly or through the payment by Landlord to Tenant of
any construction or improvement allowance, or (iii) anything that could result
in significant damage to the Building. If Tenant shall fail to remove all of its
effects from the Demised Premises prior to termination of this Lease, then
Landlord may, at its option, remove the same in any manner that Landlord shall
choose, and store said effects without liability to Tenant for loss thereof or
damage thereto, and Tenant agrees to pay Landlord upon demand any expenses
incurred for such removal and storage or Landlord may, at its option, without
notice, sell said property or any of the same, at private sale and without legal
process, for such price as Landlord may obtain and apply the proceeds of such
sale against any amounts due under this Lease from Tenant to Landlord and
against any expenses incident to the removal, storage and sale of said personal
property.

              17.9   Notwithstanding any other provision of this Article 17 to
the contrary, in no event may Tenant remove any improvement from the Demised
Premises as to which Landlord contributed payment, including, without
limitation, the Tenant Improvements made pursuant to the Work Letter without
Landlord's prior written consent, which may be withheld in Landlord's sole
discretion.

              17.10  Tenant shall pay to Landlord an amount equal to five
percent (5%) of the cost to Tenant of all changes installed by Tenant or its
contractors or agents to cover Landlord's overhead and expenses for plan review,
coordination, scheduling and supervision thereof. Notwithstanding the
immediately preceding sentence, Tenant's payment to cover Landlord's overhead
and expenses in connection with Tenant's initial alterations of the 27,410
square foot portion of the first floor of the Building that Tenant is not
altering immediately ("PHASE 2," and the 30,000 square foot portion of the first
floor of the Building that Tenant is altering immediately is referred to as
"PHASE 1") shall be governed by the Work Letter. For purposes of payment of such
sum, Tenant shall submit to Landlord copies of all bills, invoices, and
statements covering the costs of such charges, which will be accompanied by
payment to Landlord of the percentage fee set forth above. Tenant shall
reimburse Landlord for any extra expense incurred by Landlord by reason of
faulty work done by Tenant or its contractors or by reason of inadequate
cleanup.

       18.    Repairs and Maintenance.

              18.1   Landlord shall repair and maintain the structural and
exterior portions and Common Areas of the Building (including water tightness
thereof) and Project, including, without limitations, roofing and covering
materials, foundations, exterior walls, the plumbing, fire sprinkler system (if
any), heating, ventilating, air conditioning, elevator, and electrical systems
thereof (and the full cost thereof shall be included as a part of Operating
Expenses as provided in Article 7), unless such maintenance or repairs are
required in whole or in part because of any act, neglect, fault of or omissions
of any duty by Tenant, its agents, servants, employees or invitees, in which
case Tenant shall pay to Landlord the cost of such maintenance and repairs.
Notwithstanding anything to the contrary

                                       21
<PAGE>   25

set forth elsewhere in this Lease, Landlord, at its sole cost and expense and
not as an Operating Expense, shall be responsible for maintaining the structural
integrity of the roof, the exterior walls and the floor slabs of the Building.
In the event that Tenant desires to independently arrange for certain services
otherwise furnished by Landlord (other than landscaping), Tenant shall give
notice to Landlord of such desire and, subject to Landlord's approval, which
approval shall not be unreasonably withheld, Tenant may make such arrangements
in which event Tenant shall pay the entire cost therefor directly to the
provider thereof and no costs associated with any such service shall be included
in Operating Expenses. In the event Landlord approves of any such arrangement,
Landlord reserves the right to monitor the work or services provided by any such
provider. Upon request by Landlord in the event that Landlord is dissatisfied
with a provider or with the work or services provided, Tenant shall terminate
any such arrangements provided that Tenant shall have no less than forty five
(45) days following receipt of Landlord's request to effect such termination. In
addition, upon request by Landlord Tenant shall promptly furnish to Landlord
copies of all documents, contracts, work orders and other instruments executed
in connection with any such arrangement.

              18.2   Except for services of Landlord, if any, required by this
Lease, Tenant shall at Tenant's sole cost and expense keep the Demised Premises
and every part thereof in good condition and repair, damage thereto from
ordinary wear and tear excepted. Tenant shall, upon the expiration or sooner
termination of the Term, surrender the Demised Premises to Landlord in as good
condition as when received, ordinary wear and tear and damage by casualty
excepted. Except as otherwise specifically provided herein, Landlord shall have
no obligation to alter, remodel, improve, repair, decorate or paint the Demised
Premises or any part thereof.

              18.3   Except as provided in Section 16.2, Landlord shall not be
liable for any failure to make any repairs or to perform any maintenance which
is an obligation of Landlord unless such failure shall persist for an
unreasonable time after written notice of the need of such repairs or
maintenance is given to Landlord by Tenant. Tenant waives the rights under any
law, statute or ordinance now or hereafter in effect to make repairs at
Landlord's expense, Tenant's rights being only as set forth in this Lease.

              18.4   Repairs under this Article 18 which are obligations of
Landlord are subject to allocation among Tenant and other tenants as Operating
Expenses.

              18.5   This Article 18 relates to repairs and maintenance arising
in ordinary course of operation of the Building, the Project and any related
facilities. In the event of fire, earthquake, flood, vandalism, war, or similar
cause of damage or destruction, this Article 18 shall not be applicable and the
provisions of Article 22 entitled "Damage or Destruction" shall apply and
control.

       19.    Liens.

              19.1   Subject to the immediately succeeding sentence, Tenant
shall keep the Demised Premises, the Building and the real property upon

                                       22
<PAGE>   26

which the Building is situated free from any liens arising out of work
performed, materials furnished or obligations incurred by Tenant. Tenant further
covenants and agrees that any mechanic's lien filed against the Demised Premises
or against the Building for work claimed to have been done for, or materials
claimed to have been furnished to Tenant, will (unless filed as a result of
Landlord's failure to fund the cost therefor when such cost is required by this
Lease to be borne by Landlord) be discharged by Tenant, by bond or otherwise,
within ten (10) days after the filing thereof, at the sole cost and expense of
Tenant.

              19.2   Should Tenant fail to discharge any lien of the nature
described in Section 19.1 when required thereby, Landlord may at Landlord's
election pay such claim or post a bond or otherwise provide security to
eliminate the lien as a claim against title and the cost thereof shall be due
from Tenant as Additional Rent, within thirty (30) days following Tenant's
receipt of written demand therefor by Landlord.

              19.3   In the event Tenant shall lease or finance the acquisition
of office equipment, furnishings, or other personal property of a removable
nature utilized by Tenant in the operation of Tenant's business, Tenant warrants
that any Uniform Commercial Code Financing Statement executed by Tenant will
upon its face or by exhibit thereto indicate that such Financing Statement is
applicable only to removable personal property of Tenant and to property
removable by Tenant pursuant to Section 17.8 hereof. In no event shall the
address of the Building be furnished on the statement without qualifying
language as to applicability of the lien only to such removable personal
property. Should any holder of a Financing Statement executed by Tenant record
or place of record a Financing Statement which appears to constitute a lien
against any interest of Landlord, Tenant shall within ten (10) days after filing
such Financing Statement cause (i) a copy of the Security Agreement or other
documents to which Financing Statement pertains to be furnished to Landlord to
facilitate Landlord's being in a position to show such lien is not applicable to
Landlord's interest and (ii) its lender to amend documents of record so as to
clarify that such lien is not applicable to any interest of Landlord in the
Building or Project. Landlord agrees to execute customary and reasonable
subordinations and/or waivers of any landlord or similar lien with respect to
any equipment, furnishings and/or other property financed by Tenant in
accordance with this Section 19.3.

       20.    Indemnification and Exculpation.

              20.1   Tenant agrees to indemnify, defend and save Landlord
harmless from and against any and all demands, claims, liabilities, losses,
costs, expenses, actions, causes of action, damages or judgments, and all
reasonable expenses incurred in investigating or resisting the same (including,
without limitation, reasonable attorneys' fees, charges and disbursements), for
injury or death to person or injury to property occurring within or about the
Demised Premises, arising directly or indirectly out of Tenant's, its
employees', agents' or guests' use or occupancy of the Demised Premises or a
breach or default by Tenant in the performance of any of its obligations
hereunder, unless caused solely by the willful act or gross negligence of the
Landlord.

                                       23
<PAGE>   27

              20.2   Notwithstanding any provision of Section 20.1 to the
contrary, Landlord shall not be liable to Tenant and Tenant assumes all risk of
damage to personal property or scientific research, including loss of records
kept within the Demised Premises. Tenant further waives any claim for injury to
Tenant's business or loss of income relating to any such damage or destruction
of personal property including any loss of records.

              20.3   Landlord shall not be liable for any damages arising from
any act, omission or neglect of any other tenant in the Building or Project or
of any other third party other than any agent, employee or contractor of
Landlord.

              20.4   Security devices and services, if any, while intended to
deter crime may not in given instances prevent theft or other criminal acts and
it is agreed that Landlord shall not be liable for injuries or losses caused by
criminal acts of third parties and the risk that any security device or service
may malfunction or otherwise be circumvented by a criminal is assumed by Tenant.
Tenant shall at Tenant's cost obtain insurance coverage to the extent Tenant
desires protection against such criminal acts.

       21.    Insurance - Waiver of Subrogation.

              21.1   Landlord, as part of Operating Expenses, shall carry
insurance upon the Building, in an amount equal to full replacement cost
(exclusive of the costs of excavation, foundations, and footings, and without
reference to depreciation taken by Landlord upon its books or tax returns) or
such lesser coverage as Landlord may elect provided such coverage is not less
than ninety-five percent (95%) of such full replacement cost, providing
protection against any peril generally included within the classification "Fire
and Extended Coverage" together with insurance against sprinkler damage (if
applicable), vandalism and malicious mischief. Landlord, subject to availability
thereof and, as part of Operating Expenses, shall further insure as Landlord
deems appropriate coverage against flood, environmental hazard and earthquake,
loss or failure of building equipment, rental loss during the period of repair
or rebuild, workmen's compensation insurance and fidelity bonds for employees
employed to perform services. Landlord's deductible may be as Landlord shall
determine, provided, however, that in no event shall such deductible exceed
$50,000.00. Landlord's insurance obligation includes any alterations, additions
or improvements made by Tenant to the Demised Premises and which, pursuant to
the terms of this Lease, become the property of Landlord.

              21.2   Landlord, as part of Operating Expenses, shall further
carry public liability insurance with combined single limit of not less than Two
Million Dollars ($2,000,000.00) for death or bodily injury, or property damage
with respect to the Project.

              21.3   Tenant at its own cost shall procure and continue in effect
from the Term Commencement Date or the date of occupancy, whichever first
occurs, and continuing throughout the term of this Lease (and occupancy by
Tenant, if any, after termination of this Lease) comprehensive public liability
insurance with limits of not less than Two Million Dollars ($2,000,000.00) per

                                       24
<PAGE>   28

occurrence for death or bodily injury and not less than One Million Dollars
($1,000,000.00) for property damage with respect to the Demised Property.

              21.4   The aforesaid insurance required of Tenant shall name
Landlord as an additional insured. Said insurance shall be with companies having
a rating of not less than policyholder rating of A and financial category rating
of at least Class XII in "Best's Insurance Guide." Tenant shall obtain for
Landlord from the insurance companies or cause the insurance companies to
furnish certificates of coverage to Landlord. No such policy shall be cancelable
or subject to reduction of coverage or other modification or cancellation except
after thirty (30) days' prior written notice to Landlord from the insurer. All
such policies shall be written as primary policies, not contributing with and
not in excess of the coverage which Landlord may carry. Tenant's policy may be a
"blanket policy" which specifically provides that the amount of insurance shall
not be prejudiced by other losses covered by the policy. Tenant shall, at least
twenty (20) days prior to the expiration of such policies, furnish Landlord with
renewals or binders. Tenant agrees that if Tenant does not take out and maintain
such insurance, Landlord may (but shall not be required to) procure said
insurance on Tenant's behalf and at its cost to be paid as Additional Rent.

              21.5   Tenant at Tenant's cost shall carry such insurance as
Tenant desires for Tenant's protection with respect to personal property of
Tenant or business interruption.

              21.6   In each instance where insurance is to name Landlord as
additional insured, Tenant shall upon written request of Landlord also designate
and furnish certificates so evidencing Landlord as additional insured to any of
the following persons of whose identity Landlord has given Tenant written
notice: (i) any lender of Landlord holding a security interest in the Building
or real property upon which the Building is situated, and/or (ii) the landlord
under any lease wherein Landlord is tenant of the real property whereupon the
Building is located if the interest of Landlord is or shall become that of a
tenant under a ground lease rather than that of a fee owner, and/or (iii) any
management company retained by Landlord to manage the Project.

              21.7   Landlord and Tenant each hereby waive any and all rights of
recovery against the other or against the officers, directors, employees,
agents, and representatives of the other, on account of loss or damage
occasioned to such waiving party or its property or the property of others under
its control to the extent that such loss or damage is insured against under any
fire and extended coverage insurance policy which either may have in force at
the time of such loss or damage or which such party was required to maintain
hereunder.

              21.8   Landlord may require insurance policy limits to be raised
to conform with requirements of Landlord's lender and/or to bring coverage
limits to levels then being required of new tenants within the Project.

              21.9   Landlord agrees that in addition to the insurance specified
above for Landlord and Tenant to maintain, Tenant may elect to maintain property
insurance with respect to the replacement cost of alterations, improvements
and/or additions made and paid for by Tenant and, in such event,

                                       25
<PAGE>   29

Landlord shall cooperate with Tenant in securing any endorsements to Landlord's
insurance policies confirming that such Tenant maintained insurance is
secondary, not primary, to the insurance maintained by Landlord for Landlord and
may be used for the construction of replacement alterations, improvements and/or
additions at locations other than the Premises.

       22.    Damage or Destruction.

              22.1   In the event of a partial destruction of the Building
(wherein the Demised Premises are located) by fire or other perils covered by
property and casualty insurance and if the damage thereto is such that the
Building may be repaired, reconstructed or restored within a period of one
hundred eighty (180) days from the date of the happening of such casualty and
Landlord will receive insurance proceeds sufficient to cover the cost of such
repairs (except for any permitted deductible amount provided by Landlord's
policy, which permitted deductible amount if paid by Landlord shall be an
Operating Expense), Landlord shall commence and proceed diligently with the work
of repair, reconstruction and restoration and this Lease shall continue in full
force and effect.

              22.2   In the event of any damage to or destruction of the
Building wherein the Demised Premises are located, other than as provided in
Section 22.1, Landlord may elect to repair, reconstruct and restore the
Building, in which case this Lease shall continue in full force and effect. If
Landlord elects not to repair then this Lease shall terminate as of date of
destruction.

              22.3   Landlord shall give written notice to Tenant of its
election not to repair, reconstruct or restore the Building or Project within
the sixty (60) day period following the date of damage or destruction.

              22.4   Upon any termination of this Lease under any of the
provisions of this Article, the parties shall be released thereby without
further obligation to the other from the date possession of the Demised Premises
is surrendered to the Landlord except for outstanding indemnity and other
obligations which survive termination of this Lease.

              22.5   In the event of fire or other casualty under this Section
22, the rental provided to be paid under this Lease shall be abated
proportionately based on the extent to which Tenant's use of the Demised
Premises is impaired during the period of such repair, reconstruction or
restoration, except to the extent Landlord provides Tenant with other space
during the period of repair, which in Tenant's reasonable opinion is suitable
for the temporary conduct of Tenant's business.

              22.6   Notwithstanding anything to the contrary contained in this
Article, should Landlord be delayed or prevented from completing the repair or
restoration of the damage to the Demised Premises after the occurrence of such
damage or destruction by reason of acts of God or war, governmental
restrictions, inability to procure the necessary labor or materials, strikes, or
other causes beyond the control of Landlord, the time for Landlord to commence
or complete repairs shall be extended, provided, at the election of Landlord,
Landlord shall be relieved of its obligation to make such repairs or
restorations and Tenant shall be

                                       26
<PAGE>   30

released from its obligation under this Lease as of the end of two hundred forty
(240) days from date of destruction, if repairs required to provide Tenant use
of the Demised Premises are not then substantially complete.

              22.7   If Landlord is obligated to or elects to repair or restore
as herein provided, Landlord shall be obligated to make repairs or restoration
to the entire Demised Premises, Building and Project, including all alterations,
additions and improvements made thereto by Tenant which, pursuant to the terms
of this Lease, become the property of Landlord and with respect to which
Landlord had received prior written notice and plans therefor (including, but
not limited to, the improvements made by Tenant pursuant to Exhibit "B.").

              22.8   Notwithstanding anything to the contrary contained in this
Article, Landlord shall not have any obligation whatsoever to repair,
reconstruct or restore the Demised Premises when the damage resulting from any
casualty covered under this Article occurs during the last twelve (12) months of
the term of this Lease or any extension hereof, or to the extent that insurance
proceeds are not available therefor.

              22.9   Notwithstanding anything to the contrary set forth
elsewhere in this Lease, in the event that Landlord shall not have substantially
completed the restoration required to be performed by Landlord within two
hundred ten (210) days following the date of the casualty, Tenant shall have the
right, at its election, to terminate this Lease by giving written notice to
Landlord prior to the date that is two hundred forty (240) days following the
date of the casualty. In the event that Tenant so elects, this Lease shall
terminate on the date that is two hundred seventy (270) days following the date
of the casualty unless the restoration has been substantially completed
(including the issuance of a use and occupancy permit) on or prior to such two
hundred seventieth (270th) day.

       23.    Eminent Domain.

              23.1   In the event the whole of the Demised Premises, or such
part thereof as shall substantially interfere with the Tenant's use and
occupancy thereof, shall be taken for any public or quasi-public purpose by any
lawful power or authority by exercise of the right of appropriation,
condemnation or eminent domain, or sold to prevent such taking, Tenant or
Landlord may terminate this Lease effective as of the date possession is
required to be surrendered to said authority.

              23.2   In the event of a partial taking of the Building, the
Project or of drives, walkways, and parking areas serving the Building for any
public or quasi-public purpose by any lawful power or authority by exercise of
right of appropriation, condemnation, or eminent domain, or sold to prevent such
taking then without regard as to whether any portion of the Demised Premises
occupied by Tenant was so taken, Landlord may elect to terminate this Lease as
of such taking if such taking is, in the reasonable opinion of Landlord, of a
material nature such as to make it uneconomical to continue use of the
unappropriated portion for purposes of office rentals or laboratory space.

                                       27
<PAGE>   31

              23.3   Tenant shall be entitled to any award which is specifically
awarded as compensation for the taking of Tenant's personal property, which was
installed at Tenant's expense and for costs of Tenant moving to a new location.
Except as before set forth, any award for such taking shall belong to Landlord.

              23.4   If upon any taking of the nature described in this Article
23 this Lease continues in effect, Landlord shall promptly proceed to restore
the Demised Premises, Building, and Project to substantially their same
condition prior to such partial taking to the extent such restoration is
feasible, as determined by Landlord in its sole discretion. The Rent shall be
abated proportionately based upon the extent to which Tenant's use of the
Demised Premises has decreased on the basis of the percentage of the rental
value of the Demised Premises after such taking and the rental value of the
Demised Promises prior to such taking.

              23.5   Notwithstanding any other terms of this Lease:

                     (i)    Landlord shall not terminate this Lease in
connection with any condemnation, taking or similar event relating to (A) the
widening and/or improvement of West Watkins Mill Road and/or (B) any of the land
generally on the side of the Project between the Project and Clopper Road,
without Tenant's written consent, provided, however, that such consent shall not
be required if such condemnation, taking or similar event results in the
physical taking of more than five percent (5%) of the Building (Landlord
agreeing, however, to cooperate with Tenant in eliminating any such taking of
the Building),

                     (ii)   if any of the Project entrances, drives, aisles
and/or parking along West Watkins Mill Road is reduced or eliminated in
connection with any widening and/or improvement of West Watkins Mill Road then
Landlord will, (A) to the extent of any condemnation proceeds received, at
Landlord's sole expense (and, to the extent of any condemnation proceeds
received, not as an operating expense and/or reserve) subject to receipt of
applicable governmental approvals, reconfigure and/or re-stripe the remaining
such areas as reasonably requested by Tenant so as to maximize parking and
traffic flow within the Project, (B) to the extent of any condemnation proceeds
received, at Landlord's sole expense (and, to the extent of any condemnation
proceeds received, not as an operating expense and/or reserve) subject to
receipt of applicable governmental approvals, construct an alternative point of
ingress and egress from the Project, as reasonably agreed to by Landlord and
Tenant, to provide access to "Metropolitan Court (extended)" and/or to the
existing "park" road immediately to the south of the Project, and (C) subject to
Tenant's reimbursement of any out-of-pocket expenses incurred by Landlord in
connection therewith, cooperate with Tenant, from time to time as requested by
Tenant in seeking any variances, special exceptions and/or the like thereafter
required by Tenant for purposes of maintaining, operating and/or making
alterations to the Building and/or the remaining parking areas, except that any
costs for such physical changes to such parking and/or related areas that
Landlord may be required to make as provided herein shall, to the extent of any
condemnation proceeds

                                       28
<PAGE>   32

received, be at Landlord's sole expense (and, to the extent of any such
condemnation proceeds received, not as an operating expense and/or reserve),and

                     (iii)  If Landlord elects to make any of the "proposed
parking lot connections" indicated on the site-plan attached as Exhibit "G-1" to
this Lease not as a result of any condemnation, taking or similar event relating
to (A) the widening and/or improvement of West Watkins Mill Road and/or (B) any
of the land generally on the side of the Project between the Project and Clopper
Road, or in the event that Tenant shall lose the ability to make left turns
directly from the parking area in the Project onto West Watkins Mill Road,
Landlord shall, subject to receipt of all required governmental approvals,
reconfigure and/or re-stripe the remaining areas shown on Exhibit "G-1" as
reasonably requested by Tenant, at Landlord's sole cost and expense (and not as
an operating expense and/or reserve), so as to maximize parking and traffic flow
within the Project and, to the extent any parking provided to Tenant as shown on
Exhibit "G-1" is lost as a result of making such connection, Landlord shall
promptly provide alternate parking in lots 18 or 19 as depicted on Exhibit
"G-2."

                     (iv)   Except as provided in Section 23.5(iii), no loss of
parking, and, subject to Landlord's other obligations set forth in this Section
23.5, no other interference with Tenant's use and enjoyment of the parking or
other portions of the land on which the Building is located as a result of any
condemnation, taking or similar event relating to (A) the widening and/or
improvement of West Watkins Mill Road, and/or (B) any of the land generally on
the side of the Project between the Project and Clopper Road, shall result in
any reduction or abatement of Rent or otherwise reduce Landlord's rights and/or
Tenant's duties and obligations hereunder or increase Tenant's rights and/or
Landlord's duties and obligations hereunder.

       24.    Tenant's Default and Landlord's Remedies.

              24.1   An event of default ("EVENT OF DEFAULT") shall exist under
this Lease if:

                     (a)    Tenant fails to pay any rent or any other charges
due and payable by Tenant under this Lease when due and such failure continues
for more than five (5) days following Tenant's receipt of written notice thereof
from Landlord (provided, however, that no such notice shall be required in the
event that Landlord has given two (2) such notices to Tenant within the
preceding 365 days);

                     (b)    Tenant's estate created by this Lease is taken by
execution or other legal process;

                     (c)    Tenant is adjudicated bankrupt or insolvent
according to law; or any assignment is made of the property of Tenant for the
benefit of creditors; or a receiver, guardian, conservator, trustee in voluntary

                                       29
<PAGE>   33

bankruptcy or other similar officer is appointed to take charge of all or any
substantial part of Tenant's property by a court of competent jurisdiction; or a
petition is filed for the reorganization of Tenant or any guarantor of Tenant's
obligations hereunder under any provisions of the Bankruptcy Act now or
hereafter enacted, and such proceeding is not dismissed within 60 days after it
is begun; or Tenant files a petition for reorganization, or for arrangements
under any provisions of the Bankruptcy Act now or hereafter enacted and
providing a plan for a debtor to settle, satisfy or extend the time for the
payment of debts; or

                     (d)    Tenant fails to perform or observe any of its other
obligations under this Lease within thirty (30) days after written notice from
Landlord to Tenant specifying the failure, provided, however, if such
obligation(s) cannot reasonably be performed or observed within said thirty (30)
day period, Tenant shall not be in default so long as Tenant has commenced
curative action and is continuously and diligently prosecuting such curative
action to completion and same is capable of completion within ninety (90) days.

              24.2   If an Event of Default shall exist hereunder, in addition
to any and all other rights or remedies of Landlord in this Lease or at law or
in equity, Landlord may do any or all of the following, without further notice
or demand to Tenant or any other person:

                     24.2.1 Termination - Landlord may declare the Lease Term
ended (even after it has relet the Demised Premises without terminating this
Lease) and may re-enter and retake possession of the Demised Premises and remove
all persons and property from the Demised Premises. If Landlord terminates this
Lease under this Section 24.2.1., Tenant shall pay to Landlord, in addition to
any other amounts Tenant is obligated to pay to Landlord under this Lease:

                     (a)    Any unpaid Rent, including interest at the Default
Rate, that is due when this Lease is terminated; plus

                     (b)    Any other amount necessary to compensate Landlord
for its damages connected with Tenant's failure to perform its obligations under
this Lease, such as costs to re-enter and retake possession of the Demised
Premises and remove all persons and property from the Demised Premises, to
alter, repair, and decorate the Demised Premises, and reasonable attorneys'
fees, advertising, and other reletting costs; plus

                     (c)    The net present value (discounted at the then Wall
Street Journal "prime" or similar rate) of the difference between (x) the Basic
Annual Rent which would thereafter had remained to be paid under this Lease had
such termination not occurred and (y) the fair rental value of the Demised
Premises for the period following such termination and through the date upon
which the Term was otherwise, in the absence of such termination, most recently
scheduled to expire.

              Nothing in this Lease shall limit Landlord's right to recover as
damages in any bankruptcy, insolvency, receivership, reorganization or
arrangement proceeding the maximum allowed by the law then governing such

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proceedings, even if that amount is greater than the amount Landlord may recover
under this Lease.

                     24.2.2 Rent Suit without Re-entry/Termination - Landlord
may sue to collect Rent (as it accrues under this Lease) and damages (including
reasonable attorneys' fees and the cost to renovate the Demised Premises)
without retaking possession of the Demised Premises or terminating this Lease.

                     24.2.3 Re-entry without Termination - Landlord may reenter
and retake possession of the Demised Premises from Tenant by summary proceedings
or otherwise and remove Tenant and any other occupants from the Demised Premises
in such a manner as Landlord deems advisable with legal process. Landlord also
may remove from the Demised Premises all or any of the personal property in the
Demised Premises and may place it in storage at a public warehouse at the
expense and risk of the owner or owners thereof. "Re-enter" or "re-entry" as
used in this Lease are not restricted to their technical meaning but are used in
their broadest sense. Neither Landlord's commencement and prosecution of any
action in unlawful detainer, ejectment or otherwise, nor Landlord's execution of
any judgment or decree obtained in any action to recover possession of the
Demised Premises, nor any action to recover possession of the Demised Premises,
nor any other re-entry and removal, shall terminate this Lease (even if the
re-entry is done under summary proceedings or otherwise) or discharge Tenant
from any obligation under this Lease. In any of such events, Tenant shall
continue to be liable to pay Rent and to perform all of its other obligations
under this Lease, and Tenant shall pay to Landlord all monthly deficits in Rent,
after any such re-entry, in monthly installments as the amounts of such deficits
from time to time are ascertained. If Landlord retakes possession, Landlord may
relet parts or all of the Demised Premises for terms greater or less than or
equal to the unexpired part of the Lease Term on such terms and conditions and
for such rent as the Landlord deems proper. Landlord shall apply the rent from
such reletting (if and when received): first, to pay any indebtedness other than
Rent due under this Lease from Tenant to Landlord; second, to pay any cost to
relet (including costs to alter, repair or decorate the Demised Premises as
Landlord deems advisable); third, to pay Rent due and unpaid under this Lease;
and the residue, if any, to be held by Landlord and applied to pay future Rent
as it becomes due. If the Rent received from reletting, after being applied as
required in this Section 24.2.3, is not enough to pay the Rent under this Lease,
then Tenant shall have no right to any excess. Tenant also shall pay to
Landlord, as soon as ascertained, any costs to relet, alter, and repair not
covered by the Rent received from reletting, including brokerage commissions and
reasonable attorneys' fees. Nothing in this Lease shall obligate Landlord to
relet all or any part of the Demised Premises.

                     24.2.4 Landlord's Right to Cure Tenant's Default

           If an Event of Default shall exist hereunder, Landlord may perform
any action required of Tenant under the Lease, and Tenant shall pay Landlord,
within thirty (30) days following Tenant's receipt of written demand by Landlord
all of Landlord's expenses (including, without limitation, reasonable attorneys'
fees) to perform the action.

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<PAGE>   35

                     24.2.5 Landlord's and Tenant's Costs

           In the event that either party shall default hereunder and such
default shall result in the commencement of legal or other proceedings in
respect thereof, then the prevailing party in any such proceeding shall be
entitled to such reasonable attorneys' fees and expenses as the Court in such
proceeding may award it pursuant hereto.

                     24.2.6 Counterclaim

           If Landlord files suit for non-payment of Rent or other amounts due
under this Lease, Tenant will not interpose any non-compulsory counterclaim
except in a separate action brought by Tenant. The covenants to pay Rent and
other amounts hereunder are independent covenants, and Tenant shall have no
right to hold back, offset or fail to pay any such amounts for default by
Landlord or any other reason whatsoever.

                     24.2.7 Waiver of Rights of Redemption

           To the extent permitted by law, Tenant waives any and all rights of
redemption granted by or under any present or future laws if Tenant is evicted
or dispossessed for any cause, or if Landlord obtains possession of the Demised
Premises due to Tenant's default hereunder or otherwise.

                     24.2.8 Waiver of Trial by Jury

           Landlord and Tenant waive all rights to a trial by jury in any
action, counterclaim, or proceeding based upon, or related to, the subject
matter of this Lease. This waiver applies to all claims against all parties to
such actions and proceedings, including parties who are not parties to this
Lease. This waiver is knowingly, intentionally, and voluntarily made by each
party and each party acknowledges that neither the other party nor any person
acting on behalf of the other party, has made any representations to induce this
waiver of trial by jury or in any way to modify or nullify its effect. Each
party further acknowledges that it has been represented (or has had the
opportunity to be represented) in the signing of this Lease and in the making of
this waiver by independent legal counsel, selected of its own freewill and that
it has had the opportunity to discuss this waiver with counsel. Each party
further acknowledges that it has read and understands the meaning and
ramifications of this waiver provision.

              24.3   Landlord shall have the right to terminate this Lease,
without penalty or charge to Landlord or Tenant, in the event that the Demised
Premises remains vacant for more than one hundred twenty (120) days (other than
if such vacancy is in connection with an alteration, renovation, addition,
repair or improvement thereto).

       25.    Assignment or Subletting.

              25.1   Except as hereinafter provided, Tenant shall not, either
voluntarily or by operation of law, directly or indirectly, sell, hypothecate,
assign, pledge, encumber or otherwise transfer this Lease, or sublet the Demised

                                       32
<PAGE>   36

Premises or any part hereof, or permit or suffer the Demised Premises or any
part thereof to be used or occupied as work space, storage space, mailing
privileges, concession or otherwise by anyone other than Tenant or Tenant's
employees, without the prior written consent of Landlord in each instance, which
consent shall not be unreasonably withheld, conditioned or delayed. Landlord
shall be deemed to have acted reasonably in withholding its consent if, inter
alia, the proposed use of the Demised Premises by the proposed assignee or
subtenant is substantially more hazardous and burdensome than the present use by
Tenant and/or any affiliate thereof of 708 Quince Orchard Road or if the net
worth of the proposed assignee or subtenant (in the case of a proposed sublease
covering more than fifty percent (50%) of the Demised Premises) is less than
Three Million Dollars ($3,000,000).

              25.2   If Tenant is a corporation, the shares of which are not
traded upon a stock exchange or in the over-the-counter market, a transfer or
series of transfers whereby fifty (50%) or more of the issued and outstanding
shares of such corporation are or the voting control is transferred (but
excepting transfers upon deaths of individual shareholders) from a person or
persons or entity or entities (or affiliates thereof) which were owners or
warrant holders thereof (or affiliates of such owners or warrant holders) at the
time of execution of this Lease to persons or entities who were not owners of
shares or holders of warrants of the corporation (or affiliates of such owners
or warrant holders) at the time of execution of this Lease (or to any persons or
entities who are not then affiliates of any such original owners, holders or
other affiliates) shall be deemed an assignment of this Lease requiring the
consent of Landlord as provided in Section 25.1 above. The foregoing shall not
apply to transfers among stockholders existing at the time of such transfer, nor
to transfers from any such holders to affiliates, family members, spouses or
employees thereof, nor to any transfer pursuant to which all or a substantial
amount of the transferred shares are intended to be transferred or thereafter
traded on a public exchange (including in the so-called over- the-counter
market).

              25.3   If Tenant desires to assign this Lease to any entity into
which Tenant is merged, with which Tenant is consolidated, or which acquires all
or substantially all of the assets of Tenant, provided that the assignee first
executes, acknowledge and delivers to Landlord an agreement whereby the assignee
agrees to be bound by all of the covenants and agreements in this Lease and that
the assignee shall have a net worth (determined in accordance with generally
accepted accounting principles consistently applied) immediately after such
assignment which is at least equal to Three Million Dollars ($3,000,000) (as so
determined), then Landlord, upon receipt of proof of foregoing, will consent to
the assignment. The provisions of Sections 25.4, 25.5, 25.6 and 25.10 shall not
be applicable to assignments of this Lease pursuant to this Section 25.3.

              25.4   In the event Tenant desires to assign, sublease,
hypothecate or otherwise transfer this Lease or sublet the Demised Premises,
then at least fifteen (15) business days, but not more than ninety (90) days,
prior to the date when Tenant desires the assignment or sublease to be effective
(the "ASSIGNMENT DATE"), Tenant shall give Landlord a notice (the "ASSIGNMENT
NOTICE") containing information (including references) concerning the character
of the proposed assignee or sublessee, the Assignment Date, any ownership or

                                       33
<PAGE>   37

commercial relationship between Tenant and the proposed assignee or sublessee,
and the consideration and all other material terms and conditions of the
proposed assignment or sublease, all in such detail as Landlord shall reasonably
require. Landlord may, by giving written notice to Tenant within 15 business
days after receipt of the Assignment Notice: (i) grant or refuse such consent in
its reasonable discretion as provided in Sections 25.1 and 25.5 (provided that
Landlord shall further have the right to review and approve or disapprove the
proposed form of sublease or assignment prior to the effective date of any such
subletting or assignment), or (ii) terminate this Lease in accordance with
Section 25.10 with respect to the space described in the Assignment Notice as of
the Assignment Date. Tenant shall also reimburse Landlord for any, reasonable
attorneys fees and other costs or overhead expenses incurred by Landlord (not to
exceed $2,000.00 for any one request) in reviewing Tenant's request for such
assignment.

              25.5   Landlord in making its determination as to whether consent
should be given to a proposed assignment or sublease, may give consideration to
the financial strength of the proposed subtenant (in the case of a proposed
sublease covering more than fifty percent (50%) of the Demised Premises) or
assignee (notwithstanding Tenant remaining liable for Tenant's performance), any
change in use which such subtenant or assignee proposes to make in use of
Demised Premises and any desire of Landlord to exercise any rights under Section
25.10 to terminate this Lease. In no event shall Landlord be deemed to be
unreasonable for declining to consent to a transfer to a subtenant or assignee
of poor reputation, lacking financial qualifications (in the case of a proposed
sublease, only if the proposed sublease covers more than fifty percent (50%) of
the Demised Premises), or seeking change in use, subject to Section 10.1 hereby,
which would reduce the number of square feet of the Demised Premises used for
laboratories.

              25.6   As conditions precedent to Landlord considering a request
by Tenant to Tenant's transfer of rights or sharing of the Demised Premises,
Landlord may require any or all of the following:

                     (a)    Tenant shall remain fully liable under this Lease
during the unexpired Term;

                     (b)    Tenant shall provide Landlord with evidence
concerning the relevant business experience, financial responsibility and status
of the third party concerned;

                     (c)    Tenant shall reimburse Landlord for Landlord's
reasonable costs and expenses, including, without limitation, reasonable
attorneys' fees, charges and disbursements (not to exceed $2,000.00 for any one
request) incurred in connection with the review, processing, documentation and
approval or disapproval of such request;

                     (d)    If Tenant's transfer of rights or sharing of the
Demised Premises results in the receipt by, on behalf or on account of Tenant of
any consideration of any kind whatsoever (including, but not by way of
limitation, a premium rental for a sublease or lump sum payment for an
assignment) in excess of the rental and other charges due Landlord under this
Lease, Tenant shall pay

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<PAGE>   38

fifty percent (50%) of said excess to Landlord (after deduction from such excess
all costs and expenses incurred by Tenant in connection with any assignment or
sublease, including, without limitation, alterations, concessions, commissions,
advertising and legal fees). If said consideration consists of cash paid to
Tenant said payment to Landlord shall be made upon receipt by Tenant of said
cash payment;

                     (e)    Written agreement from any third party concerned
that in the event Landlord gives such third party notice that an Event of
Default has occurred under this Lease, such third party shall thereafter make
all payments otherwise due Tenant directly to Landlord for so long as such Event
of Default remains uncured, which payments will be received by Landlord without
any liability on Landlord except to credit such payment against those due under
the Lease, and any such third party shall agree to attorn to Landlord or its
successors and assigns should this Lease be terminated for any reason; provided,
however that in no event shall Landlord or its successors or assigns be
obligated to accept such attornment;

                     (f)    Any such transfer and consent shall be effected on
forms reasonably satisfactory to Landlord and Tenant as to form and substance;

                     (g)    No Event of Default shall exist hereunder in any
respect;

                     (h)    Landlord shall not be bound by any provision of any
agreement pertaining to Tenant's transfer of rights or sharing of the Demised
Premises;

                     (i)    Tenant shall deliver to Landlord one executed copy
of any and all written instruments evidencing or relating to Tenant's transfer
of rights or sharing of the Demised Premises; and

                     (j)    A list of Hazardous Material (as defined in Section
40.6 below), certified by the proposed sublessee to be true and correct, which
the proposed sublessee intends to use or store in the Demised Premises.
Additionally, Tenant shall deliver to Landlord, on or before the date any
proposed sublessee takes occupancy of the Demised Premises, all of the items
relating to Hazardous Materials of such proposed sublessee as described in
Section 40.1.1 below.

              25.7   Any sale, assignment, hypothecation or transfer of this
Lease or subletting of the Demised Premises that is not in compliance with the
provisions of this Article 25 shall constitute an Event of Default if any such
noncomplying sale, assignment, hypothecation or transfer is not rescinded within
ten (10) days after Tenant's receipt of notice from Landlord.

              25.8   The consent by Landlord to an assignment or subletting
shall not relieve Tenant or any assignees of this Lease or sublessee of the
Demised Premises from obtaining the consent of Landlord to any further

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<PAGE>   39

assignment or subletting nor shall it release Tenant or any assignee or
sublessee of Tenant from full and primary liability under the Lease.

              25.9   Notwithstanding any subletting or assignment, Tenant shall
remain fully and primarily liable for the payment of all Rent and other sums
due, or to become due hereunder, and for the full performance of all other
terms, conditions, and covenants to be kept and performed by Tenant. The
acceptance of Rent or any other sum due hereunder, or the acceptance of
performance of any other term, covenant, or condition thereof, from any other
person or entity shall not be deemed to be a waiver of any of the provisions of
this Lease or a consent to any subletting, assignment or other transfer of the
Demised Premises.

              25.10  If Tenant delivers to Landlord an Assignment Notice
indicating a desire to assign this Lease to a transferee pursuant to a
transaction requiring Landlord's consent hereunder, then Landlord shall have the
option, exercisable by giving notice to Tenant at any time within fifteen (15)
business days after Landlord's receipt of the Assignment Notice, to terminate
this Lease as of the date specified in the Assignment Notice as the Assignment
Date. If Landlord exercises such option, then Tenant shall have the right to
withdraw such Assignment Notice by delivery to Landlord written notice of such
election within five (5) days after Landlord's delivery of notice electing to
exercise such option to terminate. In the event Tenant withdraws the Assignment
Notice as hereinabove provided, this Lease shall continue in full force and
effect as if such Assignment Notice had never been given. In the event Tenant
does not so withdraw the Assignment Notice as hereinabove provided, this Lease,
and the term and estate herein granted, shall terminate as of the Assignment
Date. No failure of Landlord to exercise any such option to terminate this Lease
shall be deemed to be Landlord's consent to the proposed assignment, sublease or
other transfer.

              25.11  None of the terms of this Section 25 shall apply to any
sublease between Tenant and any affiliate or subsidiary of Tenant nor to any
arrangements (whether designated subleases, licenses or otherwise), other than
assignments, between Tenant and any person with whom Tenant or any affiliate or
subsidiary of Tenant has any scientific collaboration, joint venture, licensing
arrangement or other similar relationship.

              25.12  Any consent, approval or other action required of Landlord
under this Article 25 and not received by Tenant within fifteen (15) business
days following Tenant's written request therefor shall be deemed granted and/or
waived as the case may be in accordance with the terms of the Assignment Notice.

       26.    Intentionally omitted.

       27.    Bankruptcy.

              27.1   In the event a debtor, trustee, or debtor in possession
under the Bankruptcy Code, or other person with similar rights, duties and
powers under any other law, proposes to cure any default under this Lease or to
assume or assign this Lease, and is obliged to provide adequate assurance to
Landlord

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<PAGE>   40

that (i) a default will be cured, (ii) Landlord will be compensated for its
damages arising from any breach of this Lease, or (iii) future performance under
this Lease will occur, then adequate assurance shall include any or all of the
following, as designated by Landlord:

                     (a)    Those acts specified in the Bankruptcy Code or other
law as included within the meaning of adequate assurance, even if this Lease
does not concern a shopping center or other facility described in such laws;

                     (b)    A prompt cash payment to compensate Landlord for any
monetary defaults or actual damages arising directly from a breach of this
Lease;

                     (c)    A cash deposit in an amount at least equal to the
Security Deposit as referenced in 2.1.8 originally required at time of execution
of this Lease.

                     (d)    The assumption or assignment of all of Tenant's
interest and obligations under this Lease.

       28.    Definition of Landlord.

              28.1   The term "LANDLORD" as used in this Lease, so far as
covenants or obligations on the part of Landlord are concerned, shall be limited
to mean and include only Landlord or the successor-in-interest of Landlord under
this Lease at the time in question. In the event of any transfer, assignment or
the conveyance of Landlord's title or leasehold, the Landlord herein named (and
in case of any subsequent transfers or conveyances, the then grantor) shall be
automatically freed and relieved, from and after the date of such transfer,
assignment or conveyance, of all liability for the performance of any covenants
or obligations contained in this Lease thereafter to be performed by Landlord
and, without further agreement, the transferee of such title or leasehold shall
be deemed to have assumed and agreed to observe and perform any and all
obligations of Landlord hereunder, during its ownership or ground lease of the
Demised Premises. Landlord may transfer its interest in the Demised Premises or
this Lease without the consent of Tenant and such transfer or subsequent
transfer shall not be deemed a violation on the part of Landlord or the then
grantor of any of the terms or conditions of this Lease. The foregoing
notwithstanding, Landlord shall not be released from or in respect of any
liability or obligation accruing prior to such transfer nor shall the terms of
Section 31 apply thereto.

       29.    Estoppel Certificate.

              29.1   Tenant shall within ten (10) days of written notice from
Landlord, execute, acknowledge and deliver a statement in writing substantially
in the form attached to this Lease as Exhibit "E" with the blanks filled in, and
on any other form reasonably requested by a proposed lender or purchaser, (i)
certifying that this Lease is unmodified and in full force and effect (or, if
modified, stating the nature of such modification and certifying that this Lease
as so modified is in full force and effect) and the dates to which the rental
and other charges are paid in advance, if any, (ii) acknowledging that there are
not, to

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<PAGE>   41

Tenant's knowledge, any uncured defaults on the part of Landlord hereunder, or
specifying such defaults if any are claimed and (iii) setting forth such further
brief factual information with respect to this Lease or the Demised Premises as
may be reasonably requested thereon. Any such statement may be relied upon by
any prospective purchaser or encumbrancer of all or any portion of the real
property of which the Demised Premises are a part. Tenant's failure to deliver
such statement within such time shall, at the option of Landlord, constitute a
default under this Lease, and, in any event, shall be conclusive upon Tenant
that the Lease is in full force and effect and without modification except as
may be represented by Landlord in any certificate prepared by Landlord and
delivered to Tenant for execution. Landlord shall similarly deliver to Tenant
upon request, a similar estoppel certificate or statement setting forth such
similar or other brief factual information as Tenant may reasonably request. Any
such statement requested by Tenant may be relied upon by any assignee,
sublessee, purchaser, lender, investor, advisor or other similar person with
respect to Tenant. Landlord's failure to execute and return any such statement
requested by Tenant within ten (10) days following Landlord's receipt thereof
from Tenant shall constitute conclusive evidence of the facts recited therein.

       30.    Intentionally omitted.

       31.    Limitation of Landlord's Liability.

              31.1   If Landlord is in default of this Lease, and as a
consequence, Tenant recovers a money judgment against Landlord, the judgment
shall be satisfied only out of the proceeds of sale received on execution of the
judgment and levy against the right, title and interest of Landlord in the
Building and Project of which the Demised Premises are a part, and/or out of
rent or other income from such real property receivable by Landlord, and/or out
of the consideration received by Landlord from the sale, financing, refinancing,
or other disposition of all or any part of Landlord's right, title, and interest
in the Building and Project of which the Demised Premises are a part, and/or out
of any amounts distributed to or otherwise received by Landlord from and after
the date that Tenant has first made a written demand upon Landlord for such
amounts.

              31.2   Landlord shall not be personally liable for any deficiency.
If Landlord is a partnership or joint venture, the partners of such partnership
shall not be personally liable and no partner of Landlord shall be sued or named
as a party in any suit or action or service of process be made against any
partner of Landlord except as may be necessary to secure jurisdiction of the
partnership or joint venture. If Landlord is a corporation, the shareholders,
directors, officers, employees, and/or agents of such corporation shall not be
personally liable and no shareholder, director, officer, employee or agent of
Landlord shall be sued or named as a party in any suit or action or service of
process made against any shareholder, director, officer, employee or agent of
Landlord. If Landlord is a limited liability company, the members, managers,
employees and/or agents of such limited liability company shall not be
personally liable and no member, manager, employee or agent of Landlord shall be
sued or named as a party in any suit or action or service of process made
against any member, manager, employee or agent except as may be necessary to
secure jurisdiction of such limited liability company. No partner, shareholder,
member,

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<PAGE>   42

director, employee, or agent of Landlord shall be required to answer or
otherwise plead to any service of process and no judgment will be taken or writ
of execution levied against any partner, shareholder, director, employee or
agent of Landlord. Nothing contained in this Section 31.2 shall restrict Tenant
from commencing a legal action against any person described in this Section 31.2
seeking to obtain a return of any amounts distributed to or otherwise received
by such person from and after the date that Tenant first made a written demand
upon Landlord for such amounts. The immediately preceding sentence shall not be
applicable to shareholders or other owners (in such capacity) so long as the
stock of Landlord is publicly traded.

              31.3   Each of the covenants and agreements of this Article 31
shall be applicable to any covenant or agreement either expressly contained in
this Lease or imposed by statute or by common law and shall survive the
termination of this Lease.

       32.    Project Control by Landlord.

              32.1   Landlord reserves full control over the Building and
Project to the extent not inconsistent with Tenant's enjoyment of the Demised
Premises in accordance with the terms hereof. Subject to the foregoing, this
reservation includes but is not limited to right of Landlord to convert the
Building and or other buildings within the Project to condominium units, the
right to grant easements and licenses to others and the right to maintain or
establish ownership of Building separate from fee title to land.

              32.2   Tenant shall, should Landlord so request, promptly join
with Landlord in execution of such documents as may be reasonably appropriate to
assist Landlord to implement any such action provided Tenant need not execute
any document which is of nature wherein liability is created in Tenant or if by
reason of the terms of such document, Tenant will be deprived of the quiet
enjoyment and use of the Demised Premises as granted by this Lease.

              32.3   Landlord may, at any and all reasonable times during
business hours and upon reasonable advance notice (provided that no time
restrictions shall apply or advance notice need be given if an emergency
necessitates an immediate entry), enter the Demised Premises to (a) inspect the
same and to determine whether Tenant is in compliance with its obligations
hereunder, (b) supply any service Landlord is required to provide hereunder, (c)
show the Demised Premises to prospective mortgagees, investors (but not
competitors of Tenant), purchasers or (only during the final 400 days of the
Term) tenants, (d) post notices of nonresponsibility, (e) access the telephone
equipment, electrical substation and fire risers, and (f) alter, improve or
repair any portion of the Building other than the Demised Premises, but for
which access to the Demised Premises is necessary. In connection with any such
alteration, improvement or repair, Landlord may erect in the Demised Premises or
elsewhere in the Project scaffolding and other structures reasonably required
for the work to be performed. In no event shall Tenant's Rent abate as a result
of any such entry or work; provided, however, that all such work shall be done
in such a manner as to cause the least interference to Tenant as reasonably
possible. If an emergency necessitates immediate access to the Demised Premises,
Landlord may use

                                       39
<PAGE>   43

whatever force is necessary to enter the Demised Premises and any such entry to
the Demised Premises shall not constitute a forcible or unlawful entry to the
Demised Premises, a detainer of the Demised Premises, or an eviction of Tenant
from the Demised Premises, or any portion thereof. Other than in the case of an
emergency, Landlord's entry into the Demised Premises shall be subject to such
reasonable security restrictions as Tenant may reasonably impose and Landlord
shall not enter any of Tenant's "secure" areas of which Landlord has notice
unless accompanied by a representative of Tenant; Tenant hereby agreeing to have
a representative available to Landlord for such purpose at all times during
business hours.

       33.    Quiet Enjoyment.

           So long as Tenant is not in default, Landlord covenants that Landlord
or anyone acting through or under Landlord will not disturb Tenant's occupancy
of the Demised Premises except as permitted by the provisions of this Lease.

       34.    Intentionally Omitted.

       35.    Subordination and Attornment.

              35.1   Subject to the other terms hereof, this Lease shall be
subject and subordinate to the lien of any mortgage, deed of trust, or lease in
which Landlord is tenant now or hereafter in force against the Project and
Building and to all advances made or hereafter to be made upon the security
thereof.

              35.2   Notwithstanding the foregoing, Tenant shall execute and
deliver upon demand such further reasonable instrument or instruments,
reasonably acceptable to Tenant, evidencing such subordination of this Lease to
the lien of any such mortgage or mortgages or deeds of trust or lease in which
Landlord is tenant as may be reasonably required by Landlord. However, if any
such mortgagee, beneficiary or landlord under lease wherein Landlord is tenant
so elects, this Lease shall be deemed prior in lien to any such lease, mortgage,
or deed of trust upon or including the Demised Premises regardless of date and
Tenant will execute a statement in writing to such effect at Landlord's request.
Any such statement must be reasonably acceptable to Tenant.

              35.3   In the event any proceedings are brought for foreclosure,
or in the event of the exercise of the power of sale under any mortgage or deed
of trust made by the Landlord covering the Demised Premises, Tenant shall at the
election of the purchaser at such foreclosure or sale attorn to the purchaser
upon any such foreclosure or sale and recognize such purchaser as the Landlord
under this Lease.

              35.4   The foregoing subordination is expressly contingent upon
Landlord and each party benefitting therefrom (e.g., the lender or ground
lessor) executing a non-disturbance agreement with Tenant, in such form as the
parties thereto may reasonably agree but providing Tenant and the lender or
ground lessor, as the case may be, substantially and in all material respects
with the rights and benefits set forth in the form attached hereto as Exhibit
"F".

                                       40
<PAGE>   44

       36.    Surrender.

              36.1   No surrender of possession of any part of the Demised
Premises shall release Tenant from any of its obligations hereunder unless
accepted by Landlord.

              36.2   The voluntary or other surrender of this Lease by Tenant
shall not work a merger, unless Landlord consents and shall, at the option of
Landlord, operate as an assignment to it of any or all subleases or
subtenancies.

              36.3   The voluntary or other surrender of any ground or
underlying lease that now exists or may hereafter be executed affecting the
Building or Project, or a mutual cancellation, thereof, or of Landlord's
interest therein, shall not work a merger and shall, at the option of the
successor of Landlord's interest in the Building or Project, operate as an
assignment of this Lease.

       37.    Waiver and Modification.

              37.1   No provision of this Lease may be modified, amended or
added to except by an agreement in writing. The waiver by Landlord of any breach
of any term, covenant or condition herein contained shall not be deemed to be a
waiver of any subsequent breach of the same or any other term, covenant or
condition herein contained.

       38.    Intentionally omitted.

       39.    Intentionally omitted.

       40.    Hazardous Materials.

              40.1   Tenant shall not cause or permit any Hazardous Material (as
hereinafter defined) to be brought upon, kept or used in or about the Demised
Premises or the Project in violation of applicable law by Tenant, its agents,
employees, contractors or invitees. If (i) Tenant breaches the obligation stated
in the preceding sentence, or (ii) the presence of Hazardous Materials (except
Hazardous Materials which Tenant can prove (A) migrated onto the Project from
adjacent property or (B) were introduced to the Project as the result of an
accident or spill occurring in connection with any railroad traffic on the
railroad tracks running along the northern end of the Project) results in
contamination of the Demised Premises, the Building, the Project or any adjacent
Property, or (iii) contamination of the Demised Premises, the Building, the
Project or any adjacent Property by Hazardous Material otherwise occurs during
the term of this Lease or any extension or renewal hereof or holding over
hereunder as a result of the actions or omissions of Tenant or its agents, then
Tenant shall indemnify, defend and hold Landlord, its agents and contractors
harmless from any and all claims, judgments, damages, penalties, fines, costs,
liabilities, or losses (including, without limitation, diminution in value of
the Demised Premises or any portion of the Project, damages for the loss or
restriction on use of rentable or usable space or of any amenity of the Demised
Premises or Project, damages arising from any

                                       41
<PAGE>   45

adverse impact on marketing of space in the Demised Premises or the Project, and
sums paid in settlement of claims, attorneys' fees, consultant fees and expert
fees) which arise during or after the Lease term as a result of such
contamination. This indemnification of Landlord by Tenant includes, without
limitation, costs incurred in connection with any investigation of site
conditions or any cleanup, remedial, removal, or restoration work required by
any federal, state or local governmental agency or political subdivision because
of any such Hazardous Material present in the air, soil or ground water above on
or under the Demised Premises. Without limiting the foregoing, if the presence
of any Hazardous Material on the Demised Premises, the Building, the Project or
any adjacent Property, caused or permitted by Tenant or its agents results in
any contamination of the Demised Premises, the Building, the Project or any
adjacent Property, Tenant shall promptly take all actions at its sole expense as
are necessary to return the Demised Premises, the Building, the Project or any
adjacent Property, to the condition existing prior to the time of such
contamination, provided that Landlord's approval of such action shall first be
obtained, which approval shall not unreasonably be withheld so long as such
actions would not potentially have any material adverse long-term or short-term
effect on the Demised Premises, the Building or the Project.

                     40.1.1 Landlord acknowledges that it is not the intent of
this Article 41 to prohibit Tenant from operating its business as described in
Section 2.1.9 above. Tenant may operate its business according to the custom of
the industry so long as the use or presence of Hazardous Material is strictly
and properly monitored according to all applicable governmental requirements. As
a material inducement to Landlord to allow Tenant to use Hazardous Material in
connection with its business, Tenant agrees to deliver to Landlord prior to the
Rent Commencement Date a list identifying each type of Hazardous Material to be
present on the Demised Premises and setting forth any and all governmental
approvals or permits required in connection with the presence of such Hazardous
Material on the Demised Premises ("HAZARDOUS MATERIAL LIST"). Tenant shall
deliver to Landlord an updated Hazardous Material List at least once a year and
shall also deliver an updated list before any new Hazardous Material is brought
onto the Demised Premises. Tenant shall deliver to Landlord true and correct
copies of the following documents (if any) (hereinafter referred to as the
"DOCUMENTS") relating to the handling, storage, disposal and emission of
Hazardous Material prior to the Rent Commencement Date, or if unavailable at
that time, concurrent with the receipt from or submission to a governmental
agency: permits; approvals; reports and correspondence; storage and management
plans; notice of violations of any laws; plans relating to the installation of
any such storage tanks to be installed in or under the Project by Tenant
(provided, said installation of tanks shall only be permitted after Landlord has
given Tenant its written consent to do so, which consent may be withheld in
Landlord's sole and absolute discretion); and all closure plans or any other
documents required by any and all federal, state and local governmental agencies
and authorities for any storage tanks installed in, on or under the Project for
the closure of any such tanks. Tenant is not required, however, to provide
Landlord with any portion(s) of the Documents containing information of a
proprietary nature which, in and of themselves, do not contain a reference to
any Hazardous Material or hazardous activities. It is not the intent of this
Section to provide Landlord with information which could be detrimental to
Tenant's business should such information become possessed by Tenant's
competitors. At the written request of Landlord, Tenant agrees that it shall
enter

                                       42
<PAGE>   46

into a written agreement with other tenants at the Building concerning the
equitable allocation of fire control areas within the Building for the storage
of Hazardous Materials. In the event that Tenant's use of Hazardous Materials is
such that it utilizes fire control areas in the Building in excess of Tenant's
Pro Rata Share of the Building as set forth in Section 2.1.6 above, Tenant
agrees that it shall, at its own expense, and upon the written request of
Landlord, establish and maintain a separate area of the Demised Premises for the
use and storage of Hazardous Materials, or take such other action so that its
share of the fire control areas of the Building is not greater than Tenant's Pro
Rata Share of the Building.

              40.2   Notwithstanding the provisions of Section 40.1 above, if
(i) the proposed assignee or sublessee of Tenant has been required by any prior
landlord, lender or governmental authority to take remedial action in connection
with Hazardous Material contaminating a property if the contamination resulted
from such party's action or use of the property in question, or (ii) the
proposed assignee or sublessee is subject to an enforcement order issued by any
governmental authority in connection with the use, disposal or storage of a
Hazardous Material, it shall not be unreasonable for Landlord to withhold its
consent to the proposed assignment or subletting.

              40.3   At any time, and from time to time, prior to the expiration
of the Term (but not more often than three (3) times during the Term, unless
Landlord, in its reasonable judgment, has a demonstrable basis upon which to
believe that contamination has occurred), Landlord shall have the right to
conduct appropriate tests of the Demised Premises, Building and Project to
demonstrate that contamination has occurred as a result of Tenant's use of the
Demised Premises. Tenant shall be solely responsible for and shall defend,
indemnify and hold the Landlord, its agents and contractors harmless from and
against any and all claims, costs and liabilities including actual attorneys'
fees, charges and disbursements, arising out of or in connection with any
removal, clean up, restoration and materials required hereunder to return the
Demised Premises and any other property of whatever nature to their condition
existing prior to the time of any such contamination for which Tenant is
responsible pursuant to this Section 40. Notwithstanding the provisions of the
last sentence of Section 7.1(c), Tenant shall pay for the cost of the tests of
the Demised Premises.

              40.4   If underground or other storage tanks storing Hazardous
Materials are located on the Demised Premises by Tenant or are hereafter placed
on the Demised Premises by or for Tenant, Tenant shall monitor the storage
tanks, maintain appropriate records, implement reporting procedures, properly
close any underground storage tanks, and take or cause to be taken all other
steps necessary or required under the applicable Maryland and Federal laws.

              40.5   Tenant's obligations under this Article 40 shall survive
the expiration or earlier termination of the Lease. During any period of time
employed by Tenant or Landlord after the termination of this Lease to complete
the removal from the Demised Premises of any such Hazardous Materials for which
Tenant is responsible pursuant to this Section 40, Tenant shall continue to pay
the full Rent in accordance with this Lease, which Rent shall be prorated daily.
In the event that Landlord leases any portion of the Demised Premises to a third
party,

                                       43
<PAGE>   47

Tenant's obligation to pay Rent with respect to any such leased portion pursuant
to this Section 40.5 shall cease.

              40.6   As used herein, the term "HAZARDOUS MATERIAL" means any
hazardous or toxic substance, material or waste which is or becomes regulated by
any local governmental authority, the State of Maryland or the United States
government, including, without limitation, the following: (i) "oil" as defined
by Maryland Environment Code Ann., Section 4401(g) (1993), as amended from time
to time, and regulations promulgated thereunder; (ii) any "hazardous waste",
"hazardous substance" or "release" as defined by the Comprehensive Environmental
Response, Compensation, and Liability Act of 1980, as amended from time to time,
and regulations promulgated thereunder ("CERCLA"); (iii) any "hazardous
substance" or "hazardous waste" as defined by Maryland Environmental Code Ann.,
Title 7, Subtitle 2 (1993), as amended from time to time, and regulations
promulgated thereunder, and (iv) any "solid waste" or "disposal" as defined in
the Resource Conservation and Recovery Act of 1976, as amended from time to
time, and the regulations promulgated thereunder ("RCRA"). For purposes of this
Lease, the term "Hazardous Materials" shall not be deemed to include substances
and materials commonly used by tenants of commercial office space. Nonetheless,
Tenant shall only store reasonable quantities of such substances and materials
and shall store, use and dispose of the same in compliance with all applicable
laws, insurance and labeling requirements.

              40.7   Landlord and Tenant acknowledge that one or more prior
occupants of the Project previously maintained an underground storage tank and
an oil interceptor (the "PRIOR HM USE"). Notwithstanding anything to the
contrary contained herein, Landlord shall be solely responsible for (without
reimbursement by Tenant through Rent or otherwise) all costs and expenses
associated with any removal, disposal, remediation or other required activities
in connection with the Prior HM Use (including removal of the tank).
Notwithstanding anything herein to the contrary, Tenant shall not conduct any
testing, boring or other investigation of any kind of subsurface soil conditions
except (i) as required in connection with Tenant's obligations pursuant to this
Section 40, (ii) in connection with the initial construction of the Tenant Work
and/or the Tenant Performed Landlord Work for Phase 1 or Phase 2, (iii) as
required by law, or (iv) upon not less than fifteen (15) days prior written
notice to Landlord, if Tenant has a reasonable basis for believing that a
portion of the Project is contaminated with Hazardous Materials for which Tenant
has or may have legal liability. In any such event, Landlord may perform any
required testing, the costs of which shall be allocated to Landlord or Tenant as
otherwise provided in this Lease.

       41.    Intentionally omitted.

       42.    Options to Extend Term.

              42.1   Provided that (i) this Lease is in full force and effect,
(ii) no material adverse change in Tenant's financial condition shall have
occurred, and (iii) Tenant shall not have been in default in respect of the
payment of Rent at any time during the two (2) year period prior to the date on
which Tenant exercises its right to extend the term of this Lease, Tenant shall
have the option to extend the term of this Lease for a first renewal term of
five (5) years at a Basic Annual Rental

                                       44
<PAGE>   48

during the first renewal term equal to the Basic Annual Rental on the last day
of the term prior to the first renewal term plus three percent (3%) or such
other amount as may be agreed upon by Landlord and Tenant, and otherwise on the
same terms, covenants and conditions as are contained in this Lease.

              42.2   Tenant shall give Landlord written notice of Tenant's
election to extend the term of this Lease no less than 270 days, but not more
than 360 days, prior to the expiration of the then current term of this Lease.

              42.3   Provided that (i) Tenant shall have effectively exercised
its option to extend the term for a first renewal term, (ii) this Lease shall be
in full force and effect, (iii) no material adverse change in Tenant's financial
condition shall have occurred, and (iv) Tenant shall not have been in default in
respect of the payment of Rent at any time during the two (2) year period prior
to the date on which Tenant exercises its right to extend the term of this Lease
for a second renewal term, Tenant shall have the option to extend the term of
this Lease for a second renewal term of five (5) years at a Basic Annual Rental
during the second renewal term equal to the Basic Annual Rental on the last day
of the first renewal term plus three percent (3%) or such other amount as may be
agreed upon by Landlord and Tenant, and otherwise on the same terms, covenants
and conditions as are contained in this Lease, except that there shall be no
further option to extend the term of this Lease.

              42.4   Tenant shall give Landlord written notice of Tenant's
election to extend the term of this Lease no less than 270 days, but no more
than 360 days, prior to the expiration of the then current term of this Lease.

       43.    Miscellaneous.

              43.1   Terms and Headings. Where applicable in this Lease, the
singular includes the plural and the masculine or neuter includes the masculine,
feminine and neuter. The section headings of this Lease are not a part of this
Lease and shall have no effect upon the construction or interpretation of any
part hereof.

              43.2   Examination of Lease. Submission of this instrument for
examination or signature by Tenant does not constitute a reservation of or
option for lease, and it is not effective as a lease or otherwise until
execution by and delivery to both Landlord and Tenant.

              43.3   Time. Time is of the essence with respect to the
performance of every provision of this Lease in which time of performance is a
factor.

              43.4   Covenants and Conditions. Each provision of this Lease
performable by Tenant shall be deemed both a covenant and a condition.

              43.5   Consents. Whenever consent or approval of either party is
required, that party shall not unreasonably withhold such consent or approval,
except as may be expressly set forth to the contrary.

                                       45
<PAGE>   49

              43.6   Entire Agreement. The terms of this Lease are intended by
the parties as a final expression of their agreement with respect to the terms
as are included herein, and may not be contradicted by evidence of any prior or
contemporaneous agreement. The Basic Lease Provisions, general provisions and
Exhibits all constitute a single document and are incorporated herein.

              43.7   Severability. Any provision of this Lease which shall prove
to be invalid, void, or illegal in no way affects, impairs or invalidates any
other provision hereof, and such other provisions shall remain in full force and
effect.

              43.8   Recording. Upon request by Tenant, Landlord shall execute
and deliver to Tenant a document, in recordable form, evidencing the existence
of this Lease (without stating any of the rental provisions) which document
Tenant shall have the right to record in the land records of Montgomery County,
Maryland. Tenant shall pay any and all recordation, transfer or other taxes or
fees associated with the recordation of such document.

              43.9   Impartial Construction. The language in all parts of this
Lease shall be in all cases construed as a whole according to its fair meaning
and not strictly for or against either Landlord or Tenant.

              43.10  Inurement. Each of the covenants, conditions and agreements
herein contained shall inure to the benefit of and shall apply to and be binding
upon the parties hereto and their respective heirs, legatees, devisees,
executors, administrators, successors, assigns, sublessees, or any person who
may come into possession of said Demised Premises or any part thereof in any
manner whatsoever. Nothing contained in this Section 43.10 shall in any way
alter the provisions against assignment or subletting in this Lease provided.

              43.11  Notices. Any notice, consent, demand, bill, statement, or
other communication required or permitted to be given hereunder must be in
writing and shall be effective upon receipt (or refusal of receipt) (a) when
delivered in person, or (b) when sent by registered or certified mail, return
receipt requested, postage prepaid, or (c) when delivered by a nationally
recognized overnight courier service, addressed to Tenant or Landlord at the
addresses shown in Section 2.1.10 of the Basic Lease Provisions. Either party
may, by notice to the other given pursuant to this Section, specify additional
or different addresses for notice purposes.

              43.12  Maryland Jurisdiction. This Lease shall be governed by,
construed and enforced in accordance with the laws of the State of Maryland,
applied to contracts made in Maryland for Maryland domiciliaries to be wholly
performed in Maryland.

              43.13  Authority. That individual or those individuals signing
this Lease warrant and represent that said individual or individuals have the
power, authority and legal capacity to sign this Lease on behalf of and to bind
all entities, corporations, partnerships, joint venturers or other organizations
and/or entities on whose behalf said individual or individuals have signed.

                                       46
<PAGE>   50

              43.14  Miller Tax Abatement. Landlord agrees, at tenant's sole
cost and expense, to reasonably cooperate with Tenant in effecting in Miller Tax
Abatement or other tax abatement and/or state or local grant benefitting Tenant.

                                       47
<PAGE>   51

       IN WITNESS WHEREOF, the parties hereto have executed this Lease as of the
date first above written.

                                    TENANT:

                                    GENE LOGIC INC., a Delaware Corporation

                                    By:  /s/ Philip L. Rohrer, Jr.
                                       ---------------------------
                                    Its: Chief Financial Officer
                                        -----------------------------

                                    LANDLORD:

                                    ARE - 50 WEST WATKINS MILL, LLC,
                                    a Delaware limited liability company

                                    By:   ALEXANDRIA REAL ESTATE EQUITIES, L.P.,
                                          a Delaware limited partnership

                                          By:  ARE-QRS, CORP.,
                                               a Delaware corporation

                                               By:  /s/ Joel S. Marcus
                                                  --------------------
                                               Name:    Joel S. Marcus
                                                    ------------------
                                               Its:      Chief Executive Officer
                                                   -----------------------------

                                       48
<PAGE>   52

                              EXHIBIT "A" TO LEASE

                         LEGAL DESCRIPTION AND SITE PLAN

Description:  All that property located in the Ninth Election District of
              Montgomery County, Maryland and more particularly described as
              follows:

              Parcel lettered "B" in the subdivision known as "PARCELS A & B.
              BENNINGTON CORPORATE CENTER", as per plat recorded in Plat Book
              148 at plat 16955 among the Land Records of Montgomery County,
              Maryland.

              Being the same property as acquired from Jonathan S. England,
              etal, by deed dated February 4, 1988 and recorded in Liber 8149 at
              folio 420.

Plot Plan:    Attached

<PAGE>   53

                              EXHIBIT "B" TO LEASE

                                   WORK LETTER

       1.     Tenant's Authorized Representative. Tenant designates Donna
Voorman ("TENANT'S AUTHORIZED REPRESENTATIVE") as the person authorized to
initial all plans, drawings, change orders and approvals pursuant to this
Exhibit. Landlord shall not be obligated to respond to or act upon any such item
until such item has been initialed by Tenant's Authorized Representative.

       2.     The Work. The work shall consist of work to be done by Landlord as
described on Schedule 1-A hereto ("LANDLORD'S WORK"), work to be done by Tenant
on behalf of Landlord as described on Schedule 1-B hereto ("TENANT PERFORMED
LANDLORD WORK") and tenant improvement work to be done by Tenant ("TENANT'S
WORK").

              A.     Landlord's Work shall be done at Landlord's sole cost and
expense and shall be completed no later than January 1, 2001.

              B.     Except as noted on Schedule 1-B, the Tenant Performed
Landlord Work shall be designed by the Tenant Improvement Architect selected
pursuant to Section 2.C hereof and shall be reviewed and approved by Landlord as
provided in such Section. The Tenant Performed Landlord Work shall be done at
Landlord's sole cost and expense and shall be undertaken by Tenant pursuant to
construction contracts with the contractor or contractors approved by Landlord
following a bidding procedure reasonably approved by Landlord and Tenant.

              C.     Tenant's Work shall be done at Tenant's sole cost and
expense (except for the Allowance, as such term is hereinafter defined) and in
accordance with the plans and specifications hereinafter referred to in this
Exhibit B. All plans and specifications shall be prepared by architects and
engineers selected by Tenant and approved by Landlord, Landlord's approval not
to be unreasonably withheld, conditioned or delayed. Landlord hereby approves
Kling Lindquist as the Tenant Improvement Architect, C2C Inc as the
project/construction manager and The Whiting-Turner Contracting Company, Hitt
Contracting and Gilbane Construction as potential general contractors for the
Tenant Performed Landlord Work and the Tenant Work. Tenant shall prepare and
submit to Landlord for approval schematics covering the Tenant Performed
Landlord Work (to the extent such work must be designed) and Tenant's Work
prepared in conformity with the applicable provisions of this Exhibit B. The
schematics shall contain sufficient information to convey Tenant's proposed
design to Landlord. Landlord shall notify Tenant of any objections to such
schematics within five (5) business days after receipt thereof. If Landlord
makes objections to Tenant's schematics, Tenant shall cause such objections to
be remedied in the working drawings and specifications Tenant submits to
Landlord for approval. Within five (5) business days after receipt by Landlord
of said working drawings, Landlord shall notify Tenant of the manner, if any, in
which said working drawings and specifications as submitted by Tenant are
unacceptable and Tenant shall re-submit such working drawings and specifications
to Landlord for approval. Landlord shall respond to all requests for consents,
approvals, directions or the like made by Tenant pursuant to this

<PAGE>   54

Exhibit B within five (5) business days following Landlord's receipt of such
request. Requests need be sent only to Larry Diamond at Landlord's Maryland
office. Landlord's failure to respond within such five (5) business day period
shall be deemed approval by Landlord.

       3.     Completion of the Tenant Performed Landlord Work and Tenant's
Work. Tenant will perform and complete the Tenant Performed Landlord Work and
Tenant's Work in compliance with this Lease and such rules and regulations as
Landlord may reasonably make and in accordance with all applicable laws, orders,
regulations and requirements of all governmental authorities, Landlord's
insurance carriers and the board of fire underwriters having jurisdiction. Prior
to the commencement of the Tenant Performed Landlord Work and Tenant's Work,
Tenant shall submit to Landlord, for Landlord's approval (which approval shall
not be unreasonably withheld, conditioned or delayed), a list of project
managers and contractors (except that no further approval shall be required for
the persons identified in Section 2.C. above) who will perform the Tenant
Performed Landlord Work and Tenant's Work. Landlord shall give Tenant notice of
its approval or disapproval within five (5) business days after Landlord's
receipt of Tenant's list. Landlord may require that Tenant's contractor(s)
(other than the contractors pre-approved in Section 2.C. above) provide a
performance and payment bond in industry standard form. All the Tenant Performed
Landlord Work and Tenant's Work shall be subject to Landlord's or Landlord's
representative's reasonable approval. The Tenant Performed Landlord Work and
Tenant's Work shall be performed in accordance with the approved working
drawings and specifications and this Exhibit B. For all major subcontracts for
Tenant's Work, Tenant's general contractor shall be required to provide to
Tenant at least two (2) competitive bids. For all major subcontracts for the
Tenant Performed Landlord Work, Tenant's general contractor shall be required to
provide to Landlord and Tenant at least three (3) competitive bids, and the
subcontract shall be awarded to the subcontractor approved by Landlord. Landlord
shall be solely responsible for the costs of such Tenant Performed Landlord Work
(the "LANDLORD PAYMENT").

       4.     Obligations of Tenant Before Lease Term Begins. Tenant shall
perform promptly such of its obligations contained in this Exhibit B as are to
be performed by it prior to the beginning of the Lease Term; and Tenant shall
also observe and perform all of its obligations under this Lease (excepting its
obligations to pay Basic Annual Rent and Operating Expenses) from the date upon
which the Demised Premises are made available to Tenant for the Tenant Performed
Landlord Work and Tenant's Work until the Rent Commencement Date.

       5.     Completion of Tenant's Construction Obligations. Tenant, at
Tenant's sole cost and expense and without cost to Landlord (except for the
Allowance and the Landlord Payment), shall complete the Tenant Performed
Landlord Work and Tenant's Work described in this Exhibit B in all respects in
accordance with the provisions of this Lease. The Tenant Performed Landlord Work
and Tenant's Work shall be completed at such time as Tenant, at its sole cost
and expense and without cost to Landlord (except for the Allowance and the
Landlord Payment) shall (1) furnish evidence satisfactory to Landlord that all
of the Tenant Performed Landlord Work and Tenant's Work has been completed

<PAGE>   55

and paid for in full (which may be evidenced by the architect's certificate of
completion and the general contractor's and subcontractor's final waivers and
releases of liens) (and such work has been accepted by Landlord); that any and
all liens therefor that have been or might be filed have been discharged of
record (by payment, bond, order of a court of competent jurisdiction or
otherwise) or waived and that no security interests relating thereto are
outstanding; (2) furnish to Landlord all certifications and approvals with
respect to the Tenant Performed Landlord Work and Tenant's Work that may be
required from any governmental authority and any board of fire underwriters or
similar body for the use and occupancy of the Demised Premises; (3) furnish to
Landlord the insurance required by the Lease; and (4) furnish an affidavit from
Tenant's architect certifying that all work performed in the Demised Premises is
in substantial accordance with the working drawings and specifications approved
by Landlord. The foregoing not withstanding, Tenant's Work shall not be deemed
incomplete by reason of, nor shall Tenant have any liability with respect to
mechanics liens arising solely from Landlord's breach of its obligation to
advance Landlord Payment as herein provided.

       6.     Insurance. Tenant's contractors and subcontractors shall be
required to provide, in addition to the insurance required of Tenant pursuant to
this Lease the following types of insurance:

              A.     Builders Risk Insurance. At all times during the period
between the commencement of construction of the Tenant Performed Landlord Work
and Tenant's Work and the date of the opening for business in the Demised
Premises, Tenant shall maintain, or cause to be maintained, casualty insurance
in Builder's Risk Form, covering Landlord, Landlord's agents, Tenant and
Tenant's contractors, as their interests may appear, against loss or damage by
fire, vandalism, and malicious mischief and other such risks as are customarily
covered by the so-called "broad form extended coverage endorsement" upon all the
Tenant Performed Landlord Work and Tenant's Work and builder's machinery, tools
and equipment, all while forming a part of, or contained in, such improvements
or temporary structures while on the Demised Premises, or when adjacent thereto,
all on a completed value basis for the full insurable value at all times. Said
Builder's Risk Insurance shall contain an express waiver of any right of
subrogation by the insurer against Landlord, its agents and employees.

              B.     Workers' Compensation. At all times during the period of
construction of the Tenant Performed Landlord Work and Tenant's Work, Tenant
will require contractors and subcontractors to maintain statutory Workers'
Compensation as required by law.

       7.     Liability. It is agreed that Tenant assumes the responsibility and
liability for any and all injuries or death of any persons, including Tenant's
contractors and subcontractors, and their respective employees and for any and
all damages to property caused by, or resulting from or arising out of any act
or omission on the part of Tenant, Tenant's contractors or subcontractors or
their respective employees, in the prosecution of the Tenant Performed Landlord
Work and Tenant's Work and with respect to such work agrees to indemnify and
save free and harmless Landlord, from and against all losses and/or expenses,

<PAGE>   56

including reasonable legal fees and expenses, which Landlord may suffer or pay
as the result of claims or lawsuits due to, because of, or arising out of any
and all such injuries or death and/or damage, whether real or alleged and Tenant
and Tenant's contractors and/or subcontractors or their respective insurance
companies shall assume and defend at their own expense all such claims or
lawsuits; provided, however, that nothing contained in this Exhibit B shall be
deemed to indemnify or otherwise hold Landlord harmless from or against the
negligent or wrongful acts or omissions of Landlord, its agents, employees and
contractors nor to affect or modify the terms of Section 21.7 of the Lease. Any
approval or consent by Landlord shall in no way obligate Landlord in any manner
whatsoever in respect of the finished product designed and/or constructed by
Tenant. Any deficiency in design or construction, although the same has prior
approval of Landlord, shall be solely the responsibility of Tenant (except that
the foregoing shall not, in the case of Tenant Performed Landlord Work, release
Landlord from its maintenance, repair, replacement and similar obligations under
the Lease). All materials and equipment furnished by Tenant as Tenant Work shall
be new or "like- new" and all work shall be performed in a first-class
workmanlike manner.

       8.     Allowance. Landlord shall contribute $1,578,775 (the "ALLOWANCE")
toward the costs and expenses incurred in connection with the performance of
Tenant's Work, of which no more than $172,230 may be payable to Tenant's
architects and engineers. Upon request by Tenant the Allowance may be increased
by an amount up to $4,592,800. In the event that Tenant requests such an
increase, the Basic Annual Rent shall be increased by $0.14 per annum for each
additional $1.00 advanced by Landlord to Tenant pursuant to Tenant's request.
Landlord shall be paid by Tenant the sum of $51,205 for monitoring and
inspecting Tenant's Work, which sum shall be deducted from the Allowance. If the
entire Allowance is not applied toward or reserved for the costs of Tenant's
Work, Tenant shall receive a credit of such unused portion of the Allowance (the
"UNUSED ALLOWANCE"), provided, however, the Unused Allowance shall not exceed
$82,500 with respect to Phase 1, and shall not exceed $75,377.50 with respect to
Phase 2. Upon submission by Tenant to Landlord of a statement ("ADVANCE
REQUEST") setting forth the amount requested and a reasonably detailed summary
of the Tenant's Work and Tenant Performed Landlord Work performed (which shall
be satisfied by a copy of an AIA standard form Application for Payment (G 702)
executed by the general contractor and by the architect) accompanied by lien
releases from the general contractor and the subcontractors in respect of the
prior advance. Landlord, within five (5) business days following receipt by
Landlord of the Advance Request and the accompanying materials, shall advance to
Tenant such amounts of the Allowance and the Landlord Payment as Landlord shall
reasonably determine to be due in accordance with the Advance Request and the
accompanying statements. The Allowance and the Landlord Payment may be used for
the payment of applicable construction and other applicable costs including,
without limitation, laboratory improvements, finishes, Building fixtures,
building permits and fees, architectural, engineering, design and consulting
fees. Tenant shall have the right to retain its own specialty contractors
(subject to approval by Landlord, such approval not to be unreasonably withheld,
conditioned or delayed) to perform any portion of the work necessary to
construct and outfit the Demised Premises which work shall not be payable out of
the Allowance unless

<PAGE>   57

approved by Landlord. If approved by Landlord, the costs for such work may be
paid from the Allowance provided that all Tenant's Work has been paid for. Such
specialty work may include, without limitation, data cabling, telephone and data
equipment, security, audio/visual equipment, white noise and furniture systems.
The Allowance shall in no event be used to purchase any furniture, personal
property or other non-building system equipment of Tenant. In the event that a
portion of the Allowance is not used to pay for Tenant Work or specialty work or
credited against Annual Basic Rent, the Annual Basic Rent shall be reduced at
the rate of Fifteen Cents ($0.15) per One Dollar ($1.00) per rentable square
foot of unused or unapplied Allowance, up to a maximum Unused Allowance of Seven
and 50/100 Dollars ($7.50) per square foot. Notwithstanding anything to the
contrary set forth elsewhere in this Exhibit B, Landlord shall not have any
obligation to advance to Tenant any portion of the Allowance until Landlord
shall have reasonably approved the project budget for the Tenant's Work. Prior
to approval of the project budget Tenant shall pay all of the costs and expenses
incurred in connection with the Tenant's Work. In the event that the approved
project budget is greater than the Allowance, Landlord's advances against the
Allowance shall be in an amount equal to Landlord's pro rata portion of
requested amounts and Landlord shall reimburse Tenant in an amount equal to
Landlord's pro rata share of sums advanced by Tenant prior to approval by
Landlord of the project budget. Tenant shall have the right to designate as "to
be paid directly by Tenant" on any Application for Payment any items which
Tenant has the right to remove pursuant to Section 17.8 of the Lease. The
Allowance, the additional Allowance and the inspection and monitoring fee shall
be paid pro rata based upon the square footage then under construction. The
Allowance shall remain available for use by Tenant until four (4) years after
the Rent Commencement Date and the additional Allowance shall remain available
for use by Tenant until two (2) years after the Rent Commencement Date (i.e.,
Tenant must have commenced construction of the applicable Phase on or prior to
such dates or anniversaries). The Unused Allowance, if any, shall be determined
for Phase 1 as of the completion of the initial improvements for Phase 1, and
for Phase 2 as of the earlier of the completion of the initial improvements for
Phase 2 and the fourth annual anniversary of the Rent Commencement Date.
Landlord shall, at Tenant's request (to be submitted no later than thirty (30)
days after the date described in the immediately preceding sentence), apply such
Unused Allowance (subject to the limitations described above) toward payment of
the first full monthly payments of Annual Basic Rent due hereunder following any
such request.

       9.     Existing Building Materials; Removal of Tenant's Property. Any
existing building materials within the Demised Premises that Tenant reuses
(e.g., lights, doors, frames, hardware, etc.) shall be at no cost to Tenant and
shall not be deducted from the Allowance.

       10.    Landlord Payment. Landlord shall make available to Tenant the
Landlord Payment to be used by Tenant for the Tenant Performed Landlord Work
including all engineering, design, labor and materials associated therewith.

<PAGE>   58

                                  SCHEDULE 1-A

                                  LANDLORD WORK

       1)     Complete construction of new parking area as required to provide
              three spaces per one thousand rentable square feet in accordance
              with the design attached to the lease as Exhibit G, and make such
              other parking, curbing, aisle, landscaping and other changes
              required by the applicable governmental authorities as a condition
              to their final approval of the Site-Plan referred to in Paragraph
              6 below.

       2)     Seal and re-stripe existing parking areas.

       3)     Re-caulk and repair cracks in existing brick facade.

       4)     Obtain condition report on roof (coordinate and consult with
              Tenant) and complete all corrective, remedial and/or replacement
              work.

       5)     Lower roof overflow scuppers.

       6)     Site-Plan - file and receive approval from applicable governmental
              authority. Landlord agrees that to the extent that performance of
              the Tenant Work and/or the Tenant Performed Landlord Work is
              actually delayed as a result of Landlord's failure to obtain final
              approval of the Site Plan on or before August 24, 2000, (e.g., if
              Tenant is delayed in securing its demolition and/or building
              permits) then such delay shall, to the extent it actually delays
              the completion of the Tenant Work and/or the Tenant Performed
              Landlord Work, constitute "Landlord Delay" under the Lease.

       7)     Landlord agrees that in the event that any remediation and/or
              other work is required pursuant to Section 40.7 of the Lease
              ("EXISTING REMEDIATION") and if the performance of the Tenant
              Work and/or Tenant Performed Landlord Work is required to be
              suspended or otherwise actually delayed during or pending
              completion of such Existing Remediation, then such event shall,
              to the extent it actually delays the completion of the Tenant
              Work and/or the Tenant Performed Landlord Work, constitute
              "Landlord Delay" under the Lease.

                         LANDLORD WORK ALREADY PERFORMED

       1)     Removal of existing underground storage tanks.

       2)     Demolish and remove conveyor.

       3)     Drain, close and plug oil interceptor tank, trenches and piping in
       accordance with applicable laws.

<PAGE>   59

                                  SCHEDULE 1-B

                         TENANT PERFORMED LANDLORD WORK

       1.     Demolish and remove CO2 exhaust system, vehicle area equipment,
interior concrete masonry walls between the garage bays and open warehouse area.

       2.     Install handicap parking signage at front of building.

       3.     Install additional lighting (motion detector sensitive along
property line with railroad tracks or wall-mounted high output lighting).

       4.     Make all exterior changes necessary to cause building, parking and
related areas to comply with ADA and other Legal Requirements, including, but
not limited to, locating handicap parking at both building entrances for
Premises, constructing ramps at handicap parking locations, construction and/or
reconstruction of any access ramps (with rails) to both entrances for Premises
and replacement of building entrance doors (where required).

       5.     Install windows and related work in place of existing garage bay
doors.

       6.     Overlay existing concrete slab in accordance with the P.
Hobelmann/Kling Lindquist memorandum dated June 22, 2000.

       7.     Demolish existing natural gas piping not required for Tenant's
use.

       8.     Enclose roof ladder per OSHA and Legal Requirements.

       9.     Install window blinds.

       10.    Install automated door opener on main building entrance doors if
required by code.

       11.    Insulate the roof to achieve an R-value of 15 as required by
applicable law.

<PAGE>   60

Rules and Regulations

                                  EXHIBIT "C"

       1.     Tenant will not pile, place or permit to be placed any goods,
materials, equipment or other obstructions on the sidewalks or parking lots in
the front, rear or sides of the Building, or in a place and in a matter so as to
block the sidewalks, parking lots and loading areas. Tenant will not obstruct,
in any way, the entry passages, corridors, halls, stairways or elevators of the
Building, or use them in any way other than as a means of passage to and from
the Demised Premises. Tenant will not do anything that directly or indirectly
takes away any of the rights of ingress, egress or natural light from any other
tenant in the Building.

       2.     At any time that other tenants occupy the Project, the delivery,
shipping, loading and unloading of supplies, fixtures and all other items to and
from the Demised Premises will be subject to the reasonable rules and
regulations Landlord may promulgate from time to time with respect to deliveries
and shipments.

       3.     The plumbing facilities will not be used for any purpose other
than that for which they are constructed. No foreign substance of any kind will
be thrown into the plumbing facilities. The expense of any breakage, stoppage or
damage resulting from a violation of this provision by Tenant or any of its
servants, agents, invitees, employees and/or licensees will be borne solely by
Tenant.

       4.     No radio, speakers, television, phonograph or other sound or
similar device (other than a voice and/or phone paging and/or alert system) will
be installed or operated in the Demised Premises on any floor where Tenant is
not the sole tenant without Landlord's prior written reasonable approval. Tenant
will prevent sounds emanating from the Demised Premises from being heard outside
the Demised Premises in a manner unreasonably disturbing or annoying to other
tenants.

       5.     Tenant, before closing and leaving the Demised Premises, will
ensure that all entrance doors and all exterior windows are locked.

       6.     Tenant will not use the Demised Premises for the sale of any
goods, wares or merchandise to the general public. Tenant will not permit anyone
to lodge or sleep in the Demised Premises.

       7.     Landlord reserves to itself all rights not granted to Tenant under
this Lease, including, but not limited to, the right to install and maintain
"for sale" signs on the exterior of the Building and, during the last 400 days
of the Term (or earlier if an Event of Default has occurred and is continuing),
"for lease" signs on the exterior of the Building. In addition, Landlord shall
have the right to erect a tasteful monument sign.

<PAGE>   61

                                   EXHIBIT "D"

                          FORM OF ESTOPPEL CERTIFICATE

              This Tenant Estoppel Certificate (this "Certificate"), dated as of
       ________, is executed by Gene Logic Inc. ("Lessee") in favor of
       _____________ , a ________________________________ ("Lessor") and
       ("________").

                                    RECITALS

              A.     Lessee and Lessor have entered Into a Lease dated as of
       July __, 2000 ("Lease") for a portion of the Property located at ________
       (the "Property").

              B.     Pursuant to the Lease, Lessee has agreed that upon the
       request of Lessor, Lessee would execute and deliver a tenant estoppel
       certificate certifying to the status of the Lease.

              C.     Lessor has requested that Lessee execute this Certificate.
       Lessee certifies, warrants, and represents to Lessor ____________ and as
       follows:

       SECTION 1. LESSEE. Lessee is the lessee of the Property (the "Leased
Premises"), pursuant to the Lease, a correct copy of which is attached as
Exhibit A.

       SECTION 2. LEASED PREMISES. The Leased Premises consist of
________________ (____________) square feet of the (____________) floor of the
Property, as more particularly described in the Lease.

       SECTION 3. FULL FORCE OF LEASE. As of the date of this Certificate, the
Lease is in full force, has not been terminated, and is to Lessee's knowledge,
subject only to any offsets, counter-claims, or defenses of Lessee as are set
forth herein.

       SECTION 4. COMPLETE AGREEMENT. The Lease constitutes the complete
agreement between Lessor and Lessee for the Leased Premises and the Property,
and no amendments, modifications or extensions to the Lease, either written or
oral, currently exist, other than ______________________________________________
_______________________________________________________________________________.

       SECTION 5. ACCEPTANCE OF LEASED PREMISES. Lessee has accepted and is
currently occupying the Leased Premises.

       SECTION 6. LEASE TERM. The term of the Lease commenced on and ends on
_____________________________________ , subject to the following options to
extend:_________________________________________.

       SECTION 7. PURCHASE RIGHTS.

<PAGE>   62

              Lessee has no option, right of first refusal, right of first
       offer, or other right to purchase all or any portion of the Leased
       Premises or all or any portion of the Property, except as follows:
       ________________________________________________________________________
       ______________________________________.

       SECTION 8. RIGHTS OF LESSEE.

              Except as expressly stated in this Certificate, Lessee:

              (a) has no right to renew or extend the term of the Lease;

              (b) has no option or other right to purchase all or any part of
       the Leased Premises or all or any part of the Property;

              (c) has no right, title, or interest in the Leased Premises, other
       than as Lessee under the Lease.

       SECTION 9. RENT.

              (a) The rent under the Lease is current, and Lessee is not in
       default in the performance or any of Its obligations under the Lease.

              (b) Lessee is currently paying base rent under the Lease in the
       amount of $_________________ per month. Lessee has not received and is
       not entitled to any abatement, refunds, rebates, concessions or
       forgiveness of rent or other charges, free rent, partial rent, or
       credits, offsets or reductions in rent, except as follows: ______________
       ________________________________________________________________________.

              (c) Lessee's estimated share of operating expenses, common area
       charges, insurance, real estate taxes and administrative and overhead
       expenses is 100% and is currently being paid at the rate of $____________
       per month.

              (d) To Lessee's knowledge, there are no existing defenses or
       offsets against rent due or to become due under the terms of the Lease,
       and there has been no default or other wrongful act or omission by the
       landlord under the lease or otherwise in connection with Lessee's
       occupancy of the Leased Premises, except as follows: ____________________
       ________________________________________________________________________.
        (if none, please state "None").

       SECTION 10. SECURITY DEPOSIT.

              The amount of Lessee's security deposit hold by Lessor under the
       Lease is ___________________________ Dollars ($_______________).

       SECTION 11. PREPAID RENT.

              The amount of prepaid rent, separate from the security deposit, is
       _______________ Dollars ($___________) covering the period from ________
       to __________.

<PAGE>   63

       SECTION 12. INSURANCE.

              All insurance, if any, required to be maintained by Lessee under
       the Lease is presently in effect.

       SECTION 13. TENANT IMPROVEMENTS.

              To Lessee's know ledge, all construction of buildings, site
       improvements and facilities and interior tenant improvements and other
       requirements respecting the Leased Premises which Lessor was to have
       performed in accordance with the terms of the Lease have been performed
       and completed in all respects and accepted by Lessee, except
       ____________. All tenant allowances, reimbursements for construction
       costs and other, similar sums agreed to be paid by the landlord
       respecting the Leased Premises have been paid, except as follows: _______
       ________________________________________________________________________.

       SECTION 14. LESSOR'S OBLIGATIONS.

              As of the date of this Certificate, to Lessee's knowledge, Lessor
       has performed all obligations required of Lessor under the Lease; no
       offsets, counterclaims, or defenses of Lessee under the Lease exist
       against Lessor, and no events have occurred that, with the passage of
       time or the giving of notice, would constitute a basis for offsets,
       counterclaims, or defenses against Lessor, except as follows: ___________
       ________________________________________________________________________.

       SECTION 15. ASSIGNMENTS BY LANDLORD.

              Lessee has received no notice of any assignment, hypothecation or
       pledge of the Lease or rentals under the Lease by Landlord.

       SECTION 16. ASSIGNMENTS BY LESSEE.

              Lessee has not sublet or assigned the Leased Premises or leased
       any portion thereof to any sublessee or assignee. The address for notices
       to be sent to Lessee is as set forth in the Lease.

       SECTION 17. ENVIRONMENTAL MATTERS.

              (a) Lessee is in compliance with Section 40 of the Lease.

              (b) Lessee has not received any notice, written or oral, of
       violation of any Environmental Law and there are no writs, injunctions,
       decrees, orders or judgments outstanding, no lawsuits, claims,
       proceedings or investigations pending or threatened, relating to the use,
       maintenance or operation of the Leased Premises.

       SECTION 18. NOTIFICATION BY LESSEE.

<PAGE>   64

              From the date of this Certificate and continuing until __________.
       Lessee agrees to immediately notify Lessor and ______________ at the
       following addresses, on the occurrence of any event or the discovery of
       any fact that would make any representation contained in this Certificate
       inaccurate:

                               Alexandria Real Estate Equities, Inc.
                               135 North Los Robles Avenue
                               Suite 250
                               Pasadena, California 91101
                               Attn: General Counsel

                               -----------------------------

                               -----------------------------

                               -----------------------------

                               -----------------------------

              Lessee makes this Certificate with the knowledge that it will be
       relied on by ____________ in agreeing to _______________________________.

              Lessee has executed this Certificate as of the date first written
       above by the person named below, who are duly authorized to do so.

                            LESSEE:
                                    --------------------------------------------

                            By:
                                ------------------------------------------------
                            Its:
                                 -----------------------------------------------

                            Dated:
                                  ----------------------------------------------

<PAGE>   65

                                   EXHIBIT "E"

                    ACKNOWLEDGMENT OF RENT COMMENCEMENT DATE

       This acknowledgment is made pursuant to Section 4.4 of that certain Lease
dated July ___, 2000 by and between ARE-50 WEST WATKINS MILL, LLC, a Delaware
limited liability company, Landlord, and GENE LOGIC INC., a Delaware
corporation, Tenant, with respect to 50 West Watkins Mill Road, Gaithersburg in
the County of Montgomery, Maryland.

 We hereby acknowledge that the Rent Commencement Date of the Lease is
___________________

                            TENANT:

                            GENE LOGIC INC. , a Delaware corporation

                            By:
                               ------------------------------

                            Its:
                                ------------------------------

                            LANDLORD:

                            ARE - 50 WEST WATKINS MILL, LLC,
                            a Delaware limited liability company

                            By:       ALEXANDRIA REAL ESTATE EQUITIES, L.P.,
                                      a Delaware limited partnership

                                      By:       ARE-QRS, CORP.,
                                                a Delaware corporation

                                                By:
                                                   --------------------------
                                                Name:
                                                     ------------------------
                                                Its:
                                                    -------------------------

<PAGE>   66

                                   EXHIBIT "F"

       THIS SUBORDINATION, NON-DISTURBANCE AND ATTORNMENT AGREEMENT (the
"Agreement" is made as of ________, ________, between GENE LOGIC INC., a
Delaware Corporation ("Tenant"), having an address at ___________ , and
__________ ("Lender ") having an address at ________.

                                   WITNESSETH:

       WHEREAS, Tenant is the tenant under that certain lease (the "Lease")
dated ________, by and between Tenant and ARE-50 WEST WATKINS MILL, LLC wherein
Landlord leased to Tenant certain premises known as 50 West Watkins Mill Road,
Gaithersburg, MD 20878 (the "Premises") and located on that certain land
described in Exhibit A attached hereto and made a part hereof (the "Land"); and

       WHEREAS, Landlord is about to make, execute and deliver its Promissory
Note ("Note") to Lender, which Note shall be secured by, among other security, a
lien encumbering the Land and the improvements constructed thereon (the Land and
such improvements being hereinafter referred to as the "Mortgaged Property")
pursuant to a Mortgage, Security Agreement and Assignment of Leases and Rents
(as thereafter amended and modified, the "Mortgage") (the Mortgage and all other
instruments securing the Note are herein collectively called the "Security
Documents"); and

       WHEREAS, Lender and Tenant desire to confirm their agreements with
respect to the Lease and the Security Documents.

       NOW, THEREFORE, in consideration of the mutual covenants and agreements
herein contained, Lender and Tenant hereby agree and covenant as follows:

       1.     Subordination. The Lease and all right, title and interest in the
Mortgaged Property created thereby (including without limitation, any purchase
options, rights of first refusal, lease renewal rights, etc.) are, shall be and
shall at all times remain and continue to be subject and subordinate in all
respects to the liens and effect of the Security Documents.

       2.     Non-Disturbance. So long as the Lease is in full force and effect
and Tenant is not in default under the Lease (after notice, if required pursuant
to the Lease, and beyond any period given Tenant to cure such default) or under
this Agreement after notice and a reasonable opportunity to cure:

       (a)    Subject to Paragraph 3 hereof, Lender will recognize the Lease and
Tenant's possession of the Premises and Tenant's right and privileges under the
Lease shall not be diminished or interfered with by Lender, and Tenant's
occupancy of the Premises shall not be disturbed by Lender for any reason
whatsoever during the term of the Lease or any extensions or renewals thereof;
and

<PAGE>   67

       (b)    Lender will not join Tenant as a party defendant in any action or
proceeding to foreclose the Mortgage or to enforce any rights or remedies of
Lender under the Mortgage which would cut-off, destroy, terminate or extinguish
the Lease or Tenant's interest and estate under the Lease.

Notwithstanding the foregoing provisions of this paragraph, if it shall be
required under applicable law for Lender to name or join Tenant as a party in a
foreclosure proceeding with respect to the Mortgage, Lender may so name or join
Tenant without in any way diminishing or otherwise affecting the rights and
privileges granted to, or inuring to the benefit of, Tenant under this Agreement
and the Lease, and Lender shall not seek affirmative relief from Tenant in such
action or proceeding, nor shall the Lease be cut off or terminated, nor Tenant's
possession thereunder disturbed.

       3.     Attornment.

       (a)    Tenant acknowledges that it has notice that Landlord's interest
under the Lease and the rents and all other sums due thereunder have been
assigned to Lender as part of the security for the Note secured by the Mortgage.
Notwithstanding anything to the contrary contained herein or in the Lease, in
the event that Lender notifies Tenant of a default under the Mortgage and
demands that Tenant pay its rent and all other sums due under the Lease to
Lender, Tenant agrees that it shall pay its rent and all other sums due under
the Lease to Lender, provided, however, that Tenant shall be provided written
notice at least ten (10) days prior to Tenant's obligation to pay rent and other
sums due under the Lease to Lender, and provided, further that in such event,
upon the payment to Lender of such rent and other sums Landlord, subject to the
provisions of subparagraph 3(c), shall remain liable to Tenant for the
performance of Landlord's obligations under the Lease. All rents and other sums
paid by Tenant to Lender shall be credited against Tenant's rental obligations
under the Lease, and payment to Lender of rents and such other sums due under
the Lease will be deemed to be payment to Lender of rents and such other sums
due under the Lease will be deemed to be payment to Landlord for purposes of the
Lease. Landlord joins in the execution of this Agreement for the purpose of,
among other things, consenting to the provisions of this subparagraph 3(a).

       (b)    If Lender (or its nominee or designee) shall succeed to the rights
of Landlord under the Lease through possession or foreclosure action, delivery
of a deed or otherwise, or another person purchases the Premises upon or
following foreclosure of the Mortgage, then at the request of Lender (or its
nominee or designee) or such purchaser (Lender, its nominees and designees, and
such purchaser, each being a "Successor-Landlord"), Tenant shall attorn to and
recognize Successor-Landlord as Tenant's landlord under the Lease and shall
promptly deliver any instrument that Successor-Landlord may reasonably request
to evidence such attornment. Upon such attornment, the Lease shall continue in
full force and effect as, or as if it were, a direct lease between
Successor-Landlord and Tenant upon all terms, conditions and covenants as are
set forth in the Lease, except that Successor-Landlord shall not:

              (i)    be liable for any previous act or omission of Landlord
under the Lease; provided, however, that the foregoing provisions of this clause

<PAGE>   68

(b) shall not exculpate the Successor Landlord from liability for performing
Landlord's obligations under this Lease which are of a continuing nature
Including, without limitation, Landlord's repair and maintenance obligations
under the Lease;

              (ii)   be subject to any off-set, which shall have previously
accrued to Tenant against Landlord;

              (iii)  be bound by any modification of the Lease (if such
modification was made after the date that Successor-Landlord obtained its
mortgagee interest) or by any previous prepayment of rent or additional rent for
more than one month which Tenant might have paid to Landlord (other than any
security deposit), unless such modification or prepayment shall have been
expressly approved in writing by Lender;

              (iv)   be liable for any security deposited under the Lease unless
such security has been physically delivered to Lender; or

              (v)    be obligated to commence or complete any construction or to
make any contribution toward construction or installation of any improvements
upon the Mortgaged Property required under the Lease.

       4.     Lease Modifications. Tenant agrees that without the prior written
consent of Lender, it shall not: (a) amend, modify, terminate or cancel the
Lease or any extensions or renewals thereof; (b) tender a surrender of the Lease
or make a prepayment of any rent or additional rent in excess of one (1) month;
or (c) subordinate or permit the subordination of the Lease to any lien
subordinate to the Mortgage. Any such purported action without such consent
shall be void as against the holder of the Mortgage.

       5.     Notice of Default; Opportunity to Cure.

       (a)    Any default or similar notice required or permitted to be given by
Tenant to Landlord shall be simultaneously given also to Lender, and any right
of Tenant dependent upon such notice shall take effect only after such notice to
Lender is so given. Performance by Lender shall satisfy any conditions of the
Lease requiring performance by Landlord, and Lender shall have a reasonable time
to complete such performance as provided in section (b) below.

       (b)    Without limiting the generality of the foregoing, Tenant shall
promptly notify Lender of any default, act or omission of Landlord which would
give Tenant the right, immediately or after the lapse of a period of time, to
cancel or terminate the Lease or to claim a partial or total eviction (a
"Landlord Default") (except that the terms of this subparagraph 5(b) shall not
be applicable to Section 4.1 or Article 22 and/or 23 of the Lease). In the event
of a Landlord Default, Tenant shall not exercise any rights available to it to
cancel or terminate the Lease: i) until it has given written notice of such
Landlord Default to Lender; and ii) unless Lender has failed, within sixty (60)
days after Lender receives such notice, to cure or remedy the Landlord Default
or, if the same is of a nature that same cannot with due diligence be remedied
by Lender within such sixty (60) days after Lender receives such notice, until a
reasonable period for remedying

<PAGE>   69

such Landlord Default has elapsed following the giving of such notice and
following the time when Lender shall have become entitled under the Security
Documents to remedy the same (which reasonable period shall in no event be less
than the period during which Landlord would be entitled under the Lease or
otherwise, after similar notice, to effect such remedy); provided that Lender
shall with due diligence commence and prosecute a remedy for such Landlord
Default. If Lender cannot reasonably remedy a Landlord Default until after
Lender obtains possession of the Mortgaged Property, Tenant may not terminate or
cancel the Lease or claim a partial or total eviction by reason of such Landlord
Default until the expiration of a reasonable period necessary for the remedy
after Lender institutes proceedings to obtain possession of the Mortgaged
Property through a foreclosure or otherwise, or for the appointment of a
receiver for the Mortgaged Property, provided that Lender institutes and
prosecutes such proceedings with due diligence. Lender shall have no obligation
hereunder to remedy any Landlord Default.

       6.     Notice of Lien. To the extent that the Lease entitles Tenant to
notice of the existence of any mortgage and the identity of any lender, this
Agreement shall constitute such notice to Tenant, with respect to the Mortgage.

       7.     Limitation of Liability. Except as specifically provided in this
Agreement, Lender shall not, by virtue of this Agreement, the Mortgage or any
other instrument to which Lender may be a party, be or become subject to any
liability or obligation to Tenant under the Lease or otherwise.

       8.     Priority.

       (a)    Tenant acknowledges and agrees that this Agreement supersedes (but
only to the extent inconsistent with) any provisions of the Lease relating to
the priority or subordination of the Lease and the interests or estates created
thereby to the Mortgage.

       (b)    Tenant agrees to enter into a subordination, non-disturbance and
attornment agreement with any entity which shall succeed Lender with respect to
the Mortgaged Property, or any portion thereof, provided such agreement is
substantially similar to this Agreement.

       9.     Notices. Any notice, consent, request or other communication
required or permitted to be given hereunder shall be in writing and shall be:
(a) personally delivered; (b) delivered by Federal Express or other comparable
overnight delivery service; or (c) transmitted by postage prepaid registered or
certified mail, return receipt requested. All such notices, consents, requests
or other communications shall be addressed to Tenant or Lender at the address
for such party previously set forth in this Agreement, or to such other address
as Tenant or Lender shall in like manner designate in writing. All notices and
other communications shall be deemed to have been duly given on the first to
occur of actual receipt of the same or: (i) the date of delivery if personally
delivered; (ii) one (1) business day after depositing the same with the delivery
service if by overnight delivery service; and (iii) three (3) days following
posting if transmitted by mail. Any party may change its address for purposes
hereof by notice to the other parties given in accordance with the provisions
hereof.

<PAGE>   70

       10.    General. This Agreement may not be modified or terminated orally.
This Agreement shall inure to the benefit of and be binding upon the parties
hereto, their successors and assigns. The term "Lender" shall mean the then
holder of any interest in the Mortgage. The term "Landlord" shall mean the then
holder of the lessor's interest in the Lease. The term "person" shall mean any
individual, joint venture, corporation, partnership, trust, unincorporated
association or other entity. All references herein to the Lease shall mean the
Lease as modified by this Agreement and any amendments or modifications to the
Lease which are consented to in writing by Lender. Any inconsistency between the
Lease and the provisions of this Agreement shall be resolved in favor of this
Agreement.

       11.    Waivers. Both Tenant and Lender hereby irrevocably waive all right
to trial by jury in any action, proceeding or counterclaim arising out of or
relating to this Agreement.

       .      Governing Law. This agreement shall be governed by and construed
in accordance with the laws of the state in which the Land is located.

<PAGE>   71

       IN WITNESS WHEREOF, the parties hereto have executed this Subordination,
Non- Disturbance and Attornment Agreement to be effective as of the day and year
first stated above.

                            "LENDER"

                            ---------------------------------------------------

                            By:
                               ------------------------------------------------
                            Name:
                                 ----------------------------------------------
                            Title:
                                  ---------------------------------------------

                            "TENANT"

                            GENE LOGIC INC.
                            a Delaware Corporation

                            By:
                               ------------------------------------------------
                            Printed Name:
                                         --------------------------------------
                            Title:
                                  ---------------------------------------------

AGREED AND CONSENTED TO:

"BORROWER"

ARE - 50 WEST WATKINS MILL, LLC, a Delaware limited liability company

By:    ALEXANDRIA REAL ESTATE EQUITIES, L.P.,
       a Delaware limited partnership

       By:    ARE-QRS, CORP.,
              a Delaware corporation

              By:
                 ------------------------------------
              Name:
                   ----------------------------------
              Title:
                    ---------------------------------

<PAGE>   72

                                 ACKNOWLEDGMENTS

                   [Insert appropriate state acknowledgments]

<PAGE>   73

                                   EXHIBIT "G"

                                     PARKING

                     [SEE EXHIBITS "G-1" AND "G-2" ATTACHED]<PAGE>   1
                                                            EXHIBIT 10.2.4

              AMENDED and RESTATED REGISTRATION RIGHTS AGREEMENT

                           Dated as of July 6, 2000

                                   between

                        NEXTLINK Communications, Inc.

                                     and

             The Purchasers Listed on the Signature Pages Hereto

<PAGE>   2
                                                                 EXHIBIT 10.2.4

                  AMENDED AND RESTATED REGISTRATION RIGHTS AGREEMENT, dated as
of July 6, 2000 between NEXTLINK Communications, Inc., a Delaware corporation,
formerly known as NM Acquisition Corp. (the "Company"), and the entities
listed on the signature pages hereto under the caption "Purchasers" (each a
"Purchaser" and, collectively, the "Purchasers").

                  Pursuant to the Stock Purchase Agreement (the "1999 Stock
Purchase Agreement"), dated December 7, 1999, by and between the Old Nextlink
(defined below) and certain of the Purchasers, on January 20, 2000, the
Purchasers acquired (i) an aggregate of 584,375 shares of the Company's Series
C Preferred Stock, par value $0.01 per share (the "Series C Preferred Stock"),
and (ii) an aggregate of 265,625 shares of the Company's Series D Preferred
Stock, par value $0.01 per share (the "Series D Preferred Stock").

                  In connection with the consummation of the transactions
contemplated by the 1999 Stock Purchase Agreement, Old Nextlink and the
Purchasers entered into a Registration Rights Agreement, dated January 20,
2000 (the "Existing Registration Rights Agreement"), pursuant to which Old
Nextlink granted the Purchasers certain rights with respect to the
registration of the shares of Common Stock (as hereinafter defined) issuable
upon conversion of the Series C Preferred Stock and the Series D Preferred
Stock.

                  Old Nextlink and the Purchasers have entered it into a Stock
Purchase Agreement (the "Purchase Agreement") dated as of June 14, 2000
pursuant to which simultaneously herewith, the Purchasers are purchasing (i)
an aggregate of 268,750 shares of the Company's Series G Preferred Stock, par
value $0.01 per share (the "Series G Preferred Stock"), and (ii) an aggregate
of 131,250 shares of the Company's Series H Preferred Stock, par value $0.01
per share (the "Series H Preferred Stock" and, collectively with the Series C
Preferred Stock, Series D Preferred Stock and the Series G Preferred Stock,
the "Preferred Shares").

                  The Company is the successor to NEXTLINK Communications,
Inc. ("Old Nextlink"), a Delaware corporation that merged into the Company as
part of the Merger (as defined in the Purchase Agreement).

                  The Company and the Purchasers desire to amend and restate
the Existing Registration Rights Agreement in its entirety to provide for the
rights of the Purchasers with respect to the registration of the shares of
Common Stock issuable upon conversion of the Preferred Shares.

                  Accordingly, as part of, and as consideration for, the
acquisition of the Preferred Shares by the Purchasers from the Company
pursuant to the 1999 Stock Purchase Agreement and on the date hereof and from
time to time hereafter pursuant to the Purchase Agreement, the Company hereby
grants to the Purchasers certain registration

<PAGE>   3

and other rights with respect to its shares of Class A Common Stock as more
fully set forth herein.

                  Accordingly, the parties hereto agree to amend and restate
the Existing Registration Rights Agreement in its entirety as follows:

                  1.       Definitions.  As used herein, unless the context
otherwise requires, the following terms have the following respective
meanings:

                  "Certificate of Incorporation" means the Certificate of
Incorporation of the Company, as it may be amended or restated hereafter from
time to time.

                  "Commission" means the Securities and Exchange Commission or
any other Federal agency at the time administering the Securities Act.

                  "Common Stock" means any shares of Class A Common Stock, par
value $0.01 per share, of the Company, now or hereafter authorized to be
issued, and any and all securities of any kind whatsoever of the Company which
may be exchanged for or converted into Common Stock, any and all securities of
any kind whatsoever of the Company which may be issued on or after the date
hereof in respect of, in exchange for, or upon conversion of shares of Common
Stock pursuant to a merger, consolidation, stock split, stock dividend,
recapitalization of the Company or otherwise.

                  "Exchange Act" means the Securities Exchange Act of 1934, as
amended, or any similar Federal statute, and the rules and regulations of the
Commission thereunder, all as the same shall be in effect at the time.
Reference to a particular section of the Exchange Act shall include a
reference to the comparable section, if any, of any such similar Federal
statute.

                  "Person" means a corporation, an association, a partnership,
an organization, a business, a trust, an individual, or any other entity or
organization, including a government or political subdivision or an
instrumentality or agency thereof.

                  "Registrable Securities" means (i) any shares of Common
Stock issued or issuable upon the conversion of any Preferred Shares held by
the Purchasers and (ii) any shares of Common Stock issued with respect to the
Preferred Shares or the Common Stock referred to in clause (i) by way of a
stock dividend, stock split or reverse stock split or in connection with a
combination of shares, recapitalization, merger, consolidation or otherwise.
As to any particular Registrable Securities, such securities shall cease to be
Registrable Securities (a) when a registration statement with respect to the
sale of such securities shall have become effective under the Securities Act
and such securities shall have been disposed of in accordance with such
registration statement, (b) when such securities shall have been otherwise
transferred, new certificates for them not bearing a

                                    - 2 -

<PAGE>   4

legend restricting further transfer shall have been delivered by the Company
and subsequent public distribution of them shall not require registration of
them under the Securities Act, (c) when such securities are eligible for sale
under Rule 144(k) or any successor provision, or (d) when such securities
shall have been sold as permitted by, and in compliance with, the Securities
Act.

                  "Registration Expenses" means all expenses incident to the
registration and disposition of the Registrable Securities pursuant to Section
2 hereof, including, without limitation, all registration, filing and
applicable national securities exchange fees, all fees and expenses of
complying with state securities or blue sky laws (including fees and
disbursements of counsel to the underwriters or the Purchasers in connection
with "blue sky" qualification of the Registrable Securities and determination
of their eligibility for investment under the laws of the various
jurisdictions), all word processing, duplicating and printing expenses, all
messenger and delivery expenses, the fees and disbursements of counsel for the
Company and of its independent public accountants, including the expenses of
"cold comfort" letters or any special audits required by, or incident to, such
registration, all fees and disbursements of underwriters (other than
underwriting discounts and commissions), all transfer taxes, and all fees and
expenses of counsel to the Purchasers; provided, however, that Registration
Expenses shall exclude, and the Purchasers shall pay, underwriting discounts
and commissions in respect of the Registrable Securities being registered.

                  "Securities Act" means the Securities Act of 1933, as
amended, or any similar Federal statute, and the rules and regulations of the
Commission thereunder, all as the same shall be in effect at the time.
References to a particular section of the Securities Act shall include a
reference to the comparable section, if any, of any such similar Federal
statute.

                  2.       Registration Under Securities Act, etc.

                           2.1      Registration on Request.

                                    (a)      Request.  At any time or from
time to time after the Purchasers are permitted to transfer Registrable
Securities pursuant to Section 4.15 of the 1999 Stock Purchase Agreement or
Section 4.15 of the Purchase Agreement, as the case may be, the Purchasers
shall have the right to require the Company to effect the registration under
the Securities Act of all or part of the Registrable Securities, by delivering
a written request therefor to the Company specifying the number of shares of
Registrable Securities and the intended method of distribution. The Company
shall (i) use its reasonable best efforts to effect the registration under the
Securities Act (including by means of a shelf registration pursuant to Rule
415 under the Securities Act if so requested in such request and if the
Company is then eligible to use such a registration) of the Registrable
Securities which the Company has been so requested to

                                    - 3 -

<PAGE>   5

register by the Purchasers, for distribution in accordance with the intended
method of distribution set forth in the written request delivered by the
Purchasers, such registration to be effected as expeditiously as possible (but
in any event within 90 days of receipt of a written request), and (ii) if
requested by the Purchasers, use its reasonable best efforts to obtain
acceleration of the effective date of the registration statement relating to
such registration.

                                    (b)      Registration of Other Securities.
Whenever the Company shall effect a registration pursuant to this Section 2.1
in connection with an underwritten offering by the Purchasers of Registrable
Securities, no securities other than Registrable Securities shall be included
among the securities covered by such registration if inclusion of such other
securities would result in a request by the managing underwriters for a
reduction in the number of Registrable Securities requested to be so
registered, except (i) as required by the terms of registration rights
agreements in effect on January 20, 2000, (ii) as required by the terms of the
registration rights agreement to be entered into between NM Acquisition Corp.
and Craig O. McCaw, the form of which is attached as Exhibit D to the Merger
Agreement, (iii) as required by the terms of the Warrant Registration Rights
Agreement, dated as of December 18, 1997, by and among the Company (as
successor to Concentric Network Corporation) and certain other parties thereto
and (iv) the Registration Rights Agreement, dated as of April 11, 2000, among
the Company, Stanley Marsh 3 and the other persons party thereto (all such
registration rights agreements, collectively, the "Existing Registration
Rights Agreements"). If such Registrable Securities requested to be included
in a registration pursuant to this Section 2.1, together with other securities
requested to be included in such registration, would result in a request by
the managing underwriters for a reduction in the number of such Registrable
Securities and other securities requested to be so registered, then the
Company will be required to include in such registration only the amount of
Registrable Securities and other securities which it is so advised can be
included in such registration. In such event, securities shall be registered,
subject to the terms of the Existing Registration Rights Agreements, in the
following priority: (A) the Registrable Securities requested by the Purchasers
to be included in such registration statement pursuant to this Section 2.1,
(B) the securities proposed to be included by the Company, and then (C) any
other securities of the Company requested to be included in such registration
by any other holder having the right to include securities on a pro rata basis
in accordance with the number of securities proposed to be included by the
other stockholders with such rights.

                                    (c)      Registration Statement Form.
Registrations under this Section 2.1 shall be on such appropriate registration
form of the Commission as, subject to clause (a)(i) above, shall be selected
by the Company and as shall be reasonably acceptable to the Purchasers. The
Company agrees to include in any such registration statement all information
which, in the opinion of counsel to the Purchasers and counsel to the Company,
is necessary or desirable to be included therein.

                                    - 4 -

<PAGE>   6

                                    (d)      Expenses.  The Company shall pay
all Registration Expenses in connection with any registration requested
pursuant to this Section 2.1.

                                    (e)      Effective Registration Statement.
A registration requested pursuant to this Section 2.1 shall not be deemed to
have been effected (including for purposes of paragraph (h) of this Section
2.1) (i) unless a registration statement with respect thereto has become
effective and has been kept continuously effective for a period of at least
365 days (or such shorter period which shall terminate when all the
Registrable Securities covered by such registration statement have been sold
pursuant thereto), (ii) if after it has become effective, such registration is
interfered with by any stop order, injunction or other order or requirement of
the Commission or other governmental agency or court for any reason not
attributable to the Purchasers and has not thereafter become effective, or
(iii) if the conditions to closing specified in the underwriting agreement, if
any, entered into in connection with such registration are not satisfied or
waived.

                                    (f)      Selection of Underwriters.  The
underwriters of each underwritten offering of the Registrable Securities so to
be registered shall be selected by the Purchasers, subject to the Company's
approval, which approval shall not be unreasonably withheld.

                                    (g)      Right to Withdraw.  If the
managing underwriter of any underwritten offering shall advise the Purchasers
that the Registrable Securities covered by the registration statement cannot
be sold in such offering within a price range acceptable to the Purchasers,
then the Purchasers shall have the right to notify the Company in writing that
they have determined that the registration statement be abandoned or
withdrawn, in which event the Company shall abandon or withdraw such
registration statement. In the event of such abandonment or withdrawal, such
request shall not be counted for purposes of the requests for registration to
which the Purchasers are entitled pursuant to this Section 2.1, and the
Purchasers shall pay, or reimburse the Company for, all Registration Expenses
related thereto.

                                    (h)      Limitations on Registration on
Request. The Purchasers shall be entitled to require the Company to effect,
and the Company shall be required to effect, five registrations in the
aggregate pursuant to this Section 2.1.

                                    (i)      Postponement.  The Company shall
be entitled once in any six-month period to postpone for a reasonable period
of time (but not exceeding 60 days) (the "Postponement Period") the filing of
any registration statement required to be prepared and filed by it pursuant to
this Section 2.1 if the Company determines, in its reasonable judgment, that
such registration and offering would materially interfere with any material
financing, corporate reorganization or other material transaction involving
the Company or any subsidiary, or would require premature disclosure thereof,
and

                                    - 5 -

<PAGE>   7

promptly gives the Purchasers written notice of such determination, containing
a general statement of the reasons for such postponement (which the Purchasers
shall maintain in strict confidence in accordance with the Confidentiality
Agreement (as defined in the Purchase Agreement)) and an approximation of the
anticipated delay. If the Company shall so postpone the filing of a
registration statement, (i) the Company shall use its reasonable best efforts
to limit the delay to as short a period as is practicable and (ii) the
Purchasers shall have the right to withdraw the request for registration by
giving written notice to the Company at any time and, in the event of such
withdrawal, such request shall not be counted for purposes of the requests for
registration to which the Purchasers are entitled pursuant to this Section
2.1.

                                    (j)      Shelf Registration.  If the
Purchasers request that the Company effect a registration of Registrable
Securities by means of shelf registration pursuant to Rule 415 under the
Securities Act (a "Shelf Registration Statement"), in addition to the other
requirements contained herein, the Company shall, at its cost, use its
reasonable best efforts to keep the Shelf Registration Statement continuously
effective in order to permit the Prospectus forming part thereof to be usable
by the Purchasers until such time as all the Registrable Securities covered by
the Shelf Registration Statement have been sold pursuant to the Shelf
Registration Statement or cease to be outstanding (the "Effectiveness
Period"); provided, however, that the Effectiveness Period in respect of the
Shelf Registration Statement shall be extended to the extent required to
permit dealers to comply with the applicable prospectus delivery requirements
under the Securities Act and as otherwise provided herein.

                           2.2      Incidental Registration.

                                    (a)      Right to Include Registrable
Securities. If the Company at any time proposes to register any of its
securities for the account of any other stockholder under the Securities Act
by registration on Form S-1, S-2 or S-3 or any successor or similar form(s)
(except registrations on any such Form or similar form(s) solely for
registration of securities in connection with an employee benefit plan or
dividend reinvestment plan or a merger or consolidation or incidental to an
issuance of securities under Rule 144A under the Securities Act), it will each
such time give prompt written notice to the Purchasers of its intention to do
so and of the Purchasers' rights under this Section 2.2. At any time or from
time to time after the Purchasers are permitted to transfer Registrable
Securities pursuant to Section 4.15 of the 1999 Stock Purchase Agreement or
Section 4.15 of the Purchase Agreement, upon the written request of the
Purchasers (which request shall specify the maximum number of Registrable
Securities intended to be disposed of by the Purchasers), made as promptly as
practicable and in any event within 30 days after the receipt of any such
notice (10 days if the Company states in such written notice or gives
telephonic notice to the Purchasers, with written confirmation to follow
promptly thereafter, stating that (i) such registration will

                                    - 6 -

<PAGE>   8

be on Form S-3 and (ii) such shorter period of time is required because of a
planned filing date), the Company shall use its reasonable best efforts to
effect the registration under the Securities Act of all Registrable Securities
which the Company has been so requested to register by the Purchasers;
provided, however, that if, at any time after giving written notice of its
intention to register any securities and prior to the effective date of the
registration statement filed in connection with such registration, the Company
shall determine for any reason not to register or to delay registration of
such securities, the Company shall give written notice of such determination
and its reasons therefor (which the Purchasers will hold in strict confidence
in accordance with the Confidentiality Agreement) to the Purchasers and (i) in
the case of a determination not to register, shall be relieved of its
obligation to register any Registrable Securities in connection with such
registration (but not from any obligation of the Company to pay the
Registration Expenses in connection therewith), without prejudice, however, to
the rights of the Purchasers to request that such registration be effected as
a registration under Section 2.1 and (ii) in the case of a determination to
delay registering, shall be permitted to delay registering any Registrable
Securities, for the same period as the delay in registering such other
securities. No registration effected under this Section 2.2 shall relieve the
Company of its obligation to effect any registration upon request under
Section 2.1. The Company will pay all Registration Expenses in connection with
any registration of Registrable Securities requested pursuant to this Section
2.2.

                                    (b)      Right to Withdraw.  The
Purchasers shall have the right to withdraw its request for inclusion of its
Registrable Securities in any registration statement pursuant to this Section
2.2 at any time prior to the execution of an underwriting agreement with
respect thereto by giving written notice to the Company of its request to
withdraw.

                                    (c)      Priority in Incidental
Registrations.  If the managing underwriter of any underwritten offering shall
inform the Company by letter of its belief that the number of Registrable
Securities requested to be included in such registration, when added to the
number of other securities to be offered in such registration, would
materially adversely affect such offering, then the Company shall include in
such registration, to the extent of the number and type which the Company is
so advised can be sold in (or during the time of) such offering without so
materially adversely affecting such offering (the "Section 2.2 Sale Amount")
and to the fullest extent permitted by the terms of the Existing Registration
Rights Agreements, in the following priority: (I) securities proposed to be
included by the Company, (II) on a pro rata basis in accordance with the
number of securities proposed to be included by the stockholders, if any,
triggering such incidental registration, the securities proposed by such
stockholders triggering such incidental registration, and then (III) the
Registrable Securities requested by the Purchasers to be included in such
registration pursuant to Section 2.2(a) and any other securities of the
Company requested to be included in such registration by any other

                                    - 7 -

<PAGE>   9

holder having the right to include securities on a pro rata basis (in an
amount in the aggregate equal to the Section 2.2 Sale Amount), based on the
pro rata amount of shares of Common Stock held, or obtainable by exercise or
conversion of other securities of the Company, by the Purchasers or such
holder.

                                    (d)      Plan of Distribution.  Any
participation by holders of Registrable Securities in a registration by the
Company shall be in accordance with the Company's plan of distribution,
provided that the Purchasers shall in consultation with the Company have the
right to select a co-managing underwriter.

                           2.3      Registration Procedures.  If and whenever
the Company is required to use its reasonable best efforts to effect the
registration of any Registrable Securities under the Securities Act as
provided in Sections 2.1 and 2.2 hereof, the Company shall as expeditiously as
possible:

                           (a)      prepare and file with the Commission as
         soon as practicable the requisite registration statement to effect
         such registration (and shall include all financial statements
         required by the Commission to be filed therewith) and thereafter use
         its reasonable best efforts to cause such registration statement to
         become effective; provided, however, that before filing such
         registration statement (including all exhibits) or any amendment or
         supplement thereto or comparable statements under securities or blue
         sky laws of any jurisdiction, the Company shall as promptly as
         practicable furnish such documents to the Purchasers and each
         underwriter, if any, participating in the offering of the Registrable
         Securities and their respective counsel, which documents will be
         subject to the review and comments of the Purchasers, each
         underwriter and their respective counsel; and provided, further,
         however, that the Company may discontinue any registration of its
         securities which are not Registrable Securities at any time prior to
         the effective date of the registration statement relating thereto;

                           (b)      notify the Purchasers of the Commission's
         requests for amending or supplementing the registration statement and
         the prospectus, and prepare and file with the Commission such
         amendments and supplements to such registration statement and the
         prospectus used in connection therewith as may be necessary to keep
         such registration statement effective and to comply with the
         provisions of the Securities Act with respect to the disposition of
         all Registrable Securities covered by such registration statement for
         such period as shall be required for the disposition of all of such
         Registrable Securities in accordance with the intended method of
         distribution thereof; provided, that except with respect to any such
         registration statement filed pursuant to Rule 415 under the
         Securities Act, such period need not exceed 365 days;

                                    - 8 -

<PAGE>   10

                           (c)      furnish, without charge, to the Purchasers
         and each underwriter such number of conformed copies of such
         registration statement and of each such amendment and supplement
         thereto (in each case including all exhibits), such number of copies
         of the prospectus contained in such registration statement (including
         each preliminary prospectus and any summary prospectus) and any other
         prospectus filed under Rule 424 under the Securities Act, in
         conformity with the requirements of the Securities Act, and such
         other documents, as the Purchasers and such underwriters may
         reasonably request;

                           (d)      use its reasonable best efforts (i) to
         register or qualify all Registrable Securities and other securities
         covered by such registration statement under such securities or blue
         sky laws of such States of the United States of America where an
         exemption is not available and as the Purchasers or any managing
         underwriter shall reasonably request, (ii) to keep such registration
         or qualification in effect for so long as such registration statement
         remains in effect, and (iii) to take any other action which may be
         reasonably necessary or advisable to enable the Purchasers to
         consummate the disposition in such jurisdictions of the securities to
         be sold by the Purchasers, except that the Company shall not for any
         such purpose be required to qualify generally to do business as a
         foreign corporation in any jurisdiction wherein it would not but for
         the requirements of this subsection (d) be obligated to be so
         qualified or to consent to general service of process in any such
         jurisdiction;

                           (e)      use its reasonable best efforts to cause
         all Registrable Securities covered by such registration statement to
         be registered with or approved by such other federal or state
         governmental agencies or authorities as may be necessary in the
         opinion of counsel to the Company and counsel to the Purchasers to
         consummate the disposition of such Registrable Securities;

                           (f)      furnish to the Purchasers and each
         underwriter, if any, participating in the offering of the securities
         covered by such registration statement, a signed counterpart of (i)
         an opinion of counsel for the Company, and (ii) a "comfort" letter
         signed by the independent public accountants who have certified the
         Company's or any other entity's financial statements included or
         incorporated by reference in such registration statement, covering
         substantially the same matters with respect to such registration
         statement (and the prospectus included therein) and, in the case of
         the accountants' comfort letter, with respect to events subsequent to
         the date of such financial statements, as are customarily covered in
         opinions of issuer's counsel and in accountants' comfort letters
         delivered to the

                                    - 9 -

<PAGE>   11

         underwriters in underwritten public offerings of securities (and
         dated the dates such opinions and comfort letters are customarily
         dated) and, in the case of the legal opinion, such other legal
         matters;

                           (g)      promptly notify the Purchasers and each
         managing underwriter, if any, participating in the offering of the
         securities covered by such registration statement (i) when such
         registration statement, any pre-effective amendment, the prospectus
         or any prospectus supplement related thereto or post-effective
         amendment to such registration statement has been filed, and, with
         respect to such registration statement or any post-effective
         amendment, when the same has become effective; (ii) of any request by
         the Commission for amendments or supplements to such registration
         statement or the prospectus related thereto or for additional
         information; (iii) of the issuance by the Commission of any stop
         order suspending the effectiveness of such registration statement or
         the initiation of any proceedings for that purpose; (iv) of the
         receipt by the Company of any notification with respect to the
         suspension of the qualification of any of the Registrable Securities
         for sale under the securities or blue sky laws of any jurisdiction or
         the initiation of any proceeding for such purpose; (v) at any time
         when a prospectus relating thereto is required to be delivered under
         the Securities Act, upon discovery that, or upon the happening of any
         event as a result of which, the prospectus included in such
         registration statement, as then in effect, includes an untrue
         statement of a material fact or omits to state any material fact
         required to be stated therein or necessary to make the statements
         therein not misleading, in the light of the circumstances under which
         they were made, and in the case of this clause (v), at the request of
         the Purchasers promptly prepare and furnish to the Purchasers and
         each managing underwriter, if any, participating in the offering of
         the Registrable Securities, a reasonable number of copies of a
         supplement to or an amendment of such prospectus as may be necessary
         so that, as thereafter delivered to the purchasers of such
         securities, such prospectus shall not include an untrue statement of
         a material fact or omit to state a material fact required to be
         stated therein or necessary to make the statements therein not
         misleading in the light of the circumstances under which they were
         made; and (vi) at any time when the representations and warranties of
         the Company contemplated by Section 2.4(a) or (b) hereof cease to be
         true and correct;

                           (h)      otherwise comply with all applicable rules
         and regulations of the Commission, and make available to its security
         holders, as soon as reasonably practicable, an earnings statement
         covering the period of at least twelve months beginning with the
         first full calendar month after the effective date of such
         registration statement, which earnings statement shall

                                    - 10 -

<PAGE>   12

         satisfy the provisions of Section 11(a) of the Securities Act and
         Rule 158 promulgated thereunder, and promptly furnish to the
         Purchasers a copy of any amendment or supplement to such registration
         statement or prospectus;

                           (i)      provide and cause to be maintained a
         transfer agent and registrar (which, in each case, may be the
         Company) for all Registrable Securities covered by such registration
         statement from and after a date not later than the effective date of
         such registration;

                           (j)      (i) use its reasonable best efforts to
         cause all Registrable Securities covered by such registration
         statement to be listed on the NASDAQ "national market system" or the
         principal securities exchange on which similar securities issued by
         the Company are then listed (if any), if the listing of such
         Registrable Securities is then permitted under the rules of such
         exchange, or (ii) if no similar securities are then so listed, use
         its reasonable best efforts to (x) cause all such Registrable
         Securities to be listed on a national securities exchange or (y)
         failing that, secure designation of all such Registrable Securities
         as a NASDAQ "national market system security" within the meaning of
         Rule 11Aa2-1 of the Commission or (z) failing that, to secure NASDAQ
         authorization for such shares and, without limiting the generality of
         the foregoing, to arrange for at least two market makers to register
         as such with respect to such shares with the National Association of
         Securities Dealers, Inc.;

                           (k)      deliver promptly to counsel to the
         Purchasers and each underwriter, if any, participating in the
         offering of the Registrable Securities, copies of all correspondence
         between the Commission and the Company, its counsel or auditors and
         all memoranda relating to discussions with the Commission or its
         staff with respect to such registration statement;

                           (l)      use its reasonable best efforts to obtain
         the withdrawal of any order suspending the effectiveness of the
         registration statement;

                           (m)      provide a CUSIP number for all Registrable
         Securities, no later than the effective date of the registration
         statement; and

                           (n)      in connection with any underwritten public
         offering, make available its senior executive officers, directors and
         chairman and otherwise provide reasonable assistance to the
         underwriters (taking into account the needs of the Company's
         business) in their marketing of Registrable Securities.

                                    - 11 -

<PAGE>   13

The Company may require the Purchasers to furnish the Company such information
regarding the Purchasers and the distribution of the Registrable Securities as
the Company may from time to time reasonably request in writing.

                  The Purchasers agree that upon receipt of any notice from
the Company of the happening of any event of the kind described in paragraph
(g)(iii) or (v) of this Section 2.3, the Purchasers will, to the extent
appropriate, discontinue their disposition of Registrable Securities pursuant
to the registration statement relating to such Registrable Securities until,
in the case of paragraph (g)(v) of this Section 2.3, their receipt of the
copies of the supplemented or amended prospectus contemplated by paragraph
(g)(v) of this Section 2.3 and, if so directed by the Company, will deliver to
the Company (at the Company's expense) all copies, other than permanent file
copies, then in their possession, of the prospectus relating to such
Registrable Securities current at the time of receipt of such notice. If the
disposition by the Purchasers of their securities is discontinued pursuant to
the foregoing sentence, the Company shall extend the period of effectiveness
of the registration statement by the number of days during the period from and
including the date of the giving of notice to and including the date when the
Purchasers shall have received copies of the supplemented or amended
prospectus contemplated by paragraph (g)(v) of this Section 2.3; and, if the
Company shall not so extend such period, the Purchasers' request pursuant to
which such registration statement was filed shall not be counted for purposes
of the requests for registration to which the Purchasers are entitled pursuant
to Section 2.1 hereof.

                           2.4      Underwritten Offerings.

                                    (a)      Requested Underwritten Offerings.
If requested by the underwriters for any underwritten offering by the
Purchasers pursuant to a registration requested under Section 2.1, the Company
shall enter into a customary underwriting agreement (in the form of
underwriting agreement used at such time by the managing underwriter(s)) with
a managing underwriter or underwriters selected by the Purchasers. Such
underwriting agreement shall be satisfactory in form and substance to the
Purchasers and shall contain such representations and warranties by, and such
other agreements on the part of, the Company and such other terms as are
generally prevailing in agreements of the managing underwriter(s), including,
without limitation, their customary provisions relating to indemnification and
contribution. The Purchasers shall be party to such underwriting agreement and
may, at their option, require that any or all of the representations and
warranties by, and the other agreements on the part of, the Company to and for
the benefit of such underwriters shall also be made to and for the benefit of
the Purchasers and that any or all of the conditions precedent to the
obligations of such underwriters under such underwriting agreement be
conditions precedent to the obligations of the Purchasers.

                                    - 12 -

<PAGE>   14

                                    (b)      Incidental Underwritten
Offerings.  In the case of a registration pursuant to Section 2.2 hereof, if
the Company shall have determined to enter into any underwriting agreements in
connection therewith, all of the Registrable Securities to be included in such
registration shall be subject to such underwriting agreements. The Purchasers
shall be party to such underwriting agreement and may, at their option,
require that any or all of the representations and warranties by, and the
other agreements on the part of, the Company to and for the benefit of such
underwriters shall also be made to and for the benefit of the Purchasers and
that any or all of the conditions precedent to the obligations of such
underwriters under such underwriting agreement be conditions precedent to the
obligations of the Purchasers.

                           2.5      Preparation; Reasonable Investigation.  In
connection with the preparation and filing of each registration statement
under the Securities Act pursuant to this Agreement, the Company will give the
Purchasers, their underwriters, if any, and their respective counsel,
accountants and other representatives and agents the opportunity to
participate in the preparation of such registration statement, each prospectus
included therein or filed with the Commission, and each amendment thereof or
supplement thereto, and give each of them such access to its books and records
and such opportunities to discuss the business of the Company with its
officers and employees and the independent public accountants who have
certified its financial statements, and supply all other information
reasonably requested by each of them, as shall be necessary or appropriate, in
the opinion of the Purchasers and such underwriters' respective counsel, to
conduct a reasonable investigation within the meaning of the Securities Act.

                           2.6      Indemnification.

                                    (a)      Indemnification by the Company.
The Company agrees that in the event of any registration of any securities of
the Company under the Securities Act, the Company shall, and hereby does,
indemnify and hold harmless the Purchasers, their respective directors,
officers, members, partners, agents and affiliates and each other Person who
participates as an underwriter in the offering or sale of such securities and
each other Person, if any, who controls the Purchasers or any such underwriter
within the meaning of the Securities Act, against any losses, claims, damages,
or liabilities, joint or several, to which the Purchasers or any such
director, officer, member, partner, agent or affiliate or underwriter or
controlling person may become subject under the Securities Act or otherwise,
insofar as such losses, claims, damages or liabilities, joint or several (or
actions or proceedings, whether commenced or threatened, in respect thereof),
arise out of or are based upon (i) any untrue statement or alleged untrue
statement of any material fact contained in any registration statement under
which such securities were registered under the Securities Act, any
preliminary prospectus, final prospectus or summary prospectus contained
therein, or any amendment or supplement thereto, (ii) any omission or alleged
omission to state therein a material fact required to be stated therein or
necessary to make

                                    - 13 -

<PAGE>   15

the statements therein in light of the circumstances in which they were made
not misleading, or (iii) any violation by the Company of any federal, state or
common law rule or regulation applicable to the Company and relating to action
required of or inaction by the Company in connection with any such
registration, and the Company shall reimburse the Purchasers and each such
director, officer, member, partner, agent or affiliate, underwriter and
controlling Person for any legal or any other expenses reasonably incurred by
them in connection with investigating or defending any such loss, claim,
liability, action or proceeding; provided that the Company shall not be liable
in any such case to the Purchasers or any such director, officer, member,
partner, agent, affiliate, or controlling person to the extent that any such
loss, claim, damage, liability (or action or proceeding in respect thereof) or
expense arises out of or is based upon an untrue statement or alleged untrue
statement or omission or alleged omission made in such registration statement,
any such preliminary prospectus, final prospectus, summary prospectus,
amendment or supplement in reliance upon and in conformity with written
information furnished to the Company by or on behalf of the Purchasers,
specifically stating that it is for use in the preparation thereof. Such
indemnity shall remain in full force regardless of any investigation made by
or on behalf of the Purchasers or any such director, officer, member, partner,
agent, affiliate, underwriter or controlling Person and shall survive the
transfer of such securities by the Purchasers.

                                    (b)      Indemnification by the
Purchasers.  As a condition to including any Registrable Securities in any
registration statement, the Company shall have received an undertaking
reasonably satisfactory to it from the Purchasers so including any Registrable
Securities to indemnify and hold harmless (in the same manner and to the same
extent as set forth in paragraph (a) of this Section 2.6) the Company, and
each director of the Company, each officer of the Company and each other
Person, if any, who controls the Company within the meaning of the Securities
Act, with respect to any statement or alleged statement in or omission or
alleged omission from such registration statement, any preliminary prospectus,
final prospectus or summary prospectus contained therein, or any amendment or
supplement thereto, but only to the extent such statement or alleged statement
or omission or alleged omission was made in reliance upon and in conformity
with written information furnished to the Company by or on behalf of the
Purchasers specifically stating that it is for use in the preparation of such
registration statement, preliminary prospectus, final prospectus, summary
prospectus, amendment or supplement; provided, however, that the liability of
such indemnifying party under this Section 2.6(b) shall be limited to the
amount of proceeds (net of expenses and underwriting discounts and
commissions) received by such indemnifying party in the offering giving rise
to such liability. Such indemnity shall remain in full force and effect,
regardless of any investigation made by or on behalf of the Company or any
such director, officer or controlling Person and shall survive the transfer of
such securities by the Purchasers.

                                    - 14 -

<PAGE>   16

                                    (c)      Notices of Claims, etc.  Promptly
after receipt by an indemnified party of notice of the commencement of any
action or proceeding involving a claim referred to in the preceding
subsections of this Section 2.6, such indemnified party shall, if a claim in
respect thereof is to be made against an indemnifying party, give written
notice to the latter of the commencement of such action or proceeding;
provided, however, that the failure of any indemnified party to give notice as
provided herein shall not relieve the indemnifying party of its obligations
under the preceding subsections of this Section 2.6, except to the extent that
the indemnifying party is actually prejudiced by such failure to give notice,
and shall not relieve the indemnifying party from any liability which it may
have to the indemnified party otherwise than under this Section 2.6. In case
any such action or proceeding is brought against an indemnified party, the
indemnifying party shall be entitled to participate therein and, unless in the
opinion of outside counsel to the indemnified party a conflict of interest
between such indemnified and indemnifying parties may exist in respect of such
claim, to assume the defense thereof, jointly with any other indemnifying
party similarly notified to the extent that it may wish, with counsel
reasonably satisfactory to such indemnified party; provided, however, that if
the defendants in any such action or proceeding include both the indemnified
party and the indemnifying party and if in the opinion of outside counsel to
the indemnified party there may be legal defenses available to such
indemnified party and/or other indemnified parties which are different from or
in addition to those available to the indemnifying party, the indemnified
party or parties shall have the right to select separate counsel to defend
such action or proceeding on behalf of such indemnified party or parties,
provided, however, that the indemnifying party shall be obligated to pay for
only one counsel and one local counsel for all indemnified parties. After
notice from the indemnifying party to such indemnified party of its election
so to assume the defense thereof and approval by the indemnified party of such
counsel, the indemnifying party shall not be liable to such indemnified party
for any legal expenses subsequently incurred by the latter in connection with
the defense thereof other than reasonable costs of investigation (unless the
first proviso in the preceding sentence shall be applicable). No indemnifying
party shall be liable for any settlement of any action or proceeding effected
without its written consent. No indemnifying party shall, without the consent
of the indemnified party (which consent shall not be unreasonably withheld or
delayed), consent to entry of any judgment or enter into any settlement which
does not include as an unconditional term thereof the giving by the claimant
or plaintiff to such indemnified party of a release from all liability in
respect to such claim or litigation.

                                    (d)      Contribution.  If the
indemnification provided for in this Section 2.6 shall for any reason be held
by a court to be unavailable to an indemnified party under subsection (a) or
(b) hereof in respect of any loss, claim, damage or liability, or any action
in respect thereof, then, in lieu of the amount paid or payable under
subsection (a) or (b) hereof, the indemnified party and the indemnifying party
under subsection (a) or (b) hereof shall contribute to the aggregate losses,
claims, damages and

                                    - 15 -

<PAGE>   17

liabilities (including legal or other expenses reasonably incurred in
connection with investigating the same), (i) in such proportion as is
appropriate to reflect the relative fault of the indemnifying party on the one
hand, and the indemnified party on the other, which resulted in such loss,
claim, damage or liability, or action in respect thereof, with respect to the
statements or omissions which resulted in such loss, claim, damage or
liability, or action in respect thereof, as well as any other relevant
equitable considerations, or (ii) if the allocation provided by clause (i)
above is not permitted by applicable law or if the allocation provided in this
clause (ii) provides a greater amount to the indemnified party than clause (i)
above, in such proportion as shall be appropriate to reflect not only the
relative fault but also the relative benefits received by the indemnifying
party and the indemnified party from the offering of the securities covered by
such registration statement as well as any other relevant equitable
considerations. The parties hereto agree that it would not be just and
equitable if contributions pursuant to this Section 2.6(d) were to be
determined by pro rata allocation or by any other method of allocation which
does not take into account the equitable considerations referred to in the
preceding sentence of this Section 2.6(d). No Person guilty of fraudulent
misrepresentation (within the meaning of Section 11(f) of the Securities Act)
shall be entitled to contribution from any Person who was not guilty of such
fraudulent misrepresentation. In addition, no Person shall be obligated to
contribute hereunder any amounts in payment for any settlement of any action
or claim effected without such Person's consent, which consent shall not be
unreasonably withheld. Notwithstanding anything in this subsection (d) to the
contrary, no indemnifying party (other than the Company) shall be required to
contribute any amount in excess of the proceeds (net of expenses and
underwriting discounts and commissions) received by such party from the sale
of the Registrable Securities in the offering to which the losses, claims,
damages or liabilities of the indemnified parties relate.

                                    (e)      Other Indemnification.
Indemnification and contribution similar to that specified in the preceding
subsections of this Section 2.6 (with appropriate modifications) shall be
given by the Company and the Purchasers with respect to any required
registration or other qualification of securities under any federal, state or
blue sky law or regulation of any governmental authority other than the
Securities Act. The indemnification agreements contained in this Section 2.6
shall be in addition to any other rights to indemnification or contribution
which any indemnified party may have pursuant to law or contract and shall
remain operative and in full force and effect regardless of any investigation
made by or on behalf of any indemnified party and shall survive the transfer
of any of the Registrable Securities by the Purchasers.

                                    (f)      Indemnification Payments.  The
indemnification and contribution required by this Section 2.6 shall be made by
periodic payments of the amount thereof during the course of the investigation
or defense, as and when bills are received or expense, loss, damage or
liability is incurred.

                                    - 16 -

<PAGE>   18

                           2.7      Unlegended Certificates.  In connection
with the offering of any Registrable Securities registered pursuant to this
Section 2, the Company shall (i) facilitate the timely preparation and
delivery to the Purchasers and the underwriters, if any, participating in such
offering, of unlegended certificates representing ownership of such
Registrable Securities being sold in such denominations and registered in such
names as requested by the Purchasers or such underwriters and (ii) instruct
any transfer agent and registrar of such Registrable Securities to release any
stop transfer orders with respect to any such Registrable Securities.

                           2.8      Manner of Sale.  So long as the Purchasers
own in excess of 2.5% of the fully diluted Common Stock (after giving effect
to the exercise of all outstanding options, warrants and other rights to
purchase Common Stock whether or not such options, warrants or other rights
are then exercisable (the "Threshold Amount")), the Purchasers agree that,
except as provided below or except with the written consent of the Company
(which consent shall not be unreasonably withheld), the Purchasers shall sell
or otherwise effectuate a distribution of Registrable Securities included in a
registration effected pursuant to Section 2.1 or in a registration effected by
the Company for its own account in which the Purchasers elect, pursuant to
Section 2.2, to include Registrable Securities, only (i) pursuant to one or
more firm commitment underwritten public offerings or (ii) in one or more
block trades. Notwithstanding anything to the contrary set forth above, at any
time while the Purchasers own an amount of Common Stock in excess of the
Threshold Amount, the Purchasers shall have the right to effectuate a
distribution of Registrable Securities included in a registration effected
pursuant to Section 2.1 or in a registration effected by the Company for its
own account in which the Purchasers elect, pursuant to Section 2.2, to include
Registrable Securities, in any other manner, including pursuant to a Shelf
Registration Statement, if in the opinion of a nationally recognized
investment banker selected by the Company and the Purchasers, distributions of
Registrable Securities made in the manner proposed by the Purchasers would not
adversely affect the market for the Common Stock. Nothing contained herein
shall be deemed to restrict the Purchasers from transferring any of the Common
Stock at any time in accordance with the terms of the Purchase Agreement. In
the event the Purchasers elect, pursuant to Section 2.2, to include
Registrable Securities in any registration effected by the Company for the
account of any other stockholder triggering such registration, the Purchasers
shall sell or otherwise effectuate a distribution of Registrable Securities
pursuant to such registration subject to the same manner of sale limitations
as are applicable to such other stockholder in such registration.

                           2.9      No Required Sale.  Nothing in this
Agreement shall be deemed to create an independent obligation on the part of
the Purchasers to sell any Registrable Securities pursuant to any effective
registration statement.

                                    - 17 -

<PAGE>   19

                  3.       Rule 144. The Company shall take all actions
reasonably necessary to enable holders of Registrable Securities to sell such
securities without registration under the Securities Act within the limitation
of the exemptions provided by (i) Rule 144, or (ii) any similar rule or
regulation hereafter adopted by the Commission including, without limiting the
generality of the foregoing, filing on a timely basis all reports required to
be filed by the Exchange Act. Upon the request of the Purchasers, the Company
will deliver to such holder a written statement as to whether it has complied
with such requirements.

                  4.       Amendments and Waivers.  This Agreement may be
amended, modified or supplemented only by written agreement of the party
against whom enforcement of such amendment, modification or supplement is
sought.

                  5.       [INTENTIONALLY OMITTED].

                  6.       Notice. All notices and other communications
hereunder shall be in writing and, unless otherwise provided herein, shall be
deemed to have been given when received by the party to whom such notice is to
be given at its address set forth below, or such other address for the party
as shall be specified by notice given pursuant hereto:

                  (a)      If to the Purchasers, to:

                           c/o Forstmann Little & Co.
                           767 Fifth Avenue
                           New York, NY  10153
                           Attention:  Sandra J. Horbach

                           With a copy to:

                           Fried, Frank, Harris, Shriver & Jacobson
                           One New York Plaza
                           New York, New York  10004
                           Attention:    Robert C. Schwenkel, Esq.

                  (b)      If to the Company, to it at:

                           NEXTLINK Communications, Inc.
                           1505 Farm Credit Drive
                           McLean, VA  22102
                           Attn:  Gary D. Begeman, Esq.

                           with a copy to:

                                    - 18 -

<PAGE>   20

                           Willkie Farr & Gallagher
                           787 Seventh Avenue
                           New York, NY  10019
                           Attn:  Bruce R. Kraus, Esq.

                  7.       Assignment; Third Party Beneficiaries. This
Agreement shall be binding upon and inure to the benefit of and be enforceable
by the parties hereto and their respective successors and permitted assigns.
This Agreement may not be assigned by the Company, without the prior written
consent of the Purchasers. The Purchasers may, at their election, at any time
or from time to time, assign their rights under this Agreement, in whole or in
part, to any purchaser or other transferee of shares of Common Stock held by
them; provided, however, that any rights to withdraw shares from inclusion in
a registration statement pursuant to Section 2 shall be made only by the
Purchasers for themselves and all such purchasers and transferees; and
provided further, that no such assignment will increase the total number of
registrations pursuant to Section 2.1 or underwritten offerings the Company is
required to effect hereunder.

                  8.       Remedies. The parties hereto agree that money
damages or other remedy at law would not be sufficient or adequate remedy for
any breach or violation of, or a default under, this Agreement by them and
that, in addition to all other remedies available to them, each of them shall
be entitled to an injunction restraining such breach, violation or default or
threatened breach, violation or default and to any other equitable relief,
including without limitation specific performance, without bond or other
security being required. In any action or proceeding brought to enforce any
provision of this Agreement (including the indemnification provisions
thereof), the successful party shall be entitled to recover reasonable
attorneys' fees in addition to its costs and expenses and any other available
remedy.

                  9.       No Inconsistent Agreements. The Company will not,
on or after the date of this Agreement, enter into any agreement with respect
to its securities which is inconsistent with the rights granted to the
Purchasers in this Agreement or otherwise conflicts with the provisions
hereof. The Company further represents and warrants that the rights granted to
the Purchasers hereunder do not in any way conflict with and are not
inconsistent with any other agreements to which the Company is a party or by
which it is bound.

                  10.      Descriptive Headings.  The descriptive headings of
the several sections and paragraphs of this Agreement are inserted for
reference only and shall not control or otherwise affect the meaning hereof.

                  11.      Governing Law. This Agreement shall be construed
and enforced in accordance with, and the rights and obligations of the parties
hereto shall be governed by, the laws of the State of New York, without giving
effect to the conflicts of law principles

                                    - 19 -

<PAGE>   21

thereof. Each of the parties hereto hereby irrevocably and unconditionally
consents to submit to the exclusive jurisdiction of the courts of the State of
New York and the United States of America located in the County of New York
for any action or proceeding arising out of or relating to this Agreement and
the transactions contemplated hereby (and agrees not to commence any action or
proceeding relating thereto except in such courts), and further agrees that
service of any process, summons, notice or document by U.S. registered mail to
its respective address set forth in Section 6 hereof shall be effective
service of process for any action or proceeding brought against it in any such
court. Each of the parties hereto hereby irrevocably and unconditionally
waives any objection to the laying of venue of any action or proceeding
arising out of this Agreement or the transactions contemplated hereby in the
courts of the State of New York or the United States of America located in the
County of New York, and hereby further irrevocably and unconditionally waives
and agrees not to plead or claim in any such court that any such action or
proceeding brought in any such court has been brought in an inconvenient
forum.

                  12.      Counterparts.  This Agreement may be executed in
any number of counterparts, each of which shall be deemed an original, but all
such counterparts shall together constitute one and the same instrument.

                  13.      Invalidity of Provision. The invalidity or
unenforceability of any provision of this Agreement in any jurisdiction shall
not affect the validity or enforceability of the remainder of this Agreement
in that jurisdiction or the validity or enforceability of this Agreement,
including that provision, in any other jurisdiction. If any restriction or
provision of this Agreement is held unreasonable, unlawful or unenforceable in
any respect, such restriction or provision shall be interpreted, revised or
applied in a manner that renders it lawful and enforceable to the fullest
extent possible under law.

                  14.      Further Assurances. Each party hereto shall do and
perform or cause to be done and performed all further acts and things and
shall execute and deliver all other agreements, certificates, instruments, and
documents as any other party hereto reasonably may request in order to carry
out the intent and accomplish the purposes of this Agreement and the
consummation of the transactions contemplated hereby.

                  15.      Entire Agreement; Effectiveness. This Agreement
constitutes the entire agreement, and supersedes all prior agreements and
understandings (including, without limitation, the Existing Registration
Rights Agreement), oral and written, between the parties hereto with respect
to the subject matter hereof.

                                    - 20 -

<PAGE>   22

                  IN WITNESS WHEREOF, the parties have caused this Agreement
to be executed and delivered by their respective officers thereunto duly
authorized.

                                  NEXTLINK COMMUNICATIONS, INC.

                                  By:     /s/ Daniel F. Akerson
                                          --------------------------------------
                                          Name:     Daniel F. Akerson
                                          Title:    Chairman and Chief Executive
                                                    Officer

                                  PURCHASERS:

                                  FORSTMANN LITTLE & CO. SUBORDINATED
                                  DEBT AND EQUITY MANAGEMENT BUYOUT
                                  PARTNERSHIP-VII, L.P.

                                  By:        FLC XXXIII Partnership
                                             its general partner

                                  By:        /s/ Winston W. Hutchins
                                             --------------------------
                                             Winston W. Hutchins,
                                             a general partner

                                  FORSTMANN LITTLE & CO. EQUITY
                                  PARTNERSHIP-VI, L.P.

                                  By:        FLC XXXII Partnership, L.P.
                                             its general partner

                                  By:        /s/ Winston W. Hutchins
                                             --------------------------
                                             Winston W. Hutchins,
                                             a general partner

                                    - 21 -

<PAGE>   23

                                   FL FUND, L.P.

                                   By:       FLC XXXI Partnership, L.P.
                                             its general partner

                                          By:   FLC XXIX Partnership, L.P.
                                                a general partner

                                          By:   /s/ Winston W. Hutchins
                                                --------------------------------
                                                   Winston W. Hutchins,
                                                   a general partner

                                    - 22 -

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