Document:

<PAGE>

                                                                    EXHIBIT 10.2

                           Asset Migration Agreement

THIS ASSET MIGRATION AGREEMENT (the "Agreement"), dated as of the 1/st/ day of
June, 2000, is entered into by and between Intermedia Communications, Inc., a
Delaware corporation (hereinafter referred to as "Intermedia"), and Digex, Inc.,
a Delaware corporation (hereinafter referred to as "Digex").  Intermedia and
Digex may be referred to individually as a "Party" and collectively as the
"Parties."

                             W I T N E S S E T H:

     WHEREAS, Intermedia is engaged in the business of remotely managing
firewall products for customers of Digex pursuant to the July Agreement (as
defined herein);

     WHEREAS, Digex desires to provide firewall services independent of
Intermedia for all of its customers, including those referred to in the
preceding paragraph, and the Parties have agreed on a transfer of assets from
Intermedia to Digex and on a termination of the July Agreement; and,

     WHEREAS, accordingly, Intermedia desires to sell, assign, transfer and
migrate certain assets, including certain licensed software, and equipment to
Digex, and Digex desires to acquire such assets upon the terms and conditions
set forth below.

     NOW, THEREFORE, in consideration of the above promises, the mutual
covenants herein contained and other good and valuable consideration, the
receipt and sufficiency of which is hereby acknowledged, the Parties hereto
agree as follows:

                   ARTICLE 1 -- PURCHASE AND SALE OF ASSETS

     1.1  Sale of Assets by Intermedia.  On the Closing Date (as hereinafter
          ----------------------------
defined) and subject to and on the terms and conditions of this Agreement, Digex
will purchase and accept from Intermedia, and Intermedia will sell, transfer,
convey and deliver to Digex, as the same shall exist on the Closing Date, all of
the properties and assets (tangible and intangible), including all of the
licensed software and equipment specified in Exhibit A, which is attached hereto
and made a part hereof by this reference (the "Assets"), including without
limitation, certain licensed third-party software, machinery, equipment,
and other tangible personal property as specified in Exhibit A, including all of
Intermedia's rights, title and interest in such Assets.

                                                                           Pg. 1
<PAGE>

     1.2  No Assumption of Liabilities.  Except as set forth in Section 1.3
          ----------------------------
immediately following, Digex does not assume and shall not be responsible for
any liabilities and obligations of Intermedia with respect to the Assets, and
Intermedia agrees to pay and discharge all of its liabilities and obligations
incurred in such operations up to the Closing Date, including, without
limitation, costs for utilities, insurance, taxes, operating licenses and other
similar operational costs (the "Operational Costs").  In this regard, Intermedia
shall pay the pro rata portion of any Operational Costs that may be invoiced to
Digex after the Closing Date but that relate to time periods prior to the
Closing Date.

     1.3  Description of Assumed Liabilities.  From and after the Closing Date,
          ----------------------------------
Digex agrees to assume and pay all Operational Costs incurred.

     1.4  Purchase Price.  In consideration of the sale, transfer, conveyance,
          --------------
assignment and delivery of the Assets by Intermedia to Digex, and subject to the
conditions set forth in this Agreement, Digex shall pay to Intermedia on the
Closing Date, $4,526,357.00, in cash or by wire transfer of funds to an account
designated by Intermedia (the "Purchase Price"). The Purchase Price is expressly
agreed upon by the Parties in accordance with the Asset values set forth in
Exhibit A,.

     1.5  Support Payments. In addition to the foregoing, and in exchange for
          ----------------
Intermedia's support and consultation during the six (6) months  commencing on
July 1, 2000 and ending on December 31, 2000, Digex shall pay Intermedia
$900,000.00 payable in installments of $150,000.00 each. The first such
installment payment is due and payable as of July 31, 2000, and each successive
installment shall be due and payable as of the last day of each successive month
thereafter through and including December 31, 2000. The provision and
availability of such support and consultation shall be at the mutual agreement
of the parties.

     1.6  Scripts. Scripts developed by Intermedia for the purpose of automating
          -------
the management and maintenance of firewalls are excluded from the Assets. Digex
has developed and/or acquired certain scripts for the purpose of automating the
management and maintenance of firewalls. The Parties agree and acknowledge that
any similarity between the Intermedia and Digex scripts are purely coincidental.

     1.7  Termination of Prior Agreement.  The parties had entered into a prior
          ------------------------------
agreement titled "Managed Firewall Existing Customers" and including the
document titled "Addendum to Intermedia Secure Managed Firewall Terms and
Conditions," each of which are dated July 13, 1999, and pursuant to which
Intermedia has performed certain managed firewall services for customers of
Digex (hereafter the "July Agreement"). By the terms of the July Agreement,
Intermedia has invoiced Digex, and Digex has paid Intermedia, all due sums for
Intermedia's performance of such services. Upon execution of this Agreement, and
since Intermedia shall no longer be responsible for providing managed firewall
services for Digex customers, the July Agreement shall be terminated and shall
be of no further force or effect. Accordingly, neither Digex nor Intermedia
shall have any further liability whatsoever under the July Agreement.

                                                                           Pg. 2
<PAGE>

          ARTICLE 2 -- REPRESENTATIONS AND WARRANTIES OF  INTERMEDIA
          ----------------------------------------------------------

     2.1  Representations and Warranties.  Intermedia represents and warrants
          ------------------------------
to, and agrees with, Digex that:

     2.2  Corporate Organization; Good Standing.  Intermedia is a corporation
          -------------------------------------
duly organized, validly existing and in good standing under the laws of the
State of Delaware, and has been duly qualified as a foreign corporation and is
in good standing under the laws of each jurisdiction in which it conducts its
business or owns or leases its assets.

     2.3  Authority.  Intermedia has all requisite power and authority to
          ---------
execute, deliver and perform this Agreement and has taken all necessary action
to authorize the execution, delivery and performance of this Agreement and to
consummate the transactions contemplated hereby in accordance with the
provisions hereof.

     2.4  Binding Obligation.  This Agreement constitutes the valid and binding
          ------------------
obligation of Intermedia, enforceable in accordance with its terms.

     2.5  Marketable Title.  Intermedia has good and marketable title to the
          ----------------
Assets, free and clear of any liens, charges and encumbrances.  Upon Closing,
there shall be vested in Digex good and marketable title to all tangible and
intangible property constituting the Assets, free and clear of any liens,
security interests, encumbrances or restrictions.

     2.6  Disclaimer. Except as otherwise provided in this Agreement, the
          ----------
foregoing sets forth the entire warranty provided hereunder by Intermedia, and
Intermedia expressly disclaims any other warranty, express or implied,
including, without limitation, any implied warranties of merchantability or
fitness for purpose. Notwithstanding anything to the contrary elsewhere in this
Agreement, Intermedia does not warrant or represent that any of the Assets shall
perform in compliance with any specifications, or that the Assets are functional
or defect free, materially or otherwise; provided, however, that the Assets
shall be in working condition as of the date of Closing.  Intermedia shall
assign to Digex at Closing, all assignable warranty coverage it possesses in the
Assets as provided by any manufacturer or seller thereof.  Digex shall be solely
responsible, at its sole expense, for conducting its due diligence review of the
Assets in accordance with the terms hereof.  Nothing herein shall be construed
as to require that Intermedia repair or replace any Assets based on any
inspection or testing conducted prior to Closing, or based on any failure of, or
defect in, any Assets, patent or latent, discovered after the Closing Date.

             ARTICLE 3 -- REPRESENTATIONS AND WARRANTIES OF DIGEX

     3.1  Representations and Warranties.  Digex hereby represents and warrants
          ------------------------------
to, and agrees with, Intermedia that:

                                                                           Pg. 3
<PAGE>

     3.2  Corporate Organization; Good Standing.  Digex is a corporation duly
          -------------------------------------
organized, validly existing and in good standing under the laws of the State of
Delaware, and has been duly qualified as a foreign corporation and is in good
standing under the laws of each jurisdiction in which it conducts its business
or owns or leases its assets.

     3.3  Authority.  Digex has all requisite power and authority to execute,
          ---------
deliver and perform this Agreement, to consummate the transactions contemplated
hereby, and be bound, in accordance with the provisions hereof.

     3.4  Binding Obligation.  This Agreement constitutes the valid and binding
          ------------------
obligation of Digex, and is enforceable in accordance with its terms.

                      ARTICLE 4 -- CONDITIONS TO CLOSING

     4.1  Conditions Precedent to Closing By the Parties.  The obligations of
          ----------------------------------------------
Intermedia and Digex to consummate the transactions contemplated hereby are
conditioned on and subject to the fulfillment of the following conditions on or
before the Closing Date:

          4.1.1  The representations and warranties of Intermedia contained in
Article 2 of this Agreement shall be true and correct in all material respects
as of the Closing Date.  The representations and warranties of Digex contained
in Article 3 of this Agreement shall be true and correct in all material
respects as of the Closing Date.

          4.1.2  Intermedia shall have performed and complied in all material
respects with its obligations under this Agreement to be performed prior to the
Closing Date.  Digex shall have performed and complied in all material respects
with its obligations under this Agreement to be performed prior to the Closing
Date.

     4.2  Due Diligence.  As of the Closing Date, Digex shall have completed all
          -------------
inspections and/or testing of the Assets it shall have reasonably deemed
necessary in order to verify the working condition and acceptability thereof.

                           ARTICLE 5 -- THE CLOSING

     5.1  Closing Date; Final Inventory Date.  The closing of the transactions
          ----------------------------------
provided for herein (the "Closing") shall take place at a mutually agreed
location on a date that is on or before June 1, 2000 (the "Closing Date").
Closing shall be complete upon conveyance of the Purchase Price from Digex to
Intermedia in accordance with Section 5.3 below.  Upon Closing, all existing
Assets shall become the property of Digex, and all title and risk of loss in
such Assets shall transfer to Digex in accordance with Section 5.2 below.

     5.2  Intermedia's Obligations on the Closing Date.  At the Closing,
          --------------------------------------------
Intermedia shall deliver to Digex any bills of sale, duly executed by Intermedia
and any other reasonable documentation as may be reasonably required by Digex,
if any, to vest in Digex good and marketable title to the Assets.

                                                                           Pg. 4
<PAGE>

     5.3  Digex's Obligations on the Closing Date.  At the Closing, Digex shall
          ---------------------------------------
pay to Intermedia the Purchase Price, in cash, by wire transfer or in other
certified funds.

            ARTICLE 6 - INDEMNIFICATION AND LIMITATION OF LIABILITY

     6.1  Indemnification of Intermedia by Digex.  Digex agrees to and does
          --------------------------------------
hereby indemnify and hold Intermedia, its officers, directors, shareholders,
employees and agents, harmless, from and against any and all liability, loss,
damage or injury and all reasonable costs and expenses relating thereto,
including reasonable legal expenses, arising out of or resulting from (i) any
breach of any covenants, representations and/or warranties made by Digex
pursuant to this Agreement and/or (ii) causes of action or claims of any kind
asserted by unrelated third parties arising from acts or omissions of Digex
relating to the Assets.

     6.2  Indemnification of Digex by Intermedia.  Intermedia agrees to and does
          --------------------------------------
hereby indemnify and hold Digex, its officers, directors, shareholders,
employees and agents, harmless, from and against any and all liability, loss,
damage or injury, and all reasonable costs and expenses relating thereto,
including reasonable legal expenses, arising out of or resulting from (i) any
breach of any covenants, representations and/or warranties made by Intermedia
pursuant to this Agreement, and/or (ii) causes of action or claims of any kind
asserted by unrelated third parties arising from acts or omissions of Intermedia
relating to the Assets.

     6.3  Limitation of Liability. Notwithstanding anything to the contrary
          -----------------------
herein, neither Party shall be liable to the other for special, indirect,
incidental, consequential, exemplary or punitive damages howsoever arising, and
whether or not either Party was apprised or knew of the possibility or
likelihood of the occurrence of events giving rise to such damages. The
foregoing precludes, without limitation, any liability on the part of either
Party to the other, for lost profits, lost revenue, lost business, cost of cover
or of substitute goods or services, or damage to goodwill.

                           ARTICLE 7 - MISCELLANEOUS

     7.1  Expenses.  Each of the Parties hereto shall bear their respective
          --------
expenses incurred in the negotiation and consummation of this Agreement and the
transaction contemplated hereby.

     7.2  Waivers.  The failure of any Party hereto at any time or from time to
          -------
time to require performance of any other Party's obligations under this
Agreement shall in no manner affect the right of such Party to require
performance of any provision of this Agreement at a subsequent time, and the
waiver by any Party of any right arising out of any breach of any provision of
this Agreement shall not be construed as a waiver of any continuing or
succeeding breach of such provision, a waiver of the provision itself, or a
waiver of any right arising out of any subsequent breach.

                                                                           Pg. 5
<PAGE>

     7.3  Successors and Assigns.  This Agreement shall be binding on and shall
          ----------------------
inure to the benefit of the Parties hereto and their respective successors,
heirs, representatives and permitted assigns. Nothing contained herein shall
inure to the benefit of any other third party. This Agreement may not be
assigned by either Party hereto without the other Party's prior written consent.

     7.4  Severability.  The invalidity or illegality of any provision, term or
          ------------
agreement contained in or made a part of this Agreement shall not affect the
validity of the remainder of this Agreement.

     7.5  Headings.  The headings of the sections and subsections contained in
          --------
this Agreement are for reference purposes only and shall not affect in any way
the meaning or interpretation of this Agreement.

     7.6  Entire Agreement.  This Agreement, and any schedule appended hereto,
          ----------------
contains all of the terms agreed to by the Parties with respect to the subject
matter hereof and supersede all prior oral or written agreements,
understandings, negotiations and representations made by and between the
Parties. This Agreement may not be amended or modified in any way except by a
written amendment to this Agreement duly executed by the Parties.

     7.7  Counterparts.  This Agreement may be executed in counterparts by the
          ------------
Parties hereto, each of which when so executed shall be an original, but all of
which together shall constitute one and the same instrument.

     7.8  Applicable Law.  This Agreement shall be governed by, and construed
          --------------
(both as to validity and performance) and enforced in accordance with, the laws
of the State of Maryland applicable to contracts made and to be performed wholly
within said State.

     7.9  Survivability.  All provisions hereof shall survive the Closing Date.
          -------------

     IN WITNESS WHEREOF, the Parties hereto have caused this Agreement to be
executed as of the date first above written.

  Intermedia Communications, Inc.                        Digex, Inc.

       /s/ ROBERT M. MANNING                       /s/ TIMOTHY M. ADAMS
By: __________________________________      By: ________________________________

Name:  Robert M. Manning                    Name:  Timothy M. Adams
       -------------------------------             -----------------------------

Title: Senior Vice President                Title: Chief Financial Officer
       -------------------------------             -----------------------------
       and Chief Financial Officer
       -------------------------------

                                                                           Pg. 6
<PAGE>

                                   EXHIBIT A

Digex/Intermedia
Firewall Migration Cost Summary Statement

<TABLE>
<CAPTION>
                                               Q3/2000        Q4/2000        Q1/2000        Q2/2000        Total
-------------------------------------------------------------------------------------------------------------------
<S>                                          <C>            <C>            <C>            <C>           <C>
Asset Transfer Costs:
  Depreciated Hardware Value                 $  533,920     $  533,920     $   533,920    $   533,920   $ 2,135,679
  Depreciated Software Cost                      13,242         13,242          13,242         13,242        52,966
                                             ----------------------------------------------------------------------
     Total Asset Transfer Costs              $  547,161     $  547,161     $   547,161    $   547,161   $ 2,188,645
                                             ----------------------------------------------------------------------

Service Charge Costs:
  Monthly Recurring Costs                                                  $ 1,309,998    $ 1,027,714   $ 2,337,712
  Start-Up Costs                                                                                                  -
                                             ----------------------------------------------------------------------
     Total Service Charge Costs              $        -     $        -     $ 1,309,998    $ 1,027,714   $ 2,337,712
                                             ======================================================================

Total Migration Costs:                       $  547,161     $  547,161     $ 1,857,159    $ 1,574,875   $ 4,526,357
                                             ======================================================================
</TABLE>

Assumptions
------------------------------------------
Depreciation is straight line over 5 years.
All costs are calculated on a daily basis.
All prices are at cost.<PAGE>

                                                                    EXHIBIT 10.3

                                  DEED OF LEASE

         THIS DEED OF LEASE (this "Lease") is made as of June 29, 2000, by and
                                   -------
between

"Landlord"       RIGGS & COMPANY, a division of Riggs Bank N.A., as Trustee of
 --------
                 the Multi-Employer Property Trust, a trust organized under 12
                 C.F.R. Section 9.18

                 and

"Tenant"         DIGEX, INC., a Delaware corporation
 ------

                               Table of Contents
                               -----------------

<TABLE>
<CAPTION>
<S>                                                                                                          <C>
SECTION   1:   DEFINITIONS.................................................................................   5
 1.1      Definitions......................................................................................   5
 1.2      Access Laws......................................................................................   5
 1.3      Above Standard Tenant Improvement Allowance......................................................   5
 1.4      Additional Rent..................................................................................   5
 1.5      Base Amount of the Base Rent Operating Cost Component............................................   5
 1.6      Base Amount of the Base Rent Tax Component.......................................................   6
 1.7      Base Rent........................................................................................   6
 1.8      Base Rent Net Component..........................................................................   6
 1.9      Base Rent Operating Cost Component...............................................................   7
 1.10     Base Rent Tax Component..........................................................................   7
 1.11     Brokers..........................................................................................   7
 1.12     Building.........................................................................................   7
 1.13     Business Day.....................................................................................   7
 1.14     Claims...........................................................................................   7
 1.15     Commencement Dates...............................................................................   7
 1.16     Common Areas.....................................................................................   7
 1.17     Estimated Operating Costs for the Premises.......................................................   7
 1.18     Estimated Property Taxes for the Premises........................................................   8
 1.19     Events Of Default................................................................................   8
 1.20     Governmental Agency..............................................................................   8
 1.21     Governmental Requirements........................................................................   8
 1.22     Hazardous Substance(s)...........................................................................   8
 1.23     Land.............................................................................................   8
 1.24     Landlord.........................................................................................   8
 1.25     Landlord's Agents................................................................................   8
 1.26     Lease Term.......................................................................................   8
 1.27     Lease Termination Fee............................................................................   8
 1.27a    Lease Year.......................................................................................   8
 1.27b    Long Lead Item(s)................................................................................   8
 1.28     Manager..........................................................................................   9
 1.29     Manager's Address................................................................................   9
 1.29a    Normal Business Hours............................................................................   9
</TABLE>
<PAGE>

<TABLE>
<S>                                                                                                        <C>
 1.30     Operating Costs.................................................................................    9
 1.31     Operating Costs For The Premises................................................................    9
 1.32     Parking Ratio...................................................................................    9
 1.33     Permitted Use...................................................................................    9
 1.34     Phases..........................................................................................    9
 1.35     Plans And Specifications........................................................................    9
 1.36     Prepaid Rent....................................................................................    9
 1.37     Premises........................................................................................    9
 1.38     Prime Rate......................................................................................    9
 1.39     Property Taxes..................................................................................    9
 1.40     Punch List Work.................................................................................   10
 1.41     Security Deposit................................................................................   10
 1.42     Substantial Completion..........................................................................   10
 1.43     Tenant..........................................................................................   11
 1.44     Tenant Alterations..............................................................................   11
 1.44A    Tenant Delays...................................................................................   11
 1.45     Tenant Improvement Allowance....................................................................   11
 1.46     Tenant Improvements.............................................................................   11
 1.47     Tenant's Agents.................................................................................   12
 1.48     Year............................................................................................   12

SECTION   2: PREMISES AND TERM............................................................................   12

 2.1      Leases Of Premises..............................................................................   12
 2.2      Lease Term......................................................................................   12
 2.3      Plans and Specifications........................................................................   12
 2.4      Commencement Dates..............................................................................   12
 2.5      Tenant Improvement Construction.................................................................   15
 2.6      Tenant's Contribution to Tenant Improvement Costs...............................................   15
 2.7      Memorandum of Commencement Date.................................................................   16
 2.8      Use and Conduct of Business.....................................................................   16
 2.9      Compliance with Governmental Requirements and Rules and Regulations.............................   17

SECTION   3: BASE RENT, ADDITIONAL RENT AND OTHER SUMS PAYABLE UNDER LEASE................................   17

 3.1      Payment of Rental...............................................................................   17
 3.2      Base Rent.......................................................................................   18
 3.3      Security........................................................................................   18
 3.4      Additional Rent.................................................................................   21
 3.5      Utilities.......................................................................................   27
 3.6      Holdover........................................................................................   28
 3.7      Late Charge.....................................................................................   28
 3.8      Default Rate....................................................................................   28

SECTION   4: GENERAL PROVISIONS...........................................................................   29

 4.1      Maintenance and Repair by Landlord; Hvac; Other Utilities and Services, Service Interruption....   29
 4.2      Maintenance and Repair by Tenant................................................................   30
 4.3      Common Areas/security...........................................................................   30
 4.4      Tenant Alterations..............................................................................   31
 4.5      Tenant's Work Performance.......................................................................   33
 4.6      Surrender of Possession.........................................................................   34
 4.7      Removal of Property.............................................................................   34
 4.8      Access..........................................................................................   35
 4.9      Damage or Destruction...........................................................................   36
 4.10     Condemnation....................................................................................   37
 4.11     Parking.........................................................................................   38
</TABLE>
                                       2
<PAGE>

<TABLE>
<S>                                                                                                         <C>
 4.12     Indemnification.................................................................................   38
 4.13     Tenant Insurance................................................................................   38
 4.14     Landlord's Insurance............................................................................   40
 4.15     Waiver of Subrogation...........................................................................   40
 4.16     Assignment and Subletting by Tenant.............................................................   40
 4.17     Assignment by Landlord..........................................................................   45
 4.18     Estoppel Certificates and Financial Statements..................................................   46
 4.19     Modification for Lenders........................................................................   46
 4.20     Hazardous Substances............................................................................   47
 4.21     Access Laws.....................................................................................   48
 4.22     Quiet Enjoyment.................................................................................   49
 4.23     Signs...........................................................................................   49
 4.24     Subordination...................................................................................   50
 4.25     Workers Compensation Immunity...................................................................   51
 4.26     Brokers.........................................................................................   51
 4.27     Exculpation and Limitation of Liability.........................................................   52
 4.28     Intentionally Omitted...........................................................................   53
 4.29     Mechanic's Liens And Tenant's Personal Property Taxes...........................................   53
 4.30     Landlord's Security Interest....................................................................   53
 4.31     Recording.......................................................................................   53
 4.32     Cabling/connectivity Rights.....................................................................   53
 4.33     Backup Generator................................................................................   54

SECTION   5: DEFAULT AND REMEDIES.........................................................................   56

 5.1      Events of Default...............................................................................   56
 5.2      Remedies........................................................................................   57
 5.3      Right to Perform................................................................................   59
 5.4      Landlord's Default..............................................................................   60

SECTION   6: MISCELLANEOUS PROVISIONS.....................................................................   60

 6.1      Notices.........................................................................................   60
 6.2      Attorney's Fees and Expenses....................................................................   60
 6.3      No Accord and Satisfaction......................................................................   61
 6.4      Successors, Joint and Several Liability.........................................................   61
 6.5      Choice of Law...................................................................................   61
 6.6      No Waiver of Remedies...........................................................................   61
 6.7      Offer to Lease..................................................................................   62
 6.8      Force Majeure...................................................................................   62
 6.9      Landlord's Consent..............................................................................   62
 6.10     Severability; Captions..........................................................................   62
 6.11     Interpretation..................................................................................   62
 6.12     Incorporation of Prior Agreement; Amendments....................................................   63
 6.13     Authority.......................................................................................   63
 6.14     Time of Essence.................................................................................   63
 6.15     Survival of Obligations.........................................................................   63
 6.16     Consent to Service..............................................................................   63
 6.17     Landlord's Authorized Agents....................................................................   63
 6.18     Waiver of Jury Trial............................................................................   64
 6.19     Option to Extend Term...........................................................................   64
 6.20     First Right of Offer............................................................................   66
 6.21     Termination Option..............................................................................   66
</TABLE>

EXHIBIT A       LEGAL DESCRIPTION OF LAND

                                       3
<PAGE>

EXHIBIT B       LISTING OF PLANS AND SPECIFICATIONS FOR TENANT IMPROVEMENTS
EXHIBIT C       WORK LETTER AND CONSTRUCTION AGREEMENT
EXHIBIT D       FORM OF MEMORANDUM OF COMMENCEMENT DATE
EXHIBIT E       RULES AND REGULATIONS
EXHIBIT F       FORM OF LETTER OF CREDIT
EXHIBIT G       SCHEDULE OF CLEANING SERVICES
EXHIBIT H       BUILDING DESCRIPTION

                                       4
<PAGE>

                            SECTION 1: DEFINITIONS
                            ----------------------

     1.1 Definitions: Each underlined term in this section shall have the
         -----------
meaning set forth next to that underlined term.

     1.2 Access Laws: The Americans With Disabilities Act of 1990 (including the
         -----------
Americans with Disabilities Act Accessibility Guidelines for Building and
Facilities) and all other Governmental Requirements relating to the foregoing.

     1.3 Above Standard Tenant Improvement Allowance: In addition to the Tenant
         -------------------------------------------
Improvement Allowance described herein, Landlord will provide Tenant, at
Tenant's option,

 ***Request for confidential treatment has been submitted to the SEC for the
    amount of the Above Standard Tenant Improvement Allowance.***

comprising the Premises after the size of the Premises has been conclusively
established pursuant to the section captioned "Definitions--Premises" to be
                                               ---------------------
used for: (i) above standard tenant improvements; (ii) design and construction
documents for such above standard improvements; (iii) architectural and MEP
plans for such above standard improvements; and (iv) a four percent (4%)
Landlord's construction management fee. In the event Tenant elects to use some
or all of the Above Standard Tenant Improvement Allowance, the Base Rent Net
Component shall be increased to the sum of (i) the Base Rent Net Component
                                ----------
(expressed on a per rentable square foot basis), plus (ii) the product of (A)
                                                 ----      --------------
the Above Standard Tenant Improvement Allowance used by Tenant (expressed on a
per rentable square foot basis) multiplied by (B).1654. In addition, if Tenant
                                ----------
elects to draw on some or all of the Above Standard Tenant Improvement
Allowance, then Tenant shall increase (i) the amount of Tenant's Security
Deposit in an amount equal to the aggregate amount of the drawn portion of the
Above Standard Tenant Improvement Allowance and such additional amount of the
Security Deposit shall be added to the amounts set forth in the section
captioned "Definitions - Security Deposit", and (ii) the amount of the Lease
           ------------------------------
Termination Fee in an amount equal to the unamortized portion (assuming a
straight line amortization over the Lease Term) as of the Termination Option
Date of the aggregate amount of the drawn portion of the Above Standard Tenant
Improvement Allowance and such additional amount of the Lease Termination Fee
shall be added to the amounts set forth in the section captioned "Definitions -
                                                                 ---------------
Lease Termination Fee."
---------------------

     1.4 Additional Rent:  Defined in section captioned "Additional Rent".
         ---------------                                 ---------------

     1.5 Base Amount of the Base Rent Operating Cost Component: *** Request for
         -----------------------------------------------------
confidential treatment has been submitted to the SEC for this sentence.***
Landlord represents to Tenant that to Landlord's best knowledge and belief, such
amount constitutes the currently anticipated Operating Costs for the Premises as
if the Building were 2 years old and 100% occupied. Notwithstanding the
foregoing, Landlord reserves the right to adjust the Base Amount of the Base
Rent Operating Cost
                                       5
<PAGE>

Component if, in Landlord's reasonable judgment, Operating Costs for the
Premises for the first full year will increase or were increased due to the
Tenant's use of the Premises beyond that of a normal office tenant utilizing
similar space during Normal Business Hours. Landlord shall notify Tenant in
writing if Landlord exercises its right to so modify the Base Amount of the Base
Rent Operating Cost Component.

     1.6 Base Amount of the Base Rent Tax Component: *** Request for
         ------------------------------------------
confidential treatment has been submitted to the SEC for this sentence. ***

     1.7 Base Rent: Base Rent shall be equal to the sum of the Base Rent Net
         ---------
Component, the Base Rent Operating Cost Component, and the Base Rent Tax
Component as follows:

--------------------------------------------------------------------------------
         Lease Year*                    Rent For Rentable Square Foot***
--------------------------------------------------------------------------------
              1                                      $**.**
--------------------------------------------------------------------------------
              2                                      $**.**
--------------------------------------------------------------------------------
              3                                      $**.**
--------------------------------------------------------------------------------
              4                                      $**.**
--------------------------------------------------------------------------------
              5                                      $**.**
--------------------------------------------------------------------------------
              6                                      $**.**
--------------------------------------------------------------------------------
              7                                      $**.**
--------------------------------------------------------------------------------
              8                                      $**.**
--------------------------------------------------------------------------------
              9                                      $**.**
--------------------------------------------------------------------------------
             10                                      $**.**
--------------------------------------------------------------------------------
             11                                      $**.**
--------------------------------------------------------------------------------

   *For the purposes of this Lease, a "Lease Year" shall refer to each twelve
(12) month period during the Lease Term. The first Lease Year shall begin on the
month after the Phase I Commencement Date. Each subsequent Lease Year shall
commence on the date immediately following the last day of the preceding Lease
Year and shall continue for a period of twelve (12) calendar months, except that
the last Lease Year of the Lease Term shall terminate on the date this Lease
expires or is otherwise terminated.

***Request for Confidential treatment has been submitted to the SEC for the rent
per rentable square foot.***

   Notwithstanding the foregoing, in the event Tenant elects to use any of the
Above Standard Tenant Improvement Allowance, the rates for Base Rent set forth
above shall be adjusted and increased pursuant to the provisions of Section 1.3
of this Lease.

1.8 Base Rent Net Component: The rental component of the Base Rent Calculating
    -----------------------
for the Premises as adjusted pursuant to Section 1.3.

                                       6
<PAGE>

     1.9    Base Rent Operating Cost Component: The Operating Cost component of
            ----------------------------------
the Base Rent for the Premises.

     1.10   Base Rent Tax Component: The Property Tax component of the Base Rent
            -----------------------
for the Premises.

     1.11   Brokers: Tenant was represented in this transaction by McShea &
            -------
Company, Inc. ("McShea"), a licensed real estate broker.
                ------

           Landlord was represented in this transaction by TC MidAtlantic, Inc.
("TCMI"), a licensed real estate broker.
  ----

           McShea, TCMI, and TC MidAtlantic Development, Inc. ("TCMD") are
                                                                ----
hereinafter referred to collectively as the "Brokers" and each, individually, as
a "Broker".

     1.12   Building: The building located on the Land at 14400 Sweitzer Lane,
            --------
Laurel, Maryland, commonly known as The Maryland 95 Executive Center and
containing a total of approximately one hundred twenty thousand nine hundred
four (120,904) rentable square feet. The Building shall have those
characteristics described in Exhibit H attached to this Lease.
                             ---------

     1.13   Business Day: Calendar days, except for Saturdays and Sundays and
            ------------
holidays when banks are closed in Prince George's County, Maryland. Any
reference to "days" with respect to the calculation of time under this Lease
shall mean calendar days unless otherwise specified to be Business Days.

     1.14   Claims: An individual and collective reference to any and all
            ------
claims, demands, damages, injuries, losses, liens, liabilities, penalties,
fines, lawsuits, actions, other proceedings and expenses (including attorneys'
fees and expenses incurred in connection with the proceeding whether at trial or
on appeal).

     1.15   Commencement Dates: The Lease for the Premises shall commence in two
            ------------------
(2) Phases as follows: (i) the "Phase I Commencement Date" shall be on or about
                                -------------------------
September 15, 2000, provided that the Phase I Commencement Date shall not occur
until Substantial Completion of Phase I of the Tenant Improvements; and (ii) the
"Phase II Commencement Date" shall be on or before ninety (90) days after the
 --------------------------
Phase I Commencement Date, provided that the Phase II Commencement Date shall
not occur until Substantial Completion of Phase II of the Tenant Improvements.

     1.16   Common Areas: Those areas outside the Building which Landlord from
            ------------
time to time makes available to the public such as the parking area, sidewalks,
entrance drives, loading docks and landscaped areas.

     1.17   Estimated Operating Costs for the Premises: Defined in the section
            ------------------------------------------
captioned "Additional Rent".
           ---------------

                                       7
<PAGE>

     1.18  Estimated Property Taxes for the Premises: Defined in the section
           -----------------------------------------
captioned "Additional Rent".
           ---------------

     1.19  Events of Default: One or more of those events or states of facts
           -----------------
defined in the section captioned "Events of Default".
                                  -----------------

     1.20  Governmental Agency: The United States of America, the state in which
           -------------------
the Land is located, any county, city, district, municipality or other
governmental subdivision, court or agency or quasi-governmental agency having
jurisdiction over the Land and any board, agency or authority associated with
any such governmental entity, including the fire department having jurisdiction
over the Land.

     1.21  Governmental Requirements: Any and all statutes, ordinances, codes,
           -------------------------
laws, rules, regulations, orders and directives of any Governmental Agency as
now or later amended.

     1.22  Hazardous Substance(s): Asbestos, PCBs, petroleum or petroleum based
           ----------------------
chemicals or substances, urea formaldehyde or any chemical, material, element,
compound, solution, mixture, substance or other matter of any kind whatsoever
which is now or later defined, classified, listed, designated or regulated as
hazardous, toxic or radioactive by any Governmental Agency.

     1.23  Land: The land upon which the Building is located in Prince George's
           ----
County, Maryland, as legally described in Exhibit A attached to this Lease.
                                          ---------

     1.24  Landlord: The trust named on the first page of this Lease, or its
           --------
successors and assigns as provided in the section captioned "Assignment by
                                                             -------------
Landlord".
--------

     1.25  Landlord's Agents: Any and all partners, officers, agents, employees,
           -----------------
trustees, investment advisors and consultants of Landlord.

     1.26  Lease Term: Commencing on the Phase I Commencement Date, and ending
           ----------
one hundred and twenty (120) months after the Phase II Commencement Date,
provided that, if the Phase II Commencement Date is a date other than the first
-------------
day of a calendar month, the Lease Term shall be extended by the number of days
remaining in the month in which the Phase II Commencement Date occurs.

     1.27  Lease Termination Fee: *** Request for confidential treatment has
           ---------------------
been submitted to the SEC for this sentence. ***

     1.27A Lease Year:  As defined in Section 1.3.
           ----------

     1.27B Long Lead Item(s): As defined in Section 1.42.
           -----------------

                                       8
<PAGE>

     1.28  Manager: TC MidAtlantic, Inc., or its replacement as specified by
           -------
written notice from Landlord to Tenant.

     1.29  Manager's Address: TC MidAtlantic, Inc., c/o Trammell Crow Company,
           -----------------
7315 Wisconsin Avenue, Suite 300 West, Bethesda, Maryland 20814, Attn: Dan
Hudson, which address may be changed by written notice from Landlord to Tenant.

     1.29A   Normal Business Hours:  As defined in Subparagraph 3.4.7.
             ---------------------

     1.30  Operating Costs:  Defined in the section captioned "Additional Rent".
           ---------------                                     ---------------

     1.31  Operating Costs for the Premises: Defined in the section captioned
           --------------------------------
"Additional Rent".
 ---------------

     1.32  Parking Ratio: Approximately 4.0 stalls per one thousand (1,000)
           -------------
rentable square feet of the Premises.

     1.33  Permitted Use: General office use, so long as such use is consistent
           -------------
with Governmental Requirements and with first-class buildings of the same or
similar use as the Building located in the metropolitan area in which the
Building is located.

     1.34  Phases: The Premises shall be occupied in Phases as follows: (i)
           ------
"Phase I" shall be the initial two (2) floors of the Premises occupied by the
 -------
Tenant; (ii) "Phase II" shall be the third and fourth floors of the
              --------
Premises occupied by the Tenant.

     1.35  Plans and Specifications: (a) Those certain plans and specifications
           ------------------------
for the Tenant Improvements as listed in Exhibit B and any modifications to them
                                         ---------
approved in writing by Landlord and Tenant; or (b) if Exhibit B does not include
                                                      ---------
a listing of such plans and specifications, then such plans and specifications
shall be prepared in accordance with the Work Letter attached hereto as Exhibit
                                                                        -------
C.
-

     1.36  Prepaid Rent: *** Request for confidential treatment has been
           ------------
submitted to the SEC for this sentence. ***

     1.37  Premises: The Premises are the entire Building and, based on a
           --------
certification issued by Landlord's architect, consists of approximately one
hundred twenty thousand nine hundred and four (120,904) rentable square feet.

     1.38  Prime Rate:  Defined in the Section captioned "Default Rate".
           ----------                                     ------------

     1.39  Property Taxes: (a) Any form of ad valorem real or personal property
           --------------
tax or assessment imposed by any Governmental Agency on the Land, Building,
related improvements or any personal property owned by Landlord associated with
such Land, Building or improvements; (b) any other form of tax or assessment,
license fee, license tax, tax or excise on rent or any other levy, charge,
expense or imposition made or required by any Governmental Agency on any
interest of Landlord in such Land,

                                       9
<PAGE>

Building, related improvements or personal property; (c) any fee for services
charged by any Governmental Agency for any services such as fire protection,
street, sidewalk and road maintenance, refuse collection, school systems or
other services provided or formerly provided to property owners and residents
within the general area of the Land; (d) any governmental impositions allocable
to or measured by the area of any or all of such Land, Building, related
improvements or personal property or the amount of any base rent, additional
rent or other sums payable under any lease for any or all of such Land,
Building, related improvements or personal property, including any tax on gross
receipts or any excise tax or other charges levied by any Governmental Agency
with respect to the possession, leasing, operation, maintenance, alteration,
repair, use or occupancy of any or all of such Land, Building, related
improvements, personal property or the rent earned by any part of or interest in
such Land, Building, related improvements or personal property; (e) any
impositions by any Governmental Agency on any transaction evidenced by a lease
of any or all of such Land, Building, related improvements or personal property
or charge with respect to any document to which Landlord is a party creating or
transferring an interest or an estate in any or all of such Land, Building,
related improvements or personal property; (f) any increase in any of the
foregoing based upon construction of improvements or change of ownership of any
or all of such Land, Building, relate improvements or personal property, and (g)
reasonable expenses (including, but not limited to, attorneys' fees,
disbursements, consultant fees and expenses) incurred in obtaining or attempting
to obtain, a reduction of such taxes, rates or assessments, including appeals.
Property Taxes shall not include taxes on Landlord's net income or any
inheritance, estate or gift taxes.

     1.40  Punch List Work: Minor items of repair, correction, adjustment or
           ---------------
completion as such phrase is commonly understood in the construction industry in
the metropolitan area in which the Land is located.

     1.41  Security Deposit: Two Million and No/100 Dollars ($2,000,000.00), in
           ----------------
the form of a Letter of Credit, in accordance with the terms of the section 3.3
captioned "Security".
           --------

     1.42  Substantial Completion: The date that the applicable Phase of the
           ----------------------
Tenant Improvements have been completed substantially in accordance with the
applicable Plans and Specifications, subject to Punch List Work. The Tenant
Improvements shall be deemed to be substantially complete upon the issuance of a
temporary or permanent certificate of occupancy by the proper governmental
authority. Notwithstanding the above, the applicable Phase of the Premises shall
be considered substantially complete even though (a) there remains to be
completed Punch List items, the lack of which will not materially interfere with
Tenant's permitted use of the Premises including, without limit, minor or
insubstantial details of construction, decoration or mechanical adjustment, or
(b) there is a delay in substantial completion due to Tenant's failure to meet
its obligations under this Lease or "Tenant Delay" as such term is defined in
this Lease, including Exhibit C or (c) there are any undelivered or uninstalled
Long Lead Items previously identified as such or (d) the Certificate of

                                       10
<PAGE>

Occupancy is not issued due to Tenant's failure to complete Tenant's
installation of furniture, fixtures or equipment or other items to be installed
or constructed by Tenant pursuant to this Lease including the provision of
Exhibit C entitled "Tenant Access" and in accordance with scheduling
---------
requirements established by the Tenant Improvements General Contractor
designated pursuant to Exhibit C.
                       ---------

          As used herein, the phrase "Long Lead Item" shall mean any item of
                                      --------------
Tenant's Work or material element thereof which Landlord reasonably identifies
as unavailable at the Premises in time to be completed and installed prior to
the anticipated Commencement Date. Landlord shall so notify Tenant of such Long
                                                                           ----
Lead Items at the time Landlord provides Tenant with the Initial Tenant
----------
Improvements Pricing Letter pursuant to Paragraph 4.1.B of Exhibit C.
                                                           ---------
Notwithstanding the foregoing, Landlord will endeavor to provide information
regarding Long Lead Items as soon as reasonably available to Landlord. With
          ---------------
respect to long-lead items, Tenant (acting through Tenant's Representative
appointed pursuant to Paragraph 6.2 of Exhibit C) shall during the period
                                       ---------
provided in Exhibit C for Tenant's response to the Initial Tenant Improvements
            ---------
Pricing Letter elect to (x) omit such long-lead item(s) from the Plans, (y)
substitute such item(s) for another item(s) that does not constitute a Long Lead
                                                                       ---------
Item, or (z) retain such long-lead item(s) in the Plans to be installed when
----
delivered. In the event Tenant fails timely to affirmatively elect (x), (y), or
(z) above, Tenant shall be deemed to have elected (z). If Tenant elects (z) or
is deemed to have elected (z), any delays in completion of the construction as a
result thereof shall be Tenant Delay. Landlord shall promptly identify for
Tenant, after the time of submission by Tenant of a proposed substitution, the
reasonably estimated delay which will be caused by said substitution, if any.
The actual delay, if any, caused by such substitution shall be Tenant Delay. Any
delay in the completion and installation of the long-lead item or arising from
Tenant's election to substitute any long-lead item or retain an identified
long-lead item shall be a Tenant Delay.

     1.43  Tenant:  Digex, Inc., a Delaware corporation.
           ------

     1.44  Tenant Alterations: Defined in the section captioned "Tenant
           ------------------                                    ------
Alterations".
-----------

     1.44A   Tenant Delay(s):  As defined in Paragraph 5.3 of Exhibit C.
             ---------------                                  ---------

     1.45  Tenant Improvement Allowance: *** Request for confidential treatment
           ----------------------------
has been submitted to the SEC for this sentence. ***

     1.46  Tenant Improvements: Those alterations or improvements for each of
           -------------------
the Phases of the Premises as appear and are depicted in the Plans and
Specifications.

                                       11
<PAGE>

     1.47  Tenant's Agents: Any and all officers, partners, contractors,
           ---------------
subcontractors, consultants, licensees, agents, concessionaires, subtenants,
servants, employees, customers, guests, invitees or visitors of Tenant.

     1.48  Year:  A calendar year commencing January 1 and ending December 31.
           ----

                         SECTION 2:  PREMISES AND TERM
                         -----------------------------

     2.1   Leases of Premises: Landlord leases the Premises to Tenant, and
           ------------------
Tenant leases the Premises from Landlord, upon the terms and conditions set
forth in this Lease.

     2.2   Lease Term: The Lease Term shall be for the period stated in the
           ----------
definition of that term, unless earlier terminated as provided in this Lease.

     2.3   Plans and Specifications: To the extent clause (b) of the definition
           ------------------------
of Plans and Specifications is applicable, then Exhibit C shall apply. In any
                                                ---------
event, Tenant shall make no changes to the Plans and Specifications or the work
reflected in the Plans and Specifications without the consent of Landlord. Terms
used in Exhibit C but not defined therein shall have the meaning given in this
        ---------
Lease.

     2.4   Commencement Dates:
           ------------------

     2.4.1     Establishment of Commencement Date: Landlord shall notify Tenant
               ----------------------------------
in writing of Substantial Completion of each Phase. Tenant acknowledges that no
representations as to the condition of the Premises have been made by Landlord,
unless such are expressly set forth in this Lease. If Tenant believes that
Substantial Completion of such Phase has not occurred, Tenant shall notify
Landlord in writing of its objections within five (5) Business Days after its
receipt of the Landlord's notice described in the preceding sentence. Landlord
shall have a reasonable time after its receipt of Tenant's notice in which to
take such action as may be necessary to achieve Substantial Completion of such
Phase, and shall notify Tenant in writing when such has been completed. Taking
of possession by Tenant of a Phase shall establish the respective Commencement
Date thereof and the establishment of such fact upon the taking of possession
shall occur even if Tenant disputes whether Substantial Completion of such has
occurred or attempts to condition or qualify the taking of possession. Such
taking of possession shall further establish that the Premises are in good and
satisfactory condition when possession was so taken (subject to Punch List Work
as provided in Subsection 2.4.2 and in Section 1.42) and the relevant
Commencement Date has occurred. Notwithstanding anything to the contrary
contained herein, Tenant shall be given access to the space comprising each of
the Phases of the Premises subject to the provision of Exhibit C entitled
                                                       ---------
"Tenant Access" in order to install telephone equipment, a security system and
cable and data lines to the Premises.

                                       12
<PAGE>

     2.4.2     Punch List Work: If on the Commencement Date of a particular
               ---------------
Phase, Punch List Work remains to be completed, Landlord and Tenant shall agree
on such Punch List Work prior to occupancy by Tenant and Landlord will promptly
complete it after the Commencement Date of such Phase. In no event shall
Tenant's refusal or failure to agree on the nature and extent of Punch List Work
or the existence of items of Punch List Work delay or postpone the occurrence of
the Commencement Date for a particular Phase.

     2.4.3     Disputes Regarding Commencement Date : In the event of any
               ------------------------------------
dispute as to whether Substantial Completion of a particular Phase has occurred,
the certificate of Greenwell Goetz Architects shall be conclusive.

     2.4.4     Effect of Delay in Commencement Date:
               ------------------------------------

           A.     As provided in Sections 1.1 5 and 1.42, the Commencement Date
of the relevant Phase of the Premises shall be deemed to commence upon
Substantial Completion of the Tenant Improvements for such Phase. As provided in
Section 1.42, the applicable Phase shall be considered substantially complete
even though (i) there are punch list items remaining to be completed, the lack
of which will not materially interfere with Tenant's permitted use of the
Premises; (ii) Substantial Completion has been delayed due to Tenant Delay as
such term has been defined in Paragraph 5.3 of Exhibit C; (iii) there are any
                                               ---------
undelivered or uninstalled Long Lead Items previously identified as such or (iv)
the Certificate of Occupancy has not been issued due to Tenant's failure to
complete Tenant's installation of furniture, fixtures or equipment or other
items to be installed by Tenant pursuant to Exhibit C.
                                            ---------

           B.     Landlord agrees to use reasonable and diligent efforts to
achieve Substantial Completion for each Phase within the times provided in this
Lease. To the extent that any item of Landlord's Tenant Improvement Work or base
building work to be performed by Landlord is not completed as of such date as
will permit the Commencement Date with respect to any Phase to occur within the
timeframe set forth in Section 1.15, after adjustment for the effect of Tenant
Delays and Force Majeure, the following provisions will apply:

                  i)     If and to the extent that the applicable Phase of the
           Premises is Substantially Completed and delivered to Tenant within 30
           days after the anticipated Commencement Date provided in Section 1.15
           of this Lease (after adjustment on a day-for-day basis as a result of
           Tenant Delay and events of "Construction Force Majeure" as defined
           below); such delay shall not constitute a default by Landlord
           hereunder or give rise to any damages or penalties by Landlord to
           Tenant in connection with such delay. For the purposes of this
           Section 2.4.4, "Construction Force Majeure" shall mean those perils
           and events set forth in the definition of Force Majeure in Section
           6.8 except for strikes, lockouts, labor

                                       13
<PAGE>

           troubles or disputes involving the Tenant Improvements General
           Contractor which prevent such entity from performing its services in
           connection with the Premises as provided in this Lease and which
           could reasonably have been avoided by the Tenant Improvements General
           Contractor, except for such events precipitated by an act or omission
           of Tenant or any of Tenant's Agents.

                  ii)    If and to the extent the applicable Phase of the
           Premises is not Substantially Completed and delivered to Tenant
           within 30 days after the anticipated Commencement Date for such Phase
           (after such adjustment for the effect of Tenant Delay and events of
           Construction Force Majeure) then the validity of this Lease shall not
           be in any way affected, the Commencement Date for such Phase shall
           coincide with the date on which such Phase is Substantially Completed
           and delivered as provided in Section 2.4 (subject to adjustment for
           the effect of Tenant Delay and Construction Force Majeure) but Tenant
           shall thereafter be entitled to an abatement of all Rent payable
           under this Lease with respect to the applicable Phase in an amount
           equal to one day's Rent for each such late day (as so adjusted) over
           thirty (30) days beyond the anticipated Commencement Date which
           occurred with respect to the applicable Phase.

                  iii)   In the event Substantial Completion of the entirety of
           the Premises (i.e., Phases I and II) is not achieved by June 1, 2001,
           as such date may be extended on a day-for-day basis as a result of
           Tenant Delay and Construction Force Majeure), then upon thirty (30)
           days written notice to Landlord, during which time (the "Termination
           Cure Period") the Commencement Date for both Phases has not occurred,
           Tenant shall have the right to terminate this Lease by a subsequent
           writing (the "Termination Notice") delivered to Landlord within ten
           (10) days after the end of the Termination Cure Period and thereafter
           this Lease shall terminate. In such event, Landlord shall return any
           prepaid rent no later than twenty (20) Business Days after the
           Termination Notice has been delivered to Landlord. Except as
           specifically set forth in this Subsection 2.4.4.B, the foregoing
           shall constitute Tenant's sole and exclusive remedy in the event of
           any delay in the Commencement Date not due to Tenant Delay or
           Construction Force Majeure.

                  iv)    In the event Substantial Completion of any Phase is not
           achieved due to Tenant Delay, Landlord shall be entitled to those
           rights and remedies stated in Paragraph 5.4 of Exhibit C entitled
                                                          ---------
           "Effect of Tenant Delay."

                                       14
<PAGE>

     2.5  Tenant Improvement Construction. Landlord shall construct the Tenant
          -------------------------------
Improvements pursuant to the Work Letter attached as Exhibit C.
                                                     ---------

     2.6  Tenant's Contribution to Tenant Improvement Costs.
          -------------------------------------------------

          2.6.1  Tenant's Obligations: If the cost of the Tenant Improvements
                 --------------------
exceeds the Tenant Improvement Allowance and the Above Standard Tenant
Improvement Allowance, to the extent the Tenant elects to use the same, Tenant
shall pay to Landlord such excess within ten (10) Business Days after demand by
Landlord. If Tenant fails to pay to Landlord the cost of any such excess Tenant
Improvements as and when due, Landlord may elect to suspend work on the Tenant
Improvements pending such timely payment, and the Commencement Date of the
applicable Phase shall be deemed to have occurred on the date that the Tenant
Improvements would have achieved Substantial Completion for such Phase absent
such suspension of work.

          2.6.2  Removal of Tenant Improvements: All Tenant Improvements,
                 ------------------------------
regardless of which party constructed them, shall become the property of
Landlord and shall remain upon and be surrendered with the Premises upon the
expiration or earlier termination of this Lease. Notwithstanding the foregoing,
and subject to the provisions of Subsection 2.6.3, at Landlord's election and
upon notice to Tenant to be given at the time Landlord consents to the
construction of Tenant Improvements, Tenant shall be required to remove all or
any portion of the Tenant Improvements upon the expiration or earlier
termination of this Lease (and repair any damage caused by such removal or
restore the affected portion of the Building) if in Landlord's reasonable
judgment such Tenant Improvements are not customarily found in Class A office
buildings in the Laurel, Maryland submarket and the removal of such items would
subject Landlord to unreasonable expense.

          2.6.3  Tenant's Obligation to Remove Certain Equipment:
                 -----------------------------------------------
Notwithstanding the provisions of Subsection 2.6.2, unless Landlord agrees
otherwise in writing delivered to Tenant prior to the expiration of this Lease,
Tenant shall, prior to the expiration of this Lease, remove all of the following
items (whether such items are considered Tenant Improvements or Tenant
Alterations) at Tenant's sole cost and expense and repair any damage caused by
such removal and restore the affected portion of the Building to its condition
prior to the installation of such item, subject to ordinary wear and tear:

               a.   Cafeteria equipment or supplemental mechanical systems (e.g.
                    grease duct, roof mounted fans, etc.)

               b.   Uninterrupted Power Source ("ups") equipment

               c.   Any special fire suppression system(s) (Tenant's obligation
                    to restore the affected portion of the Building as required
                    pursuant to this Subsection 2.6.3 shall, with respect to
                    this

                                       15
<PAGE>

                    item, include restoration of the fire suppression
                    system in the affected area so that it is consistent with
                    the Building's wet pipe system).

               d.   Laboratory and telecommunications rooms, air conditioning
                    units and roof mounted condenser units

               e.   Laboratory and telecommunications switches, racks and
                    associated cabling (to the extent not referred to in Section
                    4.32).

               f.   Security system cameras, associated monitors and control
                    systems installed by Tenant

               g.   Security room door from main lobby

     In the event this Lease should terminate prior to the expiration date for
any reason, Landlord may within thirty (30) days after such termination elect to
retain any of the foregoing items as permitted pursuant to this Subsection 2.6.3
and shall deliver written notice of such election to Tenant of such election
within that time. In the absence of such notice, and after the expiration of
such 30-day period following such termination, Tenant shall promptly remove all
of the above items which Landlord has not elected to retain, which removal shall
be at Tenant's sole cost and expense and Tenant shall repair any damage caused
by such removal and restore the affected portion of the Building to its
condition prior to the installation of such items, subject to ordinary wear and
tear. If Tenant does not promptly remove such items as required by this
paragraph, Landlord may do so after written notice to Tenant which removal,
repair and restoration shall be paid for promptly by Tenant upon Landlord's
demand. Landlord's rights pursuant to this paragraph shall be in addition to any
other rights and remedies in which Landlord may have in the event of the
termination of this Lease for any reason prior to the expiration date and
Tenant's obligation under this paragraph shall survive the termination of this
Lease.

          2.6.4  Failure to Remove. If Tenant fails to remove any Tenant
                 -----------------
Improvement as required by Landlord pursuant to this Section 2.4, Landlord may
do so and Tenant shall pay the entire cost thereof within twenty (20) Business
Days after Tenant's receipt of Landlord's written demand therefor.

     2.7  Memorandum of Commencement Date. At Landlord's election and request,
          -------------------------------
Tenant shall execute a Memorandum of Commencement Date for each of the
Commencement Dates in the form attached to this Lease as Exhibit D. In no event
shall Tenant record this Lease or the Memorandum of Commencement Date.

     2.8  Use and Conduct of Business. The Premises are to be used only for the
          ---------------------------
Permitted Uses, and for no other business or purpose without the prior consent
of Landlord. Landlord makes no representation or warranty as to the suitability
of the

                                       16
<PAGE>

Premises for Tenant's intended use. Tenant shall, at its own cost and expense,
obtain and maintain any and all licenses, permits, and approvals necessary or
appropriate for its use, occupation and operation of the Premises. Tenant's
inability to obtain or maintain any such license, permit or approval necessary
or appropriate for its use, occupation or operation of the Premises shall not
relieve it of its obligations under this Lease, including the obligation to pay
Base Rent and Additional Rent. No act shall be done in or about the Premises
that is unlawful or that will increase the existing rate of insurance on any or
all of the Land or Building. Tenant shall not commit or allow to be committed or
exist: (a) any waste upon the Premises, (b) any public or private nuisance, or
(c) any act or condition which disturbs the quiet enjoyment of any other tenant
in the Building, violates any of Landlord's contracts affecting any or all of
the Land or Building, creates or contributes to any work stoppage, strike,
picketing, labor disruption or dispute, interferes in any way with the business
of Landlord or any other tenant in the Building or with the rights or privileges
of any contractors, subcontractors, licensees, agents, concessionaires,
subtenants, servants, employees, customers, guests, invitees or visitors or any
other persons lawfully in and upon the Land or Building, or causes any
impairment or reduction of the good will or reputation of the Land or Building.
Tenant shall not, without the prior consent of Landlord, use any apparatus,
machinery, device or equipment in or about the Premises that will cause any
substantial noise or vibration or any increase in the normal consumption level
of electric power. If any of Tenant's apparatus, machinery, devices or equipment
should disturb the quiet enjoyment of any other tenant in the Building, then
Tenant shall provide, at its sole cost and expense, adequate insulation or take
other such action, including removing such apparatus, machinery, devices or
equipment, as may be necessary to eliminate the disturbance. No food or beverage
dispensing machines shall be installed by Tenant in the Premises without the
prior written consent of Landlord.

     2.9  Compliance with Governmental Requirements and Rules and Regulations.
          -------------------------------------------------------------------
Tenant shall comply with all Governmental Requirements relating to its use,
occupancy and operation of the Premises and shall observe such reasonable rules
and regulations as may be adopted and published by Landlord from time to time
for the safety, care and cleanliness of the Premises and the Building, and for
the preservation of good order in the Building, including the Rules and
Regulations attached to this Lease as Exhibit E:
                                      ---------

   SECTION 3: BASE RENT, ADDITIONAL RENT AND OTHER SUMS PAYABLE UNDER LEASE
   ------------------------------------------------------------------------

     3.1  Payment of Rental. Tenant agrees to pay Base Rent, Additional Rent and
          -----------------
any other sum due under this Lease to Landlord without demand, deduction,
credit, adjustment or offset of any kind or nature, in lawful money of the
United States when due under this Lease, at the offices of Manager at Manager's
Address, or to such other party or at such other place as Landlord may from time
to time designate in writing.

                                       17
<PAGE>

     3.2  Base Rent. On execution of this Lease, Tenant shall pay to Landlord
          ---------
the amount specified in the definition of Prepaid Rent for the month specified
in the definition of that term. Tenant agrees to pay Base Rent to Landlord
without demand, in advance on or before the first day of each calendar month of
the Lease Term. Base Rent for any partial month at the beginning or end of the
Lease Term shall be prorated. Base Rent for any partial month at the beginning
of the Lease Term shall be paid by Tenant on the Commencement Date for the
respective Phase. Notwithstanding anything to the contrary contained herein,
Base Rent for each of the Phases of the Premises shall commence fifteen (15)
days after Substantial Completion of such Phase.

     3.3  Security. Tenant shall secure its performance under this Lease as
          --------
follows:

          3.3.1  Letter of Credit: Concurrently with the execution of this Lease
                 ----------------
as security for the full and faithful payment of all sums due under this Lease
and the full and faithful performance of every covenant and condition of this
Lease to be performed by Tenant, Tenant shall deliver to Landlord a Letter of
Credit in the initial amount of Two Million Dollars ($2,000,000.00). The Letter
of Credit shall be unconditional, irrevocable, transferable and issued by a
financial institution reasonably acceptable to Landlord and provide for
presentation to and draws through a financial institution in Washington, D.C.,
which is federally insured, has a net worth of at least One Hundred Million
Dollars ($100,000,000.00) and is otherwise reasonably acceptable to Landlord.
The initial Letter of Credit shall expire not less than twelve (12) months after
the delivery thereof to Landlord and shall provide that it will be automatically
renewed for successive twelve (12) month periods through a date which is not
earlier than thirty (30) days after the expiration date of this Lease, or any
renewal or extension thereof, unless written notice of nonrenewal has been given
by the issuing bank to Landlord by registered or certified mail, return receipt
requested, not less than sixty (60) days prior to the expiration of the then
current period. If the issuing bank does not renew the Letter of Credit and if
Tenant does not deliver a substitute Letter of Credit at least thirty (30) days
prior to the expiration of the then current period, then, in addition to its
rights under Section 3.3.4 of this Lease, Landlord shall have the right to draw
on the existing Letter of Credit. The Letter of Credit shall be substantially in
the form attached hereto as Exhibit F and shall be maintained for the benefit of
                            ---------
Landlord for the Term of this Lease. The Letter of Credit and any renewal or
replacement thereof (collectively, the "Letter of Credit") shall be held by
Landlord as security for the payment of Base Rent, Additional Rent and any other
sums payable by Tenant under this Lease and for the faithful performance by
Tenant of all of Tenant's obligations, covenants, conditions and agreements
hereunder. The Letter of Credit and any cash or other property held by Landlord
as security for Tenant's performance of this Lease may be referred to as the
"Security Deposit."

          3.3.2  Modification of Letter of Credit. Within ninety (90) days
                 --------------------------------
before the end of the second Lease Year, and within ninety (90) days before the
end of each Lease Year thereafter, Tenant shall provide Landlord with a copy of
the Tenant's most recent

                                       18
<PAGE>

quarterly financial statement issued prior to the 90-day period preceding the
end of the relevant Lease Year. Such statement shall be certified as correct by
Tenant's Chief Financial Officer or a certified public accountant acceptable to
Landlord. If, during the preceding Lease Year (i) Tenant has not been late in
making any payments of rent beyond applicable cure periods, (ii) no other Event
of Default has occurred during the preceding Lease Year (iii) as of such time no
event has occurred or condition exists which with the passage of time or the
giving of notice would become an Event of Default if not timely cured and (iv)
Tenant's net worth as set forth in the quarterly financial statement provided to
Landlord is Four Hundred Million Dollars ($400,000,000.00) or more
(collectively, items (i) through (v) are referred to as the "Financial
                                                             ---------
Compliance Conditions"), the then current amount of the Letter of Credit may be
---------------------
reduced by Four Hundred Thousand Dollars ($400,000.00) provided that Tenant
delivers to Landlord a replacement Letter of Credit which is otherwise in
compliance with this Lease in such reduced amount to be held subject to the
terms of this Section 3.3 and in such event, Landlord shall promptly return to
Tenant the Letter of Credit which was so replaced. If, however, the Financial
Compliance Conditions have not been satisfied as of the end of the relevant
Lease Year, then the Letter of Credit shall not thereafter be subject to a
reduction as provided in this Section 3.3.2, for the next two (2) Lease Years
following the Lease Year in which Tenant failed to satisfy the Financial
Compliance Conditions and the Letter of Credit shall be maintained at its then
level and shall not be eligible for reduction as set forth above until the
expiration of two Lease Years, at the end of which period Tenant may apply for
such a reduction only if Tenant then meets the Financial Compliance Conditions.
Tenant's failure to qualify for a reduction of the Letter of Credit at any one
time shall not preclude Tenant for applying for a subsequent reduction of the
Letter of Credit at such subsequent times as provided in this Section 3.3.2. If
all of the Financial Compliance Conditions have been satisfied throughout the
Lease Term, at the commencement of the seventh (7th) Lease Year, the Letter of
Credit shall be reduced in value to an amount equal to one month's Base Rent as
such Rent is determined as of that date and the Letter of Credit shall remain at
such amount for the remainder of the Lease Term, including any extensions or
renewals.

          3.3.3  Use of Letter of Credit: If any Monthly Base Rent, Additional
                 -----------------------
Rent or any other sum payable by Tenant to Landlord pursuant to this Lease shall
be overdue and unpaid after the expiration of the applicable cure period, or
should Landlord make payments on behalf of Tenant in accordance with this Lease
and Tenant fails to reimburse Landlord after expiration of the applicable cure
period, or if Tenant shall default under any of its other obligations under this
Lease after the expiration of applicable cure periods, then Landlord may, from
time to time at its option and without prejudice to any other remedy which
Landlord may have on account thereof, draw upon all or any portion of the Letter
of Credit and may appropriate and apply the sums so drawn, or any portion
thereof, as may be necessary to compensate Landlord on account of Base Rent,
Additional Rent or any other sums due Landlord pursuant to this Lease or any
loss or damage sustained by Landlord due to any breach of this Lease on the part
of Tenant. In the event Landlord draws on the Letter of Credit for any reason,
Landlord shall report to Tenant regarding the

                                       19
<PAGE>

use of the proceeds of such drawing and Tenant shall thereafter promptly restore
the Letter of Credit to its original amount or deposit with Landlord in cash an
amount equal to the amount drawn on the Letter of Credit which amount, together
with any cash drawn on the Letter of Credit which was not applied by Landlord to
compensate for Tenant's breach, shall be held by Landlord, in a segregated
account, with interest thereon at the money market rate as determined from time
to time and published in The Wall Street Journal. Such cash deposit shall be
held by Landlord as part of the Security Deposit to be retained, expended or
disbursed by Landlord for any amounts or sums due under this Lease to which the
proceeds of the Letter of Credit could have been applied pursuant to this Lease.

          3.3.4  Renewal of Letter of Credit: Tenant shall, not later than
                 ---------------------------
thirty (30) days prior to the expiration date of any Letter of Credit provided
by Tenant pursuant to this Section 3.3, either initially or as a replacement or
extension of such Letter of Credit, cause the expiration date thereof to be
extended or provide a replacement Letter of Credit complying with the terms of
this Section 3.3, such that a Letter of Credit remains in existence in the
amount and for the time required under this Lease. Landlord shall have the right
to draw upon the Letter of Credit in the event Tenant fails to provide Landlord
with an extension of such Letter of Credit or a replacement Letter of Credit
substantially in the form attached as Exhibit F not less than thirty (30) days
                                      ---------
prior to the expiration date thereof. In the event such Letter of Credit is
drawn upon due solely to the failure of Tenant to provide Landlord with such
amendment or replacement Letter of Credit as aforesaid, the amount drawn shall
be held by Landlord, as part of the Security Deposit in a segregated account
with interest thereon at the money market rate as determined from time to time
and published in The Wall Street Journal. Such funds shall be retained, expended
                 -----------------------
or disbursed by Landlord for any amounts or sums due under this Lease to which
the proceeds of the Letter of Credit could have been applied pursuant to this
Lease provided that in the event Tenant delivers to Landlord a replacement
Letter of Credit in the amount and in the form required by this Lease, Landlord
will substitute such Letter of Credit for such cash and return the cash to
Tenant together with any interest accrued thereon.

          3.3.5  Transfer of Security: In the event of a sale or transfer of
                 --------------------
Landlord's estate or interest in the Land and Building, Landlord shall have the
right to transfer the Security Deposit (including the Letter of Credit and any
cash held as security) to the vendee or the transferee, and Landlord shall,
after such transfer, be considered released by Tenant from all liability for the
return of the Security Deposit (including the Letter of Credit). Tenant shall
look solely to the transferee for the return of the Security Deposit, and it is
agreed that all of the foregoing shall apply to every transfer or assignment
made of the Security Deposit to a new transferee. No mortgagee or purchaser of
any or all of the Building at any foreclosure proceeding brought under the
provisions of any mortgage shall (regardless of whether the Lease is at the time
in question subordinated to the lien of any mortgage) be liable to Tenant or any
other person for any or all of the Security Deposit (or any other or additional
security deposit or other payment made by Tenant under the provisions of this
Lease), unless Landlord has actually delivered the Security Deposit to such
mortgagee or

                                       20
<PAGE>

purchaser, as the case may be. In the event of any rightful and permitted
assignment of Tenant's interest in this Lease, the Security Deposit shall be
deemed to be held by Landlord as a deposit made by the assignee, and Landlord
shall have no further liability to the assignor with respect to the return of
the Security Deposit.

          3.3.6  Return of Security: If Tenant shall have fully complied with
                 ------------------
all of the covenants and conditions of this Lease, the remaining Security
Deposit (including the Letter of Credit) shall be repaid or (in the case of the
Letter of Credit) returned to Tenant, with interest with respect to any cash so
returned as provided in Subparagraph 3.3.3, within thirty (30) Business Days
after the expiration of this Lease. Tenant may not mortgage, assign, transfer or
encumber the Security Deposit and any such act on the part of Tenant shall be
without force or effect. In the event any bankruptcy, insolvency, reorganization
or other creditor-debtor proceedings shall be instituted by or against Tenant,
the Security Deposit and the proceeds of the Letter of Credit shall be deemed to
be applied first to the payment of Base Rent, Additional Rent and all other sums
payable under this Lease to Landlord for all periods prior to the institution of
such proceedings and the balance, if any, may be retained by Landlord and
applied against Landlord's damages.

          3.3.7  Rights of Security: No right or remedy available to Landlord in
                 ------------------
this Lease shall preclude or extinguish any other right to which Landlord may be
entitled. It is understood that if Tenant fails to perform its obligations and
to take possession of the Premises as provided in this Lease, the Prepaid Rent
and the Security Deposit and the Letter of Credit shall not be deemed liquidated
damages. Landlord may apply such sums to reduce Landlord's damages and such
application of funds shall not preclude Landlord from recovering from Tenant all
additional damages incurred by Landlord.

     3.4  Additional Rent. Definitions of certain terms used in this section are
          ---------------
set forth in subparagraph 3.4.5. Tenant agrees to pay to Landlord additional
rent as computed in this section (individually and collectively the "Additional
                                                                     ----------
Rent"):
----

          3.4.1  Rental Adjustment for Estimated Operating Costs and Estimated
                 -------------------------------------------------------------
Property Taxes: Landlord shall furnish Tenant a written statement of Estimated
--------------
Operating Costs for the Premises and Estimated Property Taxes for the Premises
for each Year and the amount payable monthly by Tenant for such Costs, which
shall be Additional Rent and shall be paid monthly by Tenant for each month
during such Year after the Commencement Date for each Phase, and shall be
computed as follows: one-twelfth (1/12) of the sum of (i) the amount, if any, by
which the Estimated Operating Costs for the Premises per rentable square foot of
the Premises for a particular Year exceeds the Base Amount of the Base Rent
Operating Cost Component (as such amount may be adjusted as provided in Section
1.5), and (ii) the amount, if any, by which the Estimated Property Taxes for the
Premises per rentable square foot of the Premises for a particular Year exceeds
the Base Amount of the Base

                                       21
<PAGE>

Rent Tax Component. If the Commencement Date for a particular Phase occurs on a
date other than the first day of the Year, the statements as provided by
Landlord to Tenant and the computation of the monthly payment amounts shall be
determined based on a proration of the excess amount over a 360-day year. If
such written statement (except the first statement, which shall be prorated
pursuant to the previous sentence) is furnished after the commencement of the
Year, Tenant shall also make a retroactive lump-sum payment to Landlord equal to
the monthly payment amount multiplied by the number of months during the Year
after the Commencement Date for a particular Phase for which no payment was
paid. Notwithstanding the foregoing, Landlord reserves the right to revise the
Estimated Operating Costs for the Premises and the Estimated Property Taxes for
the Premises once each year and upon notice to Tenant of such revision, Tenant
shall adjust its payments to Landlord under this section accordingly.

          3.4.2  Actual Costs: Within 120 days after the close of each Year,
                 ------------
Landlord shall deliver to Tenant a written statement setting forth the actual
Operating Costs for the Premises and Property Taxes for the Premises during the
preceding Year. If such costs for any Year exceed the Estimated Operating Costs
for the Premises and the Estimated Property Taxes for the Premises paid by
Tenant to Landlord pursuant to subparagraph 3.4.1 for such Year, Tenant shall
pay the amount of such excess to Landlord within twenty (20) Business Days after
receipt of such statement by Tenant. If such statement shows the Operating Costs
for the Premises and the Property Taxes for the Premises to be less than the
Estimated Operating Costs for the Premises and the Estimated Property Taxes for
the Premises, as the case may be, paid by Tenant to Landlord pursuant to
subparagraph 3.4.1, then the amount of such overpayment shall be paid by
Landlord to Tenant within twenty (20) Business Days following the date of such
statement or, at Landlord's option, shall be credited towards the installment(s)
of Rent next coming due from Tenant.

          3.4.3  Determination: The determination of Operating Costs for the
                 -------------
Premises and the Property Taxes for the Premises shall be made by Landlord. Any
sums payable under this Lease pursuant to this section shall be Additional Rent
and, in the event of nonpayment of such sums, Landlord shall have the same
rights and remedies with respect to such nonpayment as it has with respect to
nonpayment of Base Rent under this Lease.

          3.4.4  Operating Cost Audit: Landlord shall maintain records
                 --------------------
concerning estimated and actual Operating Costs for the Premises for no less
than twelve (12) months following the period covered by the statement or
statements furnished Tenant, after which time Landlord may dispose of such
records. Provided that Tenant is not then in default of its obligation to pay
Base Rent, Additional Rent or other payments required to be made by it under
this Lease or Tenant is not otherwise in material default under this Lease,
Tenant may, at Tenant's sole cost and expense, cause a Qualified Person (defined
below) to inspect Landlord's records. Such

                                       22
<PAGE>

inspection, if any, shall be conducted no more than once each Year, during
Landlord's normal business hours within seventy-five (75) Business Days after
receipt of Landlord's written statement of Operating Costs for the Premises for
the previous year, upon first furnishing Landlord at least fifteen (15) Business
Days prior written notice. Any errors disclosed by the review shall be promptly
corrected by Landlord; provided, however, that if Landlord disagrees with any
such claimed errors, Landlord shall have the right to cause another review to be
made by an auditor of Landlord's choice. In the event the results of the review
of records (taking into account, if applicable, the results of any additional
review caused by Landlord) reveal that Tenant has overpaid obligations for a
preceding period, the amount of such overpayment shall be credited against
Tenant's subsequent installment of Base Rent, Additional Rent or other payments
due to Landlord under the Lease. In the event that such results show that Tenant
has underpaid its obligations for a preceding period, the amount of such
underpayment shall be paid by Tenant to Landlord with the next succeeding
installment obligation of estimated Operating Costs for the Premises. If the
actual Operating Costs for the Premises for any given Year were improperly
computed and if the actual Operating Costs for the Premises are overstated by
more than 2%, Landlord shall reimburse Tenant for the cost of its audit provided
that the cost of the audit shall not exceed $5,000. A "Qualified Person" means
                                                       ----------------
an accountant or other person experienced in accounting for income and expenses
of office projects, who is engaged solely by Tenant on terms which do not entail
any compensation based or measured in any way upon any savings in Additional
Rent or reduction in Operating Costs for the Premises achieved through the
inspection process described in this subparagraph.

          3.4.5  End of Term: Within one hundred twenty (120) days after the
                 -----------
close of the Year in which this Lease terminates, Landlord shall deliver to
Tenant a written statement setting forth the actual Operating Costs for the
Premises and Property Taxes for the Premises during the preceding Year and
Tenant's share of such expenses determined by multiplying such amount by a
fraction, the numerator of which is the number of days within the Lease Term in
such Year and the denominator of which is three hundred sixty (360). If such
prorated costs exceed the Estimated Operating Costs for the Premises together
with the Estimated Property Taxes for the Premises paid by Tenant to Landlord
for such Year, Tenant shall pay the amount of such excess to Landlord within
twenty (20) Business Days after receipt of such statement. If such statement
shows the Operating Costs for the Premises together with the Property Taxes for
the Premises to be less than the Estimated Operating Costs for the Premises
together with the Estimated Property Taxes for the Premises, as the case may be,
paid by Tenant to Landlord, then the amount of such overpayment shall be paid by
Landlord to Tenant within twenty (20) Business Days following the date of such
statement. Landlord's and Tenant's obligations under this subparagraph shall
survive the expiration or other termination of this Lease.

          3.4.6  Definitions: Each underlined term in this subparagraph shall
                 -----------
have the meaning set forth next to that underlined term:

                                       23
<PAGE>

               Estimated Operating Costs for the Premises: Landlord's estimate
               ------------------------------------------
of Operating Costs for to the Premises for a Year to be given by Landlord to
Tenant pursuant to subparagraph 3.4.l.

               Estimated Property Taxes for the Premises: Landlord's estimate of
               -----------------------------------------
Property Taxes for the Premises for a Year to be given by Landlord to Tenant
pursuant to subparagraph 3.4.1.

               Operating Costs: All expenses paid or incurred by Landlord for
               ---------------
maintaining, operating, owning and repairing any or all of the Land, Building,
related improvements, and the personal property used in conjunction with such
Land, Building and related improvements, including all expenses paid or incurred
by Landlord for: (a) utilities, including electricity, water, gas, sewers, fire
sprinkler charges, refuse collection, telephone charges, cable television or
other electronic or microwave signal reception, steam, heat, cooling or any
other service which is now or in the future considered a utility and which are
not payable directly by tenants in the Building; (b) supplies; (c) cleaning and
janitorial services (including window washing), landscaping and landscaping
maintenance (including irrigating, trimming, mowing, fertilizing, seeding and
replacing plants), snow removal and other services; (d) security services, if
any; (e) insurance; (f) management fees; (g) services of independent
contractors; (h) compensation (including employment taxes and fringe benefits)
of all persons who perform duties in connection with any service, repair,
maintenance, replacement or improvement or other work included in this
subparagraph; (i) license, permit and inspection fees, (j) assessments and
special assessments due to deed restrictions, declarations or owners
associations or other means of allocating costs of a larger tract of which the
Land is a part; (k) rental of any machinery or equipment; (l) audit fees and
accounting services related to the Building, and charges for the computation of
the rents and charges payable by tenants in the Building (but only to the extent
the cost of such fees and services are in addition to the cost of the management
fee); (m) the cost of improvements, repairs or replacements; (n) maintenance and
service contracts; (o) legal fees and other expenses of legal or other dispute
resolution proceedings; (p) maintenance and repair of the roof and roof
membranes; (q) costs incurred by Landlord for compliance with Access Laws, as
set forth in the section captioned "Access Laws"; (r) elevator service and
repair, if any; (s) business taxes and license fees; and (t) any other expense
or charge which in accordance with generally accepted accounting and management
principles would be considered an expense of maintaining, operating, owning or
repairing the Building. Without limiting the foregoing, Operating Costs shall
include replacement of roofs and roof membranes, exterior painting, parking area
resurfacing, resealing and restriping parking areas and driveways; upgrading of
the HVAC systems in the Building, and other capital improvements which are
intended to reduce Operating Costs or are required by Governmental Requirements;
provided that, such capital improvements installed after the Phase II
-------------
Commencement Date shall be amortized with market interest over their estimated
useful lives as determined by

                                       24
<PAGE>

Landlord and only the amortization installments and interest attributable to the
Lease Term shall be an Operating Cost under this Lease.

                    Operating Costs shall not include any of the following:

                         (i)    ground rent or other rental payments made under
any ground lease or underlying lease;

                         (ii)   interest and amortization of funds borrowed by
Landlord for items other than capital improvements;

                         (iii)  leasing commissions and advertising and space
planning expenses incurred in procuring tenants;

                         (iv)   salaries, wages, or other compensation paid to
officers or executives of Landlord in their capacities as officers and
executives;

                         (v)    Costs incurred by Landlord for the original
construction and development of the Building, the original construction of
Tenant Improvements and nonrecurring costs and expenses incurred by Landlord in
curing, repairing or replacing any structural portion of the Building made
necessary as a result of defects in design, workmanship or materials ;

                         (vi)   Salaries and all other compensation (including
fringe benefits and other direct and indirect personnel costs) of partners,
officers and executives above the grade of superintendent or building manager of
Landlord or the managing agent;

                         (vii)  Cost of advertising and public relations and
promotional costs associated with the promotion or leasing of the Building;

                         (viii) Any costs, fines or penalties incurred due to
the violation by Landlord of any governmental rule or authority;

                         (ix)   Any other expenses to the extent Landlord
actually receives reimbursement from insurance, condemnation awards, other
tenants or any other source;

                         (x)    Costs and expenses incurred by Landlord in
connection with damage, casualty or condemnation of all or a portion of the
Building which expenses are otherwise covered by insurance as required by this
Lease or a condemnation award, as the case may be; provided, however, that with
respect to the cost to repair damage, Landlord may include in Operating Costs
the amount of a

                                       25
<PAGE>

commercially reasonable deductible applied to each such occurrence if Landlord
actually makes such repair;

                         (xi)   Costs incurred in connection with disputes with
tenants, other occupants, or prospective tenants;

                         (xii)  Costs incurred in connection with the sale,
financing, refinancing, mortgaging, selling or change of ownership of the
Building;

                         (xiii) Costs, fines, interest, penalties, legal fees or
costs of litigation incurred due to the late payments of taxes, utility bills
and other costs incurred by Landlord's failure to make such payments when due;

                         (xiv)  General overhead and general administrative
expenses and accounting, record-keeping and clerical support of Landlord or the
management agent that are not related to the operation, management or
maintenance of the Building;

                         (xv)   That portion of any Operating Cost that is paid
to any entity affiliated with Landlord that is in excess of the amount that
would otherwise be paid to an entity that is not affiliated with Landlord for
the provision of the same service;

                         (xvi)  Increased insurance premiums caused by
Landlord's or any other tenant's hazardous acts and insurance or leasehold
improvements in spaces leased or to be leased to other tenants;

                         (xvii) Cost incurred to correct violations by Landlord
of any law, rule, order or regulation which was in effect as of the date that
the Building's Certificate of Occupancy was validly issued;

                         (xviii)All costs and expenses attributable to any
testing, investigation, management, maintenance, remediation, or removal of
Hazardous Materials other than in connection with Hazardous Materials brought
onto the Premises or the Building by Tenant or Tenant's Agents or any testing or
monitoring customarily conducted by owners of similar office buildings in the
ordinary course of operating and managing a building; and

                         (xix)  Costs incurred for any items to the extent
Landlord recovers under a manufacturer's, materialman's, vendor's or
contractor's warranty (a "Warranty").

     The foregoing definition of Operating Costs is applicable to Tenant only
and Landlord is not prohibited from assessing other tenants for any and all
other costs and expenses incurred by Landlord in connection with the operation,
management,

                                       26
<PAGE>

maintenance and repair of the Building, the land and all easements, rights and
appurtenances thereto.

                If Digex is not the only tenant in the Building and if less than
ninety-five percent (95%) of the net rentable area of the Building is occupied
by tenants at all times during any Year, then Operating Costs for such Year
shall include all additional costs and expenses that Landlord reasonably
determines would have been incurred had ninety-five percent (95%) of the
Building been occupied at all times during such Year by tenants.

          3.4.7 Tenant's Costs: Tenant agrees to reimburse or pay Landlord
                --------------
within twenty (20) Business Days after invoice from Landlord for (a) any
cleaning expenses incurred by Landlord, including carpet cleaning, garbage and
trash removal expenses, over and above the normal cleaning provided by Landlord
on Business Days pursuant to Exhibit G, (b) any expense incurred by Landlord for
usage in the Premises of heating, ventilating and air conditioning services,
elevator services, electricity, water, janitorial services, or any other
services or utilities over and above the normal usage for the Premises during
Normal Business Hours and (c) any expense incurred by Landlord relating to or
arising out of the usage by Tenant or Tenant's Agents of the public or common
areas of the Building or Land, or any of the equipment contained therein, which
usage is over and above the normal usage for such public or common areas or
equipment during Normal Business Hours. Tenant shall reimburse Landlord for
Landlord's actual costs arising from HVAC usage after Normal Business Hours.
Tenant shall notify Landlord at least 24 hours prior to its desire to use the
HVAC system at other than Normal Business Hours. For the purposes of this Lease,
"Normal Business Hours" shall be 8:00 a.m. through 6:00 p.m. Monday through
Friday and 9 a.m. to 1 p.m. on Saturdays, except for holidays as defined in the
Rules attached to this Lease as Exhibit E.
                                ---------

          3.4.8 Nonpayment of Additional Rent: Any sums payable under this Lease
                -----------------------------
pursuant to this section or otherwise shall be Additional Rent and, in the event
of nonpayment of such sums, Landlord shall have the same rights and remedies
with respect to such nonpayment as it has with respect to nonpayment of the Base
Rent due under this Lease.

     3.5  Utilities. Landlord shall have the right from time to time to select
          ---------
the company or companies providing electricity, gas, fuel, local telephone,
telecommunication and any other utility services to the Building. Tenant shall
contract directly and pay for all telephone and telecommunications utilities
used on or from the Premises together with any taxes, penalties, surcharges or
similar charges relating to such utilities. If any such service is not
separately metered to the Premises, the cost therefor shall be an Operating Cost
under this Lease. If Tenant desires to use the services of a provider of local
telephone or telecommunication services whose equipment is not then servicing
the Building, no such provider shall be permitted to

                                       27
<PAGE>

install its lines or other equipment within the Building without the prior
written consent of Landlord.

     3.6  Holdover. If Tenant, without the prior consent of Landlord, holds over
          --------
after the expiration or earlier termination of the Lease Term, Tenant shall be
deemed to be occupying the Premises under a month-to-month tenancy, which
tenancy may be terminated as provided by the laws of the state in which the
Premises are located. During such tenancy, Tenant agrees(a) to pay to Landlord
one hundred fifty percent (150%) the rate of Base Rent in effect on the
expiration or termination of the Lease Term, plus all Additional Rent and other
sums payable under this Lease for the first one hundred and twenty (120) days of
such holdover, (b) to pay to Landlord two hundred percent (200%) of the current
rate of Base Rent in effect as of the expiration or termination of the Lease
Term plus all Additional Rent and other sums payable under this Lease for any
period beyond the initial one hundred and twenty (120) days, and (c) to be bound
by all of the other covenants and conditions specified in this Lease, so far as
applicable. The preceding provisions shall not be construed as consent for
Tenant to hold over.

     3.7  Late Charge. If Tenant fails to make any payment of Base Rent,
          -----------
Additional Rent or other amount after 5 Business Days following the date when
due under this Lease, a late charge is immediately due and payable by Tenant
equal to five percent (5%) of the amount of any such payment provided, however,
that Tenant shall not be entitled to such grace period more than once in any
consecutive 12 month period and that otherwise such late charge shall be imposed
in the event any amounts payable under this Lease are not paid when due.
Landlord and Tenant agree that this charge compensates Landlord for the
administrative costs caused by the delinquency. The parties agree that
Landlord's damage would be difficult to compute and the amount stated in this
section represents a reasonable estimate of such damage. Assessment or payment
of the late charge contemplated in this section shall not excuse or cure any
Event of Default or breach by Tenant under this Lease or impair any other right
or remedy provided under this Lease or under law.

     3.8  Default Rate. Any Base Rent, Additional Rent or other sum payable
          ------------
under this Lease which is not paid when due shall bear interest at a rate equal
to the lesser of: (a) the published prime rate of Riggs Bank N.A., or such other
national banking institution designated by Landlord if such bank ceases to
publish a prime rate (the "Prime Rate"), then in effect, plus four (4)
                           ----------
percentage points, or (b) the maximum rate of interest per annum permitted by
applicable law (the "Default Rate"), but the payment of such interest shall not
                     ------------
excuse or cure any Event of Default or breach by Tenant under this Lease or
impair any other right or remedy provided under this Lease or under law.

                                       28
<PAGE>

                         SECTION 4: GENERAL PROVISIONS
                         -----------------------------

     4.1  Maintenance and Repair by Landlord; HVAC; Other Utilities and
          --------------------------------------------------------------
          Services; Service Interruption.
          ------------------------------

          4.1.1 Maintenance and Repair by Landlord: Subject to the Sections
                ----------------------------------
captioned "Damage or Destruction" and "Condemnation" and consistent with the
           ---------------------       ------------
standards for the operation of Class A office buildings in the Laurel, Maryland
area and ordinary wear and tear, Landlord shall maintain the public and common
areas of the Building as well as the roof and all base building standard
mechanical, electrical, HVAC, plumbing, fire and life safety and structural
systems in reasonably good order and condition, and shall make such repairs
thereto as become necessary after obtaining actual knowledge of the need for
such repairs, all costs of which shall be included in Operating Costs, provided,
however, that expenses due to damage occasioned by the act or omission of Tenant
or Tenant's Agents shall be paid for entirely by Tenant within ten (10) Business
Days after demand by Landlord. In the event any or all of the Building becomes
in need of maintenance or repair which Landlord is required to make under this
Lease, Tenant shall promptly give written notice to Landlord, and thereafter
Landlord shall promptly commence such maintenance or repairs.

          4.1.2 HVAC. Landlord shall provide HVAC service to the Premises during
                ----
Normal Business Hours and consistent with the standards for the operation of
Class A buildings in the Laurel, Maryland area. Landlord will provide Tenant
with HVAC service at other times ("Overtime HVAC") provided that, to the extent
possible, Tenant gives Landlord at least twenty-four (24) hours notice in
advance of its requirement for such service. Tenant shall pay Landlord for the
cost of Overtime HVAC service (including, without limit, Landlord's costs for
engineer personnel engaged in providing such Overtime HVAC service) which costs
shall be considered Additional Rent.

          4.1.3 Other Utilities and Services. Landlord shall provide hot and
                ----------------------------
cold water at all times to the lavatories, approved kitchens and janitorial
closets in the Premises, pest control service to the common areas, replacement
of light bulbs, maintenance of the parking areas and exterior and interior
window-cleaning and office cleaning services on Monday through Friday only,
excluding legal holidays, consistent with the standards for the operation of
Class A office buildings in the Laurel, Maryland area, and in accordance with
the specifications attached hereto as Exhibit G. Landlord will also provide
elevator service; provided, however, that Landlord shall have the right to
remove elevators from service as may be required for moving freight, or for
servicing or maintaining the elevators or the Building. At least one elevator
cab shall be available for use by Tenant at all times. The cost of all of the
foregoing services shall be deemed Operating Costs under Section 3.4.6.

          If Tenant requires cleaning services, light bulb or fixture
replacement or other services on weekends or holidays, Landlord shall make
reasonably efforts to

                                       29
<PAGE>

provide such services after reasonable notice from Tenant. Tenant shall
reimburse Landlord for the cost of such additional service within thirty (30)
days after receipt of Landlord's statement, which amount shall be considered
additional Rent.

          4.1.4 Service Interruption. Notwithstanding anything contained in the
                --------------------
Lease to the contrary, if (i) the HVAC, water, elevator or cleaning services
described in Section 4 are interrupted for a period of more than five (5)
consecutive Business Days as a result of Landlord's (or its agents' or
employees') negligence or willful misconduct, and (ii) such interruption renders
all or a substantial portion of the Premises untenantable by Tenant and Tenant
does not in fact use the affected areas, then, as Tenant's sole and exclusive
remedy therefor, Tenant shall be entitled to a pro rata (based on time and the
amount of space affected) abatement of rent beginning on the sixth (6th)
consecutive Business Day that the Premises are unusable and continuing to the
extent that Tenant is unable to use such portion of the Premises for such reason
until the use of the Premises is restored to Tenant and, provided further, in no
event shall Landlord be liable to Tenant for claims of business loss, business
interruption or other consequential damages.

     4.2  Maintenance and Repair by Tenant. Except as is expressly set forth as
          --------------------------------
Landlord's responsibility, Tenant shall at Tenant's sole cost and expense keep
and maintain the Premises in good condition and repair, including the
performance of maintenance and repair of Tenant's furniture, fixtures, and
equipment, including computers and telephone systems and the repair of damage
caused by the negligent or willfully wrongful acts of Tenant or Tenant's Agents.
If Tenant fails to maintain or repair the Premises or any other areas under its
control pursuant to this Lease, (e.g., the site of the generator pursuant to
Section 4.33) in accordance with this Section, then Landlord may, but shall not
be required to, enter the Premises upon two (2) Business Days prior written
notice to Tenant (or immediately without any notice in the case of an emergency)
to perform such maintenance or repair at Tenant's sole cost and expense. Tenant
shall pay to Landlord the commercially reasonable cost of such maintenance or
repair within ten (10) Business Days of written demand from Landlord. Tenant
shall, at its sole cost and expense, enter into a regularly scheduled
preventative maintenance/service contract with a maintenance contractor for
servicing all non-base building hot water, heating and air conditioning systems
and equipment dedicated solely to specific areas of the Premises including,
without limit, supplemental HVAC units servicing computer rooms, conference or
training rooms, or other specialty areas and other items for which Tenant is
responsible as provided in this Lease. The maintenance contractors and contracts
must be approved in advance by Landlord which approval will not be unreasonably
withheld, conditioned or delayed. The service contracts shall become effective
(and a copy of such contract or contracts delivered to Landlord upon request)
within thirty (30) days following the date Tenant takes possession of the
Premises.

     4.3  Common Areas/Security.
          ---------------------

                                       30
<PAGE>

     A.   The Common Areas of the Building shall be subject to Landlord's sole
management and control except as otherwise provided in this Lease including,
without limit Section 4.21.3. Without limiting the generality of the immediately
preceding sentence, Landlord reserves the exclusive right as it deems necessary
or desirable to install, construct, remove, maintain and operate lighting
systems, facilities, improvements, equipment and signs on, in or to all parts of
the common areas; change the number, size, height, layout, or locations of
walks, driveways and truckways or parking areas now or later forming a part of
the Land or Building; make alterations or additions to the Building or Common
Areas; close temporarily all or any portion of the Common Areas to make repairs,
changes or to avoid public dedication; grant easements to which the Land will be
subject, replat, subdivide, or make other changes to the Land; place, relocate
and operate utility lines through, over or under the Land and Building; and use
or permit the use of all or any portion of the roofs of the Building;

     B.   Landlord has no duty or obligation to provide any security services
in, on or around the Premises, Land or Building, and Tenant recognizes that
security services, if any, provided by Landlord will be for the sole benefit of
Landlord and the protection of Landlord's property and under no circumstances
shall Landlord be responsible for, and Tenant waives any rights with respect to,
Landlord providing security or other protection for Tenant or Tenant's Agents or
property in, on or about the Premises, Land or Building;

     C.   Subject to Landlord's prior approval, Tenant may, at its sole cost and
expense, install, establish and maintain security services within the Premises;
provided ,that such security services, including, without limitation, any
apparatus, facilities, equipment or people utilized in connection with the
provision of such security services, comply with the Governmental Requirements
and shall not cause the Building to be out of compliance with the Governmental
Requirements. Notwithstanding the foregoing, any such security services
installed, established or maintained by Tenant must not affect or impact any
portion of the Building or the Land other than the Premises and shall not in any
way limit or interfere with Landlord's ability to exercise its rights as
provided in the section captioned "Access". Tenant's rights under this
subparagraph are subject to all the obligations, limitations and requirements as
set forth in the sections captioned "Tenant Alterations" and "Tenant's Work
Performance"; and

     D.   Landlord reserves the right to relocate parking areas and driveways
and to build additional improvements in the common areas so long as Tenant's
Parking Ratio is maintained.

     4.4  Tenant Alterations.
          ------------------

          4.4.1 General Conditions. Tenant shall not make any alterations,
                ------------------
additions or improvements in or to the Premises, or make changes to locks on
doors, or add, disturb or in any way change any floor covering, wall covering,
fixtures, plumbing

                                       31
<PAGE>

or wiring (individually and collectively "Tenant Alterations"), without
                                          ------------------
first obtaining the consent of Landlord which may be withheld in Landlord's
absolute discretion provided that Landlord shall not unreasonably withhold,
condition or delay its consent to Tenant Alterations to the interior of the
Premises that (i) are not readily visible to the exterior of the Building or the
common and public areas thereof, (ii) are not structural, (iii) do not adversely
affect the electrical, mechanical, fire or life safety systems within the
Building, and (iv) are otherwise in conformance with all applicable building,
zoning and other codes or regulations affecting the Building. Notwithstanding
the foregoing, after providing at least ten (10) days prior written notice to
Landlord (which notice shall include a reasonable description of the proposed
work) Tenant shall have the right to recarpet, repaint, or to make other purely
cosmetic or decorative nonstructural Tenant Alterations in and to the Premises
that (A) meet the requirements of clauses (i)-(iv) above, (B) do not require the
issuance of a building permit, and (C) do not cost in the aggregate more than
Seventy Five Thousand Dollars ($75,000) in a twelve (12) month period (a
"Decorative Tenant Alteration"). In the event Landlord does not respond to
Tenant's written notice of Tenant's intent to perform such Decorative Tenant
Alterations within such 10 day period, Landlord shall be deemed to have
consented to the requested Decorative Tenant Alteration. In all cases of Tenant
Alterations, other than Decorative Tenant Alterations, Tenant shall deliver to
Landlord full and complete plans and specifications for any proposed Tenant
Alterations. If consent to any Tenant Alteration by Landlord is given, all such
work which involves structural, electrical, mechanical or plumbing work, the
heating, ventilation and air conditioning system of the Premises or the Building
or the roof of the Building shall be performed at Tenant's expense by Landlord
(provided Tenant shall agree in writing to the costs of such work before the
commencement of such work) or, at Landlord's election, by Tenant. Where
Landlord's consent is required, Tenant shall pay to Landlord all reasonable
out-of-pocket costs incurred by Landlord paid to third parties for any
architecture, engineering, supervisory and legal services in connection with any
Tenant Alterations, including, without limitation, Landlord's review of the
Plans and Specifications. Without limiting the generality of the foregoing,
Landlord may require Tenant (if Tenant is performing the Tenant Alterations), at
Tenant's sole cost and expense, to obtain and provide Landlord with a
certificate proving insurance coverage and a payment and performance bond, in
forms, amounts and by companies acceptable to Landlord. Should Tenant make any
alterations without Landlord's prior written consent, when such consent is
required or without satisfaction of any conditions established by Landlord, and
if Tenant fails to obtain such consent or satisfy any previously unsatisfied
conditions within five (5) Business Days after written notice from Landlord,
Landlord shall have the right, in addition to and without limitation of any
right or remedy Landlord may have under this Lease, at law or in equity, to
require Tenant to remove some or all of Tenant Alterations, or at Landlord's
election, Landlord may remove such Tenant Alterations and restore the Premises
at Tenant's expense.

     4.4.2 Removal of Tenant Alterations. All Tenant Alterations to the
           -----------------------------
Premises, regardless of which party constructed them or paid for them, shall
become the property

                                       32
<PAGE>

of Landlord and shall remain upon and be surrendered with the Premises upon the
expiration or earlier termination of this Lease. Notwithstanding the foregoing,
at Landlord's election to be made at or before the time Tenant's plans for such
Tenant Alterations are approved, Tenant shall be obligated, at Tenant's sole
cost and expense, to remove all (or such portion as Landlord may designate) of
the Tenant Alterations upon the expiration or earlier termination of this Lease
and repair any damage resulting from such removal and return the area to the
same condition existing prior to the undertaking; provided, however, that
Landlord may only require such removal if in Landlord's reasonable professional
judgment such Tenant Alterations (1) are not customarily found in Class A office
buildings in the Laurel, Maryland submarket and (11) in Landlord's reasonable
judgment would, as a result of the unique nature of such items or the
anticipated difficulty or expense required to remove such items, expose Landlord
to unreasonable expense and effort in order to remove such items.

     4.4.3 Failure to Remove. If Tenant fails to remove any Tenant Alterations
           -----------------
as required by Landlord pursuant to this Section 4.4., Landlord may do so and
Tenant shall pay the entire cost thereof to Landlord within twenty (20) Business
Days after Tenant's receipt of Landlord's written demand therefor.

     4.4.4 No Waiver.  Nothing contained in this Section or the Section
           ---------
captioned "Tenant's Work Performance" shall be deemed a waiver of the
           -------------------------
provisions of the Section captioned "Mechanic's Liens".
                                     ----------------

     4.5   Tenant's Work Performance. If Landlord elects to require Tenant to
           -------------------------
perform the Tenant Alterations, Landlord may, in its absolute discretion,
require that Tenant provide a payment and performance bond to cover the entire
work to be performed, which bond must be in form, amount and by a company
acceptable to Landlord. A ny Tenant Alterations to be performed by Tenant under
this section shall be performed by contractors employed by Tenant under one or
more construction contracts, in form and content approved in advance in writing
by Landlord. So long as the present Landlord, or any affiliated entity, is the
owner of the Building, such construction contracts, shall, in Landlord's
discretion, include a requirement that the prime contractor and the respective
subcontractors of any tier: (a) be parties to, and bound by, a collective
bargaining agreement with a labor organization affiliated with the Building and
Construction Trades Council of the AFL-CIO; and (b) employ only members of such
labor organizations to perform work within their respective jurisdictions
provided, however, that Tenant shall have the right to engage specialty
contractors who are not subject to the requirements of clauses (a) or (b) of
this sentence for the sole purpose of completing Tenant Alterations in the
Premises related to Tenant's furniture, fixtures and equipment or to perform
Decorative Tenant Alterations, as defined in Section 4.4.1. Tenant's
contractors, workers and suppliers shall work in harmony with and not interfere
with workers or contractors of Landlord or other tenants of Landlord. If
Tenant's contractors, workers or suppliers do, in the opinion of Landlord, cause
such disharmony or interference, Landlord's consent to the continuation of such
work may be withdrawn upon written notice to Tenant. All Tenant

                                       33
<PAGE>

Alterations shall be (1) completed in accordance with the plans and
specifications approved by Landlord; (2) completed in accordance with all
Governmental Requirements; (3) carried out promptly in a good and workmanlike
manner; (4) of all new materials; and (5) free of defect in materials and
workmanship. Tenant shall pay for all damage to the Premises, Building and Land
caused by Tenant or Tenant's Agents. Tenant shall indemnify, defend and hold
harmless Landlord and Landlord's Agents from any Claims arising as a result of
the Tenant Alterations or any defect in design, material or workmanship of any
Tenant Alterations.

     4.6  Surrender of Possession. Subject to the last subparagraph of the
          -----------------------
section captioned "Insurance", Tenant shall, at the expiration or earlier
                   ---------
termination of this Lease, surrender and deliver the Premises to Landlord in as
good condition as when received by Tenant from Landlord or as later improved,
reasonable use and wear excepted, and free from all tenancies or occupancies by
any person.

     4.7  Removal of Property. Unless otherwise agreed to in writing by
          -------------------
Landlord, Tenant agrees that there are and shall be no trade fixtures in the
Premises owned by Tenant. Upon expiration or earlier termination of this Lease,
Tenant may remove its personal property, office supplies and office furniture
and equipment: if (a) such items are readily moveable and are not attached to
the Premises; (b) such removal is completed prior to the expiration or earlier
termination of this Lease; (c) Tenant is not in monetary or other material
default of any covenant or condition of this Lease at the time of such removal;
and (d) Tenant immediately repairs all damage caused by or resulting from such
removal. All other property in the Premises and any Tenant Alterations
(including, wall-to-wall carpeting, paneling, wall covering or lighting fixtures
and apparatus) or any other article affixed to the floor, walls, ceiling or any
other part of the Premises or Building, shall become the property of Landlord
and shall remain upon and be surrendered with the Premises; provided, however,
subject to the provisions of Section 4.4, at Landlord's election, Tenant shall
be obligated, at its sole cost and expense, to remove all (or such portion as
Landlord shall designate) of the Tenant Alterations and repair any damages
resulting from such removal. Tenant waives all rights to any payment or
compensation for such Tenant Alterations. If Tenant shall fail to remove any of
its property from the Premises, Building or Land at the expiration or earlier
termination of this Lease or when Landlord has the right of re-entry, Landlord
may, at its option, remove and store such property without liability for loss of
or damage to such property, such storage to be for the account and at the
expense of Tenant. If Tenant fails to pay the cost of storing any such property,
Landlord may, at its option, after it has been stored for a period of twenty
(20) Business Days or more, sell or permit to be sold, any or all such property
at public or private sale (and Landlord may become a purchaser at such sale), in
such manner and at such times and places as Landlord in its sole discretion may
deem proper, without notice to Tenant, and Landlord shall apply the proceeds of
such sale: first, to the cost and expense of such sale, including reasonable
           -----
attorney's fees actually incurred; second, to the payment of the costs or
                                   ------
charges for storing any such property; third, to the payment of any other sums
                                       -----
of money

                                       34
<PAGE>

which may then be or later become due Landlord from Tenant under this Lease;
and, fourth, the balance, if any, to Tenant.
     ------

     4.8  Access. Tenant shall permit Landlord and Landlord's Agents to enter
          ------
into the Premises at any time on at least one (1) Business Day's notice (except
in case of emergency in which case no notice shall be required), for the purpose
of inspecting the same, showing the Premises to a prospective purchaser or
lender or repairing, altering or improving the Premises or the Building. Nothing
contained in this section shall be deemed to impose any obligation upon Landlord
not expressly stated elsewhere in this Lease. Landlord shall have the right to
enter the Premises at any time during the last 18 months of the Lease Term after
advance notice of at least 24 hours for the purpose of showing the Premises to
prospective tenants and to erect on the Premises a suitable sign indicating the
Premises are available provided, however, that if Landlord elects to exercise
this right during the seventeenth (17/th/) and eighteenth (18/th/) months prior
to the end of the Lease Term, such visits for the purpose of showing the
Premises to prospective tenants shall not be conducted during Normal Business
Hours; shall, if required by Tenant, be conducted with an escort provided by
Tenant; and shall not be made for the purpose of showing the Premises to a
recognized competitor of Tenant. For the purpose of implementing the preceding
sentence, at Landlord's request, prior to the end of the eighth (8/th/) Lease
Year Tenant shall notify Landlord in writing of those entities which it
considers to be competitors for the purpose of determining those entities which
may not be shown the Premises during the seventeenth (17/th/) and eighteenth
(18/th/) months prior to the end of the Lease Term as provided in such sentence
which list may be amended in writing by Tenant from time to time as necessary.
Tenant shall give written notice to Landlord at least twenty (20) Business Days
prior to vacating the Premises and shall arrange to meet with Landlord for a
joint inspection of the Premises prior to vacating. In the event of Tenant's
failure to give such notice or arrange such joint inspection, Landlord's
inspection at or after Tenant's vacating the Premises shall be conclusively
deemed correct for purposes of determining Tenant's responsibility for repairs
and restoration. Landlord shall not be liable for the consequences of admitting
by passkey, or refusing to admit to the Premises, Tenant or any of Tenant's
Agents, or other persons claiming the right of admittance.

          When reasonably necessary, Landlord may temporarily close Building or
Land entrances, Building doors or other facilities, without liability to Tenant
by reason of such closure and without such action by Landlord being construed as
an eviction of Tenant or as relieving Tenant from the duty of observing or
performing any of the provisions of this Lease. Except as otherwise provided in
the preceding sentence, Tenant shall have access to the Building on a
twenty-four (24) hour per day, seven (7) day per week basis through the
Building's card key access system, subject to such reasonable regulations and/or
security systems which Landlord may impose for security purposes.

                                       35
<PAGE>

     4.9  Damage or Destruction.
          ---------------------

          4.9.1 If the Premises are damaged by fire, earthquake or other
casualty, Tenant shall give immediate written notice thereof to Landlord.
Landlord shall, within forty-five (45) days after the date the Landlord is
notified of the casualty, provide Tenant with Landlord's good faith estimate of
how long it will take to repair or restore the Premises. If Landlord estimates
that the damage can be repaired in accordance with the then-existing
Governmental Requirements within two hundred twenty-five (225) Calendar Days
after Landlord is notified by Tenant of such damage and if there are sufficient
insurance proceeds available to repair such damage, then Landlord shall proceed
with reasonable diligence to restore the Premises to substantially the condition
which existed prior to the damage and this Lease shall not terminate. If, in
Landlord's estimation, the damage cannot be repaired within such two hundred
twenty-five (225) day period or if there are insufficient insurance proceeds
available to repair such damage, Landlord may elect in its absolute discretion
to either: (a) terminate this Lease; or (b) restore the Premises to
substantially the condition which existed prior to the damage and this Lease
will continue. If Landlord elects to restore the Premises, Landlord will use
reasonable efforts to complete such restoration within such two hundred twenty-
five (225) Calendar Day period, as such period may be extended due to Force
Majeure or any Tenant Delays (as such term is defined in Exhibit C. If such
                                                         ---------
repairs or restoration are not completed within such period as so extended, then
within 30 days following the expiration of such period (provided that Landlord
does not complete the repair or restoration of the Premises within such 30 days
period), Tenant shall have the right to terminate this Lease on 30 day notice to
Landlord, provided that if Landlord substantially completes the repair or
restoration within such 30 day period, Tenant's notice of termination shall be
deemed rescinded and ineffective for all purposes and this Lease shall continue
in full force and effect. Notwithstanding the foregoing, Tenant shall not have
the right to terminate this Lease as provided in this Section 4.9 in the event
the casualty which caused the damage to the Premises was the result of Tenant's
gross negligence or willful misconduct.

          If Landlord restores the Premises under this Section 4.9, then (1) the
Lease Term shall be extended for the time required to complete such restoration,
(2) Tenant shall pay to Landlord, upon demand, any applicable reasonable
deductible amount specified under Landlord's insurance (which deductible
currently does not exceed $25,000) and (3) Landlord shall not be required to
repair or restore Tenant Improvements, Tenant Alterations, or any or all
furniture, fixtures, equipment, inventory, improvements or other property which
was in or about the Premises at the time of the damage and was not owned by
Landlord. Base Rent, Additional Rent and any other sum due under this Lease
during any reconstruction period shall be equitably abated to the extent and for
the period that the Premises are unusable and are not used by Tenant due to the
performance of such reconstruction work by Landlord. Tenant agrees to look to
the provider of Tenant's insurance for coverage for the loss of Tenant's use of
the Premises and any other related losses or damages incurred by Tenant during
any reconstruction period.

                                       36
<PAGE>

          4.9.2 If the Building is damaged by fire, earthquake or other casualty
and more than fifty percent (50%) of the Building is rendered untenantable,
without regard to whether the Premises are affected by such damage, Landlord may
in its absolute discretion and without limiting any other options available to
Landlord under this Lease or otherwise, elect to terminate this Lease by notice
in writing to Tenant within forty-five (45) Business Days after the occurrence
of such damage. Such notice shall be effective twenty (20) Business Days after
receipt by Tenant unless a later date is set forth in Landlord's notice which
later date shall not be greater then 180 days after the occurrence of the
damage.

          4.9.3 Notwithstanding anything contained in this Lease to the
contrary, if there is damage to the Premises, or Building and the holder of any
indebtedness secured by a mortgage or deed of trust covering any such property
requires that the insurance proceeds be applied to such indebtedness or if the
insurance proceeds are otherwise inadequate to complete the repair of the
damages to the Premises, the Building or both, then Landlord shall have the
right to terminate this Lease by delivering written notice of termination to
Tenant within fifteen (15) Business Days after such requirement is made by such
holder.

          4.9.4 Notwithstanding the foregoing, if the Premises or the Building
are wholly or partially damaged or destroyed within the final six (6) months of
the Term, Landlord may, at its option, elect to terminate this Lease upon
written notice to Tenant within thirty (30) days following such damage or
destruction.

     4.10 Condemnation. If all of the Premises, or such portions of the Building
          ------------
as may be required for the Tenant's reasonable use of the Premises, are taken by
eminent domain or by conveyance in lieu thereof, this Lease shall automatically
terminate as of the date the physical taking occurs, and all Base Rent,
Additional Rent and other sums payable under this Lease shall be paid to that
date. In case of taking of a part of the Premises or a portion of the Building
not required for the Tenant's reasonable use of the Premises, then this Lease
shall continue in full force and effect and the Base Rent shall be equitably
reduced based on the proportion by which the floor area of the Premises is
reduced, such reduction in Base Rent to be effective as of the date the physical
taking occurs. Additional Rent and all other sums payable under this Lease shall
be redetermined in an equitable manner under the circumstances. Landlord
reserves all rights to damages or awards for any taking by eminent domain
relating to the Premises, Building, Land and the unexpired term of this Lease.
Tenant assigns to Landlord any right Tenant may have to such damages or award
and Tenant shall make no claim against Landlord for damages for termination of
its leasehold interest or interference with Tenant's business. Tenant shall have
the right, however, to claim and recover from the condemning authority
compensation for any loss to which Tenant may be entitled for Tenant's moving
expenses or other relocation costs; provided that, such expenses or costs may be
                                    -------------
claimed only if they are awarded separately in the eminent domain proceedings
and not as a part of the damages recoverable by Landlord.

                                       37
<PAGE>

     4.11 Parking. Landlord shall provide Tenant unreserved surface parking at
          -------
no additional charge in an aggregate amount equal to the Parking Ratio stated in
section captioned "Definitions - Parking Ratio." Landlord shall have no
                   ---------------------------
obligation whatsoever to monitor, secure or police the use of the parking or
other common areas.

     4.12 Indemnification.
          ---------------

          4.12.1 Tenant shall indemnify, defend and hold harmless Landlord and
Landlord's Agents from and against any and all Claims, arising in whole or in
part out of (a) the possession, use or occupancy of the Premises or the business
conducted in the Premises, (b) any act, omission or negligence of Tenant or
Tenant's Agents except to the extent such claims arise from Landlord's
negligence or willful misconduct, or (c) any breach or default under this Lease
by Tenant.

          4.12.2 Landlord shall indemnify, defend and hold harmless Tenant from
and against any and all Claims, arising in whole or in part out of (a) any
intentional acts or omissions or negligence of Landlord or Landlord's Agents in
the Premises except to the extent such accident, injury, damage, failure, breach
or default is a result of or is in any way caused by Tenant, or any of Tenant's
Agents, or (b) any breach or default under this Lease by Landlord.
Notwithstanding the foregoing, neither Landlord nor Landlord's Agents shall, to
the extent permitted by law, have any liability to Tenant, or to Tenant's
Agents, for any Claims arising out of any repair to any portion of the Premises;
interruption in the use of the Premises or any equipment therein; any accident
or damage resulting from any use or operation by Landlord, Tenant or any person
or entity of heating, cooling, electrical, sewerage or plumbing equipment or
apparatus; termination of this Lease by reason of damage to the Premises or
Building; fire, robbery, theft, vandalism, mysterious disappearance or any other
casualty; actions of any other tenant of the Building or of any other person or
entity; inability to furnish any service required of Landlord as specified in
this Lease; or leakage in any part of the Premises or the Building from rain,
ice or snow, or from drains, pipes or plumbing fixtures in the Premises or the
Building; except for Claims arising solely out of the negligence or willful
misconduct of Landlord in failing to repair or maintain the Building as required
by this Lease after notice by Tenant as required by the Section 4.1 captioned
"Maintenance and Repair by Landlord"; provided that, in no event shall Landlord
 ----------------------------------
be responsible for any interruption to Tenant's business or for any indirect or
consequential losses suffered by Tenant or Tenant's Agents. The obligations of
this Section 4.12 shall be subject to the Section captioned "Waiver of
                                                             ---------
Subrogation".
-----------

     4.13 Tenant Insurance.
          ----------------

          4.13.1 Tenant shall, throughout the Lease Term, at its own expense,
keep and maintain in full force and effect the following policies, each of which
shall be endorsed as needed to provide that the insurance afforded by these
policies is primary and that all insurance carried by Landlord is strictly
excess and secondary and shall not contribute with Tenant's liability insurance:

                                       38
<PAGE>

                 (a)  A policy of comprehensive general liability insurance,
including a contractual liability endorsement covering Tenant's obligations to
indemnify Landlord for the tortuous acts of Tenant or Tenant's Agents pursuant
to the Section captioned "Indemnification", insuring against claims of bodily
                          ---------------
injury and death or property damage or loss with a combined single limit at the
Phase I Commencement Date of this Lease of not less than Two Million Dollars
($2,000,000.00). The amount of insurance required pursuant to the preceding
sentence may be satisfied by the basic policy described in this subsection (a)
plus an umbrella coverage which applies to the Premises and the Land and which
policies together, will provide the required amount of coverage. The foregoing
insurance limit may be reasonably increased during the Lease Term at Landlord's
request to reflect both increases in liability exposure arising from inflation
as well as from changing use of the Premises or changing legal liability
standards, which increases shall be reasonably comparable to those imposed by
landlords of Class A buildings (if any) which are similar in size, construction,
use and level of finish as the Building and which are located within a ten (10)
mile radius of the Building. Such insurance shall be payable on an "occurrence"
rather than a "claims made" basis, and shall name Landlord and Manager and, at
Landlord's request Landlord's mortgage lender(s) or investment advisors, as
additional insureds;

                 (b)  A policy of extended property insurance (which is commonly
called "all risk") covering Tenant Improvements, Tenant Alterations, and any and
all furniture, fixtures, equipment, inventory, improvements and other property
in or about the Premise which is not owned by Landlord, for one hundred percent
(100%) of the then current replacement value of such property;

                 (c)  Business interruption insurance in an amount sufficient to
cover costs, damages, lost income, expenses, Base Rent, Additional Rent and all
other sums payable under this Lease, should any or all of the Premises not be
usable for a period of up to twelve (12) months; and

                 (d)  A policy or worker's compensation insurance as required by
applicable law and employer's liability insurance with limits of no less than
One Million Dollars ($1,000,000.00). The level of coverage required by the
preceding sentence may be satisfied in part by an umbrella policy coverage
which, together with other insurance, will provide the required amount of
coverage.

          4.13.2 All insurance policies required under this section shall be
with companies licensed to do business in Maryland and with an A.M. Best rating
of AV or better and each policy shall provide that it is not subject to
cancellation or reduction in coverage except after thirty (30) days' written
notice to Landlord. Tenant shall deliver to Landlord and, at Landlord's request
Landlord's mortgage lender(s), prior to the Phase I Commencement Date and from
time to time thereafter, certificates evidencing the existence and amounts of
all such policies.

                                       39
<PAGE>

          4.13.3 If Tenant fails to acquire or maintain any insurance or provide
any certificate required by this section, Landlord may, but shall not be
required to, obtain such insurance or certificates and the costs associated with
obtaining such insurance or certificates shall be payable by Tenant to Landlord
on demand.

     4.14 Landlord's Insurance. Landlord shall, throughout the Lease Term, keep
          --------------------
and maintain in full force and effect:

          (a)  A policy of commercial general liability insurance, insuring
against claims of bodily injury and death or property damage or loss with a
combined single limit at the Phase I Commencement Date of not less than Five
Million Dollars ($5,000,000.00), which policy shall be payable on an
"occurrence" rather than a "claims made" basis;

          (b)  A policy of extended property insurance (what is commonly called
"all risk") covering the Building and Landlord's personal property, if any,
located on the Land in the amount of one hundred percent (100%) of the then
current replacement value of such property; and

          (c)  Landlord may, but shall not be required to, maintain other types
of insurance as Landlord deems appropriate, including but not limited to,
property insurance coverage for earthquakes and floods in such amounts as
Landlord deems appropriate. Such policies may be "blanket" policies that cover
other properties owned by Landlord.

     4.15 Waiver of Subrogation. Notwithstanding anything in this Lease to the
          ---------------------
contrary, Landlord and Tenant hereby each waive and release the other from any
and all Claims or any loss or damage that may occur to the Land, Building,
Premises, or personal property located therein, by reason of fire or other
casualty regardless of cause or origin, including the negligence or misconduct
of Landlord, Tenant, Landlord's Agents or Tenant's Agents, but only to the
extent of the insurance proceeds paid to such releasor under its policies of
insurance or, if it fails to maintain the required policies, the insurance
proceeds that would have been paid to such releasor if it had maintained such
policies. Each party to this Lease shall promptly give to its insurance company
written notice of the mutual waivers contained in this subparagraph, and shall
cause its insurance policies to be properly endorsed, if necessary, to prevent
the invalidation of any insurance coverages by reason of the mutual waivers
contained in this subparagraph.

     4.16 Assignment and Subletting by Tenant.
          -----------------------------------

          4.16.1 Tenant shall not have the right to assign, transfer, mortgage
or encumber this Lease in whole or in part, nor sublet the whole or any part of
the Premises, nor allow the occupancy of all or any part of the Premises by
another, without first obtaining Landlord's consent, which consent shall not be
unreasonably withheld, conditioned or delayed, provided that upon 10 Business
Days written notice to

                                       40
<PAGE>

Landlord, Tenant shall have the right to assign this Lease or sublease any
portion of the Premises to any entity which is controlled by or under common
control with Tenant (collectively "Affiliates") for use comparable to that of
Tenant. For purposes of this Section 4.16, "control" shall mean ownership of at
least 50% of the stock or other voting interests in the entity in question.
Notwithstanding any permitted assignment or subletting, Tenant shall at all
times remain directly, primarily and fully responsible and liable for the
payment of all sums payable under this Lease and for compliance with all of its
other obligations as tenant under this Lease. Upon the occurrence of an Event of
Default, if the Premises or any part of the Premises are then subject to an
assignment or subletting, Landlord, in addition to any other remedies provided
in this Lease or by law, may at its option collect directly from such assignee
or subtenant all rents becoming due to Tenant under such assignment or sublease
and apply such rents against any sums due to Landlord from Tenant under this
Lease, and no such collection shall be construed to constitute a novation or
release of Tenant from the further performance of Tenant's obligations under
this Lease.

          In addition, notwithstanding the restrictions on assignments and
subleases set forth herein, Landlord's prior consent shall not be required with
respect to any assignment of this Lease resulting from the merger,
consolidation, or other corporate reorganization of Tenant, or the sale or
transfer of the capital stock or all or substantially all of the assets of
Tenant, provided that (i) Tenant after such merger, consolidation,
reorganization or sale of stock or assets has a creditworthiness (e.g. assets
and capitalization) and net worth (which shall be determined on a pro forma
basis using generally accepted accounting principles consistently applied and
using the most recent financial statements) not materially less than that of
Tenant prior to the date of such transfer, (ii) Tenant after such merger,
consolidation, reorganization or sale of stock or assets agrees in writing to be
bound by the terms and conditions of this Lease and to assume all of the
obligations and liabilities of Tenant under this Lease, (iii) Tenant after such
merger, consolidation, reorganization or sale of stock shall conduct a Permitted
Use pursuant to the terms of this Lease which use shall be comparable to
Tenant's use of the Premises, (iv) Tenant provides Landlord with prior written
notice of its intent to assign the Lease not more than forty-five (45) nor less
than fifteen (15) days prior to the date such assignment is to be effective, (v)
the assignment is not a so-called "sham" transaction intended by Tenant to
circumvent the provisions of this Section of the Lease, (vi) a monetary or
material non-monetary Event of Default has not occurred and is still continuing,
and (vii) the assignment (A) will not result in a material increase in Operating
Costs for the Building beyond that which Landlord now incurs for use by Tenant
and (B) will not materially increase the burden on elevators or other Building
systems or equipment over the burden prior to such assignment or sublease (a
"Permitted Transfer"). Any approved sublease or assignment shall be on a form of
sublease or assignment which has been approved in advance by Landlord.

          Notwithstanding any permitted assignment or subletting, Tenant shall
at all times remain directly, primarily and fully responsible and liable for the
payment of all

                                       41
<PAGE>

sums payable under this Lease and for compliance with all of its other
obligations as tenant under this Lease. Upon the occurrence of an Event of
Default, if the Premises or any part of the Premises are then subject to an
assignment or subletting, Landlord, in addition to any other remedies provided
in this Lease or by law, may at its option collect directly from such assignee
or subtenant all rents becoming due to Tenant under such assignment or sublease
and apply such rents against any sums due to Landlord from Tenant under this
Lease, and no such collection shall be construed to constitute a novation or
release of Tenant from the further performance of Tenant's obligations under
this Lease.

          Tenant makes an absolute assignment to Landlord of such assignments
and subleases and any rent, security deposits and other sums payable under such
assignments and subleases as collateral to secure the performance of the
obligations of Tenant under this Lease.

          In no event shall any consent by Landlord be construed to permit
reassignment or resubletting by a permitted assignee or sublessee. Upon any
assignment of this Lease or any subletting in the aggregate of one hundred
percent (100%) of the Premises for all, or substantially all, of the remainder
of the Term of this Lease, or any extension thereof, any and all option rights,
renewal rights, rights of first refusal and expansion rights (including those
rights set forth in Sections 6.19 through 6.21, and those special signage rights
as set forth in Section 4.23) shall terminate and be of no further force and
effect, unless such assignment or sublease were made in favor of an entity that
directly or indirectly controls or is controlled by or is under common control
with Tenant ("Tenant's Affiliate") or arises as a result of a Permitted Transfer
which is approved as provided in the second paragraph of this Section 4.16.1. it
being agreed that all such rights are personal to Tenant (and not to any
assignee or subtenant, other than an entity which qualifies as Tenant's
Affiliate) and are not appurtenant to the Premises or this Lease. Any assignment
or subletting not in conformance with the terms of this Lease shall be void.

          4.16.2 In the event Tenant desires to assign this Lease or to sublet
all or any portion of the Premises, Tenant shall give written notice of such
desire to Landlord setting forth the name of the proposed subtenant or assignee,
the proposed term, the nature of the proposed subtenant's or assignee's business
to be conducted on the Premises, the rental rate, and any other particulars of
the proposed subletting or assignment that Landlord may reasonably request.
Without limiting the preceding sentence, Tenant shall also provide Landlord
with: (a) such financial information as Landlord may reasonably request
concerning the proposed subtenant or assignee, including recent financial
statements certified as accurate and complete by a certified public accountant
or by the president, managing partner or other appropriate officer of the
proposed subtenant or assignee; (b) proof satisfactory to Landlord that the
proposed subtenant or assignee will immediately occupy and thereafter use the
entire Premises (or any sublet portion of the Premises) for the remainder of the
Lease Term (or for the entire term of the sublease, if shorter) in compliance
with the terms of this

                                       42
<PAGE>

Lease; and (c) a copy of the proposed sublease or assignment or letter of
intent. Tenant shall pay to Landlord, upon Landlord's demand therefor,
Landlord's reasonable attorneys' fees incurred in the review of such
documentation and in documenting Landlord's consent, plus an administrative fee
of $350.00 as Landlord's fee for processing such proposed assignment or
sublease. Receipt of such fee shall not obligate Landlord to approve the
proposed assignment or sublease.

          4.16.3 In determining whether to grant or withhold consent to a
proposed assignment or sublease, Landlord may consider, and weigh, any factor it
deems relevant, in its sole reasonable discretion. Without limiting what may be
construed as a factor considered by Landlord, Tenant agrees that any one or more
of the following will be proper grounds for Landlord's disapproval of a proposed
assignment or sublease:

                 (a)  Intentionally omitted;

                 (b)  The proposed assignee or subtenant does not, in Landlord's
good faith judgment, have financial worth or creditworthiness sufficient
financial worth to insure full and timely performance under this Lease;

                 (c)  Landlord has received insufficient evidence of the
financial worth or creditworthiness of the proposed assignee or subtenant for
Landlord to make the determination set forth in clause (b);

                 (d)  The proposed assignee or subtenant has a reputation for
disputes in contractual relations, for failure to observe and perform its
contractual obligations in a timely and complete manner or for negative business
relations in the business community as a tenant of property or otherwise;

                 (e)  Landlord has received from any prior lessor of the
proposed assignee or subtenant a negative report concerning such prior lessor's
experience with the proposed assignee or subtenant;

                 (f)  Landlord has had prior negative leasing experience with
the proposed assignee or subtenant;

                 (g)  The use of the Premises by the proposed assignee or
subtenant will not be identical with the Permitted Uses;

                 (h)  In Landlord's judgment, the proposed assignee or subtenant
is engaged in a business, or the Premises or any part of the Premises will be
used in a manner, that is not in keeping with the then standards of the
Building, or that is not compatible with the businesses of other tenants in the
Building, or that is inappropriate for the Building, or that will violate any
negative covenant as to use contained in any other lease of space in the
Building;

                                       43
<PAGE>

               (i)  The use of the Premises by the proposed assignee or
subtenant will violate any Governmental Requirement or create a violation of
Access Laws;

               (j)  Tenant is in default of any material obligation of Tenant
under this Lease, or Tenant has materially defaulted under this Lease on three
(3) or more occasions during the twenty-four (24) months preceding the date that
Tenant shall request such consent;

               (k)  Landlord does not, in good faith, approve of any of the
tenant improvements required for the proposed assignee or subtenant; or

               (l)  Intentionally omitted;

               (m)  The proposed assignee or subtenant is a party by whom any
suit or action could be defended on the ground of diplomatic or sovereign
immunity.

       4.16.4  Within fifteen(15) Business Days after Landlord's receipt of all
required information to be supplied by Tenant pursuant to this section, Landlord
shall notify Tenant of Landlord's approval, disapproval or conditional approval
of any proposed assignment or subletting or of Landlord's election to recapture
as described below. Landlord shall have no obligation to respond unless and
until all required information has been submitted. In the event Landlord
approves of any proposed assignment or subletting, Tenant and the proposed
assignee or sublessee shall execute and deliver to Landlord an assignment (or
subletting) and assumption agreement in form and content reasonably satisfactory
to Landlord.

       4.16.5  Any transfer, assignment or hypothecation of any of the stock or
interest in, or the assets of, Tenant which is either: (a) greater than fifty
percent (50%) of such stock, interest or assets or (b) intended as a subterfuge
denying Landlord the benefits of this section, shall be deemed to be an
assignment within the meaning and provisions of this section and shall be
subject to the provisions of this section.

       4.16.6  If Landlord consents to any assignment or sublease and Tenant
receives rent or any other consideration, either initially or over the term of
the assignment or sublease, in excess of the Base Rent and Additional Rent (or,
in the case of a sublease of a portion of the Premises, in excess of the Base
Rent and Additional Rent paid by Tenant on a square footage basis under this
Lease) plus all reasonable transaction costs, including rent concessions and
other inducements, reasonable brokerage commissions, legal fees, marketing
expenses, subtenant improvement allowances and other costs reasonably incurred
by Tenant in connection with such assignment or subletting ("Sublease Costs")
                                                             --------------
(which excess shall be referred to as "Sublease Profit") Tenant shall pay to
                                       ---------------
Landlord fifty percent (50%) of such excess. For the purpose of calculating
Landlord's share of any Sublease Profit, the Sublease Costs shall be allocated
proportionately to all such payments received by Tenant over the term of the
sublease. Tenant shall furnish to Landlord in the February immediately

                                       44
<PAGE>

following each calendar year during any part of which any such Sublease shall be
in effect (or within 60 days after the termination of such Sublease), a
reasonably detailed financial statement certified as being correct by Tenant's
Senior Financial Officer setting forth all sums accruing during the prior
calendar year and realized by Tenant from such Sublease and a computation of the
rent or other consideration received on account of such Sublease or Assignment
in excess of the Base Rent and Additional Rent plus Sublease Costs during the
prior calendar year. Tenant shall remit to Landlord, together with such
statement, 50% of such excess on account of such calendar year not previously
remitted to Landlord.

          4.16.7 Landlord shall have the right to recapture the Premises or the
applicable portion thereof (a "Recapture") by giving written notice (the
                               ---------
"Recapture Notice") of such Recapture to Tenant within fifteen (15) Business
Days after receipt of Tenant's written request for Landlord's consent to a
proposed assignment or subletting. Tenant shall have the right to retract its
request for Landlord's consent to assign or sublease once such request has been
made provided such retraction is given in writing within ten (10) Business Days
after Landlord delivers the Recapture Notice. Such Recapture shall terminate
this Lease as to the applicable space effective on the prospective effective
date of assignment or subletting, which shall be the last day of a calendar
month and shall not be earlier than forty-five (45) Business Days after receipt
of Tenant's request hereunder. If less than the entire Premises are recaptured,
Landlord and Tenant agree that this Lease shall remain in full force and effect
with respect to that remaining area not recaptured by Landlord and Landlord
shall cause the remaining space to be re-demised at Landlord's expense. Tenant
agrees to surrender that portion of the Premises recaptured by Landlord in
accordance with the terms and conditions of this Lease. Notwithstanding the
first sentence of this subparagraph, Landlord shall have no right to Recapture
the Premises or applicable portion thereof if: (a) Tenant's proposed assignment
or sublet is to an Affiliate, wholly-owned subsidiary or successor entity, or
(b) Tenant's proposed assignment or sublet together with any previous
assignments and sublets encompass, in the aggregate, net rentable area equal to
less than fifty percent (50%) of the total net rentable area of the Premises.

     4.17 Assignment by Landlord. Landlord shall have the right to transfer and
          ----------------------
assign, in whole or in part, its rights and obligations under this Lease and in
any and all of the Land or Building. If Landlord sells or transfers any or all
of the Building, including the Premises, Landlord and Landlord's Agents shall,
upon consummation of such sale or transfer, be released automatically from any
liability relating to obligations or covenants under this Lease to be performed
or observed after the date of such transfer, and in such event, Tenant agrees to
look solely to Landlord's successor-in-interest with respect to such liability;
provided that, as to the Security Deposit and Prepaid Rent, Landlord shall not
-------------
be released from liability therefor unless Landlord has delivered (by direct
transfer or credit against the purchase price) the Security Deposit or Prepaid
Rent to its successor-in-interest.

                                       45
<PAGE>

     4.18 Estoppel Certificates and Financial Statements. Tenant shall, from
          ----------------------------------------------
time to time, upon the written request of Landlord, execute, acknowledge and
deliver to Landlord or its designee a written statement stating (a) the date
this Lease was executed and the date it expires; (b) the date Tenant entered
into occupancy of the Phases of the Premises; (c) the amount of monthly Base
Rent and Additional Rent and the date to which such Base Rent and Additional
Rent have been paid; and (d) certifying that (1) this Lease is in full force and
effect and has not been assigned, modified, supplemented or amended in any way
(or specifying the date of the agreement so affecting this Lease); (2) Landlord
is not in breach of this Lease (or, if so, a description of each such breach)
and that no event, omission or condition has occurred which would result, with
the giving of notice or the passage of time, in a breach of this Lease by
Landlord; (3) this Lease, together with any specifically identified agreements,
represents the entire agreement between the parties with respect to the
Premises; (4) all required contributions by Landlord to Tenant on account of
Tenant Improvements have been received (or a statement as to what further
contributions are claimed as due); (5) on the date of execution, there exist no
defenses or offsets which the Tenant has against the enforcement of this Lease
by the Landlord (or a specific statement as to what, if any, such defenses or
offsets may be); (6) no Base Rent, Additional Rent or other sums payable under
this Lease have been paid in advance except for Base Rent and Additional Rent
for the then current month; (7) no security has been deposited with Landlord
(or, if so, the amount of such security); (8) it is intended that any Tenant's
statement may be relied upon by a prospective purchaser or mortgagee of
Landlord's interest or an assignee of any such mortgagee; and (9) such other
information as may be reasonably requested by Landlord. If Tenant fails to
respond within five (5) Business Days of its receipt of a written request by
Landlord ;is provided in this section, such shall be a breach of this Lease and
Tenant shall be deemed to have admitted the accuracy of any information supplied
by Landlord to a prospective purchaser, mortgagee or assignee. In addition,
Tenant shall, from time to time, upon the written request of Landlord, deliver
to or cause to be delivered to Landlord or its designee then current financial
statements (including a statement of operations and balance sheet) certified as
accurate by a certified public accountant and prepared in conformance with
generally accepted accounting principles for (i) Tenant, (ii) any entity which
owns a controlling interest in Tenant, (iii) any entity the controlling interest
of which is owned by Tenant, (iv) any successor entity to Tenant by merger or
operation of law, and (v) any guarantor of this Lease provided, however, that
such information need not be supplied by Tenant to the extent that it is readily
available to the public in an equally credible form on the Internet or otherwise
(e.g. Form 10-Q filed with the Securities and Exchange Commission).

     4.19 Modification for Lenders. If, in connection with obtaining
          ------------------------
construction, interim or permanent financing for the Building or Land,
Landlord's lender, if any, shall request reasonable modifications to this Lease
as a condition to such financing, Tenant will not unreasonably withhold or delay
its consent to such modifications; provided that,
                                   -------------

                                       46
<PAGE>

such modifications do not increase the obligations of Tenant under this Lease or
materially adversely affect Tenant's rights under this Lease.

     4.20 Hazardous Substances.
          --------------------

          4.20.1 Tenant agrees that neither Tenant nor any of Tenant's Agents
will store, place, generate, manufacture, refine, handle, or locate on, in,
under or around the Land or Building any Hazardous Substance, except for
storage, handling and use of reasonable quantities and types of cleaning fluids
and office supplies in the Premises in the ordinary course and the prudent
conduct of Tenant's business in the Premises, provided that, (a) the storage,
                                              -------------
handling and use of such permitted Hazardous Substances must at all times
conform to all Governmental Requirements and to applicable fire, safety and
insurance requirements; (b) the types and quantities of permitted Hazardous
Substances which are stored in the Premises must be reasonable and appropriate
to the nature and size of Tenant's operation in the Premises and reasonable and
appropriate for a first-class building of the same or similar use and in the
same market area as the Building; (c) no Hazardous Substance shall be spilled or
disposed of on, in, under or around the Land or Building or otherwise
discharged from the Premises or any area adjacent to the Land or Building; and
(d) in no event will Tenant be permitted to store, handle or use on, in, under
or around the Premises any Hazardous Substance which will increase the rate of
fire or extended coverage insurance on the Land or Building, unless: (1) such
Hazardous Substance and the expected rate increase have been specifically
disclosed in writing to Landlord, (2) Tenant has agreed in writing to pay any
rate increase related to each such Hazardous Substance; and (3) Landlord has
approved in writing each such Hazardous Substance, which approval shall be
subject to Landlord's discretion.

          4.20.2 Tenant shall indemnify, defend and hold harmless Landlord and
Landlord's Agents from and against any and all Claims arising out of any breach
of any provision of this Section 4.20, which expenses shall also include
laboratory testing fees, personal injury claims, clean-up costs and
environmental consultants' fees. Tenant agrees that Landlord may be irreparably
harmed by Tenant's breach of this section and that a specific performance action
may appropriately be brought by Landlord; provided that, Landlord's election to
                                          -------------
bring or not bring any such specific performance action shall in no way limit,
waive, impair or hinder Landlord's other remedies against Tenant.

          4.20.3 As of the execution date of this Lease, Tenant represents and
warrants to Landlord that, except as otherwise disclosed by Tenant to Landlord,
Tenant has no intent to bring any Hazardous Substances on, in or under the
Premises except for the type and quantities authorized in the first paragraph of
the section captioned "Hazardous Substances."
                       --------------------

          4.20.4 Landlord represents that to its actual knowledge as of the date
of this Lease, the Premises, the Building, and the Land (collectively, the
"Property") do not contain asbestos or any other Hazardous Substance in
violation of any Governmental

                                       47
<PAGE>

Requirement and that no Hazardous Substances have been or shall be used in the
construction or development of the Property in violation of any Governmental
Requirement, nor will such use of any such materials knowingly be permitted by
Landlord. In the event Landlord is advised, or it shall come to Landlord's
attention, that Hazardous Substances exist in the Premises, if mandated by any
Governmental Requirement, Landlord shall, at its expense, but subject to any
rights it may have (and any restrictions on such rights) to pass such costs on
to tenants, take all reasonable steps necessary to promptly remove, or cause to
be removed or remediated all such Hazardous Substances, and in doing so,
Landlord shall use its reasonable efforts not to materially interfere with the
conduct of Tenant's business; provided, however, that if such substances were
introduced or brought in, on or about the Property by Tenant, its employees,
agents, subcontractors, subtenants or invitees, at Landlord's election, the
removal of such substances from the Property shall be performed by Tenant, at
Tenant's expense, and in such manner as not to interfere with the operation of
the Building or the business of any other tenant in the Building. In the event
that Landlord elects to remove any Hazardous Substances from the Property that
Tenant, its employees, agents, subcontractors, subtenants or invitees have
introduced or otherwise brought in, on or about the Property, such removal shall
be at Tenant's expense as provided in Section 4.20.2.

     4.21 Access Laws.
          -----------

          4.21.1 Tenant agrees to notify Landlord immediately if Tenant receives
notification or otherwise becomes aware of: (a) any condition or situation on,
in, under or around the Land or Building which may constitute a violation of any
Access Laws or (b) any threatened or actual lien, action or notice that the Land
or Building is not in compliance with any Access Laws. If Tenant is responsible
for such condition, situation, lien, action or notice under this section,
Tenant's notice to Landlord shall include a statement as to the actions Tenant
proposes to take in response to such condition, situation, lien, action or
notice.

          4.21.2 Tenant shall not alter or permit any assignee or subtenant or
any other person to alter the Premises in any manner which would violate any
Access Laws or increase Landlord's responsibilities for compliance with Access
Laws, without the prior approval of the Landlord. In connection with any such
approval, Landlord may require a certificate of compliance with Access Laws from
an architect, engineer or other person acceptable to Landlord. Tenant agrees to
pay the reasonable fees incurred by such architect, engineer or other third
party in connection with the issuance of such certificate of compliance.
Landlord's consent to any proposed Tenant Alteration shall: (a) not relieve
Tenant of its obligations or indemnities contained in this section or this Lease
or (b) be construed as a warranty that such proposed alteration complies with
any Access Law.

          4.21.3 After the Commencement Date, Tenant shall be solely responsible
for all costs and expenses relating to or incurred in connection with: (a)

                                       48
<PAGE>

failure of the Premises to comply with the Access Laws; and (b) bringing the
Building and the Common Areas within the Building into compliance with Access
Laws, if and to the extent such noncompliance arises out of or relates to, (1)
Tenant's use of the Premises, including the hiring of employees; (2) any Tenant
Alterations to the Premises; or (3) any Tenant Improvements constructed in the
Premises at the request of Tenant, regardless of whether such improvements are
constructed prior to or after the each of the respective Commencement Dates.

          4.21.4 After the Commencement Date, Landlord shall be responsible for
all costs and expenses relating to or incurred in connection with bringing into
compliance with Access Laws Common Areas outside the Building (such as the
parking area, sidewalks, entrance drives and loading docks), unless such costs
and expenses are Tenant's responsibility as provided in the preceding
subparagraph. Any costs so incurred by Landlord shall be amortized over the
useful economic life of such improvements (not to exceed 10 years) using an
amortization rate of 12% per year and shall be an Operating Cost for purposes of
this Lease.

          4.21.5 Tenant agrees to indemnify, defend and hold harmless Landlord
and Landlord's Agents from and against any and all Claims arising out of or
relating to any failure of Tenant or Tenant's Agents to comply with Tenant's
obligations under this section.

          4.21.6 The provisions of this section shall supersede any other
provisions in this Lease regarding Access Laws, to the extent inconsistent with
the provisions of any other sections.

     4.22 Quiet Enjoyment. Landlord covenants that Tenant, upon paying Base
          ---------------
Rent, Additional Rent and all other sums payable under this Lease and performing
all covenants and conditions required of Tenant under this Lease shall and may
peacefully have, hold and enjoy the Premises without hindrance or molestation by
Landlord subject to the provisions of this Lease.

     4.23 Signs.
          -----

          4.23.1 No sign, advertisement or notice shall be inscribed, painted,
affixed or displayed on any part of the outside or the inside of the Building,
or the Premises except (i) the directories and signs on the office doors, and
then only in such places, numbers, sizes, colors and styles as are approved by
Landlord and which conform to all applicable laws and ordinances and to
Landlord's standards for permitted signs and (ii) the exterior fagade sign
described below. Any and all permitted signs shall be installed and maintained
by Landlord, at Tenant's sole expense. In addition, Tenant shall not install any
interior graphics of any nature that would be visible from the exterior of the
Demised Premises without the prior written consent of Landlord. Notwithstanding
the foregoing, Landlord shall provide Tenant with a building-standard suite-
entry sign and a listing strip on the directory board in the main lobby of the
Building identifying Tenant and Tenant's suite number. If any sign is exhibited
without Landlord's approval,

                                       49
<PAGE>

Landlord shall have the right to remove it and Tenant shall be responsible for
all expenses incurred by Landlord for such removal, which charges shall be,
treated as Additional Rent.

          4.23.2 Notwithstanding the provisions of subparagraph 4.23.1, Tenant,
at Tenant's sole cost and expense, shall have the right to install an exterior
facade sign on the Building provided that the exact size, content, appearance
and location of the sign shall be subject to Landlord's prior written reasonable
approval and provided further that (i) the size, color and style of the facade
sign complies with all covenants encumbering the Land and all applicable laws
and ordinances, (ii) Tenant obtains all necessary permits for the installation
of the sign, (iii) Landlord approves, in Landlord's sole discretion, the manner
and method that the sign shall be affixed to the Building, (iv) the sign shall
be affixed by a contractor approved by Landlord, and (v) Tenant continues to
occupy a minimum of 50% of the Rentable Space of the Building. If at any time
the Tenant fails to occupy a minimum of 50% of the Rentable Space of the
Building or upon Lease termination, Tenant shall remove the facade sign, with a
contractor approved by Landlord, and shall repair the portion of the Building
affected thereby to the condition such portion of the Building was in at the
time the fagade sign was installed.

          The sign shall be installed at Tenant's costs and expense, however,
Landlord shall reimburse Tenant for up to $3,500 with respect to expenses
incurred in the design, manufacture and installation of such sign. Shall amount
shall be paid to Tenant within 30 days after receipt by Landlord of paid
vouchers and releases of liens with respect to the sign. Tenant shall indemnify
and hold Landlord and Landlord's Agents harmless from and against any cost,
damage, claim, liability or expense (including reasonable attorney's fees)
incurred by or claimed against Landlord and its Agents, directly or indirectly,
as a result of or in any way arising from the installation and maintenance of
the facade sign. Tenant shall obtain property insurance coverage for such facade
sign and such sign shall be included in Tenant's comprehensive liability
insurance required in this Lease.

          4.23.3 If Tenant is the sole occupant of the Building, the Building
shall be named in a manner that is mutually agreeable to Landlord and Tenant. In
such event, Landlord shall use such name in press releases and other public
advertisements with regard to the Building. If at any time Tenant is no longer
the sole occupant of the Building, Landlord may rename the Building from time to
time in any manner at its sole discretion.

     4.24 Subordination. Tenant subordinates this Lease and all rights of Tenant
          -------------
under this Lease to any mortgage, deed of trust, ground lease or vendor's lien,
or similar instrument which may from time to time be placed upon the Premises
(and all renewals, modifications, replacements and extensions of such
encumbrances), and each such mortgage, deed of trust, ground lease or lien or
other instrument shall be superior to and prior to this Lease; provided that,
                                                               -------------
Landlord provides Tenant with a

                                       50
<PAGE>

commercially reasonable nondisturbance agreement on the standard form of the
applicable lender or ground lessor. Notwithstanding the foregoing, the holder or
beneficiary of such mortgage, deed of trust, ground lease, vendor's lien or
similar instrument shall have the right to subordinate or cause to be
subordinated any such mortgage, deed of trust, ground lease, vendor's lien or
similar instrument to this Lease. At the request of Landlord, the holder of such
mortgage or deed of trust or any ground lessor, Tenant shall execute,
acknowledge and deliver promptly in recordable form any instrument or
subordination agreement that Landlord or such holder may request, provided,
however, such instrument shall include a nondisturbance provision on the
standard form of the applicable Lender or ground lessor. Tenant further
covenants and agrees that if the lender or ground lessor acquires the Premises
as a purchaser at any foreclosure sale or otherwise, Tenant shall recognize and
attorn to such party as landlord under this Lease, and shall make all payments
required hereunder to such new landlord without deduction or set-off and, upon
the request of such purchaser or other successor, execute, deliver and
acknowledge documents confirming such attornment. Tenant waives the provisions
of any law or regulation, now or hereafter in effect, which may give or purport
to give Tenant any right to terminate or otherwise adversely affect this Lease
or the obligations of Tenant hereunder in the event that any such foreclosure or
termination or other proceeding is prosecuted or completed.

     4.25 Workers Compensation Immunity. If and to the extent that Tenant is
          -----------------------------
obligated to indemnify, defend or hold harmless Landlord or Landlord's Agents
from any Claims arising from its use of the Premises or any act or failure to
act by Tenant or Tenant's Agents or otherwise, Tenant expressly waives, to and
in favor of Landlord and Landlord's Agents, its statutory workers compensation
act employers immunity relative to any injury to an employee or employees of
Tenant.

     4.26 Brokers. Tenant shall indemnify, defend and hold harmless Landlord,
          -------
TCMI, TCMD and McShea from and against any and all Claims (including, without
limitation, any Claims for or related to a leasing commission, brokerage fee,
compensation or other payment) asserted against any one or more of Tenant,
Landlord, TCMI, TCMD or McShea by any real estate broker, finder, intermediary
or other person or entity (a) who claims (without regard to the truth or
validity of such claim) to act or have acted for or on behalf of Tenant,
Intermedia Communications, Inc., or any entity controlling, controlled by or
under common control with either Tenant or Intermedia Communications, Inc.; (b)
who claims (without regard to the truth or validity of such claim) to be or have
been a broker, finder, intermediary, contractor, agent or representative of or
for Tenant, Intermedia Communications, Inc. or any entity controlling,
controlled by or under common control with either Tenant or Intermedia
Communications, Inc.; or (c) who secured, presented, or delivered a proposal or
a request for proposal naming or identifying Tenant, with or without Tenant's
approval or authority, as a proposed tenant of all or any portion of the
Building. Any and all of the Claims described in clauses (a), (b) and (c) of the
preceding sentence are individually and collectively referred to as a "Tenant
                                                                       ------
Indemnified Claim". Landlord shall indemnify, defend and hold harmless Tenant
-----------------
from and against any and all Claims asserted against

                                       51
<PAGE>

Tenant by TCMI, TCMD, McShea or any other real estate broker, finder or
intermediary relating solely to the representation of Landlord in connection
with this Lease. Notwithstanding the foregoing, Landlord's obligation to
indemnify, defend or hold harmless Tenant as set forth in the preceding sentence
shall not extend to any Tenant Indemnified Claim. In all matters involving a
Tenant Indemnified Claim, Tenant shall select the counsel of its choice to
represent Tenant, Landlord, TCMI, TCMD and McShea subject to Landlord's consent
which will not be unreasonably withheld or delayed, provided that, if Landlord
                                                    -------------
in its good faith discretion is dissatisfied at any time for any reason with
Tenant's selected counsel or such counsel's representation of Landlord, TCMI,
TCMD, or McShea, Landlord shall be entitled to retain independent counsel of its
choice to defend any or all of Landlord, TCMI, TCMD or McShea in such matter and
the reasonable cost thereof (including, attorneys' fees and costs at trial and
on appeal) shall be paid by Tenant to Landlord promptly upon demand by Landlord
for such payment. No Tenant Indemnified Claim may be settled or resolved without
the consent of both Landlord and Tenant; provided that, if there is a full and
                                         -------------
complete release of Landlord, TCMI, TCMD and McShea from any and all
obligations, liabilities and responsibilities to the claimant and if any suit is
pending in connection with any Tenant Indemnified Claim, a dismissal of that
suit against all such parties with prejudice, Tenant may settle such Claim
without the consent of Landlord. Landlord has agreed to pay TCMD a fee pursuant
to a certain Maryland 95 Corporate Center Development Services Agreement between
Landlord and TCMD dated in December 1998, which Agreement may be modified on or
about the date hereof by a separate Commission Agreement between Landlord, TCMI,
TCMD and McShea.

     4.27 Exculpation and Limitation of Liability.
          ---------------------------------------

          4.27.1 Landlord has executed this Lease by its trustee signing solely
in a representative capacity. Notwithstanding anything contained in this Lease
to the contrary, Tenant confirms that the covenants of Landlord are made and
intended, not as personal covenants of the trustee, or for the purpose of
binding the trustee personally, but solely in the exercise of the representative
powers conferred upon the trustee by its principal.

          4.27.2 Liability with respect to the entry and performance of this
Lease by or on behalf of Landlord, however it may arise, shall be asserted and
enforced only against the lesser of (i) Landlord's estate and equity interest in
the Building or (ii) the equity interest that Landlord would have in and to the
Building if the Building were encumbered by debt in an amount equal to eighty
percent (80%) of the value of the Building.

          4.27.3 Neither Landlord nor any of Landlord's Agents shall have any
personal liability in the event of any claim against Landlord arising out of or
in connection with this Lease, the relationship of Landlord and Tenant or
Tenant's use of the Premises. Further, in no event whatsoever arising out of or
in connection with this Lease, the relationship of Landlord and Tenant or
Tenant's use of the Premises. Any

                                       52
<PAGE>

and all personal liability, if nay, beyond that which may be asserted under this
section, is expressly waived and released by Tenant and by all persons claiming
by, through or under Tenant.

     4.28 Intentionally omitted.

     4.29 Mechanic's Liens and Tenant's Personal Property Taxes.
          -----------------------------------------------------

          4.29.1 Tenant shall have no authority, express or implied, to create
or place any lien or encumbrance of any kind or nature whatsoever upon, or in
any manner to bind, the interest of Landlord or Tenant in the Premises or to
charge the rentals payable under this Lease for any Claims in favor of any
person dealing with Tenant, including those who may furnish materials or perform
labor for any construction or repairs. Tenant shall pay or cause to be paid all
sums legally due and payable by it on account of any labor performed or
materials furnished in connection with any work performed on the Premises on
which any lien is or can be validly and legally asserted against its leasehold
interest in the Premises and Tenant shall indemnify, defend and hold harmless
Landlord from any and all Claims arising out of any such asserted Claims. Tenant
agrees to give Landlord immediate written notice of any such Claim.

          4.29.2 Tenant shall be liable for all taxes levied or assessed against
personal property, furniture or fixtures placed by Tenant in the Premises. If
any such taxes for which Tenant is liable are levied or assessed against
Landlord or Landlord's property and Landlord elects to pay them or if the
assessed value of Landlord's property is increased by inclusion of such personal
property, furniture or fixtures and Landlord elects to pay the taxes based on
such increase, Tenant shall reimburse Landlord for the sums so paid by Landlord,
upon demand by Landlord.

     4.30 Landlord's Security Interest. Without prejudice to any other rights
          ----------------------------
granted in this Lease which are available to Landlord upon the occurrence of an
Event of Default, Landlord waives its statutory right to bring an action of
distress for rent.

     4.31 Recording. Tenant agrees not to record this Lease or any memorandum
          ---------
thereof among the relevant land records or any other recording office except and
unless specifically requested by Landlord.

     4.32 Cabling/Connectivity Rights.
          ---------------------------

          4.32.1 Subject to the provisions of this Lease, Tenant shall have the
nonexclusive right to run cabling through the Building core and raceways at
those points designated by Landlord for telecommunication conduits and, subject
to Landlord's approval, construct new conduits, install cables, equipment and
other related telecommunications facilities for the Premises. In addition,
Tenant shall have the nonexclusive right to access the fiber optic conduit
installed by Landlord from the Building to Sweitzer Lane. Tenant shall also have
the nonexclusive right to access and utilize the Building's vertical ground
risers and main electric service ground subject to

                                       53
<PAGE>

Landlord's consent which will not be unreasonably withheld. All cost associated
with the installation, use and connection to the conduit shall be borne solely
by the Tenant.

          4.32.2 Within ninety (90) days prior to the expiration of this Lease,
Landlord may elect by written notice to Tenant to either:

                 (i)   retain any or all wiring, cables, risers or similar
installations appurtenant thereto installed by Tenant in the Building's core,
raceways and risers ("Wiring")
                      ------

                 (ii)  remove any and all such Wiring and restore the Premises
and the conduits to their condition existing prior to the installation of the
Wiring ("Wire Restoration Work"), which work shall be done at Tenant's sole cost
and expense; or

                 (iii) require Tenant to perform such Wire Restoration Work at
Tenant's sole cost and expenses.

          In the event this Lease should terminate prior to the expiration date
for any reason, Landlord may make the election permitted pursuant to foregoing
section within thirty (30) days after such termination and shall deliver written
notice to Tenant of such election within that time.

          4.32.3 In the event Landlord elects to retain the Wiring as provided
above, Tenant covenants that Tenant shall be the sole owner of such Wiring,
Tenant shall have the right to surrender such Wiring and the Wiring shall be
free of all liens and encumbrances and all Wiring shall be left in good
condition and working order; to the extent reasonably possible, properly labeled
at each end and in each telecommunication junction box or electrical closet and
in safe condition.

          4.32.4 The provisions of this Section shall survive the expiration or
sooner termination of this Lease.

     4.33 Backup Generator. Subject to the provisions of this Lease, including
          ----------------
without limit, Subsections 2.6.3, Tenant shall have the right to install and
operate an emergency electrical generator and related equipment including,
without limit, transfer switches, panels and wiring (collectively, the
"Generator").
 ---------

          4.33.1 The Generator shall be placed in a location in the Building or
on the Land to be designated by Tenant, and approved by Landlord in its
reasonable discretion. The amount of space to be occupied by the Generator shall
not exceed 542 square feet. The area in which the Generator is located shall be
subject to all of the provisions of the Lease as if it were located within the
Premises.

                                       54
<PAGE>

          4.33.2 Tenant may install, maintain and use the Generator only if the
Premises are occupied by Tenant or an approved subtenant or assignee. The
Generator shall be used only solely for the business of Tenant in the event the
primary electrical service to the Premises is interrupted and shall not be used
for the benefit of any other subtenant, licensee, assignee or other occupant of
the Building without Landlord's consent, which consent shall not be unreasonably
withheld, conditioned or delayed.

          4.33.3 Tenant's right to install or modify the Generator is
conditioned upon Landlord's prior written approval of any equipment to be
installed which approval shall not be unreasonably withheld, conditioned or
delayed. Tenant shall provide Landlord a written description of such equipment,
including make, model, size and capacity. Any changes in the equipment shall be
subject to Landlord's prior approval which approval shall not be unreasonably
withheld, conditioned or delayed.

          4.33.4 Tenant will allow Landlord's designee to be present (at
Tenant's expense) during the installation of the Generator. Tenant will not make
any repairs or alterations to the Generator without obtaining Landlord's prior
written consent (not to be unreasonably withheld, conditioned or delayed) and
Landlord shall have the right to disapprove any installation or alteration or
require Tenant to remove the Generator in the event such installation or
alteration may void or adversely affect any warranty affecting the Building's
systems including, without limit, the roof.

          4.33.5 Tenant at its sole expense shall comply with all Governmental
Requirements and the requirements of Landlord's insurer with respect to the
installation, repair, maintenance or operation of the Generator including all
ancillary equipment. Tenant shall at its expense obtain all permits, variances
and licenses required by Governmental Requirements relating to the Generator and
shall deliver copies to Landlord.

          4.33.6 Tenant's use of the area in which the Generator is located, if
such site is not within the Premises, shall be nonexclusive and Landlord may
allow others to use such area. Landlord shall have the right, but not the
obligation, to enter the area where the Generator is located at any time in the
event of an emergency and at all other reasonable times upon reasonable notice
for the purpose of inspecting the Generator, making repairs or exhibiting the
Building.

          4.33.7 Landlord may from time to time require Tenant to relocate the
Generator to another site to be determined by Landlord in its sole but
reasonable discretion. In such event, Tenant's means of access to the Generator
and related cabling will be relocated at Landlord's expense in a manner so as
not to unreasonably impair the availability of the Generator as a backup power
source. If Landlord elects to relocate the Generator, the costs shall be borne
by Landlord unless such relocation is required by Governmental Requirements. In
the event Landlord elects to relocate the

                                       55
<PAGE>

Generator, Tenant shall be entitled to at least thirty (30) days written notice,
except in an emergency.

          4.33.8  The installation, use and maintenance of the Generator shall
not, in Landlord's reasonable judgment, adversely affect the use of the
Building's common areas, systems or machinery or of any other space used by
Landlord or any other Tenant in the Building.

          4.33.9  Tenant shall maintain the generator and pay the costs of all
utilities services required for Tenant's use of the Generator.

          4.33.10 The purchase, installation, repair, maintenance and operation
of the Generator will be at Tenant's sole risk, cost and expense. Landlord or
Landlord's Agents shall not be liable for any costs or expenses caused in any
manner by such purchase, installation, repair, maintenance and operation except
to the extent caused by Landlord's gross negligence or willful misconduct.
Tenant shall promptly repair at its expense all damage caused by or resulting
from the installation, maintenance, repair or operation of the Generator.

          4.33.11 Upon the expiration or earlier termination of this Lease, if
Landlord so directs by ten (10) days written notice to Tenant, Tenant shall
remove the Generator at its sole expense and shall repair any damage to the
Building or the Premises caused by or resulting from such removal.

                        SECTION 5: DEFAULT AND REMEDIES
                        -------------------------------

     5.1  Events of Default.
          -----------------

          5.1.1   The occurrence of any one or more of the following events
shall constitute a material default and breach of this Lease by Tenant ("Event
                                                                         -----
of Default"):
----------

                  (a)  vacation or abandonment of all or any portion of the
Premises,

                  (b)  failure by Tenant to make any payment of Base Rent,
Additional Rent or any other sum payable by Tenant under this Lease within five
(5) Business Days after its due date;

                  (c)  failure by Tenant to observe or perform any covenant or
condition of this Lease, other than the making of payments, where such failure
shall continue for a period of ten (10) Business Days after written notice from
Landlord provided, however, that if such failure is not reasonably capable of
being cured within such period, then the period within which such failure maybe
cured shall be extended to

                                       56
<PAGE>

a total of forty (40) days provided the Tenant promptly commences and diligently
pursues the cure of such failure;

               (d)  (1) the making by Tenant of any general assignment or
general arrangement for the benefit of creditors; (2) the filing by or against
Tenant of a petition in bankruptcy, including reorganization or arrangement,
unless, in the case of a petition filed against Tenant, unless the same is
dismissed within twenty (20) Business Days; (3) the appointment of a trustee or
receiver to take possession of substantially all of Tenant's assets located in
the Premises or of Tenant's interest in this Lease; (4) any execution, levy,
attachment or other process of law against any property of Tenant or Tenant's
interest in this Lease, unless the same is dismissed within twenty (20) Business
Days; (5) adjudication that Tenant is bankrupt; (6) the making by Tenant of a
transfer in fraud of creditors; or (7) the failure of Tenant to generally pay
its debts as they become due; or

               (e)  any information furnished by or on behalf of Tenant to
Landlord in connection with the entry of this Lease is determined to have been
materially false, misleading or incomplete when made.

       5.1.2   Tenant shall notify Landlord promptly if Tenant becomes aware of
any Event of Default or any facts, conditions or events that, with the giving of
notice or passage of time or both, would constitute an Event of Default.

       5.1.3   If a petition in bankruptcy is filed by or against Tenant, and if
this Lease is treated as an "unexpired lease" under applicable bankruptcy law in
such proceeding, then Tenant agrees that Tenant shall not attempt nor cause any
trustee to attempt to extend the applicable time period within which this Lease
must be assumed or rejected.

     5.2  Remedies. If any Event of Default occurs, Landlord may at any time
          --------
after such occurrence, with or without notice or demand except as stated in this
section, and without limiting Landlord in the exercise of any right or remedy at
law which Landlord may have by reason of such Event of Default, exercise the
rights and remedies, either singularly or in combination, as are specified or
described in the subparagraphs of this section.

          5.2.1 Landlord may terminate this Lease and all rights of Tenant under
this Lease either immediately or at some later date by giving Tenant written
notice that this Lease is terminated. If Landlord so terminates this Lease, then
Landlord may recover from Tenant the sum of:

                (a) the unpaid Base Rent, Additional Rent and all other sums
payable under this Lease which have been earned at the time of termination;

                                       57
<PAGE>

               (b)  interest at the Default Rate on the unpaid Base Rent,
Additional Rent and all other sums payable under this Lease which have been
earned at the time of termination, plus

               (c)  the amount by which the unpaid Base Rent, Additional Rent
and all other sums payable under this Lease which would have been earned after
termination until the time of award exceeds the amount of such rental loss, if
any, as Tenant affirmatively proves could have been reasonably avoided and
interest on such excess at the Default Rate; plus

               (d)  the amount by which the aggregate of the unpaid Base Rent,
Additional Rent and all other sums payable under this Lease for the balance of
the Lease Term after the time of award exceeds the amount of such rental loss,
if any, as Tenant affirmatively proves could be reasonably avoided, with such
difference being discounted to present value at the Prime Rate at the time of
award; plus

               (e)  any other amount necessary to compensate Landlord for the
detriment proximately caused by Tenant's failure to perform Tenant's obligations
under this Lease or which, in the ordinary course of things, would be likely to
result from such failure, including, leasing commissions, tenant improvement
costs, renovation costs and advertising costs; plus

               (f)  all such other amounts in addition to or in lieu of the
foregoing as may be permitted from time to time by applicable law.

         5.2.2 Landlord shall also have the right, with or without terminating
this Lease, to reenter the Premises and remove all persons and property from the
Premises. Landlord may cause property so removed from the Premises to be stored
in a public warehouse or elsewhere at the expense and for the account of Tenant.

         5.2.3 Landlord shall also have the right, without terminating this
Lease, to accelerate and recover from Tenant the sum of all unpaid Base Rent,
Additional Rent and all other sums payable under the then remaining term of the
Lease, discounting such amount to present value at the Prime Rate.

         5.2.4 If Tenant vacates, abandons or surrenders the Premises without
Landlord's consent, or if Landlord re-enters the Premises as provided in
subparagraph 5.2.2 or takes possession of the Premises pursuant to legal
proceedings or through any notice procedure provided by law, then, if Landlord
does not elect to terminate this Lease, Landlord may, from time to time, without
terminating this Lease, either: (a) recover all Base Rent, Additional Rent and
all other sums payable under this Lease as they become due; or (b) relet the
Premises or any part of the Premises on behalf of Tenant for such term or terms,
at such rent or rents and pursuant to such other provisions as Landlord, in its
sole discretion, may deem advisable, all with the right, at Tenant's cost, to
make alterations and repairs to the Premises and recover any deficiency from
Tenant as set forth in subparagraph 5.2.6.

                                       58
<PAGE>

          5.2.5 None of the following remedial actions, singly or in
combination, shall be construed as an election by Landlord to terminate this
Lease unless Landlord has in fact given Tenant written notice that this Lease is
terminated: an act by Landlord to maintain or preserve the Premises; any efforts
by Landlord to relet the Premises; any repairs or alterations made by Landlord
to the Premises, re-entry; repossession or reletting of the Premises by Landlord
pursuant to this section; or the appointment of a receiver, upon the initiative
of Landlord, to protect Landlord's interest under this Lease. If Landlord takes
any of the foregoing remedial action without terminating this Lease, Landlord
may nevertheless at any time after taking any such remedial action terminate
this Lease by written notice to Tenant.

          5.2.6 If Landlord relets the Premises, Landlord shall apply the
revenue from such reletting as follows: first, to the payment of any
                                        -----
indebtedness of Tenant to Landlord other than Base Rent, Additional Rent or any
other sums payable by Tenant under this Lease; second, to the payment of any
                                               ------
cost of reletting (including finders' fees and leasing commissions) as limited
in subparagraph 5.2.1(e), third, to the payment of the cost of any alterations,
                          -----
improvements, maintenance and repairs to the Premises, as limited in
subparagraph 5.2.1(e); and fourth, to the payment of Base Rent, Additional
                           -------
Rent and other sums due and payable and unpaid under this Lease. Landlord shall
hold and apply the residue, if any, to payment of future Base Rent, Additional
Rent and other sums payable under this Lease as the same become due, and shall
deliver the eventual balance, if any, to Tenant. Should revenue from letting
during any month, after application pursuant to the foregoing provisions, be
less than the sum of the Base Rent, Additional Rent and other sums payable under
this Lease and Landlord's expenditures for the Premises during such month,
Tenant shall be obligated to pay such deficiency to Landlord as and when such
deficiency arises.

          5.2.7 Pursuit of any of the foregoing remedies shall not preclude
pursuit of any of the other remedies provided in this Lease or by law (all such
remedies being cumulative), nor shall pursuit of any remedy provided in this
Lease constitute a forfeiture or waiver of any Base Rent, Additional Rent or
other sum payable under this Lease or of any damages accruing to Landlord by
reason of the violation of any of the covenants or conditions contained in this
Lease.

     5.3  Right to Perform. If Tenant shall fail to pay any sum of money, other
          ----------------
than Base Rent or Additional Rent, required to be paid by it under this Lease or
shall fail to perform any other act on its part to be performed under this
Lease, and such failure shall continue for ten (10) Business Days after notice
of such failure by Landlord, or such shorter time if reasonable under the
circumstances, Landlord may, but shall not be obligated to, and without waiving
or releasing Tenant from any obligations of Tenant, make such payment or perform
such other act on Tenant's part to be made or performed as provided in this
Lease. Landlord shall have (in addition to any other right or remedy of
Landlord) the same rights and remedies in the event of the nonpayment of sums
due under this section as in the case of default by Tenant in the payment of
Base Rent.

                                       59
<PAGE>

     5.4  Landlord's Default. Landlord shall not be in default under this Lease
          ------------------
unless Landlord fails to perform obligations required of Landlord within twenty
(20) Business Days after written notice is delivered by Tenant to Landlord and
to the holder of any mortgages or deeds of trust (collectively, "Lender")
                                                                 ------
covering the Premises whose name and address shall have theretofore been
furnished to Tenant in writing, specifying the obligation which Landlord has
failed to perform; provided, however, that if the nature of Landlord's
obligation is such that more than twenty (20) Business Days are required for
performance, then Landlord shall not be in default if Landlord or Lender
commences performance within such twenty (20) Business Day period and thereafter
diligently prosecutes the same to completion. All obligations of Landlord
hereunder shall be construed as covenants, not conditions. In the event of any
default, breach or violation of Tenant's rights under this Lease by Landlord,
Tenant's exclusive remedy shall be either an action for specific performance or
an action for actual damages. Tenant hereby waives the benefit of any laws
granting it the right to perform Landlord's obligation, a lien upon the property
of Landlord and/or upon Rent due Landlord, or the right to terminate this Lease
or withhold Rent on account of any Landlord default.

                      SECTION 6: MISCELLANEOUS PROVISIONS
                      -----------------------------------

     6.1  Notices. Any notice, request, approval, consent or written
          -------
communication required or permitted to be delivered under this Lease shall be:
(a) in writing; (b) transmitted by personal delivery, express or courier
service, United States Postal Service in the manner described below, or
electronic means of transmitting written material; and (c) deemed to be
delivered on the earlier of the date received or four (4) Business Days after
having been deposited in the United States Postal Service, postage prepaid. Such
writings shall be addressed to Landlord or Tenant, as the case may be, at the
respective designated addresses set forth opposite their signatures, or at such
other address(es) as they may, after the execution date of this Lease, specify
by written notice delivered in accordance with this section, with copies to the
persons at the addresses, if any, designated opposite each party's signature.
Those notices which contain a notice of breach or default or a demand for
performance may be sent by any of the methods described in clause (b) above, but
if transmitted by personal delivery or electronic means, shall also be sent
concurrently by certified or registered mail, return receipt requested.

     6.2  Attorney's Fees and Expenses. In the event either party requires the
          ----------------------------
services of an attorney in connection with enforcing the terms of this Lease, or
in the event suit is brought for the recovery of Base Rent, Additional Rent or
any other sums payable under this Lease or for the breach of any covenant or
condition of this Lease, or for the restitution of the Premises to Landlord or
the eviction of Tenant during the Lease Term or after the expiration or earlier
termination of this Lease, the non-breaching party shall be entitled to a
reasonable sum for attorney's and paralegal's fees, expenses and court costs,
including those relating to any appeal.

                                       60
<PAGE>

     6.3  No Accord and Satisfaction. No payment by Tenant or receipt by
          --------------------------
Landlord of an amount less than the Base Rent or Additional Rent or any other
sum due and payable under this Lease shall be deemed to be other than a payment
on account of the Base Rent, Additional Rent or other such sum, nor shall any
endorsement or statement on any check or any letter accompanying any check or
payment be deemed an accord and satisfaction, nor preclude Landlord's right to
recover the balance of any amount payable or Landlord's right to pursue any
other remedy provided in this Lease or at law.

     6.4  Successors, Joint and Several Liability. Except as provided in the
          ---------------------------------------
section captioned "Exculpation and Limitation of Liability" and subject to the
section captioned "Assignment and Subletting by Landlord", all of the covenants
and conditions contained in this Lease shall apply to and be binding upon
Landlord and Tenant and their respective heirs, executors, administrators,
successors and assigns. In the event that more than one person, partnership,
company, corporation or other entity is included in the term "Tenant", then each
such person, partnership, company, corporation or other entity shall be jointly
and severally liable for all obligations of Tenant under this Lease.

     6.5  Choice of Law. This Lease shall be construed and governed by the laws
          -------------
of the state in which the Land is located. Tenant consents to Landlord's choice
of venue for any legal proceeding brought by Landlord or Tenant to enforce the
terms of this Lease.

     6.6  No Waiver of Remedies. The waiver by Landlord of any covenant or
          ---------------------
condition contained in this Lease shall not be deemed to be a waiver of any
subsequent breach of such covenant or condition nor shall any custom or practice
which may develop between the parties in the administration of this Lease be
construed to waive or lessen the rights of Landlord to insist on the strict
performance by Tenant of all of the covenants and conditions of this Lease. No
act or thing done by Landlord or Landlord's Agents during the Lease Term shall
be deemed an acceptance or a surrender of the Premises, and no agreement to
accept a surrender of the Premises shall be valid unless made in writing and
signed by Landlord. The mention in this Lease of any particular remedy shall not
preclude Landlord from any other remedy it might have, either under this Lease
or at law, nor shall the waiver of or redress for any violation of any covenant
or condition in this Lease or in any of the rules or regulations attached to
this Lease or later adopted by Landlord, prevent a subsequent act, which would
have originally constituted a violation, from having all the force and effect of
an original violation. The receipt by Landlord of Base Rent, Additional Rent or
any other sum payable under this Lease with knowledge of a breach of any
covenant or condition in this Lease shall not be deemed a waiver of such breach.
The failure of Landlord to enforce any of the rules and regulations attached to
this Lease or later adopted, against Tenant or any other tenant in the Building,
shall not be deemed a waiver. Any waiver by Landlord must be in writing and
signed by Landlord to be effective.

                                       61
<PAGE>

     6.7  Offer to Lease. The submission of this Lease to Tenant or its broker
          --------------
or other agent does not constitute an offer to Tenant to lease the Premises.
This Lease shall have no force or effect until: (a) it is executed and delivered
by Tenant to Landlord; and (b ) it is executed and delivered by Landlord to
Tenant.

     6.8  Force Majeure. In the event that Landlord or Tenant shall be delayed,
          -------------
hindered in or prevented from the performance of any act or obligation required
under this Lease (except, with respect to Tenant, its obligations to pay any
sums due to Landlord) by reason of acts of God, strikes, lockouts, labor
troubles or disputes, inability to procure or shortage of materials or labor,
failure of power or utilities, delay in transportation, fire, vandalism,
accident, flood, severe weather, other casualty, Governmental Requirements
(including mandated changes in the Plans and Specifications or the Tenant
Improvements resulting from changes in pertinent Governmental Requirements or
interpretations thereof), delay in obtaining insurance reimbursements (provided
that Landlord uses commercially reasonable efforts to diligently pursue such
reimbursements), riot, insurrection, civil commotion, sabotage, explosion, war,
natural or local emergency, acts or omissions of others, including Tenant or
Landlord (as applicable), or other reasons of a similar or dissimilar nature not
solely the fault of, or under the exclusive control of, Landlord (or Tenant, as
applicable), then performance of such act or obligation (except, with respect to
Tenant, its obligations to pay any sums due to Landlord) shall be excused for
the period of the delay and the period for the performance of any such act or
obligation shall be extended for the period equivalent to the period of such
delay. Notwithstanding the foregoing provisions of this Section 6.8, in no event
will an event of Force Majeure extend the time within which Tenant must complete
its construction obligations under Exhibit C of this Lease unless otherwise
                                   ---------
specifically provided in Exhibit C.
                         ---------

     6.9  Landlord's Consent. Unless otherwise provided in this Lease, whenever
          ------------------
Landlord's consent, approval or other action is required under the terms of this
Lease, such consent, approval or action shall be subject to Landlord's judgment
or discretion exercised in good faith and shall be delivered in writing.

     6.10 Severability; Captions. If any clause or provision of this Lease is
          ----------------------
determined to be illegal, invalid, or unenforceable under present or future
laws, the remainder of this Lease shall not be affected by such determination,
and in lieu of each clause or provision that is determined to be illegal,
invalid or unenforceable, there be added as a part of this Lease a clause or
provision as similar in terms to such illegal, invalid or unenforceable clause
or provision as may be possible and be legal, valid and enforceable. Headings or
captions in this Lease are added as a matter of convenience only and in no way
define, limit or otherwise affect the construction or interpretation of this
Lease.

     6.11 Interpretation. Whenever a provision of this Lease uses the term (a)
          --------------
"include" or "including", that term shall not be limiting but shall be construed
as illustrative, (b) "covenant", that term shall include any covenant,
agreement, term or

                                       62
<PAGE>

provision, (c) "at law", that term shall mean at law or in equity, or both, and
(d) "day", that uncapitalized word shall mean a calendar day. This Lease shall
be given a fair and reasonable interpretation of the words contained in it
without any weight being given to whether a provision was drafted by one party
or its counsel.

     6.12 Incorporation of Prior Agreement; Amendments. This Lease contains all
          --------------------------------------------
of the agreements of the parties to this Lease with respect to any matter
covered or mentioned in this Lease, and no prior agreement or understanding
pertaining to any such matter shall be effective for any purpose. No provision
of this Lease may be amended or added to except by an agreement in writing
signed by the parties to this Lease or their respective successors in interest.

     6.13 Authority. If Tenant is a partnership, company, corporation or other
          ---------
entity, each individual executing this Lease on behalf of Tenant represents and
warrants to Landlord that he or she is duly authorized to so execute and deliver
this Lease and that all partnership, company, corporation or other entity
actions and consents required for execution of this Lease have been given,
granted or obtained. If Tenant is a partnership, company, corporation or other
business organization, it shall, within ten (10) Business Days after demand by
Landlord, deliver to Landlord satisfactory evidence of the due authorization of
this Lease and the authority of the person executing this Lease on its behalf.

     6.14 Time of Essence. Time is of the essence with respect to the
          ----------------
performance of every covenant and condition of this Lease.

     6.15 Survival of Obligations. Notwithstanding anything contained in this
          -----------------------
Lease to the contrary or the expiration or earlier termination of this Lease,
any and all obligations of either party accruing prior to the expiration or
termination of this Lease shall survive the expiration or earlier termination of
this Lease, and either party shall promptly perform all such obligations whether
or not this Lease has expired or terminated. Such obligations shall include any
and all indemnity obligations set forth in this Lease.

     6.16 Consent to Service. Tenant irrevocably consents to the service of
          ------------------
process of any action or proceeding at the address of the Premises or to such
other address as Tenant may in writing designate to Landlord. Nothing in this
section shall affect the right to serve process in any other manner permitted by
law.

     6.17 Landlord's Authorized Agents. Notwithstanding anything contained in
          ----------------------------
the Lease to the contrary, including without limitation, the definition of
Landlord's Agents, only officers of Riggs Bank N.A., are authorized to amend,
renew or terminate this Lease, or to compromise any of Landlord's claims under
this Lease or to bind Landlord in any manner. Without limiting the effect of the
previous sentence, no property manager or broker shall be considered an
authorized agent of Landlord to amend, renew or terminate this Lease or to
compromise any of Landlord's claims under this Lease or to bind Landlord in any
manner.

                                       63
<PAGE>

     6.18 Waiver of Jury Trial. LANDLORD AND TENANT AGREE TO WAIVE TRIAL BY JURY
          --------------------
IN ANY ACTION, PROCEEDING OR COUNTERCLAIM BROUGHT BY EITHER AGAINST THE OTHER ON
ANY MATTER ARISING OUT OF OR RELATING IN ANY WAY TO THIS LEASE.

     6.19 Option to Extend Term.
          ---------------------

          6.19.1 Extension Option: Tenant shall have and is hereby granted two
                 ----------------
(2) options (the "Extension Options") to extend the Lease Term for two (2)
                  -----------------
periods of five (5) additional Lease Years each (the "Extension Periods")
                                                      -----------------
provided (i) Tenant gives written notice to Landlord of its election to exercise
the Extension Option no later than sixteen (16) months prior to the Termination
Date of the initial Lease Term or the first Extension Option, as applicable,
(ii) as of the exercise of the Extension Option no uncured Event of Default
exists and no condition shall then exist, which is an Event of Default or which
after notice and/or the passage of time would constitute an Event of Default if
not cured within the applicable period and no monetary default shall arise
subsequent to the exercise of the Extension Option, and (iii) Tenant elects to
extend the Lease Term for no less than three (3) full floors of the Building.

          6.19.2 Terms of Extension: All terms and conditions of this Lease,
                 ------------------
shall remain in full force and effect during the Extension Period, except that
the Base Rent and Additional Rent payable during the Extension Period shall be
the then Current Market Rental Rate as of the commencement of the Extension
Period, as such rate is defined pursuant to this section, provided that such
amount as so calculated shall not be less than the Base Rent and Additional Rent
for the Premises which is in effect for the calendar month immediately prior to
the commencement of the Extension Period.

          6.19.3 Current Market Rental Rate:
                 --------------------------

                 (a) The "Current Market Rental Rate" for purposes of this
                          --------------------------
section shall mean the current market rent as of the relevant date for a
renewing tenant with space in excess of twenty-five thousand (25,000) square
feet in comparable class A buildings of the same quality, size and level of
finish within a ten (10) mile radius of the Building, taking into account all
relevant factors including, without limit, the size of the Tenant's space; the
term of the Lease; types and amounts of escalations and rent steps; base year
and passthrough of real estate taxes and operating expenses; the building's age,
condition and use and giving consideration to any free rent periods, retrofit
allowances or other concessions.

                 (b) Within ten (10) days after receipt of Tenant's notice of
its election to exercise the Extension Option, Landlord shall provide Tenant
with Landlord's good faith determination of the Current Market Rental Rate
("Landlord's Extension Rent Notice"). In the event Tenant agrees with Landlord's
  --------------------------------
determination of such Rate, Tenant shall so notify Landlord within fifteen (1 5)
days after Tenant's receipt of

                                       64
<PAGE>

Landlord's Extension Rent Notice and the parties shall be bound by the
Landlord's determination of such Rate.

                   (c) In the event Tenant does not agree with Landlord's
determination of the Current Market Rental Rate within the fifteen (15) day
period provided in this section, the relevant Current Market Rental Rate shall
be determined by a board of three (3) licensed real estate brokers, one of whom
shall be named by Landlord, one by Tenant, and the third selected by the two so
appointed. Each member of the board of brokers shall be licensed in Maryland as
a real estate broker, specializing in the field of commercial office leasing in
the Prince George's County, having no less than ten (10) years' experience in
such field, and recognized as ethical and reputable within the field. Landlord
and Tenant shall each make their appointments within five (5) days after the
expiration of the fifteen (15) day period and shall notify the other of their
choices within such time. If either party fails to select a broker within such
time, the broker selected by the other party shall establish the Current Market
Rental Rate. The two brokers selected by Landlord and Tenant shall promptly
select a third broker within ten (10) days after they both have been appointed.
If the brokers selected by the parties fail to select a third broker within such
time, the parties may select such third broker or either party may request such
appointment be made by the American Arbitration Association ("AAA") pursuant to
its Commercial Arbitration Rules. Within fifteen (15) days after the third
broker is selected, each broker shall submit to the parties in writing his or
her determination of the Current Market Rental Rate. The Current Market Rental
Rate shall be the average of the two (2) closest rental rate determinations and
the parties shall be bound by such decision. Landlord and Tenant shall each pay
the fee of the broker selected by it, and shall equally share the payment of the
fee of the third broker and, if applicable, the AAA.

          6.19.4   Lease Addendum:
                   --------------

                   (a) Within twenty (20) days following the date that the Base
Rent and Additional Rent is established for the Extension Period, Landlord and
Tenant shall execute an Addendum to this Lease reflecting the extension and the
new Base Rent and Additional Rent. Failure of the parties to execute such
Addendum shall not affect the commencement of the Extension Term or Tenant's
obligation to pay Rent during that term at the rate established pursuant to this
section.

                   (b) In the event the final determination of the Current
Market Rental Rate shall not be made on or before the first day of the Extension
Period in accordance with the provisions of this Section, pending such final
determination, Tenant shall continue to pay, as the Base Rent and Additional
Rent the same Base Rent and Additional Rent then payable by Tenant on the
Termination Date of the original Term. If, based upon the final determination of
the brokers or the agreement of the parties, such payments made by Tenant on
account of Base Rent and Additional Rent for such portion of the Extension
Period differ from the Base Rent and Additional

                                       65
<PAGE>

Rent which should have been paid by Tenant during that portion of the Extension
Period, the parties shall promptly adjust such amount by a cash payment.

     6.20 First Right of Offer. Provided no uncured Event of Default then exists
          --------------------
under this Lease, Tenant shall have a first right of offer on the leasing of all
of any building that Landlord may construct on that certain parcel of land
currently owned by The Washington Suburban Sanitary Commission ("WSSC") and
located on Sweitzer Lane just north of the Building (the "WSSC Site"), provided
                                                          ---------
that Landlord shall acquire the same. Landlord shall notify Tenant at such time
as Landlord elects to lease space in any building constructed by Landlord on the
WSSC Site. Tenant shall have ten (10) Business Days of receipt of such notice to
exercise its right to lease such space at the then Current Market Rental Rate as
determined pursuant to the section captioned "Current Market Rental Rate" and
                                              --------------------------
otherwise on all the terms and conditions of this Lease and an additional
fifteen (15) calendar days within which to execute such lease. If Tenant does
not exercise this First Right of Offer or execute such Lease within such times,
this First Right of Offer shall terminate.

     6.21 Termination Option. Tenant shall have and is hereby granted a one time
          ------------------
right to terminate this Lease to be effective at the end of the eighty-fourth
(84th) month after the Phase II Commencement Date (the "Termination Option
                                                        ------------------
Date"), provided (i) Tenant gives written notice to Landlord of its election to
----
terminate this Lease no later than fourteen (14) months prior to the Termination
Option Date (the "Termination Option Notice"), (ii) as of the receipt by
                  -------------------------
Landlord of the Termination Option Notice no uncured Event of Default exists and
no condition shall then exist, which is an Event of Default or which after
notice and/or the passage of time would constitute an Event of Default if not
cured within the applicable period and no monetary default shall arise
subsequent thereto, (iii) Tenant delivers to Landlord the Lease Termination Fee
with the delivery of the Termination Option Notice, and (iv) Tenant has not
subleased more than thirty thousand (30,000) square feet of rentable space.

                                       66
<PAGE>

     IN WITNESS WHEREOF, this Lease has been executed the day and year first
above set forth.

     Designated Address for Landlord:       LANDLORD:
     -------------------------------        --------

     c/o Riggs Trust Group                  RIGGS & COMPANY, a division of
     Attn: Patrick Mayberry                 Riggs Bank N.A., as Trustee of the
     808 17th Street, N.W.                  Multi-Employer property Trust, a
     Washington, DC 20006                   trust organized under 12 C.F.R.
     Facsimile: 202-835-6887                Section 9.18

                                            By: /s/ S. Kay Chase
                                               --------------------------
                                            Name: S. Kay Chase
                                                  -----------------------
                                            Its: Managing Director
                                                 ------------------------

     with a copy to Manager at:
     -------------------------
     Trammell Crow Real Estate
     Services, Inc.
     7315 Wisconsin Avenue
     Suite 300W
     Bethesda, Maryland 20814
     Attn: Dan Hudson

     Designated Address for Tenant:         TENANT:
     -----------------------------          ------

     ___________________________            DIGEX, INC., a Delaware Corporation
     ___________________________
     ___________________________
     Facsimile:______________________

                                            By: /s/ Timothy M Adams
                                                -------------------------
                                            Name: Timothy M Adams
                                                 ------------------------
                                            Its: CFO
                                                 ------------------------

                                       67
<PAGE>

                              EXHIBIT A to Lease

                           LEGAL DESCRIPTION OF LAND
                           -------------------------

All that certain lot or parcel of land, lying and being situate in Prince
George's County, Maryland and more particularly described as follows:

     BEING KNOWN AND DESIGNATED AS LOT 10, as shown on a Plat entitled "Lots 4
     thru 13 Maryland 95 Corporate Park", which Plat is recorded in Plat Book
     NLP 140, page 19, among the Land Records of Prince George's County,
     Maryland.

                                     Ex.A
                                       1
<PAGE>

                              EXHIBIT B to Lease

          LISTING OF PLANS AND SPECIFICATIONS FOR TENANT IMPROVEMENTS

                       LIST OF PHASE I CONTRACT DRAWINGS

1.   ARCHITECTURAL SHEETS by Greenwell Goetz Architects all dated 5/30/00
     --------------------------------------------------------------------
     Al       TITLE SHEET
     A2       STANDARDS AND SCHEDULES
     01-A4    FIRST FLOOR ARCHITECTURAL PLAN
     01-A4.1  ENLARGED ARCHITECTURAL PLAN
     01-A5    FIRST FLOOR ARCHITECTURAL REFLECTED CEILING PLAN
     01-A5.1  ENLARGED REFLECTED CEILING PLAN
     01-A6    FIRST FLOOR ARCHITECTURAL TELEPHONE & ELECTRIC PLAN
     01-A7    FIRST FLOOR FINISH WALL PLAN
     01-A8    FIRST FLOOR FINISH FLOOR PLAN
     02-A4    SECOND FLOOR ARCHITECTURAL PLAN
     02-A4.1  SECOND FLOOR ENLARGED ARCHITECTURAL PLAN
     02-A5    SECOND FLOOR ARCHITECTURAL REFLECTED CEILING PLAN
     02-A5.1  SECOND FLOOR ENLARGED REFLECTED CEILING PLAN
     02-A6    SECOND FLOOR ARCHITECTURAL TELEPHONE AND ELECTRICAL PLAN
     02-A7    SECOND FLOOR FINISH WALL PLAN
     02-A8    SECOND FLOOR FINISH FLOOR PLAN
     02-A9    SECOND FLOOR FURNITURE PLAN
     R-10     ROOF PLAN
     A20      FIRST FLOOR ELEVATIONS
     A21      SECOND FLOOR ELEVATIONS
     A24      MILLWORK ELEVATIONS
     A25      MILLWORK SECTIONS & DETAILS
     A27      DETAILS
     A28      CEILING DETAILS

2.   MECHANICAL SHEETS by Meta Engineers, P.C. all dated 5/30/00
     -----------------------------------------------------------

     TM-1     COVER SHEET - HVAC
     TM-2     FIRST FLOOR PLAN - HVAC
     TM-3     SECOND FLOOR PLAN - HVAC
     TM-4     DETAILS AND PART PLAN - HVAC
     TM-5     SCHEDULED AND RISER DIAGRAM-HVAC

3.   SUPPLEMENT to BASE BUILDING SPECIFICATIONS dated 5/30/00
     --------------------------------------------------------

4.   PLUMBING SHEETS by Meta Engineers, P.C. all dated 5/30/00
     ---------------------------------------------------------

     TP-1     COVER SHEET - PLUMBING AND FIRE PROTECTION
     TP-2     FIRST FLOOR PLAN - PLUMBING AND FIRE PROTECTION
     TP-3     SECOND FLOOR PLAN - PLUMBING AND FIRE PROTECTION
     TP-4     DETAILS AND RISER DIAGRAMS - PLUMBING

                                     Ex.B
                                       1
<PAGE>

5.   ELECTRICAL SHEETS by Meta Engineers, P.C. all dated 05/30/00
     ------------------------------------------------------------

     TE-1     COVER SHEET - ELECTRICAL
     TE-2     FIRST FLOOR LIGHTING PLAN - ELECTRICAL
     TE-3     FIRST FLOOR POWER PLAN - ELECTRICAL
     TE-4     SECOND FLOOR PLAN - ELECTRICAL
     TE-5     SECOND POWER FLOOR PLAN - ELECTRICAL
     TE-6     PANEL SCHEDULES - ELECTRICAL
     TE-7     PANEL SCHEDULES - ELECTRICAL
     TE-8     PANEL SCHEDULES - ELECTRICAL
     TE-9     RISER DIAGRAMS - ELECTRICAL
     TE-10    RISER DIAGRAMS, DETAILS & SCHEDULES - ELECTRICAL

                                     Ex.B
                                       2
<PAGE>

                              EXHIBIT C to Lease

                    WORK LETTER AND CONSTRUCTION AGREEMENT
                    --------------------------------------
                     (Landlord to Construct Improvements)

     1.   Tenant's Improvements.

     Except as set forth in this Work Letter and Construction Agreement (the
"Work Letter"), Tenant accepts the Premises and existing improvements therein in
their "as is" condition. Landlord shall furnish and install within the Premises
those items of general construction, but not personal property or trade fixtures
(the "Tenant Improvements"), shown on the plans and specifications attached to
      -------------------
this Lease as Exhibit B or, if the foregoing is not applicable, as finally
              ---------
approved by Landlord and Tenant, pursuant to Paragraph 2 below. All Tenant
Improvements shall be constructed pursuant to this Work Letter and shall be
performed by Landlord's Tenant Improvements General Contractor (defined below)
utilizing those subcontractors selected in accordance with this Work Letter. All
subcontractors shall satisfy those union labor requirements set forth in this
Work Letter and in the paragraph captioned "Tenant's Work Performance" of the
                                            -------------------------
Lease.

     2.   Plans and Specifications for Improvements.

          2.1  Tenant has retained Greenwell Goetz Architects as architects
("Tenant's Architect") and Meta Engineers as MEP engineers (together, the
"Design Professionals"). Landlord has approved the Design Professionals to
prepare the plans and specifications described hereinafter for the Tenant
Improvements. The plans and specifications shall be subject to Landlord's
approval, which approval shall not be unreasonably delayed, provided that such
plans and specifications comply with and satisfy requirements (i) through (iii)
set forth below in subparagraph 2.4.

          2.2  The parties have agreed that the construction of the Tenant
Improvements (the "Work") will proceed in two Phases. Phase I will consist of
the Work on floors one (1) and two (2) of the Building. Phase II will consist of
the Work on floors three (3) and four (4) of the Building.

          2.3  The Space Plan for Phase I has been approved by Landlord and such
approved plans are referred to in Exhibit B of the Lease.

               No later than June 21, 2000, Tenant shall cause Tenant's
Architect to furnish to Landlord for Landlord's approval space plans sufficient
to convey the architectural design of the third (3/rd/ ) and fourth (4/th/)
floors of the Premises (i.e., Phase II), including, without limitation, the
location of doors, partitions, electrical and telephone outlets, plumbing
fixtures, heavy floor loads and other special requirements. If required by
Landlord, Tenant's Architect shall consult with Landlord's engineer in preparing
the

                                     Ex.C
                                       1
<PAGE>

Phase II Space Plan, and incorporate Landlord's engineer's requirements for that
Space Plan. If Landlord fails to disapprove the Space Plan for Phase II within
the five (5) day period following Landlord's receipt of the Phase II Space Plan,
such Space Plan shall be deemed approved. If Landlord shall disapprove of any
portion of such Space Plan within such five (5) day period, Landlord shall
notify Tenant of the reasons therefor and of the revisions that are reasonably
required by Landlord. Tenant shall within five (5) days following receipt of
Landlord's notice submit to Landlord, for Landlord's approval, a redesign of the
Phase II Space Plan, incorporating the revisions required by Landlord. If
Landlord in good faith does not approve the redesign of that Space Plan within
five (5) days following Landlord's receipt of same, then Landlord may in its
reasonable discretion elect (a) to terminate this Lease or (b) designate as
Tenant Delay (as hereinafter defined) the period from the date of Tenant's
receipt of Landlord's rejection of such redesign until the date Landlord
approves a subsequent redesign.

               Within fifteen (15) days of submission of the Space Plan to the
Landlord for approval, Tenant shall deliver to Landlord a complete list of the
equipment that Tenant proposes to install initially and in the future within the
Premises (the "Equipment List") which shall include the following: the number
and location of computer, copiers, printers, telephones, faxes, UPS equipment,
back-up power supplies, servers, kitchen equipment, racks, telephone switch, LAN
equipment and any other heat generating equipment with the specifications and
cut sheets for these items which shall include the name of the manufacturer,
model number, dimensions, power requirements (voltage, phasing, full load
amperage, wafts, horsepower, etc.), heat generation (in BTU's), exhausting
requirements, grounding requirements and any other load that Tenant requires.

          2.4  Tenant shall cause Tenant's Architect to prepare from the
approved Space Plans, complete architectural and engineering plans, drawings and
specifications ("Plans") by May 31, 2000 with respect to Phase I and within
thirty (30) days after Landlord approves the Phase II Space Plan. The Plans for
both Phases shall (i) be compatible with the Building shell and with the design,
construction and equipment of the Building; (ii) comply with all applicable laws
and ordinances, and the rules and regulations of all governmental authorities
having jurisdiction; (iii) comply with all applicable insurance regulations;
(iv) be in a form sufficient for the permitting and the construction of the
Tenant Improvements shown thereon and (v) be consistent with the approved Space
Plans. Tenant shall submit the Plans of the relevant Phase for Landlord's
approval in the same manner as provided in Subparagraph 2.2 above for approval
by Landlord of Tenant's Phase II Space Plan. Landlord will have ten (10) days to
review such Plans. If Landlord fails to respond in ten (10) days after receipt
of the Plans from Tenant, the Plans will be deemed to have been approved by
Landlord. If Landlord requests modifications which are acceptable to Tenant,
within five (5) days after Tenant's receipt of Landlord's request, the Plans
shall be revised by Tenant's Architect to reflect the applicable changes. If
Tenant does not agree with Landlord's requested modifications, Landlord and
Tenant shall exercise good faith efforts to reach

                                     Ex.C
                                       2
<PAGE>

agreement on the Plans and the period from the date of Tenant's receipt of
Landlord's rejection of the redesigned plans until the date Landlord approves a
subsequent redesign shall be deemed Tenant Delay. If Landlord and Tenant are
unable to agree upon mutually acceptable Plans within five (5) days after the
delivery to Tenant of Landlord's request for modifications, then Landlord may in
its discretion terminate this Lease without liability to Tenant upon five (5)
business days notice during which time the Plans are not approved by Landlord
and Tenant.

               Within twenty-two (22) days after Landlord has received the Plans
for each Phase, Landlord will cause the Tenant Improvements General Contractor
to prepare and submit to Landlord, and Landlord will submit to Tenant, an
Initial Tenant Improvements Pricing Letter which will include in reasonable
detail the costs of permitting and construction of the Tenant Improvements for
the relevant Phase. Tenant will approve the Initial Tenant Improvements Pricing
Letter for such Phase within four (4) days of receipt or advise Landlord of
changes, if any which Tenant reasonably requires to be made to the Plans in
order to reduce such costs. Based on such changes, Landlord will cause the
Tenant Improvements General Contractor to prepare a Final Tenant Improvements
Pricing Letter for Tenant's approval, which approval shall not be unreasonably
withheld, conditioned or delayed. Landlord shall, within four (4) days of
receipt of Tenant's approval of the Final Tenants Improvement Pricing Letter
issue a Notice to Proceed ("NTP") to the Tenant Improvements General Contractor.
Any changes in the Plans for any Phase directed by Tenant after approval of the
Final Tenant Improvements Pricing Letter for such Phase or delays by Tenant in
approving the Final Tenant Improvements Pricing Letter shall be Tenant Delay.

               Concurrent with the completion and delivery to Landlord of the
Plans for either Phase, Tenant shall provide to Landlord four (4) sets of
architectural and engineering plans signed and sealed by professionals licensed
in the State of Maryland (the "Permit Documents") for permit submission.
Landlord will promptly submit the Permit Documents to the local government
authorities no later than two (2) Business Days after receipt of the Permit
Documents. If the government authorities do not accept the Permit Documents due
to delay, error or omission on the part of the Design Professionals, the period
between the date that the Permit Documents were so rejected and the date the
Permit Documents are resubmitted to the governmental authorities will constitute
a Tenant Delay. However, if the Building Permit is still obtained within twenty-
eight (28) days following Landlord's first receipt of the Permit Documents, no
actual Tenant Delay will be incurred as a result of such rejection and delay by
the local government authorities.

               If the Building Permit for either Phase is not obtained within
twenty-eight (28) days from its submission to the local government authority
having jurisdiction, there will be a day-for-day extension to Landlord's
required Substantial Completion Date for such Phase for each day beyond such
twenty-eight (28) day period that the Permit is delayed except that if such
delay is due to Tenant Delay, the extension of time

                                     Ex.C
                                       3
<PAGE>

provided pursuant to this paragraph shall not impair or affect Landlord's rights
under Section 5.4 of this Exhibit C entitled "Effect of Tenant Delay."
                          ---------

          In the event there is a conflict between the following charts and the
times set forth in the preceding provisions of Paragraphs 2.3 and 2.4 of this
Exhibit C relating to the times for the approval or processing of documents, the
times set forth in the following charts shall control.

          The schedule for approval and preparation of Documents as described in
Paragraphs 2.3 and 2.4 above may be summarized as follows:

<TABLE>
<CAPTION>
---------------------------------------------------------------------------------------------------------------------
Phase I                                  Required Completion Date              Responsible Party
---------------------------------------------------------------------------------------------------------------------
<S>                                      <C>                                   <C>
Space Plan Completed                     Done                                  Tenant
---------------------------------------------------------------------------------------------------------------------
Equipment List provided to Landlord      Done                                  Tenant
---------------------------------------------------------------------------------------------------------------------
Space Plan approved by Landlord          Done                                  Landlord
---------------------------------------------------------------------------------------------------------------------
Phase I Plans                            Done                                  Tenant
---------------------------------------------------------------------------------------------------------------------
Landlord approves/comments to Phase I    Done                                  Landlord
Plans
---------------------------------------------------------------------------------------------------------------------
Permit Documents                         Done                                  Tenant
---------------------------------------------------------------------------------------------------------------------
Apply for Building Permit                Done                                  Landlord
---------------------------------------------------------------------------------------------------------------------
Obtain Building Permit                   28 days after application for         Landlord
                                         permit is filed
---------------------------------------------------------------------------------------------------------------------
Prepare Cost Estimate                    Done                                  Landlord
---------------------------------------------------------------------------------------------------------------------
Tenant Approval of Initial TI Pricing    4 days after receipt of estimate      Tenant
Letter
---------------------------------------------------------------------------------------------------------------------
Issue NTP to start construction          2 Business Days after Tenant          Landlord
                                         Approves Final TI Pricing Letter
---------------------------------------------------------------------------------------------------------------------
Substantial Completion of Phase I        98 days after NTP                     Landlord
---------------------------------------------------------------------------------------------------------------------
</TABLE>

                                     Ex. C

                                       4
<PAGE>

<TABLE>
<CAPTION>
---------------------------------------------------------------------------------------------------------------------
Phase II                                 Required Completion Date              Responsible Party
---------------------------------------------------------------------------------------------------------------------
<S>                                      <C>                                   <C>
Space Plan ("SP") completed              Done                                  Tenant
---------------------------------------------------------------------------------------------------------------------
Equipment List provided to Landlord      Done                                  Tenant
---------------------------------------------------------------------------------------------------------------------
Space Plans approved/commented           5 days after receipt of SP            Landlord
---------------------------------------------------------------------------------------------------------------------
Tenant Revise SP (if necessary)          5 days after receipt of LL comments   Tenant
---------------------------------------------------------------------------------------------------------------------
Revised SP approved/commented            5 days after receipt of revised SP    Landlord
---------------------------------------------------------------------------------------------------------------------
Phase II Plans                           30 days after approved SP             Tenant
---------------------------------------------------------------------------------------------------------------------
Landlord approves/comments to Phase II   10 days after receipt of Plans        Landlord
Plans
---------------------------------------------------------------------------------------------------------------------
Permit Documents                         30 days after approved SP
---------------------------------------------------------------------------------------------------------------------
Apply for Building Permit                2 Business Days after Landlord        Landlord
                                         receives Permit Documents
---------------------------------------------------------------------------------------------------------------------
Obtain Building Permit                   28 days after application for permit  Landlord
---------------------------------------------------------------------------------------------------------------------
Prepare Cost Estimate                    21 days after receipt of Phase II     Landlord
                                         Plans
---------------------------------------------------------------------------------------------------------------------
Tenant Approval of Initial TI Pricing    4 days after receipt of estimate      Tenant
Letter
---------------------------------------------------------------------------------------------------------------------
Issue NTP to start construction          2 Business Days after Tenant          Landlord
                                         Approval of Final TI Pricing Letter
---------------------------------------------------------------------------------------------------------------------
Substantial Completion of Phase II       98 days after issuance of NTP         Landlord
---------------------------------------------------------------------------------------------------------------------
</TABLE>

Landlord will not be required to issue a Notice to Proceed to the Tenant
Improvements General Contractor with respect to the construction of any Phase
until Landlord has approved the Plans for the relevant Phase in accordance with
this Paragraph 2.4.

          2.5  Tenant shall cause the Design Professionals to provide
documentation for all changes to the Plans at the time each change is authorized
for construction, pursuant to the requirements of Paragraph 4.9 of this Work
Letter. At the conclusion of construction, Tenant shall cause the Design
Professionals to update the Plans as necessary to reflect all changes approved
during the course of construction and to issue a set of sepias to the contractor
for its review and mark up. Tenant shall cause the Design Professional to review
and certify the contractor's marked up plans

                                     Ex. C

                                       5
<PAGE>

and provide to Landlord's designated construction representative a "record set"
of as-built sepias within thirty (30) days following completion of the Tenant
Improvements. Landlord shall have no liability to Tenant or to any other person
for errors or omissions in the Plans, Landlord's review being for Landlord's own
purposes. Tenant shall rely solely on the advice and experience of the Design
Professionals in assuring the accuracy and sufficiency of the Plans for Tenant's
purposes. The fees of the Design Professionals (plus fees for food service
design, acoustical engineers and other special consultants) shall be a Cost of
Tenant Improvements (as hereinafter defined).

     3.   Building Shell Changes.

     If the Plans or any amendment thereof or supplement thereto shall require
changes in the Building shell, the cost of the Building shell work caused by
such Plans, amendment or supplement, shall be charged against Tenant. The
preceding sentence shall not be construed as requiring that Landlord must
approve any Plans which specify changes in the Building shell. If Building shell
work is permitted by Landlord, the cost thereof shall include all architectural
and/or engineering fees and expenses in connection therewith, as well as
compensation to Landlord for the costs of any delays which arise from such
changes (which delays shall also constitute Tenant Delay).

     4.   Tenant Improvement Construction and Cost.

          4.1  Tenant Improvements General Contractor.
               --------------------------------------

               A.   James G. Davis Construction Corporation shall be retained by
Landlord as the General Contractor with respect to Tenant Improvement work (the
"Tenant Improvements General Contractor"). The subcontracting work shall be
awarded subject to bid, provided any subcontractor selected to perform work on
Tenant Improvements is a party to and is bound by a collective bargaining
agreement with a labor organization affiliated with the Building and
Construction Trades Council of the AFL-CIO and employs only members of such
labor organizations to perform work within their respective jurisdictions. In
addition, the successful bidders must be reputable and licensed and bonded for
performing such services in Prince George's County, Maryland. Landlord will
cause the Tenant Improvements General Contractor to use reasonable efforts to
obtain at least three (3) bids from qualified subcontractors located in the
Washington/Baltimore metropolitan area for any subcontractor work. The cost of
any payment or performance bonds shall be at Tenant's expense which may be paid
from the Tenant Improvement Allowance. The Tenant Improvements General
Contractor shall warrant its work with respect to both Phases for one full year
following Substantial Completion of the subject Phase.

               B.   Upon receipt of the Tenant Improvements General Contractor's
cost of construction, Landlord shall provide Tenant with a detailed breakdown of
the cost of furnishing and installing the Tenant Improvements, (the "Initial
                                                                     -------

                                     Ex. C

                                       6
<PAGE>

Tenant Improvements Pricing Letter" referred to in Paragraph 2.4 of this Exhibit
----------------------------------                                       -------
C) including, without limitation: the cost of constructing improvements; the
-
cost of preparing engineering plans; governmental agency plan check, permit and
other fees; sales and use taxes; all other costs to be expended by Tenant in the
construction of the Tenant Improvements; provisions for payment in favor of
Landlord in the event of contractors late delivery which payment shall not be
less than the penalties imposed upon Landlord for late delivery provided in
Section 2.4.4 of the Lease; and the Construction Manager's Fee described in
Paragraph 4.5 of this Exhibit C (collectively, the "Cost of Tenant
                      ---------                     --------------
Improvements"). The Cost of Tenant Improvements shall also include expenses and
------------
"soft costs" incurred by Tenant, such as the fees of the Design Professionals.
Tenant shall approve in writing the estimated Cost of Tenant Improvements within
five (5) days following its receipt of same. No construction of Tenant
Improvements shall commence until such approval is received by Landlord as
provided in Paragraph 2.4 of this Exhibit C. At Landlord's election, any delay
                                  ---------
by Tenant in giving such approval shall constitute Tenant Delay.

          4.2  Tenant Improvement Allowance. Landlord shall establish the Tenant
               ----------------------------
Improvement Allowance as set forth in the Lease, which shall be used by Landlord
solely for the design and installation of the Tenant Improvements. In the event
Tenant elects to require Landlord to provide the Above Standard Tenant
Improvement Allowance pursuant to Section 1.3 of the Lease, references to the
"Tenant Improvement Allowance" in this Work Letter shall be deemed to include
such additional amount. Tenant shall have the right to use the Tenant
Improvement Allowance for the Cost of Tenant Improvement. In no event shall the
Tenant Improvement Allowance be used to pay for costs of Tenant's furniture or
other personal property, which shall be paid for by Tenant at its sole cost and
expense. If the Cost of Tenant Improvements is less than the Tenant Improvement
Allowance, Landlord shall retain such excess portion of the Tenant Improvement
Allowance as its sole and separate property and Tenant shall have no rights or
claims to it whatsoever, nor shall Tenant be entitled to any credit as a result
of such excess. Notwithstanding anything to the contrary contained in this Work
Letter, if at any time Landlord determines in its reasonable judgment that the
Cost of Tenant Improvements will exceed the Tenant Improvement Allowance
("Excess Cost of Tenant Improvements"), Tenant shall deposit with Landlord, in
  ----------------------------------
cash, the amount of such Excess Cost of Tenant Improvements as provided in
Section 2.6 of the Lease, to be disbursed by Landlord following full
disbursement of the Tenant Improvement Allowance. The balance of any amount so
deposited which is not so applied, if any, shall be returned to Tenant, without
interest, following completion of, and full payment for, the Tenant
Improvements.

          4.3  Subsequent Increases in Costs. If the Cost of Tenant Improvements
               -----------------------------
increases due to the requirements of any governmental agency subsequent to
Landlord's approval of the bids pursuant to Paragraph 4.1, or for any other
reason other than Landlord's negligence or willful misconduct, such expense
shall be added to the Cost of Tenant Improvements or, if the Tenant Improvement
Allowance

                                     Ex. C

                                       7
<PAGE>

is insufficient, paid to Landlord by Tenant within twenty (20) days after
receipt of notice of such cost increases as provided in Paragraph 4.2 of this
Work Letter.

          4.4  Ownership of Tenant Improvements. Subject to the terms of
               --------------------------------
Section 2.6 of the Lease and Paragraph 4.7 of this Work Letter, all of the
Tenant Improvements, whether or not the cost thereof is covered by the Tenant
Improvement Allowance, shall become the property of Landlord upon expiration or
earlier termination of the Lease and shall remain on the Premises at all times
during the Term.

          4.5  Construction Management.  TC MidAtlantic Development Inc. shall
               -----------------------
be the Construction Manager with respect to construction of the Tenant
Improvements. If such company ceases to be the Construction Manager, Landlord
shall select a Construction Manager which is reasonably satisfactory to Tenant.
The Construction Manager's fee shall be paid by Landlord and deducted from the
Tenant Improvement Allowance.

          4.6  Costs of Tenant Improvements. Except for the Tenant Improvement
               ----------------------------
Allowance or as otherwise provided in the Lease or this Work Letter, Tenant
shall pay all costs associated with the Tenant Improvements including, without
limitation, all permits, inspection fees, fees of space planners, architects,
engineers, consultants, contractors, the costs of all labor and materials,
bonds, insurance and any structural or mechanical work, additional HVAC
equipment or modifications to any building, mechanical, electrical,
plumbing or other systems and equipment, either within or outside the Premises
required as a direct result of the layout, design or construction of the Tenant
Improvements and the cost of design and permitting and installation of Tenant's
fixtures, specialized equipment, systems, furniture and data and phone cabling
systems.

          Notwithstanding the foregoing provisions of this Paragraph 4.6, Tenant
shall not be liable for costs associated with the Tenant Improvements to the
extent such costs (including related increases in the Construction Manager's
Fee) may have been incurred or increased due to:

               (a)  The failure by Landlord to timely furnish or timely respond
to Tenant's Plans and Specifications, as and when required by this Work Letter,
or the failure of either of them to comply with the provisions of the Lease or
this Work Letter relating to the construction of the Tenant Improvements; or

               (b)  The negligence or willfully wrongful act of Landlord.

Costs of the Tenant Improvements payable from the Tenant Improvement Allowance
shall be advanced as provided in Paragraph 4.8. Costs of Tenant Improvements in
excess of the Tenant Improvement Allowance shall be paid as provided in
Paragraph 4.2.

                                     Ex. C

                                       8
<PAGE>

          4.7  Landlord Approvals. Landlord shall not unreasonably withhold,
               ------------------
condition or delay the approval of the Plans (or clarifications thereto) except
that Landlord may withhold its approval with regard to proposed Tenant
Improvements which (a) will have an adverse visible impact from the exterior of
the Building, or (b) will adversely affect the structure of the Building (as a
result of heavy loads or otherwise) or the electrical, heating, air
conditioning, ventilation, plumbing, fire protection, life safety or other
systems or equipment of the Building including the penthouse and the core. As a
condition of Landlord's approval of the proposed Tenant Improvements, Landlord
shall have the right to notify Tenant in writing at the time of such approval
that Tenant will be required upon termination or expiration of this Lease to
remove any specified Tenant Improvements constructed by the General Contractor
or Tenant's contractors if in Landlord's reasonable judgment such Tenant
Improvements are not customarily found in Class A office buildings in the
Laurel, Maryland submarket and removal of such items would subject Landlord to
unreasonable expense. If Tenant fails to remove such Tenant Improvements which
were installed subject to such condition, Landlord may do so and Tenant shall
pay Landlord the entire cost thereof within ten (10) Business Days after receipt
of Landlord's written demand therefor and this obligation shall survive the
termination or expiration of this Lease.

          4.8  Advances of Tenant Allowance. Payments with respect to the
               ----------------------------
Tenant Improvement Allowance or amounts deposited by Tenant with Landlord on
account of excess Cost of Tenant Improvements will be advanced by Landlord in
amounts approved in writing by Landlord no more frequently than monthly during
the planning and construction of the Tenant Improvements (a) to the Tenant
Improvements General Contractor, based upon written invoices and lien waivers
submitted on forms satisfactory to Landlord and (b) with respect to amounts paid
by Tenant to other parties, based on vouchers or written invoices submitted to
Landlord by Tenant accompanied by paid invoices, lien waivers and such
additional information as Landlord may reasonably request. Such invoices, lien
waivers and vouchers shall be submitted no later than thirty (30) days prior to
the monthly disbursement. Landlord shall reduce the Tenant Improvement Allowance
during the course of construction as costs which are eligible for application of
funds from the Tenant Improvement Allowance are incurred and advanced.

          4.9  Changes.
               -------

               4.9.1     Tenant may request a change, addition or alteration in
the Tenant Improvements as shown by the Plans after Landlord's final approval of
such Plans (a "Change Order") by delivery of a written request to Landlord for
its approval and for the Tenant Improvements General Contractor's determination
of (i) the increase in the cost of work to implement the Change Order, and (ii)
the estimated delay, if any, in the construction of the Tenant Improvements
occasioned by the Change Order. Tenant's architect shall complete all working
drawings necessary to show the change, addition or alteration, and a Change
Order in form satisfactory to Landlord. If Landlord approves the Change Order
and any delays in construction occasioned by the Change

                                     Ex. C

                                       9
<PAGE>

Order (which delays shall constitute Tenant Delay), Landlord shall deliver to
Tenant its written approval of the Change Order and authorization to proceed
with the work as shown by the Change Order, conditioned upon payment by Tenant
to Landlord, in advance and in full, of any cost increase occasioned thereby.
Landlord may decline any proposed Change Order if the change is inconsistent
with the provisions of any of paragraphs 1 through 4 above or as otherwise
provided in the Lease. Any delay caused by work stoppage pending Landlord's
approval of a Change Order or payment by Tenant of any cost increase shall
constitute Tenant Delay.

               4.9.2   No changes, modifications, alterations or additions to
the approved Plans (except minor changes resulting from field conditions) may be
made without the prior written consent of the Landlord and Tenant as set forth
above, after written request therefore. In the event a change requested by
Tenant with respect to the Plans causes the costs of the Tenant Improvements to
exceed the Tenant Improvement Allowance and any amount deposited with Landlord
by Tenant on account of Excess Cost of Tenant Improvements, then all additional
costs attributable to any such change requested by Tenant and approved by
Landlord, including the Tenant Improvements General Contractor's general
conditions fee as applied solely to the net increase in the cost of the Tenant
Improvements, shall be payable by Tenant, within twenty (20) Business Days after
Landlord's submission of a statement of the additional costs attributable to
such change order, as Additional Rent. Any actual delay in the Commencement Date
which results from a change requested by Tenant shall constitute a Tenant Delay.

          4.10 Coordination of Tenant Improvements. Construction of the
               -----------------------------------
Tenant Improvements shall be coordinated, under Landlord's direction, so that
the Tenant Improvements will not interfere with or delay the completion of any
other construction work in or about the Building or the Land.

          4.11 Right to Stop Work. If Tenant shall default under any of the
               ------------------
terms of this Work Letter, and shall not cure such default within five (5)
Business Days after receipt of written notice thereof or, in case of an
emergency, immediately, Landlord may order that work on the Tenant Improvements
be stopped at once and that no further deliveries to the Premises be made until
such default is cured, without limitation as to any other remedy provided
Landlord under this Lease and any delay resulting from such cessation of work
shall be Tenant Delay and any delay in Substantial Completion as a result of
such default by Tenant shall be Tenant Delay.

          4.12 Additional Rent.  Any amounts payable by Tenant to Landlord
               ---------------
pursuant to this WorkLetter shall be paid as Additional Rent under the Lease.

          4.13 Time of the Essence.  Time is of the essence with respect to
               -------------------
Landlord and Tenant's obligations under this Work Letter.

                                     Ex. C

                                      10
<PAGE>

          4.14 Tenant Access. Upon Tenant's request, Landlord shall
               -------------
grant to Tenant and its subcontractors non-exclusive access to the Premises at
times reasonably determined by Landlord for the purpose of installing telephone
equipment, cabling and wiring, a security system and other items necessary for
Tenant to conduct its business (collectively, "Tenant's Installations"),
provided, however, that the performance of Tenant's Installations does not
materially interfere with or delay the work of Landlord's general contractor
engaged in the construction of the Building or the Tenant Improvements General
Contractor or their respective subcontractors. Such periods of access by Tenant
and its contractors shall hereinafter be referred to as the "Non-Exclusive
Access Period." Tenant shall coordinate with Landlord's general contractor
engaged in the construction of the Building or the Tenant Improvements General
Contractor for the performance of Tenant's Installations during the
Non-Exclusive Access Period and comply with their scheduling requirements so
that the construction of Tenant's Installations does not delay or impede
required approvals or construction of the Building or the Tenant Improvements.
Any delay caused by Tenant's failure to do so shall be considered Tenant Delay.
Tenant acknowledges that employees of such general contractors and
subcontractors shall have access to and be working in the Building and the
Premises during the Non-Exclusive Access Period and the Building and Premises
shall not be locked during the times work is being performed. Tenant shall be
liable for any damage caused by persons engaged in installing Tenant's
Installations and any delay caused by such damage shall be Tenant Delay.
Landlord, its agents and employees shall not be liable to Tenant for any theft,
damage or destruction that may occur during the Non-Exclusive Access Period to
Tenant's Installations or other property in the Premises or the Building except
for such loss due to Landlord's gross negligence or willful misconduct. Tenant
shall obtain and maintain "Direct Causes of Physical Loss or Damage" coverage
insurance on all of Tenant's Installations in the Premises from the date of
their installation, with a waiver of subrogation in favor of Landlord. Prior to
the Non-Exclusive Access Period, Tenant shall, in addition, obtain the public
liability insurance and contractors' insurance required by the provisions of
Paragraph 4.13 of this Lease. Tenant shall deliver a certificate of such
policies to Landlord prior to entering the Premises for the purposes described
in this Paragraph 4.14. Tenant shall not be charged for the use of elevators
during the Non-Exclusive Access Period or Tenant's actual move into the
Premises.

     5.   Construction of Tenant Improvements.

          5.1  Upon approval by Landlord of the Plans and Cost of the
Tenant Improvements, the Tenant Improvements General Contractor shall commence
construction of the Tenant Improvements. The Tenant Improvements General
Contractor shall secure such permits as are necessary to construct the Tenant
Improvements.

          5.2  The construction of Tenant Improvements shall be subject to the
following:

                                     Ex. C

                                      11
<PAGE>

               (i)  As part of the Cost of the Tenant Improvements to
          be paid by Tenant (subject to Landlord's contribution of the Tenant
          Improvement Allowance), Tenant shall reimburse Landlord for all
          reasonable costs directly or indirectly related to the Tenant
          Improvements, including, without limitation: costs of site services,
          facilities and utilities (such as trash removal, use of vertical
          transportation, electrical service, etc.); costs of remedying
          deficient or faulty work or inadequate clean-up done by Tenant or its
          contractor(s); and costs incurred by reason of delays caused by such
          work. While Tenant's prior approval of the costs referred to in the
          preceding sentence shall not be required, Landlord agrees to exercise
          reasonable efforts (except in the event of an emergency) to notify
          Tenant prior to committing to incurring such costs. Tenant agrees to
          respond to such notice promptly.

               (ii) All Tenant Improvements shall be installed only under the
          supervision of Landlord's Construction Manager.

          5.3  "Tenant Delay" shall include, without limitation, any delay
                ------------
in the Phase I Commencement Date or the Phase II Commencement Date beyond
the dates stated in Section 1.5 of the Lease resulting from (i) Tenant's failure
to comply with the provisions of this Work Letter or the Lease, including
without limitation Tenant's failure to meet any time deadlines established
herein, (ii) any additional time as reasonably determined by Landlord required
for ordering, receiving, fabricating and/or installing Long Lead Items or items
                                                       ---------------
of materials or other components of the construction of Tenant Improvements,
including, without limitation, mill work, which are not used in the construction
of Tenant Improvements in accordance with Landlord's building standards and
which causes a delay in the Substantial Completion of the Tenant Improvements
beyond the time when such improvements would otherwise be completed if
constructed in accordance with the standards used in the remainder of the
Building, (iii) delay in work caused by submission by Tenant of a request for
any Change Order following Landlord's approval of the Plans, (iv) any additional
time, as reasonably determined by Landlord, required for implementation of any
Change Order with respect to the Tenant Improvements, (v) any changes in the
Building Shell required by the Tenant Improvements, (vi) any other delay arising
from the act or omission of Tenant or Tenant's Agents or vendors, including
providers and installers of furniture and equipment, (vii) delay caused by
Tenant's architect, contractor or subcontractor, (viii) Tenant's failure to
provide any of the items called for in Paragraph 2.4 of this Exhibit C within
                                                             ---------
the times required, unless such failure is a result of Landlord's failure to
meet a mandatory response time or Landlord's failure to promptly deliver to
Tenant any available information reasonably required by Tenant in order to meet
its response time or (ix) the occurrence of any other act, omission, failure or
event which this Work Letter or the Lease describes as "Tenant Delay". If there
shall be any Tenant Delay, then Landlord may require Tenant to commence the
payment of Rent under the Lease based upon that date when Substantial Completion
would have occurred but for the

                                     Ex. C

                                      12
<PAGE>

Tenant Delay, or if not previously required by Landlord, Tenant shall pay such
Rent to Landlord prior to Tenant occupying the Premises. Landlord shall not be
liable for, and Tenant waives all claims against Landlord for, any defaults of
the Tenant Improvements General Contractor and all subcontractors and suppliers
relating to construction of the Tenant Improvements. In the event of any such
default, Tenant shall look solely to the Tenant Improvements General Contractor
or such subcontractors or suppliers.

          5.4  Effect of Tenant Delay. To the extent that completion of
               ----------------------
the Building or any of the Tenant Improvements to be performed by Landlord is
delayed as a result of Tenant Delay, but the delayed completion of such items
does not affect Landlord's achievement of Substantial Completion of any Phase of
     ---
the Tenant Improvement Work by the earliest date required for the delivery of
such Phase, then, provided Tenant continues to pursue the resolution of such
Tenant Delay with due diligence, such Tenant Delay shall not affect the
Commencement Date of such Phase, provided, however, that Tenant shall be
responsible for any increase in the cost of the Tenant Improvement Work with
respect to such Tenant Improvements caused by such Tenant Delay.

               If Tenant Delay does affect Landlord's ability to achieve
                               ----
Substantial Completion of any Phase by the date required for completion of that
Phase, then, as provided in Section 2.4 of the Lease, the Commencement Date for
such Phase shall be deemed to have occurred on the day on which such
Commencement Date for such Phase would have occurred but for such Tenant Delay
and Tenant shall be responsible for any increase in the cost of such Tenant
Improvement Work as a result of such Tenant Delay.

     6.   Miscellaneous.

          6.1  Any default of Tenant under this Work Letter shall constitute a
default of Tenant under the Lease, and Landlord's remedies shall be as set forth
therein. All provisions of the Lease are fully incorporated in this Work Letter
as though set forth herein at length.

          6.2  Tenant shall designate in writing one (1) construction
representative ("Tenant's Representative") authorized to act for Tenant upon
whom Landlord can rely, and who shall, on Tenant's behalf, consult with
Landlord, the Design Professionals, the Tenant Improvements General Contractor
and Landlord's contractors, employees and agents in connection with the
construction of the Tenant Improvements. Tenant's Representative shall have the
power to legally bind to Tenant with respect to notices from Tenant making
requests for and approving changes, giving approval of plans or Work or
otherwise giving direction to Landlord for the Work to be completed under this
Work Letter. Tenant hereby designates Richard Alexander as Tenant's
Representative.

                                     Ex. C

                                      13
<PAGE>

          6.3  Tenant shall indemnify, defend, protect and hold Landlord's
Agents harmless from all Claims which arise in any way, directly or indirectly
from or in connection with the design of the Tenant Improvements, including,
without limitation, claims arising from the work of the Design Professionals or
Tenant's employees or agents.

          6.4  Landlord will endeavor to complete the Tenant Improvement
Work for each Phase by the respective Commencement Dates set forth in Section
1.15 of the Lease. If at any time Landlord believes that any Completion Date
will change, Landlord will promptly so notify Tenant in writing.

          6.5  The Commencement Date for each Phase shall be as determined
pursuant to Section 2.4 of the Lease.

                                     Ex. C

                                      14
<PAGE>

                              EXHIBIT D to Lease

                    FORM OF MEMORANDUM OF COMMENCEMENT DATE
                    ---------------------------------------

         RIGGS & COMPANY, a division of Riggs Bank N.A., as Trustee of the
MultiEmployer Property Trust, a trust organized under 12 C.F.R. Section 9.18, as
Landlord, and DIGEX, INC., a Delaware corporation, as Tenant, executed that
certain Lease dated as of _______________, 2000 (the "Lease").

         The Lease contemplates that upon satisfaction of certain conditions
Landlord and Tenant will agree and stipulate as to certain provisions of the
Lease. All such conditions precedent to that stipulation have been satisfied.

         Landlord and Tenant agree as follows:

         1.   The Phase ____ Commencement Date of the Lease is_________________.

         2.   The Termination Date of the Lease is_____________________________.

         3.   The Premises consist of __________________ rentable square feet.

         4.   Base Rent is as follows:
              ______________ through ______________ ; $ ____________ per month
              ______________ through ______________ ; $ ____________ per month
              ______________ through ______________ ; $ ____________ per month
              ______________ through ______________ ; $ ____________ per month

         5.   The Lease is in full force and effect as of the date hereof,
         Landlord has fulfilled all of its obligations under the Lease required
         to be fulfilled by Landlord on or prior to such date, and Tenant has no
         right of set-off against any rentals.

         IN WITNESS WHEREOF, the parties have caused this Memorandum to be duly
executed as of _________, 2000.

LANDLORD:                                             TENANT:
--------                                              ------

RIGGS & COMPANY, a division of Riggs Bank N.A.,       DIGEX, INC.,
as Trustee of the Multi-                              a Delaware corporation
------------------------------------------------
Employer property Trust, a trust organized
under 12 C.F.R. Section 9.18

By:__________________________        By:____________________________
Name:________________________        Name:__________________________
Its:_________________________        Its:___________________________

                                     Ex. D
                                       1
<PAGE>

                              EXHIBIT E to Lease

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

     1.   No sign, placard, picture, advertisement, name or notice shall be
installed or displayed on any part of the outside or inside of the Building or
Land without the prior written consent of the Landlord. Landlord shall have the
right to remove, at Tenant's expense and without notice, any sign installed or
displayed in violation of this rule. All approved signs or lettering on doors
and walls shall be printed, painted, affixed or inscribed at the expense of
Tenant by a person chosen by Landlord.

     2.   If Landlord objects in writing to any curtains, blinds, shades,
screens or hanging plants or other similar objects attached to or used in
connection with any window or door of the Premises, Tenant shall immediately
discontinue such use. No awning shall be permitted on any part of the Premises.
Tenant shall not place anything against or near glass partitions or doors or
windows that may appear unsightly from outside the Premises.

     3.   Tenant shall not obstruct any sidewalk, halls, passages, exits,
entrances, elevators, escalators, or stairways of the Building. The halls,
passages, exits, entrances, elevators, escalators and stairways are not open to
the general public. Landlord shall in all cases retain the right to control and
prevent access to such areas of all persons whose presence in the judgment of
Landlord would be prejudicial to the safety, character, reputation and interest
of the Land, Building and the Building's tenants; provided that, nothing in this
Lease contained shall be construed to prevent such access to persons with whom
any Tenant normally deals in the ordinary course of its business, unless such
persons are engaged in illegal activities. Tenant shall not go upon the roof of
the Building.

     4.   The directory of the Building will be provided exclusively for the
display of the name and location of tenants only, and Landlord reserves the
right to exclude any other names therefrom.

     5.   All cleaning and janitorial services for the Building and the
Premises shall be provided exclusively through Landlord, and except with the
written consent of Landlord, no person or persons other than those approved by
Landlord shall be employed by Tenant or permitted to enter the Building for the
purpose of cleaning the same. Cleaning and janitorial services shall be provided
five (5) days per week. Tenant shall not cause any unnecessary labor by
carelessness or indifference to the good order and cleanliness of the Premises.
Landlord shall not in any way be responsible to any Tenant for any loss of
property on the Premises, however occurring, or for any damage to any Tenant's
property by the janitor, any of Landlord's Agents or any other person.

     6.   Landlord will furnish Tenant, free of charge, two (2) keys to each
door lock in the Premises. Landlord may make a reasonable charge for any
additional keys.

                                     Ex. E
                                       1
<PAGE>

Tenant shall not make or have made additional keys, and Tenant shall not alter
any lock or install a new additional lock or bolt on any door of its Premises.
Tenant, upon the termination of its tenancy, shall deliver to Landlord the keys
of all doors which have been furnished to Tenant, and in the event of loss of
any keys so furnished, shall pay Landlord therefor.

     7.   HVAC service shall be provided to the Premises Monday through Friday
from 800 a.m. to 6.00 p.m., except for holidays as defined in these Rules.

     8.   If Tenant requires telegraphic, telephonic, computer circuits,
burglar alarm or similar services, it shall first obtain, and comply with,
Landlord's instructions for their installation, and shall pay the entire cost of
such installation(s).

     9.   Tenant shall not place a load upon any floor of the Premises which
exceeds the load per square foot which such floor was designed to carry and
which is allowed by Governmental Requirements. Landlord shall have the right to
prescribe the weight, size and position of all equipment, materials, furniture
or other property brought into the Building. Heavy objects shall, if considered
necessary by Landlord, stand on such platforms as determined by Landlord to be
necessary to properly distribute the weight. Business machines and mechanical
equipment belonging to Tenant, which cause noise or vibration that may be
transmitted to the structure of the Building or to any space in the Building or
to any other tenant in the Building, shall be placed and maintained by Tenant,
at Tenant's expense, on vibration eliminators or other devices sufficient to
eliminate noise or vibration. The persons employed to move such equipment in or
out of the Building must be acceptable to Landlord. Landlord will not be
responsible for loss of, or damage to, any such equipment or other property from
any cause, and all damage done to the Building by maintaining or moving such
equipment or other property shall be repaired at the expense of Tenant.

     10.  Tenant shall not use or keep in the Premises any kerosene, gasoline
or inflammable or combustible fluid or material other than those limited
quantities permitted by the Lease. Tenant shall not use or permit to be used in
the Premises any foul or noxious gas or substance, or permit or allow the
Premises to be occupied or used in a manner offensive or objectionable to
Landlord or other occupants of the Building by reason of noise, odors or
vibrations nor shall Tenant bring into or keep in or about the Premises any
birds or animals.

     11.  Tenant shall not use any method of heating or air-conditioning other
than that supplied by Landlord.

     12.  Tenant shall not waste any utility provided by Landlord and agrees
to cooperate fully with Landlord to assure the most effective operation of the
Building's heating and air-conditioning and to comply with any governmental
energy-saving rules, laws or regulations of which Tenant has actual notice.

                                     Ex. E
                                       2
<PAGE>

     13.  Landlord reserves the right, exercisable without notice and without
liability to Tenant, to change the name and street address of the Building.

     14.  Landlord reserves the right to exclude from the Building between
the hours of 6 p.m. and 7 a.m. the following day, or such other hours as may be
established from time to time by Landlord, and on Sundays and legal holidays,
any person unless that person is known to the person or employee in charge of
the Building and has a pass or is properly identified. Tenant shall be
responsible for all persons for whom it requests passes and shall be liable to
Landlord for all acts of such persons. Landlord shall not be liable for damages
for any error with regard to the admission to or exclusion from the Building of
any person. Landlord reserves the right to prevent access to the Building in
case of invasion, mob, riot, public excitement or other commotion by closing the
doors or by other appropriate action.

     15.  Tenant shall close and lock the doors of its Premises and entirely
shut off all water faucets or other water apparatus, and electricity, gas or air
outlets before Tenant and its employees leave the Premises. Tenant shall be
responsible for any damage or injuries sustained by other tenants or occupants
of the Building or by Landlord for noncompliance with this rule.

     16.  Tenant shall not obtain for use on the Premises ice, drinking water,
food, beverage, towel or other similar services, except at such hours and under
such regulations as may be fixed by Landlord.

     17.  The toilet rooms, toilets, urinals, wash bowls and other apparatus
shall not be used for any purpose other than that for which they were
constructed and no foreign substance of any kind whatsoever shall be deposited
in them. The expenses of any breakage, stoppage or damage resulting from the
violation of this rule shall be borne by Tenant if it or its employees or
invitees shall have caused it.

     18.  Tenant shall not sell, or permit the sale at retail, of newspapers,
magazines, periodicals, theater tickets or any other goods or merchandise to the
general public in or on the Premises. Tenant shall not make any room-to-room
solicitation of business from other tenants in the Building. Tenant shall not
use the Premises for any business or activity other than that specifically
provided for in the Lease.

     19.  Tenant shall not install any radio or television antenna, loudspeaker
or other device on the roof or exterior walls of the Building. Tenant shall not
interfere with radio or television broadcasting or reception from or in the
Building or elsewhere.

     20.  Tenant shall not mark, drive nails, screws or drill into the
partitions, woodwork or plaster or in any way deface the Premises. Landlord
reserves the right to direct electricians as to where and how telephone and
telegraph wires are to be introduced to the Premises. Tenant shall not cut or
bore holes for wires. Tenant shall not affix any floor covering to the floor of
the Premises in any manner except as

                                    Ex. E
                                       3
<PAGE>

approved by Landlord. Tenant shall repair any damage resulting from
noncompliance with this rule.

     21.  Tenant shall not install, maintain or operate upon the Premises any
vending machine without the written consent of Landlord.

     22.  Canvassing, soliciting and distribution of handbills or any other
written material, and peddling in the Building or Land are prohibited, and
Tenant shall cooperate to prevent the same.

     23.  Landlord reserves the right to exclude or expel from the Building and
Land any person who, in Landlord's judgment, is intoxicated, under the influence
of liquor or drugs or in violation of any of these Rules and Regulations.

     24.  Tenant shall store all of its trash and garbage within the Premises.
Tenant shall not place in any trash box or receptacle any material that cannot
be disposed of in the ordinary and customary manner of trash and garbage
disposal. All garbage and refuse disposal shall be made in accordance with
directions issued from time to time by Landlord.

     25.  The Premises shall not be used for lodging or any improper or immoral
or objectionable purpose. No cooking shall be done or permitted by Tenant,
except that use by Tenant of Underwriters' Laboratory approved equipment for
brewing coffee, tea, hot chocolate and similar beverages shall be permitted;
provided that, such equipment and its use is in accordance with all Governmental
Requirements.

     26.  Tenant shall not use in the Premises or in the public halls of the
Building any hand truck except those equipped with rubber tires and side guards
or such other material-handling equipment as Landlord may approve. Tenant shall
not bring any other vehicles of any kind into the Building.

     27.  Without the prior written consent of Landlord, Tenant shall not use
the name of the Building in connection with or in promoting or advertising the
business of Tenant except as Tenant's address.

     28.  Tenant shall comply with all safety, fire protection and evacuation
procedures and regulations established by Landlord or any governmental agency.

     29.  Tenant assumes any and all responsibility for protecting the Premises
from theft, robbery and pilferage, which includes keeping doors locked and other
means of entry to the Premises closed.

     30.  The requirements of Tenant will be attended to only upon appropriate
application to the Manager of the Building by an authorized individual.
Employees of Landlord are not required to perform any work or do anything
outside of their regular duties unless under special instructions from Landlord,
and no employee of Landlord is

                                     Ex. E
                                       4
<PAGE>

required to admit Tenant to any space other than the Premises without specific
instructions from Landlord.

     31.  Tenant shall not park its vehicles in any parking areas designated
by Landlord as areas for parking by visitors to the Building or Land. Tenant
shall not leave vehicles in the parking areas overnight nor park any vehicles in
the Building parking areas other than automobiles, motorcycles, motor driven or
nonmotor driven bicycles or four-wheeled trucks.

     32.  Landlord may waive any one or more of these Rules and Regulations
for the benefit of Tenant or any other tenant, but no such waiver by Landlord
shall be construed as a waiver of such Rules and Regulations in favor of any
other person, nor prevent Landlord from thereafter revoking such waiver and
enforcing any such Rules and Regulations against any or all of the tenants of
the Building.

     33.  These Rules and Regulations are in addition to, and shall not be
construed to in any way modify or amend, in whole or in part, the covenants and
conditions of any lease of premises in the Building. If any provision of these
Rules and Regulations conflicts with any provision of the Lease, the terms of
the Lease shall prevail.

     34.  Landlord reserves the right to make such other and reasonable Rules
and Regulations as, in its judgment, may from time to time be needed for safety
and security, the care and cleanliness of the Building and Land and the
preservation of good order in the Building. Tenant agrees to abide by all the
Rules and Regulations stated in this exhibit and any additional rules and
regulations that are so made by Landlord.

     35.  Tenant shall be responsible for the observance of all of the foregoing
rules by Tenant and Tenant's Agents.

     36.  The Landlord designates the following as holidays (on the dates
observed by the Federal Government (as applicable): New Year's Day, Memorial
Day, Independence Day, Labor Day, Columbus Day, Veterans Day, Thanksgiving Day
and Christmas.

                                     Ex. E
                                       5
<PAGE>

                              EXHIBIT F TO LEASE

                                    FORM OF

                               LETTER OF CREDIT
                               ----------------

                                  ______ BANK
                                    (Address)

NUMBER:_________________                    ________________,1999

                         IRREVOCABLE LETTER OF CREDIT

Riggs & Company, a division of Riggs Bank N.A.
As Trustee of the Multi-Employer Property Trust,
   a trust organized under 12 C.F.R. 9.18
808 17/th/ St. N.W.
Washington, D.C. 20006

Gentlemen:

         We hereby issue our Irrevocable Letter of Credit No.___________ (the
"Letter of Credit") authorizing you or your transferees or assignees (each, a
"Beneficiary") to draw on us for the account of Digex, Inc., ("Applicant") for
an aggregate amount up to _____________ Dollars _____________) which may be made
in one (1) or more draws of any sum or sums up to such amount, available by your
drafts at sight presented at our office at the address noted below, delivery of
such draft to be made either (i) in person; or (ii) by overnight courier; or
(iii) by facsimile, provided that an original draft confirming such facsimile is
sent to us by overnight courier within twenty-four (24) hours following such
facsimile.

         Each draft submitted must state that it is "DRAWN UNDER IRREVOCABLE
LETTER OF CREDIT NO. ___________, DATED ___________, OF _________ BANK" and be
accompanied by a statement purportedly signed by an authorized representative of
the Beneficiary stating either that (a)a default of tenant has occurred under
that certain Deed of Lease (the "Lease") by and between the Beneficiary and
Applicant and remains uncured beyond the applicable notice and cure period
provided for in such Lease or (b) the Tenant under the said Lease has failed to
provide a substitute Letter of Credit or an amendment to this Letter of Credit
in

                                     Ex. F
                                       1
<PAGE>

accordance with the terms of the Lease and that therefore Beneficiary is
entitled to demand and receive payment under the subject Letter of Credit.

     We agree to accept the foregoing statement furnished by Beneficiary as
binding and correct, without our investigation or responsibility for accuracy,
veracity or conclusive correctness or validity of the same or any part thereof.
Upon receipt of such draft in accordance with the foregoing, we will wire
payment of such funds directly to Beneficiary's account in accordance with
wiring instructions delivered by Beneficiary.

     This Letter of Credit remains in force until _____20__. This Letter of
Credit shall be automatically extended for one (1) additional period of one (1)
year from the present expiration date unless Beneficiary notifies us in writing
not less than thirty (30) days before such date that such extension shall not be
necessary.

     This Letter of Credit is assignable and transferable and may be assigned or
transferred one (1) or more times, without charge, upon our receipt of your, or
your successor Beneficiary's, written notice by certified mail, return receipt
requested, that an agreement to transfer or assign this Letter of Credit has
been executed. Following our receipt of such notice, any such designated new
beneficiary shall thereafter be deemed to constitute the Beneficiary hereunder.

     We hereby agree that drafts drawn under and in compliance with the terms of
this Letter of Credit will be honored upon presentation at the office of _______
Bank, _______Street, Washington, D.C.

     Except as otherwise provided hereafter, this Letter of Credit sets forth in
full the terms of our undertaking and such undertaking shall not in any way be
modified, amended, amplified or limited by reference to any document, instrument
or agreement in which this Letter of Credit is referred to, or to which this
Letter of Credit relates and any such reference shall not be deemed to
incorporate by reference any such document, instrument or agreement.

     Except so far as otherwise expressly stated herein, this Letter of
Credit is subject to the Uniform Customs and Practices for Documentary Credits
(1993 Revision), International Chamber of Commerce Publication No. 500 and, as
to matters not governed by such publication, by the laws of the State of
Maryland, including, without limit, the Uniform Commercial Code in effect
therein.

     We hereby agree with you that drafts drawn under and in compliance with the
terms of this Letter of Credit will be duly honored if presented to us on or
before the above stated expiration date.

                                                  Very truly yours,

                                     Ex .F
                                       2
<PAGE>

                                               _________________ Bank

                                               By: _________________________

                                                      Authorized Signature

                                     Ex. F
                                       3
<PAGE>

                              EXHIBIT G to Lease

                         SCHEDULE OF CLEANING SERVICES
                         -----------------------------

Introductory Note: All services set forth in this Exhibit shall only be
performed if and to the extent the applicable surface to be vacuumed, buffed,
polished, swept, moped, dusted, wiped, washed or otherwise cleaned is exposed
and readily accessible.

Daily Cleaning Services
-----------------------

1.   Empty waste baskets and remove refuse to designated area. Reline and wipe
     clean receptacles as needed.

2.   Break down all boxes or any items marked trash and remove to designated
     areas.

3.   Thorough vacuuming of all carpeted area, including corner and crevice
     vacuuming in all tenant spaces and common areas.

4.   Vacuum upholstered chairs and sofas where necessary.

5.   Sweep all hard floors (tile, wood, etc.).

6.   Sweep and damp mop all vinyl, marble and quarry tile floors. Spot buff as
     needed.

7.   Spot clean all tenant and common area carpets as needed. Shampoo all common
     area high traffic lanes as needed.

8.   Dust and/or wipe clean the following surfaces

     .    desks
     .    chairs
     .    file cabinets
     .    tables
     .    telephones
     .    pictures and frames
     .    doors
     .    lamps
     .    ledges and shelves
     .    desk/furniture partitions
     .    any other horizontal surface of a fixture or furniture subject to
          collecting dust

                                     Ex. G
                                       1
<PAGE>

9.   Wipe clean the following surfaces.

     .    window sills and ledges
     .    counter tops and kitchen cabinets
     .    switch plates
     .    private entrance doors
     .    glass, mirrored and wood doors, panels, windows and walls
     .    walls in kitchen and disposal area
     .    conference tables

10.  Wash, clean and disinfect water fountains and/or coolers. Give special
     attention to adjacent floor areas.

11.  Establish regular cleaning maintenance program for floor in public lobby
     area in conjunction with Property Manager; standard necessary to maintain
     is high quality shine with no water marks, stains, scuffing or other signs
     of wear.

12.  Wipe and polish all glass, chrome and metal surfaces such as windows
     (interior and up to standard ceiling height), partitions, banisters, door
     knobs, light switch plates, kick plates, directional signs and door
     saddles.

13.  Dust and wipe clean sand urns.

14.  Polish directory.

15.  Vacuum and spot shampoo all carpet entrance mats.

16.  Spot clean all wall surfaces.

17.  Clean all entrance doors.

Daily Elevators
---------------

1.   Wash and polish wood and stainless walls, doors and hall plate. Keep tracks
     clean of dust, dirt and debris. Vacuum carpet. Spot clean carpet as needed.

Daily Vending Areas
-------------------

1.   Thoroughly vacuum carpeting and damp mop tile flooring daily.

2.   Thoroughly wipe all tops and sides of vending machines and express mail box
     cabinets with damp cloth. Spot clean all wall surfaces. Thoroughly clean
     microwave inside and outside.

                                     Ex. G
                                       2
<PAGE>

3.   Empty trash and reline can daily.

4.   Wash trash container as needed.

Daily Lavatories
----------------

1.   Sweep and wet mop all tile floors using disinfectant.

2.   Thoroughly clean all mirrors, top to bottom.

3.   Scour, wash and disinfect all sink basins, counter tops, bowls, and
     urinals, including undersides.

4.   Wash toilet seats, both sides.

5.   Wipe clean all partitions.

6.   Wipe clean all wall tile as needed.

7.   Remove all trash and sanitary waste, wash receptacles as necessary. Remove
     rubbish to designated area.

8.   Restock hand soap and paper products.

9.   Polish all stainless dispensers.

Weekly Cleaning Services
------------------------

1.   Wash and sanitize metal partitions. Dust horizontal surfaces exceeding 70"
     height. Damp clean ceiling and exhaust fans.

2.   Wash all interior glass, including hallways, windows (excluding second
     story atrium windows), lobby doors, partitions and glass door panels.

3.   Dust all blinds in common areas.

4.   Sweep fire tower stairwells. Wet mop as needed. Wipe hand rails and dust
     metalwork.

5.   Wipe clean all desk tops and credenzas.

6.   Remove all finger prints and dirt from door frames, kick and push plates,
     handles and railings.

                                     Ex. G
                                       3
<PAGE>

7.   Wet wipe all horizontal surfaces to 70" including moldings, shelves, etc.

8.   Polish all fine wood furniture including desks, chairs and cabinets.

9.   Spray buff all vinyl tiles floors as necessary.

10.  Machine buff other hard surfaces, floors to include ceramic, quarry and
     marble title as necessary.

11.  Wipe clean all plant containers in common areas.

Monthly / Quarterly Cleaning Services
-------------------------------------

1.   Thoroughly wipe clean all ceiling vents and exhaust fans and area
     immediately adjacent: monthly to quarterly, as needed.

2.   Strip and refinish all tile floors including restroom floors on a quarterly
     basis.

3.   Wipe clean and remove all fingerprints from full height doors.

4.   Vacuum all upholstered chairs.

5.   Thoroughly clean all venetian blinds, pipes, ventilating and air
     conditioning louvers, ducts and high molding: monthly to quarterly, as
     needed.

6.   Wipe clean as needed all vinyl base. Vacuum as needed all carpet cove base:
     monthly to quarterly, as needed.

7.   Thoroughly wash all trash receptacles, inside and outside.

8.   Spot clean all vertical surfaces.

9.   Spray buff all vinyl floors (both tenant and common areas) quarterly.

Semi-Annual Cleaning Services
-----------------------------

1.   Wash all common area walls including wallcovering, paint, marble and vinyl
     base.

                                     Ex. G
                                       4
<PAGE>

                              EXHIBIT H to Lease

                         MARYLAND 95 EXECUTIVE CENTER

                             BUILDING DESCRIPTION

FOUR STORY BUILDINGS - 120,904 SF
---------------------------------

     Site Work and Landscaping
     -------------------------

     The four-story building will be landscaped to provide a park-like
     atmosphere. Free surface parking will be provided.

     Building Structure
     ------------------

     The building will be designed with a composite deck providing one
     hundred pounds per square foot loading on the second, third and fourth
     floors and a slab on grade allowing two hundred pounds per square foot
     on the first floor.

     Skin and Glass
     --------------

     The brick veneer with "ribbon" windows is planned on all elevations.
     Brick work will included accent landing such as recessed soldier
     courses and row locks. Store front windows will consist of stock color
     aluminum extrusions and one inch (1") insulated glass. Glass will
     either be muted or low "E" treated for maximum energy conservation. One
     inch (1") miniblinds will be installed on all windows.

     Lobby and Care
     --------------

     The building's main lobby on the first floor will be predominately
     finished with granite flooring, accent lighting, and polymix wall
     covering. Building core bathrooms will be finished with ceramic tile
     floors, vinyl wall covering, and granite surface vanity tops. Bathroom
     partitions will be the ceiling hung, painted metal type.

     Elevator/Stairs
     ---------------

     The building will be supplied with three hydraulic elevators finished
     in plastic laminate panels, stainless steel doors and jambs, and carpet
     flooring. Three sets of stairs will also provide access to the other
     floors. The stairwells will be well lit and conductive to use by the
     tenants.

     HVAC System
     -----------

     The HVAC system will be a split system with self contained units on
     each floor connected to a cooling tower. Base Building distribution
     will be through a
<PAGE>

     variable air volume (VAV) system equipped with perimeter diffusers
     (relocation will be Tenant workletter cost). All interior zone ductwork and
     diffusers will be installed as part of the tenant improvements.

     Sprinkler System
     ----------------

     The buildings will be fully sprinkled to include detector check valves and
     U. L. monitoring station. Sprinkler heads will be the semi-recessed style.
     The Base Building sprinkler system will be in place as required by code
     (i.e. distributed with upright heads), all relocation or additional heads
     will be part of the Tenant Improvements.

     Electric
     --------

     The shell improvement will include all distribution panels (both 277v and
     110v) to provide tenants with 6 wafts psf of low voltage power. All
     circuitry outside of the core areas will be installed as part of the Tenant
     Improvements.

                                     Ex. H
                                       2

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