<PAGE>   1
                                                                   EXHIBIT 10.14

                           BURLINGTON BUSINESS CENTER
                            BURLINGTON, MASSACHUSETTS
                         LEASE dated as of March 5, 1997

ARTICLE I

1.1   Reference Data

Each reference in this Lease to any of the following subjects shall be construed
to incorporate the data stated for that subject in this Article:

LANDLORD:  SUMITOMO LIFE REALTY (N.Y.), INC.

LANDLORD'S ORIGINAL ADDRESS:        245 Park Avenue
                                    34th Floor
                                    New York, New York 10167

LANDLORD'S CONSTRUCTION REPRESENTATIVE:

TENANT:  Lightbridge, Inc.
         a Delaware corporation

TENANT'S ORIGINAL ADDRESS:          281 Winter Street, Waltham, MA


TENANT'S CONSTRUCTION REPRESENTATIVE:

TENANT'S FINAL PLANS DATE: Not applicable

TERM COMMENCEMENT DATE:             March 15, 1997

RENT COMMENCEMENT DATE:             The earlier of: (x) June 1, 1997, or (y) the
                                    date that Tenant first commences to use the
                                    Premises for business purposes. Tenant shall
                                    not be considered to be using the Premises
                                    for business purposes during the time that
                                    Tenant is making improvements to the
                                    Premises or in moving the Tenant's furniture
                                    and trade fixtures.

TENANT'S SPACE:            An area on the first (1st) floor East Pod of the
                           Building, containing 21,055 rentable square feet,
                           substantially as shown on Lease Plan,


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                           Exhibit F, Sheet 1; an area on the second (2nd) floor
                           East Pod of the Building, containing 21,892 rentable
                           square feet, substantially as shown on Lease Plan,
                           Exhibit F, Sheet 2; and an area on the third (3rd)
                           floor East Pod of the Building, containing 3,411
                           rentable square feet, substantially as shown on Lease
                           Plan, Exhibit F, Sheet 3

TERMINATION DATE: Seven (7) years from the Rent Commencement Date

<TABLE>
<CAPTION>
ANNUAL FIXED RENT:         Lease Year(1)             Yearly Rent           Monthly Payment

<S>                            <C>                     <C>                       <C>
                               1-3                  $1,054,644.40             $87,887.04

                               4-5                  $1,112,592.00             $92,716.00

                               6-7                  $1,193,718.40             $99,476.54
</TABLE>

TENANT'S ANNUAL
ELECTRICITY CHARGE:        Forty-Four Thousand Forty and 00/100 ($44,040.00)
                           Dollars ($.95) Cents per square foot of Rentable
                           Floor Area of the Premises per annum.

TENANT'S TAX BASE:         The actual amount of Tax Expenses Allocable to the
                           Premises for fiscal/tax year 1997 (i.e., July 1, 1996
                           - June 30, 1997)

TENANT'S OPERATING EXPENSE BASE:    The actual amount of Operating Expenses
                                    Allocable to the Premises for calendar year
                                    1997

RENTABLE FLOOR AREA OF THE BUILDING:  170,310 Rentable Square Feet

PERMITTED USES:            General business offices. Subject to Tenant's
                           obligations to pay for overtime services, in
                           accordance with Section II of Exhibit E, and subject
                           to Landlord's reasonable security requirements,
                           Tenant shall have the right to operate its business
                           in the Premises twenty-four hours a day, seven days a
                           week throughout the term of this Lease.

(1) For the purposes of this Lease, "Lease Year" shall be defined as any
twelve-(12)-month period during the term of the Lease commencing as of the Rent
Commencement Date, or as of any anniversary of the Rent Commencement Date


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PUBLIC LIABILITY INSURANCE:         Bodily Injury - $5,000,000
                                    Property Damage - $5,000,000

1.2    Exhibits. There are eleven (11) Exhibits incorporated as a part of this
       Lease:

               EXHIBIT A - Description of Lot

               EXHIBIT B - Condition of Premises and Landlord's Contribution

               EXHIBIT C - Intentionally Omitted

               EXHIBIT D - Building Standard Tenant Improvements

               EXHIBIT E - Landlord's Services

               EXHIBIT F - Floor Plan

               EXHIBIT G - Required Tenant Work General
                          Conditions

               EXHIBIT H - Intentionally Omitted

               EXHIBIT I  - Form of Letter of Credit

               EXHIBIT J - Approved Exterior Signage

               EXHIBIT K - Present Rights of Existing Tenants to RFO Premises

1.3   Tables of Articles and Sections

                           ARTICLE I - Reference Data

<TABLE>
<S>                                                          <C>
1.1   Subjects Referred To.................................. 1

1.2   Exhibits.............................................. 2

1.3   Table of Articles and Sections ........................ 2

                      ARTICLE II - Premises, Term and Rent

2.1   The Premises.......................................... 8
</TABLE>


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<TABLE>
<S>                                                                          <C>
2.2   Rights to Use Common Facilities.......................                  8

2.3   Landlord's Reservations...............................                  8

2.4   Commencement of Term..................................                  9

2.5   Monthly Fixed Rent Payments...........................                  9

2.6   Adjustment for Operating Expenses.....................                  9

2.7   Adjustment for Real Estate Taxes......................                 15

2.8   Due Date of Additional Payments; No Offsets...........                 17

                   ARTICLE III - Alterations and Construction

3.1   Alterations and Additions by Tenant...................                 17

3.2   Real Estate Taxes on Leasehold Improvements...........                 19

3.3   Landlord's Right to Make Alterations..................                 20

3.4   Signage...............................................                 22

           ARTICLE IV - Landlord's Covenants; Interruptions and Delays

4.1   Services Furnished by Landlord........................                 23

4.2   Additional Services Available to Tenant...............                 23

4.3   Additional Air Conditioning Equipment.................                 23

4.4   Roof, Exterior Wall, Floor Slab and Common
          Facility Repair...................................                 24

4.5   Door Signs............................................                 24

4.6   Quiet Enjoyment.......................................                 24
</TABLE>


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                         ARTICLE V - Tenant's Covenants

<TABLE>
<S>                                                                          <C>
5.1   Payments..............................................                 24

5.2   Repair and Yield Up...................................                 25

5.3   Use...................................................                 25

5.4   Obstructions, Items Visible from Exterior;
          Rules and Regulations.............................                 26

5.5   Safety Appliances.....................................                 26

5.6   Assignment; Sublease..................................                 26

5.7   Indemnity; Insurance..................................                 30

5.8   Personal Property at Tenant's Risk....................                 30

5.9   Right of Entry........................................                 32

5.10  Floor Load; Prevention of Vibration and Noise.........                 32

5.11  Personal Property Taxes...............................                 33

5.12  Payment of Litigation Expenses........................                 33

5.13  Compliance with Insurance Regulations.................                 33

                        ARTICLE VI - Casualty and Taking

6.1   Termination or Restoration; Rent Adjustment...........                 33

6.2   Eminent Domain Damages Reserved.......................                 35

6.3   Temporary Taking......................................                 35

                              ARTICLE VII - Default

7.1   Events of Default.....................................                 35
</TABLE>


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<TABLE>
<S>                                                                          <C>
7.2   Damages...............................................                 36

                          ARTICLE VIII - Miscellaneous

8.1   Computation of Rentable Floor Areas...................                 38

8.2   Notice of Lease; Consent of Approval;
          Notices; Bind and Inure...........................                 38

8.3   Landlord's Failure to Enforce.........................                 39

8.4   Acceptance of Partial Payments of Rent;
          Delivery of Keys..................................                 39

8.5   Cumulative Remedies...................................                 39

8.6   Partial Invalidity....................................                 40

8.7   Self-Help.............................................                 40

8.8   Tenant's Estoppel Certificate.........................                 40

8.9   Waiver of Subrogation.................................                 41

8.10  All Agreements Contained..............................                 41

8.11  Brokerage.............................................                 41

8.12  Submission Not an Option..............................                 42

8.13  Applicable Law........................................                 42

8.14  Waiver of Jury Trial..................................                 42

8.15  Holdover..............................................                 42

8.16  Arbitration...........................................                 43

8.17  Requirements of Law - Fines and Penalties.............                 44

8.18  Inability to Perform - Exculpatory Clause.............                 44
</TABLE>


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<TABLE>
<S>                                                                          <C>
8.19  Parties Bound - Seizin of Title.......................                 45

             ARTICLE IX - Rights of Parties Holding Prior Interests

9.1   Lease Subordinate.....................................                 45

9.2      Rights of Holder of Mortgage to Notice of
         Defaults by Landlords and to Cure Same.............                 46

                           ARTICLE X - Letter of Credit

10.1     Requirements for Letter of Credit..................                 47

10.2     Landlord's Right to Draw Down Letter of Credit.....                 47

10.3     Tenant's Failure to Deliver Substitute Letter of Credit ..          48

10.4     Return of Collateral...............................                 48

              ARTICLE XI - Tenant's Option to Extend Term of Lease

11.1     Tenant's Option to Extend Term of Lease ............                48

                   ARTICLE XII - Tenant's Right of First Offer

12.1     Tenant's Right of First Offer.......................                51

              ARTICLE XIII - Definition of Fair Market Rental Value

13.1     Definition of Fair Market Rental Value..............                52

                 ARTICLE XIV - Condition of Landlord's Execution

14.1     Condition of Landlord's Execution ..................                54
</TABLE>


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                                   ARTICLE II

                             PREMISES, TERM AND RENT

2.1  The Premises

         Landlord hereby leases to Tenant and Tenant hereby hires from Landlord
Tenant's Space in the Building. The demise herein excludes exterior faces of
exterior walls, the common stairways and stairwells, elevators and elevator
shafts, fan rooms, electric and telephone closets, janitor closets, freight
elevator vestibules, and pipe, ducts, conduits, wires and appurtenant fixtures
serving exclusively or in common other parts of the Building, and if Tenant's
Space includes less than the entire rentable area of any floor, excluding the
common corridors, elevator lobbies and toilets located on such floor. Tenant's
Space with such exclusions is hereinafter referred to as "the Premises." The
term "Building" means the building erected on the Lot, and the term "Lot" means
all, and also any part of, the land described in Exhibit A in whole or in part
and subject to minor adjustments of the lot boundaries. "Property" means the
Building and Lot.

2.2  Rights to Use Common Facilities

         Tenant shall have, as appurtenant to the Premises, rights to use in
common, subject to reasonable rules of general applicability to tenants of the
Building from time to time made by Landlord of which Tenant is given notice: (a)
the common lobbies, corridors, stairways, elevators, exercise room and cafeteria
(to the extent that the exercise room and cafeteria area available to the other
tenants in the Building), and loading platform of the Building, and the pipes,
ducts, conduits, wires and appurtenant meters and equipment serving the Premises
in common with others, (b) common walkways and driveways for access to the
Building, (c) if the Premises included less than the entire rentable area of any
floor, the common toilets, corridors and elevator lobbies of such floor and (d)
the common parking facilities adjacent to the Building (Tenant hereby
acknowledging that parking is available on a first-come, first-served basis
only); and no other appurtenant rights or easements.

2.3  Landlord's Reservations

         Landlord reserves the right from time to time, without unreasonable
interference with Tenant's use and upon reasonable notice to Tenant when any
such activities shall directly affect the Premises (except that no notice shall
be required in emergency situations): (a) to install, use, maintain, repair,
replace and relocate for service to the Premises and other parts of the
Building, or either, pipes, ducts, conduits, wires and appurtenant fixtures,
wherever located in the Premises or Building, and (b) to alter or relocate any
other common facility, provided that substitutions are substantially equivalent
or better. Installations, replacements and relocations referred to in clause


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<PAGE>   9
(a) above shall be located so far as practicable in the central core area of the
Building, above ceiling surfaces, below floor surfaces or within perimeter walls
of the Premises; provided, however, that Landlord will not substantially reduce
the usable floor area of the Premises nor will any such work materially
adversely affect the appearance of the Premises.

2.4  Commencement of Term

         Tenant shall have and hold the Premises for a period commencing on the
date ("Term Commencement Date", as defined in Section 1.1, and, subject to the
provisions of this Lease, expiring as of the date ("Termination Date") seven (7)
years after the Rent Commencement Date, as defined in Section 1.1.
Notwithstanding the foregoing, if the Rent Commencement Date occurs on other
than the first day of a calendar month, then the Termination Date shall be the
last day of the calendar month in which the seventh (7th) anniversary of the
Rent Commencement Date occurs.

2.5  Monthly Fixed Rent Payments

         Commencing as of the Rent Commencement Date, and continuing thereafter
throughout the term of this Lease, Tenant shall pay as of the Rent Commencement
Date, without notice or demand, monthly installments of 1/12 of (a) the Annual
Fixed Rent, and (b) a charge ("Annual Electricity Charge") equal to 95(cent) per
annum for each square foot of Rentable Floor Area of the Premises for tenant
electricity, as described in Paragraph VI (A) of Exhibit E, in advance on the
first day of each month for each full calendar month of the Term, and the
corresponding fraction of said amounts for any fraction of a calendar month at
the beginning or end of the Term. Notwithstanding the provisions hereof, Tenant
shall pay the first monthly installment of Annual Fixed Rent on the execution of
this Lease.

         Rental and any other sums due hereunder not paid within ten (10) days
after the date due shall bear interest for each month or fraction thereof from
the due date until paid computed at the annual rate of two (2) percentage points
over the so-called prime rate then currently from time to time charged by The
First National Bank of Boston, or at any applicable lesser maximum legally
permissible rate for debts of this nature.

         In addition, should Tenant fail to pay when due rental and any other
sums due hereunder, Tenant acknowledges that Landlord will incur additional
administrative expenses which are difficult to determine. Therefore, in such
event, Landlord may assess against Tenant, from and after the tenth business
(10th) day following the date on which any sum shall be due and payable, a late
payment fee equal to five (5%) of the sum due from Tenant to Landlord.

2.6  Adjustment for Operating Expenses


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<PAGE>   10
         A.       Terms used herein are defined as follows:

                  (1) "Operating Year" shall mean any 12 month period elected by
Landlord for operating purposes. Landlord's current Operating Year commences on
January l of each year. If Landlord should elect to change said Operating Year,
Landlord shall notify Tenant thereof, and all calculations required to be made
at the end of a Operating Year shall be made and proportioned accordingly.

                  (2) "Operating Expenses for the Property" means the cost of
operation of the Property which shall exclude Excluded Expenses, as hereinafter
defined, but shall include, without limitation, the following: Premiums for
insurance carried with respect to the Property (including insurance against loss
in case of fire or casualty, monthly installments of Annual Fixed Rent and any
additional rent which may be due under this Lease and other leases of space in
the Building and, if there be any first mortgage of the Property, including such
insurance as may be required by the holder of such first mortgage); compensation
and all fringe benefits, Workmen's Compensation Insurance premiums and payroll
taxes paid to, for or with respect to all persons engaged in the operating,
repairing, maintaining, or cleaning of the Building or Lot (provided however,
that if any individual performs services to the Property on other than a full
time basis, the compensation, benefits, premiums and taxes payable in respect of
such individual shall be allocated between the Property and other properties for
which such individual provides services on the basis of the relative time spent
by such individual in providing services for each property); steam, water,
sewer, gas, oil and telephone charges; electricity provided to the Building and
to the Premises; cost of building and cleaning supplies and equipment; related
equipment, facilities and appurtenances, elevators, cooling and heating
equipment, provided, however, that (i) if, during the term of this Lease,
Landlord shall replace any capital items or make any capital expenditures
(collectively called "capital expenditures") the total amount of which is not
properly includible in Operating Expenses for the Operating Year in which they
were made, there shall nevertheless be included in such Operating Expenses and
in Operating Expenses for each succeeding Operating Year the amount, if any, by
which the annual charge-off (determined as hereinafter provided) of such capital
expenditure (less insurance proceeds, if any, collected by Landlord by reason of
damage to, or destruction of the capital item being replaced) exceeds the annual
charge-off of the capital expenditure for the item being replaced; and (ii) if a
new capital item is acquired which does not replace another capital item which
has worn out, has become obsolete, etc., then there shall be included in
Operating Expenses for each Operating Year in which and after such capital
expenditure is made the annual charge-off of such capital expenditure. (Annual
charge-off shall be determined by (i) dividing the original cost of the capital
expenditure by the number of years of useful life thereof [The useful life shall
be reasonably determined by Landlord in accordance with generally accepted
accounting principles and practices in effect at the time of acquisition of the
capital item]; and (ii) adding to such quotient an interest factor computed on
the unamortized balance of such capital expenditure at an annual rate of either
one percentage point over the AA Bond rate [Standard & Poor's corporate
composite or, if unavailable, its equivalent] as reported in


                                      -10-
<PAGE>   11
the financial press at the time the capital expenditure is made or, if the
capital item is acquired through third-party financing, then the actual
[including fluctuating] rate paid by Landlord in financing the acquisition of
such capital item.) Provided, further, that if Landlord reasonably concludes on
the basis of engineering estimates that a particular capital expenditure will
effect savings in Operating Expenses for the Property, including, without
limitation, energy-related costs, and that such annual projected savings will
exceed the annual charge-off of capital expenditure computed as aforesaid, then
and in such events, the annual charge-off shall be determined by dividing the
amount of such capital expenditure by the number of years over which the
projected amount of such savings shall fully amortize the cost of such capital
item or the amount of such capital expenditure; and by adding the interest
factor, as aforesaid; cost of maintenance, cleaning and repairs, cost of snow
removal and care of landscaping; payments under service contracts with
independent contractors or subsidiaries or affiliates of Landlord; management
fees not in excess of management fees paid to manage other first class office
buildings in the greater Burlington area; and all other expenses paid, in good
faith, in connection with the operation, repair, cleaning and maintenance of the
Building and Lot.

         If during all or part of any Operating Year, Landlord is not performing
or furnishing any item to any portion of the Building (the cost of which, if
performed or furnished by Landlord to such portion of the Property would
constitute a part of Operating Expenses for the Property) on account of (a) such
portion of the Building not being occupied or leased, (b) such item not being
required or desired by a tenant, (c) any tenant itself obtaining or providing
such item, or (d) any other reason, whether similar or dissimilar to the
foregoing; then, Operating Expenses for the Property shall be deemed to be
increased by an amount equal to the additional costs and expenses which would
reasonably have been incurred during such period by Landlord if it had performed
or furnished such item to 100% of the Building.

                  (3) Operating Expenses for the Property shall exclude the
following costs ("Excluded Expenses"):

                           1.       Salaries of officers and executives of
                                    Landlord not connected with the operation of
                                    the Property;

                           2.       The personnel costs of any employee above
                                    the grade of building superintendent, senior
                                    building manager or chief engineer;

                           3.       All costs related to the preparation of the
                                    Premises or another tenant's premises for
                                    occupancy by a tenant or other occupant;

                           4.       Legal fees and expenses incurred by the
                                    Landlord in connection with negotiating
                                    leases and occupancy agreements and in


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<PAGE>   12
                                    connection with any disputes between
                                    Landlord and any tenant or occupant of the
                                    Building;

                           5.       costs of special services rendered to
                                    tenants (including Tenant) for which a
                                    separate charge is made,

                           6.       Advertising and promotional expenses
                                    associated with the marketing of vacant
                                    space in the Building;

                           7.       Depreciation and amortization, except to the
                                    extent provided above;

                           8.       Mortgage charges, and interest, except to
                                    the extent included in the annual charge-off
                                    for a capital item which is permitted to be
                                    included in Operating Expenses for the
                                    Property in accordance with this
                                    Subparagraph (b);

                           9.       Costs and expenses incurred by the Landlord
                                    in connection with the repair of damage to
                                    the Building or Property caused by fire or
                                    other casualty, insured or required to be
                                    insured against hereunder, to the extent
                                    that such costs and expenses exceed the
                                    deductible under Landlord's insurance
                                    policy;

                           10.      Insurance premiums to the extent any unusual
                                    tenant activity causes the Landlord's
                                    existing insurance premiums to increase or
                                    requires the Landlord to purchase additional
                                    insurance, but only to the extent such
                                    additional cost is identified by the insurer
                                    and attributed to another tenant;

                           11.      The cost of installing any specialty service
                                    such as luncheon club, retail store, sundry
                                    shop, newsstand, concession, or athletic or
                                    recreational club (Tenant acknowledging that
                                    certain costs of operating the exercise room
                                    and cafeteria are included in Operating
                                    Expenses for the Property);

                           12.      The cost of constructing any additions to
                                    the Property;

                           13.      Damages or penalties incurred due to
                                    violation by the Landlord or any other
                                    tenant of the Building of any lease;


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                           14.      The cost of making any alterations to the
                                    Building or the Property for the purpose of
                                    complying with any laws, rules, regulations
                                    or ordinances applicable to the Building
                                    which are in effect as of the Execution Date
                                    of this Lease;

                           15.      The cost of any work performed or service
                                    provided to the extent that the Landlord is
                                    otherwise reimbursed, other than through
                                    Operating Expense escalation provisions
                                    included in the leases of the tenants of the
                                    Building; and

                           16.      items of expense referred to in Section 2.7
                                    hereof.


                  (4) "Operating Expenses Allocable to the Premises", as may be
adjusted pursuant to Subparagraph (c) hereof, shall mean the same proportion of
the Operating Expenses for the Property as the Rentable Floor Area of Tenant's
Space bears to the Rentable Floor Area of the Building actually leased on an
average annual basis for said Operating Year.

                  (5) The "Statement" shall mean a statement rendered to Tenant
by Landlord within 90 days or as soon thereafter as reasonably possible after
the end of each Operating Year. The Statement shall be in reasonable detail,
certified by Landlord's representative, and show the Operating Expenses for the
Property, the Operating Expenses Allocable to the Premises, amounts already paid
by Tenant for Operating Expenses Allocable to the Premises (including Tenant's
Operating Expense Base, amounts received on account of Annual Electricity Charge
pursuant to Section 2.5 hereof, and amounts paid pursuant to part C of this
Section 2.6), and the amount of Operating Expenses Allocable to the Premises
remaining due from or overpaid by Tenant for the Operating Year or fraction
thereof covered by the Statement with appropriate prorations for fractional
years.

         B. If with respect to any Operating Year of the Term, Operating
Expenses Allocable to the Premises exceed Tenant's Operating Expense Base, then
Tenant shall pay to Landlord as additional rent the amount of such excess. Such
payments shall be made at the times and in the manner hereinafter provided in
this Section 2.6. Appropriate prorations shall be made for those periods at the
beginning or end of the Term which are less than a full Operating Year (Tenant's
Operating Expense Base includes the $.95 per Rentable Square Foot charge for
Annual Electricity Charge to be paid pursuant to Section 2.5 hereof).

         Within 30 days after the date of delivery of such Statement, Tenant
shall pay to Landlord or Landlord shall pay to Tenant as the case may be, the
balance of the amounts, if any, required to be paid pursuant to the above
provisions of this Section 2.6, except that Landlord may at its


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<PAGE>   14
option credit any amounts due from it to Tenant against monthly installments of
Annual Fixed Rent next thereafter coming due.

         C. Commencing on the first day of the first month following the
delivery to Tenant of the Statement referred to above and on the first day of
each month thereafter until delivery to Tenant of the next such Statement,
Tenant shall pay to Landlord, on account of Tenant's share of increases in
Operating Expenses Allocable to the Premises reasonably anticipated by Landlord
for the then current Operating Year, 1/12th of the difference between Operating
Expenses Allocable to the Premises calculated by Landlord on the basis of the
most recent Operating Expense data or budget available from time to time, and
Tenant's Operating Expense Base. Landlord agrees to keep proper books and
records of Operating Expenses.

         D. Subject to the provisions of this paragraph, Tenant shall have the
right, at Tenant's cost and expense, to examine all documentation and
calculations prepared in the determination of Operating Expenses Allocable to
the Property:

         (1) Such documentation and calculation shall be made available to
         Tenant at the offices where Landlord keeps such records during normal
         business hours within a reasonable time after Landlord receives a
         written request from Tenant to make such examination. Tenant's review
         shall be conducted in a manner so as not to unreasonably interfere with
         the conduct of Landlord's business.

         (2) Tenant shall have the right to make such examination no more than
         once in respect of any period in which Landlord has given Tenant a
         statement of the actual amount of Operating Expenses Allocable to the
         Premises.

         (3) Any request for examination in respect of any Operating Year may be
         made no more than ninety (90) days after Landlord advises Tenant of the
         actual amount of Operating Expenses Allocable to the Premises in
         respect of such period.

         (4) Such examination may be made only by a national recognized
         independent certified public accounting firm approved by Landlord.
         Without limiting Landlord's approval rights, Landlord may withhold its
         approval of any examiner of Tenant who is, or has, within the last five
         years prior to Tenant's request, represented any other tenant in the
         Building or in other buildings owned by Landlord or an affiliate of
         Landlord, or any examiner of Tenant who is being paid by Tenant on a
         contingent fee basis.

         (5) As a condition to performing any such examination, Tenant and its
         examiners shall be required to execute and deliver to Landlord an
         agreement, in form acceptable to Landlord, agreeing to keep
         confidential any information which it discovers about Landlord or the
         Building in connection with such examination. Without limiting the
         foregoing, such


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<PAGE>   15
         examiners shall be required to agree that they will not represent any
         other tenant in the Building or in other buildings owned by Landlord or
         an affiliate of Landlord.

         E. Any dispute which arises in connection with Operating Expenses
Allocable to the Property as the result of any such examination by Tenant shall
be submitted to arbitration in accordance with Section 8.16 of this Lease. If,
based upon the resolution of any such dispute (whether by agreement of the
parties, or by arbitration, as aforesaid), it is determined that Tenant has
overpaid Landlord on account of Operating Expenses Allocable to the Property,
Landlord shall, at Landlord's election, either promptly refund such overpayment
to Landlord or shall credit such overpayment against the next installments of
Annual Fixed Rent and other charges due under this Lease.

2.7  Adjustments for Real Estate Taxes

         A.       Terms used herein are defined as follows:

         (1) "Tax Year" means the twelve-month period beginning July 1 each year
during the Term or if the appropriate governmental tax fiscal period shall begin
on any date other than July 1, such other date.

         (2) In any Tax Year when the Building has an average annual occupancy
rate of less than 95% then "Tax Expenses Allocable to the Premises" means the
same proportion of the Landlord's Tax Expenses as Rentable Floor Area of
Tenant's Space bears to 95% of the Rentable Floor Area of the Building. In any
Tax Year when the Building has an average annual occupancy rate of 95% or more
"Tax Expenses Allocable to the Premises" means the same proportion of Landlord's
Tax Expenses as Rentable Floor Area of Tenant's Space bears to the Rentable
Floor Area of the Building actually leased on an average annual basis for said
Tax Year.

         (3) "Landlord's Tax Expenses" with respect to any Tax Year means the
aggregate Real Estate Taxes on the Property with respect to that Tax Year,
reduced by any abatements actually received with respect to that Tax Year.

         (4) "Real Estate Taxes" means all taxes, levies, betterments, and
special assessments of every kind and nature assessed by National, State,
Municipal or by any other governmental authority on the Lot or the Building or
the Property which the Landlord shall become obligated to pay because of or in
connection with the ownership, leasing, operating, use or occupancy of the Lot,
the Building, and the Property or based upon rentals derived therefrom; charges,
fees and assessments for transit, housing, police, fire or other governmental
services or purported benefits to the Building; service or user payments in lieu
of taxes; and reasonable expenses of any proceedings for abatement of taxes. The
amount of special taxes or special assessments to be included shall be limited
to the amount of the installment (plus any interest, other than penalty


                                      -15-
<PAGE>   16
interest, payable therein) of such special tax or special assessment required to
be paid during the year in respect of which such taxes are being determined.
There shall be excluded from such taxes all income, estate, succession,
inheritance and transfer taxes; provided, however, that if at any time during
the Term the present system of ad valorem tax of real property shall be changed
so that in lieu of or in addition to the whole or any part of the ad valorem tax
on real property, there shall be assessed on Landlord a capital levy or other
tax on the gross rents received with respect to the Lot or Building or Property,
or a federal, state, county, municipal, or other local income, franchise, excise
or similar tax, assessment, levy or charge (distinct from any now in effect in
the jurisdiction in which the Property is located) measured by or based, in
whole or in part, upon any such gross rents, than any and all of such taxes
shall be included within the term "Real Estate Taxes" but only to the extent
that the same would be payable if the Lot, Building or Property were the only
property of Landlord. Landlord agrees that all assessments for real estate
betterments shall be included in Landlord's Tax Expenses as if apportioned over
the longest period permitted by law and Tenant shall only be obligated to pay
its respective share of each payment which falls due during the Term.
Notwithstanding the foregoing, to the extent that it is determinable from the
records of the assessing authority that any increase in Real Estate Taxes is
based solely upon improvements to any tenants premises which exclude the
Building Standard Tenant Improvement level, as set forth on Exhibit D, such
increase shall be excluded from Landlord's Tax Expenses. For any Tax Year in
which the assessing authority determines the assessed value of the Property is
based upon an income approach, then the immediately preceding sentence shall not
apply.

         B. If with respect to any Tax Year of the Term, Tax Expenses Allocable
to the Premises exceed Tenant's Tax Base, then Tenant shall pay to Landlord as
additional rent the amount of such excess. Such payments shall be made at the
times and in the manner hereinafter provided in this Section 2.7. Appropriate
prorations shall be made for those periods at the beginning or end of the Term
which are less than a full Tax Year. Within ninety (90) days or as soon
thereafter as reasonably possible after the end of such first Tax Year or
fraction thereof at the beginning of the Term, and of each succeeding Tax Year
during the Term and within ninety (90) days or as soon thereafter as reasonably
possible after lease termination, Landlord shall render to Tenant a statement in
reasonable detail certified by a representative of Landlord showing for the
preceding Tax Year or fraction thereof, as the case may be, Landlord's Tax
Expenses for the Property, and Tax Expenses Allocable to the Premises.

         C. Commencing on the first day of the first month following the
delivery to Tenant of the statement referred to above and on the first day of
each month thereafter until delivery to Tenant of the next such statement,
Tenant shall pay to Landlord, on account toward Tenant's share of increases in
Tax Expenses Allocable to the Premises anticipated for the then current Tax
Year, 1/12th of the total amount of Tax Expenses Allocable to the Premises as
shown on the most recent such statement delivered to Tenant. The statements to
be rendered to Tenant referred to above shall also show for the preceding Tax
Year amounts of Real Estate Taxes already paid by


                                      -16-
<PAGE>   17
Tenant on account for such year and the amount of Tax Expenses Allocable to the
Premises remaining due from or overpaid by Tenant for the Tax Year or fraction
thereof covered by the statement. Within 30 days after the date of delivery of
such statement, Tenant shall pay to Landlord or Landlord shall pay to Tenant as
the case may be, the balance of the amounts, if any, required to be paid
pursuant to the above provisions of this Section 2.7, except that Landlord may
at its option credit any amounts due from it to Tenant against monthly
installments of Annual Fixed Rent next thereafter coming due.

         D. To the extent that Real Estate Taxes shall be payable to the taxing
authority in installments for periods less than a Tax Year, the foregoing
statement shall be rendered and payments made on account of such installments
with respect to such periods rather than with respect to such full Tax Year.

2.8  Due Date, Additional Rent; No Offsets

         Except as otherwise specifically provided herein, all sums, amounts,
items or charges payable by Tenant to Landlord under this Lease shall be
considered as additional rent, and shall be paid by Tenant to Landlord on the
first day of the month following the date on which Landlord notifies Tenant of
the amount payable or on the tenth day after the giving of such notice,
whichever shall be later. Any such notice shall specify in reasonable detail the
basis of such additional rent. Annual Fixed Rent and additional rent shall be
paid by Tenant to Landlord without offset or deduction.


                                   ARTICLE III

                       TENANT ALTERATIONS AND CONSTRUCTION

3.1  Alterations and Additions by Tenant

         (a) This Section 3.1 shall apply before and during the Term. Tenant
shall not make alterations and additions to Tenant's Space except in accordance
with plans and specifications and a time schedule therefor first approved by
Landlord, in writing which approval shall not be unreasonably withheld or
delayed. All alterations and additions to Tenant's Space shall equal or exceed
the specifications and quantities provided in Exhibit D. No amendments or
additions to Tenant's approved plans shall be made without the prior written
consent of Landlord. Such approval shall not be unreasonably withheld or
delayed. Landlord shall not be deemed unreasonable for withholding approval of
any alterations or additions which (a) involve or might affect any structural or
exterior element of the Building, any area or element outside of the Premises,
or any facility serving any area of the Building outside the Premises, or (b)
will delay completion of the Premises or Building or (c) will require unusual
expense to readapt the


                                      -17-
<PAGE>   18
Premises to normal office use on Lease termination or increase the cost of
construction or of insurance or taxes on the Building or of the services called
for by Section 4.1 unless Tenant first gives assurance reasonably acceptable to
Landlord for payment of such increased cost and that such readaption will be
made prior to such termination without expense to Landlord.

         (b) All alterations and additions shall be part of the Building unless
and until Landlord shall specify the same for removal pursuant to Section 5.2.
Landlord may elect to require Tenant at the expiration or sooner termination of
the term of this Lease to restore the Premises to substantially the same
condition as existed at the Term Commencement Date.

         (c) All of Tenant's alterations and additions and installation of
furnishings shall be coordinated with any work being performed by Landlord in
such manner as to not damage the Property or interfere with Building
construction or operation and, except for installation of furnishings, shall be
performed by contractors or workmen first approved by Landlord. Such approval
shall not be unreasonably withheld or delayed. In the event that Tenant shall
engage its own contractors to perform such work, Tenant shall pay to Landlord
the reasonable cost of services provided by Landlord or Landlord's contractor to
Tenant and to Tenant's contractors while performing such work, which services
shall include, but not be limited to, cleaning, security, rubbish removal,
electricity, toilet facilities, and elevators. Tenant's contract with any such
contractors shall include the Required Tenant Work General Conditions attached
hereto as Exhibit G, and Landlord shall have the right to enforce such General
Conditions directly against any of Tenant's contractors. Tenant shall defend,
save harmless, exonerate and indemnify Landlord from all injury, loss or damage
to any person or property occasioned by or growing out of such work, except to
the extent that such injury, loss or damage is caused by the negligence of
Landlord or the agents and employees of Landlord. Tenant agrees that it will
not, either directly or indirectly, use any contractors and/or materials if
their use will create any difficulty, whether in the nature of a labor dispute
or otherwise, with other contractors and/or labor engaged by Tenant or Landlord
or others in the construction, maintenance and/or operation of the Building or
any part thereof. Except for work by Landlord's general contractor, Tenant,
before its work is started, shall: secure all licenses and permits necessary
therefor; deliver to Landlord a statement of the names of all its contractors
and subcontractors and the estimated cost of all labor and material to be
furnished by them; and cause each contractor to carry Workmen's Compensation
Insurance in statutory amounts covering all the contractor's and subcontractor's
employees, Automobile Liability Insurance and comprehensive public liability
insurance and property damage insurance with such limits as Landlord may
reasonably require but in no event less than, with respect to public liability
insurance, $5,000,000.00 and with respect to property damage insurance,
$5,000,000.00 (all insurance to be written in companies reasonably approved by
Landlord and insuring Landlord and Tenant as well as the contractors), and to
deliver to Landlord certificates of all such insurance. No installations or work
shall be undertaken or begun by Tenant until Tenant has made provision for the
receipt by Tenant of written waivers of liens (i.e. for work performed, or
materials supplied, through the date of requisition) from all contractors,
laborers


                                      -18-
<PAGE>   19
and suppliers of materials for installations or work, as a condition to payment
of each requisition. If the cost of any installation or work to be performed by
Tenant in the premises exceeds One Million ($1,000,000.00) Dollars, then Tenant
shall, prior to commencing such work, obtain a payment, performance and lien
bond, which shall name Landlord as an additional obligee, on behalf of its
general contractor.

         (d) In no event shall any material or equipment be incorporated in or
added to the Premises, so as to become a fixture or otherwise a part of the
Building, in connection with any such alteration, decoration, installation,
addition or improvement which is subject to any lien, charge, mortgage or other
encumbrance of any kind whatsoever or is subject to any security interest or any
form of title retention agreement. Any mechanic's lien filed against the
Premises or the Building for work claimed to have been done for, or materials
claimed to have been furnished to, Tenant shall be discharged by Tenant within
ten (10) days thereafter, at Tenant's expense, by filing the bond required by
law or otherwise. If Tenant fails so to discharge any lien, Landlord may do so
at Tenant's expense and Tenant shall reimburse Landlord for any expense or cost
incurred by Landlord in so doing within fifteen (15) days after rendition of a
bill therefor.

         (e) All installations or work done by Tenant shall be at its own
expense (subject, however, to Landlord's obligation to provide Landlord's
Contribution in accordance with Exhibit B), and shall at all times comply with
(i) laws, rules, orders and regulations of governmental authorities having
jurisdiction thereof; (ii) orders, rules and regulations of any Board of Fire
Underwriters, or any other body hereafter constituted exercising similar
functions, and governing insurance rating bureaus; (iii) Rules and Regulations
of Landlord; and (iv) plans and specifications prepared by and at the expense of
Tenant theretofore submitted to and approved by Landlord. All construction work
required or permitted by this Lease shall be done in a good and workmanlike
manner. Tenant agrees to pay promptly when due the entire cost of any work done
on the Premises by Tenant, its agents, employees, or independent contractors.

3.2  Real Estate Taxes on Leasehold Improvements

         If under Massachusetts law or regulations, the tax assessor is required
to include leasehold (real property) improvements in determining the assessed
value of the Building, then to the extent that Tenant makes leasehold
improvements (including Tenant's original installation and Tenant's subsequent
alterations, additions, substitutions and improvements) which are in excess of
the Building Standard Tenant Improvements set forth in Exhibit D, whether done
prior to or after the commencement of the Term of this Lease, Tenant shall pay
the real estate taxes attributable to the value of such excess leasehold
improvements throughout the Term of this Lease within thirty (30) days after
being billed therefor by Landlord.

3.3  Landlord's Right to Make Alterations


                                      -19-
<PAGE>   20
         A. Upon at least forty-eight (48) hours' advance notice to Tenant,
except in case of emergency, Landlord reserves the right, exercisable by itself
or its nominee, at any time and from time to time without the same constituting
an actual or constructive eviction and without incurring any liability to Tenant
therefor or otherwise affecting Tenant's obligations under this Lease, to make
such changes, alterations, additions, improvements, repairs or replacements in
or to the Building (including the Premises, provided however, that Landlord's
right to make improvements within the Premises shall be subject to limitations
set forth in Section 2.3) and the fixtures and equipment thereof, as well as in
or to the street entrances, halls, passages, elevators, escalators, and
stairways thereof, as it may deem necessary or desirable, and to change the
arrangement and/or location of entrances or passageways, doors and doorways, and
corridors, elevators, stairs, toilets, or other public parts of the Building,
provided, however, that: (i) there be no unreasonable obstruction of the right
to access to, or unreasonable interference with the use of the Premises by
Tenant, (ii) Landlord does not reduce the useable floor area of the Premises, or
(iii) Landlord does not diminish or materially adversely affect the current
quality of the Building. Nothing contained in this Section 3.3 shall be deemed
to relieve Tenant of any duty, obligation or liability of Tenant with respect to
making any repair, replacement or improvement or complying with any law, order
or requirement of any governmental or other authority.

         B. Landlord reserves the right to adopt at any time and from time to
time to change the name or address of the Building. In the event that Landlord
makes any such change in name or address more than once during the term of this
Lease, then Landlord shall promptly reimburse Tenant for the reasonable cost
(not to exceed $2,500.00) incurred by Tenant in replacing its stationery and
business cards.

         C. Neither this Lease nor any use by Tenant shall give Tenant any right
or easement for the use of any door or any passage or any concourse connecting
with any other building or to any public convenience, and the use of such doors,
passes and concourses and of such conveniences may be regulated or discontinued
at any time and from time to time by Landlord without notice to Tenant and
without affecting the obligation of Tenant hereunder or incurring any liability
to Tenant therefor, provided, however, that there be no unreasonable obstruction
of the right to access to, or unreasonable interference with the use of the
Premises by Tenant.

         D. Subject to Paragraphs F and G of this Section 3.3, Landlord shall
not be liable to Tenant for any compensation or reduction of rent by reason of
inconvenience or annoyance or for loss of business arising from the necessity of
Landlord or its agents entering the Premises for any of the purposes in this
Lease authorized, or for repairing the Premises or any portion of the Building,
however the necessity may occur provided, however, that Landlord shall use
reasonable efforts not to interfere with Tenant's use of the Premises. In case
Landlord is prevented or delayed from making any repairs, alterations or
improvements, or furnishing any services or performing any other covenant or
duty to be performed on Landlord's part, by reason of any cause reasonably
beyond Landlord's control, Landlord shall not be liable to Tenant therefor, nor,


                                      -20-
<PAGE>   21
except as expressly otherwise provided in Paragraphs F and G of this Section 3.3
and in Section 6.1, shall Tenant be entitled to any abatement or reduction of
rent by reason thereof, nor shall the same give rise to a claim in Tenant's
favor that such failure constitutes actual or constructive, total or partial,
eviction from the Premises; provided however, that Landlord shall use reasonable
efforts to make such repair, restoration or improvements or restore such service
as soon as is reasonably practicable.

         E. Landlord reserves the right to stop any service or utility system,
when necessary by reason of accident or emergency, or until necessary repairs
have been completed; provided, however, that in each instance of stoppage
Landlord shall exercise reasonable diligence to eliminate the cause thereof.
Except in case of emergency repairs Landlord will give Tenant reasonable advance
notice of any contemplated stoppage and will use reasonable efforts to avoid
unnecessary inconvenience to Tenant by reason thereof.

         F. Notwithstanding anything to the contrary in this Lease contained, if
due to: (i) any such repairs, alterations, replacements, or improvements made by
Landlord, (ii) to Landlord's failure to make any repairs, alterations, or
improvements required to be made by Landlord, or (iii) any interruption of
services required to be provided by Landlord to Tenant under this Lease, any
portion of the Premises becomes untenantable so that for the Premises
Untenantability Cure Period, as hereinafter defined, the continued operation in
the ordinary course of Tenant's business is materially adversely affected, then,
provided that Tenant ceases to use the affected portion of the Premises during
the entirety of the Premises Untenantability Cure Period and that such
untenantability and Landlord's inability to cure such condition is not caused by
the fault or neglect of Tenant or Tenant's agents, employees or contractors,
Annual Fixed Rent, Annual Electricity Charges, Operating Expenses Allocable to
the Premises, and Tax Expenses Allocable to the Premises shall thereafter be
abated in proportion to such untenantability until the day such condition is
completely corrected. For the purposes hereof, the "Premises Untenantability
Cure Period" shall be defined as ninety (90) consecutive days after Landlord's
receipt of written notice from Tenant of the condition causing untenantability
in the Premises.

         G. Notwithstanding anything to the contrary herein contained, if due
to: (i) such repairs, alterations, replacements or improvements made by
Landlord, (ii) Landlord's failure to make any repairs, alterations or
improvements required to be made by Landlord, or (iii) Landlord's failure to
provide any services which Landlord is required to provide under this Lease, any
material portion of the Premises becomes untenantable for a period of eleven
(11) months after Landlord's receipt of written notice of such condition from
Tenant, then, provided that Tenant ceases to use the affected portion of the
Premises during the entire period of such untenantability, such untenantability
and Landlord's inability to cure such condition is not caused by the fault or
neglect of Tenant, or Tenant's agents, employees or contractors, then Tenant may
terminate this Lease by giving Landlord written notice as follows:


                                      -21-
<PAGE>   22
         (1) Said notice shall be given after said eleven (11) month period.

         (2) Said notice shall set forth an effective date which is not earlier
         than thirty (30) days after Landlord receives said notice.

         (3) If said condition is remedied on or before said effective date,
         said notice shall have no further force and effect.

         (4) If said condition is not remedied on or before said effective date
         for any reason other then Tenant's fault, as aforesaid, the Lease shall
         terminate as of said effective date, and the Annual Fixed Rent,
         escalations and other charges due under the Lease shall be apportioned
         as of said effective date.

         H. The provisions of Paragraphs F and G of this Section 3.3 shall not
apply in the event of untenantability caused by fire, other casualty, or taking
(see Article 6).

3.4      Signage

         Except as provided in Section 4.5 and this Section 3.4, Tenant shall
have no right to install or maintain any signage in or about the Premises, the
Building or the Property. Notwithstanding the foregoing, provided that
Lightbridge, Inc. is occupying the entirety of the Premises initially demised to
Tenant, Tenant shall be permitted, subject to Landlord's approval to erect a
sign on the facade of the Building. Such sign shall be the same size and in the
same location ("Present Exterior Sign Location") as the existing signage of the
present tenant of the Premises. Landlord hereby approves the signage (if any)
shown on Exhibit J to be installed in the Present Exterior Sign Location. Said
sign shall be erected in accordance with the by-laws of the Town of Burlington,
Massachusetts. Tenant shall, at Tenant's sole cost and expense, maintain such
signage in good condition throughout the term of the Lease. Notwithstanding
anything to the contrary herein contained, upon the earlier of: (x) the
termination of the term of this Lease, or (y) the date that Lightbridge, Inc.,
itself, ceases to occupy the entirety of the Premises initially demised to
Tenant, Tenant shall, at Tenant's sole cost and expense, remove such signage
from the Building and shall repair any damage to the Building caused by the
installation, maintenance or removal of such signage. Landlord shall, prior to
June 15, 1997, remove or cause to be removed, the existing Tenant's sign on the
facade of the Building and shall repair or cause to be repaired any damage
caused by such removal.


                                      -22-
<PAGE>   23
                                   ARTICLE IV

                 LANDLORD'S COVENANTS; INTERRUPTIONS AND DELAYS

Landlord covenants:

4.1  Services Furnished by Landlord

         To furnish services, utilities, facilities and supplies ("Landlord's
Services") set forth in Exhibit E, which Landlord's Services Landlord shall have
the right to change, from time to time, provided that Landlord's Services (i.e.
at the time that Landlord changes such services) shall be equal in quality and
quantity to those customarily provided by landlords in comparable buildings in
the Burlington area.

4.2  Additional Services Available to Tenant

         To furnish, at Tenant's expense, reasonable additional Building
operation services which are usual and customary in similar office buildings in
the Burlington area upon reasonable advance request of Tenant at reasonable and
equitable rates from time to time established by Landlord. Landlord represents
that, as of the Execution Date of this Lease, the additional charge for heat is
$33.00 per hour per Pod and the additional charge for air-conditioning is $48.00
per hour per Pod. Such charges are subject to change, from time to time, based
upon the actual cost to Landlord of providing such service.

4.3  Additional Air Conditioning Equipment

         In the event Tenant requires additional air conditioning for business
machines, meeting rooms or other special purposes, or because of occupancy or
excess electrical loads, any additional air conditioning units, chillers,
condensers, compressors, ducts, piping and other equipment, such additional air
conditioning equipment will be installed and maintained by Landlord at Tenant's
sole cost and expense, but only if Tenant has obtained Landlord's prior written
consent, which consent shall not be unreasonably withheld and if the same will
not cause damage or injury to the Building or create a dangerous or hazardous
condition or entail excessive or unreasonable alterations, repairs or expense or
interfere with or disturb other tenants; and Tenant shall reimburse Landlord in
such an amounts as will compensate it for the cost incurred by it in operating
such additional air conditioning equipment.


                                      -23-
<PAGE>   24
4.4  Roof, Exterior Wall, Floor Slab, and Common Facility Repair

         Except as otherwise provided in Article VI to make such repairs to the
roof, exterior walls, floor slabs, plumbing, electrical and mechanical systems
installed by Landlord and common areas and facilities as may be necessary to
keep them in good condition, the expense of which shall be charged in accordance
with Section 2.6. Landlord shall maintain the landscaping, driveways and parking
areas in a clean and neat condition and shall remove snow and ice from driveways
and parking areas as is reasonably necessary.

4.5  Door Signs

         To provide and install, at Tenant's expense, letters or numerals on
doors in the Premises to identify Tenant's name and Building address; all such
letters and numerals shall be in the building standard graphics and no others
shall be used or permitted on the Premises. Landlord agrees, during the term of
this Lease, to list Tenant's name in any building directory. The initial listing
shall be at Landlord's cost and expense. Any change in any such building
directory listing shall be at Tenant's cost and expense.

4.6  Quiet Enjoyment

         Landlord covenants that if, and so long as, Tenant keeps and performs
each and every covenant, agreement, term, provision and condition herein
contained on the part and on behalf of Tenant to be kept and performed, Tenant
shall quietly enjoy the Premises from and against the claims of all persons
claiming by, through or under Landlord subject, nevertheless, to the covenants,
agreements, terms, provisions and conditions of this Lease.


                                    ARTICLE V

                               TENANT'S COVENANTS

         Tenant covenants during the Term and such further time as Tenant
occupies any part of the Premises:

5.1  Payments

         To pay when due all Annual Fixed Rent and additional rent and all
charges for utility services rendered to the Premises (except as otherwise
provided in Exhibit E) and, as further additional rent, all charges for
additional services rendered pursuant to Section 4.2;


                                      -24-
<PAGE>   25
5.2  Repair and Yield Up

         Except as otherwise provided in Article VI and Section 4.4, to keep the
Premises in as good order, repair and condition as they were on the Term
Commencement Date, reasonable wear and tear, damage caused by casualty, and
damage caused by taking only excepted, and all glass in windows (except glass in
exterior walls of the Building unless the damage thereto is attributable to
Tenant's negligence or misuse) and doors of the Premises whole and in good
condition with glass of the same quality as that injured or broken, damage by
fire only excepted; and at the expiration or termination of this Lease,
peaceably to yield up the Premises and all alterations and additions thereto in
good order, repair and condition, reasonable wear and tear, damage caused by
casualty, and damage caused by taking only excepted, first removing all goods
and effects of Tenant and, to the extent specified by Landlord by notice
("Improvement Removal Notice") to Tenant given at least ten (10) days before
such expiration or termination, all alterations and additions made by Tenant and
all partitions, and repairing any damage caused by such removal and restoring
the Premises and leaving them clean and neat. If Tenant so requests in writing
at the time that Tenant requests Landlord's approval of any alteration or
addition, Landlord shall give its Improvement Removal Notice (i.e. Landlord
shall make its election as to whether such alteration or addition is to be
removed at the end of the term of this Lease), at the time that Landlord
approves Tenant's plans for the same.

         Tenant will remove any personal property from the Building and the
Premises upon or prior to the expiration or termination of this Lease and any
such property which shall remain in the Building or the Premises thereafter
shall be conclusively deemed to have been abandoned, and may either be retained
by Landlord as its property or sold or otherwise disposed of in such manner as
Landlord may see fit. If any part thereof shall be sold, then Landlord may
receive and retain the proceeds of such sale and apply the same, at its option,
against the expenses of the sale, the cost of moving and storage, any arrears of
Annual Fixed Rent, additional or other charges payable hereunder by Tenant to
Landlord and any damages to which Landlord may be entitled under Section 7.2
hereof or pursuant to law.

5.3  Use

         Continuously from the commencement of the Term to use and occupy the
Premises for the Permitted Uses, and not to injure or deface the Premises,
Building or Lot, nor to permit in the Premises any auction sale, vending
machine, or inflammable fluids or chemicals, or nuisance, or the emission from
the Premises of any objectionable noise or odor, nor to use or devote the
Premises or any part thereof for any purpose other than the Permitted Uses, nor
any use thereof which is inconsistent with the maintenance of the Building as an
office building of first class quality in maintenance, use and occupancy, or
which is improper, offensive, contrary to law or ordinance or liable to
invalidate or increase the premiums for any insurance on the Building or its
contents or liable to render necessary any alteration or addition to the
Building.


                                      -25-
<PAGE>   26
5.4      Obstructions, Items Visible from Exterior;
         Rules and Regulations

         Not to obstruct in any manner any portion of the Building not hereby
leased or any portion thereof or of the Lot used by Tenant in common with
others; not without prior consent of Landlord to permit the painting or placing
of any signs, curtains, blinds, shades, awnings, aerials or flagpoles, or the
like, visible from outside the Premises; and to comply with all reasonable Rules
and Regulations now or hereafter made by Landlord, or which Tenant has been
given notice, for the care and use of the Building and Lot and their facilities
and approaches. Landlord shall use reasonable efforts to enforce such Rules and
Regulations; provided however, that in no event shall Landlord be liable to
Tenant for the failure of other occupants of the Building to conform to such
Rules and Regulations or for any other act or omission of other occupants of the
Building.

5.5  Safety Appliances

         To keep the Premises equipped with all safety appliances required by
law or ordinance or any other regulation of any public authority because of any
use made by Tenant other than normal office use, and to procure all licenses and
permits so required because of such use and, if requested by Landlord, to do any
work so required because of such use, it being understood that the foregoing
provisions shall be construed to broaden in any way Tenant's Permitted Uses.

5.6  Assignment; Sublease

         A. Except as provided in this Section 5.6, Tenant covenants and agrees
that neither this Lease nor the term and estate hereby granted, nor any interest
herein or therein, will be assigned, mortgaged, pledged, encumbered or otherwise
transferred, voluntarily, by operation of law or otherwise, and that neither the
Premises, nor any part thereof will be encumbered in any manner by reason of any
act or omission on the part of Tenant, or used or occupied, or permitted to be
used or occupied, or utilized for desk space for mailing privileges, by anyone
other than Tenant, or for any use or purposes other than the Permitted Uses
stated in Article 1, or be sublet, or offered or advertised for subletting.
Notwithstanding the foregoing, it is hereby expressly understood and agreed,
however, if Tenant is a corporation, that the assignment or transfer of this
Lease, and the term and estate hereby granted, to any corporation into which
Tenant is merged or with which Tenant is consolidated which corporation shall
have a net worth at least equal to that of Tenant immediately prior to such
merger or consolidation (such corporation being hereinafter called "Tenant
Successor"), shall not be deemed to be prohibited hereby is, and upon the
express condition that such Tenant Successor and Tenant shall promptly execute,
acknowledge and deliver to Landlord an agreement in form and substance
satisfactory to Landlord whereby such Tenant Successor shall agree to be
independently bound by and upon all the covenants,


                                      -26-
<PAGE>   27
agreements, terms, provisions and conditions set forth in this Lease on the part
of Tenant to be performed, and whereby such Tenant Successor shall expressly
agree that the provisions of this Section 5.6 shall, notwithstanding such
assignment or transfer, continue to be binding upon it with respect to all
future assignments and transfers.

         B.       Notwithstanding anything to the contrary in the Lease
                  contained:

                  1.       Tenant shall, prior to offering or advertising the
                           Premises, or any portion thereof for sublease or
                           assignment give Landlord a Recapture Offer, as
                           hereinafter defined.

                  2.       For the purposes hereof a "Recapture Offer" shall be
                           defined as a notice in writing from Tenant to
                           Landlord which:

                           (a)      States that Tenant desires to sublet the
                                    Premises, or a portion thereof, or to assign
                                    its interest in this Lease.

                           (b)      Identifies the affected portion of the
                                    Premises ("Recapture Premises").

                           (c)      Identifies the period of time ("Recapture
                                    Period") during which Tenant proposes to
                                    sublet the Recapture Premises or to assign
                                    its interest in the Lease.

                           (d)      Offers to Landlord to terminate the Lease in
                                    respect of the Recapture Premises (in the
                                    case of a proposed assignment of Tenant's
                                    interest in the Lease or a subletting for
                                    the remainder of the term of the Lease) or
                                    to suspend the term of the Lease pro tanto
                                    in respect of the Recapture Period (i.e. the
                                    term of the Lease in respect of the
                                    Recapture Premises shall be terminated
                                    during the Recapture Period and Tenant's
                                    rental obligations shall be reduced in
                                    proportion to the ratio of the Total
                                    Rentable Area of the Recapture Premises to
                                    the Total Rentable Area of the premises then
                                    demised to Tenant).

                  3.       Landlord shall have forty-five (45) days to accept a
                           Recapture Offer. If Landlord does not timely give
                           written notice to Tenant accepting a Recapture Offer,
                           then Landlord agrees that it will not unreasonably
                           withhold or delay its consent to a sublease of the
                           Recapture Premises for the Recapture Period, or an
                           assignment of


                                      -27-
<PAGE>   28
                           Tenant's interest in the Lease, as the case may be,
                           to a Qualified Transferee, as hereinafter defined.

                  4.       For the purposes hereof, a "Qualified Transferee"
                           shall be defined as a person, firm or corporation
                           which, in Landlord's reasonable opinion:

                           (a)      is financially responsible and of good
                                    reputation; and

                           (b)      is engaged in a business, the functional
                                    aspects of which, with respect to the
                                    Premises, are similar to the use of other
                                    premises made by other office space tenants
                                    in the Building; and

                           (c)      is not a Restricted Building Occupant, as
                                    hereinafter defined.

                  5.       For the purposes hereof, a "Restricted Building
                           Occupant" shall be defined as any tenant or subtenant
                           of the Building who:

                           (a)      Desires to sublease the Recapture Premises
                                    for expansion purposes only; and

                           (b)      Such Occupant's occupancy of the Recapture
                                    Premises will not, either directly or
                                    indirectly, cause a vacancy in the premises
                                    which such occupant then occupies in the
                                    Building; and

                           (c)      Such Occupant's need, as to the size of
                                    premises and length of term, cannot then
                                    (i.e., at the time that Tenant requests
                                    Landlord's consent to such Occupant) be
                                    satisfied by Landlord.

                  6.       Notwithstanding anything to the contrary in this
                           Paragraph B contained:

                           (a)      If Tenant is in default (i.e. after giving
                                    of any applicable notice and the expiration
                                    of any applicable grace periods) of its
                                    obligations under the Lease at the time that
                                    it makes the aforesaid offer to Landlord,
                                    such default shall be deemed to be a
                                    "reasonable" reason for Landlord withholding
                                    its consent to any proposed subletting or
                                    assignment; and


                                      -28-
<PAGE>   29
                           (b)      If Tenant does not enter into a sublease
                                    with a subtenant (or an assignment to an
                                    assignee, as the case may be) approved by
                                    Landlord, as aforesaid, on or before the
                                    date which is one hundred (100) days after
                                    the earlier of: (x) the expiration of said
                                    forty-five (45) day period, or (y) the date
                                    that Landlord notifies Tenant that Landlord
                                    will not accept Tenant's offer to terminate
                                    or suspend the Lease, then Landlord shall
                                    have the right arbitrarily to withhold its
                                    consent to any subletting or assignment
                                    proposed to be entered into by Tenant after
                                    the expiration of said one hundred (100) day
                                    period unless Tenant again offers, in
                                    accordance with this Paragraph B, either to
                                    terminate or to suspend the Lease in respect
                                    of the portion of the premises proposed to
                                    be sublet (or in respect of the entirety of
                                    the premises in the event of a proposed
                                    assignment, as the case may be). If Tenant
                                    shall make any subsequent offers to
                                    terminate or suspend the Lease pursuant to
                                    this Paragraph B, any such subsequent offers
                                    shall be treated in all respects as if it is
                                    Tenant's first offer to suspend or terminate
                                    the Lease pursuant to this Paragraph B,
                                    provided that the period of time Landlord
                                    shall have in which to accept or reject such
                                    subsequent offer shall be thirty (30) days.

                  7.       Notwithstanding anything to the contrary herein
                           contained, Tenant shall have no right, under this
                           Paragraph B hereof, prior to the date one (1) year
                           after the Term Commencement Date. Without limiting
                           the foregoing, Tenant shall have no right to give
                           Landlord a Recapture Offer prior to the date one (1)
                           year after the Term Commencement Date.

                  8.       No subletting or assignment shall relieve Tenant of
                           its primary obligation as party-Tenant hereunder, nor
                           shall it reduce or increase Landlord's obligations
                           under the Lease provided, however, that Tenant's
                           obligations or Tenant hereunder shall be suspended
                           with respect to the Recapture Space during the
                           Recapture Period if Landlord elects to accept a
                           Recapture Offer.

         C. In the event of an assignment of this Lease or a sublease of the
premises or any portion thereof to anyone other than a Tenant Successor, Tenant
shall pay to Landlord fifty (50%) percent of any Net Sublease Profits (as
defined below), payable in accordance with the following.


                                      -29-
<PAGE>   30
In the case of an assignment of this Lease, "Net Sublease Profit": (1) shall be
defined as a lump sum in the amount (if any) by which any consideration paid by
the assignee in consideration of or as an inducement to Tenant to make said
assignment exceeds the reasonable attorneys' fees, construction costs and
brokerage fees incurred by Tenant in order to effect such assignment
(collectively, "Sublease Expenses"), and (2) be payable concurrently with the
payment to be made by the assignee to Tenant. In the case of a sublease, "Net
Sublease Profit": (3) shall be defined as a monthly amount equal to the amount
by which the sublease rent and other charges payable by the subtenant to Tenant
under the sublease exceed the sum of the rent and other charges payable under
this Lease for the premises or allocable to the sublet portion thereof, plus a
monthly amount equal to the Sublease Expenses divided by the number of months in
the term of the sublease, and (4) shall be payable on a monthly basis
concurrently with the subtenant's payment of rent to Tenant under the sublease.

         D. If Tenant is an individual who uses and/or occupies the Premises
with partners, or if Tenant is a partnership, then:

                  (i) Each present and future partner shall be personally bound
by and upon all of the covenants, agreements, terms, provisions and conditions
set forth in this Lease on the part of Tenant to be performed; and

                  (ii) In confirmation of the foregoing, Landlord may (but
without being required to do so) request (and Tenant shall duly comply) that
Tenant, at the time that Tenant admits any new partner to its partnership, shall
require each such new partner to execute an agreement in form and substance
satisfactory to Landlord whereby such new partner shall agree to be personally
bound by and upon all of the covenants, agreements, terms, provisions and
conditions of this Lease on the part of Tenant to be performed, without regard
to the time when such new partner is admitted to partnership or when any
obligations under any such covenants, etc., accrue.

         E. The listing of any name other than that of Tenant, whether on the
doors of the Premises or on the Building directory, or otherwise, shall not
operate to vest in any such other person, firm or corporation any right or
interest in this Lease or in the Premises or be deemed to effect or evidence any
consent of Landlord, it being expressly understood that any such listing is a
privilege extended by Landlord revocable at will by written notice to Tenant.

         F. If this Lease be assigned, or if the Premises or any part thereof be
sublet or occupied by anybody other than Tenant, Landlord may, at any time and
from time to time, collect rent and other charges from the assignee, subtenant
or occupant, and apply the net amount collected to the rent and other charges
herein reserved, then due and hereafter becoming due, but no assignment,
subletting, occupancy or collection shall be deemed a waiver of this covenant,
or the acceptance of the assignee, subtenant or occupant as a tenant, or a
release of Tenant from the further performance by Tenant of covenants on the
part of Tenant herein contained. Any consent


                                      -30-
<PAGE>   31
by Landlord to a particular assignment or subletting shall not in any way
diminish the prohibition stated in the first sentence of this Section 5.6 or the
continuing liability of the Tenant named in Article 1 as the party-Tenant under
this Lease. No assignment or subletting or use of the Premises by an affiliate
of Tenant shall affect the Permitted Uses for which the Premises may be used as
stated in Article 1.

5.7  Indemnity; Insurance

         To defend with counsel first reasonably approved by Landlord, save
harmless, and indemnify Landlord from any liability for injury, loss. accident
or damage to any person or property, and from any claims, actions, proceedings
and expenses and costs in connection therewith (including without limitation
reasonable counsel fees), (i) arising from (a) the omission, fault, willful act,
negligence or other misconduct of Tenant, or of Tenant's employees, agents or
contractors, or (b) from any use made or thing done or occurring on the Premises
not due to the omission, fault, willful act, negligence or other misconduct of
Landlord or of Landlord's employees, agents, or contractors, or (ii) resulting
from the failure of Tenant to perform and discharge its covenants and
obligations under this Lease; to maintain in responsible companies qualified to
do business, and in good standing, in Massachusetts public liability insurance
covering the Premises insuring Landlord as well as Tenant with limits which
shall, at the commencement of the Term, be at least equal to those stated in
Article 1 and from time to time during the Term shall be for such higher limits,
if any as are customarily carried in the Burlington area with respect to similar
properties, and Workmen's Compensation Insurance with statutory limits covering
all of Tenant's employees working in the Premises, and to deposit promptly with
Landlord certificates for such insurance, and all renewals thereof bearing the
endorsement that the policies will not be canceled until after ten (10) days'
written notice to Landlord.

5.8  Personal Property at Tenant's Risk

         That all of the furnishings, fixtures, equipment, effects and property
of every kind, nature and description of Tenant, and all persons claiming by,
through or under Tenant which, during the continuance of this Lease or any
occupancy of the Premises by Tenant or anyone claiming under Tenant, may be on
the Premises or elsewhere in the Building or on the Lot, shall be at the sole
risk and hazard of Tenant, and if the whole or any part thereof shall be
destroyed or damaged by fire, water or otherwise, or by the leakage or bursting
of water pipes, steam pipes, or other pipes, by theft or from any other cause,
no part of said loss or damage is to be charged to or be borne by Landlord,
except that Landlord shall in no event be indemnified or held harmless or
exonerated from any liability to Tenant or to any person, for any injury, loss,
damage or liability to the extend such indemnity, hold harmless or exoneration
is prohibited by law.

5.9  Right of Entry


                                      -31-
<PAGE>   32
         To permit Landlord and its agents: to examine the Premises at
reasonable times and upon reasonable notice (except that no notice shall be
required during an emergency or during normal cleaning operations), if Landlord
shall so elect, to make any repairs or replacements Landlord may deem necessary;
to remove, at Tenant's expense, any alterations, additions, signs, curtains,
blinds, shades, awnings, aerials, flagpoles, or the like not consented to in
writing; and at reasonable times and upon reasonable notice to Tenant to show
the Premises to prospective tenants during the eighteen months preceding
expiration of the Term and to prospective purchasers and mortgagees at all
reasonable times. At Tenant's election, a representative of Tenant may accompany
Landlord and its agents during any such entry.

         Without incurring any liability to Tenant, Landlord may permit access
to the Premises and open the same, whether or not Tenant shall be present, upon
any demand or any receiver, trustee, assignee for the benefit of creditors,
sheriff, marshall or court officer entitled to, or reasonably purporting to be
entitled to, such access for the purposes of taking possession of, or removing,
Tenant's property or for any other lawful purposes (but this provision and any
action by Landlord hereunder shall not be deemed a recognition by Landlord that
the person or official making such demand has any right or interest in or to
this Lease, or in or to the Premises), or upon demand of any representation of
the fire, police, building, sanitation or other department of the city, state or
federal governments.

5.10  Floor Load; Prevention of Vibration and Noise

         Not to place a load upon the Premises exceeding an average rate of 70
pounds of live load per square foot of floor area (partitions shall be
considered as part of the live load); Landlord reserves the right to prescribe
the weight and position of all safes, files and heavy equipment which Tenant
desires to place in the Premises so as properly to distribute the weight
thereof; Tenant's business machines and mechanical equipment which cause
vibration or noise that may be transmitted to the Building structure or to any
other space in the Building shall be so installed, maintained and used by Tenant
as to eliminate such vibration or noise. Notwithstanding the foregoing, subject
to obtaining Landlord's prior written approval, which approval shall not be
unreasonably withheld, Tenant shall have the right to exceed the foregoing floor
loading limit for its data center, provided that Tenant construct such
structural support as is necessary to allow such floor loading.


                                      -32-
<PAGE>   33
5.11  Personal Property Taxes

          To pay promptly when due all taxes which may be imposed upon personal
property (including without limitation, fixtures and equipment) in the Premises
to whomever assessed.

5.12  Payment of Litigation Expenses

          As additional rent, to pay all reasonable costs, counsel and other
fees incurred by Landlord in connection with the successful enforcement (in
litigation or arbitration proceedings, as the case may be) by Landlord of any
obligations of Tenant under this Lease. Landlord agrees to pay all reasonable
costs, counsel and other fees incurred by Tenant in connection with the
successful enforcement (in litigation or arbitration proceedings, as the case
may be) by Tenant of any obligation of Landlord under this Lease.

5.13  Compliance with Insurance Regulations

          Not to do or permit to be done any act or thing upon the Premises
which will invalidate or be in conflict with the terms of the Massachusetts
standard form of fire, boiler, sprinkler, water damage or other insurance
policies covering the Building and the fixtures and property therein; Tenant
shall, at its own expense, comply with all rules, regulations, and requirements
of the National Board of Fire Underwriters or any state or other similar body
having jurisdiction, and shall not knowingly do or permit anything to be done in
or upon the Premises in a manner which increases the rate of fire insurance upon
the building or on any property or equipment located therein.


                                   ARTICLE VI

                               CASUALTY AND TAKING

6.1  Termination or Restoration; Rent Adjustment

         A. In case during the Term all or any material part of the Premises or
the Building or the Lot are damaged materially by fire or other casualty or by
action of public or other authority in consequence thereof, or are taken by
eminent domain or Landlord receives compensable damage by reason of anything
lawfully done in pursuance of public or other authority, this Lease shall
terminate at Landlord's election, which may be made notwithstanding Landlord's
entire interest may have been divested, by notice given to Tenant within three
(3) months after the casualty or taking specifying the effective date of
termination. The effective date of termination specified by Landlord shall not
be less than 15 nor more than 30 days after the date of notice of


                                      -33-
<PAGE>   34
such termination. Unless terminated pursuant to the foregoing provisions, this
Lease shall remain in full force and effect following any such damage or taking,
subject, however, to the following provisions.

         B. If in any such case the Premises, Tenant's means of access thereto,
rendered unfit for use and occupation and this Lease is not so terminated,
Landlord shall use due diligence (following the expiration of the period in
which Landlord may terminate this Lease pursuant to the foregoing provisions of
this Section 6.1), subject to the then applicable statutes, building codes,
zoning ordinances, and regulations of any governmental authority and at the
expense of Landlord (but only to the extent of insurance proceeds made available
to Landlord) to put the Premises or Tenant's means of access, or in case of
taking what may remain thereof (excluding in case of both casualty and taking
any items installed or paid for by Tenant which Tenant may be required to remove
pursuant to Section 5.2), into proper condition for use and occupation and a
just proportion of the Annual Fixed Rent and additional rent according to the
nature and extent of the injury shall be abated from the date of such casualty
or taking until the Premises or the means of access, or such remainder shall
have been put by Landlord in such condition; and in case of taking which
permanently reduces the area of the Premises, a just proportion of the Annual
Fixed Rent and additional rent shall be abated for the remainder of the Term.

         C. In the event that the premises or the Building are damaged by fire
or other casualty to such an extent so as to render the premises untenantable,
and if Landlord shall fail to substantially complete said repairs or restoration
within a period ("Restoration Period") which is eleven (11) months after the
date of such fire or other casualty for any reason other than Tenant's fault,
Tenant may terminate this Lease by giving Landlord written notice as follows:

         (1)      Said notice shall be given after said Restoration Period.

         (2)      Said notice shall set forth an effective date which is not
                  earlier than thirty (30) days after Landlord receives said
                  notice.

         (3)      If said repairs or restoration are substantially complete on
                  or before the date thirty (30) days (which thirty-(30)-day
                  period shall be extended by the length of any delays caused by
                  Tenant or Tenant's contractors) after Landlord receives such
                  notice, said notice shall have no further force and effect.

         (4)      If said repairs or restoration are not substantially complete
                  on or before the date thirty (30) days (which thirty-(30)-day
                  period shall be extended by the length of any delays caused by
                  Tenant or Tenant's contractors) after Landlord receives such
                  notice, the Lease shall terminate as of said effective date.

                                      -34-
<PAGE>   35
         D. If there is taking which reduces the ratio of parking spaces serving
the Building to less than 3.0 parking spaces per 1,000 square feet of occupied
rentable area in the Building ("Minimum Parking Ratio"), Tenant shall have the
right to terminate the term of this Lease by giving written notice to Landlord
within thirty (30) days of the loss of the use of parking spaces by Tenant. If
Landlord fails, within ninety (90) days of Landlord's receipt of Tenant's notice
to provide alternate parking within a reasonable distance from the Building
satisfying the Minimum Parking Ratio, then the term of this Lease shall
terminate as of the date ninety (90) days after Landlord receives such notice.

6.2  Eminent Domain

         Landlord reserves to itself any and all rights to receive awards made
for damages to the Premises and Building and Lot and the leasehold hereby
created, or any one or more of them, accruing by reason of exercise of eminent
domain or by reason of anything lawfully done in pursuance of public or other
authority. Tenant hereby releases and assigns to Landlord all Tenant's rights to
such awards, and covenants to deliver such further assignments and assurances
thereof as Landlord may from to time request. Tenant hereby irrevocably
designates and appoints Landlord as its attorney-in-fact to execute and deliver
in Tenant's name and behalf all such further assignments thereof.
Notwithstanding anything to the contrary herein contained, Tenant shall be
entitled to receive any separate award for relocation expenses and for the cost
of its trade fixtures.

6.3  Temporary Taking

         In the event of taking of the Premises or any part thereof for
temporary use, (i) this Lease shall be and remain unaffected thereby and rent
shall not abate, and (ii) Tenant shall be entitled to receive for itself such
portion or portions of any award made for such use with respect to the period of
the taking which is within the Term, provided that if such taking shall remain
in force at the expiration or earlier termination of this Lease, Tenant shall
then pay to Landlord a sum equal to the reasonable cost of performing Tenant's
obligations under Section 5.2 with respect to surrender of the Premises and upon
such payment shall be excused from such obligations.


                                   ARTICLE VII

                                     DEFAULT

7.1  Events of Default

         If (a) Tenant shall neglect or fail to perform or observe any of
Tenant's covenants or agreements herein, including the obligation to pay, when
due, Annual Fixed Rent or additional rent, and such failure continues, in the
case of Annual Fixed Rent or additional rent, for more than


                                      -35-
<PAGE>   36
ten (10) days after written notice thereof, or in any other case, for more than
thirty (30) days after written notice thereof and such additional time, if any,
as is reasonably necessary to cure the default if the default is of such a
nature that it cannot reasonably be cured in thirty (30) days, provided however,
that no such notice need be given and no such default shall be curable if on two
(2) prior occasions within the same calendar year there had been a default which
had been cured after notice thereof had been given by Landlord to Tenant as
herein provided; or if Tenant or any guarantor or any guarantor of any of
Tenant's obligations under this Lease, (b) is not paying its debts as such debts
become due, becomes insolvent, seeks relief under any chapter of the U.S.
Bankruptcy Code (or any insolvency or similar law of any jurisdiction), or (c)
proposes any dissolution, liquidation, composition, financial reorganization or
recapitalization with creditors; or (d) makes an assignment or trust mortgage
for the benefit of creditors or (e) if a receiver, trustee, custodian or similar
agent is appointed or takes possession with respect to any property or business
of Tenant or such guarantor, or (f) Tenant shall desert or abandon the Premises
or the same shall become, or appear to have become, vacant (whether or not the
key shall have been surrendered or the rent shall have been paid), or (g) any
event shall occur or any contingency shall arise whereby this Lease, or the term
and estate thereby created, would (by operation of law or otherwise) devolve
upon or pass to any person, firm or corporation other than Tenant, except as
expressly permitted under Section 5.6 hereof then, in any such case, whether or
not the Term shall have begun, Landlord may immediately, or at any time while
such default exists and without further notice, terminate this Lease by entry by
Landlord or upon the giving of notice to Tenant, and this Lease shall come to an
end as fully and completely as if such date were the date herein originally
fixed for the expiration of the Term, and Tenant shall then quit and surrender
the Premises to Landlord, but Tenant shall remain liable as hereinafter
provided.

7.2  Damages

         In the event that this Lease is terminated under any of the provisions
contained in Section 7.1 or shall be otherwise terminated for breach of any
obligation of Tenant, Tenant covenants to pay forthwith to Landlord, as
compensation, the present value of the excess of the total rent reserved for the
residue of the Term over the rental value of the Premises for said residue of
the Term. In calculating the rent reserved there shall be included, in addition
to the Annual Fixed Rent and all additional rent, the value of all other
considerations agreed to be paid or performed by Tenant for said residue. Tenant
further covenants as an additional and cumulative obligation after any such
ending to pay punctually to Landlord all the sums and perform all the
obligations which Tenant covenants in this Lease to pay and to perform in the
same manner and to the same extent and at the same time as if this Lease had not
been terminated. In calculating the amounts to be paid by Tenant under the next
foregoing covenant Tenant shall be credited with any amount paid to Landlord as
compensation as in this Section 7.2 provided and also with the net proceeds of
any rent obtained by Landlord by reletting the Premises, after deducting all
Landlord's expenses incurred by Landlord in good faith in connection with such
reletting, including, without limitation, all repossession costs, brokerage
commissions, fees for legal services and expenses of


                                      -36-
<PAGE>   37
preparing the Premises for such reletting, it being agreed by Tenant that
Landlord may (i) relet the Premises or any part or parts thereof, for a term or
terms which may at Landlord's option be equal to or less than or exceed the
period which would otherwise have constituted the balance of the Term and may
grant such concessions and free rent as Landlord in its sole judgment considers
advisable or necessary to relet the same and (ii) make such alterations, repairs
and decorations in the Premises as Landlord in its sole judgment considers
advisable or necessary to relet the same, and no action of Landlord in
accordance with the foregoing or failure to relet or to collect rent under
reletting shall operate or be construed to release or reduce Tenant's liability
as aforesaid.

         In lieu of any other damages or indemnity and in lieu of full recovery
by Landlord of all sums payable under all the foregoing provisions of this
Section 7.2, and Landlord may, by written notice to Tenant, at any time after
this Lease is terminated under any of the provisions contained in Section 7.1 or
is otherwise terminated for breach of any obligation of Tenant and before such
full recovery, elect to recover, and Tenant shall thereupon pay, as liquidated
damages, an amount equal to: (i) the aggregate of the Annual Fixed Rent and
additional rent accrued under Section 2.5, 2.6 and 2.7 in the period commencing
as of the date of such termination and ending as of the earlier of: (x) the date
12 months ended next following such termination, and (y) the last day of the
then current term of the Lease, plus (ii) the amount of Annual Fixed Rent and
additional rent of any kind accrued and unpaid at the time of termination and
less the amount of any recovery by Landlord under the foregoing provisions of
this Section 7.2 up to the time of payment of such liquidated damages.

         Nothing contained in this Lease shall limit or prejudice the right of
Landlord to prove for and obtain in proceedings for bankruptcy or insolvency by
reason of the termination of this Lease, an amount equal to the maximum allowed
by any statute or rule of law in effect at the time when, and governing the
proceedings in which, the damages are to be proved, whether or not the amount be
greater, equal to, or less than the amount of the loss or damages referred to
above.

                                      -37-
<PAGE>   38
                                  ARTICLE VIII

                                  MISCELLANEOUS

8.1  Computation of Rentable Floor Areas

         For all purposes of this Lease, (a) the rentable area for single tenant
office floors is the gross area of the floor measured from the plane of the
inside surface of the exterior glass line deducting therefrom the non rentable
areas of the floor and adding a pro-rata share of the building common area, but
allowing no deductions for columns or projections within such floor, (b) the
rentable area for multi-tenant office floors is the gross area of Tenant's Space
measured from the plane of the inside surface of the exterior glass line to the
middle of the demising walls, and adding a pro-rata share of the building common
areas and of the floor common area, but allowing no deductions for columns or
projections within such floor, (c) non-rentable areas of the floor are: public
elevator shafts and elevator machine rooms, machinery shafts and common
stairways and stairwells, (d) floor common areas are restrooms, elevator lobby,
janitor closets, common corridors, and mechanical rooms, (e) the building common
area is the first floor lobby, loading dock, mail room, electrical equipment,
mechanical room and health club.

8.2  Notice of Lease; Consent of Approval; Notices;
     Bind and Inure

         The titles of the Articles are for convenience only and are not to be
considered in construing this Lease. Tenant agrees not to record this Lease, but
upon request of either party both parties shall execute and deliver a notice of
this Lease in form appropriate for recording or registration, and if this Lease
is terminated before the term expires, an instrument in such form acknowledging
the date of termination. Whenever any notice, approval, consent, request or
election is given or made pursuant to this Lease it shall be in writing.
Communications and payments shall be addressed if to Landlord at Landlord's
Original Address or at such other address as may have been specified by prior
notice to Tenant, and if to Tenant, at Tenant's Original Address or at such
other place as may have been specified by prior notice to Landlord. Any
communication so addressed shall be deemed duly given when mailed by registered
or certified mail, return receipt requested. If Landlord by notice to Tenant at
any time designates some other person to receive payments or notices, all
payments or notices thereafter by Tenant shall be paid or given to the person
designated until notice to the contrary is received by Tenant from Landlord. The
obligations of this Lease shall run with the land, and this Lease shall be
binding upon and inure to the benefit of the parties hereto and their respective
successors and assigns, except that only the original Landlord named herein
shall be liable for obligations accruing before the beginning of the Term, and
thereafter the original Landlord named herein and each successive owner of the
Premises shall be liable only for obligations accruing during the period of
ownership.


                                      -38-
<PAGE>   39
8.3  Landlord's Failure to Enforce

         The failure of Landlord to seek redress for violation of, or to insist
upon strict performance of, any covenant or condition of this Lease, or with
respect to such failure of Landlord to enforce any of the Rules and Regulations
referred to in Section 5.4, whether heretofore or hereafter adopted by Landlord,
shall not be deemed a waiver of such violation nor prevent a subsequent act
which would have originally constituted a violation, from having all the force
and effect of an original violation, nor shall the failure of Landlord to
enforce any of said Rules and Regulations against any other tenant of the
Building be deemed a waiver of any such Rule or Regulation. Notwithstanding the
foregoing, Landlord agrees to use reasonable efforts to enforce said Rules and
Regulations against such other tenants of the Building, provided however, that
in no event shall Landlord be liable to Tenant on account of the acts or
omissions of the tenants of the Building. The receipt by Landlord of Annual
Fixed Rent or additional rent with knowledge of the breach of any covenant of
this Lease shall not be deemed a waiver of such breach. No provision of this
Lease shall be deemed to have been waived by Landlord, or by Tenant, unless such
waiver be in writing signed by the party to be charged. No consent or waiver,
express or implied, by Landlord or Tenant, to or of any breach of any agreement
or duty shall be construed as a waiver or consent to or of any other breach of
the same or any other agreement or duty.

8.4  Acceptance of Partial Payments of Rent; Delivery of Keys

         No acceptance by Landlord of a lesser sum than the Annual Fixed Rent
and additional rent then due shall be deemed to be other than on account of the
earliest installment of such rent due, nor shall any endorsement or statement on
any check or any letter accompanying any check or payment as rent be deemed an
accord and satisfaction, and Landlord may accept such check or payment without
prejudice to Landlord's right to recover the balance of such installment or
pursue any other remedy in this Lease provided. The delivery of keys to any
employee of Landlord or to Landlord's agent or any employee thereof shall not
operate as a termination of this Lease or surrender of the Premises.

8.5  Cumulative Remedies

         The specific remedies to which Landlord may resort under the terms of
this Lease are cumulative and are not intended to be exclusive of any other
remedies or means of redress to which it may be lawfully entitled in case of any
breach or threatened breach by Tenant of any provisions of this Lease. In
addition to other remedies provided in this Lease, Landlord shall be entitled to
the restraint by injunction of the violation or attempted or threatened
violation of any of the covenants, conditions or provisions of this Lease or to
a decree compelling specific performance of any such covenants, conditions or
provisions.


                                      -39-
<PAGE>   40
8.6  Partial Invalidity

         If any term of this Lease, or the application thereof to any person or
circumstances, shall to any extent be invalid or unenforceable, the remainder of
this Lease, or the application of such term to persons or circumstances other
than those as to which it is invalid or unenforceable shall not be affected
thereby, and each term of this Lease shall be valid and enforceable to the
fullest extent permitted by law.

8.7  Self-Help

         If Tenant shall at any time default in the performance of any
obligation under this Lease, Landlord shall have the right, but shall not be
obligated, to enter upon the Premises and to perform such obligation
notwithstanding the fact that no specific provision for such substituted
performance by Landlord is made in this Lease with respect to such default. In
performing such obligation, Landlord may make any payment of money or perform
any other act. All sums so paid by Landlord (together with interest at the rate
of 2 1/2 percentage points over the then prevailing prime rate in Boston as set
by The First National Bank in Boston) and all necessary incidental costs and
expenses in connection with the performance of any such act by Landlord, shall
be deemed to be additional rent under this Lease and shall be payable to
Landlord immediately on demand. Landlord may exercise the foregoing rights
without waiving any other of its rights or releasing Tenant from any of its
obligations under this Lease.

8.8  Tenant's Estoppel Certificate

         Tenant agrees from time to time, upon not less than fifteen (15) days'
prior written request by Landlord, to execute, acknowledge and deliver to
Landlord a statement in writing certifying that this Lease is unmodified and in
full force and effect and that Tenant has no defenses, offsets or counterclaims
against its obligations to pay the Annual Fixed Rent and additional rent and to
perform its other covenants under this Lease and that, to the best of Tenant's
knowledge, there are no uncured defaults of Landlord or Tenant under this lease
(or, if there have been any modifications that the same is in full force and
effect as modified and stating the modifications and, if there are any defenses,
offsets, counterclaims, or defaults, setting them forth in reasonable detail),
and the dates to which the Annual Fixed Rent, additional rent and other charges
have been paid. Any such statement delivered pursuant to this Section 8.8 may be
relied upon by a prospective purchaser or mortgagee of the Premises or any
prospective assignee of any mortgagee of the Premises. Time is of the essence in
respect of any such requested certificate, Tenant hereby acknowledging the
importance of such certificates in mortgage financing arrangements, prospective
sale and the like. Tenant hereby appoints Landlord Tenant's attorney-in-fact in
its name and behalf to execute such statement if Tenant shall fail to execute
such statement within such fifteen-(15)-day period.


                                      -40-
<PAGE>   41
8.9  Waiver of Subrogation

         In any case in which Tenant shall be obligated to pay to Landlord any
loss, cost, damage, liability, or expense suffered or incurred by Landlord,
Landlord shall allow to Tenant as an offset against the amount thereof (i) the
net proceeds of any insurance collected by Landlord for or on account of such
loss, cost, damage, liability or expense, provided that the allowance of such
offset does not invalidate or prejudice the policy or policies under which such
proceeds were payable, and (ii) if such loss, cost, damage, liability or expense
shall have been caused by a peril against which Landlord has agreed to procure
insurance coverage under the terms of this Lease, the amount of such insurance
coverage, whether or not actually procured by Landlord.

         In any case in which Landlord or Landlord's agents shall be obligated
to pay to Tenant any loss, cost, damage, liability or expense suffered or
incurred by Tenant, Tenant shall allow to Landlord and Landlord's agents as an
offset against the amount thereof (i) the net proceeds of any insurance
collected by Tenant for or on account of such loss, cost, damage, liability, or
expense, provided that the allowance of such offset does not invalidate the
policy or policies under which such proceeds were payable and (ii) the amount of
any loss, cost, damage, liability or expense caused by a peril covered by fire
insurance with the broadest form of property insurance generally available on
property in buildings of the type of the Building, whether or not actually
procured by Tenant.

         The parties hereto shall each procure an appropriate clause in, or
endorsement on, any property insurance policy covering the Premises and the
Building and personal property, fixtures and equipment located thereon and
therein, pursuant to which the insurance companies waive subrogation or consent
to a waiver of right of recovery. Having obtained such clauses and/or
endorsements each party hereby agrees that it will not make any claim against or
seek to recover from the other for any loss or damage to its property or the
property of others resulting from firm or other perils covered by such property
insurance.

8.10  All Agreements Contained

          This Lease contains all of the agreements of the parties with respect
to the subject matter thereof and supersedes all prior dealings between them
with respect to such subject matter.

8.11  Brokerage

          Landlord and Tenant each warrant that they have had no dealings with
any broker or agent other than Fallon, Hines & O'Connor and Meredith & Grew
("Co-Brokers") in connection with the Lease and covenant to defend, hold
harmless and indemnify each other from and against any and all cost, expense or
liability for any compensation, commissions and charges claimed by


                                      -41-
<PAGE>   42
any broker or agent claiming by or through them with respect to dealings in
connection with this Lease or the negotiation thereof. Landlord agrees to pay
Co-Brokers a commission in connection with the execution of this Lease pursuant
to separate agreements between Landlord and Co-Brokers.

8.12  Submission Not an Option

          The submission of this Lease or a summary of some or all of its
provisions for examination does not constitute a reservation of or option for
the Premises or an offer to lease.

8.13  Applicable Law

          This Lease, and the rights and obligations of the parties hereto,
shall be construed and enforced in accordance with the laws of the Commonwealth
of Massachusetts.

8.14  Waiver of Jury Trial

          Landlord and Tenant hereby waive trial by jury in any action,
proceeding or counterclaim brought by either of the parties hereto against the
other, on or in respect to any matter whatsoever arising out of or in any way
connected with this Lease, the relationship of Landlord and Tenant hereunder,
Tenant's use or occupancy of the Premises, and/or claim of injury or damages.

8.15  Holdover

          If Tenant or anyone claiming under Tenant shall remain in possession
of the Premises or any part thereof after the expiration or prior termination of
the term of this Lease without any agreement in writing between Landlord and
Tenant with respect thereto, then, prior to the acceptance of any payments for
rent or use and occupancy by Landlord, the person remaining in possession shall
be deemed a tenant-at-sufferance. Whereas the parties hereby acknowledge that
Landlord may need the Premises after the expiration or prior termination of the
term of the Lease for other tenants and that the damages which Landlord may
suffer as the result of Tenant's holding-over cannot be determined as of the
date of this Lease, in the event that Tenant so holds over, Tenant shall pay to
Landlord in addition to all rental and other charges due and accrued under the
Lease prior to the date of termination, charges (based upon the fair market
rental value of the Premises) for use and occupation of the Premises thereafter
and, in addition to such sums and any and all other rights and remedies which
Landlord may have at law or in equity, an additional use and occupancy charge in
the amount of fifty percent (50%) of either the Annual Fixed Rent and other
charges calculated (on a daily basis) at the highest rate payable under the
terms of this Lease, but measured from the day on which Tenant's hold-over
commenced and terminating on the day on which Tenant vacates the Premises or the
fair market rental value of the Premises for such period, whichever is greater.
Notwithstanding the foregoing, Landlord shall


                                      -42-
<PAGE>   43
have the right to elect to recover any other damages which Landlord is permitted
to recover under this Lease in lieu of said liquidated damages by giving Tenant
written notice of such election. From and after the date on which Landlord gives
Tenant such notice, said liquidated damages shall cease to accrue and Tenant
shall be liable to Landlord for any damages recoverable under this Lease which
accrue thereafter.

8.16  Arbitration

          Any disputes relating to provisions or obligations in this Lease as to
which a specific provision for a reference to arbitration is made herein shall
be submitted to arbitration in accordance with the provisions of applicable
state law, as from time to time amended. Arbitration proceedings, including the
selection of an arbitrator, shall be conducted pursuant to the rules,
regulations and procedures from time to time in effect as promulgated by the
American Arbitration Association. Prior written notice of application by either
party for arbitration shall be given to the other at least ten (10) days before
submission of the application to the said Association's office in the city
wherein the Building is situated (or the nearest other city having an
Association office). The arbitrator shall hear the parties and their evidence.
The decision of the arbitrator shall be binding and conclusive, and judgment
upon the award or decision of the arbitrator may be entered in the Superior
Court of the Commonwealth of Massachusetts. The parties consent to the
jurisdiction of the Superior Court of the Commonwealth of Massachusetts and
further agree that any process or notice of motion or other application to the
Superior Court or a Judge thereof may be served outside the Commonwealth of
Massachusetts by registered mail or by personal service, provided a reasonable
time for appearance is allowed. The costs and expenses of each arbitration
hereunder and their apportionment between the parties shall be determined by the
arbitrator in his award or decision. No arbitrable dispute shall be deemed to
have arisen under this Lease prior to (i) the expiration of the period of twenty
(20) days after the date of the giving of written notice by the party asserting
the existence of the dispute together with a description thereof sufficient for
an understanding thereof; and (ii) where a Tenant payment is in issue, the
amount billed by Landlord having been paid by Tenant.

8.17  Requirements of Law - Fines and Penalties

          Tenant at its sole expense shall comply with all laws, rules, orders
and regulations, including, without limitation, all energy-related requirements,
of Federal, State, County and Municipal Authorities and with any direction of
any public officer or officers, pursuant to law, which shall impose any duty
upon Landlord or Tenant with respect to or arising out of Tenant's use or
occupancy of the Premises provided, however, that Tenant shall not be required
to make structural alterations or to replace Building systems unless such
changes are required because of Tenant's particular use of the Premises. Tenant
shall reimburse and compensate Landlord for all expenditures made by, or damages
or fines sustained or incurred by, Landlord due to nonperformance or
noncompliance with or breach or failure to observe any item, covenant, or


                                      -43-
<PAGE>   44
condition of this Lease upon Tenant's part to be kept, observed, performed or
complied with. If Tenant receives notice of any violation of law, ordinance,
order or regulation applicable to the Premises, it shall give prompt notice
thereof to Landlord. Landlord represents that, as of the Execution Date,
Landlord has not received any notice that the Buildings are with any such laws,
rules, orders and regulations.

8.18  Inability to Perform - Exculpatory Clause

          This Lease and the obligations of Tenant to pay rent hereunder and
perform all the other covenants, agreements, terms, provisions and conditions
hereunder on the part of Tenant to be performed shall in no way be affected,
impaired or excused because Landlord is unable to fulfill any of its obligations
under this Lease or is unable to supply or is delayed in supplying any service
expressly or impliedly to be supplied or is unable to make or is delayed in
making any repairs, replacement, additions, alterations, improvements or
decorations or is unable to supply or is delayed in supplying any equipment or
fixtures if Landlord is prevented or delayed from so doing by reason of strikes
or labor troubles or any other similar or dissimilar cause whatsoever beyond
Landlord's reasonable control, including but not limited to, governmental
preemption in connection with a national emergency or by reason of any rule,
order or regulation of any department thereof of any governmental agency or by
reason of the conditions of supply and demand which have been or are affected by
war, hostilities or other similar or dissimilar emergency. In each such instance
or inability of Landlord to perform, Landlord shall exercise reasonable
diligence to eliminate the cause of such inability to perform. This paragraph
shall not extend Tenant's abatement and termination rights as set forth in
Paragraphs F and G of Section 3.3 or Tenant's termination right as set forth in
Section 6.1.

         Tenant shall neither assert nor seek to enforce any claim or breach of
this Lease against any of Landlord's assets other than Landlord's equity
interest in the Building and in the uncollected rents, issues and profits
thereof, and Tenant agrees to look solely to such interest for the satisfaction
of any liability of Landlord or Landlord's agents under this Lease or otherwise,
it being specifically agreed that in no event shall Landlord (or any of the
officers, trustees, directors, partners, beneficiaries, joint venturers,
members, stockholders or other principals, agents or representatives, and the
like, disclosed or undisclosed, thereof) ever by personally liable for any such
liability. This paragraph shall not limit any right that Tenant might otherwise
have to obtain injunctive relief against Landlord or to take any other action
which shall not involve the personal liability of Landlord to respond in
monetary damages from Landlord's assets other than the Landlord's interest in
the Building, as aforesaid. In no event shall Landlord (or any of the officers,
trustees, directors, partners, beneficiaries, joint venturers, members,
stockholders or other principals or representatives and the like, disclosed or
undisclosed, thereof) ever be liable for consequential damages. If by reason of
Landlord's failure to complete construction of the Premises, Landlord shall be
held to be in breach of this Lease, Tenant's sole and exclusive remedy shall be
a right to terminate this Lease.


                                      -44-
<PAGE>   45
8.19  Parties Bound - Seizin of Title

          The covenants, agreements, terms, provisions and conditions of this
Lease shall bind and benefit the successors and assigns of the parties hereto
with the same effect as if mentioned in each instance where a party hereto is
named or referred to, except that no violation of the provisions of Section 5.6
hereof shall operate to vest any rights in any successor or assignee of Tenant
and that the provisions of this Section 8.19 shall not be construed as modifying
the default provisions contained in Article VII hereof.

         If, in connection with or as a consequence of the sale, transfer or
other disposition of Landlord's interest in the Building, any party who is
Landlord ceases to be the owner of the reversionary interest in the Premises,
Landlord shall be entirely freed and relieved from the performance and
observance thereafter of all covenants and obligations hereunder on the part of
Landlord to be performed and observed, it being understood and agreed in such
event (and it shall be deemed and construed as a covenant running with the land)
that the person succeeding to Landlord's ownership of said reversionary interest
shall thereupon and thereafter assume, and perform and observe, any and all of
such covenants and obligations of Landlord.


                                   ARTICLE IX

                    RIGHTS OF PARTIES HOLDING PRIOR INTERESTS

9.1  Lease Subordinate

         This Lease shall be subject and subordinate to any mortgage now or
hereafter on the Lot or Building, or both, which are separately and together
hereinafter in this Article IX referred to as "the mortgaged premises", and to
each advance made or hereafter to be made under any mortgage, and to all
renewals, modifications, consolidation, replacements and extensions thereof and
all substitutions therefor, provided that the holder thereof enters into an
agreement with Tenant by the terms of which such holder will agree to recognize
the rights of tenant under this Lease and to accept Tenant as tenant of the
Premises under the terms and conditions of this Lease in the event of
acquisition of title by such holder through foreclosure proceedings or otherwise
and Tenant will agree to recognize the holder of such mortgage as Landlord in
such event, which agreement shall be made expressly to bind and inure to the
benefit of the successors and assigns of Tenant and of the holder and upon
anyone purchasing the Premises at any foreclosure sale, provided however, that
such holder shall not: (i) be liable for any previous act or omission of
Landlord under this Lease; (ii) be subject to any offset, defense or
counterclaim which shall theretofore have accrued to Tenant against Landlord;
(iii) have any obligation with respect to any security deposit unless it shall
have been paid over or physically delivered to such successor; or


                                      -45-
<PAGE>   46
(iv) be bound by any previous modification of this Lease or by any previous
payment of Annual Fixed Rent for a period greater than one (1) month, made
without the consent of such holder where such consent is required by the
applicable instrument. Notwithstanding the foregoing any such holder may at its
election subordinate its mortgage to this Lease without the consent or approval
of Tenant. Tenant and Landlord agree to execute and deliver any appropriate
instruments necessary to carry out the agreements contained in this Section 9.1.
Tenant acknowledges that, where applicable, any consent or approval hereafter
given by Landlord may be subject to the further consent or approval of the
holder; and the failure or refusal of such holder to give such consent or
approval shall, notwithstanding anything to the contrary in this Lease
contained, constitute reasonable justification for Landlord's withholding its
consent or approval. Tenant hereby irrevocably constitutes and appoints Landlord
or any holder, and their respective successors in interest, acting singly,
Tenant's attorney-in-fact to execute and deliver any such certificate or
instrument for, on behalf and in the name of Tenant, but only if Tenant fails to
execute, acknowledge and deliver any such certificate or instrument within ten
(10) days after Landlord or such holder has made written request therefor.

9.2  Rights of Holder of Mortgage to Notice of Defaults
         by Landlord and to Cure Same

         No act or failure to act on the part of Landlord which would entitle
Tenant under the terms of this Lease, or by law, to be relieved of Tenant's
obligations hereunder or to terminate this Lease, shall result in a release or
termination of such obligations or a termination of this Lease unless (i) Tenant
shall have first given written notice of Landlord's act or failure to act to
Landlord's mortgagees (if any) of which Tenant has been notified in writing,
such notice to specify the act or failure to act on the part of Landlord which
could or would give basis to Tenant's rights; and (ii) such mortgagees after
receipt of such notice, have failed or refused to correct or cure the condition
complained of within a reasonable time thereafter; but nothing contained in this
Section 9.3 shall be deemed to impose any obligation on any such mortgagees to
correct or cure any condition. "Reasonable time" as used above means and
includes a reasonable time to obtain possession of the mortgaged premises if the
mortgagee elects to do so and a reasonable time to correct or cure the condition
if such condition is determined to exist. Notwithstanding anything to the
contrary herein contained, if Landlord's failure causes Tenant to be unable to
use the Premises for their intended purposes, a reasonable time shall not exceed
ninety (90) days after the period of time which Landlord has to cure such
default, provided however, that if such mortgagee is prevented from curing such
default by reason of causes beyond its reasonable control, such ninety (90) day
period shall be extended for an additional period (which shall not exceed an
additional ninety days) equal to the length of such delays.


                                      -46-
<PAGE>   47
                                    ARTICLE X

                                LETTER OF CREDIT

10.1     Requirements for Letter of Credit

         Tenant acknowledges that Landlord is unwilling to execute the Lease
unless Tenant provides Landlord with additional security for Tenant's
obligations under the Lease. Therefore, Tenant shall deliver to Landlord, on the
date that Tenant executes and delivers the Lease to Landlord, an Irrevocable
Standby Letter of Credit ("Letter of Credit") which shall be (1) in the form
attached hereto as Exhibit I, (2) issued by a bank reasonably acceptable to
Landlord which has an office in either New York or Boston at which said Letter
of Credit may presented for payment, (3) in an amount equal to One Million and
00/100 ($1,000,000.00) Dollars and (4) for a term of one (1) year, subject to
extension in accordance with the terms of the Letter of Credit. Tenant shall, on
or before the date thirty (30) days prior to the expiration of the term of such
Letter of Credit, deliver to Landlord a new Letter of Credit satisfying the
foregoing conditions ("Substitute Letter of Credit") in lieu of the Letter of
Credit then being held by Landlord. Such Letter of Credit shall be automatically
renewable in accordance with the second to last grammatical paragraph of Exhibit
6; provided that, in such event, Tenant shall be required to deliver a
Substitute Letter of Credit satisfying the conditions hereof, on or before the
date thirty (30) days prior to the expiration of the term of such Letter of
Credit, if the issuer of such Letter of Credit gives notice of its election not
to renew such Letter of Credit for any additional period pursuant thereto.

10.2     Landlord's Right to Draw Down Letter of Credit

         In the event that Tenant is in default of its obligations under the
Lease, beyond any applicable period for notice and cure, then the Landlord shall
have the right, at any time after such event, without giving any further notice
to Tenant, to draw down from said Letter of Credit (Substitute Letter of Credit
or Additional Letter of Credit, as defined below, as the case may be) (a) the
amount necessary to cure such default or (b) if such default cannot reasonably
be cured by the expenditure of money, to exercise all rights and remedies
Landlord may have on account of such default, the amount which, in Landlord's
opinion, is necessary to satisfy Tenant's Liability in account thereof. In the
event of any such draw by the Landlord, Tenant shall, within fifteen (15)
business days of written demand therefor, deliver to Landlord an additional
Letter of Credit satisfying the foregoing conditions ("Additional Letter of
Credit"), except that the amount of such Additional Letter of Credit shall be
the amount of such draw. In addition, in the event of a termination based upon
the default of Tenant under the Lease, or a rejection of the Lease pursuant to
the provisions of the Federal Bankruptcy Code, Landlord shall have the right to
draw upon the Letter of Credit (from time to time, if necessary) to cover the
full amount of damages and other


                                      -47-
<PAGE>   48
amounts due from Tenant to Landlord under the Lease. Any amounts so drawn shall,
at Landlord's election, be applied first to any unpaid rent and other charges
which were due prior to the filing of the petition for protection under the
Federal Bankruptcy Code. In no event shall the proceeds of any Letter of Credit
be deemed to be a prepayment of rent nor shall it be considered as a measure of
liquidated damages.

10.3     Tenant's Failure to Deliver Substitute Letter of Credit

         In the event that Tenant fails timely to deliver to Landlord a
Substitute Letter of Credit, then the Landlord shall have the right, at any time
after such event, without giving any further notice to Tenant or to Landlord, to
draw down the Letter of Credit (or Substitute Letter of Credit and/or Additional
Letter(s) of Credit) and to hold the proceeds thereof ("Security Proceeds") in a
segregated bank account in the name of the Landlord as security for Tenant's
obligations under the Lease in accordance with the provisions of this Paragraph
1.

10.4     Return of Collateral

         To the extent that Landlord has not previously drawn upon any Letter of
Credit, Substitute Letter of Credit, Additional Letter of Credit or Security
Proceeds (collectively "Collateral") held by the Landlord, and to the extent
that Tenant is not otherwise in default of its obligations under the Lease as of
the termination date of the Lease, Landlord shall return such Collateral to
Tenant on the termination of the term of the Lease.

         E. In no event shall the proceeds of any Letter of Credit be deemed to
be a prepayment of rent nor shall it be considered as a measure of liquidated
damages.

                                   ARTICLE XI

                 TENANT'S OPTION TO EXTEND THE TERM OF THE LEASE

11.1     Tenant's Option to Extend the Term of the Lease

         A. On the conditions, which conditions Landlord may waive, at its
election, by written notice to Tenant at any time, that Tenant is not in default
of its covenants and obligations under the Lease beyond any applicable period of
notice and cure, and that Lightbridge, Inc., itself, is occupying the entirety
of the premises then demised to Tenant, both as of the time of option exercise
and as of the commencement of the hereinafter described additional term, Tenant
shall have the option to extend the term of this Lease for one (1) additional
five (5) year term, such additional term commencing as of the expiration of the
initial term of the Lease. Tenant may exercise such option to extend by giving
Landlord written notice on or before the date twelve (12) months prior to the
expiration date of the initial term of the Lease. Upon the timely giving of


                                      -48-
<PAGE>   49
such notice, the term of this Lease shall be deemed extended upon all of the
terms and conditions of this Lease, except that Landlord shall have no
obligation to construct or renovate the premises and that the Annual Fixed Rent,
the Annual Electricity Charge, Tenant's Operating Expense Base, and Tenant's Tax
Base during such additional term shall be as hereinafter set forth. If Tenant
fails to give timely notice, as aforesaid, Tenant shall have no further right to
extend the term of this Lease, time being of the essence of this Article XI..

         B.       Annual Fixed Rent

         The Annual Fixed Rent during the additional term shall be based upon
the Fair Market Rental Value, as defined in Article XIII herein, as of the
commencement of the additional term, of the premises then demised to Tenant,
provided however, that in no event shall the sum of Annual Fixed Rent, the
Annual Electricity Charge, Operating Expenses Allocable to the Premises and Tax
Expenses Allocable to the Premises payable by Tenant for any twelve-(12)- month
period during the additional term be less than the sum of Annual Fixed Rent,
Annual Electricity Charge, Operating Expenses Allocable to the Premises and Tax
Expenses Allocable to the Premises payable by Tenant during the seventh (7th)
Lease Year of the initial term, as defined in Section 1.1.

         C. Tenant shall have no further option to extend the term of the Lease
other than the one (1) additional five (5) year term herein provided.

         D. Notwithstanding the fact that upon Tenant's exercise of the herein
option to extend the term of the Lease such extension shall be self-executing,
as aforesaid, the parties shall promptly execute a lease amendment reflecting
such additional term after Tenant exercises the herein option, except that the
Annual Fixed Rent payable in respect of such additional term, the Annual
Electricity Charge payable during the initial term, Tenant's Operating Expenses
Base during such additional term, and Tenant's Tax Base during such additional
term, may not be set forth in said amendment. Subsequently, after such Annual
Fixed Rent, the Annual Electricity Charge, Tenant's Operating Expenses Base, and
Tenant's Tax Base are determined, the parties shall execute a written agreement
confirming the same. The execution of such lease amendment shall not be deemed
to waive any of the conditions to Tenant's exercise of its rights under this
Article XI, unless otherwise specifically provided in such lease amendment.


                                      -49-
<PAGE>   50
                                   ARTICLE XII

                          TENANT'S RIGHT OF FIRST OFFER

12.1     Tenant's Right of First Offer

         On the conditions (which conditions Landlord may waive, at its
election, by written notice to Tenant at any time) that Tenant is not in default
of its covenants and obligations under the Lease beyond any applicable period of
notice and case and that Lightbridge, Inc., itself is occupying the entirety of
the premises then demised to Tenant, both at the time that Landlord is required
to give Landlord's Notice, as hereinafter defined, and as of the Term
Commencement Date in respect of the RFO Premises, Tenant shall have the
following right to lease the RFO Premises, as hereinafter defined, when the RFO
Premises become available for lease to Tenant, as hereinafter defined.

         A.       Definition of RFO Premises

                  "RFO Premises" shall be defined as any area on the third (3rd)
and fourth (4th) floors of Pod C in the Building, when such area becomes
available for lease to Tenant, as hereinafter defined, during the initial term
of this Lease. For the purposes of this Article XII, an RFO Premises shall be
deemed to be "available for lease to Tenant" if, during the term of this Lease,
Landlord, in its sole judgment, determines that such area will become available
for leasing to Tenant (i.e. when Landlord determines that the current tenant of
such RFO Premises will vacate such RFO Premises after its termination of its
present lease, as the same may be extended pursuant to the provisions of such
lease, the rights of all other tenants which are in effect as of the Execution
Date of this Lease to lease such RFO Premises have been waived or have lapsed
unexercised, and when Landlord intends to offer such area for lease). In no
event shall Tenant have any rights under this Article XII on or after the date
twelve (12) months prior to the expiration of the initial term of the Lease
(i.e. Landlord shall have no obligation to give Landlord's Notice, as
hereinafter defined, to Tenant on or after the date twelve (12) months prior to
the expiration of the initial term of the Lease). Landlord hereby represents
that the tenants listed on Exhibit K have pre-existing rights to the RFO
Premises.

         B.       Exercise of Right to Lease RFO Premises

                  Landlord shall give Tenant written notice ("Landlord's
Notice") at the time that Landlord determines, as aforesaid, that an RFO
Premises will become available for lease to Tenant. Landlord's Notice shall set
forth the exact location of the RFO Premises in question, Landlord's designation
of the Fair Market Rental Value (as defined in Article XIII hereof) applicable
to such RFO Premises and the Specified Commencement Date in respect of such RFO


                                      -50-
<PAGE>   51
Premises. Tenant shall have the right, exercisable upon written notice
("Tenant's Exercise Notice") given to Landlord within ten (10) days after the
receipt of Landlord's Notice, to lease such RFO Premises. If Tenant fails timely
to give Tenant's Exercise Notice, Tenant shall have no further right to lease
such RFO Premises pursuant to this Article XII, provided however, that Tenant
shall have the right from time to time thereafter throughout the term of the
Lease until Tenant's right to lease any RFO Premises has lapsed, to give
Tenant's Request as to any other subsequently available RFO Premises. Upon the
timely giving of such notice, Landlord shall lease and demise to Tenant and
Tenant shall hire and take from Landlord, such RFO Premises, upon all of the
same terms and conditions of the Lease except as hereinafter set forth. Tenant's
rights under this Article XII shall be subject to, and subordinate to the rights
of the existing tenants in the Building.

         C.       Lease Provisions Applying to RFO Premises

                  The leasing to Tenant of such RFO Premises shall be upon all
of the same terms and conditions of the Lease, except as follows:

                  (1)      Term Commencement Date

                  The Term Commencement Date in respect of such RFO Premises
shall be the later of: (x) the Specified Commencement Date in respect of such
RFO Premises as set forth in Landlord's Notice, or (y) the date that Landlord
delivers such RFO Premises to Tenant.

                  (2)      Annual Fixed Rent

                  The Annual Fixed Rent rental rate in respect of such RFO
Premises shall be based upon the Fair Market Rental Value, as defined in Article
XIII hereof, of such RFO Premises as of the Term Commencement Date in respect of
such RFO Premises.

                  (4)      Condition of RFO Premises

                  Tenant shall take such RFO Premises "as-is" in its then (i.e.
as of the date of premises delivery) state of construction, finish, and
decoration, without any obligation on the part of Landlord to construct or
prepare any RFO Premises for Tenant's occupancy.

         D.       Execution of Lease Amendments

                  Notwithstanding the fact that Tenant's exercise of the
above-described option to lease RFO Premises shall be self-executing, as
aforesaid, the parties hereby agree promptly to execute a lease amendment
reflecting the addition of an RFO Premises, except that the Annual Fixed Rent
payable in respect of


                                      -51-
<PAGE>   52
such RFO Premises, Tenant's Operating Expense Base in respect of such RFO
Premises, and Tenant's Tax Base in respect of such RFO Premises may not be as
set forth in such Amendment. At the time that such Annual Fixed Rent, such
Annual Electricity Charge, Tenant's Operating Expense Base and Tenant's Tax Base
are determined, the parties shall execute a written agreement confirming the
same. The execution of such lease amendment shall not be deemed to waive any of
the conditions to Tenant's exercise of the herein option to lease the RFO
Premises, unless otherwise specifically provided in such lease amendment.

                                  ARTICLE XIII

                  DEFINITION OF FAIR MARKET RENTAL VALUE

13.1     Definition of Fair Market Rental Value

         A. "Fair Market Rental Value" shall be computed as of the date in
question at the then current annual rental charge (i.e., the sum of Annual
Yearly Rent plus escalation and other charges), including provisions for
subsequent increases and other adjustments for leases or agreements to lease
then currently being negotiated, or executed in comparable space located in the
Building, or if no leases or agreements to lease are then currently being
negotiated or executed in the Building, the Fair Market Rental Value shall be
determined by reference to leases or agreements to lease then currently being
negotiated or executed for comparable space located elsewhere in comparable
office buildings located in the Burlington area. In determining Fair Market
Rental Value, the following factors, among others, shall be taken into account
and given effect: size, location of premises, lease term, condition of building,
services provided by the Landlord, and economic concessions (e.g., tenant
improvements, brokerage commissions, etc.) the being granted by landlords to
tenants.

         B. Notwithstanding anything to the contrary herein contained, the
parties hereby agree that upon the determination of any Fair Market Rental
Value, Landlord shall have the right, exercisable by written notice to Tenant on
or before the time that Landlord gives Tenant its initial designation of Fair
Market Rental Value:

                  (1)      to change Tenant's Operating Expense Base as stated
                           in Section 1.1 from the amount stated in Section 1.1
                           to an amount equal to the actual amount of Operating
                           Expenses for the immediately preceding Operating
                           Year, and

                  (2)      to change Tenant's Tax Base as stated in Section 1.1
                           from the amount stated in Section 1.1 to an amount
                           equal to the actual amount of Taxes for the
                           immediately preceding fiscal/tax year for which
                           Landlord has actual data.


                                      -52-
<PAGE>   53
                  If Landlord shall exercise such right, the amount of Annual
Fixed Rent payable hereunder shall be commensurately adjusted to reflect such
change in Tenant's Operating Expense Base and in Tenant's Tax Base.

         C.       Dispute as to Fair Market Rental Value

                  Landlord shall initially designate Fair Market Rental Value
and Landlord shall furnish data in support of such designation. If Tenant
disagrees with Landlord's designation of a Fair Market Rental Value, Tenant
shall have the right, by written notice given within thirty (30) days after
Tenant has been notified of Landlord's designation, to submit such Fair Market
Rental Value to arbitration. Fair Market Rental Value shall be submitted to
arbitration as follows: Fair Market Rental Value shall be determined by
impartial arbitrators, one to be chosen by the Landlord, one to be chosen by
Tenant, and a third to be selected, if necessary, as below provided. The
unanimous written decision of the two first chosen, without selection and
participation of a third arbitrator, or otherwise, the written decision of a
majority of three arbitrators chosen and selected as aforesaid, shall be
conclusive and binding upon Landlord and Tenant. Landlord and Tenant shall each
notify the other of its chosen arbitrator within ten (10) days following the
call for arbitration and, unless such two arbitrators shall have reached a
unanimous decision within thirty (30) days after their designation, they shall
so notify the President of the Boston Bar Association (or such organization as
may succeed to said Boston Bar Association) and request him to select an
impartial third arbitrator, who shall be an office building owner, a real estate
counselor or a broker dealing with like types of properties, to determine Fair
Market Rental Value as herein defined. Such third arbitrator and the first two
chosen shall, subject to commercial arbitration rules of the American
Arbitration Association, hear the parties and their evidence and render their
decision within thirty (30) days following the conclusion of such hearing and
notify Landlord and Tenant thereof. Landlord and Tenant shall bear the expense
of the third arbitrator (if any) equally. The decision of the arbitrator shall
be binding and conclusive, and judgment upon the award or decision of the
arbitrator may be entered in the appropriate court of law; and the parties
consent to the jurisdiction of such court and further agree that any process or
notice of motion or other application to the Court or a Judge thereof may be
served outside the State wherein the Building is situated by registered mail or
by personal service, provided a reasonable time for appearance is allowed. If
the dispute between the parties as to a Fair Market Rental Value has not been
resolved before the commencement of Tenant's obligation to pay rent based upon
such Fair Market Rental Value, then Tenant shall pay Annual Fixed Rent and other
charges under the Lease in respect of the premises in question based upon the
Fair Market Rental Value designated by Landlord until either the agreement of
the parties as to the Fair Market Rental Value, or the decision of the
arbitrators, as the case may be, at which time Tenant shall pay any underpayment
of rent and other charges to Landlord, or Landlord shall refund any overpayment
of rent and other charges to Tenant.


                                      -53-
<PAGE>   54
                 ARTICLE XIV - Condition of Landlord's Execution

14.1     Condition of Landlord's Execution

         Reference is made to the fact that the Premises are presently leased to
Fax International, Inc. ("FAX"). Therefore, Landlord shall have the right,
exercisable upon written notice to Tenant, to render the foregoing Lease void
and without force or effect, unless both of the following events occur:

         A. Tenant executes and delivers to Landlord the foregoing Lease; and

         B. FAX executes and delivers to Landlord an agreement, in form and
substance acceptable to Landlord, whereby FAX agrees to terminate the term of
its lease.

         EXECUTED as a sealed instrument in two or more counterparts on the day
and year first above written.

                                     LANDLORD:

                                     SUMITOMO LIFE REALTY (N.Y.), INC.


                                     By: /s/ S. Kurematsi
                                         ---------------------------------
                                         Hereunto Duly Authorized


                                     TENANT:

                                     LIGHTBRIDGE, INC.


                                     By: /s/ William G. Brown
                                         ---------------------------------
                                         (Name)            (Title)
                                         Hereunto Duly Authorized


                                      -54-
<PAGE>   55
                                    EXHIBIT A

                                   Description


         The land in Burlington, Middlesex County, Massachusetts being shown as
Lot 75 on a plan by Raymond C. Pressey, Inc. dated December 16, 1980 filed with
the Land Court Engineer's office as Plan No. 26172R and bounded and described
according to said plan as follows:

by the southwesterly line of South Bedford Street, one hundred fifty (150) feet;

SOUTHWESTERLY, SOUTHEASTERLY AND NORTHEASTERLY by Lot 74 on said plan,
thirty-five (35) feet, ninety-seven and 70/100 (97.70) feet, five hundred
seventy-one and 80/100 (571.80) feet and four hundred forty-eight (448),
respectively;

by the northwesterly line of Northern Circumferential Highway (Route 128 non
access), eight hundred seventy-nine and 81/100 (879.81) feet;

by Lot 27 as shown on said plan, five hundred eight and 19/100 (508.19) feet;
and

by Lots 73 and 68 shown on said plan, one thousand four hundred sixty-three and
37/100 (1463.37) feet.


                                      -55-
<PAGE>   56
                                    EXHIBIT B

                              CONDITION OF PREMISES

         A. Notwithstanding anything to the contrary herein or in the Lease
contained, Tenant shall take the Premises "as-is", in the condition in which the
Premises are in as of the Term Commencement Date without any obligation on the
part of Landlord to prepare or construct the Premises for Tenant's occupancy and
without any representation or warranty by Landlord as to the condition of the
Premises or the Building.

         B. Landlord shall, in the manner hereinafter set forth, provide to
Tenant up to Four Hundred Sixty-Three Thousand Five Hundred Eighty and 00/100
($463,580.00) Dollars ("Landlord's Contribution") towards the cost of leasehold
improvements to be installed by Tenant in the Premises, which shall include
electrical work and removal of HVAC units left by the prior tenant of the
Premises ("Tenant's Work"), to the cost of space planning, architectural
services, construction management fees, and for the cost of replacing light
bulbs in the Premises. In no event shall Landlord's Contribution be applied
towards the cost of installing cabling, wiring, or furniture, fixtures or
equipment. Tenant's Work shall be performed in accordance with Article 3.1 of
the Lease. Provided that Tenant is not in default of its obligations under the
Lease beyond any applicable period of notice and case at the time that Tenant
requests any requisition on account of Landlord's Contribution, Landlord shall
pay the cost of the work shown on each requisition (as hereinafter defined)
submitted by Tenant to Landlord within thirty (30) days of submission thereof by
Tenant to Landlord.

         C. For the purposes hereof, a "requisition" shall mean written
documentation (including, without limitation, invoices from Tenant's contractor,
written lien waivers and such other documentation as Landlord may reasonably
request) showing in reasonable detail the costs of the improvements installed by
Tenant to date in the premises, accompanied by certifications from Tenant,
Tenant's architect, and Tenant's contractor that the work performed to date has
been performed in accordance with applicable laws and in accordance with
Tenant's approved plans, and that the amount of the requisition in questions
does not exceed the amount of the work covered by such requisition. Each
requisition shall be accompanied by evidence reasonably satisfactory to Landlord
that all work covered by previous requisitions has been fully paid by Tenant.
Landlord shall have the right, upon reasonable advance notice to Tenant, to
inspect Tenant's books and records relating to each requisition in order to
verify the amount thereof. Tenant shall submit requisition(s) no more often than
monthly.

         D. Notwithstanding anything to the contrary herein contained:

                  (i) Landlord shall have no obligation to advance funds on
account of Landlord's Contribution unless and until Landlord has received the
requisition in question, together with the


                                      -56-
<PAGE>   57
certifications required by Subparagraph B hereof, certifying that the work shown
on the requisition has been performed in accordance with applicable law and in
accordance with Tenant's plans.

                  (ii) Except with respect to work and/or materials previously
paid for by Tenant, as evidenced by paid invoices and written lien waivers
provided to Landlord, Landlord shall have the right to have Landlord's
Contribution paid to both Tenant and Tenant's contractor(s) and vendor(s)
jointly.

                  (iii) Tenant shall not be entitled to any portion of
Landlord's Contribution, and Landlord shall have no obligation to pay Landlord's
Contribution in respect of any requisition submitted after September 30, 1997.
Notwithstanding, said September 30, 1997 date shall be extended if Tenant is
unable to complete Tenant's Work by such date by reason of strikes or labor
troubles or any other similar or dissimilar cause whatsoever beyond Tenant's
reasonable control, including, but not limited to, governmental preemption in
connection with a national emergency of by reason of any rule, order or
regulation of any department thereof of any governmental agency or by reason of
the conditions of supply and demand which have been or are affected by war,
hostilities or other similar or dissimilar emergency, and if Tenant gives
Landlord written notice on or before September 30, 1997 of its inability timely
to complete its work and of the reasons therefore. In such event, said September
30, 1997 date shall be extended by the length of delays in Tenant's work arising
from causes beyond Tenant's reasonable control.

         E. Landlord shall have the same rights and remedies which Landlord has
upon the nonpayment of Annual Fixed Rent and other charges due under this Lease
for nonpayment of any amounts which Tenant is required to pay to Landlord or
Landlord's contractor in connection with any construction in the Premises
performed for Tenant by Landlord, Landlord's contractor or any other person,
firm or entity.


                                      -57-
<PAGE>   58
                                    EXHIBIT C

                              INTENTIONALLY OMITTED


                                      -58-
<PAGE>   59
                                    EXHIBIT D

                      Building Standard Tenant Improvements

                 Attached to and made part of Lease dated as of

                                     Between

                        Sumitomo Life Realty (N.Y.), Inc.

                                       and

                                Lightbridge, Inc.


         A.       Partitions

                  One (1) linear foot of tenant partition shall be provided for
                  each 13.5 square feet of Useable Area. Partitions shall extend
                  six inches beyond the ceiling height and be comprised of
                  2 1/2" metal studs and one (1) layer of 5/8" gypsum board on
                  each side of the studs. All partitions shall have a vinyl base
                  4" high, color selections from building standard.

         B.       Tenant Entries

                  1.       Where possible, Tenants will have double-leaf, full
                           height mahogany doors set in a wood frame with glass
                           sidelights on each side.

                  2.       Alternatively, a single-leaf full-height mahogany
                           door set in a wood frame with a glass sidelight.

                  3.       First Floor - all Tenant Entries visible to the first
                           floor lobby areas will consist of double glass doors
                           with butt-glazed glass on each side.

         C.       Interior Doors

                  One (1) door unit shall be provided for each 314 square feet
                  of Useable Area. Doors shall be (3'0" x 8'3" nominal). Solid
                  core with sealed or stained mahogany face, set in aluminum
                  frames. Hardware shall include 1 1/2 pairs of paint grade
                  butts, a lever handled chrome finished latchset and one floor
                  stop.


                                      -59-
<PAGE>   60
         D.       Paint

                  All building standard interior partitioning shall receive two
                  (2) coats of eggshell latex paint, one (1) color per room.
                  Color selection from building standard samples.

         E.       Ceiling

                  Acoustical ceiling shall consist of 3/4", foil backed,
                  revealed edge, 2' x 2' U.S.G. Glacier textured ceiling tiles.

         F.       Flooring

                  J&J Industries "Echelon" 30 oz. plush nylon pile carpet. Color
                  to be selected from options offered by landlord.

         G.       Electrical Outlets

                  One (1) 15 amp. 120 volt duplex wall-type electrical outlet
                  with brushed chrome cover shall be provided for each 135
                  square feet of Useable Area.

         H.       Telephone Outlets

                  One (1) wall-type telephone pull string prepared to receive a
                  telephone outlet, installation by Tenant's telephone company,
                  shall be provided for each 180 square feet of Useable Area.
                  Telephone outlets does not include any conduit.

         I.       Lighting

                  One (1) 2' x 4' fluorescent light fixture with parabolic
                  reflector and (1) 18 cell cover shall be provided for each 80
                  square feet of Useable Area.

         J.       Switching

                  One (1) single pole light switch with brushed chrome cover
                  shall be provided for each 314 square feet of Useable Area.

         K.       Sprinklers


                                      -60-
<PAGE>   61
                  One (1) recessed chrome pendant sprinkler head shall be
                  provided to meet all applicable code requirements up to a
                  maximum of one per 157 square feet of Useable Area.

         L.       Sun Control

                  All exterior windows shall receive Louver Drape Model E1 Elite
                  Vertical Blinds with solid vinyl traversing and rotating
                  louvers. Track will be finished in bronze baked enamel to
                  match window frames.

         M.       Drinking Fountain

                  All floors will have a drinking fountain accessible to all
                  Tenants on the floor.

         N.       Wet Stacks

                  Wet Stacks containing cold water, waste and vents will be
                  available on each floor. Tenant equipment can be connected at
                  the Tenant's expense.

         O.       Heating, Ventilating and Air Conditioning

                  A variable air volume (VAV) system will be employed for both
                  heating and air conditioning.

         P.       Exit Sign

                  One (1) exit sign shall be provided for every 1,000 square
                  feet of Useable Area.


         Q.       Emergency Light

                  One (1) emergency light shall be provided for every 1,000
                  square feet of Useable Area.


                                      -61-
<PAGE>   62
                                    EXHIBIT E

                                Landlord Services


                    Attached to and made part of Lease dated

                                     Between

                        Sumitomo Life Realty (N.Y.), Inc.

                                       and

                                Lightbridge, Inc.

I.  CLEANING

         A.       Office Area

                  Daily: (Monday through Friday, inclusive. Holidays excepted.)

                  Empty and clean all waste receptacles and ash trays and remove
                  waste material from Premises; wash receptacles as necessary.

                  Sweep and dust mop all uncarpeted areas using a dust-treated
                  mop.

                  Vacuum all rugs and carpeted areas.

                  Hand dust and wipe clean with treated cloths all horizontal
                  surfaces including furniture, office equipment, window sills,
                  door ledges, chair rails, and convector tops, within normal
                  reach.

                  Wash clean all water fountains.

                  Remove and dust under all desk equipment and telephones and
                  replace same.

                  Wipe clean all brass and other bright work.

                  Hand dust all grill work within normal reach.


                                      -62-
<PAGE>   63
                  Upon completion of cleaning, all lights will be turned off and
                  doors locked, leaving the Premises in an orderly condition.

                  Weekly:

                  Dust coat racks, and the like.

                  Remove all finger marks from private entrance doors, light
                  switches and doorways.

                  Quarterly:

                  Render high dusting not reached in daily cleaning to include:

                  Dusting all pictures, frames, charts, graphs, and similar wall
                  hangings.

                  Dusting all vertical surfaces, such as walls, partitions,
                  doors and bucks.

                  Dusting of all pipes, ducts and high moldings.

                  Dusting of all venetian blinds.

         B.       Lavatories

                  Daily: (Monday through Friday, inclusive, holidays excepted.)

                  Sweep and damp mop floors.

                  Clean all mirrors, powder shelves, dispensers and receptacles,
                  bright work, flushometers, piping, and toilet seat hinges.

                  Wash both sides of all toilet seats.

                  Wash all basins, bowls and urinals.

                  Dust and clean all powder room fixtures.

                  Empty and clean paper towel and sanitary disposal receptacles.

                  Remove waste paper and refuse.


                                      -63-
<PAGE>   64
                  Refill tissue holders, soap dispensers, towel dispensers,
                  vending sanitary dispensers; materials to be furnished by
                  Landlord.

                  A sanitizing solution will be used in all lavatory cleaning.

                  Monthly:

                  Machine scrub lavatory floors.

                  Wash all partitions and tile walls in lavatories.

         C.       Main Lobby, Elevators, Building Exterior and Corridors

                  Daily: (Monday through Friday, inclusive, holidays excepted.)

                  Sweep and wash all floors. (Buff both main public lobby
                  floors.)

                  Wash all rubber mats.

                  Clean elevators, wash or vacuum floors, wipe down walls and
                  doors.

                  Spot clean any metal work inside lobby.

                  Spot clean any metal work surrounding Building Entrance doors.

                  Weekly:

                  All resilient tile floors in public areas to be treated
                  equivalent to spray buffing.

         D.       Window Cleaning

                  Windows of exterior walls will be washed semiannually.

         E.       Tenant requiring services in excess of those described above
                  shall request same through Landlord, at Tenant's expense.

II.  HEATING, VENTILATING, AIR CONDITIONING

         A. Landlord shall furnish space heating and cooling as normal seasonal
changes may require to provide reasonably comfortable space temperature and
ventilation for occupants of the


                                      -64-
<PAGE>   65
Premises under normal business operation, daily from 8:00 a.m. to 6:00 p.m.
(Saturdays to 1:00 p.m.), Sundays and holidays excepted.

         After hours heating, venting and air conditioning to be billed to
tenant at cost, including reasonable cost and management expense.

         B. The air conditioning system is based upon an occupancy of not more
than one person per 150 square feet of floor area, and upon a combined lighting
and standard electrical load not to exceed 2.5 watts per square foot of usable
area. In the event Tenant exceeds this condition or introduces onto the Premises
equipment which overloads the system, and/or in any other way causes the system
not adequately to perform their proper functions, supplementary systems may at
Landlord's option be provided by Landlord at Tenant's expense, and Tenant shall
reimburse Landlord in such an amount as will compensate it for the cost incurred
by it in operating such supplementary systems.

III.  WATER

         A. Cold water at temperatures supplied by the local utility water mains
for drinking, lavatory, kitchen, restaurant and toilet purposes and hot water
for lavatory purposes only from regular building supply at prevailing
temperatures; provided however, that Landlord may, at its expense, install a
meter or meters to measure the water supplied to any kitchen (including
dishwashing) and restaurant areas in the Premises, in which case Tenant shall
upon Landlord's request reimburse Landlord for the cost of the water (including
heating thereof) consumed in such areas and the sewer use charge resulting
therefrom.

IV.  ELEVATORS

         A. The passenger elevator system shall be in automatic operation and
available to Tenant at all times. Use of the elevators for service purposes will
have to be scheduled with the Landlord and coordinated with the needs of the
other tenants.

V.  ELECTRICAL SERVICE

         A. Landlord shall provide electric power for up to 1.8 watts per square
foot of usable area for lighting plus 1.0 watts per square foot of usable area
for office machines through standard receptacles for the typical office space.

         B. Landlord, at his option, may require separate metering and billing
to Tenant for the electric power required for any special equipment (such as
computers and reproduction equipment) that require either 3-phase electrical
power or any voltage other than 120. Landlord will furnish and install at
Tenant's expense all replacement lighting tubes, lamps, and ballasts


                                      -65-
<PAGE>   66
required by Tenant. Landlord will clean lighting fixtures on a regularly
scheduled basis at Tenant's expense.


                                      -66-
<PAGE>   67
                                  EXHIBIT F
                                      
                                  FLOOR PLAN

                           [Diagram of floor plan]




                                     -67-
<PAGE>   68
                               EXHIBIT G, SHEET 1
                    (Required Tenant Work General Conditions)

         The following General Conditions are promulgated pursuant to Section
3.1 of the Lease ("Lease").

1.    DEFINITIONS      
                       
1.1   Building:         Burlington Business Center
                       
1.2   Consultant:       Any architectural, engineering, or design consultant 
                        engaged by a Tenant in connection with Tenant Work.
                       
1.3   Contractor:       Any Contractor engaged by a Tenant of the Building for
                        the performance of any Tenant Work, and any 
                        Subcontractor employed by any such Contractor.
                       
1.4   Plans:            All architectural, electrical and mechanical 
                        construction drawings and specifications required for 
                        the proper construction of the Tenant Work.
                       
1.5   Regular Business  Monday through Friday, 9:00 a.m. through 5:00 p.m., 
      Hours:            holidays excluded.
                       
1.6   Construction      Such individual or organization as Landlord may 
      Coordinator:      designate from time to time.
                        
                       
1.7   Senior Tenant     Such individual as Landlord may designate from time to
      Design            time.
      Coordinator:  
                       
1.8   Tenant:           Any occupant of the Building.
                       
1.9   Tenant Work:      Any alterations, improvements, additions, repairs or
                        installations in the Building performed by or on 
                        behalf of any Tenant.
                       


                                      -68-
<PAGE>   69
<TABLE>
<S>               <C>                    <C>
         1.10     Tradesperson:          Any employee (including, without limitation, any mechanic,
                                         laborer, or Tradesperson) employed by a Contractor
                                         performing Tenant Work.
</TABLE>

2.       GENERAL

         2.1      All Tenant Work shall be performed in accordance with these
                  General Conditions and the applicable provisions of the Lease.

         2.2      The provisions of these General Conditions shall be
                  incorporated in all agreements governing the performance of
                  all Tenant Work, including, without limitation, any agreements
                  governing services to be rendered by each Contractor and
                  Consultant.

3.       PRECONSTRUCTION NOTIFICATION AND APPROVALS

         3.1      Approval to Commence Work

                  a. Tenant shall submit to Construction Coordinator, for the
                  approval of Retail Construction Coordinator, the names of all
                  prospective Contractors prior to issuing any bid packages to
                  such Contractors.

                  b. No Tenant Work shall be undertaken by any Contractor or
                  Tradesperson unless and until all the matters set forth in
                  Article 3.2 below have been received for the Tenant Work in
                  question and unless Construction Coordinator has approved the
                  matters set forth in Article 3.2 below.

         3.2      No Tenant Work shall be performed unless, at least three days
                  before any Tenant Work is to begin, all of the following has
                  been provided to the Construction Coordinator and approved. In
                  the event that Tenant proposes to change any of the following,
                  the Construction Coordinator shall be immediately notified of
                  such change and such change shall be subject to the approval
                  of the Construction Coordinator.

                  a.       Schedule for the work, indicating start and
                           completion dates, any phasing and special working
                           hours, and also a list of anticipated shutdown of
                           building systems.

                  b.       List of all Contractors and Subcontractors, including
                           addresses, telephone numbers, trades employed, and
                           the union affiliation of each Contractor and
                           Subcontractor.


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<PAGE>   70
                  c.       Names and telephone numbers of the supervisors of the
                           work.

                  d.       Copies of all necessary governmental permits,
                           licenses and approvals.

                  e.       Proof of current insurance, to the limits set out in
                           Exhibit A to these General Conditions, naming
                           Landlord and Construction Coordinator as an
                           additional insured party.

                  f.       Notice of the involvement of any Contractor in any
                           ongoing or threatened labor dispute.

                  g.       Payment, Performance and Lien Bonds from sureties
                           acceptable to Landlord, in form acceptable to
                           Landlord, naming Landlord as an additional obligee.

                  h.       Evidence that Tenant has made provision for either
                           written waivers of lien from all Contractors and
                           suppliers of material, or other appropriate
                           protective measures approved by Landlord.

         3.3      Reporting Incidents

                  All accidents, disturbances, labor disputes or threats
                  thereof, and other noteworthy events pertaining to the
                  Building or the Tenant's property shall be reported
                  immediately to the Construction Coordinator. A written report
                  must follow within 24 hours.

4.       CONSTRUCTION SCHEDULE

         4.1      Coordination

                  a. All Tenant Work shall be carried out expeditiously and with
                  minimum disturbance and disruption to the operation of the
                  Building and without causing discomfort, inconvenience, or
                  annoyance to any of the other tenants or occupants of the
                  Building or the public at large.

                  b.       All schedules for the performance of construction,
                           including materials deliveries, must be coordinated
                           through the Construction Coordinator. The
                           Construction Coordinator shall have the right,
                           without incurring any liability to any Tenant, to
                           stop activities and/or to require rescheduling of


                                      -70-
<PAGE>   71
                           Tenant Work based upon adverse impact on the tenants
                           or occupants of the Building or on the maintenance or
                           operation of the Building.

                  c.       If any Tenant Work requires the shutdown of risers
                           and mains for electrical, mechanical, sprinklers and
                           plumbing work, such work shall be supervised by a
                           representative of Landlord. No Tenant Work will be
                           performed in the Building's mechanical or electrical
                           equipment rooms without both Landlord's prior
                           approval and the supervision of a representative of
                           Landlord, the cost of which shall be reimbursed by
                           the Tenant.

         4.2      Time Restrictions

                  a.       Subject to Paragraph 4.1 of these General Conditions,
                           general construction work will generally be permitted
                           during Regular Business Hours.

                  b.       Tenant shall provide the Construction Coordinator
                           with at least twenty-four (24) hours notice before
                           proceeding with Special Work, as hereinafter defined,
                           and such Special Work will be permitted only at times
                           agreed to by the Building Manager during periods
                           outside of Regular Business Hours. Tenant shall pay
                           for all additional supervisory and other premium
                           costs incurred by Landlord as the result of any such
                           Special Work. "Special Work" shall be defined as the
                           following operations:

                           (1) All utility disruptions, shutoffs and turnovers;

                           (2) Activities involving high levels of noise,
                           including demolition, coring, drilling and
                           ramsetting;

                           (3) Activities resulting in excessive dust or odors,
                           including demolition and spray painting; and

                           (4) Any other work which Tenant proposes to perform
                           outside of Regular Business Hours.

                  c.       If coordination, labor disputes or other
                           circumstances require, the Construction Coordinator
                           may change the hours during which regular
                           construction work can be scheduled and/or restrict or
                           refuse entry to and exit from the Building by any
                           Contractor.

5.       CONTRACTOR PERSONNEL


                                      -71-
<PAGE>   72
         5.1      Work in Harmony

                  a. All Contractors shall be responsible for employing skilled
                  and competent personnel and suppliers who shall abide by the
                  Supplemental Conditions herein set forth as amended from time
                  to time by Landlord.

                  b. No Tenant shall at any time, either directly or indirectly,
                  employ, permit the employment, or continue the employment of
                  any Contractor if such employment or continued employment will
                  or does interfere or cause any labor disharmony, coordination
                  difficulty, delay or conflict with any other contractors
                  engaged in construction work in or about the Building.
                  Notwithstanding anything to the contrary herein or in the
                  Lease contained, Tenant shall not be required to employ union
                  labor in connection with the initial Tenant Work.

                  c. Should a work stoppage or other action occur anywhere in or
                  about the Building as a result of the presence, anywhere in
                  the Building, of a Contractor engaged directly or indirectly
                  by a Tenant, or should such Contractor be deemed by Landlord
                  to have violated by applicable rules or regulations, then upon
                  twelve hours written notice, Landlord may, without incurring
                  any liability to Tenant or said contractor, require any such
                  Contractor to vacate the premises demised by such Tenant and
                  the Building, and to cease all further construction work
                  therein.

                  d. Tenant agrees that all Tenant Work shall be performed by
                  Contractors employing Union labor only. The failure of
                  Landlord or the Retail Construction Coordinator to disapprove
                  a proposed contractor which is, in fact, a Contractor not
                  employing Union labor, shall not constitute a waiver by
                  Landlord of this provision since Landlord and the Retail
                  Construction Coordinator may be unable to determine readily
                  whether a proposed contractor employs such labor.

                  e. In the employment of all workmen by any Contractor, working
                  arrangements generally accepted and prevailing on so-called
                  Union jobs in the Boston area shall be complied with.

                  f. Tenant shall use, and Tenant shall require the Contractor
                  to use his best efforts to prevent work stoppages on the
                  Premises, or elsewhere in the Building, to the extent
                  attributable to work being performed on the Premises,
                  irrespective of the reason for any such stoppage, in
                  recognition of the fact that it is of the utmost importance to
                  Landlord and all those occupying space in the Building that
                  there be no interruption in the progress of the work. Tenant's
                  agreement to utilize one hundred percent (100%) Union labor in
                  Tenant's work, and its performance of


                                      -72-
<PAGE>   73
                  such obligation, shall not be treated as, by the fact,
                  compliance with this requirement.

         5.2      Conduct

                  a. Tradespersons shall wear clothing suitable for their work
                  and shall remain fully attired at all times. All Contractors
                  will be responsible for their Tradespersons' proper behavior
                  and conduct.

                  b. The Construction Coordinator reserves the right to remove
                  anyone who, or any Contractor which is causing a disturbance
                  to any Tenant or Occupant of the Building or any other person
                  using or servicing the Building; is interfering with the work
                  of others; or is in any other way displaying conduct or
                  performance not compatible with the Landlord's standards.
                  Tenant shall exonerate, indemnify and hold Landlord and the
                  Construction Coordinator harmless from any loss, cost,
                  damages, or liability incurred by reason of compliance with
                  any such demand.

         5.3      Access

                  a. All Contractors and Tradespersons shall contact the
                  Construction Coordinator prior to commencing work, to confirm
                  work location and Building access, including elevator usage
                  and times of operation. Access to the Building before and
                  after Regular Business Hours or any other hours designated
                  from time to time by the Building Manager and all day on
                  weekends and holidays will only be provided when twenty-four
                  (24) hours advance notice is given to the Construction
                  Coordinator.

                  b. No Contractor or Tradesperson will be permitted to enter
                  any private or public space in the Building except through
                  entrances designated by the Construction Coordinator.

         5.4      Parking

                  Parking is not allowed in or near truck docks, in handicapped
                  or fire access lanes, or any private ways in or surrounding
                  the property. Vehicles so parked will be towed at the expense
                  of the Tenant who has engaged the Contractor for whom the
                  Owner of such vehicle is employed.

6.       BUILDING MATERIALS

         6.1      Delivery


                                      -73-
<PAGE>   74
                  a. All deliveries of construction materials shall be made at
                  the predetermined times approved by the Construction
                  Coordinator and shall be effected safely and expeditiously
                  only at the location determined by the Construction
                  Coordinator.

                  b. Tenant shall give the Construction Coordinator at least
                  twenty-four (24) hours notice of deliveries of any materials
                  in the Building.

         6.2      Transportation in Building

                  a. Distribution of materials from delivery point to the work
                  area in the Building shall be accomplished with the least
                  disruption to the operation of the Building possible.
                  Elevators will be assigned for material delivery and will be
                  controlled by the Construction Coordinator.

                  b. Contractors shall provide adequate protection to all
                  carpets, wall surfaces, doors and trim in all public areas
                  through which materials are transported. Contractors shall
                  continuously clean all such areas. Protective measures shall
                  include runners over carpet, padding in elevators and any
                  other measures determined by the Construction Coordinator.

                  c. Any damage caused to the Building through the movement of
                  construction materials or otherwise shall be the
                  responsibility of Tenant who has engaged the Contractor
                  involved. Charges for such damage will be submitted by the
                  Landlord directly to the Tenant.

         6.3      Storage and Placement

                  a. All construction materials shall be stored only in the
                  premises where they are to be installed. No storage of
                  materials will be permitted in any public areas, loading docks
                  or corridors leading to the premises.

                  b. No flammable, toxic, or otherwise hazardous materials may
                  be brought in or about the Building unless: (i) authorized by
                  the Construction Coordinator, (ii) all applicable laws,
                  ordinances, rules and regulations are complied with, and (iii)
                  all necessary permits have been obtained. All necessary
                  precautions shall be taken by the Contractor handling such
                  materials against damage or injury caused by such materials.


                                      -74-
<PAGE>   75
                  c. All materials required for the construction of the premises
                  must conform with the plans and specifications approved by
                  Landlord, and must be installed in the locations shown on the
                  drawings approved by the Landlord.

                  d. All work shall be subject to reasonable supervision and
                  inspection by a representative of Landlord.

                  e. No alterations to approved plans will be made without prior
                  knowledge and approval of the Senior Tenant Design
                  Coordinator. Such changes shall be documented on the as-built
                  drawings required to be delivered to Landlord pursuant to
                  Paragraph 10 of these General Conditions. At the time that
                  such changes are prepared by the Tenant and approved by
                  Landlord, Tenant shall submit such approved changes to the
                  Construction Coordinator. At the time that any shop drawing is
                  approved by the Senior Tenant Design Coordinator, Tenant shall
                  submit such approved shop drawings to the Construction
                  Coordinator.

                  f. All protective devices (e.g., temporary enclosures and
                  partitions) and materials, as well as their placement, must be
                  approved by the Construction Coordinator.

                  g. It is the responsibility of Contractors to ensure that the
                  temporary placement of materials does not impose a hazard to
                  the Building or its occupants, either through overloading, or
                  interference with Building systems, access, egress or in any
                  other manner whatsoever.

                  h. All existing and/or new openings made through the floor
                  slab for piping, cabling, etc. must be firestopped in
                  accordance with applicable codes. All holes in the floor slab
                  at abandoned floor outlets, etc. will be filled with solid
                  concrete.

         6.4      Salvage and Waste Removal

                  a. All rubbish, waste and debris shall be neatly and cleanly
                  removed from the Building by Contractors daily and placed in a
                  trash container designated by the Construction Coordinator,
                  unless otherwise approved by the Construction Coordinator. For
                  any demolition and debris, each Contractor must make
                  arrangements with the Construction Coordinator for the
                  scheduling and location of an additional dumpster to be
                  supplied at the cost of the Tenant engaging such Contractor.
                  Where, in the opinion of the Construction Coordinator, such
                  arrangements are not practical, such Contractors will make
                  alternative arrangements for removal at the cost of the
                  Tenants engaging such Contractors.


                                      -75-
<PAGE>   76
                  b. Toxic or flammable waste is to be properly removed daily
                  and disposed of in full accordance with all applicable laws,
                  ordinances, rules and regulations.

                  c. Contractors shall, prior to removing any item from the
                  Building, notify the Construction Coordinator that it intends
                  to remove such item. At the election of Construction
                  Coordinator, Contractors shall deliver any such items to the
                  Construction Coordinator. Such items will be delivered,
                  without cost, to an area designated by the Construction
                  Coordinator which area shall be within the Building or the
                  complex in which the Building is located.

7.       PAYMENT OF CONTRACTORS

         Tenant shall promptly pay the cost of all Tenant Work so that Tenant's
         premises and the Building shall be free of liens for labor or
         materials. If any mechanic's lien is filed against the Building or any
         part thereof which is claimed to be attributable to the Tenant, its
         agents, employees or contractors, Tenant shall give immediate notice of
         such lien to the Landlord and shall promptly discharge the same by
         payment or filing any necessary bond within ten (10) days after Tenant
         has first notice of such mechanic's lien.

8.       CONTRACTOR'S INSURANCE

         Prior to commencing any Tenant Work, and throughout the performance of
         the Tenant Work, each Contractor shall obtain and maintain insurance in
         accordance with Exhibit A attached hereto. Each Contractor shall, prior
         to making entry into the Building, provide Landlord with certificates
         that such insurance is in full force and effect.

9.       SUBMISSIONS UPON COMPLETION

         a. Upon completion of any Tenant Work and prior to taking occupancy,
         Tenant shall submit to Landlord a permanent Certificate of Occupancy
         and final approval of any other governmental agencies having
         jurisdiction.

         b. Tenant shall submit to the Senior Tenant Design Coordinator a final
         "as-build" set of drawings showing all items of the work in full detail
         as required in the Tenant Design Criteria Manual.

10.      ADJUSTMENTS OF REGULATIONS

         In accordance with Section 5.4 of the Lease, Landlord has the right to
cancel or amend these General Conditions.


                                      -76-
<PAGE>   77
11.      CONFLICT BETWEEN RULES AND REGULATIONS AND LEASE

         In the event of any conflict between the Lease and these General
         Conditions, the term of the Lease shall control.


                                      -77-
<PAGE>   78
                                    EXHIBIT A
                                       TO
                     REQUIRED TENANT WORK GENERAL CONDITIONS

                     INSURANCE REQUIREMENTS FOR CONTRACTORS


         When Tenant Work is to be done by Contractors in the Building, the
Tenant authorizing such work shall be responsible for including in the contract
for such work the following insurance and indemnity requirements to the extent
that they are applicable. Insurance certificates must be received prior to
construction. Landlord and the Construction Coordinator shall be name as an
additional insured party on all certificates.

INSURANCE

         Each Contractor and each Subcontractor shall, until the completion of
the Tenant Work in question, procure and maintain at its expense, the following
insurance coverages with companies acceptable to Landlord in the following
minimum limits:

         Worker's Compensation
         (including coverage for Occupational Disease)
                                                             Limit of Liability

         Worker's Compensation                               As required by law
         Employer's Liability

         Comprehensive General Liability
         (including Broad Form Comprehensive Liability Endorsement, Contractual
         Liability assumed by the Contractor and the Tenant under Article 15.3
         of the Lease and Completed Operations coverage)

                                                             Limit of Liability

         Bodily Injury & Property Damage       $5,000,000 combined single limit

         Comprehensive Automobile Liability
         (including coverage for Hired and Non-owned Automobiles)

                                                             Limit of Liability


                                      -78-
<PAGE>   79
         Bodily Injury & Property Damage              $5,000,000 per occurrence

INDEMNITY

         Each Contractor shall indemnify, defend with counsel acceptable to
Landlord, and hold Landlord and Landlord's agents from and against any claims,
losses, and damages arising out of the work performed by such Contractor, unless
such claim, loss or damage arises from the negligence or willful misconduct of
Landlord or its agents.


                                      -79-
<PAGE>   80
                                    EXHIBIT H

                              INTENTIONALLY OMITTED





                                      -80-
<PAGE>   81
                                    EXHIBIT I

                                LETTER OF CREDIT

BENEFICIARY:                                                  ISSUANCE DATE:

                                                         ________________, 1997


SUMITOMO LIFE REALTY (N.Y.), INC.           IRREVOCABLE STANDBY
245 Park Avenue - 34th Floor                LETTER OF CREDIT NO.
New York, NY  10167

ACCOUNTEE/APPLICANT:                        MAXIMUM/AGGREGATE
                                            CREDIT AMOUNT: $1,000,000
LIGHTBRIDGE, INC.                           USD One Million and 00/100 Dollars


GENTLEMEN:

         We hereby establish our irrevocable letter of credit in your favor for
account of the applicant up to an aggregate amount not to exceed One Million and
00/100 US Dollars ($1,000,000.00) available by your draft(s) drawn on ourselves
at sight accompanied by:

         Your statement, signed by a purportedly authorized officer/official
certifying that the Beneficiary is entitled to draw upon this Letter of Credit
(in the amount of the draft submitted herewith) pursuant to Article X of the
Lease (the "Lease") dated March 5, 1997 by and between Sumitomo Life Realty
(N.Y.), Inc., as Landlord, and Lightbridge, Inc., as Tenant.

         Draft(s) must indicate name and issuing bank and credit number and must
be presented at this office.

         You shall have the right to make partial draws against this Letter of
Credit, from time to time.

         Except as otherwise expressly stated herein, this Letter of Credit is
subject to the "Uniform Customs and practice for Documentary Credits,
International Chamber of Commerce, Publication No. 500 (1993 Revision)".

         This Letter of Credit shall expire at our office on ________________,
199__ (the "Stated Expiration Date"). It is a condition of this Letter of Credit
that the Stated Expiration Date shall


                                      -81-
<PAGE>   82
be deemed automatically extended without amendment for successive one (1) year
periods from such Stated Expiration Date, unless at least forty-five (45) days
prior to such Stated Expiration Date )or any anniversary thereof) we shall
notify you and the Accountee/Applicant in writing by registered mail (return
receipt) that we elect not to consider this Letter of Credit extended for any
such additional one (1) year period.


                                      -82-