<PAGE>

                                                              Exhibit 10.18



                        Deed of Lease For Office Space
                                       at

                            1861 International Drive

                                     Between

                          TYSONS CORNER PROPERTY, LLC,
                      a Virginia limited liability company

                                   as Landlord

                                       and

                              MICROSTRATEGY, INC.,
                             a Delaware corporation

                                    as Tenant
<PAGE>

                                TABLE OF CONTENTS

ARTICLE I.
BASIC LEASE PROVISIONS AND DEFINITIONS                                        1
         1.1      Building                                                    1
         1.2      Premises                                                    1
         1.3      Lease Term                                                  1
         1.4      Base Rent                                                   2
         1.5      Tenant's Share of Operating Costs                           2
         1.6      Tenant's Share of Real Estate Taxes                         2
         1.7      Adjustment to Base Rent                                     2
         1.8      Permitted Uses                                              2
         1.9      Security Deposit                                            2
         1.10     Commitment Deposit                                          7
         1.11     Definition of Landlord's Agents and Tenant's Agents         7

ARTICLE II.   PREMISES                                                        7
         2.1      Additional Rights and Limitations                           7
         2.2      Condition of the Premises                                   8
         2.3      Signs                                                       9
         2.4      Net Rentable Area                                          12
         2.5      Intentionally Omitted                                      12
         2.6      Intentionally Omitted                                      12

ARTICLE III.  COMMENCEMENT DATE                                              13
         3.1      Commencement Date                                          13
         3.2      Holding Over                                               17

ARTICLE IV.   RENT                                                           18
         4.1      Payment                                                    18
         4.2      Base Rent                                                  19
         4.3      Tenant's Share of Operating Costs                          19
         4.4      Tenant's Share of Real Estate Taxes                        24
         4.5      Rent Definition                                            27
         4.6      Other Impositions                                          27
         4.7      Tenant's Audit Rights                                      28

ARTICLE V.    LANDLORD'S SERVICES                                            28
         5.1      Services, Utilities and Electricity                        28
         5.2      Heat and Air-Conditioning                                  30
         5.3      Water                                                      31
         5.4      Janitorial Services                                        32
         5.5      Elevator Service                                           32
<PAGE>

         5.6      No Liability                                               32
         5.7      Security/Access                                            33
         5.8      Maintenance and Repair                                     34
         5.9      Communications                                             35

ARTICLE VI.    TENANT'S CARE OF PREMISES                                     36
         6.1      Waste                                                      36
         6.2      Compliance with Law                                        37
         6.3      Alterations, Additions or Improvements: Moving             38
         6.4      No Overloading or Overcrowding                             39
         6.5      No Liens                                                   39
         6.6      Property and Improvements at Tenant's Risk                 40
         6.7      Flammable, Explosives or Toxic Substances                  40
         6.8      Hazardous Materials Defined                                40
         6.9      Environmental Compliance                                   41
         6.10     ADA Compliance                                             42
         6.11     Termination and Surrender                                  42
         6.12     Indoor Air Quality                                         43

ARTICLE VII.    TRANSFER OF INTEREST: PRIORITY OF LIEN                       44
         7.1      Assignment and Sublease                                    44
         7.2      Intentionally Omitted                                      48
         7.3      Subordination                                              48
         7.4      Notice to Lender                                           49
         7.5      Tenant's Financing                                         49

ARTICLE VIII.   DAMAGE AND DESTRUCTION: EMINENT DOMAIN                       49
         8.1      Damage and Destruction                                     49
         8.2      Eminent Domain                                             51

ARTICLE IX.     LIABILITY: INDEMNIFICATION: INSURANCE                        51
         9.1      Waiver of Claims                                           51
         9.2      Indemnification                                            51
         9.3      Insurance Requirements                                     52
         9.4      General Provisions with Respect to Tenant's Insurance      53
         9.5      Waiver of Subrogation                                      54
         9.6      Landlord's Insurance                                       55

ARTICLE X.      ACCESS TO THE PREMISES                                       55
         10.1     Access to the Premises                                     55

ARTICLE XI.     FAILURE TO PERFORM, DEFAULTS, REMEDIES                       56
         11.1     Defaults                                                   56
         11.2     Remedies                                                   57
         11.3     Deficiency                                                 59
         11.4     Mitigation                                                 59
         11.5     Payments                                                   59
<PAGE>

         11.6     Landlord's Default                                         60
ARTICLE XII.    QUIET ENJOYMENT: RESERVATIONS BY LANDLORD:
                  NO CONSTRUCTIVE EVICTION                                   60
         12.1     Quiet Enjoyment                                            60
         12.2     Reservations by Landlord                                   60
         12.3     No Constructive Eviction                                   61

ARTICLE XIII.   RULES AND REGULATIONS                                        61
         13.1     Rules and Regulations                                      61

ARTICLE XIV.    COMMUNICATIONS                                               62
         14.1     Communications                                             62
         14.2.    Notice Addresses                                           63

ARTICLE XV.     MISCELLANEOUS PROVISIONS                                     64
         15.1     Tenant Estoppel Certificates                               64
         15.2     Brokerage Fees                                             64
         15.3     Intentionally Omitted                                      65
         15.4     Liability of Landlord                                      65
         15.5     Authority                                                  65
         15.6     Parking                                                    65
         15.7     Landlord Approval                                          65
         15.8     Unenforceability/Joint and Several Liability               65
         15.9     Headings, Miscellaneous                                    66
         15.10    Force Majeure                                              66
         15.11    Entire Agreement                                           66
         15.12    Governing Law                                              66
         15.13    Waiver of Jury Trial                                       66
         15.14    Recordation of Lease                                       67
         15.15    No Binding Effect Until Execution and Delivery             67
         15.16    No Partnership                                             67
         15.17    Intentionally Omitted                                      67
         15.18    Days                                                       67
         15.19    Successors and Assigns                                     67
         15.20    Non-Waiver                                                 67
         15.21    Counterparts                                               67
         15.22    Survival of Tenant Obligations                             67
         15.23    Renewal Options                                            67
         15.24    Right of First Offer                                       70
         15.25    Generator, Transformer and Rooftop Mechanical Equipment    73
         15.26    Roof Rights                                                76
<PAGE>

EXHIBIT "A"       OUTLINE OF THE PREMISES                                    A-1

EXHIBIT "B"       RULES AND REGULATIONS                                      B-1

EXHIBIT "C"       WORK LETTER                                                C-1

EXHIBIT "C-1"     FINAL THIRD AND FIFTH FLOOR  PLANS                         C-7

EXHIBIT "C-2"     LANDLORD'S COMMENTS REGARDING TENANT'S PLANS              C-11

EXHIBIT "D"       STATEMENT SPECIFYING COMMENCEMENT DATES
                    AND TERMINATION DATE                                     D-1

EXHIBIT "E"       PARKING                                                    E-1

EXHIBIT "F"       ACCELERATED DEPRECIATION SCHEDULE REGARDING
                   AFTER HOURS HVAC SERVICE                                  F-1

EXHIBIT "G"       CLEANING SPECIFICATIONS                                    G-1

EXHIBIT "H"       TENANT'S SIGNAGE                                           H-1

EXHIBIT "I"       TENANT'S GENERATOR EQUIPMENT                               I-1

EXHIBIT "J"       TENANT'S TRANSFORMER EQUIPMENT                             J-1

EXHIBIT "K"       TENANT'S ROOFTOP MECHANICAL EQUIPMENT                      K-1

EXHIBIT "L"       GUIDELINES AND LIMITATIONS REGARDING IMPROVEMENTS          L-1

EXHIBIT "M"       TENANT'S COMMUNICATIONS EQUIPMENT                          M-1

EXHIBIT "N"       PRELIMINARY CONCEPTUAL FOURTH FLOOR  PLANS                 N-1

EXHIBIT "O""      PRELIMINARY CONCEPTUAL ELEVATOR LOBBY  PLANS               O-1

<PAGE>

                                  DEED OF LEASE

         This  Deed of Lease  (the  "Lease")  is  entered  into  this 7th day of
January,  2000, between Tysons Corner Property LLC, a Virginia limited liability
company ("Landlord"), and MicroStrategy, Inc. a Delaware corporation ("Tenant").

         Landlord  hereby leases to Tenant and Tenant hereby rents from Landlord
the Premises (as defined in Section  1.2).  Intending to be legally  bound under
this Lease and in  consideration  of the agreements  herein made, and other good
and valuable consideration, Landlord and Tenant hereby agree as follows:

                ARTICLE I. BASIC LEASE PROVISIONS AND DEFINITIONS
                           --------------------------------------
         1.1 Building.  That building,  which is currently being  constructed by
Landlord,  to be known as 1861 International  Drive, which building will consist
of  approximately  one hundred  seventy  seven  thousand four hundred fifty nine
(170,471)  square feet of Net  Rentable  Area  (defined  in Section  2.4) and be
located at 1861 International Drive, McLean, Virginia 22102 (the "Building").

         1.2 Premises.  The Premises,  designated as Suites #200,  300, 400, 500
and 600 to be located  on the  entire  second,  third,  fourth,  fifth and sixth
floors of the  Building,  which  will  consist of a total of  approximately  one
hundred forty six thousand and four hundred eighty  (146,480) square feet of Net
Rentable Area, and is outlined on Exhibit A hereto attached (the "Premises").

         The rentable square footage of the Premises consists of the following
approximate rentable square footage ("RSF") by floor:
                  Floor                              RSF
                  2                                  29,176
                  3                                  29,176
                  4                                  29,176
                  5                                  29,176
                  6                                  29,776

         1.3 Lease  Term.  The  "Lease  Term" or "Term"  (herein  so  called) is
approximately  one hundred  twenty-seven  (127) full  calendar  months (plus any
partial  calendar  month at the beginning of the Lease Term),  commencing on the
Commencement  Date (as  defined in Article  III),  and ending at midnight on the
last day of the one hundred  twentieth (120th) full calendar month following the
Final Commencement Date (as defined in Article III) (the "Termination  Date") or
at such earlier date as this Lease may be terminated as provided in this Lease.

         1.4 Base  Rent.  The  initial  "Base  Rent"  (herein so called) is Four
Million  Six   Hundred   Six   Thousand   Seven   Hundred   Ninety  Six  Dollars
($4,606,796.00)  annually,  payable  monthly  in  advance in the amount of Three
Hundred  Eighty Three  Thousand and Eight Hundred Ninety
<PAGE>

Nine and 66/100 Dollars ($383,899.66)  per month. The Base Rent shall be
increased during the Lease Term in accordance with Section 1.7 of this Lease.

         1.5 Tenant's Share of Operating  Costs.  "Tenant's Share" of "Operating
Costs" (defined in Section 4.3) is eighty two and 543/1000ths  percent  (85.93%)
of such costs. [The parties  acknowledge that the foregoing Share was determined
by dividing  the Net Rentable  Area of the Premises by the Net Rentable  Area of
the Building].

         1.6  Tenant's  Share of Real Estate  Taxes.  "Tenant's  Share" of "Real
Estate  Taxes"  (defined in Section 4.4) is eighty two and  543/1000ths  percent
(85.93%) of such costs.  [The parties  acknowledge  that the foregoing Share was
determined by dividing the Net Rentable Area of the Premises by the Net Rentable
Area of the Building].

         1.7  Adjustment to Base Rent.  Beginning on the first day of the second
Lease Year (as defined  below),  Base Rent will be increased on the first day of
each Lease Year during the Term in  accordance  with the terms of the  following
schedule:

    Lease Year             Annual Base Rent          Monthly Base Rent
    ----------             ----------------          -----------------
         1                   $4,606,796.00*               $ 383,899.66
         2                   $4,721,965.90                $ 393,497.16
         3                   $4,840,015.05                $ 403,334.59
         4                   $4,961,015.42                $ 413,417.95
         5                   $5,085,040.81                $ 423,753.40
         6                   $5,212,166.83                $ 434,347.24
         7                   $5,342,471.00                $ 445,205.92
         8                   $5,476,032.78                $ 456,336.07
         9                   $5,612,933.60                $ 467,744.47
         10                  $5,753,256.93                $ 479,438.08
         11                  $5,897,088.35*               $ 491,424.03

[* The parties  acknowledge  that:  (i) the eleventh  (11th) Lease Year will not
necessarily be a full twelve (12) month period,  and (ii) during the first (1st)
Lease Year, Tenant will not be occupying the entire Premises for the full twelve
(12) months,  and as a result,  (iii) Tenant's total Base Rent  obligations  for
such  Lease  Years will be less than the  annualized  Base Rent set forth in the
schedule  above.  The amounts payable by Tenant with respect to such Lease Years
(as determined in accordance  with the terms hereof) will be pro-rated  portions
of the aforesaid  annual  amounts.  The parties  further  acknowledge  that with
respect to the period beginning on the Commencement  Date and ending on December
31, 2000,  Tenant's total Base Rent obligations  shall be $3,074,342.00 (as such
amount may be  increased  by virtue of  Tenant's  accelerated  occupancy  of the
fourth  (4th)  floor  portion of the  Premises in  accordance  with the terms of
Section 3.1).  If,  pursuant to the terms of this Lease,  Tenant is obligated to
pay Base  Rent for any  partial  calendar  month,  Tenant's  Monthly  Base  Rent
obligations  with respect to such partial  calendar month shall be determined by
dividing the applicable  Monthly Base Rent in the schedule above by total number
of days in such calendar month and  multiplying the result by the number of days
in such month for which Tenant is obligated to pay Base Rent hereunder].
<PAGE>

If,  pursuant to the terms of this Lease,  Tenant is  obligated to pay Base Rent
with respect to only a portion of the Premises,  Tenant's Base Rent  obligations
with respect to such portion of the Premises  shall be determined by multiplying
the  applicable  Monthly  Base Rent in the  schedule  above by a  fraction,  the
numerator  of  which  shall  be the Net  Rentable  Area of that  portion  of the
Premises for which Tenant is obligated to pay Base Rent and the  denominator  of
which  shall be the total Net  Rentable  Area of the  Premises  (as set forth in
Section 1.2 above).].

The  first  "Lease  Year,"  as such  term  is used  herein  shall  begin  on the
Commencement  Date and end on the last day of the twelfth  (12th) full  calendar
month following such Commencement  Date. The second Lease Year shall commence on
the date immediately following the expiration of the first Lease Year and extend
for a period of twelve (12) consecutive  calendar months.  Each subsequent Lease
Year shall  commence  on the annual  anniversary  of the first day of the second
Lease Year and extend for a period of twelve (12)  consecutive  calendar months,
except for the eleventh  (11th) Lease Year which shall commence as aforesaid and
end on the Termination Date (as defined in Section 3.1).

         1.8 Permitted Uses.  Tenant shall have the right to occupy the Premises
solely for general  office and  professional  business use (which shall  include
uses incidental and ancillary to Tenant's  professional office use provided that
the same are in  compliance  with  applicable  zoning and other laws,  statutes,
regulations,  codes and orders),  and for no other purpose.  Tenant's use of the
Premises  is  subject  to the terms of this  Lease,  including  the  "Rules  and
Regulations"  (herein so  called)  set forth on  Exhibit B hereto  attached,  as
modified from time to time in accordance  with Section 13.1.  Provided that such
uses  are in  compliance  with  applicable  zoning  and  other  laws,  statutes,
regulations, codes and orders, the Permitted Use shall include the right to: (i)
conduct operations in the Premises on a twenty-four (24) hour per day, seven (7)
day per week basis,  (ii) host in the Premises  receptions  and other  functions
related to its  professions  business use and (iii) serve food and  beverages to
Tenant's  employees  and  its  invitees  at  such  reception  or  functions.  To
Landlord's knowledge as of the date of this Lease the foregoing Permitted Use is
permitted under applicable zoning ordinances and land use regulations and is not
in violation of any exclusive use rights granted by Landlord to other tenants in
the Building.

         1.9 Security Deposit.  (a) Upon the full execution and delivery of this
Lease by both of the parties  hereto,  Tenant shall  deliver a Security  Deposit
(herein so called) to Landlord in one of the two following  forms.  Tenant shall
either:  (i) deposit with Landlord a "Cash Security  Deposit" (herein so called)
in the amount of Two Million Three Hundred Three  Thousand  Three Hundred Ninety
Seven and  90/100  Dollars  ($2,303,397.90),  or (ii)  deliver  to  Landlord  an
unconditional,  irrevocable  letter of credit in the amount of Two Million Three
Hundred Three  Thousand Three Hundred  Ninety Eight Dollars  ($2,303,398)  to be
held by Landlord as a Security Deposit  hereunder.  The Cash Security Deposit or
the  Letter  of  Credit  shall be held by  Landlord  as  security  for  Tenant's
performance  under this Lease, and not as an advance payment of Rent (defined in
Section 4.5) or a measure of Landlord's  damages for Default (defined in Section
11.1 and in this Section 1.9).  Provided no Default (as defined in Section 11.1,
in this  Section 1.8 and  elsewhere  in this Lease) has  occurred  prior to such
date,  the amount of such Cash  Security  Deposit  or Letter of Credit  shall be
subject to subsequent  adjustment in accordance with the
<PAGE>

following  terms: on the first day of the thirteenth  (13th) full calender month
following  the Final  Commencement  Date (as  defined in Section 3.1 hereof) and
thereafter on the first day of the twenty-fifth (25th) and thirty-seventh (37th)
full calendar months  following the Final  Commencement  Date, the amount of the
Security  Deposit  shall  be  reduced  by  an  amount  equal  to  Three  Hundred
Eighty-three  Thousand Three Hundred Ninety Dollars  ($383,390.00) per year, and
on the first day of the  forty-ninth  (49th) full calendar  month  following the
Final  Commencement  Date the amount of the Security Deposit shall be reduced by
Three   Hundred   Eighty-five   Thousand  Four  Hundred   Twenty-eight   Dollars
($385,428.00).  Therefore, subject to the conditions set forth above, the amount
of the Security Deposit shall be periodically  reduced as follows:  on the first
day  of  the  thirteenth   (13th)  full  calendar  month   following  the  Final
Commencement  Date, to One Million Nine Hundred  Twenty  Thousand  Eight Dollars
($1,920,008.00); on the first day of the twenty-fifth (25th) full calendar month
following the Final  Commencement  Date, to One Million Five Hundred  Thirty Six
Thousand Six Hundred Eighteen Dollars  ($1,536,618.00);  on the first day of the
thirty-seventh (37th) full calendar month following the Final Commencement Date,
to One Million One Hundred Fifty Three Thousand Two Hundred Twenty Eight Dollars
($1,153,228.00),  and, on the first day of the forty-ninth  (49th) full calendar
month  following  the  Final  Commencement  Date to Seven  Hundred  Sixty  Seven
Thousand  Eight Hundred  Dollars  ($767,800.00).  The remaining  balance of such
Security  Deposit shall be held by Landlord  throughout the balance of the Lease
Term in accordance with the terms of this Section 1.9.

         (b) Any such Cash Security Deposit shall be held in an interest-bearing
account.  Ninety-percent  (90%) of any  interest  earned on such  Cash  Security
Deposit  shall be credited to Tenant on an annual  basis and increase the amount
of the Cash  Security  Deposit held  hereunder by Landlord.  The  remaining  ten
percent  (10%) of such  interest  earned on the Cash  Security  Deposit shall be
retained by  Landlord in order to  compensate  Landlord  for its  administrative
costs associated with  maintaining  such account.  Tenant shall have no claim to
the remaining ten percent (10%) of such interest.

         (c) The Letter of Credit  described in subparagraph  (a) above shall at
all  times  satisfy  all of the  requirements  set  forth in this  Section  1.9,
including  those set forth  below.  Such Letter of Credit shall : (i) be in form
and substance satisfactory to Landlord in its reasonable discretion; (ii) at all
times be in the  amount  set forth in  subparagraph  (a) above (as  adjusted  in
accordance with such terms), (iii) permit multiple draws without a corresponding
reduction  in the  aggregate  amount of the Letter of Credit;  (iv) be issued by
Bank  of  America  or  another  federally  insured  commercial  bank  reasonably
acceptable  to Landlord  from time to time;  (v) made payable to, and  expressly
transferable  and  assignable  at no charge by Landlord  (and its  successor and
assigns as owners of the Building);  (vi) payable at sight upon presentment to a
local  branch of the issuer of a simple sight draft  accompanied  by a notarized
certificate  stating  that Tenant is in default  under this Lease and the amount
that Landlord is owed in connection therewith;  (vii) be of a term not less than
one (1) year (or automatically and  unconditionally  extended) from time to time
through  the  sixtieth  (60th) day after the  expiration  of the Lease Term ("LC
Return Date"); and (viii) expressly provide that at least thirty (30) days prior
to the then current  expiration date of such Letter of Credit,
<PAGE>

the same shall be automatically  renew or be extended for at least an additional
one (1) year period  unless at least sixty (60) days prior to the  expiration of
such Letter of Credit,  Landlord is provided  with written  notice that the same
shall not be renewed or extended.  Each Letter of Credit contemplated  hereunder
shall be  issued by a  commercial  bank  that has a LACE  Financial  Institution
Credit Rating of "B" or better, and shall be otherwise acceptable to Landlord in
its reasonable  discretion.  If the issuer's Financial Institution Credit Rating
is reduced below B by LACE, or if the financial condition of such issuer changes
in any other  materially  adverse  way,  then  Landlord  shall have the right to
require that Tenant obtain from a different issuer a substitute Letter of Credit
that  complies in all respects  with the  requirements  of this Section 1.9, and
Tenant's  failure to obtain such substitute  Letter of Credit within twenty (20)
days following  Landlord's written demand therefor (with no other notice or cure
or grace period being applicable thereto, notwithstanding anything in this Lease
to  the  contrary)  shall  entitle   Landlord  to  immediately   draw  upon  the
then-existing Letter of Credit in whole or in part, without notice to Tenant. In
the event the issuer of any Letter of Credit  held by  Landlord  is placed  into
receivership or conservatorship by the Federal Deposit Insurance Corporation, or
any  successor  or  similar  entity,   then,  effective  as  of  the  date  such
receivership or conservatorship occurs, said Letter of Credit shall be deemed to
not meet the  requirements  of this  Section  1.9,  and,  within  ten (10)  days
thereof,  Tenant  shall  replace  such  Letter of Credit with a Letter of Credit
issued  by an  institution  which  satisfies  the  foregoing  requirements  (and
Tenant's  failure  to do so  within  said ten (10) days  shall,  notwithstanding
anything in this Lease to the contrary,  constitute a Default under the Lease if
the same is not  cured  within  five  (5) days  following  written  notice  from
Landlord).  Any  failure  or refusal of the issuer to honor the Letter of Credit
shall be at Tenant's sole risk and shall not relieve  Tenant of its  obligations
hereunder with respect to the Security Deposit.

         (d) Tenant  shall renew or replace such Letter of Credit as required by
this Section 1.9, and shall deliver to Landlord  written proof that the same has
been timely renewed, extended or replaced at least thirty (30) days prior to the
expiration thereof. Tenant will take whatever action is necessary to ensure that
said Letter of Credit (or an appropriate replacement thereof which satisfies the
requirements  of this Section 1.9  automatically  renews or extends or is timely
replaced (by a new Letter of Credit or a Cash Security  Deposit in the amount of
the Security Deposit) with written notice and proof to Landlord thereof at least
thirty (30) days prior to the expiration thereof, and maintain the same in force
in  effect   through  at  least  the  LC  Return   Date  (as   defined   above).
Notwithstanding  anything  in this  Lease to the  contrary  (including,  without
limitation,  any cure or grace periods set forth in this Lease),  Any failure by
Tenant to timely  renew or  replace  said  Letter of Credit  and any  failure by
Tenant to timely  deliver  to  Landlord  in  writing  proof of such  renewal  or
replacement shall be deemed a Default (as such term is defined in Article XI and
used herein)  hereunder by Tenant,  without the necessity for further  notice to
Tenant, entitling Landlord to immediately draw upon such Letter of Credit in the
full amount thereof. At all times during the Term, Landlord shall be entitled to
draw upon the  entire  amount of such  Letter of Credit to cure any  outstanding
Default (as defined in Article XI , in this  Section 1.9 and  elsewhere  in this
Lease).  In the event that Landlord draws upon the Letter of Credit by reason of
Tenant's  failure to timely renew or replace the Letter of Credit,  the proceeds
thereof (except for any portion  thereof  necessary to cure any other default by
Tenant, if any) shall constitute a Cash Security Deposit hereunder, and shall be
held in accordance with the terms of subparagraph (b) above.
<PAGE>

         (e) If Landlord transfers the Security Deposit to any transferee of the
Building or Landlord's  interest  therein,  then such transferee shall be liable
for the return of the Security Deposit,  and Landlord shall be released from all
liability for the return thereof.

         (f) Upon Tenant's  Default,  Landlord,  without  prejudice to any other
remedy,  may apply any applicable  portion of the Cash Security  Deposit or draw
upon the Letter of Credit and apply the same to:  (i) an  arrearage  of Rent due
and owing as a result of a Default, and (ii) any other expense, damages, cost or
liabilities  incurred or suffered  by  Landlord  or  Landlord's  Agents due to a
Default by Tenant.  In the event that  Landlord  applies any portion of the Cash
Security  Deposit or draws  upon said  Letter of Credit in  accordance  with the
foregoing terms,  Tenant shall  immediately,  upon demand from Landlord,  pay to
Landlord the amount so applied in order to restore the Cash Security  Deposit to
the amount of the Security  Deposit (as determined in accordance  with the terms
of subparagraph  (a)), or, if necessary by virtue of any reduction in the amount
of the Letter of Credit,  deliver to Landlord a replacement  Letter of Credit in
the amount of the Security  Deposit (as determined in accordance  with the terms
of subparagraph  (a)). If Tenant is not then in Default,  on the LC Return Date,
Landlord shall deliver the Letter of Credit (and any portion  thereof  converted
to the Cash  Security  Deposit)  to Tenant  less any amount  thereof  applied by
Landlord to cure any Default by Tenant.

         (g)  Notwithstanding  anything  contained  in this  Section  1.9 to the
contrary:  (1) if at any time  during the Term:  (i) Tenant is not in Default of
any of its  obligations  hereunder,  and (ii) Tenant has achieved an  Investment
Grade Rating (as hereafter  defined) with respect to its senior  unsecured debt,
the amount of the  Security  Deposit  and  delivered  written  proof  thereof to
Landlord,  Landlord  shall  permit  Tenant to reduce the amount of the  Security
Deposit  to Zero  Dollars  ($0) and  Landlord  shall,  within  twenty  (20) days
following  receipt of written proof from Tenant of such Investment Grade Rating,
return any Cash  Security  Deposit or Letter of Credit  then held by Landlord to
Tenant;  and (2) Without limiting the generality of the foregoing  clause, it is
specifically  agreed that if Tenant  achieves an Investment  Grade  Rating,  and
subsequently  loses such Rating,  then the amount of the Security  Deposit shall
again  immediately be established  pursuant to subparagraph (a) above, and shall
be computed as if an Investment Grade Rating had never been achieved, and Tenant
shall  immediately  deliver  to  Landlord a Cash  Security  Deposit or Letter of
Credit in the amount of the Security  Deposit.  Tenant's  failure to immediately
restore the  Security  Deposit  shall  constitute a material  Default  hereunder
without further notice from Landlord.  The term "Investment  Grade Rating" shall
mean that Tenant has either:

         (1)      (i) a Standard & Poor's Corporation rating of "BBB" (or
                  equivalent) or better, and (ii) a Moody's Investors Service,
                  Inc. rating of "baa2" (or equivalent) or better;

or       (2)      (i) a Duff & Phelps rating of "BBB" (or equivalent) or better,
                  and (ii) either: (a) a Standard & Poor's Corporation rating of
                  "BBB" (or equivalent) or better, or (b) a Moody's Investor's
                  Service, Inc. rating of "baa2" (or equivalent) or better.

         1.10  Commitment  Deposit.  In  consideration  of the execution of this
Lease by Landlord, upon the full execution and delivery of this Lease by both of
the parties  hereto,  Tenant shall pay
<PAGE>

to Landlord Two Hundred  Thirty  Thousand  Nine Hundred  Sixty-eight  and 75/100
Dollard ($230,968.75) (the "Commitment Deposit"),  which amount will be credited
by  Landlord  against  the first  due  installments  of Base Rent due  hereunder
following the Commencement Date.

         1.11 Definition of Landlord's  Agents and Tenant's  Agents.  As used in
this Lease:  "Landlord's  Agents"  includes any asset manager,  agent,  managing
agent, affiliate,  contractor, employee, director or officer of Landlord, or any
corporate  entity  affiliated with Landlord or third party operator and owner of
the Building,  and "Tenant's Agents" includes any agent,  officer,  employee, or
licensee of Tenant.

                              ARTICLE II. PREMISES

         2.1 Additional Rights and Limitations.  Landlord leases the Premises to
Tenant,  and Tenant leases the Premises from Landlord complete with improvements
(the "Improvements") described in Exhibit C hereto attached (the "Work Letter").
The lease of the Premises includes the right, together with other tenants of the
Building  (as  defined in Section  1.1) and members of the public and subject to
the Rules and Regulations  attached hereto as Exhibit B and such other Rules and
Regulations promulgated by Landlord in its reasonable discretion during the Term
of the Lease,  to use the common and public areas of the Building (as  described
in further  detail  below),  but includes no other rights not  specifically  set
forth  herein.  The lease of the Premises  does not include the right to use the
roof of the Building (except as may be expressly provided in Section 15.26), nor
does this Lease  grant any right to light or air over or about the  Premises  or
Building.  As used  in this  Lease,  the  term  "Common  Areas"  means,  without
limitation, the hallways,  entryways,  stairs, elevators,  driveways,  walkways,
terraces,  docks, loading areas, restrooms,  trash facilities,  lobbies (but not
the  elevator  lobbies on floors  which are leased in their  entirety  to Tenant
hereunder)  and all other areas and  facilities  in the Building and on the Land
that are provided from time to time by Landlord for the general nonexclusive use
or  convenience  of Tenant with  Landlord and other  tenants of the Building and
their respective employees,  invitees,  licensees,  or other visitors.  Landlord
grants  Tenant,  its  employees,  invitees,  licensees,  and  other  visitors  a
nonexclusive license for the Term to use the public portions of the Common Areas
in  common  with  others  entitled  to use the  same,  subject  to the terms and
conditions of this Lease and the reasonable Rules and Regulations established by
Landlord from time to time pursuant to Section 13.1.  Except as may be otherwise
agreed upon in writing from time to time, at all times the Common Areas shall be
under the exclusive control of Landlord. Upon reasonable prior notice to Tenant,
subject to the  limitations  set forth below in this Section 2.1,  Landlord will
have the right to:  (i) close off any of the  Common  Areas to  whatever  extent
required in the opinion of Landlord and its counsel to prevent a  dedication  of
any of the same or the  accrual of any rights by any person or the public to the
Common Areas;  (ii)  temporarily  close any of the Common Areas for maintenance,
alteration,  or improvement  purposes;  and (iii) change the size,  use,  shape,
location  or nature of any such  Common  Areas,  including  erecting  additional
improvements on the same,  expanding the existing Building or other buildings to
cover a portion of the Common Areas,  converting  Common Areas to leasable space
or other use or  converting  any other  portion of the Building  (excluding  the
Premises) or other  buildings to Common Areas.  In  exercising  its rights under
this Section 2.1, Landlord will not permanently, materially and adversely impair
or affect Tenant's use and enjoyment of the Premises as
<PAGE>

contemplated  herein or Tenant's access to (including  ingress and egress to and
from)  the  Building  and the  Premises,  and  Landlord  will  use  commercially
reasonable efforts to not temporarily  materially and adversely impair or affect
Tenant's use and  enjoyment of the Premises as  contemplated  herein or Tenant's
access to  (including  ingress  and  egress to and  from) the  Building  and the
Premises  . If, in  exercising  its  rights  under this  article:  (i)  Landlord
violates the terms of the immediately  preceding  sentence,  (ii) Tenant, in the
exercise of its commercially  reasonable  judgment,  is unable to operate in the
Premises or a portion  thereof as a result of such  violation  by  Landlord  and
ceases operations in the Premises or a portion thereof as a result thereof,  and
(iii)  Landlord  fails to cure such  violation  within  ten (10) days  following
written notice of such violation from Tenant,  then Tenant should be entitled to
a temporary  abatement  of Base Rent on an  equitable  and  proportionate  basis
(based  upon that  portion of the  Premises  which  Tenant is unable to use as a
result of Landlord's violation) until Tenant can once again use the Premises.

         2.2 Condition of the Premises.  (a) As of the Delivery Date, the Common
Areas of the Building shall be in compliance  with all  applicable  governmental
codes,  laws and regulations,  including the Americans with  Disabilities Act of
1990, as amended as of such  Delivery Date (the "ADA") and all Building  systems
will be in good  operating  order.  The  issuance  of a valid  Certification  of
Occupancy for the Building shall be conclusive evidence of Landlord's compliance
with the  foregoing  requirements,  except as to latent  defects,  and as to the
completion of punchlist items.  (However,  any delay in the issuance of the same
shall  in no way  imply  that  Landlord  has not  complied  with  the  foregoing
requirements). Tenant's acceptance of possession of the Premises (or any portion
thereof),  shall constitute an  acknowledgement  by Tenant:  (a) that it has had
full  opportunity to examine the Building,  including the applicable  portion of
the Premises,  and is fully  informed,  independently  of Landlord or Landlord's
Agents, as to the character,  construction and structure of the Building and the
Premises, and (b) except for latent defects (which shall be repaired by Landlord
at Landlord's cost only in accordance with the terms of subparagraph  (b) below)
and items  expressly  set  forth in a timely  punchlist  delivered  by Tenant to
Landlord in accordance  with the terms of  subparagraph  (b) below,  that Tenant
accepts the applicable  portion of the Premises in accordance  with the terms of
the Lease and the Exhibits thereto.

         (b) Upon delivery of possession of any portion of the Premises,  Tenant
or its designated  representative will inspect the Premises and, within five (5)
business days of such delivery,  give Landlord written notice (a "punchlist") of
contended  defects in Landlord's  Work (as defined in Exhibit C), if any, and of
any contended  variances of Landlord's Work from the  requirements of this Lease
and Landlord shall endeavor to remedy such defects within thirty (30) days after
notice thereof by Tenant.  Landlord will use commercially  reasonable efforts to
remedy any such actual defect or variance described in Tenant's timely delivered
punchlist. Tenant's failure to timely give such notice, or specify any defect or
variance in such notice,  is a waiver of all rights with respect to such defects
(other than latent defects, which shall be warranted by Landlord for a period of
one year following the date of delivery of possession of the applicable  portion
of the Premises) or variance not specified in such notice.
<PAGE>

         (c) Landlord represents and warrants that, to Landlord's knowledge,  as
of the  Delivery  Date,  the Common Areas of the  Building  (including  Building
entrance doors, lobby areas, stairwells,  elevators and common restrooms) are in
compliance with ADA and with all laws, statutes, ordinances, rules, regulations,
requirements  and  directives of applicable  government  authorities  (including
police, fire, health and environmental authorities or agencies). During the Term
of  the  Lease,   Landlord,   at  its  cost  and  expense  (subject  to  partial
reimbursement  in  accordance  with the terms of Section  4.3,  and except  with
respect to compliance costs which are specifically  related to Tenant operations
in the Premises,  the cost of which shall be borne exclusively by Tenant),  will
continue to ensure  that the Common  Areas of the  Building  comply with ADA and
with all  laws,  statutes,  ordinances,  rules,  regulations,  requirements  and
directives of applicable government  authorities (including police, fire, health
and environmental authorities or agencies). Landlord further represents that, to
Landlord's knowledge, as of the Delivery Date, the zoning regulations applicable
to the Building and any covenants,  conditions or  restrictions  appertaining to
the Building permit the use of the Premises for the uses contemplated hereunder.

         2.3  Signs.  (a) Except as  expressly  set forth in this  Section  2.3,
without the prior written  consent of Landlord (which consent may be withheld in
Landlord's sole and absolute discretion), Tenant may not erect or install on the
exterior of the Building,  on any exterior window, or in any tenant floor lobby,
hallway or door therein located, any sign or other type display. Notwithstanding
the foregoing: (1) Landlord hereby consents to Tenant's installation of Tenant's
Exterior Signs (as further  described in subparagraph  (c) below) provided that:
(i) such  Exterior  Signs are designed  and  installed  in  accordance  with the
preliminary  plans and  specifications  therefor set forth in Exhibit H attached
hereto and  incorporated  herein by this reference,  and (ii) Landlord  approves
specific  plans  and  specifications   therefor  (which  approval  will  not  be
unreasonably withheld, conditioned or delayed so long as the same are consistent
with the preliminary plans and  specifications  set forth in Exhibit H) prior to
such installation;  and (2) Landlord will not unreasonably  withhold its consent
to the installation of any sign inside of the Premises which is not visible from
outside of the Premises or any internal  lobby signage on floors of the Premises
which  are  leased  in  their  entirety  by  Tenant  (as  further  described  in
subparagraph (b) below).

         (b) On those  floors of the  Building  which are  leased  hereunder  by
Tenant in their entirety,  Tenant, at its cost, may install signage or lettering
on the exterior doors to Tenant's space and in the elevator  lobbies  consistent
with the approved plans and  specifications  therefor approved by Landlord prior
to the  installation of the same.  Prior to installing any signage or lettering,
Tenant  shall  provide  plans  and  specifications   therefor  to  Landlord  for
Landlord's  review  and  approval,  which  approval  will  not  be  unreasonably
withheld,  conditioned or delayed with respect to signage inside of the Premises
which is not visible  from outside of the Premises or with respect to signage in
the lobby of any floor which is leased in its entirety by Tenant hereunder. With
respect to those  portions  of the  Premises  which may,  from time to time,  be
located on portions of floors in the Building (which floors are also occupied or
leased in part by third parties), Landlord will provide and install, at Tenant's
sole cost and expense,  in the standard  graphics for the  Building,  letters or
numerals on doors of the  Premises,  and Tenant may not use any other signage or
lettering on the exterior of the Premises on such  multi-tenant  floors  without
Landlord's  prior written  consent,  which consent may be withheld in Landlord's
sole and  absolute  discretion.
<PAGE>

Landlord  agrees  to  provide  at a  convenient  location  in the  lobby  of the
Building,  a directory of tenant names and locations.  Landlord will provide and
install  directory  strips  identifying the Tenant (and its designated  practice
groups and senior  executives) and signifying,  the appropriate  suite number or
numbers.  The  initial  directory  strips  installed  at the outset of  Tenant's
tenancy  hereunder  shall be installed  at  Landlord's  cost.  Any future new or
replacement  strips which contain changes requested by Tenant shall be installed
by Landlord at Tenant's  request and at Tenant's cost.  During the Term,  Tenant
shall be entitled to a  proportionate  share of the directory  strips  available
based upon  Tenant's  Share set forth in Section 1.5 of the Lease (as such Share
may be adjusted from time to time based upon an increase or decrease in the size
of the Premises).

         (c)  Subject  to the terms  set  forth  below,  Tenant  shall  have the
exclusive right to exterior Building signage  ("Exterior  Signs") except for any
retail  tenants  who may,  at any time,  occupy  space on the first floor of the
Building,  which  retail  tenants  shall have the right to install  signs on the
exterior of the Building below the level of the third floor. One such Sign shall
be  located  on the  upper  facade of the front of the  Building  in a  location
visible to street traffic on Route 7 ("Leesburg  Pike"), and the other such Sign
shall be  located  on the  uppermost  part of the  facade of the  Building  in a
location  visible  from the opposite  side of the Building as the Leesburg  Pike
sign, as such general  locations  are set forth in greater  detail on pages 5, 6
and 7 of Exhibit H (subject to Tenant's right to relocate the smaller of the two
signs to the alternative  location specified in Exhibit H in accordance with the
terms set forth below).  Subject to any limitations  imposed by applicable codes
and laws, said Exterior Signs shall incorporate Tenant's logo and/or trade name.
The  precise  size,  location,  materials  and  method of  installation  of such
Exterior  Signs are subject to Landlord prior written  approval,  which approval
shall not be  unreasonably  withheld,  conditioned or delayed  provided that the
plans and specifications  therefor are consistent with the preliminary plans and
specifications  therefor in Exhibit H hereto.  The parties  acknowledge that the
total square footage of Tenant's two Exterior Signs shall not exceed one hundred
eighty-five (185) square feet (of which  approximately  one hundred  twenty-five
(125)  square  feet  will be  utilized  for one of the two  signs),  and no such
Exterior Sign shall be a neon sign. The parties  further  acknowledge  that said
one hundred eighty-five (185) square foot total: (i) includes twenty (20) square
feet of exterior signage space available to the Building  pursuant to applicable
code which  Landlord was  previously  reserving for use by an  additional  first
floor tenant,  and (ii) is based upon the method of  measurement  which Landlord
expects  will be applied by Fairfax  County to the proposed  Exterior  Signs set
forth in  Tenant's  preliminary  plans  therefor.  Tenant,  at its sole cost and
expense,  with Landlord's  approval,  which will not be  unreasonably  withheld,
conditioned or delayed, and Landlord's cooperation (it being understood that any
costs incurred by Landlord  shall be borne by Tenant as well),  may request that
Fairfax County measure and/or calculate the size of Tenant's  proposed  Exterior
Signs in an alternative manner which will result in a lower total square footage
being  applied  to the same  (thereby  allowing  for larger  individual  letters
forming a part of the Signs).  If Tenant is  successful in its appeal to Fairfax
County in this  regard:  (1) Tenant may relocate the smaller of the two Exterior
Signs to the  alternative  location  specified in Exhibit H and,  subject to the
terms of clause (2) below,  increase the size of the smaller of the two Exterior
Signs subject to Landlord's approval in accordance with the foregoing terms; and
(2) without  reducing that portion of the total Building  signage square footage
available to Tenant  below one hundred  eighty-five  (185)  square feet,
<PAGE>

Tenant shall use only such additional Building signage square footage allocation
which  becomes  available  based  upon  Tenant's  appeal as will also  result in
Landlord  regaining the option of utilizing up to twenty (20) square feet of the
Building's  signage  square  footage  allocation  for an additional  first floor
Tenant.  If at any time during the Term,  Tenant leases less than three (3) full
floors in the Building, Tenant, at its cost and expense, shall remove one (1) of
the  Exterior  Signs  from the  Building,  in  accordance  with  the  procedures
described in subparagraph  (d) below.  Such removal shall be completed by Tenant
within thirty (30) days of the reduction in the size of the Premises  below such
three (3) full floor threshold.  Landlord shall, in its sole  discretion,  shall
determine  which of the two (2)  Exterior  Signs  is to be  removed  under  such
circumstances.  If at any time during the Term,  Tenant leases less than two (2)
full floors in the Building,  Tenant, at its cost and expense,  shall remove any
remaining  Exterior  Signs from the Building in accordance  with the  procedures
described in subparagraph  (d) below.  Such removal shall be completed by Tenant
within thirty (30) days of the reduction in the size of the Premises  below such
two (2) full floor threshold.

         (d)  Tenant  shall,  at its  sole  cost  and  expense,  subject  to any
limitations  imposed by applicable  Fairfax County  regulations  and other laws,
ordinances,  regulations,  orders or other legal  requirements  of  governmental
authorities,  design,  fabricate and install said  Exterior  Signs in accordance
with plans and  specifications  approved  by  Landlord  in  accordance  with the
foregoing terms prior to the installation thereof (which Exterior Signs shall be
consistent with the preliminary plans therefor attached hereto in Exhibit H). At
all times  during the Term,  Tenant  shall,  at its sole cost and  expense:  (i)
insure said Exterior Signs in accordance with reasonable insurance  requirements
relating to the Building or said  Exterior  Signs,  (ii)  maintain said Exterior
Signs in good  condition  and  repair,  and (iii) take any action  necessary  to
ensure  that said  Exterior  Signs  comply  with all  present  and future  laws,
ordinances (including zoning ordinances and land use requirements), regulations,
orders  or other  legal  requirements  of the  United  States  of  America,  the
Commonwealth  of Virginia,  Fairfax County and any other public or  quasi-public
authority  having  jurisdiction  over the  Building or said  Exterior  Signs and
insurance  requirements  relating to or affecting  the Building or said Exterior
Signs.  Other than as set forth in  paragraph  (c) above,  as may be required to
comply with the terms of this Lease,  or upon the termination of Tenant's rights
under this Lease (by virtue of the expiration of the Lease Term, the termination
of this Lease by mutual  agreement  of the  parties or the  termination  of this
Lease or Tenant's  right to  possession  of the Premises by process of law) once
Tenant shall have installed the Exterior  Signs,  such Exterior Signs may not be
removed  except as required by a change in any statute,  law or regulation or as
otherwise required by Law. Prior to the expiration or earlier termination of the
Term of the  Lease  (or  prior to a  reduction  in the size of the  Premises  as
described  in  subparagraph  (c)  above),  Tenant  shall,  at its sole  cost and
expense,  remove said Exterior  Signs from the Building and repair all damage to
the  Building  and the Land caused by the  installation  or removal of the same,
provided  however  that with  respect  to the  removal  of said  Sign,  Tenant's
obligation  with respect to any  discoloration  or "shadow"  resulting  from the
presence or removal of said Sign, Tenant's obligations shall be fulfilled by the
Tenant's exercise of diligent commercially  reasonable efforts to eliminate such
discoloration or shadow.  Tenant shall reimburse  Landlord,  as additional rent,
for any reasonable  costs incurred by Landlord with respect to Tenant's  failure
to comply with any  requirement  in this Lease  regarding  said Exterior  Signs,
which failure  continues for a period of ten (10) days following  written notice
from
<PAGE>

Landlord  (which  costs  shall  include  but  not be  limited  to any  increased
insurance  premiums  related to the same).  Tenant hereby  indemnifies and holds
Landlord  harmless from and against any claims,  liabilities,  causes of action,
losses,  damages and costs incurred by Landlord as a result of the installation,
maintenance,  existence,  relocation or removal of said Exterior  Signs.  Tenant
covenants  not to damage the  Building or the Land in the course of  installing,
maintaining   and  removing  said  Exterior   Signs.   In  the  event  that  the
installation,  maintenance or removal of said Exterior Signs results in any such
damage,  or Landlord incurs any liability  relating to the same,  Tenant agrees:
(i) to pay Landlord  within  thirty (30) days after  Landlord's  written  demand
therefor,  the  reasonable  costs  incurred by Landlord  in  repairing  any such
damage, and (ii) to indemnify Landlord against any such liability.

         (e) Landlord  will install a monument  sign  identifying  the Building.
Tenant,  at its sole cost and expense,  will install an identifying  sign in the
uppermost  position  on such  monument,  the design of which shall be subject to
Landlord's  prior written  approval,  which will not be  unreasonably  withheld,
conditioned or delayed.  If at any time during the Term, Tenant leases less than
three (3) full floors in the Building, Landlord, at its sole option, may require
Tenant, at its cost and expense,  to relocate Tenant's sign on the monument sign
to another  location thereon and to repair any damage caused by such relocation.
Such relocation  shall be completed by Tenant prior to the reduction in the size
of the Premises below such three (3) full floor  threshold.  In addition,  if at
any time  during the Term,  Tenant  leases  less than two (2) full floors in the
Building,  Landlord,  at its sole option,  may require  Tenant,  at its cost and
expense,  to remove its sign from the monument sign and repair any damage caused
by such  removal.  Such removal  shall be completed by Tenant within thirty (30)
days of the reduction in the size of the Premises  below such two (2) full floor
threshold.

         2.4 Net Rentable  Area.  The term "Net Rentable  Area" is as determined
using the Greater Washington,  D.C.  Association of Realtors' Standard Method of
Measurement (GWDCAR, June 13, 1995). The parties stipulate that the Net Rentable
Area of the Premises is that stated in Section 1.2.

         2.5  Intentionally Omitted.
              ---------------------
         2.6  Intentionally Omitted.
              ---------------------

                         ARTICLE III. COMMENCEMENT DATE
                                      -----------------

         3.1  Commencement  Date.  (a) Landlord,  at its cost and expense,  will
complete the Landlord's  Work (as defined and described in Exhibit C) and obtain
a  Certificate  of Occupancy  for the  Building,  prior to the  commencement  of
construction of the  Improvements (as defined and described in Exhibit C) in the
Premises [except for that portion of Landlord's Work related to the installation
of certain  variable air volume boxes in the Premises  ("Landlord VAV Work, " as
defined in Paragraph  A.2 of Exhibit C), which the parties  acknowledge  will be
completed by Landlord after Landlord's delivery of possession of the Premises to
Tenant but prior to: (i) January 31,  2000,  with respect to the third and fifth
floor portions of the Premises,  and (ii) with respect to the remaining portions
of  the  Premises,  within  forty  -  five  (45)  days  following  the
<PAGE>

Tenant's  commencement  of  construction  with  respect  to each  portion of the
Premises [which  commencement of construction  shall be no earlier than the date
by which Tenant has received  written  approval from Landlord of Final Plans (as
defined in Exhibit C) for the  Improvements  (as  defined in Exhibit C) for such
portion of the Premises  (which Final Plans shall contain all necessary  details
and  specifications  regarding  such  Landlord  VAV Work)]  (collectively,  "VAV
Completion Dates").  Following Landlord's delivery of possession of the Premises
in accordance with the terms hereof, the Improvements will be constructed in the
Premises at Tenant's expense (subject to contribution  from Landlord in the form
of the Tenant Allowance,  as defined and provided in Exhibit C). Tenant will act
as  construction  manager with respect to the  performance of the  Improvements.
Landlord and Tenant will  cooperate in order to allow Tenant to timely  complete
the Improvements and Landlord to timely complete the Landlord VAV Work following
the delivery of possession of the Premises to Tenant.

         (b) Landlord shall  substantially  complete Landlord's Work (other than
the Landlord VAV Work),  obtain a Certificate  of Occupancy for the Building and
deliver  possession  of the  Premises  to  Tenant  in order to allow  Tenant  to
complete  the  Improvements  therein.  On the date that  Landlord  substantially
completes  Landlord's  Work  (except for the Landlord VAV Work) and obtains such
Certificate of Occupancy,  Landlord shall deliver  possession of the Premises to
Tenant,  and such date shall be deemed the "Delivery Date," as such term is used
herein.  The parties shall both execute and deliver (which  delivery may be made
initially by delivery of executed  signature pages via facsimile to the parties'
respective  counsel) this Lease on such Delivery Date, which date is targeted to
be  January 7, 2000.  However,  if the  Delivery  Date is  delayed  beyond  such
targeted  Delivery Date or any other date  scheduled or targeted as the Delivery
Date by mutual  agreement  of Landlord and Tenant,  Landlord  shall not have any
liability  whatsoever to Tenant on account of such failure to deliver possession
of the  applicable  portion  of the  Premises  to Tenant  (except  as  expressly
provided in this  subparagraph (b)) and this Lease shall not be rendered void or
voidable as a result of such delay. However,  notwithstanding the foregoing,  if
Landlord  does not deliver  possession  of the Premises to Tenant in  accordance
with the foregoing terms on the targeted Delivery Date, provided that such delay
is not caused  solely by an act or  omission  of Tenant or  Tenant's  employees,
agents or contractors, Tenant shall receive a credit against its first occurring
Base Rent obligations  hereunder beginning on the Commencement Date in an amount
equal to one (1) days' Base Rent (which  amount will be determined by pro-rating
one full  monthly  installment  of Base Rent payable with respect to the Initial
Portion of the
<PAGE>

Premises  beginning  on the  Commencement  Date on a per diem basis based upon a
thirty-one (31) day month) for each day that Landlord's delivery of the Premises
in accordance with the foregoing terms is delayed beyond such targeted  Delivery
Date.  In addition,  if Landlord  fails to complete the Landlord VAV Work by the
targeted VAV Completion Dates set forth in subparagraph (a) above, provided that
such  delay is not caused  solely by an act or  omission  of Tenant or  Tenant's
employees,  agents or  contractors,  Tenant shall  receive a credit  against its
first occurring Base Rent obligations  hereunder with respect to that portion of
the Premises for which such Landlord VAV Work is not completed  beginning on the
Commencement  Date applicable to such portion of the Premises (the  Commencement
Date,  Interim  Commencement  Date or Final  Commencement  Date, as set forth in
greater  detail  below) in an amount  equal to one (1)  days'  Base Rent  (which
amount will be  determined by pro-rating  one full monthly  installment  of Base
Rent payable with respect to the applicable Portion of the Premises beginning on
the  applicable  Commencement  Date on a per diem basis based upon a  thirty-one
(31) day month) for each day that  Landlord's  completion  of such  Landlord VAV
Work  is  delayed  beyond  such  targeted  VAV  Completion   Date.  The  parties
acknowledge  that  Tenant  shall not be  obligated  to pay Base Rent during such
period of early occupancy  between the Delivery Date and the Commencement Date .
However,  Tenant  covenants and agrees that such occupancy shall be deemed to be
under all of the other terms, covenants, conditions and provisions of this Lease
(except that Tenant shall not be obligated to pay for temporary electric service
to the Premises prior to the Commencement Date).

         (c) Upon the full  execution  and delivery of this Lease,  Tenant shall
take  possession of the Premises and shall have the right to enter upon the same
to construct the Improvements  therein.  The Improvements  shall be completed by
Tenant  in a  safe  manner  and in  conformity  and  compliance  with:  (i)  the
requirements and  specifications  set forth in this  subparagraph  (c), (ii) all
applicable  laws,  statutes,  rules,  regulations,  orders,  ordinances,  codes,
approvals,  permits,  interpretations,   directives  and  requirements,  of  all
federal,  state,  county,  municipal and city  legislatures,  executive offices,
courts, departments,  bureaus, boards, agencies, offices,  commissions and other
sub-divisions thereof, or of any official thereof, or of any other governmental,
judicial,  public,   quasi-public  or  quasi-judicial  authority  (collectively,
"governmental authorities"),  and the National Board of Fire Underwriters or any
other  body  exercising   similar   functions   (collectively,   "Requirements")
applicable thereto, and (iii) the Final Plans (as defined in Exhibit C) (and any
additional or modified plans and specifications) approved therefor in writing by
Landlord.  All  Improvements  shall be  completed  in a first class  workmanlike
manner, using only new materials, fixtures and equipment, and shall be performed
by reputable contractors and subcontractors who are licensed to conduct business
in the Commonwealth of Virginia,  and such contractors and subcontractors  shall
be subject to Landlord's  prior written  approval  (which  approval shall not be
unreasonably withheld,  conditioned or delayed). At all times during performance
of the Improvements,  Landlord and its  representatives  shall have the right to
enter upon the Premises for the purpose of inspecting  construction and progress
of the same and compliance with the foregoing  (provided that in exercising such
right,   Landlord  will  not  materially   interfere  with  performance  of  the
Improvements).  Prior to commencing  any work with respect to the  Improvements,
and thereafter  until the same are  completed,  Tenant shall obtain and maintain
and/or  cause  Tenant's  contractor  to obtain and maintain  insurance  against:
claims under workmen's compensation and other employee benefit acts, with limits
not less  than  $500,000.00;  claims  for  damages  because  of  bodily  injury,
including death, to said  contractor's  employees and all others,  with a single
limit of  $5,000,000.00  per person and per occurrence;  and damages to property
with  limits  of   $5,000,000.00.   Throughout   the  period  during  which  the
Improvements   are  being  performed,   Tenant  and  Tenant's   contractors  and
subcontractors  shall:  (1) keep the Building,  the Land and all areas  adjacent
thereto free to debris, refuse, equipment,  materials and personal property, (2)
initiate,  maintain and supervise all necessary safety  precautions and programs
in connection  with the work and take all reasonable  precautions for the safety
of, and provide all reasonable  protection to prevent damage,  injury or loss to
all  employees on the work site and other  persons who may be affected  thereby,
all the work and all the materials and equipment to be incorporated therein, and
other property at the work site or adjacent thereto, such precautions to include
without  limitations  the  furnishings  of guard  rails and  barricades  and the
securing of the Premises.
<PAGE>

Immediately upon the completion of the Improvements: (i) Tenant shall remove and
cause Tenant's  contractors and any subcontractors to remove any and all debris,
refuse, equipment,  materials and personal property left on the Premises, in the
Building,  on the Land or any area  adjacent  thereto,  and  (ii)  Tenant  shall
deliver to Landlord full and complete lien releases  executed by all of Tenant's
contractors  and  subcontractors  and any  other  party  providing  services  or
materials  with respect to the  Improvements  or the Premises.  During  Tenant's
performance  of  the  Improvements  and  Tenant's  initial  "move-in"  into  the
Premises,  Tenant will have exclusive use, at no additional  cost to Tenant,  of
one (1) freight elevator or hoist and one (1) passenger elevator.

         (d) (1) The  Commencement  Date  shall be the  earlier  to occur of (i)
March 1, 2000,  and (ii) the date on which Tenant  substantially  completes  the
Improvements  in the Initial Portion (as defined below) of the Premises and such
Initial  Portion  can  be  occupied  for  business  operations   (including  the
completion of other work and installations beyond the Improvements necessary for
Tenant's business  operations);  (2) the Interim  Commencement Date shall be the
earlier  to occur  of:  (i)  June 1,  2000,  and  (ii) the date on which  Tenant
substantially completes the Improvements with respect to an additional (over and
above the Initial Portion) full floor of the Premises (the "Interim  Portion" of
the Premises) and such Interim  Portion can be occupied for business  operations
(including   the  completion  of  other  work  and   installations   beyond  the
Improvements  necessary for Tenant's  business  operations)  (subject to further
adjustment  as set  forth  below in this  subparagraph  (d));  and (3) the Final
Commencement  Date shall be the  earlier to occur of: (i)  October 1, 2000,  and
(ii) the date on which Tenant  substantially  completes the  Improvements in the
remaining Balance (as defined below) of the Premises (the "Final Portion" of the
Premises)  and such  Final  Portion  can be  occupied  for  business  operations
(including   the  completion  of  other  work  and   installations   beyond  the
Improvements  necessary for Tenant's business operations) (subject to adjustment
in accordance with the terms of subparagraph (e) below). The parties acknowledge
that  Tenant  shall  complete  the  Improvements  in the  Premises  on a  phased
construction  schedule which will include a first phase  consisting of three (3)
full floors (the "Initial  Portion" of the Premises),  a second phase consisting
of one (1) full floor (the "Interim Portion" of the Premises, which Phase may be
completed in stages as set forth  below),  and a final phase  consisting  of the
remaining full floor (the "Final Portion" of the Premises).  That portion of the
Premises  which is not a part of the Initial  Portion  consists of the  "Interim
Portion"  and  the  "Final  Portion,"  and  is  sometimes   referred  to  herein
collectively  as the  "Balance"  of the  Premises.  Tenant,  at its option,  may
substantially complete the Improvements with respect to distinct portions of the
fourth (4th) floor of the Premises,  provided that Tenant shall commence payment
of Base Rent with  respect to such  portions  on the date that the  Improvements
with respect to such portion are substantially completed and such portion can be
occupied for business  operations  (including  the  completion of other work and
installations   beyond  the   Improvements   necessary  for  Tenant's   business
operations)  (provided  that,   notwithstanding  the  foregoing  terms  of  this
sentence, all of Tenant's Base Rent obligations with respect to the fourth (4th)
floor  portion of the  Premises  shall  commence  no later  than June 1,  2000).
Landlord  agrees to  cooperate  with  Tenant in any  reasonable  manner to allow
Tenant to complete  construction  of the  Improvements  in  accordance  with the
construction schedule,  which cooperation will include: (i) providing reasonable
approval of Tenant proposed plans and specifications related to the Improvements
in a timely  manner  (Landlord  will  endeavor  to  provide  such  approval  (or
<PAGE>

disapproval  with comments,  as  applicable)  within two (2) business days after
submittal of the same by Tenant provided that engineering review is not required
with respect to the same,  in which case Landlord will provide such approval (or
disapproval  with comments,  as applicable)  within five (5) business days after
submittal of the same by Tenant);  (ii) allowing Tenant to commence certain work
prior to obtaining a final permit therefor under appropriate circumstances as is
customarily  done in the Fairfax County area with respect to tenant  improvement
construction  (subject to issuance of such final permit and compliance  with all
applicable  governmental  requirements).  In order to  further  ensure  that the
Improvements are completed in accordance with the construction schedule,  Tenant
agrees that all plans and specifications for the Improvements will be consistent
with the design and finish of a Class A office building and the terms of Exhibit
J hereto,  which is  incorporated  herein by this  reference,  and  Tenant  will
reasonable  cooperate with Landlord and provide  Landlord with progress plans as
they are developed and involve  Landlord's  construction  representatives in the
planning process and in meetings related thereto.

         (e) Notwithstanding the terms of subparagraph (d) above with respect to
the dates on which Tenant's Base Rent obligations  commence with respect to each
portion  of the  Premises:  (1)  Tenant,  at its  sole  option,  may  elect,  by
delivering  written  notice to Landlord or on before March 1, 2000,  to commence
paying Base Rent with respect to the Final Portion of the Premises  prior to the
Final Commencement Date on a date selected by Tenant, which date shall be either
July 1, 2000,  August 1, 2000 or September 1, 2000; and (2) if Tenant makes such
an election  the  additional  Base Rent to be paid by Tenant with respect to the
Final  Portion of the Premises  for July,  August  and/or  September,  2000,  as
applicable, shall be applied by Landlord as a credit against the first Base Rent
obligations  coming due  hereunder  with  respect to the Initial  Portion of the
Premises beginning on the Commencement Date (subject to the condition subsequent
that such  additional Base Rent amounts with respect to the Final Portion of the
Premises are  subsequently  timely paid by Tenant in accordance with its written
notice to  Landlord  regarding  the same),  provided  that in no event shall any
election by Tenant  under this  subparagraph  (e) result in: (i) a reduction  or
abatement  of any of Tenant's  Base Rent  obligations  with respect to the Final
Portion of the Premises for any period  following the Final  Commencement  Date,
(ii) the  payment by Tenant to  Landlord  of Base Rent with  respect to calendar
year 2000 in an amount less than  $3,074,342.00 (as such amount may be increased
by virtue of Tenant's accelerated occupancy of the fourth (4th) floor portion of
the Premises),  or (iii) any modification of the Final  Commencement Date (which
Date  shall be  determined  in  accordance  with the terms of  subparagraph  (d)
above).
<PAGE>

         (f) Promptly after the Commencement Date, Interim Commencement Date and
Final  Commencement  Date are  ascertained,  Landlord and Tenant shall execute a
certificate,  in the form of Exhibit D hereto, which certificate shall set forth
the Commencement  Date, the Interim  Commencement  Date, the Final  Commencement
Date and the date upon which the  initial  term of this Lease will  expire.  The
parties  acknowledge that Tenant's failure to accept  possession of the Premises
(or any part thereof)  when the same is tendered by Landlord in accordance  with
the terms  hereof  shall in no way affect the Delivery  Date,  the  Commencement
Date,  the  Interim  Commencement  Date,  or the Final  Commencement  Date,  and
Tenant's  rental  obligations  shall in no way be  affected  by such  failure to
accept possession.

         3.2 Holding  Over.  (a) If Tenant shall not  immediately  surrender the
entire  Premises on the date of the  expiration  or earlier  termination  of the
Lease Term,  the Base Rent payable by Tenant  hereunder  (which shall be payable
with respect to the entire  Premises  regardless of what portion thereof remains
occupied by Tenant)  shall be increased to equal the greater of: (i) fair market
rent for the  Premises,  or (ii) (1) during the first sixty (60) days  following
the  expiration  or  termination  of the Lease Term,  one hundred  fifty percent
(150%) of the Base Rent payable hereunder during the month immediately preceding
the  expiration or  termination  date  (determined  without giving effect to any
abatement  thereof),  and (2) for all  periods  after the first  sixty (60) days
following the expiration or  termination of the Lease Term, two hundred  percent
(200%) of the Base Rent payable hereunder during the month immediately preceding
the  expiration or  termination  date  (determined  without giving effect to any
abatement thereof)  ("Holdover Rent"). In addition to such Holdover Rent, Tenant
shall also  continue to pay to Landlord all  additional  rent in the amount that
was payable hereunder during the month  immediately  preceding the expiration or
termination date or as otherwise determined in accordance with the terms of this
Lease.  Such  Holdover Rent shall be computed by Landlord on a monthly basis and
shall be  payable  by Tenant on the first day of such  holdover  period  and the
first day of each calendar month  thereafter  during such holdover  period until
the entire  Premises  shall have been vacated by Tenant and  possession  thereof
returned to Landlord.  Landlord's  acceptance  of such Holdover Rent from Tenant
shall not in any manner impair or adversely  affect  Landlord's other rights and
remedies hereunder, including, but not limited to, (i) Landlord's right to evict
Tenant from the Premises,  and (ii) Landlord's right to recover damages pursuant
to this Lease and such other  damages as are  available to Landlord at law or in
equity (which damages shall be limited as provided below).

         (b) Except for Tenant's  obligation to pay the aforesaid  Holdover Rent
and the  limitations on such waiver set forth below in this Section 3.2, so long
as Tenant  does not  holdover  in the  Premises  for more than  sixty  (60) days
following  the  expiration or  termination  of the Lease Term,  Landlord  hereby
waives its right to collect any damages from Tenant based upon Tenant's  failure
to timely  vacate the  Premises.  The  foregoing  waiver  shall in no way affect
Tenant's  obligation  to pay the  aforesaid  Holdover  Rent with respect to such
sixty  (60) day  period,  nor  shall  such  waiver  in any way  affect or impair
Landlord's right to pursue and collect (and Tenant's obligation to pay): (1) any
damages (other than consequential or punitive damages
<PAGE>

which Landlord hereby waives), costs,  liabilities,  costs and expenses suffered
or incurred by  Landlord  as a result of Tenant's  failure to timely  vacate the
Premises if Tenant shall fail within sixty (60) days following the expiration or
termination  of the Lease Term,  to  completely  vacate the  Premises and return
possession  thereof to Landlord in accordance  with the terms of this Lease,  or
(2) any costs or  expenses  incurred by  Landlord  related  directly to Tenant's
failure,  upon vacating the Premises to remove any alterations,  improvements or
other  personal  property  from the same in  accordance  with the  terms of this
Lease.

         (c) Subject to Landlord's  partial  damage  waiver set forth above,  if
Tenant fails to surrender the Premises on the expiration or earlier  termination
of this Lease with such  removal  and repair  obligations  completed,  then,  in
addition to its other  obligations  under this Section 3.2 and Landlord's rights
and  remedies  under this  Section 3.2 and the other  provisions  of this Lease,
Tenant shall indemnify,  defend and hold Landlord  harmless from and against any
and all claims, judgments, suits, causes of action, damages, losses, liabilities
and expenses  (including  reasonable  attorneys' fees and court costs) resulting
from such failure to timely surrender. The foregoing indemnity shall survive the
expiration or earlier termination of this Lease.

         (d) To the extent  that the  aforesaid  monthly  Holdover  Rent paid by
Tenant  exceeds  the  greater of: (i) one  hundred  five  percent  (105%) of the
monthly  Base  Rent  payable  hereunder  during  the last  full  calendar  month
immediately  preceding the expiration or termination of the Term (without giving
effect to any  abatement  thereof);  or (ii) the  monthly  Fair  Market Rent (as
defined  in Section  15.23)  for the  Premises,  then any such  excess  shall be
credited by Landlord against any damages  recoverable by Landlord from Tenant as
a result of such holdover.

                                ARTICLE IV. RENT
                                            ----

         4.1  Payment.  Tenant shall pay to Landlord in advance on or before the
first day of each month  during the Lease  Term,  in legal  tender of the United
States of America, and, except as may be expressly set forth herein or expressly
required  by law,  without any demand,  set-off or  deduction,  at the office of
Landlord in _  Institutional  Property  Managers,  Inc., 1961 Chain Bridge Road,
Suite 105, McLean, Virginia 22102-4562,  Attn: General Manager, or at such place
or to such of Landlord's  Agents from time to time  designated in writing,  Rent
comprised  of a Base Rent and  Additional  Rent  (defined  in Section  4.5).  If
Landlord  shall at any time  accept  rent  after it shall  have  become  due and
payable,  such acceptance shall not excuse a delay upon subsequent  occasions or
construe or be construed as a waiver of any of Landlord's rights  hereunder.  No
payment by Tenant or receipt by Landlord of a lesser amount than any installment
or payment of Base Rent or Additional  Rent due shall be deemed to be other than
on account of the amount due,  and no  endorsement  or statement on any check or
payment of Rent shall be deemed an accord and satisfaction.  Landlord may accept
such check or payment  without  prejudice  to  Landlord's  right to recover  the
balance of such  installment  or payment of Rent,  or pursue any other  remedies
available to Landlord.

         4.2 Base Rent.  (a)  Beginning  on the  Commencement  Date,  subject to
Tenant's rights under Section 3.1(e),  Tenant shall pay (with or without receipt
of a written  statement from Landlord) the Base Rent (as defined in Sections 1.4
and 1.7 hereof) in advance, promptly upon
<PAGE>

the first day of every  month of the Lease  Term.  If the initial or final month
is less than a full calendar month, the Base Rent for such month will be reduced
proportionately.

         (b)  Notwithstanding  the terms of subsection (a) above to the contrary
Tenant's obligation to pay its monthly Base Rent obligations with respect to the
Interim  Portion and Final  Portion of the  Premises  shall not  commence on the
Commencement  Date provided that the  Improvements  with respect thereto are not
substantially completed on or before such Commencement Date and such Portions of
the Premises are not ready for occupancy for business  operations  (as set forth
in greater detail in Section 3.1) . Tenant's obligation to pay monthly Base Rent
with respect to the portions of the Balance of the  Premises  shall  commence on
the Interim  Commencement  Date and the Final  Commencement Date (and such other
dates as may be  determined  with  respect to each portion of the Balance of the
Premises in  accordance  with the terms of Section  3.1).  In the event that the
Commencement  Date,  Interim  Commencement  Date or the Final  Commencement Date
occur on a date which is not the first day of a calendar  month,  Tenant's  Base
Rent  obligations  with  respect  to the  applicable  portion  of  the  Premises
commencing  on such Date shall be pro-rated  for the partial  calendar  month in
which  such Date  occurs  and shall be paid on such  Date to  Landlord.  For the
purposes of determining what portion of Tenant's Base Rent obligations set forth
in Section 1.4 hereof are attributable to the Initial Portion and the Balance of
the Premises,  such determination shall be made in accordance with the terms set
forth in Section 1.7.

         4.3  Tenant's Share of Operating Costs.
              ---------------------------------

         (a)  "Operating  Costs" means,  for any calendar  year,  the sum of all
reasonable  expenses,  costs and  disbursements  of every kind and  nature  that
Landlord  pays or becomes  obligated to pay in connection  with the  management,
operation and maintenance of the Building, the parking facilities,  and the land
upon which the Building is situated (the "Land"),  including but not limited to:
all reasonable  management office expenses,  all applicable sales and use taxes;
expenses incurred for heat, cooling and other utilities;  cost of insurance (for
general  liability,  all  risk,  rent  loss and  other  commercially  reasonable
coverage  carried by Landlord  with  respect to the Building  with  commercially
reasonable  deductibles,  excluding increases in insurance premiums directly and
specifically related to other tenants); cost of janitorial and cleaning service,
trash  collection and recycling  services,  pest control;  concierge,  lobby, or
security  service  (if  any);  salaries,  wages  and  other  personnel  costs of
engineers,  superintendents,  watch  persons,  and all  other  employees  of the
Building at and under the level of Senior Property Manager directly  involved in
the  management  and operation of the Building,  including any sales tax imposed
upon  their  service;  charges  under  maintenance  and  service  contracts  for
elevators, chillers, boilers and controls; window cleaning; building and grounds
maintenance; parking lot maintenance; management fees; permits and licenses; all
maintenance and repair expenses and supplies including  replacement and disposal
of fluorescent light bulbs and ballasts in building standard lighting  fixtures;
costs (including finance charges) of improvements to the Building,  equipment or
capital items that are designed to increase safety, improve energy efficiency or
expand  telecommunications  service; the cost of replacing existing equipment or
systems or other costs incurred for the purpose of complying with the directives
of a public or quasi-public  entity or authority which directive is issued after
the  Delivery  Date  (which  may  include  a  different  or new  application  or
interpretation of a pre-existing  directive,  law, statute, order or regulation)
and as
<PAGE>

the same may be  amortized  over their  useful life (as  determined  by industry
standard) on a straight  line basis;  costs of complying  with all  governmental
regulations,  including, without limitation, the disposal of chlorofluorocarbons
and  compliance  with Title III of the Americans With  Disabilities  Act of 1990
("ADA")  or any  other  Virginia  statute  regarding  barriers  (subject  to the
limitations  set forth  below)  which  such  regulations  are  issued  after the
Delivery   Date  (which  may  include  a  different   or  new   application   or
interpretation of a pre-existing regulation);  costs of independent contractors;
any costs incurred in implementing and operating any  transportation  management
program, ride sharing program or similar program including,  but not limited to,
the cost of any transportation program fees, mass transportation fees or similar
fees  charged or  assessed  by any  governmental  or  quasi-governmental  entity
(collectively,  "Transportation  Fees"); any payments made by the Landlord under
any  easement  or  license  agreement   affecting  the  Building  or  the  Land,
declaration,  restrictive  covenant or  instrument  pertaining to the payment of
sharing of costs among  property  owners or users  affecting the Building or the
Land; reasonable reserves for replacements,  repairs and contingencies;  and all
other  reasonable  costs and expenses  properly  incurred in the  operation  and
maintenance of this office building.  Any such costs and expenses which Landlord
shares with any adjacent  landowner and the cost of any item of Operating  Costs
which is incurred by Landlord  with  respect to the  Building  and any  adjacent
property shall be fairly and equitably  apportioned by Landlord,  in good faith,
between the  Building and any  adjacent  property  (or between  Landlord and any
adjacent  landowner,  as  applicable).  In the event that at any time during the
Term,  Operating  Costs  include any  Transportation  Fees, so long as Tenant is
leasing at least three (3) full floors in the Building, Tenant, at its sole cost
and expense,  may appeal any such Transportation  Fees, and Tenant shall receive
Tenant's  Share of the  benefit  of any  reduction  in the  same.  Tenant  shall
indemnify  and hold  Landlord  harmless  from and against  any costs,  expenses,
liabilities,  claims, actions, causes of action or damages in any way associated
with or related to Tenant's appeal of any such Transportation Fees.

         "Operating Costs" shall not include:  (i) Real Estate Taxes (as defined
in Section 4.4 below); (ii) the initial cost of constructing the Building; (iii)
the cost of  alterations  to other  rentable  spaces in the Building  (including
renovation,   refurbishment  and  tenant   improvements  and  architectural  and
engineering costs associated therewith); (iv) lease commissions;  (v) payment of
principal  and  interest  on  mortgages  and other  fees  payable  to lenders in
connection  with any such  mortgages;  (vi) rents payable under any ground lease
with respect to the Building or the Land; (vii) costs to Landlord of any work or
service performed  specifically for any other tenant at the cost of such tenant;
(viii)  advertising  and marketing  costs  associated with leasing the Building,
(ix) the cost of  maintaining  a  leasing  and  marketing  office  in or for the
Building,  including  overhead or deemed rent relating thereto;  (x) salaries or
other compensation to any employees, partners, trustees, shareholder,  directors
or officers of Landlord who are not actively  involved in the  management of the
Building or the Project;  (xi)  expenses  for which  Landlord is  reimbursed  by
insurance  (or for which  Landlord  would have been  reimbursed  if Landlord had
carried  the  insurance  coverage  required  pursuant  to Section  9.6  hereof),
condemnation proceeds, warranties or any other source (other than the payment by
tenants of the Building of Operating  Costs in a manner  similar to the terms of
this Section 4.3);  (xii) late charges  incurred by Landlord as a result of late
payment of Real Estate Taxes; (xiii) Landlord's income taxes; (xiv) improvements
or  replacements  to the  Building,  equipment or other  capital  items having a
useful
<PAGE>

life (as  determined in accordance  with industry  standards) in excess of three
(3) years from the date of installation  (collectively "Capital Costs"),  except
those that are  reasonably  calculated by Landlord to increase  safety,  improve
energy  efficiency,  expand  telecommunications  service,  or  comply  with  the
directives of a public or  quasi-public  entity or authority [in which case such
Capital Costs shall be amortized over the useful life (as determined by industry
standard) of the improvement,  replacement,  equipment or other capital item and
included in Operating Costs]; (xv) the cost of correcting defects in the initial
design or construction of the Building;  (xvi) costs associated with maintaining
the  existence  of and  the  operation  of the  business  of the  corporate  (or
partnership or trust) entity which  constitutes  the Landlord (such as trustee's
fees,  partnership  organization or  administration  expenses,  deed recordation
expenses and general overhead  expenses and legal and accounting fees related to
the same) apart from the costs of the operation of the Building and the Project;
(xvii) income, excess profits, franchise taxes or other such taxes imposed on or
measured  by the net  income of  Landlord  from the  operation  of the  Building
(except for any Fairfax  County BPOL taxes or other similar  local taxes,  which
shall  also be  included  in Real  Estate  Taxes,  as  defined  below);  (xviii)
attorney's  fees incurred in  connection  with any  disputes,  controversies  or
defaults under leases of other tenants;  (xix) costs incurred in connection with
the  transfer,  taking or  condemnation  of the  Building or the Real  Property;
(xx)any amounts paid to any person,  firm or corporation related to or otherwise
affiliated  with  Landlord  or  any  general  partner,   officer,   director  or
shareholder of Landlord or any of the foregoing,  to the extent the same exceeds
arm's length competitive prices paid in the Washington,  D.C.  metropolitan area
for similar  services or goods;  (xxi)  reserves  for repairs,  maintenance  and
replacements  (until  utilized for purposes for which such costs may be included
in Operating Costs pursuant to this Lease);  (xxii) costs or expenses associated
with leasing  space in the Building or the sale of any interest in the Building,
including without limitation,  advertising and marketing, legal fees, commitment
fees,  commissions  or any similar  amounts paid for or on behalf of any tenant,
such as space planning,  moving costs, improvement allowances,  rental and other
tenant  concessions;  (xxiii) costs of HVAC service outside normal HVAC Business
Hours sold to tenants of the  Building  by  Landlord  or the cost to Landlord of
providing any other special services to other tenants; (xxiv) the costs incurred
to remove any hazardous  materials or other toxic  material or  substances  from
either  the  Building  or the  Land;  (xxv)  any  compensation  paid to  clerks,
attendants,  or other persons in commercial  concessions operated by Landlord in
the Building;  (xxvi) costs and expenses resulting from the negligence or wilful
misconduct of Landlord or its employees,  contractors or agents; (xxvii)fines or
penalties  assessed against Landlord by reason of Landlord's  violation of laws;
(xxviii) the cost of investment grade art, sculpture and paintings not purchased
in the ordinary course of operating the Building;  (xxix) costs of disputes with
Landlord's  management  agent or any  prospective  purchaser or mortgagee of the
Building; (xxx) depreciation of the Building or any improvements therein; (xxxi)
with respect to employees  shared with buildings  outside of the Project,  those
portions of the personnel costs  attributable  to such buildings  outside of the
Project;  (xxxii) utility costs specifically reimbursed by individual tenants of
the  Building  and  not  provided  to  all  tenants  of the  Building;  (xxxiii)
independent  contractor  and related  costs  associated  with the  financing  or
leasing of the Building;  and (xxxiv) the cost of correcting known violations of
ADA existing as of the Delivery Date;  (xxxv) owner's  association  assessments,
condominium  and  association  dues;  or,  (xxxvi)  costs and expenses  Landlord
expends  for the benefit of the  adjacent  Tyson's I Mall to the extent that the
Building does not directly benefit from those costs or expenses.
<PAGE>

         (b) The initial  Operating Costs (the "Initial Basic Operating  Costs")
to be used in calculations  regarding Excess Operating Costs (defined below) are
the actual Operating Costs for the calendar year 2000,  subject to adjustment as
set forth in Section  4.3(d),  Section  4.4(b)  and  Section  4.4(d)  (the "Base
Year").

         (c) In addition to Base Rent,  beginning on February 1, 2001,  for each
calendar year (or partial year) during the Lease Term  thereafter,  Tenant shall
pay as  Additional  Rent,  Tenant's  Share of the amount by which the  Operating
Costs for such  calendar  year exceed the Initial  Basic  Operating  Costs (such
excess hereinafter referred to as "Excess Operating Costs") as follows:

                  (i) No less than once per calendar year during the Lease Term,
Landlord  will  provide  Tenant with a detailed  written  statement of estimated
Excess  Operating  Costs  (broken  down on a  line-item  basis  with  reasonable
supporting  documentation)  for  the  upcoming  or  current  calendar  year,  as
applicable.  Said  estimate  shall be based upon an increase  calculated in good
faith over the previous year's Operating Costs,  which increase shall not exceed
the sum of: (1) Landlord's  reasonable  good faith estimate of  non-controllable
Operating  Costs,  and (2) the  applicable  Controllable  Operating Cost Cap (as
defined  below)with  respect  to such  calendar  year.  If  Landlord  reasonably
determines,  pursuant to  commercially  standard  criteria in the Tyson's Corner
submarket,  that the Excess  Operating  Costs are  materially  or  significantly
greater than Landlord's  initial estimate thereof,  then Landlord may deliver to
Tenant not more than once  during  any  calendar  year,  a revised  estimate  of
Tenant's Share of Excess  Operating Costs subject to the foregoing  limitations.
Tenant  shall pay to Landlord  within  thirty (30) days of  notification  of the
revised  amount,  the difference  between the previous  estimate and the revised
estimate  for  the  expired  portion  of  the  current  calendar  year.  Monthly
installments  of Tenant's Share of Excess  Operating Costs will be increased for
the remainder of the months and year following  Tenant's  receipt of the revised
estimate  to  one-twelfth  (1/12) of the revised  estimate of Tenant's  Share of
Excess Operating Costs.

                  (ii) Not more than one hundred twenty (120) days following the
last day of each  calendar  year,  Landlord  will provide  Tenant with a written
statement   (setting  forth  separate  line  items  of  costs,  with  reasonable
supporting  documentation)  of the amount of Tenant's Share of estimated  Excess
Operating Costs paid for the preceding  calendar year (or partial calendar year)
to Tenant's Share of Excess  Operating  Costs actually  incurred by Landlord for
such  calendar  year.  If the  amount  of  Tenant's  Share of  estimated  Excess
Operating Costs paid by Tenant for such prior calendar year (or partial calendar
year): (A) exceeds the Tenant's Share of actual Excess  Operating Costs,  within
thirty  (30) days of such  statement,  Landlord  will give  Tenant an  immediate
credit in such amount against  current  payments of Rent (or if in the last year
of the Lease Term, refund the excess within the aforesaid thirty (30) days), (B)
is less than Tenant's Share of actual Excess Operating  Costs,  Tenant shall pay
Landlord,  as Additional Rent, the difference  within thirty (30) days following
Tenant's receipt of such written comparison. Any delay or failure of Landlord in
billing any Excess  Operating Cost escalation shall not be construed as a waiver
of and  shall  not  impair  the  continuing  obligation  of  Tenant  to pay such
escalation  for any such  escalation  incurred  within  the  previous  three (3)
calendar years.
<PAGE>

                  (iii) For the purpose of calculating  Tenant's Share of Excess
Operating Costs,  Landlord's Controllable Operating Costs (as defined below) for
any calendar year  following the Base Year shall be limited to the  Controllable
Operating Cost Cap (as hereinafter defined). The Controllable Operating Cost Cap
for the first  three (3)  calendar  years  following  the Base Year  shall be an
amount equal to Landlord's actual Controllable Operating Costs for the Base Year
increased  by five  percent  (5%)  annually,  on a  cumulative  basis,  for each
calendar  year  following  said Base Year through the calendar year in question.
Stated alternatively,  the Controllable Operating Expenses for any calendar year
shall  not  exceed  one  hundred  ten  and  25/100th  percent  (110.25%)  of the
Controllable  Operating Expenses for the calendar year two (2) years immediately
preceding that calendar year. The Controllable  Operating Cost Cap for all other
calendar  years  during the Term shall be an amount equal to  Landlord's  actual
Controllable  Operating  Costs for the calendar  year two (2) years prior to the
year in question  ("Rolling Base Year") increased by five percent (5%) annually,
on a cumulative  basis,  for each calendar year following said Rolling Base Year
through the calendar  year in question.  [By way of  illustration  only,  if the
actual per square foot  Controllable  Operating  Costs are $7.00 during the Base
Year of 2000,  the Control  Operating  Cost Cap for 2001 will be $7.35  ($7.00 x
1.05), the Controllable Operating Cost Cap for 2002 will be $7.72 ($7.35 x 1.05)
and the  Controllable  Operating Cost Cap for 2003 will be $8.10 ($7.72 x 1.05).
If the  actual  Controllable  Operating  Costs  for  2002  are  $7.25,  then the
Controllable  Operating  Cost Cap for 2004 will be $7.99 ($7.25 x 1.05 x 1.05)].
For the purposes hereof the term  "Controllable  Operating Costs" shall mean all
Operating Costs except:  Real Estate Taxes, sales, use and any other taxes, cost
of insurance,  costs of procuring and providing  utility  services,  union labor
costs (to the extent  controlled by a collective  bargaining  agreement),  costs
associated with procuring permits and licenses,  and costs of complying with all
governmental  laws and  regulations  (to the extent that the same are properly a
part of Operating  Costs  pursuant to the  definition  thereof set forth above).
However,  notwithstanding the foregoing, for the purpose of calculating Tenant's
Share of Excess  Operating  Costs, the cost of making changes or improvements to
the Common Areas of the Building for the purpose of complying with  governmental
laws  and  regulations   (except  those  changes  or   improvements   which  are
necessitated by Tenant's particular use of the Premises), to the extent that the
same are properly a part of Operating  Costs pursuant to the definition  thereof
set forth above,  shall not exceed  ($0.30) per square foot of Net Rentable Area
in the Building during any calendar year.

         (d) Operating  Costs for the Base Year and for any calendar year during
which  the  Building  is not yet  ninety-five  percent  (95%)  leased,  shall be
determined by Landlord in its good faith,  commercially  reasonable  discretion,
based upon the amount  that such Costs  would be if the  Building  were at least
ninety-five  percent (95%) leased.  Real Estate Taxes for the Base Year shall be
determined  by Landlord in its good faith  commercially  reasonable  discretion,
based  upon the  amount  that such  Costs  would be if the  Building  were fully
completed and assessed and stabilized at ninety-five percent (95%) occupancy.

         4.4  Tenant's Share of Real Estate Taxes.
              -----------------------------------

         (a) "Real Estate Taxes" means all general and special real estate taxes
and assessments, ordinary or extraordinary, foreseen or unforeseen, any state or
local business
<PAGE>

personal  property tax, and other ad valorem taxes,  levies and assessments (net
of any refund) paid upon or in respect of the Building, the parcel or parcels of
Land on which the Building is located  (together  with the  Building,  the "Real
Property"),  or the rents  therefrom,  and all taxes or other charges imposed in
lieu of any  such  taxes,  as well as fees of  counsel  and  experts  which  are
reasonably  incurred by, or  reimbursable  by,  Landlord in contesting  any such
taxes or in seeking any  reduction in the assessed  valuation of the Building or
the Land or a  judicial  review  thereof  (regardless  of  whether  the same are
reduced),  whether  incurred  under  the  current  or  any  future  taxation  or
assessment  system or  modification  of,  supplement  to, or substitute for such
system.  Real Estate Taxes also shall include special  assessments  which are in
the  nature of or in  substitution  for real  estate  taxes,  including  but not
limited to road improvement  assessments,  special use area assessments,  school
district  assessment,  vault space  rentals and any business,  professional  and
occupational  license tax (including any Fairfax County Business,  Professional,
and  Occupational  License Tax ("BPOL"))  payable by Landlord in connection with
the Real Property.  If at any time the method of taxation prevailing at the Date
of Lease shall be altered so that in lieu of, as a substitute for or in addition
to the whole or any part of the Real Estate Taxes now levied or assessed,  there
shall be levied or  assessed a tax of  whatever  nature,  then the same shall be
included as Real Estate Taxes hereunder. If any application or review results in
a refund on  account  of any  prior  assessment,  after  payment  of  reasonable
expenses incurred in connection therewith (whether by Landlord,  Tenant or other
tenants of the Building),  and after  recalculation  of Excess Real Estate Taxes
(as  hereinafter  defined) if the Base Year has been affected,  and if Tenant is
not in default hereunder beyond any applicable notice and cure period,  Landlord
will  reimburse  Tenant an amount equal to Tenant's Share (as defined in Section
1.6) of the refund  applicable to the Lease Term. Any  determination  whether or
not to appeal or seek a reduction  in Real Estate  Taxes shall be in  Landlord's
sole and absolute  discretion.  However, the foregoing shall not affect Tenant's
rights under subparagraph (e) below. Notwithstanding the foregoing, "Real Estate
Taxes" does not include:  (i) any interest,  penalties or additional tax paid by
or imposed upon  Landlord as a result of  Landlord's  failure to pay Real Estate
Taxes when due and payable,  or (ii) any net income,  franchise or capital gains
tax,  inheritance tax or estate tax imposed or constituting a lien upon Landlord
or all or any part of the Real Property.

         (b) The initial Real Estate Taxes  ("Initial  Basic Real Estate Taxes")
to be used in  calculations  regarding  Excess Real Estate Taxes (defined below)
are the actual  (subject  to  adjustment  in  accordance  with the terms of this
subparagraph  (b)) Real  Estate  Taxes for  calendar  year  2000  ("Base  Year")
(determined consistent with the terms of this subparagraphs (b) and subparagraph
(d) below). For the purpose of determining  Tenant's Share of Excess Real Estate
Taxes (as  defined  below),  the Initial  Real Estate  Taxes and the Real Estate
Taxes applicable to any subsequent calendar year shall be grossed up pursuant to
the following  terms.  If, during the Base Year, the amount of Real Estate Taxes
payable by Landlord  with respect to the  Building  does not reflect an assessed
value of the  Building  equal to or greater  than the Fully
<PAGE>

Assessed  Value (as defined  below) of the Building in the first  calendar  year
subsequent  to the Base Year  during  which the  Building  is  assessed at Fully
Assessed  Value (as defined  below),  then in such event Landlord shall increase
the amount of Real  Estate  Taxes  hereunder  for the Base Year to reflect  such
Fully Assessed Value. In addition,  if, during any calendar year during the Term
following  the Base Year,  the amount of Real Estate  Taxes  payable by Landlord
with respect to the Building does not reflect an assessed  value of the Building
equal to or greater  than the Fully  Assessed  Value (as  defined  below) of the
Building  in any  previous  calendar  year,  then in such event  Landlord  shall
increase the amount of Real Estate Taxes  hereunder  for such  calendar  year to
reflect such Fully  Assessed  Value.  As used herein,  the term "Fully  Assessed
Value"  means the value of the  Building,  for the  purposes  of Real Estate Tax
assessment by the appropriate officials of Fairfax County,  Virginia,  using the
income  method of valuation  then being  employed by Fairfax  County,  Virginia,
based  upon the  following  assumptions  for  valuation  purposes:  (i) that the
Building is substantially  completed  (including base Building  improvements and
tenant  improvements in at least ninety five percent (95%) of the tenant space);
(ii) the Building is at least ninety five percent (95%) leased;  and,  (iii) (A)
with respect to the grossing up of the Base Year, the "average"  rental rate for
valuation  purposes  shall be the  expected  average  rental rate  payable  with
respect  to space in the  Building  for first  calendar  year  during  which the
requirements  set forth in (i) and (ii)  above  are  reasonably  expected  to be
satisfied;  and  (B)  with  respect  to the  grossing  up of any  calendar  year
subsequent to the Base Year,  the "average"  rental rate for valuation  purposes
shall be the average  rental rate  payable  with  respect to leased space in the
Building for such calendar year. If Landlord obtains any subsequent reduction in
Real Estate Taxes  attributable  to the Base Year, the Excess Real Estate Taxes,
as defined in Section  4.4(c),  shall be  recomputed  for the entire  Lease Term
using the new Base Year amount,  and Tenant  shall,  within  thirty (30) days of
receipt of invoice, pay to Landlord any additional amount due.

         (c)  Beginning on January 1, 2001,  in addition to Base Rent,  for each
calendar year (or partial year) subsequent to the Base Year, Tenant shall pay as
Additional  Rent,  Tenant's  Share of the amount by which the Real Estate  Taxes
with respect to such  calendar  year exceed the Initial  Basic Real Estate Taxes
(such excess  hereinafter  referred to as "Excess  Real Estate  Taxes") for such
calendar year as follows:
                  (i) Prior to the last day of each  calendar  year  during  the
Lease Term,  Landlord will provide  Tenant with a statement of estimated  Excess
Real  Estate  Taxes  for the  upcoming  calendar  year  (based  upon  Landlord's
reasonable  good faith  estimate of anticipated  Real Estate  Taxes).  Beginning
January 1 of the upcoming  calendar year,  Tenant shall pay in twelve (12) equal
monthly  installments,  based  on  Landlord's  estimate,  Tenant's  Share of the
estimated Excess Real Estate Taxes. If Landlord  reasonably  determines that the
Excess Real Estate Taxes are greater than Landlord's  initial estimate  thereof,
then Landlord may deliver to Tenant not more
<PAGE>

than once during any  calendar  year,  a revised  estimate of Tenant's  Share of
Excess Real Estate Taxes.  Tenant shall pay to Landlord within thirty (30) days
of notification  of the revised  estimate,  the difference  between the previous
estimate  and the  revised  estimate  for the  expired  portion  of the  current
calendar  year.  Monthly  installments  of Tenant's  Share of Excess Real Estate
Taxes will be increased for the remaining months in the year following  Tenant's
receipt of the revised estimate to one-twelfth  (1/12) of the revised annualized
estimate of Tenant's Share of Excess Real Estate Taxes.

                  (ii) Not more than one hundred eighty (180) days following the
last day of each  calendar  year,  Landlord  will provide  Tenant with a written
comparison of the amount of the Tenant's  Share of estimated  Excess Real Estate
Taxes paid for the  immediately  preceding  calendar  year (or partial  calendar
year) to  Tenant's  Share of Excess  Real  Estate  Taxes  actually  incurred  by
Landlord  for  such  calendar  year.  If the  amount  of the  Tenant's  Share of
estimated  Excess Real Estate Taxes paid by Tenant for such prior  calendar year
(or partial  calendar  year):  (A) exceeds  Tenant's Share of actual Excess Real
Estate  Taxes,  within  thirty (30) days of such  statement,  Landlord will give
Tenant a credit in such  amount  against  current  payments of  Additional  Rent
applicable  to  Excess  Real  Estate  Taxes (or if in the last year of the Lease
Term,  refund the excess with the aforesaid  thirty (30) days), (B) is less than
Tenant's Share of actual Excess Real Estate Taxes, Tenant shall pay Landlord, as
Additional  Rent,  the  difference  within thirty (30) days  following  Tenant's
receipt of such written comparison.  Any delay or failure by Landlord in billing
any Excess Real Estate Tax escalation  shall not be construed as a waiver of and
shall not impair the continuing obligation of Tenant to pay such escalation.

         (d)  Landlord  shall use  reasonable  good  faith  efforts to effect an
equitable proration of real estate taxes and assessments on the Building and any
other property owned by Landlord or an Affiliate of Landlord. Landlord shall not
recover  from tenants  more than one hundred  percent  (100%) of the real estate
taxes, assessments and insurance premiums actually incurred by Landlord.

         (e) If Landlord elects not to contest Real Estate Taxes with respect to
any calendar  year during the Term,  so long as Tenant leases at least three (3)
full floors in the  Building,  Tenant may, by written  request,  ask Landlord to
retain an independent  tax consultant  reasonably  satisfactory  to Landlord and
Tenant,  at Tenant's sole cost and expense,  to assist  Landlord in  determining
whether  or not  Real  Estate  Taxes  should  be  contested.  If the  consultant
recommends  that the Real Estate Taxes be contested  and Landlord  elects not to
contest the same in spite of such recommendation,  Landlord shall deliver a copy
of any written report  received from such consultant to Tenant.  Thereafter,  so
long as Tenant leases at least three (3) full floors in the Building, Tenant, at
its sole cost and expense,  may elect within thirty (30) days of the delivery of
such report (or, if no report is available, receipt of notice from Landlord that
Landlord  will not  contest  such Taxes) to contest  said Real  Estate  Taxes by
delivering  thirty (30) days' prior written notice of such election to Landlord.
Any  contesting  of such Real Estate Taxes by Tenant shall be  performed  using
counsel reasonably  acceptable to Landlord and approved by Landlord prior to the
commencement of any action relating to such contest.  In the event that any such
contest by Tenant or any other  action by Tenant with respect to the Real Estate
Taxes  results in an  increase in the Real Estate  Taxes,  Tenant  shall pay the
entire amount of
<PAGE>

any such increase,  and Tenant shall  indemnify and hold Landlord  harmless from
and against any and all costs,  claims,  liabilities,  losses or expenses in any
way relating to any such contest by Tenant.

         4.5 Rent Definition.  The term "Rent" includes, without limitation, (a)
Base Rent;  (b) Tenant's  Share of Operating  Costs,  (c) Tenant's Share of Real
Estate Taxes;  and (d) all other amounts payable by Tenant to Landlord  (whether
or not the same are specifically  referred to herein as additional rent pursuant
to the terms of this Lease). Items (b), (c) and (d) above are herein referred to
as "Additional  Rent".  Notwithstanding  anything in this Lease to the contrary,
all amounts payable by Tenant to Landlord as Rent,  including but not limited to
any  amounts  due and  payable by Tenant  with  respect  to the Excess  over the
Improvement  Allowance,  shall  constitute  rent  for  the  purpose  of  Section
502(b)(7), as it may be amended of the Federal Bankruptcy Code, 11 U.S.C.
ss.ss.101 et seq. (the "Bankruptcy Code").

         4.6  Other  Impositions.  In  addition  to all  other  obligations  and
liabilities of Tenant to Landlord,  Tenant shall: (a) reimburse Landlord for any
increase in ad valorem taxes that Landlord becomes obligated to pay, and (b) pay
all  license and permit  fees and all taxes  levied or assessed by  governmental
authorities  by  virtue  of:  (i) any  specific  leasehold  improvements  to the
Premises  which are not in the nature of customary  office  improvements  in the
Fairfax County  submarket,  (ii) Tenant  specifically (as opposed to any tenant)
conducting  business or operating  the  Premises,  (iii) the acts,  omissions or
practices of Tenant's Agents or Tenant's  employees or contractors,  (iv) any of
Tenant's personal property located in the Premises or the Building, (v) Tenant's
assets,  existence or sales and (vi) any other reason related to Tenant, and (c)
pay Landlord the amount of any  interest or  penalties  in  connection  with the
foregoing unless caused by the fault of Landlord.

         4.7 Tenant's Audit Rights. At any time within  one-hundred eighty (180)
days of Landlord's delivery of the aforesaid year-end  reconciliation  statement
regarding  Excess Operating Costs or Excess Real Estate Taxes (but not more than
once per  year),  Tenant  or a  nationally  recognized  public  accounting  firm
retained by Tenant may,  upon at least thirty (30) days' prior  written  notice,
inspect  Landlord's  records  pertaining to such Operating  Costs or Real Estate
Taxes assessed by Landlord as set forth in Landlord's statement. Landlord or its
agents shall produce said records at Landlord's offices in the Washington,  D.C.
metropolitan  area upon the request of Tenant.  Tenant's  audit  rights shall be
expressly  limited to the records  relating to most  recent  year-end  statement
delivered by Landlord to Tenant.  However,  in addition,  if Tenant's  review of
such Landlord's records reveals,  in Tenant's  reasonable opinion, an error or a
billing by Landlord  which is  inconsistent  with the  definitions  of Operating
Costs or Real  Estate  Taxes  set  forth in  Sections  4.3 and 4.4,  Tenant  may
request,  and  Landlord  shall  produce  its  records  relating to the three (3)
previous  years only with  respect  to the line item with  respect to which such
error or incorrect  billing was  discovered by Tenant.  If Tenant's  audit shall
conclusively  disclose an overbilling by Landlord (and commensurate  overpayment
by Tenant) of the amount actually owed for such period,  Landlord shall promptly
credit the amount of such  overpayment  against Tenant's next due installment of
Rent. In addition,  if Tenant's audit shall conclusively disclose an overbilling
by  Landlord  (and  commensurate  overpayment  by Tenant) of more than seven and
one-half  percent (7.5%) of the amount  actually owed for such period,
<PAGE>

Landlord  shall  promptly  reimburse  Tenant for all  reasonable  accounting and
attorneys  fees  related  to the costs of such  audit,  provided  that:  (i) the
maximum reimbursement payable by Landlord with respect to the cost of such audit
shall be Three  Thousand  Dollars  ($5,000.00)  and (ii)  Landlord  shall not be
obligated to reimburse  any audit costs  payable to the auditor on a contingency
basis based upon a percentage  of the amount of the  discrepancy  discovered  in
such audit.

                         ARTICLE V. LANDLORD'S SERVICES
                                    -------------------

         Landlord will provide the following  services in a manner comparable to
the manner in which the same are provided in first class office Buildings in the
Tyson's Corner, Virginia submarket.

         5.1 Services, Utilities and Electricity.
             -----------------------------------

         (a) Landlord  will furnish or cause to be furnished to the Building and
the Premises  electricity  for normal first class office usage (at least a total
of eight (8)watts per square foot).  Tenant's use of electricity in the Premises
may not at any  time  exceed  the  capacity  of the  electrical  conductors  and
equipment serving the Premises.  Landlord reserves the right to install,  at the
Tenant's sole cost, check meters, which will be utilized to determine the amount
Tenant will reimburse  Landlord for Tenant's  excess usage.  If such meter(s) or
prior  testing  or  measurement  by  Landlord  determines  that  Tenant's  total
electrical  usage with respect to the Premises is  excessive,  then Tenant shall
pay for the cost of installing  such meter and  thereafter  Tenant shall pay for
any excess  electricity based upon the determination of Tenant's actual usage by
such meter.  The  determination  of whether Tenant's usage is excessive (and the
extent,  if any, to which the same is excessive) shall be made by an independent
third  party  building  engineer,  which  engineer:  (i) shall have  significant
experience in Class A office buildings in the Tysons Corner submarket,  and (ii)
shall not have  worked  for  Landlord,  Tenant  or  either  of their  respective
affiliates  during the five (5) years  immediately  preceding the hiring of said
engineer by the parties to make the  aforesaid  determination.  Said third party
engineer shall be chosen as follows:  If Landlord  concludes that Tenant's usage
is excessive,  Landlord will notify Tenant of the same.  Unless Tenant agrees in
writing to Landlord's conclusions regarding excessive usage within ten (10) days
of  Landlord's  notification  regarding the same (in which case Tenant shall pay
for the excessive  usage as  determined  by Landlord),  Landlord will provide to
Tenant  a  list  of  at  least  three  (3)  qualified  engineers  who  meet  the
requirements set forth above.  Within five (5) days of Landlord's  submission of
said list of qualified engineers,  Tenant will select one such engineer, and the
parties shall retain said selected engineer to make the foregoing  determination
as to whether Tenant's usage is excessive, and if so, to what extent the same is
excessive. If Tenant fails to choose an engineer from such list within such five
(5) day period,  Landlord  shall  select an  engineer  from the list to make the
determination.  The  determination by said engineer shall include  consideration
usage of  electricity  by  tenants in similar  Class A office  buildings  in the
Tysons  Corner  submarket,   Tenant's  use  of  the  Premises,   the  plans  and
specifications  for the  Building  and the  Final  Plans  for the  Improvements.
(However,  the parties  acknowledge  that Landlord's  approval of any such Final
Plans  shall  in no way  be  construed  as  consent  by  Landlord  to  excessive
electrical  use  which may be  associated  with the  improvements,  alterations,
<PAGE>

equipment or fixtures  described in the same).  The parties shall split the cost
of such engineer  equally and the  determination  of such  engineer  selected by
Landlord or Tenant in accordance  with the foregoing terms shall be binding upon
the parties for the purposes of this Section 5.1. In addition to the  foregoing,
Landlord reserves the right to install,  at Tenant's cost and expense,  separate
meters to determine  Tenant's  electrical usage associated with any supplemental
HVAC units or other equipment installed or operated by Tenant.  Tenant shall pay
for all electric service measured by any such separate meter. Without Landlord's
prior  written  consent  which  consent  shall  not  be  unreasonably  withheld,
conditioned or delayed,  Tenant shall not: (i) connect equipment in the Premises
that  consumes  more  electricity  than  permitted  by,  the  building  standard
specifications or (ii) make any alteration or addition to the electric system of
the Premises. If Landlord grants such consent, Landlord will provide the same at
the cost to Landlord, which cost Tenant shall pay to Landlord within thirty (30)
days  of  Landlord's  demand  therefor,  additional  risers  or  other  required
equipment. In addition,  Landlord may require Tenant to pay, as additional rent,
the cost of any excess  electrical  capacity  utilized  by Tenant as a result of
such risers or other  required  equipment.  In  addition,  Landlord  may require
Tenant to install separate  meters,  at Tenant's sole cost, and to pay utilities
directly to the utility company.

         (c) Landlord has advised Tenant that Virginia Power (`Electric  Service
Provider")  is the utility  company  selected  by  Landlord to provide  electric
service for the Building.  Notwithstanding  the foregoing,  if permitted by law,
Landlord shall have the right at any time and from time to time during the Lease
Term to either  contract  for  service  from a  different  company or  companies
providing  electric  service  (each such company is hereafter  referred to as an
"Alternate  Service  Provider")  or continue to  contract  for service  from the
Electric  Service  Provider.  So long as Tenant  leases at least  three (3) full
floors in the  Building,  Landlord will consult with Tenant prior to making such
change to an Alternate  Service  Provider.  Tenant will cooperate with Landlord,
the Electric Service Provider,  and any Alternate Service Provider at all times,
and, as reasonably  necessary,  shall allow Landlord,  Electric Service Provider
and any Alternate  Service  Provider  reasonable  access to the electric  lines,
feeders,  risers, wiring, and any other machinery within the Premises.  Landlord
shall in no way be liable or responsible for any loss,  damage,  or expense that
Tenant may  sustain  or incur by reason of any  change,  failure,  interference,
disruption,  or  defect  in the  supply  or  character  of the  electric  energy
furnished  to the  Premises,  or if the  quantity or  character  of the electric
energy  supplied  by the  Electric  Service  Provider or any  Alternate  Service
Provider is no longer  available or suitable for Tenant's  requirements,  and no
such change, failure, defect,  unavailability,  or unsuitability will constitute
an actual or constructive  eviction,  in whole or in part, entitle Tenant to any
abatement or diminution of Rent, or relieve  Tenant from any of its  obligations
under the Lease.

         5.2  Heat and Air-Conditioning.
              -------------------------

         (a)  Landlord  will  furnish or cause to be  furnished  to the Premises
Monday through Friday from 8:00 a.m. to 7:00 p.m. and Saturday from 9:00 a.m. to
1:00 p.m.  (but,  not on Sundays or legal  holidays  recognized  by the  federal
government)  (collectively,  "HVAC Business Hours"), heat or air-conditioning at
reasonable  temperatures as determined by Landlord in its reasonable  discretion
to provide  reasonably  comfortable  occupancy of the  Premises  during all HVAC
Business  Hours under  normal  business  conditions  (as the same are defined in
paragraph  A.1 of
<PAGE>

Exhibit C). Such HVAC service to the Premises  shall be consistent  with service
customarily provided in Class A office buildings in the Tysons Corner submarket.
Without  limiting  the  generality  of Section  5.6 below,  except to the extent
caused by Landlord's gross negligence or wilful  misconduct,  Landlord shall not
be responsible if the normal operation of the Building  air-conditioning  system
shall fail to provide conditioned air within comfortable temperatures levels (i)
in any portions of the Premises which have a connected  electrical  load for all
purposes  (including  lighting  and  power) or which have a human  occupancy  in
excess of the average  electrical load and human occupancy factors for which the
Building  air-conditioning  system is  designed,  (ii)  because of  alterations,
additions,  improvements  or  modifications  made by or on behalf of Tenant,  or
(iii) because of the failure by Tenant or Tenant's Agents to use the HVAC system
in the manner in which it was designed to be used.  Tenant agrees to observe and
comply with all  reasonable  rules from time to time  prescribed by Landlord for
the proper functioning and protection of the HVAC systems in the Building.

         (b) If Tenant  requests,  Landlord  will furnish  services at times not
specified  above in exchange  for Tenant's  payment  therefor at the hourly rate
established  in  accordance  with the  following  terms.  Such service  shall be
provided  using a direct  digital  controlled  energy  management  system in the
Premises, which will incorporate dial-up capability. If Tenant does not directly
request the same using the aforesaid dial-up capability,  Tenant shall deliver a
written  request to Landlord  before 12:00 p.m. on the day prior to the date for
which such usage is requested.  The hourly rate for HVAC service  outside of the
Building  standard hours set forth above shall be equal to: (i) the actual costs
incurred by Landlord to provide such service, plus (ii) additional  depreciation
costs with respect to the HVAC system and  equipment as determined in accordance
with the schedule attached hereto as Exhibit F, and incorporated  herein by this
reference.
<PAGE>

         5.3 Water. Landlord will furnish or cause to be furnished to the Common
Areas water from the Fairfax County mains for drinking, lavatory (including warm
water at  reasonable  temperatures  as  reasonably  determined  by Landlord) and
toilet  purposes.  Water will be available in the Building  core for purposes of
bringing the same to the Premises.  However,  any  improvements  or  alterations
necessary  to bring water to the Premises  shall be at Tenant's  cost as part of
the Improvements.  Tenant will not install any equipment that uses extraordinary
amounts of water without Landlord's prior written consent. Tenant will not waste
or permit the waste of water.  Landlord  reserves  the right to install,  at the
Tenant's sole cost, check meters, which will be utilized to determine the amount
Tenant will reimburse  Landlord for Tenant's  excess usage.  If such meter(s) or
prior testing or  measurement by Landlord  determines  that Tenant's total water
usage with respect to the Premises is  excessive,  then Tenant shall pay for the
cost of  installing  such meter and  thereafter  Tenant shall pay for any excess
water usage based upon the determination of Tenant's actual usage by such meter.
The  determination  of whether  Tenant's usage is excessive  shall be made by an
independent  third party  building  engineer  mutually  chosen by  Landlord  and
Tenant, which engineer:  (i) shall have significant experience in Class A office
buildings  in the Tysons  Corner  submarket,  and (ii) shall not have worked for
Landlord,  Tenant or either of their respective  affiliates  during the five (5)
years  immediately  preceding the hiring of said engineer by the parties to make
the  aforesaid  determination.  Said  third  party  engineer  shall be chosen as
follows:  If Landlord concludes that Tenant's usage is excessive,  Landlord will
notify  Tenant of the  same.  Unless  Tenant  agrees in  writing  to  Landlord's
conclusions  regarding  excessive  usage  within  ten  (10)  days of  Landlord's
notification  regarding  the  same  (in  which  case  Tenant  shall  pay for the
excessive  usage as determined  by Landlord),  Landlord will provide to Tenant a
list of at least three (3)  qualified  engineers who meet the  requirements  set
forth  above.  Within  five (5) days of  Landlord's  submission  of said list of
qualified engineers, Tenant will select one such engineer, and the parties shall
retain said selected engineer to make the foregoing  determination as to whether
Tenant's usage is excessive, and if so, to what extent the same is excessive. If
Tenant  fails to choose an  engineer  from  such list  within  such five (5) day
period,   Landlord   shall  select  an  engineer  from  the  list  to  make  the
determination.  The  determination by said engineer shall include  consideration
usage of water by  tenants  in similar  Class A office  buildings  in the Tysons
Corner submarket, Tenant's use of the Premises, the plans and specifications for
the Building  and the Final Plans for the  Improvements.  (However,  the parties
acknowledge that Landlord's  approval of any such Final Plans shall in no way be
construed as consent by Landlord to excessive  water use which may be associated
with the  improvements,  alterations,  equipment  or fixtures  described  in the
same).

         5.4 Janitorial Services. Landlord will furnish or cause to be furnished
to the Premises  janitorial  and cleaning  services in accordance  with cleaning
specifications  attached  hereto as Exhibit G, and  incorporated  herein by this
reference, as the same may be reasonably modified from time to time by Landlord.
At all times  during  the Term,  such  janitorial  and  cleaning  service to the
Premises shall be consistent with service customarily  provided in similar Class
A office buildings in the Tysons Corner submarket. Tenant shall pay Landlord for
any services not included on Exhibit G requested by Tenant at the amount charged
to Landlord.  Tenant shall have the right to contract separately with Landlord's
Janitorial  Services  vendor for additional  Janitorial  Services,  without such
contract being deemed to be interference  with Landlord's
<PAGE>

contract.  So long as  Tenant  leases  at least  three  (3) full  floors  in the
Building,  Landlord  will  consult  with  Tenant  prior to making  change to the
Janitorial Services vendor.

         5.5 Elevator  Service.  Landlord  will furnish or cause to be furnished
twenty-four  (24) hours per day, (with at least one (1) elevator subject to call
at all times)  normal  passenger  elevator  service  for  Landlord,  tenants and
visitors of the Building.  Landlord  may,  from time to time, as Landlord  shall
reasonably  determine,  in the  operation  of a Class A  office  building,  take
elevators out of service to perform maintenance. The Building elevators shall be
installed  so  that  each  elevator  can be  configured  to be  restricted  from
accessing any particular floor or floors in the Building, except through the use
of a pass key or other similar  device.  So long as Tenant leases at least three
(3) full floors in the Building  Landlord  will  consult  with Tenant  regarding
which elevators shall have access to which floors of the Building (except Tenant
shall have no right to consult with Landlord  regarding the elevators  access to
the first  floor of the  Building  or to the  parking  garage).  Landlord  shall
provide to Tenant,  at no  additional  cost,  such pass keys or similar  devices
which Landlord can provide to Tenant without  exceeding the total budget for the
base building  security  system.  Each of these pass keys shall be programmed to
allow the holder  access,  as directed by Tenant,  to  particular  floors of the
Building,  provided that such  programming does not cause Landlord to exceed its
security system budget for the Building.

         5.6  No Liability.
              ------------

         (a) Subject to the other terms of this Lease,  if there is a failure by
Landlord to furnish the  utilities or services  specified  in this Lease,  which
failure:  (1)  interferes  substantially  with or prevents  Tenant's  use of the
Premises  or any part  thereof,  and (2) can be  remedied in whole or in part by
Landlord,  Landlord  shall  use  commercially  reasonable  efforts  to  promptly
commence  action to  restore  same and  thereafter  continue  such  action  with
reasonable  diligence  until same are  restored or Landlord has  completed  such
commercially  reasonable  efforts as are possible under the circumstances to aid
in  the  return  of  such  utilities  or  services.  However,   interruption  or
malfunction  of any utility,  telephone or other service shall not  constitute a
breach by Landlord,  nor shall it cause an eviction or disturbance of Tenant, or
release  Tenant from any obligation  hereunder,  or grant Tenant any right to an
offset against rent or rent abatement (except as expressly  provided below), and
neither   Landlord   nor   Landlord's   Agents   shall  be  liable  for  damages
(consequential or otherwise) as a result thereof.

         (b) If there is a failure by  Landlord  to  furnish  the  utilities  or
services specified in this Lease to be provided by Landlord,  which failure: (i)
interferes  substantially  with or prevents  Tenant's use of the Premises or any
part thereof,  (ii) is capable of being  remedied by Landlord by the exercise of
commercially  reasonable  efforts  (as  opposed to being  outside of  Landlord's
control),  and (iii)  continues  for five (5)  consecutive  business  days,  the
Monthly Base Rent and  regularly-recurring  Additional  Rent charges shall abate
for the period of such  interruption and continuing  until such  interruption is
remedied,  based upon the portion or portions of the Premises  rendered unusable
by such interruption of utilities or services.

         (c) If there is a failure by  Landlord  to  furnish  the  utilities  or
services specified in this Lease to be provided by Landlord , which failure: (i)
interferes  substantially  with or prevents  Tenant's use of the Premises or any
part thereof,  (ii) is not capable of being remedied by
<PAGE>

Landlord by the exercise of commercially reasonable efforts (in that such remedy
is outside of Landlord's control), and (iii) continues for seven (7) consecutive
business days,  the Monthly Base Rent and  regularly-recurring  Additional  Rent
charges shall abate for the period of such  interruption  and  continuing  until
such  interruption  is  remedied,  based  upon the  portion or  portions  of the
Premises  rendered  unusable by such  interruption of utilities or services.  In
addition,  if such  interruption as described in this subparagraph (c) continues
for a period in excess of forty-five (45) consecutive business days, then Tenant
may terminate  this Lease by providing  written  notice to Landlord on or before
the earlier to occur of (1) thirty (30) days  following  the  expiration  of the
aforesaid  forty-five (45) business day period,  and (2) the restoration of such
interrupted service.

         5.7      Security/Access.
                  ---------------

         (a) Tenant shall have access to the Premises twenty-four (24) hours per
day, seven (7) days per week.  Tenant's  access to the Building and the Premises
shall be subject to all security measures as Landlord shall reasonably undertake
with respect to the Building,  which security  measures may include a Kastle Key
access system for use outside of normal Building  operating  hours,  and a lobby
attendant  during normal office hours. It is understood that no security systems
or procedures  installed or mandated by Landlord shall (except due to Landlord's
gross negligence or wilful misconduct), in any way increase Landlord's liability
for  occurrences  and/or  consequences  which  such  systems or  procedures  are
designed to detect or avert and that Tenant shall look solely to all  applicable
insurance  policies as set forth  herein for claims for damages or injury to any
person or property.  So long as Tenant  leases at least three (3) full floors in
the  Building,  Landlord  will consult with Tenant prior to making change to the
security  services  vendor with respect to the  Building.  Tenant shall have the
right to  contract  separately  with  Landlord's  security  services  vendor for
additional  security  services,   without  such  contract  being  deemed  to  be
interference with Landlord's contract.

         (b) Tenant shall also have the right, at its option, to take additional
security  measures by modifying or expanding the Building  security  systems and
installing  additional  security systems as Tenant may deem necessary,  provided
that Tenant obtains Landlord's prior written consent (which consent shall not be
unreasonably  withheld,  conditioned or delayed), and further provided that such
additional security measures or systems shall not interfere with: (i) Landlord's
access rights with respect to the Premises (as set forth in Section 10.1),  (ii)
Landlord's and other tenant's rights with respect to the Common Areas, and (iii)
other tenant's rights with respect to their respective  premises in the Building
 . Any such additional  security  systems or adaptations or  modifications of the
base Building system  suggested by Tenant:  (1) shall be  incorporated  into the
base Building  system,  and (2) will be subject to the limitation  that any such
systems  must  accommodate  and be usable by the  Landlord  in a  multi-tenanted
Building framework. The cost of any such additional security measures or systems
or changes or adaptations to the base Building  system shall be borne by Tenant.
However,  to the extent that the total final cost of such additional systems and
measures,  along with the other systems and security measures installed or taken
by Landlord (including the costs associated with providing Tenant with key cards
as required  hereunder),  does not exceed thirty thousand dollars  ($30,000.00),
Landlord  shall  bear a portion  of such cost (up to a  maximum  expenditure  by
Landlord for security  systems,  equipment and security measures in the Building
of $30,000.00).  At Landlord's sole option  (exercised at the time of Landlord's
approval of any such systems if the same are properly  submitted to Landlord for
approval as required  hereunder),  upon the expiration or earlier termination of
the Term, all such additional security systems,  equipment
<PAGE>

and measures  shall be removed from the Building by Tenant at Tenant's sole cost
and expense.

         (c) In addition to the  foregoing,  for as long as Tenant leases all of
the leasable office space in the Building above the first floor,  Tenant, at its
option  and at its  sole  cost  and  expense,  may:  (i)  provide  up to two (2)
employees or representatives in the first floor lobby of the Building to provide
additional  security for Tenant  and/or to answer  questions or direct  Tenant's
visitors,  employees,  contractors or invitees in the Building, and (ii) subject
to Landlord's prior written  approval,  which approval shall not be unreasonably
withheld,  erect  minor  non-structural  improvements  in such first floor lobby
(such as a reception desk) to accommodate  the stationing of Tenant's  employees
in such lobby, if Landlord has not previously erected the same.

         (d) Tenant shall have the right to contract  separately with Landlord's
Building  management  or  concierge  services  vendor  for  additional  Building
management  or  concierge  services,  without such  contract  being deemed to be
interference with Landlord's contract.

         5.8  Maintenance  and  Repair.  Landlord,  at its  expense  (subject to
partial  reimbursement in accordance with the terms of Section 4.3 hereof) will,
consistent with similar Class A office  buildings in the Tyson's Corner markets:
(i) comply  with all  present  and future  laws,  ordinances  (including  zoning
ordinances  and land  use  requirements),  regulations,  orders  or other  legal
requirements of the United States of America, the Commonwealth of Virginia,  and
any other public or quasi-public authority having jurisdiction over the Building
with respect to the Common Areas of the Building [except as otherwise  expressly
provided in this Lease and except as to compliance which becomes  necessary as a
direct  result of  Tenant's  unique use of the  Premises  (as opposed to general
office use thereof),  which  compliance  costs shall be borne solely by Tenant],
(ii)  maintain in good order and repair the Common Areas of the Building and the
Building's  structural  portions  (exterior  walls,  load  bearing  elements and
foundation), as well as the roof and the base Building mechanical,  life/safety,
electrical,  HVAC and plumbing  systems (unless the same are damaged as a result
of the acts or omissions of Tenant or Tenant's  Agents,  in which case  Landlord
shall  perform  any  necessary  repairs or  replacements  arising  therefrom  at
Tenant's  sole cost and  expense in  accordance  with the terms of  Section  6.1
below),  (iii)  provide  replacement  light bulbs for  building  standard  light
fixtures,  (iv) remove trash from the Common Areas of the  Building,  (v) remove
ice and snow from the Common  Areas  outside of the  Building  and (vi)  provide
bathroom  supplies  for the  bathroom  facilities  in the  Common  Areas  of the
Building.

         5.9   Communications.   (a)  Tenant  and  Tenant's   telecommunications
companies,  including  but not  limited  to  local  exchange  telecommunications
companies and alternative  access vendor services  companies approved in writing
by Landlord in its reasonable discretion ("Telecommunications Companies"), shall
have, at all times during the Term and all renewal  terms,  subject to the terms
of this Section 5.9 and the other  provisions  of this Lease,  a reasonable  and
necessary  right of access to a  proportionate  share (as defined  below) of the
risers and other portions of the Building  (other than the roof, with respect to
which  Tenant's  rights  are  governed
<PAGE>

by the terms of Section  15.26  hereof)  utilized to provide  telecommunications
service to the Premises and the Building at no  additional  fee, cost or expense
to Tenant for the purpose of installing and operating  telecommunications  lines
and systems  including  but not  limited to voice,  video,  data,  and any other
telecommunications services provided over wire, fiber optic, microwave, wireless
and  any   other   transmission   systems,   for   part   or  all  of   Tenant's
telecommunications  within  the  Building  and from the  Building  to any  other
location (hereinafter  collectively referred to as "Telecommunications  Lines").
All such access, and the identity of all such Telecommunications Companies shall
be subject to Landlord's prior written consent,  which shall not be unreasonably
withheld,  conditioned or delayed.  Notwithstanding  the  foregoing,  Tenant may
perform any installation,  repair and/or  maintenance to its  Telecommunications
Lines without Landlord's consent (provided that Landlord has previously approved
in writing the party  performing such work) where the equipment being installed,
repaired or maintained is not located in an area in which the Telecommunications
Lines or any part  thereof  of any other  tenant  or of  Landlord  are  located.
Tenant's  proportionate  share of the risers and other  portions of the Building
utilized to provide  telecommunications service to the Premises and the Building
shall be determined  from time to time as follows:  the total square feet of Net
Rentable  Area leased in the  Building  by Tenant  pursuant to the terms of this
Lease  shall be divided by the total Net  Rentable  Area of the  Building  (in a
manner  similar to the  calculations  set forth in Sections 1.5 and 1.6 hereof).
Tenant shall be entitled to use the resulting  percentage of that portion of the
risers and other portions of the Building utilized to provide telecommunications
service to the Premises and the Building  which are not reserved by Landlord for
its use in connection with the operation and management of the Building.

         (b) If at any time,  including,  at all times  during  the Term and all
renewal terms, Tenant's Telecommunications Companies or appropriate governmental
authorities  relocate  the point of  demarcation  from the  location of Tenant's
telecommunications  equipment  in  Tenant's  telephone  equipment  room or other
location,  to some other point,  or in any other manner transfer any obligations
or liabilities for telecommunications  service to Landlord or Tenant, whether by
operation  of law or  otherwise,  then,  within  ninety (90) days of  Landlord's
election, Tenant shall, at Tenant's sole expense and cost: cause to be completed
by an appropriate  telecommunications  engineering entity approved in advance in
writing by Landlord, all details of the Telecommunications  Lines serving Tenant
in the Building which details shall include all appropriate  plans,  schematics,
and  specifications  therefor;  and  (ii) if  Landlord  so  elects  in its  sole
discretion,  after written notice to Tenant of same,  immediately  undertake the
operation, repair and maintenance of the Telecommunications Lines serving Tenant
in the Building.

         (c) Subject to the  limitations  set forth in this Section 5.9,  Tenant
shall have the right to receive telecommunications services, at all times during
the Term and all  renewal  terms,  from the  vendor(s)  of  Tenant's  choice and
Landlord  shall  cooperate  in  accommodating  such  service  and shall  provide
reasonable access to those portions of the Real Property  allocated to Tenant in
accordance  with the foregoing terms (and such other portions of the Building as
may reasonably be necessary to access those  portions of the Building  allocated
to Tenant in accordance  with the  foregoing  terms) for said  services.  At all
times during the Term and all renewal  terms,  Landlord  shall  provide free and
unencumbered  access to Tenant to all Building risers,  conduits,  shafts,  etc.
allocated to Tenant in accordance with the foregoing  terms, as needed by Tenant
to connect such
<PAGE>

service  through  the Real  Property  to the  Premises.  To the degree  that any
easement  rights are needed for any such  service  necessary  for the conduct of
Tenant's business, Landlord will grant same, provided that: (i) no such easement
rights shall in any way be  construed to increase the size of those  portions of
the Real Property allocated to Tenant in accordance with the foregoing terms (or
increase any of Tenant's rights with respect to the roof as set forth in Section
15.26), and (ii) no such easements shall in any way interfere with Landlord's or
other  tenants  operations  in the Building (or the  operations  of any adjacent
landowners  or their  tenants)  or any other  easements,  rights of way or other
rights or obligations binding upon Landlord with respect to the Building. Tenant
hereby  indemnifies  and holds  Landlord  harmless  from and against any and all
costs,  expenses,  liabilities,  claims,  causes of  action,  actions or damages
incurred or suffered by Landlord in any way related to any such easements or the
exercise by Tenant or its vendors of Tenant's rights hereunder.

                      ARTICLE VI. TENANT'S CARE OF PREMISES
                                  -------------------------

         6.1 Waste.  Neither  Tenant nor  Tenant's  Agents will commit  waste or
nuisance and will keep the  Premises  and the  fixtures  therein in good repair.
Tenant shall be responsible  for  maintenance and repair of appliances and shall
pay for unstopping any drains or water closets in the Premises. Except as may be
expressly  provided in Section 5.8, Tenant shall,  at its own expense,  maintain
the Premises  and all of Tenant's  Property in good,  clean and safe  condition,
promptly making all necessary repairs and  replacements.  Tenant shall repair at
its expense,  any and all damage,  other than ordinary wear and tear,  caused by
Tenant or Tenant's  Agents to the  Building,  Common  Area,  the  Premises,  and
Tenant's Property, including equipment within and serving the Building, ordinary
wear and tear excepted. Such maintenance and repairs shall be performed with due
diligence,   lien-free  and  in  a  first-class   workmanlike  manner,  by  such
contractor(s) selected by Tenant and approved by Landlord,  which approval shall
not be  unreasonably  withheld,  conditioned  or  delayed.  Notwithstanding  the
foregoing,  Tenant shall bear the cost of, but shall not itself perform any such
repairs  which  (i)  subject  to the  terms  of this  Lease,  would  affect  the
Building's structure or mechanical or electrical systems,  (ii) would be visible
from the  exterior  of the  Building  or from any  interior  Common  Area of the
Building,  or  (iii)  were  originally  performed  by  Landlord  under  the Work
Agreement.  Tenant  shall not have  access to the roof of the  Building  for any
purpose whatsoever, except for the purposes of accessing any equipment of Tenant
which may be permitted on the roof of the Building in accordance  with the terms
of Section 15.26, and any such access shall only be upon prior written notice to
Landlord and accompanied by representatives  of Landlord at mutually  convenient
times. If: (1) Tenant fails to perform any of the foregoing  required repairs or
maintenance to the Premises,  and  thereafter  fails to cure such failure within
thirty (30) days following  written notice from Landlord (except in the event of
an emergency in which no such notice shall be required), (2) Landlord, following
written notice to Tenant  (except in the event of an emergency)  performs any of
the foregoing  repairs or maintenance which are to be made at Tenant's cost, (3)
Tenant requests that Landlord perform any other repairs or maintenance (although
Landlord  shall not be  obligated  to make  same),  or (4) any act or neglect of
Tenant or Tenant's  Agents  results in damage to the  Premises or the  Building,
Landlord may make such  repairs or undertake  such  necessary  maintenance,  and
within thirty (30) days of receipt of Landlord's invoice, Tenant shall reimburse
Landlord  for the cost thereof  (plus  Landlord's  overhead  cost of ten percent
(10%) of the cost) as
<PAGE>

Additional Rent. Tenant will not deface or injure the Building, and will pay the
cost of repairing  any damage or injury done to the Building or any part thereof
by Tenant. Tenant will participate in any reasonable Landlord-required recycling
program  applicable  to Tenant which is required by law.  Tenant shall not smoke
tobacco in any part of the  Building  except in those  areas,  if any,  that are
clearly designated by Landlord as smoking areas.  Tenant shall not use, store or
handle or permit the usage,  storing or handling of any materials in levels that
exceed those established for indoor air quality pursuant to applicable law.

         6.2 Compliance with Law. Tenant, at its cost and expense,  will observe
and comply  promptly  with all present and future  laws,  ordinances  (including
zoning ordinances and land use requirements), regulations, orders or other legal
requirements of the United States of America, the Commonwealth of Virginia,  and
any other public or quasi-public authority having jurisdiction over the Premises
and insurance  requirements relating to or affecting the Premises, the condition
thereof,  all machinery,  equipment and  furnishings  therein,  Tenant's use and
occupancy  thereof,  any Tenant sign,  or incident to Tenant's  occupancy of the
Building and its use thereof. It is expressly  understood that if any present or
future law,  ordinance,  regulation or order requires an occupancy or use permit
for the Premises (other than the initial  Certificate of Occupancy,  which shall
be obtained by Landlord if Landlord  performs  the  Improvements),  Tenant shall
obtain  such permit at Tenant's  own expense and shall  promptly  deliver a copy
thereof to Landlord. Use of the Premises is subject to all covenants, conditions
and restrictions of record.  Breach of this Section 6.2 which continues  uncured
beyond the  applicable  notice and cure  periods set forth in Section  11.1 is a
Default under this Lease.
<PAGE>

         6.3 Alterations, Additions or Improvements: Moving. Tenant may not make
any alterations,  improvements, door lock changes (except as otherwise set forth
herein) or other modifications to the Premises without the prior written consent
of Landlord.  Landlord's consent to purely cosmetic alterations,  which will not
affect the HVAC, any Building system, or the exterior appearance or structure of
the  Building  or the  Premises,  or, in  Landlord's  reasonable  determination,
adversely  effect the ability to lease the Premises,  shall not be  unreasonably
withheld,  conditioned or delayed.  All other  approvals  shall be in Landlord's
sole and  absolute  discretion.  Requests  must be in writing  and  detailed  to
Landlord's  reasonable  satisfaction.  Notwithstanding  the  foregoing,  Tenant,
without the prior written consent of Landlord,  may perform minor non-structural
alterations  costing  less than two dollars  ($2.00) per square foot (of the Net
Rentable  Area of that  floor  of the  Premises  affected  by such  alterations)
provided  that:  (i) such  alterations  do not affect  the HVAC or any  Building
system, or the exterior appearance of the Building,  (ii) the same are performed
using  finishes  and  materials  of at least the same quality and grade as those
used in the  Improvements,  and (iii) the same are performed in accordance  with
the other  requirements of this Lease.  Such minor structural  alterations shall
include: (1) painting and installing wall coverings, (2) installing and removing
office furniture,  (3) installing and removing workstations,  (4) installing and
removing Tenant's equipment and performing cable pulls in connection  therewith,
(5) installing and removing  carpeting and other floor coverings  (provided that
such  alterations  include the  replacement of the same with other  carpeting or
other floor coverings),  and (6) other similar  alterations.  Upon completion of
any  alterations  which  require the  issuance of building  permits or otherwise
involve the  erection of walls,  doors or other  permanent  barriers or means of
ingress or egress,  Tenant, at Tenant's cost
<PAGE>

and expense, shall provide Landlord with "as built" drawings of such alterations
and the Premises.  Tenant shall give Landlord  reasonable  advance notice before
beginning work on any  Alterations.  Except as set forth below, all alterations,
additions or  improvements  (including,  but not limited to carpets,  drapes and
anything bolted,  nailed or otherwise secured in a manner  customarily deemed to
be  permanent)  are  fixtures,  not subject to  attachment  of a  mechanic's  or
materialman's  lien,  and will become the property of Landlord and remain in the
Premises at the end of the Lease Term.  Notwithstanding  the  foregoing,  Tenant
property,  which shall include  fixtures in the Premises  which may be installed
and removed without  material damage to the Premises,  and any and all equipment
and/or supplies in the Premises  utilized by Tenant in its business  operations,
including  computers,   telephone  or  telecommunications  equipment  and  other
business  equipment  and systems  ("Tenant's  Property")  shall  remain the sole
property  of Tenant  and  Tenant  shall have the right to remove the same at any
time without Landlord's consent All alterations,  additions or improvements made
in or upon the  Premises,  either by  Landlord or Tenant in order to comply with
ADA are Landlord's  property upon the termination of this Lease and shall remain
on the Premises without  compensation to Tenant.  Notwithstanding the foregoing:
(i) other than the  Improvements  (as defined in Exhibit C) (except as expressly
provided  below) and any subsequent  improvements  or  alterations  installed by
Tenant with Landlord's  consent,  which  improvements or alterations are typical
and customary office  improvements in the Tysons Corner submarket,  Landlord has
the  option to  require  Tenant  to remove  any  fixtures,  equipment  and other
improvements  installed  in the  Premises,  and (ii)  Landlord has the option to
require Tenant to remove any raised flooring and associated  cabling,  equipment
and improvements (even if the same forms a part of the  Improvements),  provided
that  Landlord  may not require  Tenant to remove (and  restore the floor to the
condition   that  the  same  was  delivered  to  Tenant)  any  raised   flooring
improvements  on the fourth  (4th) floor of the  Building to the extent that the
total square footage of such raised  flooring on the fourth (4th) floor consists
of no more than 15,000  square feet of Net  Rentable  Area.  With respect to any
alterations or  improvements  which require  Landlord's  prior written  consent,
provided  that Tenant  properly and timely seeks such  consent,  Landlord  shall
advise  Tenant at the time of  granting  such  consent as to whether the subject
alterations or improvements  must be removed at the expiration or termination of
the Term.  If Landlord  requires  removal and Tenant fails to comply  within ten
(10) days after  written  notice  from  Landlord,  Landlord  may remove  same at
Tenant's  cost,  and Tenant shall pay Landlord upon demand all costs incurred by
Landlord in removing  the  alterations,  additions  and  improvements.  Tenant's
performance of its obligations to maintain and repair and any moving of Tenant's
furnishings,  equipment or other  property may be conducted  only by contractors
and subcontractors reasonably approved in writing by Landlord.  Landlord may, at
Landlord's option,  require that alterations be performed or constructed outside
of normal  business hours.  Tenant must maintain and cause such  contractors and
subcontractors  to maintain  insurance  coverage  against  such  risks,  in such
amounts and with such  companies as Landlord  reasonably  requires in connection
with any alterations,  improvements or other modifications. Such contractors and
subcontractors  must provide  Landlord with  certificates  of insurance prior to
commencement  of work, and such  certificates  shall list Landlord and its asset
manager,  property manager, managing agent and any other designee of Landlord as
additional insured.

         6.4 No Overloading or Overcrowding.  Tenant shall not place a load upon
the floor of the  Premises  exceeding  the load per  square  foot such floor was
designed to carry, as reasonably
<PAGE>

determined by Landlord's  structural  engineer.  (In making such  determination,
partitions  shall be  considered as part of the load).  Landlord may  reasonably
prescribe the weight and position of all safes,  files and heavy  equipment that
Tenant desires to place in the Premises,  to allow proper  distribution of their
weight.  Tenant's business machines and mechanical  equipment shall be installed
and  maintained  so as  not to  transmit  noise  or  vibration  to the  Building
structure or to any other space in the Building outside of the Premises.  Tenant
shall be  responsible  for the  reasonable  cost of all  structural  engineering
required to determine structural load and all acoustical  engineering reasonably
required to address any noise or vibration  caused by Tenant  which  affects any
other  tenant  in the  Building,  the  Building's  structure  or any of the base
Building systems or equipment.  All such engineers and/or  consultants  shall be
selected by Landlord.  Tenant will not employ or maintain at the  Premises  more
than one (1) employee for each one hundred seventy-five (175) square feet of Net
Rentable  Area of the Premises.  Tenant shall not walk,  nor install any item of
any kind or nature,  upon the roof of the  Building  (except as may be expressly
provided in Section 15.26), nor make any installments or alterations of any kind
upon or through the roof or walls of the  Building,  without  the prior  written
consent of  Landlord,  which may be withheld  in  Landlord's  sole and  absolute
discretion.

         6.5 No Liens.  Landlord's  title is and always will be paramount to the
title of Tenant,  and  Tenant  will not do or be  empowered  to do any act which
encumbers  or may  encumber  Landlord's  title or subjects  the  Premises or the
Building  or any part of  either  to any  lien.  Tenant  must,  within  ten (10)
business day of the filing  thereof,  remove (or bond off pursuant to applicable
statutes) any and all liens or encumbrances which are filed against the Premises
or the Building as a result of any act or omission of Tenant or Tenant's Agents.
If Tenant fails to remove any such lien within ten business (10) days of receipt
of notice  thereof,  then  Landlord  may,  but is not  obligated  to,  remove or
bond-off  such lien,  and Tenant  shall pay all  reasonable  costs of removal or
bonding the lien,  plus  interest at the Default Rate to Landlord  within thirty
(30) days of Landlord's written demand therefor.

         6.6 Property and Improvements at Tenant's Risk.  Except as to the gross
negligence or wilful misconduct of Landlord or Landlord's  Agents,  all personal
property,  betterments and improvements in the Premises,  the Building,  parking
areas or related  facilities,  whether  owned,  leased or installed by Landlord,
Tenant or any other  person,  are at  Tenant's  sole risk,  and except as to the
gross negligence or wilful misconduct of Landlord or Landlord's Agents,  neither
Landlord  nor  Landlord's  Agents will be liable for any damage  thereto or loss
thereof from any cause,  including  but not limited to theft,  misappropriation,
casualty,  overflowing or leaking of the roof, the bursting or leaking of water,
sewer or  steam  pipes  (including  sprinklers),  or from  heating  or  plumbing
fixtures.

         6.7 Flammable,  Explosive or Toxic  Substances.  Tenant will not use or
permit in the  Premises or the Building  any  flammable  or explosive  material,
toxic  substances,  environmentally  hazardous  materials (as defined  below) or
other items  hazardous to persons or property.  Tenant will not use the Premises
in a manner that (a)  invalidates or is in conflict with fire,  insurance,  life
safety or other policies covering the Building or the Premises, or (b) increases
the rate of fire or other  insurance  on the  Building or the  Premises.  If any
insurance  premium is higher than it otherwise would be due to Tenant's  failure
to comply with this Section 6.7, Tenant shall
<PAGE>

reimburse  Landlord  as  Additional  Rent,  that  part of  Landlord's  insurance
premiums  that are  charged  because of  Tenant's  failure  to comply  with this
provision.  The  foregoing  terms of this Section 6.7 shall not preclude  Tenant
from using materials  commonly used in a business office setting,  provided that
Tenant  properly  uses,  handles  and  disposes of the same in  accordance  with
applicable law and the manufacturers instructions with respect thereto.

         6.8 Hazardous Materials Defined.  "Hazardous  Materials" means: (a) any
"hazardous  waste" as defined by the Resource  Conservation  and Recovery Act of
1976 (42 U.S.C.  ss.6901 et. seq.)  ("RCRA"),  as amended from time to time, and
regulations  promulgated   thereunder;   (b)  any  "hazardous  substance"  being
"released"  in   "reportable   quantity"  as  such  terms  are  defined  by  the
Comprehensive Environmental Response, Compensation and Liability Act of 1980 (42
U.S.C.  ss.9601  et.  seq.)  ("CERCLA"),  as  amended  from  time to  time,  and
regulations promulgated thereunder; (c) asbestos; (d) polychlorinated biphenyls;
(e) urea  formaldehyde  insulation;  (f)  "hazardous  chemicals"  or  "extremely
hazardous   substances",   in  quantities   sufficient  to  require   reporting,
registration,  notification or special treatment or handling under the Emergency
Planning and Community  Right-to-Know  Act of 1986 (42 U.S.C.  ss.ss.11001,  et.
seq.)  ("EPCRA"),  as  amended  from  time to time and  regulations  promulgated
thereunder;  (g) any  "hazardous  chemicals"  in  levels  that  would  result in
exposures greater than those allowed by permissible  exposure limits established
pursuant to the Occupational Safety and Health Act of 1970 (29 U.S.C. ss.651 et.
seq.)  ("OSHA"),  as  amended  from  time to time  and  regulations  promulgated
thereunder;   (h)  any  substance   which  requires   reporting,   registration,
notification,  removal,  abatement or special  treatment,  storage,  handling or
disposal under Section 6, 7 or 8 of the Toxic Substances  Control Act (15 U.S.C.
ss.ss.2601  et.  seq.)  ("TSCA")  as amended  from time to time and  regulations
promulgated  thereunder;  (i) any toxic or hazardous  chemicals described in the
Occupational  Safety and Health Standards (29 C.F.R.  1910.1000-1047)  in levels
which would result in exposures  greater than those  allowed by the  permissible
exposure  limits pursuant to such  regulations;  (j) the contents of any storage
tanks,  whether above or below ground; (k) medical wastes; (l) materials related
to those  described in  subparagraphs  (a) through (k) hereof;  and (m) anything
defined as  hazardous  or toxic under any now  existing or  hereinafter  enacted
statute.

         6.9  Environmental  Compliance.  (a) Tenant  will not use or permit the
Premises to be used in violation of any  Environmental  Regulations  (as defined
below).  Tenant assumes sole and full responsibility for, and will remedy at its
cost,  all such  violations,  provided that Tenant must first obtain  Landlord's
written  approval of any  remedial  actions,  which  approval  Landlord  may not
unreasonably  withhold.  Tenant will not use, generate,  release,  store, treat,
dispose of, or  otherwise  deposit,  in, on,  under or about the  Premises,  any
Hazardous  Materials,  nor will Tenant permit or allow any third party to do so,
without  Landlord's  prior written  consent.  The  foregoing  shall not preclude
Tenant from using materials commonly used in a business office setting, provided
that Tenant  properly uses,  handles and disposes of the same in accordance with
applicable  law  and  the  manufacturers   instructions  with  respect  thereto.
Landlord's  election to conduct  inspections  of the Premises is not approval of
Tenant's use of the Premises or any activities  conducted thereon, and is not an
assumption  by  Landlord of any  responsibility  regarding  Tenant's  use of the
Premises or  Hazardous  Materials.  Tenant's  compliance  with the terms of this
Section 6.9 and with all Environmental  Regulations is at Tenant's sole cost. If
<PAGE>

Tenant violates its covenants or obligations under this Section 6.9, Tenant will
pay or  reimburse  Landlord  for the  reasonable  costs or expenses  incurred by
Landlord,  including reasonable attorneys',  engineers',  consultants' and other
experts'  fees and  disbursements  incurred  or  payable to  determine,  review,
approve,   consent  to  or  monitor  the   requirements   for  compliance   with
Environmental Regulations. If Tenant fails to comply with the provisions of this
Section  6.9,  or if  Landlord  receives  notice or  information  asserting  the
existence  of any  Hazardous  Materials,  Landlord  has the  right,  but not the
obligation, without in any way limiting Landlord's other rights and remedies, to
enter upon the Premises or to take such other actions  Landlord deems  necessary
or  advisable  to clean up,  remove,  resolve,  or  minimize  the  impact of any
Hazardous  Materials on or affecting the Premises.  Tenant shall pay to Landlord
within thirty (30) days of Landlord's  demand therefor,  as Additional Rent, all
reasonable  costs and  expenses  paid or incurred by Landlord in the exercise of
any such rights.  Tenant will notify Landlord in writing,  immediately  upon the
discovery by Tenant or receipt by Tenant of written  notice (from a governmental
authority or other  entity),  of the presence in the Premises or the Building of
any  Hazardous  Materials or  conditions  that result in a violation of or could
reasonably  be  expected  to violate  this  Section  6.9,  together  with a full
description thereof to the extent known to Tenant.  "Environmental  Regulations"
means any law, statute,  regulation,  order or rule now or hereafter promulgated
by any Governmental Authority,  whether local, state or federal, relating to air
pollution,  water pollution,  noise control or transporting,  storing, handling,
discharge,  disposal or recovery of on-site or off-site hazardous  substances or
materials,  as same may be amended from time to time.  To the best of Landlord's
knowledge,  there are no Hazardous  Materials  present in the Building or on the
Landlord in violation  of any  Environmental  Regulations.  Landlord  shall,  at
Landlord's  expense,  indemnify  Tenant  against any costs and expenses  arising
from,  and perform any work (removal or  encapsulment)  necessary to satisfy the
applicable  legal  requirements  with  respect to: (i) any  Hazardous  Materials
brought onto the Premises by Landlord or Landlord's  Agents,  (ii) any violation
of  Environmental  Regulations  by Landlord or Landlord's  Agents,  or (iii) any
Hazardous Materials in the Building or on the Land prior to the Delivery Date.

         (b) Landlord  represents  and warrants  that, to Landlord's  knowledge,
there are no Hazardous  Materials on in or under the  Premises,  the Land or the
Building.  Landlord covenants not to violate any Environmental  Regulations with
respect to the  Building,  and  Landlord  shall  indemnify  and hold  Tenant and
Tenant's  Agents  harmless  from and  against  any  claims,  damages,  losses or
liabilities  (including  reasonable  attorneys'  fees)  arising from  Landlord's
breach of the foregoing warranty or violation of any Environmental Regulations.

         6.10 ADA  Compliance.  Nothing  contained  in this Lease is intended to
prevent or prohibit  compliance by either party with ADA nor is any provision of
this Lease  intended to violate  ADA, and any  provision  that does so is hereby
modified  to allow  compliance  or  deleted  as  necessary.  Tenant  indemnifies
Landlord,  Landlord's Agents, its affiliates,  agents,  officers,  employees and
contractors,  for all  costs,  liabilities  and  causes of action  occurring  or
arising as a result of Tenant's failure to comply with ADA or as a result of any
violation of ADA by Tenant or Tenant's Agents, and, at Landlord's option, Tenant
will defend  Landlord,  Landlord's  Agents,  its affiliates,  agents,  officers,
employees and  contractors,  against all such costs,  liabilities  and causes of
action.  Landlord  represents  and  warrants  that as of the Delivery  Date,  to
Landlord's
<PAGE>

knowledge,  the  Building and  Landlord's  Work are not in violation of ADA, and
Landlord shall,  at its cost and expense  (subject to partial  reimbursement  in
accordance  with the terms of Section 4.3 of the Lease),  ensure that the common
areas of the  Building are not in violation of ADA during the Term of the Lease.
The existence of a validly issued Certificate of Occupancy for the Building from
the appropriate governmental authorities shall constitute evidence of Landlord's
compliance  with the  foregoing.  Breach of this  Section  6.10 which  continues
uncured beyond the applicable  notice and cure periods set forth in Section 11.1
is a Default under this Lease

         6.11  Termination and Surrender.  Tenant shall,  upon the expiration or
sooner  termination  of the  Term  hereof:  (i)  peaceably  and  quietly  leave,
surrender and yield up to the Landlord the Premises, free of subtenancies, broom
clean and in the same good  order and  condition  as when  received  except  for
reasonable  wear and tear,  fire or other  casualty,  (ii)  surrender  any keys,
electronic  ID cards,  and other  access  devices to  Landlord at the place then
fixed for the payment of rent,  (iii)  deliver the Premises to Landlord  free of
any and all Hazardous Materials present on the Premises in violation of Tenant's
covenants or obligations under Section 6.9 so that the condition of the Premises
conforms with all  applicable  Environmental  Regulations,  (iv) at its expense,
remove from the Premises all movable trade  fixtures,  furniture,  equipment and
other  personal  property  (collectively,  "Tenant's  Property")  as well as any
alterations or  improvements  which Tenant is required to remove pursuant to the
terms  of  this  Lease,  (v)  at its  expense,  remove  from  the  Premises  any
alterations or improvements which Landlord  designates for removal in accordance
with  Landlord's  rights to so  designate  pursuant  to the terms of this  Lease
(including but not limited to the terms of Sections 6.3,  15.25 and 15.26),  and
(vi) at its expense,  promptly repair any damage caused by such removal.  Any of
Tenant's  Property which are not so removed may, at the Landlord's  election and
without limiting Landlord's right to compel removal thereof,  shall be stored by
Landlord at Tenant's expense, for not less than thirty (30) days, and thereafter
shall be deemed  abandoned and may be retained by Landlord as its property or be
disposed of at Tenant's sole cost and expense,  without accountability,  in such
manner as Landlord may see fit. In the event the Tenant fails to comply with the
provisions  of this  Section  6.11:  (i)  Tenant  shall,  at the  option  of the
Landlord,  be deemed to occupy  the  Premises  after the  expiration  or earlier
termination of the Term or any renewal  thereof,  and be subject to the holdover
provisions  of this Lease,  and (ii) Tenant shall  indemnify  and hold  Landlord
harmless  from and against any costs  incurred  by Landlord in  connection  with
Tenant's  failure to comply with such  provisions  (including but not limited to
the  cost of  performing  Tenant's  obligations  hereunder).  All  installments,
alterations,  additions,  betterments  and  improvements to the Premises made by
Tenant, including,  without limitation, all wiring, paneling,  partitions, floor
coverings, lighting fixtures, and the like (other than Tenant's Property), shall
become the  property of Landlord  when  installed  and shall  remain upon and be
surrendered  with the Leased  Premises as a part  thereof at the  expiration  or
sooner termination of the Term, except that: (1) subject to the terms of Section
6.3,  Landlord shall have the right,  by notice to Tenant (which notice shall be
provided  to Tenant at the time of  Landlord's  approval  of any  alteration  or
improvements as required under the terms hereof, provided that Tenant timely and
properly obtains such consent), to require Tenant, at its expense, to remove any
alterations,  additions and improvements (other than the Improvements, except as
provided in Section  6.3) in the  Premises,  and to repair any damage  caused by
such  removal,  and (2) Tenant  shall comply with its
<PAGE>

obligations  set forth in Exhibit C hereto  with  respect to the  removal of any
internal  staircases.  The  provisions  of this Section  6.11 shall  survive any
expiration or termination of this Lease.

         6.12 Indoor Air  Quality.  (a) So long as Tenant  leases at least three
(3) full floors in the Building,  Landlord, upon Tenant's written request, shall
have the Building and Premises  tested for indoor air quality on an annual basis
with the cost of such testing to be included in annual Operating Costs. Landlord
shall  promptly  provide to Tenant  copies of such annual  written  test reports
relating  to the air  quality  in the  Premises,  or any other  written  report,
information,  or date prepared as an evaluation of the indoor air quality of the
Building and/or Premises.  Landlord shall implement recommendations set forth in
the  report as  appropriate  to cause all air  quality in the  Premises  and the
Common Areas of the Building to conform to then existing local, state or federal
regulations.  The cost of implementing any of the foregoing shall be included in
Operating  Costs.   Notwithstanding  the  foregoing,   Tenant  shall  be  solely
responsible  for, at its cost and expense  (including  reimbursement of Landlord
for the cost of said testing)  implementing any recommendation which result from
Tenant's  specific and unique use (as opposed to office use  generally) or which
result from the negligence or wilful misconduct of Tenant or Tenant's Agents.

         (b) In the event that any  material  problem  with  indoor air  quality
which is not caused by Tenant,  Tenant's  Agents or by Tenant's use or occupancy
of the Premises:  (i) interferes  substantially with or prevents Tenant's use of
the Premises or any part thereof due to the hazardous nature of such air quality
problem,  (ii) is not cured or remedied by Landlord  within  seven (7)  business
days following written notice thereof from Tenant, and (iii) continues for seven
(7)  consecutive  business days,  the Monthly Base Rent and  regularly-recurring
Additional Rent charges shall abate for the period that such hazardous condition
with respect to air quality continues until the same is remedied, based upon the
portion  or  portions  of the  Premises  rendered  unusable  by  such  hazardous
condition.

         (c) Tenant shall endeavor in good faith and use its reasonable  efforts
not to  permit  any  employee  to smoke  tobacco  in any  part of the  Building.
Landlord  shall  designate all of the office space in the Building  "smoke-free"
and Landlord shall enact nondiscriminatory Rules and Regulations in the Building
to enforce such designation.

               ARTICLE VII. TRANSFER OF INTEREST: PRIORITY OF LIEN
                            --------------------------------------

         7.1 Assignment and Sublease.
             -----------------------

         (a) Except as expressly  provided  below:  (i) Tenant shall not assign,
transfer,  mortgage or otherwise  encumber  this Lease or all or any of Tenant's
rights hereunder or interest herein, or sublet,  rent or permit anyone to occupy
the Premises or any part  thereof,  and (ii) no  assignment  or transfer of this
Lease or the right of occupancy hereunder may be effectuated by operation of law
or otherwise.

         (b) Tenant may assign Tenant's  rights  hereunder or interest herein or
sublet all or a portion of the Premises, subject to the prior written consent of
Landlord,  which  consent shall not be  unreasonably  withheld,  conditioned  or
delayed  provided  that such proposed  assignment or
<PAGE>

sublease  complies  with the  other  requirements  of this  Section  7.1 and the
following conditions are met:

                  (1) Tenant is not in Default of any of its obligations under
         this Lease;

                  (2) Landlord receives at least thirty (30) days' prior written
         notice of Tenant's  intention to assign or sublet accompanied by all of
         the information required pursuant to subclause (7) below;

                  (3) The proposed  assignee or  sublessee is of good  character
         and reputation and reasonably  consistent in kind and character as good
         tenants  approved for occupancy in similar Class A office  buildings in
         the  Tysons  Corner  submarket,  and the  proposed  assignee  satisfies
         appropriate  reasonable  credit  criteria  applied by Landlord to other
         tenants or  subtenants  of  comparable  size in the  Building  or other
         similar buildings owned or managed by Landlord or its related entities;

                  (4) (Intentionally Omitted);

                  (5) The proposed  assignee or sublessee is not a  governmental
         entity or agency or any other entity that may be entitled under any law
         to diplomatic or sovereign immunity;

                  (6) The proposed use of the  Premises is  consistent  with the
         Permitted Use under this Lease and the tenancy  requirements of a first
         class  office  building,  and such  proposed use will not violate or be
         likely to violate any other  agreements  affecting  the Premises or the
         Building,  and will not be likely to  increase  Operating  Costs of the
         Building  or the burden on Building  elevators  parking  facilities  or
         other Common Areas beyond that imposed by Tenant;

                  (7) The  financial  capability  of any  proposed  assignee  is
         reasonably  acceptable  to  Landlord  and Tenant  submits  to  Landlord
         sufficient  information  upon  which  Landlord  can  reasonably  base a
         judgment  on the above  criteria  including,  in addition to such other
         information as Landlord shall reasonably  require,  the name,  business
         experience, financial net worth including, without limitation, its most
         recent  balance  sheet and  income  statements  certified  by the chief
         financial  officer  or a  certified  public  accountant,  and  business
         references (including any landlords in other locations) of the proposed
         sublessee or assignee,  a description of the proposed transaction which
         shall include any and all documents relating thereto, the consideration
         to be delivered to Tenant for the proposed assignment or sublease,  any
         proposed  alterations or improvements  to the Premises  associated with
         such proposed  transaction,  and (except as to publicly held companies)
         the identity of any controlling  partners or principals of the proposed
         sublessee  or  assignee  who may be  involved  in  such a  transaction,
         regardless  of whether it is the  intention of such parties to actively
         participate  in the  operation  of the  premises,  the  identity of any
         broker entitled to a commission in respect of such proposed  subletting
         or
<PAGE>

         assignment and the commission,  if any, payable to such broker,  and
         any other information reasonably requested by Landlord; and

                  (8) Tenant shall deliver a copy of any proposed  assignment or
         sublease  with the notice  referred to in  subclause  two (2) above for
         approval by  Landlord  provided  that:  (a) any such  assignment  shall
         include an  assumption  by the  assignee,  from and after the effective
         date of such  assignment,  of the  performance  and  observance  of the
         covenants  and  conditions  to be performed and observed on the part of
         the Tenant as contained in this Lease,  and (b) any such sublease shall
         specify that such  sublease  shall not be further  assigned,  unless in
         accordance with the criteria set forth herein, nor the Premises further
         sublet  unless in accordance  with the criteria set forth  herein,  and
         shall  specify that the term of such  sublease  shall not extend beyond
         one day prior to the expiration of the Term of this Lease.

         Landlord  agrees to review any request for consent  complying  with the
conditions hereunder and to advise Tenant of its approval or disapproval of such
proposed  assignment  or sublease  not later than ten (10)  business  days after
receipt by Landlord of all  information  required under this  subsection (b). If
Landlord  shall fail to timely  approve or  disapprove a proposed  assignment or
sublease  within the aforesaid  time period,  and such failure  continues for an
additional  period of five (5) days following  written notice from Tenant,  then
such proposed  assignment or sublease shall be deemed  approved.  The consent by
Landlord to any assignment,  subletting or occupancy shall not be construed as a
waiver or release of Tenant from  liability for the  performance of any covenant
or  obligation  to be  performed  by  Tenant  under  this  Lease,  nor shall the
collection  or  acceptance  of rent from any  assignee,  subtenant  or  occupant
constitute  a  waiver  or  release  of  Tenant  from any of its  liabilities  or
obligations under this Lease.  Landlord's consent to any assignment,  subletting
or  occupancy  shall not be  construed  as  relieving  Tenant  or any  assignee,
subtenant or occupant from the obligation of obtaining  Landlord's prior written
consent to any subsequent  assignment,  subletting or occupancy.  For any period
following a Default  hereunder  by Tenant  until such  Default is cured,  Tenant
hereby assigns to Landlord the rent due from any assignee, subtenant or occupant
of Tenant and hereby authorizes each such assignee, subtenant or occupant to pay
said rent directly to Landlord until such Default has been cured.

         (c) Subject to the terms set forth below,  if Tenant is a  partnership,
any  dissolution  of  Tenant  or a  withdrawal  or  change,  whether  voluntary,
involuntary or by operation of law, of partners owning a controlling interest in
Tenant shall be deemed a voluntary  assignment  of this Lease and subject to the
provisions of this Article VII, and if Tenant is a corporation, any dissolution,
merger, consolidation or other reorganization of Tenant, or the sale or transfer
of a  controlling  interest of the capital  stock of Tenant  (except as to sales
made on a nationally  recognized  stock  exchange),  shall be deemed a voluntary
assignment  of  this  lease  and  subject  to the  provisions  of  Article  VII.
Notwithstanding  the foregoing,  Tenant shall be permitted to assign or sublease
its interest  hereunder  without the prior written consent of Landlord  provided
that:  (i) the assignee or subtenant of such  interest is an Affiliate of Tenant
(as defined below),  and (ii) Tenant notifies Landlord of the effective date and
terms  of  such  assignment  or  sublease,  and  memorializes  the  same  in  an
appropriate  written amendment to this Lease at least ten (10) days
<PAGE>

prior to the effective date of such assignment or sublease.  For the purposes of
this  Article  VII,  an  "Affiliate  of  Tenant"  shall  mean (i) any  person or
corporation  that prior to and  following  the  effective  date of the  proposed
assignment or sublease, directly or indirectly, controls, is controlled by or is
under  common  control with  Tenant,  or (ii) any entity  which  purchases or is
merged with and/or owns  substantially all of the assets of Tenant or any entity
into which or with which Tenant is merged or  consolidated or which is merged or
consolidated  into or with  Tenant,  provided  that the entity  purchasing  such
assets  or  resulting  from  such  merger  or  consolidation  has  a  net  worth
(determined  based upon market  capitalization)  of Three Billion,  Five Hundred
Million Dollars  ($3,500,000,000.00)  or, if the resultant  entity does not meet
such net worth test, the resultant entity causes another entity meeting such net
worth test to guarantee  for the benefit of Landlord the  obligations  of Tenant
under the Lease. For purposes of this definition, "control" means possessing the
power to direct or cause the  direction  of the  management  and policies of the
entity by the ownership of a majority of the voting securities of the entity.

         (d) If Landlord consents to an assignment or sublease,  pursuant to the
terms of this Lease,  Landlord will document its consent in accordance  with the
requirements  and  procedures  set forth  above.  Tenant  shall  pay  reasonable
attorneys'  fees and related  expenses which  Landlord  incurs in processing and
documenting  any  request  of Tenant  for such  consent,  up to a maximum of Two
Thousand  Dollars  ($2,000.00)  per  proposed  transaction.   No  assignment  or
subletting, whether in violation hereof, approved by Landlord or permitted under
this Article VII relieves Tenant from liability or the obligation to comply with
the  provisions  of this Lease.  If any excess rent is payable  under a sublease
over the Rent payable hereunder or any payment is made to Tenant specifically on
account of or in consideration of an assignment or sublease of Tenant's interest
hereunder:  (i) if the  assignee,  sublessee  or  transferee  is an Affiliate of
Tenant (as  defined  above),  then Tenant  shall  retain any such excess rent or
payment;  (ii) if the  assignee,  sublessee or transferee is not an Affiliate of
Tenant,  and such  assignment,  sublease  or transfer  does not  result,  in the
aggregate (when considered  cumulatively  with prior  assignments,  subleases or
transfers by Tenant),  in the total  assignment,  sublease or other  transfer of
Tenant's  rights  hereunder  with respect to more than twenty nine  thousand one
hundred  seventy six  (29,176)  square feet in the  Building,  then Tenant shall
retain any such excess  rent or payment;  (iii) if the  assignee,  sublessee  or
transferee  is not an  Affiliate  of Tenant,  and such  assignment,  sublease or
transfer  results,  in the aggregate (when  considered  cumulatively  with prior
assignments,  subleases  or  transfers  by  Tenant),  in the  total  assignment,
sublease or other  transfer of Tenant's  rights  hereunder  with respect to more
than twenty nine  thousand one hundred  seventy six (29,176)  square feet in the
Building,  then Tenant shall pay Landlord an amount equal to fifty percent (50%)
of such excess rent or other  payment  which  exceeds the costs of subleasing or
assigning  (including  attorneys,  consultants  and brokers fees,  and all other
reasonable inducements, concessions and improvements to the space) within thirty
(30) business  days of the date on which such amount is paid to Tenant  pursuant
to its agreement  with the sublessee,  assignee or other  transferee of Tenant's
interest hereunder.

         (e) Except for a proposed  assignment  or sublease to an  Affiliate  of
Tenant which does not require  Landlord's  prior written consent pursuant to the
foregoing  terms,  in addition to  Landlord's  right to approve or  disapprove a
proposed  assignment,  sale or other  transfer  of this Lease or sublease of any
portion of the Premises in accordance  with the foregoing  terms,  upon
<PAGE>

Tenant's  submission  of  request  for  approval  and the  necessary  additional
information described above,  Landlord shall have the right,  exercisable within
ten (10)  business  days of Tenant's  request for consent and  submission of all
necessary  information  related thereto,  to recapture Tenant's interest in this
Lease or such  portion of the  Premises  which is the  subject of such  proposed
sublease or  assignment  by  termination  of the Lease or  Tenant's  rights with
respect to that  portion of the Premises  which is the subject of such  proposed
sublease  or  assignment  as of the  proposed  effective  date of such  proposed
sublease or assignment. Landlord's failure to exercise the foregoing right shall
not  constitute a consent to the proposed  assignment or sublease,  but it shall
act as a full waiver of Landlord's rights under this paragraph.  Notwithstanding
the  foregoing  terms of this  paragraph  (e),  Landlord  shall  not  have  said
recapture  right with  respect to the first  twenty  nine  thousand  one hundred
seventy  six  (29,176)  square  feet  of  Net  Rentable  Area  in  the  Premises
(determined  on a  cumulative  basis by  accumulating  the  total  effect of all
transactions) which are assigned, transferred or sublet by Tenant.

         7.2  Intentionally Omitted.
              ---------------------

         7.3  Subordination.  Subject to  Landlord's  obligations  stated  below
regarding providing Tenant with a subordination,  non-disturbance and attornment
agreement,  this Lease (including all rights of Tenant hereunder) is subject and
subordinate to: (a) any ground lease or underlying lease (each a "Ground Lease")
now or hereafter affecting the Land or the Building,  (b) any mortgage,  deed of
trust or other  indenture  (each a  "Mortgage")  now or hereafter  affecting the
Building,  any Ground  Lease or the Land,  and all  renewals,  replacements  and
extensions  thereof,  and (c) all  advances  and  interest  under any  Mortgage;
provided,  however,  that the  subordination  of this Lease to any  Mortgage  or
Ground  Lease  pursuant to this Section 7.3 is  expressly  conditioned  upon the
holder   thereof   executing   and   delivering   to  Tenant  a   subordination,
non-disturbance and attornment agreement in the holder's commercially reasonable
form reasonably acceptable to Tenant (by which such holder agrees not to disturb
Tenant's  possession of the Premises and recognize  Tenant's  rights  hereunder,
including any and all cure and offset rights,  provided Tenant is not in Default
of its obligations  hereunder,  and by which Tenant agrees to attorn to any such
holder or the transferee or assignee of their interest hereunder). Tenant agrees
to execute within twenty (20) business days of Landlord's  written request,  any
documents  reasonably  required  by any  Mortgage  holder  or  ground  lessor to
evidence such subordination.  If in connection with existing or future financing
of the  Building,  the holder of any  Mortgage  requests  modifications  in this
Lease,  Tenant  will not  unreasonably  withhold  or delay its  consent  to such
modifications,  provided that they do not increase the financial  obligations of
Tenant  hereunder or  materially  or  adversely  affect the  leasehold  interest
created by this Lease. Upon termination of this Lease through foreclosure of any
Mortgage (or deed in lieu thereof) or if the Ground Lease is terminated,  Tenant
will  attorn  to and  accept  the  purchaser  at the  foreclosure  sale  (or the
transferee under the deed in lieu) or ground lessor as Landlord under this Lease
and,  upon  demand,  enter  unto a new  lease  agreement  with  such  purchaser,
transferee  or ground  lessor for the  unexpired  term of this Lease at the same
Rent and under the same  provisions  of this  Lease.  This Lease is subject  and
subordinate to any other arrangement or right to possession under which Landlord
is in control of the  Premises,  and to the rights of the owners of the Land and
the Building.  The parties acknowledge that no individual or entity currently is
the beneficiary of any mortgage,  deed of trust or other indenture  (hereinafter
collectively,  a "Mortgage") affecting the
<PAGE>

Land or the  Building.  Landlord  shall  deliver  from the  holder of any future
Mortgage or future ground lessor a written  subordination,  non-disturbance  and
attornment  agreement  for the  benefit of Tenant in the  holder's  commercially
reasonable  and  recordable  form (by which  such  holder  agrees not to disturb
Tenant's  possession  of the Premises  provided  Tenant is not in Default of its
obligations  hereunder,  and by which Tenant agrees to attorn to any such holder
or the  transferee  or assignee of such  holder's  interest  hereunder).  Tenant
agrees to  reasonably  cooperate  with such efforts by Landlord by executing any
such agreement if requested.

         7.4 Notice to Lender.  At any time the  Premises  or any portion of the
Building  are  subject  to a  mortgage  or deed of trust  and this  Lease or any
portion of the Rent are assigned to a  mortgagee,  trustee or  beneficiary,  and
Tenant is given written notice thereof,  including the address of such assignee,
Tenant shall not terminate  this Lease or exercise any remedy  against  Landlord
without first giving written notice  thereof,  by certified or registered  mail,
return receipt requested, to such assignee, specifying the default in reasonable
detail,  and affording  such  assignee a reasonable  period of time (in no event
less than thirty (30) days) within which, at its election, to perform for and on
behalf of Landlord.

         7.5 Tenant's Financing. Landlord hereby waives any lien rights which it
may otherwise have concerning Tenant's Property (as defined herein),  and Tenant
shall have the right to remove the same at any time without Landlord's  consent.
Landlord acknowledges that Tenant has financed or may finance some or all of its
furniture,  fixtures  (other  than  those  forming a part of the  Improvements),
equipment  and  supplies  utilized  in  the  Premises  (collectively,  "Tenant's
Property") through financing arrangements  (including promissory notes, security
agreement) with third parties. In connection therewith,  Landlord (i) consent to
the  installation  of Tenant's  Property (ii) disclaims any interest in Tenant's
Property, and (iii) if requested by any such third parties, agrees to not attach
or levy upon such  Tenant's  Property  to satisfy  Tenant's  rental  obligations
hereunder.  Any such  Tenant's  Property  may be removed by Tenant or such third
parties  from the  Premises at any time during the Term in  accordance  with the
conditions  of  limitations  of this Lease without the necessity of resorting to
legal proceedings in order to remove the same.

              ARTICLE VIII. DAMAGE AND DESTRUCTION: EMINENT DOMAIN
                            --------------------------------------

         8.1 Damage and Destruction. (a) If the Building is totally destroyed by
fire, tornado or other casualty (a "Total Casualty"),  which determination shall
be made within sixty (60) days of the date of such  casualty by Landlord in good
faith and in a commercially  reasonable  manner,  then either Landlord or Tenant
may elect to terminate the Term of this Lease as hereinafter provided.  The term
"Total  Casualty" shall mean that the Building cannot be repaired or restored in
a commercially  reasonable  manner to a physical  condition that is structurally
sound or  cannot  be  repaired  or  restored  without  first  accomplishing  the
demolition  of the base  Building.  If a Total  Casualty is  determined  to have
occurred, then either Landlord or Tenant may elect to terminate the Term of this
Lease by giving written notice of such election to the other party within thirty
(30) days after the date of Landlord's  determination  that a Total Casualty has
occurred.  If either  Landlord or Tenant  timely elects to terminate the Term of
this  Lease,  then the
<PAGE>

termination  shall be effective as of the date of such  election or as of a date
specified  in the  notice,  which  date may not be later  than  sixty  (60) days
following the date of the election by that party.  In addition to the foregoing,
if  the  Premises  or  the  Building  is so  damaged  that  Landlord  reasonably
determines in good faith and in a commercially  reasonable  manner (and provides
written  notice of such  determination  to Tenant within sixty (60) days of such
casualty) that rebuilding or repairs cannot be completed  within one hundred and
eighty (180) days after the date of such damage,  or prior to the  expiration of
the seventh (7th) Lease Year hereunder,  Landlord may, at its option,  terminate
this Lease.  If this Lease is terminated  in  accordance  with the terms of this
subparagraph  (a), Rent will abate for the  unexpired  portion of the Lease Term
effective as of the date of such casualty. If neither Landlord nor Tenant timely
elects to terminate, then the parties' shall perform their respective repair and
restoration obligations as set forth in subparagraph (b) below.

         (b) If  Landlord  or  Tenant do not elect to  terminate  this  Lease as
provided above (or the conditions  applicable to such termination rights are not
met), then within sixty (60) days after the date of such casualty, Landlord will
commence to rebuild or repair the  Building  and the  Premises  and will proceed
with reasonable  diligence to restore the Building and Premises to substantially
the same condition  that existed  immediately  prior to the casualty;  provided,
however,  Landlord  will not  rebuild,  repair or  replace  Tenant's  furniture,
fixtures,  equipment or the Improvements,  and Tenant, at its sole expense, will
perform "Tenant's Repairs," which shall include the restoration of the foregoing
to  substantially  the same  condition  that  existed  immediately  prior to the
casualty.  If more than  twenty-five  percent  (25%) of the Premises is rendered
unusable by such casualty and Landlord  does not complete its  foregoing  repair
and restoration obligations within three hundred sixty (360) days of the date of
such casualty, then Tenant may terminate this Lease by delivering written notice
of such  termination  to Landlord  within ten (10) days of the expiration of the
aforesaid  three  hundred  sixty (360) day period.  Landlord will allow Tenant a
fair diminution of Base Rent during the time and to the extent that the Premises
are unfit for Tenant's use in the ordinary conduct of Tenant's  business,  which
abatement  will  continue  only  until the  earlier  of:  (a)  thirty  (30) days
following the completion of Landlord's  restoration of the Building and Premises
as herein  provided or (b) the  completion  of Tenant's  Repairs.  Any insurance
carried by Landlord or Tenant  against  loss or damage to the Building or to the
Premises is for the sole benefit of the party  carrying such insurance and under
its sole control,  and Landlord's  obligation to rebuild or restore hereunder is
limited to the extent of recoverable  insurance proceeds available therefor.  If
any  mortgagee  under a deed of trust,  security  agreement  or  mortgage on the
Building  requires the  insurance  proceeds to be used to retire debt,  Landlord
will have no obligation to rebuild, and this Lease will terminate upon notice to
Tenant.

         8.2 Eminent  Domain.  If the whole Premises are taken or condemned,  or
purchased  in lieu  thereof,  by any  government  authority  for any  public  or
quasi-public use or purpose,  then, this Lease will terminate from the time when
the possession is required for such use or purpose. The Rent will be apportioned
to the date  when the  possession  is  required  to be given to such  government
authority. If more than twenty-five percent (25%) of the Premises are taken, or,
if by virtue of a taking access to the Premises is  permanently  and  materially
impaired,  Landlord  will  notify  Tenant in  writing,  and Tenant will have the
option to cancel this Lease,  by giving  Landlord  written  notice within thirty
(30) days after  receipt of such notice from  Landlord;
<PAGE>

provided  Tenant  cannot  suitably  use  the  balance  of the  Premises  for its
purposes.  If Tenant  exercises  said  option,  then such  cancellation  will be
effective and the Rent will be  apportioned  to the date when the  possession is
required to be given to such government authority.  If Tenant is not entitled to
cancel  the Lease or, if it is  entitled  to do so,  but does not  exercise  its
option,  as of the  date  when  possession  is  required  to be  given  to  such
government  authority,  the Rent will be reduced in the proportion  that the Net
Rentable Area contained in the remaining Premises bears to the Net Rentable Area
contained in the  Premises  before the taking.  Any award of proceeds  resulting
from a condemnation or sale in lieu thereof of the whole or part of the Premises
will belong  solely to Landlord,  and Tenant hereby waives any right to make any
claim therefore as the result of this Lease, provided, however, that Landlord is
not entitled to any award  specifically  made to Tenant for relocation  expenses
and the  taking  of  Tenant's  fixtures,  furniture  or  leasehold  improvements
(exclusive of that portion paid for by  Landlord),  less  depreciation  computed
from the date of said  improvements  to the  expiration  of the original term of
this Lease.

                ARTICLE IX. LIABILITY: INDEMNIFICATION: INSURANCE
                            -------------------------------------

         9.1 Waiver of  Claims.  Except as  expressly  provided  herein,  to the
extent permitted by law,  Landlord and Landlord's  Agents shall not be liable to
Tenant or Tenant's Agents, for any damage (including  indirect and consequential
damage), injury, loss, obligation, liability,  compensation, or claim, including
but not limited to claims for the interruption of or loss to Tenant's  business,
based on, arising out of or resulting from any cause  whatsoever  (collectively,
"claims")  (unless such claim is the direct  result of  Landlord's or Landlord's
Agent's gross negligence or willful misconduct),  which claims shall include but
not be limited to those arising from or related to the  following:  (a) any part
of the Building or Premises or any  equipment or  appurtenances  becoming out of
repair, or (b) any accident in or about the Building, (c) directly or indirectly
any act or neglect of Tenant,  Tenant's Agents,  any occupant of the Building or
of any other person,  including  Landlord and Landlord's  Agents, or (d) injury,
loss or damage to any person or property on or about the  Premises.  Tenant will
indemnify and hold Landlord and Landlord's  Agents harmless from and against any
such claims.

         9.2  Indemnification.  (a) Except for any  claims  (as  defined  below)
arising from the  negligence or willful  misconduct  of Landlord and  Landlord's
Agents  or  Landlord's  default  in its  obligations  hereunder,  Tenant  hereby
indemnifies and agrees to hold Landlord and Landlord's  Agents harmless from and
against  any  and  all  costs,  penalties,   damages  (except  for  punitive  or
consequential  damages which are expressly  waived),  claims,  causes of action,
obligations,  liabilities and expenses  (including  reasonable  attorneys' fees)
(collectively,  "claims")  suffered by or claimed against Landlord,  directly or
indirectly,  based on,  arising out of or resulting  from:  (i) Tenant's use and
occupancy of the Premises or the business conducted by Tenant therein,  (ii) any
act or omission by Tenant or Tenant's  Agents on the Premises,  (iii) any breach
or default in the performance or observance of Tenant's covenants or obligations
under  this Lease or the  Exhibits  hereto,  including  without  limitation  any
failure to surrender the Premises upon the expiration or earlier  termination of
the Lease Term, or (iv) damage to or destruction of the Building  structure,  or
any part thereof,  or of any abutting real property caused by or attributable to
the gross negligence or willful misconduct of Tenant or Tenant's Agents.  Tenant
will employ  counsel  reasonably  satisfactory  to  Landlord,  or at  Landlord's
option,  Landlord  may retain  its own  counsel
<PAGE>

at the expense of Tenant,  to  prosecute,  negotiate  and defend any such claim,
action or cause of action.  Landlord has the right to  compromise  or settle any
such claim,  action or cause of action  without  admitting  liability,  provided
Landlord obtains Tenant's prior consent, which consent shall not be unreasonably
withheld, conditioned or delayed.

         (b)  Except  for  any  claims  (as  defined  below)  arising  from  the
negligence  or  willful  misconduct  of Tenant or  Tenant's  Agents or  Tenant's
default in its obligations hereunder,  Landlord hereby indemnifies and agrees to
hold Tenant and  Tenant's  Agents  harmless  from and against any and all costs,
penalties,  damages  (except for  punitive or  consequential  damages  which are
expressly  waived),  claims,  causes of  action,  obligations,  liabilities  and
expenses  (including  reasonable   attorneys'  fees)  (collectively,   "claims")
suffered by or claimed against Tenant, directly or indirectly, based on, arising
out of or resulting from  Landlord's or Landlord's  Agents' gross  negligence or
willful misconduct.  Landlord will employ counsel  satisfactory to Tenant, or at
Tenant's  option,  Tenant may retain its own  counsel at  Tenant's  expense,  to
prosecute,  negotiate  and  defend  any such  claim,  action or cause of action.
Tenant has the right to compromise or settle any such claim,  action or cause of
action without  admitting  liability,  provided Tenant obtains  Landlord's prior
consent,  which  consent  shall not be  unreasonably  withheld,  conditioned  or
delayed.

         9.3  Insurance Requirements:
              ----------------------

         (a) Tenant will provide and maintain a Broad Form Commercial  Liability
Policy of  insurance  with respect to the Premises  with  coverage  limits of at
least Five Million and No/100 Dollars  ($5,000,000.00) per occurrence,  combined
single limit,  naming Landlord,  Landlord's  managing agent, and any other party
specifically  designated by Landlord's  Mortgagee as additional  insureds.  Such
policy will protect  Landlord,  Landlord's  Agents,  its managing agent, and any
such designee  against any liability which: (i) arises from any occurrence on or
about the  Premises,  (ii)  arises  with  respect  to  Tenant's  operations  in,
maintenance  and use of the  Premises,  Building and Common  Area,  and (iii) is
related to Tenant's  liability assumed under this Lease, or which results in any
claims  related  thereto.  The  coverage of such  policy will extend  beyond the
Premises to portions of the Common  Area,  the  Building  and the Land,  if any,
which Tenant or Tenant's Agents use from time to time.

         (b) If Landlord reasonably determines that the increase in the level of
liability  exposure  to  Landlord  is  such  that  it  becomes  customary  for a
significant number of tenants of office buildings of similar size in the area in
which the  Building  is located to be required  to provide  liability  insurance
policies with limits higher than the  foregoing  limits,  within sixty (60) days
after Landlord's request therefor Tenant will obtain (and provide a copy thereof
to  Landlord)  an  insurance  policy  whose  limits  are not less  than the then
customary limits.

         (c)  Tenant  will  carry  fire and  all-risk  coverage,  vandalism  and
malicious   mischief   insurance   covering  the   Improvements  and  all  other
improvements  (whether  existing  or  installed  by  Tenant or by  Landlord  for
Tenant's benefit), stock in trade, fixtures, furniture,  furnishings,  removable
floor coverings,  trade equipment,  signs and all other decorations and personal
property  in  the  Premises  for  one  hundred  percent  (100%)  of  their  full
replacement  cost.  All
<PAGE>

proceeds  of such  insurance  shall be used to repair or replace  the  foregoing
covered  items.  If this Lease is  terminated  as the  result of a  casualty  in
accordance with the terms hereof, the proceeds of said insurance attributable to
the  repair  and/or   replacement  of  any   Improvements  or  any  alterations,
improvements or modifications performed by or on behalf of Tenant or by Landlord
on behalf of Tenant  shall be the  property of the Landlord and paid to Landlord
upon demand.

         (d) Tenant will also carry adequate workers' compensation  insurance in
no less  than  statutorily  required  amounts,  covering  its  employees  in the
Premises  containing a waiver of  subrogation  in favor of Landlord,  and Tenant
hereby  indemnifies,  agrees to hold harmless,  and at Landlord's option defend,
Landlord and  Landlord's  Agents from and against all claims  arising out of any
loss suffered by any of Tenant's Agents at the Building which would have been or
is covered by an appropriate workers' compensation insurance policy.

         (e) Tenant  shall  also  procure  and  maintain  business  interruption
insurance in an amount not less than the Base Rent due  hereunder  for the first
full calendar  year during the Term,  which amount shall be revised from time to
time upon the reasonable request of the Landlord or its Mortgagee.

         9.4  General Provisions with Respect to Tenant's Insurance:
              -----------------------------------------------------

         (a) On or before Tenant  enters the Premises for any reason,  and again
before any insurance policy expires, Tenant will deliver to Landlord an original
certificate of insurance.  Any insurance required to be carried under this Lease
may be carried under a blanket policy  covering the Premises and other locations
of Tenant.

         (b) The insurance policies required to be carried under Sections 9.3(a)
and (c) shall name  Landlord  and the holder of any  mortgage,  if  required  by
Landlord, as an additional insured thereunder.

         (c) All insurance  policies  required to be carried under this Lease by
or on  behalf  of  Tenant  will  provide  (and any  certificate  evidencing  the
existence of any insurance policies, will certify) that unless Landlord is given
ten (10) days' written notice: (i) the insurance will not be canceled,  (ii) the
insurer will renew the insurance  policies,  and (iii) no material change may be
made in the insurance policies.

         (d) If Tenant  fails to comply with any of the  Insurance  Requirements
stated in this  Lease  and fails to  immediately  cure  such  failure  following
written notice from Landlord and a reasonable  opportunity to cure, Landlord may
in addition  to, and not in lieu of, all other  remedies  available to Landlord,
obtain  such  insurance  and keep the same in  effect  and  Tenant  shall pay to
Landlord the premium cost thereof upon demand.

         (e) All  policies of  insurance  required to be carried by Tenant under
this  Lease  shall  (1) be  written  by good  and  solvent  insurance  companies
reasonably  satisfactory  to Landlord  having a Best's  "General  Policy Holding
Rating"  of A or better and a  financial  rating  class of VIII or  better,  (2)
contain a Cross  Liability  endorsement,  (3) contain a provision  stating  "the
<PAGE>

insurance provided Landlord hereunder shall be primary and non-contributing with
any other  insurance  available  to, or  carried  by,  Landlord,"  and (4) shall
provide  that  the  policy  shall  not be  canceled,  failed  to be  renewed  or
materially  amended  without at least thirty (30) days' prior written  notice to
Landlord and, at Landlord's request, any Mortgagee.

         (f) Landlord makes no representation to Tenant that the limits or forms
of coverage  specified  above or approved by Landlord are adequate to insure the
items or obligations  required to be insured or the contractual  liability under
this Lease,  and the limits of any  insurance  carried by Tenant shall not limit
its duties and obligations under this Lease.

         9.5 Waiver of  Subrogation.  Each party  hereby  waives  every right or
cause of action for the events  which occur or accrue  during the Lease Term for
any and all loss of, or damage to, any of its property (whether or not such loss
or damage is caused by the gross  negligence  of the other  party or anyone  for
whom said other  party may be  responsible),  which loss or damage is covered by
valid and collectible fire,  extended  coverage,  "All Risk" or similar policies
covering real property,  personal  property or business  interruption  insurance
policies,  to the  extent  that  such loss or damage  is  recovered  under  said
insurance  policies or would have been  recovered had such party  maintained the
coverage required of such party hereunder.  Said waivers are in addition to, and
not in  limitation or  derogation  of, any other waiver or release  contained in
this Lease with respect to any loss or damage to property of the parties hereto.
Each party will give its insurance  carrier  written notice of the terms of such
mutual  waiver,  and the  insurance  policies  will  be  properly  endorsed,  if
necessary, to prevent the invalidation of coverage by reason of said waiver.

         9.6   Landlord's Insurance.
               --------------------

         (a) Landlord, at its cost (subject to partial reimbursement from Tenant
in  accordance  with the terms of Section  4.3),  shall obtain and  continuously
maintain  in full force and effect at all times  during the Term of this  Lease,
policies of insurance  covering the Building,  which  insurance shall be for the
benefit of Landlord and Landlord's designated mortgagees, as the named insureds,
against:  (i) loss or damage by fire;  and (ii) loss or damage  from such  other
risks or hazards now or hereafter embraced by an "All Risk" form, but including,
without  limitation,  windstorm,  hail,  explosion,  vandalism,  riot and  civil
commotion,  damage from  vehicles and aircraft,  smoke damage,  water damage and
debris removal (collectively,  "Property Insurance"). At all times, the Property
Insurance  coverage shall be in an amount equal to at least one hundred  percent
(100%) of the then "Full Replacement Cost" of the Building.

         (b) Landlord, at its cost (subject to partial reimbursement from Tenant
in  accordance  with the terms of Section  4.3),  shall obtain and  continuously
maintain  in full  force and  effect,  Commercial  General  Liability  insurance
covering  claims for bodily injury,  personal  injury or property damage for any
loss, liability or damage on, about or relating to the Premises,  or any portion
thereof,  having  limits  of not less  than Five  Million  Dollars  ($5,000,000)
combined single limit on an occurrence basis.

         (c) At  all  times,  the  insurance  coverage  maintained  by  Landlord
pursuant to the terms hereof shall be in  commercially  reasonable form and upon
commercially  reasonable  terms,  and
<PAGE>

shall,  as applicable;  (i) be written with reputable  companies  licensed to do
business  in the  Commonwealth  of  Virginia,  having a Best's  "General  Policy
Holding  Rating" of A or better and a financial  rating class of VIII or better;
(ii) cite the  interest  of  Landlord  and  Landlord's  mortgagees  in  standard
mortgagee clauses effective as of the commencement date of the policy; and (iii)
be maintained continuously throughout the Term.

                        ARTICLE X. ACCESS TO THE PREMISES
                                   ----------------------

         10.1 Access to the Premises.  Landlord and  Landlord's  Agents have the
right to enter the Premises at all reasonable times under the circumstances upon
reasonable  prior  notice  (which,  the  parties  acknowledge  shall be at least
twenty-four (24) hours in virtually all  circumstances)  (except in the event of
an emergency  in which no notice  shall be  required)  to: (i) examine the same,
(ii) to show them to prospective  purchasers,  mortgagees or to public officials
lawfully having an interest  therein,  or, during the last twelve (12) months of
the  Lease  Term,  to  prospective  lessees  or  tenants,  or (iii) to make such
decorations,  repairs,  alterations  improvements  or  additions as Landlord may
reasonably  deem  necessary or  desirable,  or (iv) to close  entrances,  doors,
corridors,  elevators or other  facilities.  In exercising its rights under this
Section 10.1, Landlord shall take reasonable steps to minimize interference with
Tenant's use of and access to the Premises.  However, the foregoing  requirement
shall in no way be construed to require  Landlord to access the Premises for the
purposes  set forth  above  during  non-business  hours  unless  such  access by
Landlord  would  be  materially  disruptive  to  Tenant's  use of the  Premises.
Landlord,  Tenant and all other tenants in the Building have a revocable license
to use all common public areas of the  Building,  provided that (a) Landlord has
the right to regulate  and control such access and the days and hours of access,
subject to the other  provisions  of this  Lease,  and (b) if the amount of such
areas is diminished,  neither Landlord nor Landlord's Agents shall be subject to
any liability nor shall Tenant be entitled to any  compensation  or abatement of
Rent, nor will such diminution of such areas constitute a constructive or actual
eviction.  The  exercise of  Landlord's  rights  under this  article  should not
materially and adversely affect Tenant's use of the Premises.  If, in exercising
its rights under this article,  Landlord  interferes  with  Tenant's  ability to
operate in the Premises,  Landlord  fails to cure such  interference  within ten
(10) days following written notice of the same from Tenant, and Tenant ceases to
operate in the Premises as a result  thereof,  then Tenant should be entitled to
an abatement of Base Rent on an equitable  and  proportional  basis until Tenant
can once again operate in that portion of the Premises so affected.

               ARTICLE XI. FAILURE TO PERFORM, DEFAULTS, REMEDIES
                           --------------------------------------

11.1     Defaults.
         --------

         (a) Each of the  following is a "Default"  (herein so called) by Tenant
under this Lease:

                  (i) Tenant fails to pay any  installment of Rent when the same
is due and  payable  and such  failure  continues  for a period of ten (10) days
after written notice to Tenant of such failure;
<PAGE>

                  (ii) Tenant fails to pay any installment of Rent when the same
is due and payable during any calendar year in which two (2) Defaults defined in
clause  (i) above  have  previously  occurred,  which  Defaults  were based upon
Tenant's  failure  to pay  Monthly  Base  Rent or  regularly-recurring  items of
Additional Rent;

                  (iii) Tenant fails to comply with any  provision of this Lease
(including the Rules and Regulations),  other than the payment of Rent, and does
not cure such failure  within  thirty (30) days after  written  notice to Tenant
(or, if such failure to comply is of a nature that the same cannot reasonably be
cured within thirty (30) days,  Tenant's  failure to commence within said thirty
(30) day period and thereafter diligently pursue a cure of such failure); and

                  (iv) The filing or execution or  occurrence  of: a petition in
bankruptcy or other insolvency  proceeding by or against Tenant or any guarantor
of Tenant's obligations;  an assignment for the benefit of creditors; a petition
or  other  proceeding  by  or  against  Tenant  or  any  guarantor  of  Tenant's
obligations for the  appointment of a trustee,  receiver or liquidator of Tenant
or any guarantor of Tenant's  obligations or any of Tenant's or such guarantor's
property;  or a proceeding by any governmental  authority for the dissolution or
liquidation of Tenant or any guarantor of Tenant's obligations.

         (b) If there shall be any Default by Tenant under this Lease, including
without  limitation any default by Tenant prior to the Lease  Commencement Date,
then, in addition to its accrued and continuing obligations set forth herein (as
set forth in greater  detail in Section 11.3 hereof),  and  notwithstanding  any
re-entry,  repossession or dispossession  under the terms of this Lease,  Tenant
shall be liable to Landlord for any damages  suffered by Landlord as a result of
such Default, which damages shall constitute additional rent hereunder, shall be
payable to Landlord within thirty (30) days of Landlord's  demand therefor,  and
shall  include  but not be limited  to: (i) the  reasonable  costs and  expenses
(including  reasonable  attorneys'  fees) incurred by Landlord in its efforts to
cure Tenant's Default and/or enforce the terms of this Lease, (ii) the costs and
expenses  (including  brokerage  commissions  and the  cost  of any  remodeling,
alterations  and  improvements  to the Premises which Landlord deems  reasonably
necessary  to allow  Landlord  to relet the  Premises)  reasonably  incurred  by
Landlord  in its  efforts  to relet the  Premises,  and (iii) any  consequential
damages resulting from the acts or omissions of Tenant or the termination of the
Lease.

         11.2  Remedies.  Without  further  notice or demand except as elsewhere
provided  in  this  Lease,  if  a  Default  occurs,  Landlord  has  the  option,
immediately,  or at any  time  thereafter,  to  pursue  any  one or  more of the
following remedies together with any other remedies available to Landlord at law
or in equity:

         (a) Landlord  shall use diligent  efforts to terminate the Lease (which
shall in no way affect  Tenant's  obligation  to pay all Rent accrued  under the
Lease  through  the date of such  termination,  plus  all  damages  suffered  by
Landlord as a result of such Default and termination);

         (b) Terminate Tenant's right to possession of the Premises,  enter upon
and take possession of the Premises by process of law and expel or remove Tenant
and any other  person
<PAGE>

who may be occupying any portion of the Premises;  If Landlord  exercises either
of its  remedies  set forth in clause (a) or (b) above;  (i) Tenant  will not be
entitled to any Notice to Quit (the  provisions of this Article XI shall operate
as a notice to quit,  any other  notice to quit or of  Landlord's  intention  to
re-enter  the  Premises  being hereby  expressly  waived),  and (ii) Tenant will
immediately  surrender the Premises to Landlord upon demand, and if Tenant fails
to do so, Landlord may, without  prejudice to any other remedy for possession or
arrearages in Rent, enter upon and take possession of the Premises by process of
law and expel or remove  Tenant and any other  person who may be  occupying  any
portion of the Premises,  without being liable for  prosecution  or any claim of
damages therefor;

         (c)  Declare  immediately  due and payable the amount by which the Rent
reserved  hereunder for the unexpired  balance of the Lease Term  (including any
increase  and  estimated  increase in  Operating  Expenses and Real Estate Taxes
which would be payable by Tenant hereunder) exceeds the fair market rental value
of the Premises for such balance of the Lease Term,  (determined  as of the date
of the Default,  and both figures  discounted  at the rate of eight percent (8%)
per annum to the then present value thereof),  which amount shall be immediately
payable by Tenant;
<PAGE>

         (d) Landlord may relet the Premises and receive the rent therefor under
terms  and  conditions  acceptable  to  Landlord  in  its  sole  but  reasonable
discretion and judgment. Under such circumstances,  Tenant shall pay to Landlord
within thirty (30) days after written demand by Landlord, sums equivalent to the
monthly Rent reserved  hereunder less the rents received by Landlord as a result
of any such reletting, if any;

         (e) In the event of an emergency,  enter upon the Premises, by force if
necessary,  without  being  liable  for  prosecution  or any claim  for  damages
therefor,  and do  whatever  Tenant is  obligated  to do under the terms of this
Lease. [Under such circumstances, Tenant shall reimburse Landlord, within thirty
(30) days of Landlord's  demand  therefor,  as Additional Rent, for any expenses
Landlord  incurs in curing such Default and/or  performing  such  obligations of
Tenant. Neither Landlord nor Landlord's Agents will be liable for any damages to
Tenant or Tenant's Agents due to such action,  unless such damages are caused by
the gross negligence of Landlord or Landlord's Agents];

         (f) Cure the Default at the  reasonable  expense of Tenant,  and Tenant
shall,  after receiving written request  therefor,  reimburse  Landlord,  within
thirty  (30) days of  Landlord's  demand  therefor,  for any amount  expended by
Landlord in connection with the cure, plus interest at the Default Rate from the
date such cost is incurred by Landlord; and

         (g)  Enjoin  any  breach or  threatened  breach by Tenant of any of the
covenants,  agreements,  terms of  conditions  in this  Lease.  If any  property
belonging  to  Tenant,  or  otherwise,  is found  upon the  Premises  after  the
termination  of Tenant's  right to occupy the Premises,  Landlord will store the
same for not less than thirty (30) days at  Tenant's  (commercially  reasonable)
cost and expense,  after written notice to Tenant,  remove and store the same in
any warehouse, at Tenant's reasonable commercial cost. Thereafter,  Landlord may
deem the same abandoned and retain or dispose of the same in a manner determined
by Landlord in its sole discretion.  Pursuit of any of the foregoing remedies is
not a  forfeiture  or waiver  of any Rent due to  Landlord  hereunder  or of any
damages accruing to Landlord by reason of the violation of any of the provisions
herein  contained.  Tenant  shall pay all Rent and  Additional  Rent to Landlord
without  any  set-off  or  counterclaim,  except as may be  otherwise  expressly
provided  herein.  The  foregoing  rights and  remedies  are  cumulative  and in
addition to any other rights granted to Landlord by law, and the exercise of any
of them shall not  constitute an election  excluding the exercise by Landlord at
any time of  another,  a different  or an  inconsistent  remedy.  The failure of
Landlord  at any time to  exercise  any  right or  remedy is not a waiver of its
right to exercise such right or remedy at any other future time.

         11.3 Deficiency.  Notwithstanding  any termination of Tenant's right to
possession of the Premises under Section 11.1 or Tenant's vacating or abandoning
the Premises,  Tenant will remain liable (in addition to accrued liabilities and
obligations  hereunder)  for the Rent as defined  in  Section  4.5 and all other
charges  Tenant would have been  required to pay until the date this Lease would
have  expired had such  termination  not occurred as such amounts are reduced by
all Rent payments  received by any replacement  tenant(s) in the Premises or any
portion thereof.  Landlord shall have the right, at its option,  to recover sums
due hereunder through  litigation or otherwise:  (i) as such sums come due, (ii)
from time to time on one or more occasions without
<PAGE>

being  obligated to wait until the  expiration  of the Lease Term before  filing
suit, or (iii)  following the date on which the Term hereof would have naturally
expired (in which case,  such amounts  shall not be deemed to have accrued until
such  date  for the  limited  purpose  of  determining  the  limitations  period
applicable to Landlord's claim for Rent).

         11.4  Mitigation.  Upon the return to  Landlord  of  possession  of the
Premises  following  a  Default  by  Tenant,   Landlord  will  use  commercially
reasonable  efforts to  mitigate  its  damages  resulting  from such  default by
reletting the Premises  subject to the limitations set forth in this Article XI.
Any proceeds  received by Landlord as a result of such reletting of the Premises
shall be  applied  to:  (i) all costs  and  expenses  incurred  by  Landlord  in
connection with attempting to secure  performance by Tenant and Tenant's cure of
Tenant's Default; then to (ii) all costs incurred by Landlord in connection with
its  efforts  to relet the  Premises;  then to (iii) any other  damages,  costs,
expenses or liabilities arising from Tenant's Default; and then to (iv) Tenant's
ongoing rental obligations hereunder.

         11.5 Payments.  Except as elsewhere  provided herein (i.e. with respect
to Base Rent and regularly  recurring  additional  rent charges which are due on
the first day of each calendar  month),  all amounts Tenant owes to Landlord are
due within  thirty  (30) days from the date that  Landlord  renders a  statement
therefor.  Tenant shall pay Landlord a late fee with respect to any  installment
of Base Rent or additional rent, which installment is not paid by the date which
is ten (10) days after the due date thereof, to cover Landlord's  administrative
costs incurred in connection with Tenant's  failure to timely meet its Base Rent
obligations. The amount of such late fee shall be: (i) three percent (3%) of the
applicable  installment with respect to the first two (2) installments which are
not paid when due during any  calendar  year,  and (ii) five percent (5%) of the
applicable  installment with respect to any further late payments.  In addition,
all Base Rent amounts not paid by the due date and all  Additional  Rent amounts
not paid by the due date will bear interest from the date  originally due, until
the date  fully paid at the  lesser of  fifteen  percent  (15%) per annum or the
highest rate permitted by law (the "Default Rate"), to cover Landlord's cost for
administrative  fees and expenses incurred in conjunction with the collection of
late payments.  Notwithstanding  the  foregoing,  on the first two (2) occasions
during any calendar  year that any  installment  of Base Rent is not timely paid
when due hereunder,  no late fee will be assessed  unless Tenant fails to timely
cure its default  following  written notice from Landlord in accordance with the
terms of Section 11.1 hereof. Time is of the essence in Tenant's payment of Rent
and Landlord's and Tenant's performance of every provision of this Lease and all
Exhibits hereto.

         11.6 Landlord's Default. If Landlord defaults in the performance of any
of its obligations under this Lease, Tenant will notify Landlord, in writing, of
the default and Landlord will have thirty (30) days after  receiving such Notice
(or such  additional  period  as may be  necessary  if the same  cannot be cured
within said thirty (30) day period provided that Landlord  commences  efforts to
cure within said thirty (30) day period and  thereafter  diligently  pursues the
same to completion)  to cure the default.  If Landlord does not cure the default
within such  period,  then Tenant may exercise or pursue such rights or remedies
as are available to Tenant under  applicable law. In the event that Tenant shall
have  performed  such  obligation on Landlord's  account in accordance  with the
terms of this  Lease and  Tenant  obtains a final,  non-appealable
<PAGE>

judgment or decree as to such matter  against  Landlord,  Tenant  shall have the
right to offset the amount of such judgment or decree against the  next-accruing
installment  of Rent due under the Lease until fully  satisfied,  provided  that
Tenant  shall not be  permitted  to offset  in any  calendar  month an amount in
excess of fifty  percent  (50%) of the monthly  Base Rent  payable  hereunder by
Tenant with respect to such calendar month. In addition, Tenant shall first seek
recovery  from the value of the  proceeds  of  insurance  policies  Landlord  is
obligated  to carry  pursuant  to this Lease in the event of a  casualty  of the
Premises.

             ARTICLE XII. QUIET ENJOYMENT: RESERVATIONS BY LANDLORD:
                          -----------------------------------------
                                NO CONSTRUCTIVE EVICTION
                                ------------------------

         12.1 Quiet Enjoyment.  So long as Tenant is not in Default, Tenant will
have peaceful and quiet  possession of the Premises against all parties claiming
adversely thereto by or under or through Landlord.

         12.2 Reservations by Landlord. Provided that Landlord's exercise of its
rights reserved  hereunder shall not materially impair Tenant's rights under the
Lease,  access to or use of the Premises or Tenant's parking rights, in addition
to other rights conferred by this Lease or by law,  Landlord reserves the right,
to be exercised  in  Landlord's  sole but  reasonable  discretion,  to: (a) upon
reasonable  prior  notice to Tenant,  change the name of the  Building (in which
case,  Landlord  shall pay any costs  incurred by Landlord  in  connection  with
redoing  business  cards and  stationary  which  contained the prior name of the
building, provided that Landlord shall not be obligated to replace more than the
lesser of the amount of such business cards and stationary which were on hand at
the time of the name change,  or a six (6) month  supply of the same);  (b) upon
reasonable  prior notice to Tenant,  change  entrances and exits to the Building
and to the parking lot adjacent to the Building;  (c) subject to the limitations
of Section 2.3, install and maintain a sign or signs on the exterior or interior
of the Building;  (d) change the street  address of the  Building;  (e) take all
measures as may be necessary or desirable  for the safety and  protection of the
Premises or of the  Building;  (f) sell or mortgage the Building and assign this
Lease in  connection  therewith;  (g)  issue  pass keys to the  Building  or the
Premises;  (h) repair,  alter, add to, improve,  build additional stories on, or
build adjacent to the Building, so long as same does not impair the light or air
to the Premises or the view from the Premises;  (i) upon reasonable prior notice
to Tenant,  run necessary  pipes,  conduits and ducts through the Premises above
the finished ceiling,  below the finished floor, inside of and through walls and
closets;  (k) carry on any work, repairs,  alterations or improvements in, on or
about the Building or in the vicinity thereof and, during the continuance of any
such work, to temporarily close doors, entryways,  public space and corridors in
the  Building;  (l)  upon  reasonable  prior  notice  to  Tenant,  interrupt  or
temporarily suspend Building services and facilities;  (m) upon reasonable prior
notice  to  Tenant,   change  the  arrangement  and  location  of  entrances  or
passageways, doors and doorways, corridors, elevators, stairs, toilets, or other
public parts of the Building (without permanently substantially interfering with
Tenant's access to the Premises); and (n) grant to anyone the exclusive right to
conduct any business or render any service in or to the Building.  Tenant hereby
waives any claim or cause of action  arising out of or connected  with such work
performed in accordance  with the terms of this Section 12.2.  This paragraph is
not to be construed to diminish the obligations of Tenant provided  herein,  nor
to create or increase  any
<PAGE>

obligation  on the part of  Landlord  with  respect to repairs or  improvements.
Landlord will use reasonable  efforts to minimize any interference with Tenant's
business  caused by the  exercise  by  Landlord  of its rights set forth in this
Section  12.2.  However,  the same  shall in no way  obligate  the  Landlord  to
exercise  any such rights  during  non-business  hours,  and except as expressly
provided herein, neither Landlord nor Landlord's Agents will be liable to Tenant
or  Tenant's  Agents for any  inconvenience,  interference,  annoyance,  loss or
damage  resulting  from work done in or upon the  Premises or any portion of the
Building or adjacent grounds.

         12.3 No Constructive  Eviction. No act or failure to act by Landlord or
Landlord's  Agents during the Lease Term to enforce the terms of this Lease,  or
the  Rules and  Regulations,  will  constitute  an  eviction  or  acceptance  of
surrender of the Premises.  No agreement to accept  surrender of the Premises is
valid  unless in writing  signed by  Landlord,  and no  employee  of Landlord or
Landlord's Agent has any power to accept such surrender prior to the termination
of the  Lease.  Tenant's  delivery  of  keys  to any  employee  of  Landlord  or
Landlord's  Agent shall not constitute a termination of the Lease or a surrender
of the Premises.  The terms of this Section 12.3 shall in no way be construed to
limit Tenant's rights under Section 5.6..

                       ARTICLE XIII. RULES AND REGULATIONS
                                     ---------------------

         13.1 Rules and Regulations.  Tenant must observe and abide by the Rules
and  Regulations  attached  as Exhibit B hereto,  and by such other and  further
reasonable  Rules and  Regulations  as  Landlord  may  prescribe  which,  in its
judgment,  are needed for the  reputation,  safety,  care or  cleanliness of the
Building  or  Premises,  or the  operations  and  maintenance  thereof  and  the
equipment  therein,  or for the  comfort of Tenant and the other  tenants of the
Building.  Landlord has the right to add to,  change,  or waive (with respect to
any  tenant,   in   Landlord's   reasonable   discretion   without  in  any  way
discriminatorily  enforcing  the  same  against  Tenant)  any of the  Rules  and
Regulations.  Tenant's breach of any of the Rules and Regulations and failure to
cure the same following  written notice in accordance  with the terms of Section
11.1 may, at Landlord's  option,  constitute a Default  hereunder.  Further,  in
addition  to,  and not in lieu of,  any  other  right  or  remedy  available  to
Landlord,  for each violation of Rules and Regulations,  upon the third instance
thereof, Landlord may assess Tenant liquidated damages in the amount of $300.00,
which liquidated damages shall constitute  Additional Rent hereunder,  and shall
be due and  payable  within  ten  (10)  days of the date of  Landlord's  invoice
therefor.  Neither  Landlord nor Landlord's  Agents shall be liable to Tenant or
Tenant's  Agents for failure to enforce or for violation of any of the Rules and
Regulations  or the breach of any  provision in any lease by any other tenant in
the  Building.   Landlord  will  not  discriminatorily  enforce  the  Rules  and
Regulations against Tenant.

                           ARTICLE XIV. COMMUNICATIONS
                                        --------------

         14.1 Communications:  No notice, request, consent,  approval, waiver or
other  communication under this Lease is effective unless the same is in writing
and is hand delivered,  sent via nationally recognized overnight courier, mailed
by registered or certified mail,  postage  prepaid,  or sent via facsimile (with
electronic  or  telephonic  verification  of receipt  and copy by regular  mail,
certified mail or overnight courier) addressed as follows:
<PAGE>

         (a) If sent to  Landlord,  a  communication  shall be  effective on the
earlier to occur of: (i) the date of actual receipt by Landlord,  (ii) three (3)
days after said  communication  is mailed or transmitted,  as provided above, to
the address  designated as Landlord's  Notice Address in Section 14.2 or to such
other address as Landlord  designates  by giving  notice to Tenant,  or (iii) if
sent via facsimile (which shall be done during business hours only), the date of
actual receipt,  if the same is sent with  verification to the facsimile  number
provided  to Tenant by  Landlord in  writing.  Copies of all  communications  to
Landlord  shall be sent to the  address  designated  as  Landlord's  Notice Copy
Address in  Section  14.2 (or sent via  facsimile  to the  additional  facsimile
number with  verification as provided above),  and to such other person or party
as Landlord shall designate by notice to Tenant.

         (b) If sent to  Tenant,  a  communication  shall  be  effective  on the
earlier  to occur of: (i) the date of actual  receipt by Tenant,  (ii) three (3)
days after said  communication  is mailed or transmitted,  as provided above, to
the address  designated  as Tenant's  Notice  Address in Section 14.2 or to such
other address as Tenant  designates by notice to Landlord,  or (iii) if sent via
facsimile,  the date of actual receipt, if the same is sent with verification to
the facsimile  number  provided to Landlord by Tenant.  Copies of all notices to
Tenant shall be sent to the address  designated as Tenant's  Notice Copy Address
in Section 14.2 (or sent via facsimile to the additional  facsimile  number with
verification  as provided  above),  and to such other  person or party as Tenant
designates  by notice to Landlord.  Notice may be given to Tenant by Landlord or
Landlord's attorney acting as Landlord's authorized agent.
<PAGE>

         14.2.  Notice Addresses:
                ----------------

         (a)      Landlord's Notice Address:
                  -------------------------

                  Institutional Property Managers, Inc.
                  1961 Chain Bridge Road
                  Suite 105
                  McLean, Virginia 22101-4562

         (b)      Landlord's First Notice Copy Address:
                  ------------------------------------

                  L & B Realty Advisors, Inc.
                  Attn: Ed Daley
                  Director, Office Buildings
                  8750 N. Central Expressway
                  Suite 800
                  Dallas, Texas 75231-6437

                  Landlord's Second Notice Copy Address:
                  -------------------------------------

                  Jeffrey M. Guelcher, Esq.
                  Bregman, Berbert & Schwartz, L.L.C.
                  7315 Wisconsin Avenue
                  Suite 800 West
                  Bethesda, Maryland 20814

         (c)      Tenant's Notice Address:
                  -----------------------

                  Vice President and Chief Financial Officer
                  MicroStrategy
                  8000 Towers Crescent Drive
                  Vienna, Virginia 22182
                  facsimile: (703) 848-4837
                  telephone: (703) 848-8600
<PAGE>

         And with a copy to:
         ------------------

                  Director, Administration
                  MicroStrategy
                  8000 Towers Crescent Drive
                  Vienna, Virginia 22182
                  facsimile: (703) 848-8610
                  telephone: (703) 848-8600

         (d)      Tenant's Notice Copy Address:
                  ----------------------------

                  Watt, Tieder, Hoffar & Fitzgerald, L.L.P.
                  7929 Westpark Drive
                  Suite 400
                  McLean, Virginia 22102-4224
                  Attn: John G. Lavoie, Esquire
                  facsimile: (703) 748-1343
                  telephone: (703) 749-1000


                      ARTICLE XV. MISCELLANEOUS PROVISIONS
                                  ------------------------

         15.1 Tenant Estoppel Certificates. Tenant agrees, at any time, and from
time to time, upon not less than fifteen (15) business days prior written notice
by Landlord, to execute, acknowledge and deliver to Landlord a written statement
containing all information  reasonably requested by Landlord,  including but not
limited to: (a)  certification  that this Lease is unmodified  and in full force
and effect (or if there have been modifications, that the Lease is in full force
and effect as modified and stating the modifications), (b) a statement regarding
the dates to which  Tenant has paid the Rent  hereunder,  (c) a statement  as to
whether,  to the best of  Tenant's  knowledge,  Landlord  is in  default  in the
performance  of any  covenant,  agreement or condition  contained in this Lease,
and,  if so, a  specification  of each such  default  of which  Tenant  may have
knowledge,  (d) a statement of the amount of the  then-applicable  monthly Rent,
(e) a  statement  of the  amount  of the  Security  Deposit,  if any,  and (f) a
statement  of the address to which  notices to Tenant  should be sent.  Any such
statement  delivered  pursuant  hereto  may be  relied  upon by any owner of the
Building,  any  prospective  purchaser  of the  Building,  and  any  present  or
prospective  mortgage,  deed of trust  holder or trustee for bond  holders  with
respect to the Building or of Landlord's interest.

         15.2  Brokerage  Fees.  Except as listed  below,  Tenant  and  Landlord
represent  to each  other  that the  indemnifying  party  has not  incurred  any
liability for commissions or similar compensation to third parties in connection
with this Lease,  and, except for commissions due Brokers (defined below) (which
shall be paid by Landlord pursuant to a separate agreement with Brokers), Tenant
and Landlord shall indemnify and hold each other harmless  against any liability
arising from any claims for such  compensation,  including  costs and reasonable
attorneys' fees. "Brokers" means CB Commercial ("Landlord's Broker") and Cushman
& Wakefield of Virginia, Inc. and Zalco Realty, Inc. (collectively, "Tenant's
Broker").
<PAGE>

         15.3 Intentionally Omitted.
              ---------------------

         15.4 Liability of Landlord. Neither Landlord, Landlord's asset advisor,
nor any member of any joint  venture,  partnership,  tenancy-in-common,  pension
fund,  association  or other form of joint  ownership  that forms Landlord shall
have any personal  liability  under this Lease.  Tenant agrees that in the event
Tenant or any of  Tenant's  agents,  contractors,  clients,  guests,  licensees,
customers or invitees is awarded a money judgment against  Landlord,  its agents
or  partners,  the sole  recourse for  satisfaction  of such  judgment  shall be
limited to execution against the estate and interest of Landlord in the Building
(including any interest in any sale, condemnation or insurance proceeds from the
Building).  In no event shall any other assets of Landlord, or of any partner of
Landlord or of any person or entity be held to have any personal  liability  for
satisfaction of any claims or judgments  against  Landlord and/or any partner of
Landlord in such partner's  capacity as a partner of Landlord (provided that the
foregoing  will not reduce or be deemed to reduce  any  rights  Tenant has as an
additional insured under Landlord's liability insurance policies.

         15.5 Authority.  Tenant and Landlord and the persons signing this Lease
on behalf of Tenant  and  Landlord  agree  that with  respect  to  Tenant's  and
Landlord's   respective   corporation   (including  any  form  of   professional
association or  corporation):  (i) the  individual  executing this Lease is duly
authorized to execute and deliver this Lease on behalf of Tenant and Landlord in
accordance  with Tenant's and  Landlord's  organizational  documents;  (ii) this
Lease is binding  upon Tenant and  Landlord;  (iii) Tenant and Landlord are each
duly  organized  and legally  existing in the state of its  organization  and is
qualified to do business in the state in which the Building is located; and (iv)
upon  the  other  party's  request  each  party  will  provide  the  other  with
satisfactory evidence of such authority.

         15.6 Parking. Tenant's parking rights are set forth in Exhibit E hereto
attached.

         15.7 Landlord  Approval.  Landlord's  approval when required  under the
Lease is non-technical and non-legal in nature,  and Tenant remains  responsible
for all technical and legal aspects of any item requiring Landlord's approval.

         15.8  Unenforceability/Joint  and Several Liability.  The invalidity or
unenforceability  of any  provision  hereof  will not affect or impair any other
provision  hereof.  If Tenant  consists  of more than one person or entity,  the
obligations of each are joint and several.
<PAGE>

         15.9  Headings,  Miscellaneous.  The headings of the several  articles,
paragraphs and sections  contained  herein are for  convenience  only and do not
define,  limit  or  construe  the  contents  of such  articles,  paragraphs  and
sections. All negotiations,  considerations,  representations and understandings
between the parties are incorporated herein and are superseded hereby. There are
no terms, obligations,  covenants,  statements,  representations,  warranties or
conditions  relating to the subject matters hereof other than those specifically
contained  herein as of the date of the Lease.  This Lease may not be amended or
modified  by any act or conduct  of the  parties  or by oral  agreements  unless
reduced and agreed to in writing  signed by both Landlord and Tenant.  No waiver
of any of the terms of this Lease is binding  upon either  party  hereto  unless
reduced to writing and signed by such party.

         15.10 Force  Majeure.  Each party will be excused from  performing  any
obligation  or  undertaking  provided  for in this Lease  (other  than  Tenant's
obligation to pay all items of Base Rent and additional  rent which shall not be
covered by this Section  15.10),  and such party's  failure to perform shall not
constitute a default  hereunder for so long as such  performance is prevented or
delayed,  retarded or  hindered by  circumstances  beyond such  party's  control
(including,  but  not  limited  to an  act  of  god,  fire,  earthquake,  flood,
explosion,  action of the  elements,  war,  invasion,  insurrection,  riot,  mob
violence,   sabotage,  general  shortage  of  or  inability  to  procure  labor,
equipment,  facilities,  materials  or supplies in the open  market,  failure of
electronic or computer operated  equipment,  failure of transportation,  strike,
lockout,  action  of labor  unions,  a  taking,  requisition,  laws,  orders  of
government  or  civil or  military  authorities,  or any  other  similar  cause,
including reasonable delays for adjustments of insurance).

         15.11  Entire  Agreement.  This Lease,  the  exhibits  and any addendum
attached hereto set forth the entire agreement between Landlord and Tenant,  and
no other oral or written understandings, representations, promises or agreements
have been made or relied upon by either party hereto.. All prior oral or written
agreements are merged herein and superseded by this Lease.

         15.12  Governing  Law.  THIS  LEASE  IS  GOVERNED  BY THE  LAWS  OF THE
COMMONWEALTH  OF  VIRGINIA  (without  regard  to any  choice  of law  provisions
thereof).

         15.13 Waiver of Jury Trial. The parties each hereby waive trial by jury
in any action,  proceeding,  claim or  counterclaim  brought by either  party or
their  Agents  in  connection  with  any  matter  arising  out of or in any  way
connected with this Lease,  the  relationship of Landlord and Tenant  hereunder,
Tenant's use or occupancy of the Premises, Landlord's operation of the Building,
and/or any claim of injury or damage.  Tenant  hereby  waives any right to plead
any counterclaim  (other than compulsory  counterclaims),  offset or affirmative
defense in any action or summary or other proceeding brought by Landlord against
Tenant  seeking  payment of rent or possession  of the  Premises.  The aforesaid
waiver  shall not be construed  however as a waiver of Tenant's  right to assert
any claim in a separate action brought by Tenant against Landlord.

         15.14  Recordation  of Lease.  Tenant may not record  this Lease or any
memorandum  hereof  without  Landlord's  prior  written  consent,  which  may be
withheld in Landlord's sole discretion.
<PAGE>

         15.15 No Binding Effect Until Execution and Delivery. The submission of
this Lease to Tenant is not an offer.  This  instrument  is not  effective  as a
Lease or otherwise unless and until executed by and distributed to both Landlord
and Tenant.

         15.16  No  Partnership.  Nothing  contained  in  this  Lease  shall  be
construed as creating a partnership  or joint venture of or between  Landlord an
Tenant,  or to create any other  relationship  between the parties  hereto other
than that of Landlord and Tenant.

         15.17  Intentionally Omitted.
                ---------------------

         15.18  Days. Whenever there is a reference to "days" in this Lease,  it
shall be deemed to mean calendar days, unless expressly stated otherwise.

         15.19  Successors  and  Assigns.  This Lease is binding  upon and shall
inure to the benefit of the respective parties herein,  their heirs,  executors,
administrators, successors and permitted assigns.

         15.20 Non-Waiver.  Neither party's failure to enforce or require strict
performance of any provision of this Lease or any of the Rules and  Regulations,
nor Landlord's  acceptance of Rent with knowledge of a breach shall constitute a
waiver of such breach or any future breach.

         15.21 Counterparts. This Lease may be executed in counterparts, each of
which  shall be  deemed  an  original,  and all of which  taken  together  shall
constitute one and the same Lease.

         15.22  Survival of Rental  Obligations.  Except as  expressly  provided
herein,  Tenant's  obligations  to pay Rent accruing  hereunder will survive the
expiration or earlier termination of this Lease.

         15.23  Renewal Options.
                ---------------

         (a) Tenant shall have the  conditional  right to extend the term of the
Lease for two (2) additional  consecutive  terms (the "First" and "Second Option
Terms")  of five (5) years  each  beyond  the  initial  Lease  Term set forth in
Section 1.3 upon the same terms and  conditions  set forth  herein  (except that
there will be no further  privilege of extension  beyond the Second Option Term)
and pursuant to the Base Rent terms  determined in accordance with  subparagraph
(b) below, provided that the following conditions are met:

                  (i) Tenant notifies  Landlord of its election to exercise such
right at least  fourteen  (14) and no more than twenty (20) months  prior to the
expiration  of the then  current  Term (the  initial  Lease Term or First Option
Term, as applicable as stated in Exhibit D);

                  (ii) at the time of the  exercise  of such  right  and for the
remainder of the Term  thereafter  prior to the  commencement  of the applicable
Option  Term,  there is no existing  default  which is not  remedied  within the
applicable cure periods set forth in Article XI hereof;
<PAGE>

                  (iii)  that  the  Lease  has  not  terminated   prior  to  the
commencement of the Option Term;

                  (iv) at the time of the  exercise  of such  option and for the
remainder of the Term thereafter,  the original named Tenant or its Affiliate as
defined in Article VII hereof is occupying the Premises (or the portion  thereof
with  respect to which this Lease is being  renewed) [it being the intent of the
parties that this option is personal to the Tenant  hereunder  and its Affiliate
(i.e.,  it does not inure to the benefit of any other  assignee or  subtenant of
the  Lease)  and if such  original  Tenant  or its  Affiliate  is no  longer  in
possession of a portion of the  Premises,  then this option is void with respect
to that  portion of the  Premises  which is no longer  occupied by Tenant or its
Affiliate]; and

                  (v)  Tenant  exercises  the first  option  with  respect  to a
portion of the Premises consisting completely of full floors in the Building (it
being  the  understanding  of the  parties  that  the  first  option  may not be
exercised  with  respect to portions of any floor in the  Premises);  and Tenant
exercises the second option with respect to the entire  Premises (as the same is
constituted at the time of such exercise).

         (b) During each  Option  Term,  Landlord  shall  provide  Tenant with a
Refurbishment Allowance of up to fifteen dollars ($15.00) per square foot of Net
Rentable  Area  in the  Premises  for  such  Option  Term,  which  Refurbishment
Allowance shall be utilized  solely for the purpose of performing  improvements,
alterations and  modifications  to the Premises.  Said  Refurbishment  Allowance
shall be paid to Tenant in accordance  with the  procedures set forth in Article
III and Exhibit C depending upon whether Landlord or Tenant manages construction
of such  refurbishment  work.  During  each Option Term  (which,  upon  Tenant's
exercise of the option  becoming  binding in  accordance  with the terms hereof,
shall be deemed  to be a part of the  "Term" of this  Lease),  Tenant  shall pay
Landlord  Base Rent equal to  ninety-five  percent (95%) of the Fair Market Rent
(as defined  below) for the Premises for the  applicable  Option Term. The "Fair
Market  Rent," as used in this  Article XV,  shall mean the face  market  annual
rental value (plus any market-appropriate annual escalations thereof) in renewal
transactions  for comparable Class A office space in similar office buildings in
the Tyson's Corner submarket for the applicable Option Term, taking into account
all appropriate  factors and  transactional  components  customarily  taken into
account with respect to such transactions  assuming both Landlord and Tenant are
at arms-length. Within thirty (30) days of Landlord's receipt of Tenant's notice
of its exercise of the option,  Landlord  shall  notify  Tenant of the Base Rent
applicable  to the  Option  Term  based upon the  foregoing  parameters.  Within
fifteen (15) days  following  Landlord's  notification  regarding the Base Rent,
Tenant shall notify Landlord in writing of Tenant's  agreement to such Base Rent
set forth in Landlord's  notification,  or if Tenant  disagrees with  Landlord's
determination  of the  Base  Rent  applicable  to  said  Option  Term,  of  such
disagreement  and  provide  Landlord  with an  alternative  proposed  Base  Rent
structure based upon the foregoing  parameters.  Unless Tenant notifies Landlord
in writing of Tenant's agreement with Landlord's determination of the Base Rent,
then the Term  shall not be deemed  extended.  If Tenant  notifies  Landlord  in
writing of Tenant's  agreement with Landlord's  determination  of Base Rent, the
Lease shall be extended for five (5) years beyond the  Termination  Date (or the
expiration of the
<PAGE>

First Option Term, as applicable)  during such Option Term, and Tenant shall pay
Landlord the Base Rent set forth in  Landlord's  notification.  If Tenant timely
notifies Landlord of Tenant's disagreement with Landlord's  determination of the
Base Rent  applicable to said Option Term,  thereafter  Landlord and Tenant will
negotiate  in good  faith for a period of sixty  (60)  days  following  Tenant's
initial  exercise of the renewal option to determine the  appropriate  Base Rent
applicable to said Option Term in accordance with the foregoing  parameters.  In
the event that the parties  cannot agree upon the  appropriate  Base Rent within
sixty (60) days of Tenant's exercise of the option,  then Tenant shall deliver a
written notice to Landlord  prior to the expiration of the aforesaid  sixty (60)
day period  setting forth whether or not Tenant  desires to exercise the renewal
option or withdraw its exercise of the same.  If Tenant fails to timely  deliver
such a notice, Tenant shall be deemed to have exercised (and waived its right to
withdraw)  such option and the Base Rent shall be determined in accordance  with
the  following  terms.  If Tenant  chooses not to withdraw  its  exercise of the
option  (or is  deemed  to  have  not  withdrawn  the  same as  provided  in the
immediately preceding sentence) said Base Rent shall be determined in accordance
with the  following  terms.  Within ten (10) days after the  expiration  of such
sixty (60) day period, each party shall give written notice to the other setting
forth the name and address of a Broker (as hereinafter defined) selected by such
party  who has  agreed  to act in such  capacity,  to  determine  the Base  Rent
applicable  to the Option Term. If either party shall fail to select a Broker as
aforesaid,  then the  party  which  has  selected  a Broker  as  aforesaid  (the
"Appointing  Party") shall have the right to issue a written notice to the party
which  failed to  select a Broker  as  aforesaid  (the  "Non-Appointing  Party")
advising such Non-Appointing  Party that it has failed to appoint its Broker, in
which  case,  if the  Non-Appointing  Party does not then  designate  its Broker
within  five (5)  business  days  following  receipt of the  Appointing  Party's
Notice,  then the Base Rent shall be  determined  by the Broker  selected by the
other party. Each Broker shall thereupon independently make his determination of
the Base Rent  applicable  to the  Option  Term based  upon the  parameters  for
determining  Base  Rent  outlined  above  within  twenty  (20)  days  after  the
appointment of the second Broker. If the two Brokers' determinations are not the
same, but the higher of such two  determinations  (based upon the initial annual
Base Rent and average Base Rent over the course of the  applicable  Option Term)
is not more than one hundred five percent (105%) of the lower of them,  then the
Base Rent shall be deemed to be the  average of the two  determinations.  If the
higher of such two  determinations  is more than one hundred five percent (105%)
of the lower of them,  then the two Brokers shall jointly appoint a third Broker
within ten (10) days after the second of the two determinations  described above
has been rendered.  The third Broker shall  independently make his determination
of the Base Rent within twenty (20) days after his appointment.  The highest and
the lowest  determinations  among the three Brokers shall be disregarded and the
remaining  determination  shall be deemed to be the Base Rent  payable by Tenant
with respect to the  applicable  Option Term.  Within thirty (30) days after the
Base Rent is determined as aforesaid,  the parties shall execute an amendment to
this  Lease  setting  forth  the new Base Rent to be paid for the  Option  Term.
Notwithstanding  any provision hereof to the contrary,  within fifteen (15) days
following the determination of the Base Rent following  appointment of the third
Broker in accordance with the foregoing term, Tenant may, by delivering  written
notice to Landlord, revoke its exercise of the Option, in which case the Term of
the Lease shall  terminate  upon the  expiration  of the  then-current  Term. If
Tenant fails to timely exercise the foregoing revocation right, such right shall
be deemed waived. For the purposes of this Section 15.23,  "Broker" shall mean a
real  estate  broker  licensed in the
<PAGE>

Commonwealth of Virginia, who has been regularly engaged in such capacity in the
business of commercial office leasing in the Tyson's Corner,  Virginia submarket
for at least ten (10) years  immediately  preceding  such  person's  appointment
hereunder.  Each party shall pay for the cost of its Broker and  one-half of the
cost of the third Broker, if any.

         (c) Prior to the  commencement of each Option Term, upon the reasonable
request of Landlord,  Tenant  hereby agrees to execute an amendment to the Lease
memorializing  said extension of the Lease Term and the Base Rent payable during
such Option Term as determined in accordance with the terms of subparagraph  (b)
above.  If  Tenant  refuses  to  execute  a  commercially   reasonable  document
memorializing  the terms of such  extension of the Lease Term within thirty (30)
days of Landlord's  delivery of the same to Tenant, or if Tenant fails to timely
notify Landlord of Tenant's desire to exercise each renewal option,  then Tenant
shall be deemed to have waived the renewal options granted hereby.

         15.24  Right of First Offer.
                --------------------

         (a) Subject to the terms of this Section  15.24 and any renewal  rights
of other tenants in the Building and any existing (as of the date of this Lease)
expansion  rights of  Fidelity  Investments  or other  tenants in the  Building,
following the initial  lease up of the first floor of the  Building,  so long as
Tenant or its  Affiliate  continues to lease at least sixty percent (60%) of the
office  space in the  Building  other than any which may be located on the first
floor of the  Building,  Tenant shall have an ongoing  Right of First Offer with
respect to any leasable spaces which becomes available during the Term after the
first  anniversary of the  Commencement  Date on the first floor of the Building
("Offer Space"). If, at any time during the Term, Tenant or its Affiliate leases
less than sixty percent (60%) of the office space in the Building other than any
which may be located on the first floor of the  Building,  then  notwithstanding
any provision  hereof to the contrary,  Tenant's rights under this Section 15.24
shall be subject and  subordinate  to the renewal,  expansion or offer rights of
tenants  which lease  those  portions of the  Building's  office  space which no
longer are part of the Premises.  The parties  acknowledge  that portions of the
Offer Space may currently be occupied by other  tenants,  and Landlord shall not
have any obligation to take action to regain  possession of any portion  thereof
for the  purpose  of  offering  the  same to  Tenant  until  the  expiration  or
termination of such other tenants' rights thereto.

         (b) Landlord will notify Tenant of any portion of the Offer Space which
becomes   available  during  the  Term  after  the  first   anniversary  of  the
Commencement Date on the first floor of the Building and the terms on which said
Offer Space may be leased by Tenant  ("Offer  Notice").  Tenant will have thirty
(30)  days  following  delivery  of such  Offer  Notice  during  which to notify
Landlord in writing of  Tenant's  intent to lease the  available  portion of the
Offer Space described in Landlord's  Offer Notice or to reject leasing the same.
Tenant's  failure to timely exercise its Right of First Offer within said thirty
(30) day  period  shall be deemed an  absolute  waiver by Tenant of its right to
lease said  portion of the Offer Space  specified  in  Landlord's  Offer  Notice
(unless and until such Offer Space shall again become  available during the Term
following  its leasing to a third  party).  Upon  Tenant's  rejection (or deemed
rejection)  of the  portion of the Offer Space  specified  in  Landlord's  Offer
Notice,  Landlord shall be free to lease said Offer Space to any other person or
entity upon terms  substantially  consistent (which
<PAGE>

the parties agree shall mean basic economic terms which do not vary by more than
five percent (5%)) with those offered to Tenant hereunder.

         (c)  Tenant's  Right of First Offer  shall be subject to the  following
conditions:

                  (i) at the time of the  exercise of such right and  throughout
the period prior to Landlord's delivery of such Offer Space to Tenant,  there is
no existing Default by Tenant;

                 (ii) throughout the  period  following  Landlord's  delivery of
the Premises to Tenant and prior to Landlord's  delivery of any such Offer Space
to Tenant,  the original named Tenant (or its  Affiliate,  as defined in Article
VII hereof) is occupying the entire  Premises as then configured (as the same is
defined in Section 1.2 hereof, as subsequently  expanded or contracted  pursuant
to the terms hereof); and

                (iii) Tenant must lease  the entire  portion of  the Offer Space
specified in Landlord's Offer Notice.

In  addition  to the  foregoing,  notwithstanding  any  provision  hereof to the
contrary, if Tenant's Base Rent obligations with respect to any such Offer Space
will not  commence  prior to the date on which  only  sixty  (60) full  calendar
months  remain in the then current  Term of this Lease,  then Tenant shall lease
such Offer Space pursuant to one of the following  sets of terms:  (1) on an "as
is"  basis for the  remainder  of the then  current  Term,  with no  improvement
allowance  of any  kind  payable  by  Landlord  and upon  all of the  terms  and
conditions of this Lease, including the then-escalated per square foot Base Rent
payable hereunder with respect to the Premises, or (2) upon all of the terms and
conditions of this Lease,  as the same may be modified by the terms set forth in
Landlord's  Offer Notice  (including,  but not limited to the "Term" of Tenant's
leasing of such Offer Space).

         (d) Except as expressly  provided in subparagraph  (c) above, if Tenant
timely and properly exercises its Right of First Offer with respect to any Offer
Space and the  conditions  applicable  thereto  have been  met,  Landlord  shall
deliver and Tenant shall lease from Landlord such Offer Space upon the terms and
conditions  set forth in Landlord's  Offer Notice to Tenant for a Term beginning
on the Expansion  Commencement  Date (as defined below) and extending for a Term
conterminous with the then remaining Term hereunder.  The Expansion Commencement
Date,  as such term is used  herein,  shall be the date that  Landlord  delivers
possession  of the  applicable  portion  of the  Offer  Space to  Tenant  having
substantially  completed any agreed-upon  improvements  or alterations  thereto.
Notwithstanding  the foregoing,  if Tenant elects (by written notice to Landlord
at the time of its  exercise  of the Right of First  Offer) to manage or perform
the  improvements  or alterations  to the applicable  portion of the Offer Space
(which  improvements  or alterations  shall be performed by Tenant in accordance
with the procedures outlined in Article III and Exhibit C hereto), the Expansion
Commencement  Date shall be: (i) the sixtieth  (60th) day  following  Landlord's
delivery  of the  applicable  portion  of the  Offer  Space  to  Tenant  if such
applicable portion
<PAGE>

of the Offer Space was previously improved for office use, or (ii) the ninetieth
(90th) day following  Landlord's delivery of the applicable portion of the Offer
Space to Tenant if such applicable portion of the Offer Space was not previously
improved for office use.

         (e) If Tenant  timely and properly  exercises  the Right of First Offer
granted hereby,  prior to Landlord's  delivery of the applicable  Offer Space to
Tenant,   Tenant  and  Landlord   shall   execute  an  amendment  to  the  Lease
memorializing  said expansion of the Premises and the terms applicable  thereto.
If Tenant refuses to execute a commercially  reasonable  document  memorializing
the terms of such expansion within thirty (30) days of Landlord's  tender of the
same to Tenant,  then  Tenant  shall be deemed to have waived its Right of First
Offer granted hereby.

         (f) In the event of: (i) a failure of any of the  conditions  set forth
in subparagraph  (c) above prior to Landlord's  delivery of the applicable Offer
Space to Tenant,  or (ii) Tenant's  failure to take possession of the applicable
Offer Space when the same is tendered by Landlord, then notwithstanding the fact
that Tenant shall not occupy the Offer Space, Tenant shall pay Landlord,  as and
when the same come due all Base Rent and  Additional  Rent due with  respect  to
said Offer Space for the  remainder of the Term (less any  proceeds  received by
Landlord with respect to any reletting of same).

         (g) A space  shall be deemed to be  "available  for  leasing,"  as such
phrase is used in this Section 15.24 on the date on which the previous  tenant's
rights to lease the space expire or are terminated.  The parties  understand and
acknowledge  that  Landlord  may notify  Tenant that a space is  "available  for
leasing"  on a certain  date in the  future  based  upon  Landlord's  reasonable
expectation of the date on which such space will become  available.  The parties
also  acknowledge  that the Offer  Space may be  occupied  by other  tenants  or
occupants,  and that,  if such tenants or occupants  fail to timely  vacate such
Space,  the date on which such space may actually be "available for leasing" may
be postponed.  No such delay shall in any way constitute a default  hereunder by
Landlord or subject to any liability. However, if Landlord is unable to delivery
such Offer Space  within one hundred  eighty (180) days of the date by which the
parties have mutually  agreed the same shall be delivered for reasons other than
force majeure or delays attributable to Tenant, Tenant may terminate its leasing
of such Offer Space by providing  written notice to Landlord of such termination
within  fifteen (15) days of the  expiration of the aforesaid one hundred eighty
(180) day period.  If Tenant  exercises  its rights  under this  Section  15.24,
Landlord will use commercially  reasonable  efforts to regain  possession of the
applicable  Offer Space upon the expiration of such other tenant's or occupant's
rights with respect  thereto,  but Tenant shall have no obligation to execute an
amendment  to the  Lease or  otherwise  pay any rent for the Offer  Space  until
Landlord can offer Tenant actual possession.

         15.25  Generator, Transformer and Rooftop Mechanical Equipment.
                -------------------------------------------------------

         (a)  Provided  Tenant  is not  in  Default  of  any of its  obligations
hereunder  beyond any  applicable  notice and cure  period  provided  hereunder,
Tenant shall have the continuing  right to: (i) install and maintain up to three
(3) backup  generators,  related  wiring and cabling  connecting the same to the
Premises and diesel fuel tanks for each such generator (collectively, "Generator
Equipment')  in the  location  designated  in Exhibit  I, which is  incorporated
herein by this
<PAGE>

reference,  and  in  accordance  with  the  terms  of  this  Section  15.25  the
specifications,  if any,  contained  in  Exhibit  I,  and the  final  plans  and
specifications   therefor   approved  by  Landlord  in  writing   prior  to  the
installation  of the same;  (ii) install and maintain a transformer  and related
wiring  and  cabling   connecting  the  same  to  the  Premises   (collectively,
"Transformer  Equipment")  in the  location  designated  in  Exhibit J, which is
incorporated herein by this reference,  and in accordance with the terms of this
Section 15.25, the specifications, if any, contained in Exhibit J, and the final
plans and  specifications  therefor approved by Landlord in writing prior to the
installation  of the same;  and (iii)  install and maintain  rooftop  mechanical
equipment  and related  wiring and cabling  connecting  the same to the Premises
(collectively,  "Rooftop  Mechanical  Equipment") in the location  designated in
Exhibit K, which is  incorporated  herein by this  reference,  and in accordance
with the terms of this Section 15.25, the  specifications,  if any, contained in
Exhibit K, and the final plans and specifications  therefor approved by Landlord
in writing  prior to the  installation  of the same.  The  Generator  Equipment,
Transformer   Equipment   and  Rooftop   Mechanical   Equipment   are  sometimes
collectively referred to herein as the "Equipment."

         (b)  Prior to  installing  any such  Generator  Equipment,  Transformer
Equipment or Rooftop  Mechanical  Equipment,  Tenant shall submit detailed plans
and  specifications  therefor  to  Landlord  for  its  review.  Said  plans  and
specifications  shall describe in detail the proposed size,  weight,  number and
configuration of the such Equipment (including cabling or other conduits between
the generator, transformer or rooftop installation themselves and the Premises),
the  proposed  location of the same on the  Building or the Land,  the manner in
which the same shall be installed and removed,  and the name and license  number
of  the  competent   Virginia   licensed   contractors  who  will  perform  such
installation.  All such  plans  shall be  subject to  Landlord's  prior  written
approval,  which  shall not be  unreasonably  withheld,  conditioned  or delayed
provided that the same are consistent  with the  preliminary  plans therefor set
forth in Exhibits I, J and K respectively,  and further  provided that the size,
weight,  number,  configuration,  location  and method of  installation  of such
Equipment  may be  limited  by  Landlord  in its sole and  absolute  discretion.
However,  while (pursuant to the foregoing  terms),  Landlord can prescribed the
size, weight, number, configuration, location and method of installation of such
Equipment,  Landlord  cannot refuse to permit  Tenant to install the  applicable
Equipment,  so long as the  same are  consistent  with the  terms  set  forth in
Exhibits  I, J and K, as  applicable.  In  addition,  Landlord  may  request any
reasonable  additional changes to the plans and specifications,  as Landlord, in
its  reasonable  discretion,  deems  necessary  to  protect  the  structure  and
aesthetic  appearance of the Building or the Land and/or  Landlord's  ability to
properly maintain and operate the Building and the Land. As a result, the design
and installation of said Equipment shall be subject to the design limitations of
the Building and its structural,  electrical and mechanical systems. No work may
commence with respect to the  installation of said Equipment until: (i) Landlord
has provided  Tenant with Landlord's  prior written  approval of final plans and
specifications  therefor in accordance with the terms of this  subparagraph (b),
and (ii)  Tenant has  provided  Landlord  with  written  proof  that  Tenant has
obtained  all  licenses,   permits  and  approvals  from  applicable  government
authorities necessary for the installation and operation of said Equipment.

         (c) The installation, operation and maintenance of the Equipment shall,
at all times,  comply with all  applicable  present and future laws,  ordinances
<PAGE>

(including zoning ordinances and land use requirements),  regulations, orders or
other legal  requirements of the United States of America,  the  Commonwealth of
Virginia,  and any other public or quasi-public  authority  having  jurisdiction
over the Building or the Land, as well as all insurance requirements relating to
or affecting the Premises,  the Building,  the Land, the condition  thereof,  or
machinery,  equipment and furnishings  therein incident to Tenant's occupancy of
the Building and its use thereof.  The Equipment  shall be modified,  removed or
relocated  (subject to Landlord's  prior written approval which shall be granted
in accordance with the parameters set forth in subparagraph (b) above) from time
to time by Tenant in order to ensure  continued  compliance  with the  foregoing
requirements.  Landlord's  approval of any plans and specifications  shall in no
way  constitute a  representation  or warranty by Landlord  that the same are in
compliance  with  any  of  the  foregoing  requirements.  The  installation  and
subsequent  maintenance  of the  Equipment  shall be subject to such  reasonable
regulations and  restrictions  as are imposed thereon by Landlord.  In the event
that the installation,  maintenance or use of the Equipment results in damage to
the Building or the Land, or any part thereof,  or Landlord incurs any liability
relating to or arising  from the same,  Tenant  agrees:  (i) to pay  Landlord on
demand the costs incurred by Landlord in repairing any such damage if Tenant has
failed to repair the same  within  ten (10) days of  Landlord's  written  notice
regarding the same (or such shorter period as Landlord deems necessary to ensure
the proper  condition of the Building),  and (ii) to indemnify  Landlord against
any such  liability.  Tenant's rights under this Section 15.25 shall not include
any rights on the part of Tenant or Tenant's  Agents to directly access the roof
at any time.  All such access to the roof shall be obtained by prior  request to
Landlord,  whose permission for such access shall not be unreasonably  withheld,
conditioned or delayed.

         (d) At any time  during  the Term,  Tenant  may  remove  the  Equipment
(except that if any portion of the Generator Equipment is removed the same shall
be replaced with generators of similar capacity and quality so that two (2) such
generators remain at the expiration or termination of this Lease), provided that
Tenant, at its sole cost and expense,  immediately restores the Building and any
damage caused by such removal.  Tenant shall pay all costs  associated  with the
design,  installation,  maintenance,  operation,  relocation  and removal of the
Equipment.  Tenant shall reimburse  Landlord,  as additional rent, for any costs
incurred by Landlord  with respect to the  Equipment,  including but not limited
to: (i) any increased  insurance  premiums,  and (ii) any reasonable third party
engineering or  architectural  fees related to reviewing the aforesaid plans and
specifications  (excluding those of Landlord's  managing  agent).  Tenant hereby
indemnifies   and  holds   Landlord   harmless  from  and  against  any  claims,
liabilities, causes of action, losses, damages and costs incurred by Landlord as
a result of the installation,  operation, maintenance,  relocation or removal of
the Equipment.  Tenant covenants not to damage the roof or any other part of the
Building or the Land in the course of  installing,  maintaining,  operating  and
removing  the  Equipment.  Except as expressly  set forth in the approved  plans
therefor,  no  such  installation,  maintenance,  operation  or  removal  of the
Equipment  shall  involve any  penetration  of the  Building's  roof or exterior
walls.

         (e) Tenant  covenants that the  installation,  maintenance,  operation,
relocation  and  removal  of  the  Equipment  shall  in no  way  interfere  with
Landlord's  operation of the  Building's  systems or with other  tenants' use of
their  premises  or  operation  of  their  equipment.  In the  event of any
<PAGE>

such  interference,  the  equipment  shall be  modified,  removed  or  relocated
(subject to Landlord's prior written approval) from time to time by Tenant.

         (f) Tenant  shall use any such  Equipment  for service to the  Premises
only. No Equipment  which Tenant is permitted to install in accordance  with the
terms of this Section 15.25 shall be utilized by anyone other than Tenant or its
Affiliate (as defined in Article VII) or in any manner as a source of revenue to
Tenant.

         (g) The maintenance and operation of the Equipment shall be at Tenant's
sole risk,  and any  damage to the  Equipment  will in no way  operate to affect
Tenant's obligations under this Lease. Similarly, any condemnation which affects
Tenant's  ability to maintain and operate the  Equipment  shall in no way affect
Tenant's  obligations under this Lease,  except as set forth below. In the event
that any applicable  government  authority or other legal  requirement  prevents
Tenant from operating or maintaining the Equipment, Tenant shall promptly remove
the same.  The rights of Tenant set forth in this Section  15.25 are personal to
the named Tenant  herein and its  Affiliates  (as defined in Article VII hereof)
and may not be sublet or  otherwise  transferred  to any third  person or entity
except to an  Affiliate  of Tenant.  Except with respect to one (1) of the three
(3)  generators,  any  associated  fuel tank linked to such  generator  (and not
connected to the remaining two (2) generators) and the associated battery backup
system  (as  provided  below),  Tenant  shall not be  obligated  to  remove  the
Equipment  from the Building and the Land and restore the same to its  condition
prior to the installation  thereof.  Notwithstanding any provision hereof to the
contrary,  upon the  expiration  or  termination  of the term of this Lease,  at
Landlord's  option,  Landlord  may  designate  that  one  (1) of the  three  (3)
generators, any associated fuel tank linked to such generator (and not connected
to the remaining two (2) generators) and the associated battery backup system be
removed by Tenant at Tenant's  sole cost and expense,  and any damage  caused by
such removal shall be repaired by Tenant at its sole cost and expense.

         15.26    Roof Rights.
                  -----------

         (a)  Provided  Tenant  is not  in  default  of  any of its  obligations
hereunder, Tenant shall have the conditional right to install and maintain up to
eight (8)  antenna  dishes of not more than forty (40)  inches in height and any
associated  equipment  (including  cabling or other  conduits  between  the said
rooftop  equipment  itself  and  the  Premises)  (collectively,  "Communications
Equipment") on the roof of the Building in the locations specified in Exhibit M,
which is incorporated herein by this reference,  in accordance with the terms of
this Section 15.26, and in accordance with the specifications, if any, contained
in Exhibit M.

         (b) Prior to installing any such Communications Equipment, Tenant shall
submit  detailed plans and  specifications  therefor to Landlord for its review.
Said  plans and  specifications  shall  describe  in detail the  proposed  size,
weight,  color,  number and configuration of the Communications  Equipment,  the
proposed  location  of the same on the  Building,  the  manner in which the same
shall be installed and removed, and the name and license number of the competent
Virginia licensed contractor who will perform such installation.  All such plans
shall be subject to Landlord's  prior written  approval,  and the size,  weight,
color,  number  (provided  that  Landlord may not  determine  that the number of
pieces of Communications  Equipment shall be
<PAGE>

zero) configuration and location of such Communications Equipment may be limited
by Landlord in its sole and  absolute  discretion.  In  addition,  Landlord  may
request any reasonable  additional changes to the plans and  specifications,  as
Landlord,  in its sole discretion,  deems necessary to protect the structure and
aesthetic  appearance  of the  Building  and/or  Landlord's  ability to properly
maintain and operate the Building.  As a result,  the design and installation of
said Communications  Equipment shall be subject to the design limitations of the
Building and its  structural,  electrical  and mechanical  systems.  No work may
commence  with  respect to the  installation  of said  Communications  Equipment
until:  (i) Landlord has provided Tenant with Landlord's  prior written approval
of final plans therefor in accordance with the terms of this  subparagraph  (b),
and (ii)  Tenant has  provided  Landlord  with  written  proof  that  Tenant has
obtained  all  licenses,   permits  and  approvals  from  applicable  government
authorities  necessary for the installation and operation of said Communications
Equipment.

         (c) The installation,  operation and maintenance of the  Communications
Equipment  shall,  at all times,  comply with all applicable  present and future
laws,  ordinances  (including  zoning  ordinances  and land  use  requirements),
regulations, orders or other legal requirements of the United States of America,
the  Commonwealth of Virginia,  and any other public or  quasi-public  authority
having jurisdiction over the Building and insurance  requirements relating to or
affecting the Premises,  the Building,  the condition  thereof,  all  machinery,
equipment and furnishings therein incident to Tenant's occupancy of the Building
and its use thereof. The Communications Equipment shall be modified,  removed or
relocated  (subject to Landlord's  prior written  approval) from time to time by
Tenant in order to ensure continued compliance with the foregoing  requirements.
Landlord's approval of any plans and specifications shall in no way constitute a
representation  or warranty by Landlord that the same are in compliance with any
of the foregoing  requirements.  The installation and subsequent  maintenance of
the Communications Equipment shall be subject to such reasonable regulations and
restrictions  as are  imposed  thereon  by  Landlord.  In  the  event  that  the
installation or maintenance of the Communications Equipment results in damage to
the Building or the Project,  or Landlord  incurs any  liability  relating to or
arising from the same,  Tenant  agrees:  (i) to pay Landlord on demand the costs
incurred by Landlord in repairing any such damage if Tenant has failed to repair
the same within ten (10) days of Landlord's  written  notice  regarding the same
(or such  shorter  period as  Landlord  deems  necessary  to ensure  the  proper
condition  of the  roof),  and  (ii) to  indemnify  Landlord  against  any  such
liability. Tenant's rights under this Section 15.26 shall not include any rights
on the part of Tenant or  Tenant's  Agents to  directly  access  the roof at any
time.  All  such  access  to the roof  shall be  obtained  by prior  request  to
Landlord,  whose permission for such access shall not be unreasonably  withheld,
conditioned or delayed.

         (d)  Tenant   shall  pay  all  costs   associated   with  the   design,
installation,   maintenance,   operation,   relocation   and   removal   of  the
Communications  Equipment.  Tenant shall reimburse Landlord, as additional rent,
for any costs incurred by Landlord with respect to the Communications Equipment,
including  but not limited to: (i) any  increased  insurance  premiums,(ii)  any
engineering or  architectural  fees related to reviewing the aforesaid plans and
specifications,  and (iii) any legal fees related to the review of the aforesaid
requirements and Tenant's  compliance  therewith.  Tenant hereby indemnifies and
holds  Landlord  harmless  from and against any claims,  liabilities,  causes of
action,  losses,  damages  and costs  incurred  by  Landlord  as a result of the
installation,  existence, operation,  maintenance,  relocation or removal
<PAGE>

of the Communications Equipment.  Tenant covenants not to damage the roof or any
other  part  of  the  Building  or the  Project  in the  course  of  installing,
maintaining and removing the Communications  Equipment.  Except as expressly set
forth in the approved  plans  therefor,  no such  installation,  maintenance  or
removal of the  Communications  Equipment  shall involve any  penetration of the
Building's roof or exterior walls.

         (e) Tenant  covenants that the  installation,  maintenance,  operation,
relocation and removal of the Communications Equipment shall in no way interfere
with Landlord's  operation of the Building's  systems or with other tenants' use
of their  premises or  operation  of their  equipment.  In the event of any such
interference,  the  Communications  Equipment  shall  be  modified,  removed  or
relocated  (subject to Landlord's  prior written  approval) from time to time by
Tenant.  Landlord shall have the right to require Tenant to temporarily relocate
the  Communications  Equipment in order to allow  Landlord to complete  repairs,
maintenance or modification of the Building.  In exercising its rights set forth
in the immediately  preceding sentence,  Landlord will use reasonable efforts to
minimize any interference with Tenant's use of the Communications Equipment.

         (f) Tenant shall use any such  Communications  Equipment  for corporate
purposes only. No Communications  Equipment which Tenant is permitted to install
on the roof of the Building in  accordance  with the terms of this Section 15.26
shall be utilized by anyone  other than Tenant or an  Affiliate  of Tenant or in
any  manner as a source of revenue to Tenant  not  related to  Tenant's  regular
business  operations  (it being the intent of the  parties,  that Tenant may not
sublease,  sell or otherwise  transfer its rights under this Section  15.26 to a
third party as a separate source of revenue to Tenant).

         (g) The maintenance and operation of the Communications Equipment shall
be at Tenant's sole risk, and any damage to the Communications Equipment will in
no way operate to affect Tenant's obligations under this Lease.  Similarly,  any
condemnation  or other  governmental  action which affects  Tenant's  ability to
maintain  and  operate  the  Communications  Equipment  shall  in no way  affect
Tenant's  obligations under this Lease,  except as set forth below. In the event
that any applicable  government  authority or other legal  requirement  prevents
Tenant from operating or maintaining the Communications Equipment,  Tenant shall
promptly  remove the same.  The rights of Tenant set forth in this Section 15.26
are  personal  to the named  Tenant  herein and its  Affiliates  (as  defined in
Article VII hereof) and may not be assigned,  sublet or otherwise transferred to
any third person or entity (notwithstanding a permitted assignment,  sublease or
other  transfer of Tenant's  other rights  hereunder)  except to an Affiliate of
Tenant  (as  defined  in  Article  VII  hereof).  Prior  to  the  expiration  or
termination of the Lease Term, Tenant shall remove the Communications  Equipment
from  the  Building  and  restore  the  same  to  its  condition  prior  to  the
installation thereof. Tenant's failure to so remove the same shall constitute an
Event of Default under this Lease and a holdover by Tenant in the Premises.

                           (signature pages to follow)
<PAGE>

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

LANDLORD:
--------
                           TYSONS CORNER PROPERTY LLC,
                           a Virginia limited liability company
                           ATTEST:
                           ------
                           By:      L&B Realty Advisors, Inc.,
                                    a Delaware corporation,
                                    its investment manager

                                    /s/ M. Welch
                                    --------------------------

                           By:      /s/ David H. Phumlet [SEAL]
                                    --------------------------
                                    Name:    David H. Phumlet
                                    Title:   President
                                    Date:    1-7-00


                        (second signature page to follow)
<PAGE>

ATTEST:                    TENANT:
------                     ------
/s/ James Cappelli         MICROSTRATEGY, INC.,
------------------         a Delaware corporation
                           By:      /s/ Mark Lynch    [SEAL]
                                    -----------------------
                                    Name:    Mark Lynch
                                    Title:   CFO
                                    Date:    1/6/00
<PAGE>

                                   EXHIBIT "A"
                                   -----------

                              OUTLINE OF THE PREMISES
                              -----------------------

(The parties  understand and acknowledge that the following  depiction is merely
an approximation  of the location of the Premises in the Building,  and Landlord
makes no representations regarding the specific accuracy of said depiction).

                                 (see attached)
<PAGE>

                            [Schematic of Building]

                                   Exhibit A
                                  Page 1 of 2
<PAGE>

                            [Schematic of Building]

                                   Exhibit A
                                  Page 2 of 2
<PAGE>

                                   EXHIBIT "B"
                                   -----------

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

         To the extent that there is a conflict  between the Lease and the Rules
and  Regulations,  the Lease shall take  precedence  over the contrary Rules and
Regulations.

        1. Tenant may not: (a) obstruct sidewalks, doorways, vestibules, halls,
stairways,  or other areas,  (b) place refuse,  furniture,  boxes or other items
therein or (c) use such areas for any purpose  other than  ingress and egress to
and from the Premises.  Canvassing,  soliciting and peddling in the Building are
prohibited.

        2. Tenant  may use  plumbing  fixtures  and  appliances  only  for the
purposes for which constructed, and may place no unsuitable material therein.

         . Tenant may not paint or place any signs or notices on any  windows or
doors or in  other  parts of the  Building  which  are  visible  outside  of the
Premises, without Landlord's prior written approval (which Landlord may withhold
in its sole  discretion) of the design and placement.  Without notice to Tenant,
Landlord has the right to remove all unapproved signs at Tenant's expense.

         . (Intentionally Omitted).

         . (Intentionally Omitted).

         . Tenant will  notify the  Building  manager  when safes or other heavy
equipment are to be taken in or out of the Building,  and will move same only in
accordance with any reasonable Landlord requirements.

         . Suite entry doors, when not in use, will be kept closed.

         . All  deliveries  must be made via the  service  entrance  and service
elevator,  when  provided,  during  normal  working  hours.  Tenant  must obtain
Landlord's  written  approval for any delivery after normal  working hours.  All
moving  (except the  initial  move-in at the  commencement  of the Term) must be
conducted  after normal  working  hours,  and the manner  (including  any moving
company to be used) approved in advance by Landlord, which approval shall not be
unreasonably withheld so long as Tenant is not in Default under the Lease.

         . Tenant  will  cooperate  with  Landlord's  employees  in keeping  the
Premises neat and clean.

         . Tenant will not cause or permit any improper  noises in the Building,
or allow  any  unpleasant  odors to  emanate  from  the  Premises,  and will not
interfere with, injure or annoy other tenants or their invitee.
<PAGE>

         .  No  animals  other  than  seeing  eye  dogs  and  other  handicapped
assistance animals are allowed in or about the Building.

         . At Tenant's  cost,  Landlord  will dispose of crates,  boxes or other
large items throughout the business day. Landlord is responsible for the removal
of waste generated by normal office operations only.

         . Tenant may not  operate any  machinery,  other than  ordinary  office
machines customarily found in a modern office in the Tysons Corner submarket. No
space heaters or fans are allowed.

         . Tenant  must  comply  with  all  emergency  and  safety   procedures
established by Landlord,  the fire department,  or any other governmental agency
having   jurisdiction  over  the  Building,   including,   without   limitation,
participation in periodic drills,  familiarization with emergency procedures and
the designation of individuals  responsible for the  implementation of emergency
action.  Landlord  has the right to  evacuate  the  Building  in the event of an
emergency or catastrophe.

         . No  bicycles,  motorcycles  or similar  vehicles  are  allowed in the
Building  or any part  thereof  with the  exception  of the  garage or  Landlord
designated areas.

         . Tenant may not insert any nails,  hooks,  or screws  into any part of
the Building  (excepting small nails, hooks or screws for the purpose of hanging
pictures on the interior walls of the Premises),  except as approved by Building
maintenance personnel.

         . Tenant may not  distribute  any food or  beverages  from the Premises
(except for food brought into the Premises for consumption by Tenant's employees
in the Premises) without the prior written approval of the Building manager.

         . Tenant  may not  place  any  additional  locks on or rekey any doors
without  the prior  coordination  with and  consent  of  Landlord.  Tenant  must
surrender all keys upon termination of this Lease. Tenant will give Landlord the
combination to any vault,  which  combination  will be held in confidence by the
Landlord, and only used in the event of an emergency.

         . Tenant will not locate furnishings or cabinets adjacent to mechanical
or electrical access panels or over air conditioning  outlets,  and Tenant shall
pay on  demand  as  Additional  Rent the cost of  moving  such  furnishings  for
servicing  such  units.  Building  personnel  will  perform  any  repairs  on or
replacements of the lighting and air conditioning equipment of the Building.

         . Tenant will comply with any parking rules and regulations.

         .  Tenant  may not use the  Premises  or any part of the  Building  for
residential purposes or for overnight lodging.
<PAGE>

         . Tenant will not place vending machines in the Premises except for use
by Tenant and its invitees.

         . (Intentionally Omitted).

         . (Intentionally Omitted).

         . (Intentionally Omitted).

         . Tenant will not ask building  personnel to perform such  functions as
furniture  moving,  deliveries,  picture  hanging,  or other  similar  tasks not
related to the general operation of the Building.

         . Tenant will comply with all  reasonable  written  procedures  for the
security and safety of the Building, including without limitation, the manner of
access to the Building  after normal  business  hours,  keeping  doors to Tenant
areas locked and cooperating with all reasonable  requests of Building  security
personnel.

         . Before leaving the Premises  unattended,  Tenant shall close and lock
outside  (between the Premises and the Common Areas) doors,  and use  reasonable
efforts to turn off lights, coffee pots, and office equipment.  Tenant shall pay
for any damage resulting from failure to do so.

         . Tenant may use a microwave  oven and  appliances of the type commonly
used to  prepare  coffee and tea in the  Premises;  provided,  however,  that no
offensive  cooking  odors shall be allowed to escape the Premises  (for purposes
hereof an offensive  odor shall be deemed to be offensive if it is complained of
by another Tenant).

         . The Building has been  designated as a non-smoking  building.  Tenant
shall comply and shall cause its employees to comply with this  prohibition  and
applicable non-smoking ordinances.
<PAGE>

         . Landlord may refuse  admission  to the  Building  outside of ordinary
business hours to any person not known to the watchman in charge or not properly
identified,  and may  require all  persons  admitted to or leaving the  Building
outside of ordinary business hours to register. Any person whose presence in the
Building  at any  time  shall,  in  the  reasonable  judgment  of  Landlord,  be
prejudicial to the safety,  character,  reputation and interests of the Building
or its tenants may be denied access to the Building or may be ejected therefrom.
Landlord reserves the right to exclude or expel from the Building any person who
in the judgment of Landlord is  intoxicated  or under the influence of liquor or
drugs or who violates these Rules and  Regulations.  In case of invasion,  riot,
public  excitement  or other  commotion,  Landlord may prevent all access to the
building  during the continuance of the same, by closing the doors or otherwise,
for the safety of the tenants,  the Building and  protection  of property in the
Building.  Landlord may require any person leaving the Building with any package
or other  object to  exhibit a pass from the  tenant  from  whose  premises  the
package or object is being removed,  but the  establishment  and  enforcement of
such  requirement  shall not  impose  any  responsibility  on  Landlord  for the
protection  of any tenant  against the removal of  property  from its  premises.
Landlord  shall not be liable to any tenant for damages or loss arising from the
admission,  exclusion or ejection of any person to or from any tenant's premises
or the Building under the provisions of this rule.
<PAGE>

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

                                   WORK LETTER
                                   -----------

A. At Landlord's sole cost, Landlord will complete  construction of the Building
(including Landlord's Work described below,  Building core improvements,  garage
facilities,   plaza  and  retail  areas)  in  accordance   with  the  plans  and
specifications  therefor  issued for permit dated January 8, 1999, as revised in
accordance with  construction  bulletins  through July 23, 1999, which plans and
specifications are incorporated herein by this reference. To the extent that the
Landlord's Work described below is inconsistent  with the  aforementioned  plans
and specifications, the definition of Landlord's Work below will control.

         With respect to the Premises,  said  construction of the Building shall
consist of the  preparation  and delivery of the Premises in Base Building Shell
Condition, which shall be defined as the following ("Landlord's Work"):

         1.       Two (2)  self-contained  HVAC  units  have been  installed  in
                  mechanical  rooms on each floor (except at the 6th Floor,  for
                  which  the  mechanical  room / units  have  been  specifically
                  placed on the penthouse level) and all main  distribution duct
                  work has been  installed  and designed for variable air volume
                  terminal  units at interior  zones and fan  powered  induction
                  units with electric heat at exterior zones;  The Base Building
                  shall  be in  substantial  compliance  with the  revised  1996
                  ASHRAE requirements  including ASHRAE specifications for fresh
                  air   mix  as   part   of  the   building   HVAC   performance
                  specifications for an average density of not less than one (1)
                  person per one hundred fifty (150) usable square feet.

         2.       Seven (7) freeze  protector fan powered  induction  units with
                  electric heaters and electronic  thermostatic  control will be
                  installed  at the  perimeter  of  each  floor  ("Landlord  VAV
                  Work").

         3.       The  sprinkler  system  on  each  floor  has,  in  place,  the
                  sprinkler  supply  distribution  loop  with  branch  lines and
                  upturned  heads  installed in  accordance  with code for light
                  hazard / shell  building  occupancy,  ready for  tenant  use /
                  modification.

         4.       Core  areas  have been  provided  with code  required  and ADA
                  compliant  fire alarm  devices  (The fire alarm system will be
                  addressable and expandable for tenant required alarm devices).
                  All Base Building  life/safety  equipment  and related  panels
                  will be fully installed.

         5.       Core areas have been provided with code required  restroom and
                  water fountains fully installed and code compliant.

         6.       The  building  has been  designed to  accommodate  diversified
                  tenant  electrical  loads for lighting and power up to 8 watts
                  per  square  foot  of  usable  area.   High  and  low  voltage
                  electrical  panels have been installed  within the core of the
                  building  at each
<PAGE>

                  floor with space for tenant electrical circuits.  Transformers
                  have been  included in the shell  building  to provide  tenant
                  power  at  120/208  volts.  (Capacity  has  been  provided  to
                  accommodate additional  transformers which may be added during
                  tenant  improvements,  at the  tenant's  expense)  to  provide
                  additional 120/208 volt power.

         7.       Windows will include high performance  low-E insulated glazing
                  units.  Window sills heights above finish floor vary depending
                  location on the floor.  Window mullions will be spaced at 5' -
                  0" on center.

         8.       All standard window coverings and blinds  fully installed  and
                  operational.

         9.       All  perimeter  square  columns,  wet stacks and all  spandrel
                  walls (north and east) have been fully  furred,  finished with
                  drywall and taped,  in paint ready  condition;  all core walls
                  have been fully furred,  finished  with drywall and taped,  in
                  paint ready  condition.  All other  columns will be unfinished
                  except as specifically noted on the base building construction
                  documents.

         10.      Four (4) wet stacks have been installed on each floor.

         11.      Elevator lobbies will be unfinished  except for the mechanical
                  distribution  ductwork on floors two through six. All elevator
                  equipment will be in place and working.

         12.      There will be no ceiling grid or tile installed  on the tenant
                  floors.

         13.      Core  signage  (stairs,  elevators,   bathrooms,   mechanical,
                  electrical  and telephone  rooms) will be provided as required
                  for occupancy.

         14.      A perimeter Building security system with card key access will
                  be installed with the possibility of connection / expansion of
                  the security  system for tenant security access and monitoring
                  as well.  (The parties will coordinate the Building system and
                  Tenant's security system in accordance with and subject to the
                  limitations set forth in Section 5.7 of the Lease).

All additional  improvements  and alterations to the Premises beyond  Landlord's
Work (the  "Improvements")  shall be at Tenant's  cost and expense in accordance
with the following terms.

B. Attached hereto as Exhibit C-1 and incorporated herein by this reference is a
list  of  permit-ready   drawings  and   specifications   with  respect  to  the
Improvements  to be  performed  on the  third and fifth  floor  portions  of the
Premises,  which plans and specifications are hereby approved by Landlord as the
"Final Plans" (as defined  below) with respect to such portions of the Premises,
subject to: (1) conformance of the same to Landlord's comments on such plans and
specifications  (which  comments  are  attached  hereto as Exhibit  C-2 and also
incorporated  herein  by this  reference),  and (2)  further  modification  with
respect to the  elevator  lobby  portions of such
<PAGE>

plans  (which  elevator  lobby  portions  the  parties  acknowledge  are not yet
complete and must be submitted to Landlord for approval in  accordance  with the
terms set forth below).  Attached hereto as Exhibit N and incorporated herein by
this  reference,   is  a  preliminary   conceptual  plan  with  respect  to  the
Improvements  to be  performed  on the fourth  floor  portion  of the  Premises.
Attached  hereto as Exhibit O and  incorporated  herein by this  reference,  are
preliminary conceptual plans with respect to the Improvements to be performed in
the elevator lobby  portions of the Premises.  Within thirty (30) days following
the execution of this Lease,  Tenant will submit to Landlord for approval  final
working  drawings and  specifications  of materials  for all  Improvements  that
Tenant  desires  with  respect  to the second and sixth  floor  portions  of the
Premises,  and within  sixty (60) days  following  the  execution of this Lease,
Tenant  will  submit  to  Landlord  for  approval  final  working  drawings  and
specifications  of  materials  for all  Improvements  that Tenant  desires  with
respect to the fourth floor  portions of the  Premises.  All such final  working
drawings will:  (i) comply with the ADA and all other  applicable  codes,  laws,
rules,  regulations  and  statutes,  (ii)  be  consistent  with  the  terms  and
limitations set forth in Exhibit L hereto,  which is incorporated herein by this
reference,  (iii)  incorporate the Tenant VAV Work (as described below) which is
consistent  with the  limitations on the Tenant VAV Work set forth below in this
Exhibit  C,  (iv) with  respect  to the plans  for the  second  and sixth  floor
portions of the Premises,  be  substantially  consistent  with the  Improvements
described in the attached  Final Plans  (Exhibit  C-1) with respect to the third
and fifth floor portions of the Premises,  (v) with respect to the plans for the
fourth floor portion of the Premises,  be consistent with the preliminary  plans
with  respect  to such  fourth  floor  attached  hereto as  Exhibit N, (vi) with
respect to the plans for the fourth floor portion of the Premises, not adversely
affect any  Building  systems,  (vii)  with  respect to the plans for the fourth
floor portion of the Premises,  incorporate  screening reasonably  acceptable to
Landlord  with  respect  to any  portions  of  the  Improvements  or  associated
equipment  which are  visible  from the  exterior  of the  Building  or  located
adjacent  to the windows of the  Building  in order to ensure that the  exterior
appearance of the Building is consistent  with that of Class A office  buildings
in the  Tysons  Corner  submarket,  (viii)  with  respect  to the  plans for the
elevator  lobby  portions of the Premises,  be consistent  with the  preliminary
plans with respect to such elevator  lobbies  attached  hereto as Exhibit O, and
(ix) with respect to the plans and  specifications  for the Tenant VAV Work,  be
consistent with the terms of Exhibits C-1 and N, as the same are modified by the
terms of Exhibit C-2. All plans for the  Improvements  require  Landlord's prior
written approval (and  notwithstanding  any time periods set forth above, Tenant
shall  not  commence  performance  of any  Improvements  in any  portion  of the
Premises until Landlord has approved the Final Plans for such  Improvements with
respect  to  such  portion  of  the  Premises),   which  approval  will  not  be
unreasonably  withheld  provided  that the  foregoing  conditions  are  met.  As
modified by any  Landlord-required  changes,  the final working drawings will be
the "Final Plans".  Tenant is solely responsible for determining  whether or not
it is a public  accommodation  and for compliance  with ADA within the Premises.
Tenant's  approval of the Final Plans  constitutes an  acknowledgment  by Tenant
that  they  comply  with  ADA and  all  other  applicable  codes,  laws,  rules,
regulations and statutes.  Landlord's approval of the plans,  specifications and
working  drawings  for  the  Improvements  shall  create  no  responsibility  or
liability on the part of Landlord for their completeness, design sufficiency, or
compliance with any codes, laws, rules,  regulations or statutes of governmental
agencies or authorities.
<PAGE>

         If  Tenant  requires  any  changes  in the  Final  Plans  (the  "Tenant
Changes"),   Tenant  must   present   Landlord   with   revised   drawings   and
specifications. If Landlord approves the Tenant Changes, Tenant will incorporate
such changes in the Improvements.

         Tenant shall not be obligated to utilize building standard materials in
connection with the Improvements, provided that the materials selected by Tenant
shall be subject to Landlord's  prior  written  approval and shall be consistent
with the  design  and  finishes  of Class A office  space in the  Tysons  Corner
submarket.  In  addition,  the  Improvements  may include an internal  staircase
between the floors of the Premises  subject to the terms of this paragraph.  The
design,  location and manner of construction of any internal staircases shall be
subject  to  Landlord's  approval.  If the  Improvements  contain  only  one (1)
continuous internal  staircase,  Tenant shall not be required to remove the same
prior to the expiration or  termination  of the Lease Term. If the  Improvements
include more than one (1) continuous internal  staircase,  at Landlord's option,
Tenant,  at its cost and  expense,  shall be required  to remove any  additional
internal staircases prior to the expiration or termination of the Lease Term and
restore the portions of the Premises  affected  thereby to Base  Building  Shell
condition.  In the event that Tenant  exercises  the first  renewal  option with
respect to less than the entire Premises, prior to the commencement of the First
Option  Term,  Tenant,  at its sole cost and  expense,  will remove any internal
staircases  affecting  any portion of the  Premises  with  respect to which this
Lease has not been renewed, and will restore the floor,  structure and any other
portion of the Building to Base Building Shell condition.

         The  Improvements  shall  include  the  installation  of  ductwork  and
additional  variable  air volume  boxes in the  Premises  (beyond the  equipment
described  in  Paragraph 2 of the  Landlord's  Work,  as defined in  Paragraph A
above)  which shall be attached to and  incorporated  into the  Building's  HVAC
system serving the Premises ("Tenant VAV Work").

C.       Tenant will bear the cost of  architectural  and  engineering  fees, if
any, relating to the Improvements [including: (i) the architectural fees related
to  the  preparation  of  all  drawings,  (including  CAD  drawings)  plans  and
specifications  (collectively,  "plans"), (ii) any architectural and engineering
fees which Landlord incurs in reviewing plans prepared by Tenant's  architect or
work  performed  by Tenant  or its  contractors  which  plans or work are in the
nature of above- building  standard  improvements  (including but not limited to
stairs, rooftop, lobbies,  generator placement, floor loading and the like), all
of which will be subject to review by Landlord's  architect at Tenant's cost and
expense, (iii) engineering fees related to Tenant's engineer's  participation in
the  planning  and  performance  of the  Improvements  in the Premises (it being
understood  that  Tenant is  required  to use  Landlord's  engineer  and may not
utilize an outside  engineer in connection with the  Improvements)]  the cost of
any necessary  permits and associated fees, and all costs and expenses  incurred
in  the  construction  of  Improvements  over  and  above  Base  Building  Shell
condition,  including  the  construction  management  fee payable to Landlord in
connection with the  Improvements (as determined in accordance with the terms of
Paragraphs  D and F below  (collectively  "Tenant's  Costs")  [In the event that
Tenant employs its own architect to prepare the Final Plans,  upon completion of
the  Improvements,  Tenant's  architect,  at Tenant's  cost and  expense,  shall
deliver to Landlord  computer  disks  containing  "as-built"  CAD  drawings  and
specifications regarding such Improvements];  provided,  however,  Landlord will
credit
<PAGE>

against the foregoing Tenant's Costs, an allowance (the "Improvement Allowance")
consisting of the following components: (i) up to $4,760,600.00, plus (ii) up to
an additional  $150,000.00 (which additional amount is calculated at the rate of
$30,000  per  floor  to  offset  the  costs   associated  with  the  design  and
construction  of the elevator lobby on each full floor in the Building leased by
Tenant).

         In addition,  Landlord will credit against that portion of the Tenant's
Costs  attributable  to the Tenant VAV Work an  additional  amount not to exceed
$320,000.00 ("VAV Allowance") to offset costs of completing the Tenant VAV Work.
[By way of  clarification  only, and without  affecting  the parties  respective
rights and obligations: The parties acknowledge that the foregoing VAV Allowance
was determined  based upon a total agreed upon cost with respect to VAV boxes in
the Premises of $428,000.00,  of which $108,000 was allocated to the Landlord in
order to allow Landlord to complete the Landlord VAV Work].

         In addition to the Improvement Allowance,  upon execution of this Lease
and  submission  by  Tenant to  Landlord  of  approved  invoices  from  Tenant's
architect for at least the amount  requested by Tenant  detailing work performed
for Tenant in connection with the preparation of preliminary  plans and drawings
for the  Improvements,  Landlord  will  pay  Tenant  a  Preliminary  Space  Plan
Allowance of up to $14,648.00. No invoices submitted by Tenant for reimbursement
from the  Preliminary  Space Plan  Allowance and reimbursed  therefrom  shall be
included in Tenant's Costs or submitted to Landlord for reimbursement or payment
pursuant to the other terms of this Exhibit C.

         Tenant  shall  follow the  procedures  set forth in  Paragraphs E and F
below in order to receive  reimbursement  or payment for such Tenant's Costs and
the Additional Costs.

D.       Tenant will complete  construction  of the  Improvements  in accordance
with the Final Plans, the terms of Article III and the terms set forth below:

         1.       For the purpose of determining Tenant's Costs, Tenant will pay
                  Landlord a supplementary construction manager's fee of one and
                  one-half percent (1.5%) of Tenant's hard costs associated with
                  the  construction  of the  Improvements in order to compensate
                  Landlord for costs incurred in connection with the supervision
                  and coordination of work being performed in the Building. Such
                  construction  manager's fee shall be deducted by Landlord from
                  the aforesaid Improvement Allowance.

         2.       During Tenant's construction of the Improvements, Landlord and
                  its consultants and architect will have access to the Premises
                  for  the  purpose  of  monitoring  the   construction  of  the
                  Improvements  and  ensuring  their  compliance  with the Final
                  Plans and the  requirements  of this Lease.  Landlord  and its
                  consultants  and architect will not interfere with Tenant's or
                  its contractors'  construction of the Improvements,  except to
                  the extent necessary to ensure such compliance.
<PAGE>

E.       Tenant,  as  construction  manager,  will enter into contracts with all
contractors and subcontractors performing the Improvements. As such, Tenant will
be  responsible  for all Tenant's  Costs,  subject to partial  reimbursement  in
accordance  with the terms set forth  below.  Tenant will approve in writing and
thereafter submit to Landlord for payment invoices from Tenant's contractors and
subcontractors  who have  performed  work and delivered  materials in connection
with: (i) the Improvements  (which may include, in addition to hard construction
costs,  only the  following  "soft"  costs  associated  with  the  Improvements:
architectural,  design and engineering fees and the cost of procuring  permits),
and (ii) the reasonable cost of installing two of the three generators forming a
part of the  Generator  Equipment  described  in Section  15.25 of the Lease and
Exhibit  I  hereto   ("Reimbursable   Generator  Costs"),   provided  that  such
Reimbursable  Generator  Costs  shall not  exceed the lesser of: (A) the cost of
installing two  generators,  or (B) the cost of installing one larger  generator
with the same aggregate capacity as such two generators (collectively, "Approved
Invoices").  It is  understood  and agreed  that no  portion of the  Improvement
Allowance  shall be paid with  respect to any costs  other than those  described
above in this Paragraph E with respect to Approved  Invoices.  Without  limiting
the  generality  of  the  immediately  preceding  sentence,  no  portion  of the
Improvement  Allowance or VAV Allowance (nor any amounts payable pursuant to the
terms of Paragraph F below)  shall be paid with respect to any costs  associated
with  the  third  generator  described  in  Section  15.25,   relocation  costs,
furniture, fixtures not attached to the Building, computers or equipment, and no
unused portion,  if any, of the Improvement  Allowance or VAV Allowance shall be
utilized in any way to grant Tenant any rent abatement hereunder.  Said Approved
Invoices  shall be paid from the  Improvement  Allowance in accordance  with the
following terms:
<PAGE>

         1.       Following  execution  of this Lease,  Tenant  shall  submit to
                  Landlord from time to time Approved  Invoices  accompanied  by
                  partial  lien  waivers  (in  form  reasonably   acceptable  to
                  Landlord) from all contractors and  subcontractors  submitting
                  such  Invoices.  Such Invoices and  accompanying  lien waivers
                  shall be  delivered  to  Landlord  on or before the  fifteenth
                  (15th) day of each calendar month.

         2.       To the extent  that any portion of the  Improvement  Allowance
                  remains unpaid up to a total of $4,419,540.00 ($4,284,540 plus
                  $135,000.00),  any such previously  unpaid  Approved  Invoices
                  (other than those  associated with the Tenant VAV Work,  which
                  shall be paid in accordance with the terms of Paragraphs 4 and
                  5 below) shall be paid by Landlord on or before the  thirtieth
                  (30th) day of the immediately succeeding calendar month.

         3.       Upon completion of the  Improvements and delivery by Tenant to
                  Landlord  of: (i)  Certificates  of  Occupancy  for the entire
                  Premises,  (ii)  full  and  complete  lien  waivers  from  all
                  contractors or  subcontractors  performing  work or delivering
                  materials  with  respect  to  the   Improvements,   and  (iii)
                  previously  unpaid  Approved  Invoices for work and  materials
                  forming  a  part  of  the   Improvements   (other  than  those
                  associated  with the Tenant VAV Work,  which  shall be paid in
                  accordance  with  the  terms  of  Paragraphs  4 and  5  below)
                  totaling  at least the amount  requested  by Tenant,  Landlord
                  will pay such  Invoices  to the extent that any portion of the
                  total Improvement Allowance ($4,910,600.00 [$4,760,600.00 plus
                  $150,000.00]) remains unpaid.

         4.       To the extent  that any portion of the VAV  Allowance  remains
                  unpaid  up to a total  of  $288,000.00,  any  such  previously
                  unpaid Approved Invoices for the Tenant VAV Work shall be paid
                  by  Landlord  on or before  the  thirtieth  (30th)  day of the
                  immediately succeeding calendar month.

         5.       Upon completion of the  Improvements and delivery by Tenant to
                  Landlord  of: (i)  Certificates  of  Occupancy  for the entire
                  Premises,  (ii)  full  and  complete  lien  waivers  from  all
                  contractors or  subcontractors  performing  work or delivering
                  materials  with  respect  to  the   Improvements,   and  (iii)
                  previously  unpaid  Approved  Invoices for work and  materials
                  forming a part of the  Tenant VAV Work  totaling  at least the
                  amount requested by Tenant, Landlord will pay such Invoices to
                  the  extent  that  any  portion  of the  total  VAV  Allowance
                  ($320,000.00) remains unpaid.

F.       If Tenant's  Costs  exceed the  Improvement  Allowance,  subject to the
limitations set forth below,  Tenant,  at its option,  may finance any Excess in
accordance  with the terms of this  Paragraph  F. Tenant will submit to Landlord
Approved  Invoices (as defined in Paragraph E above),  which  invoices have also
been approved in writing by Tenant (provided that no such Approved Invoices have
been previously submitted,  reimbursed or paid from a portion of the Improvement
Allowance or the Preliminary  Space Plan Allowance).  Such invoices (which shall
be  accompanied by lien waivers) shall be delivered to Landlord on or before the
fifteenth  (15th) day of each calendar  month,  and any such  previously  unpaid
Approved  Invoices  shall be paid by Landlord on or before the thirtieth  (30th)
day of the  immediately  succeeding  calendar  month  subject to the Maximum set
forth  below.  The total amount paid by Landlord  pursuant to this  Paragraph F,
which shall not exceed, in the aggregate $732,400.00, shall be paid by Tenant to
Landlord,   as  additional  rent,  in  equal  monthly  installment  payments  of
additional  Base Rent under the Lease.  The amount of such  monthly  installment
payments  shall be  determined  as  follows:  The total  amount paid by Landlord
pursuant to this Paragraph F, along with interest  thereon at the rate of eleven
percent  (11%) per annum shall be amortized on a straight line basis and payable
by Tenant to Landlord in equal monthly installments (along with Tenant's monthly
payment of Base Rent)  beginning on the Final  Commencement  Date and continuing
through the balance of the initial Lease Term (as set forth in Section 1.3). [By
way of illustration  only, if the total amount paid by Landlord pursuant to this
Paragraph F is $100,000.00 and the Final  Commencement  Date is October 1, 2000,
said  $100,000  will be  amortized  over a 120 month  period  (October 1, 2000 -
September 1, 2010) at eleven percent interest per annum,  resulting in a monthly
installment payment of $1,377.50 per month, payable by Tenant as Additional Base
Rent for each of the120 full calendar months of the initial Lease Term following
the Final Commencement Date].

 G.      Substantial  Completion  with respect to any full floor of the Premises
shall be deemed  to occur  when the  Improvements  specified  in this  Exhibit C
(excluding  long lead time items) have been  completed  in  accordance  with the
Final Plans,  except for punch-list items which do not  substantially  interfere
with Tenant's intended use of the Premises.
<PAGE>

                                  EXHIBIT "C-1"
                                  -------------

                        FINAL THIRD AND FIFTH FLOOR PLANS
                        ---------------------------------

         The  following  plans and  specifications  are hereby  incorporated  by
reference into this Exhibit C-1. Said plans and  specifications  are approved by
Landlord subject to Tenant's  conformance of the same to Landlord's comments set
forth in Exhibit C-2. [The parties  acknowledge that some of Landlord's comments
set forth in Exhibit C-2 have been  addressed,  in whole or in part, by Tenant's
January 4th revisions of the December 23rd plans].

MicroStrategy Phase One Floors 3 & 5 1861 International Drive, McLean, Virginia,
dated December 23, 1999, consisting of the following sheets:

         CS.01             Abbreviations, Drawing Index, Symbols, Project
                           Information, Keyplans and Consultants

         CS.02             General Notes

         CS.03             General Notes

         A1.01             Partition Plan Third Floor

         A1.02             Partition Plan Fifth Floor

         A2.01             Reflected Ceiling Plan Third Floor

         A2.02             Reflected Ceiling Plan Fifth Floor

         A3.01             Power/Signal Plan Third Floor

         A3.02             Power/Signal Plan Fifth Floor

         A4.01             Finish Plan Third Floor

         A4.02             Finish Plan Fifth Floor

         A5.01             Furniture and Equipment Plan Third Floor (for
                           information only)

         A5.02             Furniture and Equipment Plan Fifth Floor (for
                           information only)

         A7.01             Elevations

         A8.01             Partition Types Sections/Details

         A8.02             Sections/Details
<PAGE>

         A9.01             Schedules

         M-1               Cover Sheet Mechanical (revised January 4, 2000)

         M-2               Third Floor Plan HVAC (revised January 4, 2000)

         M-3               Fifth Floor Plan HVAC (revised January 4, 2000)

         M-5               Roof Plan HVAC (revised January 4, 2000)

         M-6               Details Mechanical (revised January 4, 2000)

         M-7               Flow Diagrams Mechanical (revised January 4, 2000)

         M-8               Schedules Mechanical (revised January 4, 2000)

         P-1               Cover Sheet Plumbing (revised January 4, 2000)

         P-2               Third Floor Plan Plumbing (revised January 4, 2000)

         P-3               Fifth Floor Plan Plumbing (revised January 4, 2000)

         E-1               Cover Sheet Electrical (revised January 4, 2000)

         E-2               Third Floor Plan Lighting (revised January 4, 2000)

         E-3               Fifth Floor Plan Lighting (revised January 4, 2000)

         E-4               P-2 Parking Level Plan-Power (revised January 4,2000)

         E-5               Third Floor Plan Power (revised January 4, 2000)

         E-6               Fifth Floor Plan Power (revised January 4, 2000)

         E-7               Roof Plan Power (revised January 4, 2000)

         E-8               Power Riser Diagram (revised January 4, 2000)

         E-9               Panel Schedules (revised January 4, 2000)
<PAGE>

                                  EXHIBIT "C-2"
                                  -------------

                  LANDLORD'S COMMENTS REGARDING TENANT'S PLANS
                  --------------------------------------------

                                 (See attached)
<PAGE>

[LOGO OF L&B]

<TABLE>
<S>                                       <C>     <C>
                                                  L&B Realty Advisors, Inc.
                                                  Dedicated to Superior Client Service

                                                  1961 Chain Bridge Road
DESIGN/CONSTRUCTION DOCUMENT REVIEW               Suite 105
                                                  McLean, Virginia 22102
                                                  Tel: 703-893-9400, Ext. 266
                                                  Fax: 703-893-1022
                                                  www.lbrealty.com


DATE:        December 30, 1999           PROJ. NAME:   1861 International Drive, Tyson's

TENANT NAME: Microstrategy (MSI)         LOCATION:     3rd and 5th Floors

DOCUMENT     "Peer Review and Pricing"   DOCUMENT      December 23, 1999
REVIEWED:                                DATE:
REVIEWER:    P. Comey / B. Yagmur        SUBMITTED BY: Peter T. Comey

ARCHITECT:   Ai (Interiors)              ENGINEER:     K.T. Associates, PC
---------------------------------------------------------------------------------------------------------------
<CAPTION>

---------------------------------------------------------------------------------------------------------------
ITEM    DWG SHT    DETAIL OR                              REMARKS                              FOLLOW-UP/
 NO.    OR PAGE      PAGE                                                                     ACTION REQ'D
---------------------------------------------------------------------------------------------------------------
<S>     <C>     <C>               <C>                                                        <C>
   1.   CS.01      Permit         "High Rise" designation should be "Yes" (building stairs       Confirm;
                    info.         and elevators descend into parking garage).                     Revise.
---------------------------------------------------------------------------------------------------------------
   2.   CS.01      Permit         Floor Area of Tenant Space is incorrect; should be the         Confirm;
                    info.         area for 'Single Tenant Usable - 27,062.74 SF/Floor            Revise.
---------------------------------------------------------------------------------------------------------------
   3.   CS.01      Base           Base building contractor (Davis Construction) address          Confirm;
                   Bldg.          incorrect - 12500 Parklawn Dr., Rockville, MD 20852)            Revise
---------------------------------------------------------------------------------------------------------------
   4.   CS.01      Index          Drawing index does not include engineering drawings.            Revise.
---------------------------------------------------------------------------------------------------------------
   5.   A1.01      Plans          Corridor dimension at core (4'-10") is not acceptable to        Review;
        A1.02   (3rd & 5th        the landlord; 5'-0" clear is minimum (5'-6" is preferred).      Revise.
                  Floors)         NOTE: Corridor under construction at 4th  Floor = 6'-0".     [Coordinate]
---------------------------------------------------------------------------------------------------------------
   6.   A1.01       Wall          Corridor Partition Type 'B' noted with drywall stopping         Review;
        A1.02       Type          3" above ceiling; Partition Detail (02/A8.01) shows it          Revise.
                   Legend         up to deck above/caulked. Landlord prefers this detail.
---------------------------------------------------------------------------------------------------------------
   7.   A1.01    Plan (3rd        Operable Partition at Conference rooms No. 328A & B             Confirm;
                   Floor)         may conflict with large base building ductwork above.          Coordinate.
---------------------------------------------------------------------------------------------------------------
   8.   A1.01      Plans          No Specification/Note/Detail is included for required           Review;
        A1.02    (3rd/5th)        waterproofing of concrete slab below future raised floor.       Revise.
---------------------------------------------------------------------------------------------------------------
   9.   A1.01      Floor          No floor plans/details have been included for the               Review;
        A1.02      Plans          proposed construction of electrical switchgear and              Detail:
                                  emergency generator/UPS rooms in the garage levels.            Coordinate.
                                  Additional plans/details/layout/information required.
---------------------------------------------------------------------------------------------------------------
  10.   A1.01      Floor          No floor plans/details have been included for the               Review;
        A1.02      Plans          proposed installation and related construction required         Detail;
                                  for rooftop equipment. Additional architectural plans/         Coordinate.
                                  details/layout/information/coordination required.
---------------------------------------------------------------------------------------------------------------
</TABLE>

                                  Exhibit C-2
                                  Page 2 of 5

<PAGE>

1861 International Drive
Proposed Tenant Space Design Review
December 30, 1999

<TABLE>
<S>     <C>     <C>               <C>                                                        <C>
---------------------------------------------------------------------------------------------------------------
  11.   A1.02      Plan &         Office No. 516 wall return to window mullion behind            Confirm;
        A2.02      Ceiling        door (south window) is not clearly drawn/indicated;             Revise.
                 (5th Flr.)       return detail layout needs adjustment/clarification.          Coordinate.
---------------------------------------------------------------------------------------------------------------
  12.   A2.01     Ceilings        Elevator lobby/corridor ceilings are not sufficiently           Review;
        A2.02    (3rd & 5th       detailed (upgrade/finishes) commensurate with lease             Design;
                   Floors)        requirement for improvement of lobbies/corridors.               Submit.
---------------------------------------------------------------------------------------------------------------
  13.   A2.01     Ceilings        Conduit and cable tray at east side of elevator lobby/          Review;
        A2.02    (3rd & 5th       corridor is within the corridor ceiling space; need to          Revise.
                   Floors)        extend conduit/move transition east into tenant space.
---------------------------------------------------------------------------------------------------------------
  14.   A2.01      Ceiling        Bulkhead at operable partition at Conference Room No.           Confirm;
                 (3rd Flr.)       328A & B may be in conflict with large HVAC ductwork.         Coordinate.
---------------------------------------------------------------------------------------------------------------
  15.   A2.01      Ceiling        Surface mounted strip fluorescent light fixtures (2) at         Review;
                 (3rd Flr.)       Conference Room Closet No. 328C are not acceptable;             Revise.
                                  replace these with building standard 2x2 or 2x4 fixture.
---------------------------------------------------------------------------------------------------------------
  16.   A3.01      Power/         Conference Room No. 328B center floor outlets will              Confirm;
                   Signal         penetrate floor slab above the base building main              Coordinate.
                 (3rd Flr.)       distribution ductwork below; access may be difficult.
---------------------------------------------------------------------------------------------------------------
  17.   A4.01     Finishes        Wall finishes planned for elevator lobby/corridors not          Review;
        A4.02    (3rd & 5th       indicated on Finish Plan. Floor/base finishes at lobby          Design;
                   Floors)        & corridors will require samples/submittals for review.         Submit.
---------------------------------------------------------------------------------------------------------------
  18.   A8.01       Wall          Corridor Partition Type 'B' Detail (02/A8.01) shows it          Review;
        A1.01       Type          up to deck above/caulked. Landlord prefers this detail.         Revise.
        A1.02      Detail         [Conflicting notes indicated on Plan Wall Type Legend.)
---------------------------------------------------------------------------------------------------------------
  19.   A8.01      Raised         Raised Floor Closure Details (11-13/A8.01) does not             Review;
                    Floor         include condition at curtain wall window (at proposed 4th       Revise.
                   Details        Floor). Standard detail required by Landlord.
---------------------------------------------------------------------------------------------------------------
  20.   A8.01      Raised         Raised Floor Detail (14/A8.01) refers to manufacturer           Review;
                    Floor         as Tate Access Floors; Floor Plans (A1.01/02) indicate          Revise;
                   Detail         flooring manufacturer as same as the systems furniture.        Coordinate.
---------------------------------------------------------------------------------------------------------------
  21.   A9.01       Door          Frame Type 'D' (corridor doors 3'-0" X 8'-0) is to be           Review;
                   Sched.         aluminum as required for building standard.                     Revise.
---------------------------------------------------------------------------------------------------------------
  22.   A9.01     Finishes        No room/space finish schedule provided. Wall finishes           Review;
                 (3rd & 5th       planned for elevator lobby/corridors not indicated on           Design;
                   Floors)        Finish Plan. Finishes at lobby/corridors submittal.             Submit.
---------------------------------------------------------------------------------------------------------------
  23.   A9.01     Finishes        Floor Finish Carpet Type 'C-1' is listed as "Not Used".         Review;
        A4.01    (3rd & 5th       Carpet Type 'C-1' is indicated on Finish Plans (A4.01 &         Design;
        A4.02      Floors)        A4.02) throughout tenant space, lobby and corridors.            Submit.
---------------------------------------------------------------------------------------------------------------
  24.    M-2        HVAC          VAV box design (sizing/heater) do not meet landlord's           Review;
         M-3       Plans          standard box configurations/material order. Design              Design;
         M-8     (3rd & 5th       includes four (4) sizes of cooling only ['A'] and three (3)     Revise.
                   Floors)        sizes of fan powered boxes ['F']; need to standardize.
---------------------------------------------------------------------------------------------------------------
  25.    M-2        HVAC          VAV box design/system layout is not consistent from             Review;
         M-3       Plans          3rd Floor to 5th Floor. All heater 4kW or larger are            Design;
         M-8     (3rd / 5th)      shown to be 480v. Landlord 4kW boxes are 1P 277v.               Revise;
                                  Design needs to be standardized/coordinated.                  Coordinate.
---------------------------------------------------------------------------------------------------------------
</TABLE>

                                  Exhibit C-2
                                  Page 3 of 5
<PAGE>

1861 International Drive                                                Exh. C-2
Proposed Tenant Space Design Review
December 30, 1999

--------------------------------------------------------------------------------
26.  M-2    HVAC    VAV box heater design/layout appears to         Review;
     M-3   Plans    concentrate heater box units away from          Design;
         (3rd/5th)  north side of building; this is not             Revise.
                    consistent with landlord's anticipated
                    layout.
--------------------------------------------------------------------------------
27.  M-2    HVAC    Main base building distribution ductwork        Review;
     M-3   Plans    is indicated in the wrong location on           Revise;
         (3rd/5th)  floor plans; actual ductwork was installed     Coordinate.
                    approximately 15'-0" from exterior building
                    walls (east/west). Coordinate layout with
                    lights, VAV'S.
--------------------------------------------------------------------------------
28.  M-2    HVAC    Thermostats/Control wiring indicated on         Review;
     M-3   Plans    exterior round concrete columns (west) will     Revise;
         (3rd/5th)  be required to be surface mounted in approved  Coordinate.
                    raceway enclosure.
--------------------------------------------------------------------------------
29.  M-2    HVAC    Perimeter linear diffusers are shown as set     Review;
     M-3   Plans    into the suspended acoustical ceiling grid.     Revise;
         (3rd/5th)  This is not consistent with building standard  Coordinate.
                    details for diffusers to be placed in the
                    vertical return of perimeter drywall
                    bulkhead.
--------------------------------------------------------------------------------
30.  M-2    HVAC    Perimeter linear diffusers (supply and return)  Review;
     M-3   Plans    in the elevator lobby are shown as set into     Revise;
         (3rd/5th)  the suspended acoustical ceiling grid.         Coordinate.
                    This ceiling is not acceptable.
--------------------------------------------------------------------------------
31.  M-5    HVAC    Plan/Notes/Details (Sheet M-6) lack             Review;
            Roof    sufficient details and information on rooftop   Revise;
            Plan    mechanical units, piping and support          Coordinate.
                    equipment. Equipment sizes, weight, supports,
                    connections, etc. need to be included with
                    the design. Screening of units may be
                    required (as outlined).
--------------------------------------------------------------------------------
32.  M-5    HVAC    Plan/Note No. 1 Indicate a new 8" Diameter      Review;
     M-7    Roof    Supply/Return riser for Glycol system. Riser    Revise;
           Plan/    Schematic indicates a 6" Diameter riser. Base  Coordinate.
           Riser    building includes spare riser piping for
                    similar installation. Size to be confirmed; if
                    appropriate, Landlord would consider use.
--------------------------------------------------------------------------------
33.  M-5    HVAC    Air Separation Detail indicates supporting      Review;
     M-6    Roof/   expansion tank from above. On Roof Plan,        Revise;
     M-7   Details/ expansion and most/all Glycol system           Coordinate.
            Riser   components are shown as outside (in the open
                    air/no structure above). Additional detail
                    and coordination required for placement of all
                    equipment.
--------------------------------------------------------------------------------
34.  M-6    HVAC    Pipe Support Detail indicates pressure treated  Review;
           Details  wood supports. These  are not permitted. Pre-   Revise:
                    fabricated curbs and supports are required in  Coordinate.
                    all applications.
--------------------------------------------------------------------------------
35.  M-6    HVAC    No detail are included for roof surface or      Revise;
           Details  exterior wall piping penetrations and closure/ Detail.
                    sealant construction.
--------------------------------------------------------------------------------
36.  M-6    HVAC    No details are included for roof top equipment  Revise;
           Details  structural support, building connections or     Detail.
--------------------------------------------------------------------------------
37.  M-7    HVAC    HVAC equipment listed as supporting the "UPS"   Revise;
            Riser   system is indicated on the P-3 level (future).  Detail.
                    Additional detail/layout/location/
                    information is required.
--------------------------------------------------------------------------------
38.  E-2  Lighting  Surface mounted strip fluorescent light         Review;
    A2.01/Ceiling   fixtures (2) at Conference Room Closet No. 328C Revise.
         (3rd Fir.) are not acceptable; replace these with building
                    standard 2x2 or 2x4 fixture.
--------------------------------------------------------------------------------

                                  Exhibit C-2
                                  Page 4 of 5
<PAGE>

1861 International Drive
Proposed Tenant Space Design Review
December 30, 1999                                                    Exhibit C-2



--------------------------------------------------------------------------------
  39.     E-2    Lighting    Elevator lobby/corridor ceilings and       Review;
          E-3    /Ceiling    lighting are not sufficiently detailed     Design;
                 (3rd/5th)   (upgrade/finishes) commensurate with       Submit.
                             lease requirements for improvement of
                             lobbies/corridors. Revised lighting type
                             /layout required.
--------------------------------------------------------------------------------
  40.     E-4      P-2       Transformer location, layout, duct bank   Review;
                  Power      and connection indicated must be          Detail;
                             considered schematic. Actual location,  Coordinate.
                             feeds, connections and coordination
                             requires landlord and Virginia Power
                             review and approval.
--------------------------------------------------------------------------------
  41.     E-4      P-2       Proposed new tenant switchgear room       Review;
                  Power      layout and location indicated must be     Revise;
                             considered schematic. Actual location,    Detail;
                             feeds, connections and coordination     Coordinate.
                             will depend on final landlord and
                             Virginia Power review and approval.
                             Landlord preference is for the proposed
                             new tenant switchgear room to be
                             immediately adjacent to existing base
                             building switchgear room. Additional
                             detail/layout/information required.
--------------------------------------------------------------------------------
  42.     E-4      P-2       No details are included for proposed      Review;
          E-8     Power/     emergency generator(s), UPS system(s),    Revise;
                  Riser      new bus new riser routing and other       Detail;
                 Diagram     electrical service and support          Coordinate.
                             equipment. Additional detail/layout/
                             information required.
--------------------------------------------------------------------------------
  43.     E-5     Power/     Power connection to Type 'A' VAV (shut-   Review;
          E-6    Ceiling     off) boxes not specified as circuited     Design;
                (3rd/5th)    to Mechanical Panels (MA3, MA5). Assume   Submit.
                             low voltage, transformer(s), and series
                             connections. Additional information
                             required.
--------------------------------------------------------------------------------
  44.     E-9    Panel       Electrical power panels (typical) are     Review;
                Sched.       not indicated as properly balanced or     Revise;
                             labeled with new circuits and existing  Coordinate.
                             circuits. Adjustments are required to
                             remedy.
--------------------------------------------------------------------------------
  45.


--------------------------------------------------------------------------------
  46.


--------------------------------------------------------------------------------
  47.


--------------------------------------------------------------------------------
  48.


--------------------------------------------------------------------------------
  49.


--------------------------------------------------------------------------------
  50.


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

                                  Exhibit C-2
                                  Page 5 of 5
<PAGE>

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

                     STATEMENT SPECIFYING COMMENCEMENT DATES
                              AND TERMINATION DATE
                              --------------------

The parties agree that notwithstanding anything to the contrary contained in the
Lease, the Delivery Date is _____________,the Commencement Date is __________,
the Interim Commencement Date is __________,the Final  Commencement Date is
_______________, and the Termination Date is _______________________.



LANDLORD                                 TENANT


                                         --------------------------
<PAGE>

                                   EXHIBIT "E"
                                   -----------

                                     PARKING
                                     -------

         A.  Landlord is  "Landlord"  and Tenant is "Tenant"  under that certain
Lease (the  "Lease"),  wherein  Tenant  leased from  Landlord  certain  premises
located in  Landlord's  office  building  (the  "Building")  in Fairfax  County,
Virginia, located at 1861 International Drive, McLean, Virginia.

         B.  Landlord  desires  to grant and Tenant  desires to use 3.7  parking
spaces for every 1,000 square feet of Net Rentable Area in the Premises (as such
Net Rentable  Area may change from time to time)  ("Tenant's  Allocated  Parking
Space" or "Spaces"), which Spaces shall be located inside the Building's parking
garage  (the  "Garage"),  and  shall be used by  Tenant  all upon the  terms and
conditions set forth below.

         NOW,  THEREFORE,  for and in  consideration  of Ten and No/100  Dollars
($10.00) and other valuable consideration,  the receipt and sufficiency of which
are hereby acknowledged, the parties hereto hereby agree as follows:

         . Subject  to  Landlord's  agreement  with any  operator  of the Garage
("Garage  Tenant") and any agreements,  easements or restrictions  affecting the
Building (which shall not materially  impair Tenant's rights with respect to the
Spaces),  Landlord  hereby  grants  Tenant a right to use the Spaces  during the
Lease  Term  (including  any  Option  Terms)   (terminating   upon  any  earlier
termination  of the Lease for whatever  reason) for parking motor  vehicles.  In
light of Tenant's phased-in  occupancy of the Premises,  as set forth in greater
detail in Section 3.1 of the Lease,  Tenant's  obligation  to pay for the Spaces
shall be similarly phased-in.  As a result, on the applicable  Commencement Date
set forth in Section 3.1 with respect to each portion of the Premises,  Tenant's
obligation  to pay for the  number of Spaces  allocable  to such  portion of the
Premises  (at the 3.7 per 1,000  square feet ratio set forth  above)  shall also
commence.  The number of Tenant's  Allocated Parking Spaces actually useable for
parking by Tenant  shall be reduced by the number of spaces in the Garage  which
are not usable due to the presence of Tenant's  Generator  Equipment therein (as
described in Section 15.25 of the Lease). However, Tenant shall remain obligated
to pay the Fee (as defined  below) with respect to the Allocated  Parking Spaces
which are occupied by Tenant's Generator Equipment.

         . Tenant shall pay the then current market rental rate (the "Fee"),  as
adjusted  from time to time by Landlord or the  operator of the Garage  ("Garage
Tenant"), for each of the Spaces (per parking space), payable monthly in advance
on or before the first day of each month  throughout  the Lease Term to Landlord
(unless Landlord designates otherwise in writing). Any such payments to Landlord
will constitute  Additional Rent under the Lease.  Notwithstanding any provision
hereof  to the  contrary,  the  initial  Fee per  Space  shall be Fifty  Dollars
($50.00), and said Fee shall be escalated by two and one half percent (2.5%) per
year.  Except as set forth below,  all such Spaces shall be used by Tenant on an
unreserved basis in common with other tenants and visitors. However, twenty-five
(25) of the Spaces shall be reserved  specifically  for Tenant's use  ("Reserved
Spaces") and marked with appropriate  signage  provided by Tenant,  and shall be
designated  as such in the Garage at no  additional  cost to Tenant.  Tenant may
also
<PAGE>

designate a portion of the Spaces for "Tenant's Visitor's Parking." The location
of such reserved and visitor spaces in the Garage shall be determined by Tenant,
subject to Landlord's reasonable review.

         . All motor vehicles  (including all contents  thereof) shall be in the
Garage  at the  sole  risk of their  owners  and  Tenant,  and  Landlord  is not
responsible for the protection and security of such vehicles.  Neither  Landlord
nor  Landlord's  Agents has any  liability  for any property  damage or personal
injury arising out of or in connection with said motor vehicles  (unless arising
out of the gross negligence of Landlord or Landlord's Agents),  and Tenant shall
indemnify and hold Landlord and Landlord's  Agents harmless against all demands,
claims,  damages,  or causes of action arising out of or connected with Tenant's
use of the  Spaces,  or the  negligence  of Tenant or Tenant's  Agents,  acts or
omissions arising out of or in connection with said motor vehicles.

         . This Exhibit E does not create a bailment between the parties hereto,
it being expressly  agreed that the only  relationship  created between Landlord
and Tenant hereby is that of Landlord and Tenant.

         . In its use of the  Spaces,  Tenant will have input to and will follow
all  applicable  Rules and  Regulations  established  by  Landlord or any Garage
Tenant and provided in writing to Tenant.  Tenant's  employees shall not use any
of the parking spaces  designated for use by visitors only.  Upon the occurrence
of a breach of any applicable Rules and  Regulations,  failure to pay the Fee or
Tenant's  Default under the Lease,  Landlord will be entitled to terminate  this
Agreement  following  written notice to Tenant and an opportunity to cure as set
forth in Section 11.1 of the Lease, in which event Tenant's right to utilize the
Spaces will cease.

         . If: the Garage is damaged by fire or other  casualty,  then  Landlord
will proceed to restore the Garage at its sole cost and expense and  immediately
provide Tenant,  at the same fee as  then-applicable  with  alternative  parking
during such  restoration  period  throughout the remainder of the Lease Term, or
until the Garage is fully restored.  Any such alternative parking shall: (1) not
cause a reduction  in  Tenant's  Allocated  Parking  Spaces,  (2) be  reasonable
convenient in term of location,  quality and safety as the Garage, (3) except in
the case of an  emergency,  be designated by prior  specific  written  notice to
Tenant.

         . If all or any  portion  of the  Garage  is taken  for any  public  or
quasi-public use, by right of eminent domain or otherwise, or be sold in lieu of
condemnation,  then  Landlord  will keep this  Agreement  in effect by providing
Tenant with  alternative  parking in  accordance  with the terms of  Paragraph 6
above.

         . To further  ensure  that only  those  parties  leasing  Non-Allocated
Spaces in the Garage are  utilizing  such parking  spaces,  Tenant will, no more
than  once  every six (6)  months,  provide  Landlord  with a  complete  list of
Tenant's  employees  license  plate  numbers  their  vehicles.  Tenant  will use
commercially  reasonable  efforts to update the list, as necessary  from time to
time.
<PAGE>

         9.  Subject to  Landlord's  receipt of any  permits or other  necessary
governmental  approvals with respect  thereto,  the Garage will be configured so
that the majority of the parking  spaces  therein will be located behind a gate,
which,  during regular office  business hours will restrict access to only those
persons to whom Landlord has leased spaces  therein.  All of Tenant's  Allocated
Parking  Spaces  except those Spaces  designated  by Tenant for use as "Tenant's
Visitor Parking" will be located behind said gate. The parties  acknowledge that
Landlord may "oversell"  parking  behind the gate on a  commercially  reasonable
basis,  provided  that,  upon  written  request from Tenant  detailing  problems
associated  with the  unavailability  of Tenant's  Allocated  Spaces  (including
Tenant's Reserved Spaces) behind the gate, Landlord will take whatever action is
reasonably  necessary  (including  retaining a parking attendant or reducing the
number of spaces that Landlord "oversells") to alleviate any problems associated
with the  unavailability of any portion of Tenant's  Allocated Spaces behind the
gate.  The cost of any such actions to remedy such a problem  shall be a part of
the Operating Costs described in Section 4.3 of the Lease.
<PAGE>

                                   EXHIBIT "F"
                                   -----------

                   ACCELERATED DEPRECIATION SCHEDULE REGARDING
                            AFTER HOURS HVAC SERVICE
                            ------------------------

                                 (see attached)
<PAGE>

                                  EXHIBIT "F"
                                  -----------

              CALCULATION METHOD REGARDING AFTER-HOURS HVAC COST
              --------------------------------------------------

The attached worksheets calculate the estimated hourly overtime HVAC costs as of
the date of this Lease (under two different scenarios, running HVAC on one
floor, and running HVAC throughout the Premises). The calculation of the
depreciation component of Landlord's HVAC costs will be made in accordance with
the terms of the attached worksheets. The other components of Landlord's costs
will be made in the same manner as set forth in the attached worksheets based
upon Landlord actual costs for such other components as of the date of Tenant's
use of such overtime HVAC, as set forth in Section 5.2 of the Lease.

                                   EXHIBIT F
                                  Page 1 of 7
<PAGE>

                                                                       Exhibit F

                       OVERTIME HVAC CALCULATION FORMAT
                             1/6/2000 @ 17:45 Hrs

Project:       1861 International Drive      Cost to run one floor
A/C Units                            = 2
Design KW:                           = n/a
Minimum Load Package Units           = 2
Chiller Tonage Rating:               = 116   (58x2)

                                    REVISED

Step One:  Electrical Costs:

Average KW Cost:                      =            $0.090  Per Kwh
Building Average Voltage:             =               460  Volts

A. Package Units (Two per floor). Each unit has three (3) compressors & one fan.
   Min. Load (2 Units)=                   116 Min. Tonage
   One fan @ 26.5a=                    21.089 Kw
   Two compressors @ 20.5a=            32.628
   Total Kw                            53.717                          53.72 KWh

B. Condenser Water Pumps (2                50 HP each
   Condenser pumps needed:         1 =   62.0 AMPS
   Total Kw                              49.34 Kw
                                                                       49.34 KWh

C. Cooling Tower Fans:
   Fan motors:            1          =   24.9 AMPS
   Run Time (Full time w/VFD)        =    50%
   Total Kw                          = 9.9077                           9.91 KWh

D. VAV Boxes:
   5 w/14 Kw heat & 1/2 hp fan, 277  = 74.709 Kw
   10 w/10 Kw heat & 1/3 hp fan 277  = 106.09 Kw
   4 w/4 Kw heat & 1/3 hp fan, 277v  = 18.438 Kw
   Run Time:                         =    50%
   Total Kw                          =  99.62 Kw                       99.62 KWh

 Total A-D Kw:
   Water Chilling Unit:                                    =           53.72 KWh
   Chilled/Condenser Pumps:                                =           49.34 Kwh
   Cooling Tower Fans                                      =            9.91 Kwh
   VAV Boxes::                                             =           99.62 KWh

 Total KWh Condition:                                      =          212.58 KWh

                                   EXHIBIT F
                                  Page 2 of 7
<PAGE>

Step Two: Cooling Tower Water Usage


# of Pumps Used:          =        1 Pumps
Condenser Pump Rate:      =     1275 GPM's
Chiller Tonage Rating:    =       116 Tons



(A) Cooling Tower Evaporation Make-up & Bleed:                Total Values:
    Minimum Load (2 A/C Units)=                 116 Tons
    Evaporation Rate = 1% of GPM rate:                            1.00 %Ton
    # of Pumps:              1                                 1275.00 PGPM
    Total Pump GPM Rate:           1275                          12.75 1%Rt
    Bleed Cycles = (Egpm/C-1)                     3 cycl          6.38 CGPM
    Total Make-up = Rate + Cycles                                19.13 TMup
    Hourly Evaporation rate = E rate x 60 min.                 1147.50 HMup
    #1 Load Tonage x Hourly E rate = Make-up Rate               1147.5 LMup

Water & Sewage charges:
    Water is supplied by City of Fairfax.  Cooling towers have to be
    metered to qualify for the water only  (no sewer) rate:
    1,000 gallons = 1 unit charge             = $ 2.33
    One gallon =                                          $ 0.002330
    LMup/1 unit = Unit x Cost = Cost per/hr.                   $2.67

Total Water Make-up Unit Cost:                                        $2.67 Hr



Step Three: Equipment Depreciation

Equipment cost:
Package A/C Units (12 total):               $350,000.00
Package A/C Units Operating (2 total):                       $   58,333.33
Cooling Towers (2 total):                   $ 60,000.00
Cooling Towers Operating (1 total):                          $   30,000.00
Condenser Pumps (2 total):                  $ 10,000.00
Condenser Pumps Operating (1 total):                         $    5,000.00
Tower and Pump Piping:                                       $   48,000.00
VAV Boxes:                                  $428,000.00
VAV Boxes Operating (20% total):                             $   85,600.00

    1. Equipment Cost:                                       $  226,933.33
    2. Estimated Life:                                                  20 Yrs
    3. Annual Run Time:                                               3208 Hrs

Total Equipment Depreciation Cost:                                   $3.54 Hr



                                   EXHIBIT F
                                  Page 3 of 7

<PAGE>

                                                                       Exhibit F

Step Four: Equipment Maintenance Cost
<TABLE>
<S>                                                                    <C>
E.M.C. = Maintenance Cost divided by Annual operating hours.           Total Cost per Year
  Maintenance Cost:
   1. Air Filters                                                           $4,000.00
   2. Water Treatment & Supplies                                            $4,500.00
   3. HVAC Supplies                                                         $4,200.00
   4. MISC. Supplies                                                        $1,500.00
      Annual Operating Hours:                 3208
Total Cost:                                                                $14,200.00

Total Equipment Maintenance Cost:                                               $0.74  Prhr




Step Five: Calculation Totals Per Condition                            Total Cost Per Hour

   1. Electrical Cost:                                            =            $19.13  E.C.
   2. Water Cost:                                                 =             $2.67  W.C.
   3. Equipment Depreciation Cost:                                =             $3.54  EDC
   4. Equipment Maintenance Cost:                                 =             $0.74  EMC

Total Cost Per Hour:                                              =            $26.08  Prhr


Step Six: Operating Cost per Floor:                               =            $26.08  PrHr

Maintenance Engineering Costs                                     =             $5.85

Total Operating Cost Per Hour:                                    =            $31.93

</TABLE>

                                   EXHIBIT F
                                  Page 4 of 7


<PAGE>

                                                                       Exhibit F

                       OVERTIME HVAC CALCULATION FORMAT
                                    1/6/00

Project:       1816 International Drive      Cost To Run Five Floors
A/C Units                            = 10
Design KW:                           = n/a
Minimum Load Package Units           = 10
Chiller Tonage Rating:               =     580


Step One:   Electrical Costs:


Average KW Cost:                      =            $0.090  Per Kwh
Building Average Voltage:             =               460  Volts

A. Package Units (Two per floor):
   Min. Load 10 Units)=                 580 Min. Tonage
   Ten fans @ 26.5a=                 210.89 Kw
   Twenty compressors @ 20.5a=       326.28 Kw
   Total Kw                          537.17                           537.17 KWh

B. Condenser Water Pumps (2              50 HP each
   Condenser pumps needed:        2 = 124.0 amps
   Total Kw                           98.68 Kw
                                                                       98.68 KWh

C. Cooling Tower Fans:
   Fan motors:            4         =   99.6  amps
   Run Time (Full time w/2-VFD)     =    50%
   Total Kw                         =  39.63                           39.63 KWh

D. VAV Boxes:
   25 w/14 Kw heat & .5hp fan, 277  = 373.55 Kw
   50 w/10 Kw heat & 1/3 hp fan 27  = 530.47 Kw
   20 w/4 Kw heat & 1/3 hp fan, 277 =  92.19 Kw
   Run Time:                        =    50%
   Total Kw                         =  498.1 Kw                       498.10 KWh

Total A-D Kw:
  Water Chilling Unit:                                     =          537.17 KWh
  Chilled/Condenser Pumps:                                 =           98.69 KWh
  Cooling Tower Fans                                       =           39.63 KWh
  VAV Boxes::                                              =          498.10 KWh

Total KWh Condition:                                       =         1173.58 KWh


                                   EXHIBIT F
                                  Page 5 of 7

<PAGE>

                                                                       Exhibit F

Step Two. Coding Tower Water Usage

# of Pumps Used:           =      2 Pumps
Condenser Pump Rate:       =   2550 GPM's
Chiller Tonage Rating:     =    580 Tons


(A) Cooling Tower Evaporation Make-up & Bleed:            Total Values:
  Minimum Load (10 A/C Units)=                  580 Tons
  Evaporation Rate =  1% of GPM rate:                           1.00 %Ton
  # of Pumps:               2                                2550.00 PGPM
  Total Pump GPM Rate:               2550                      25.50 1%Rt
  Bleed Cycles=(Egpm/C-1)                         3 cycl       12.75 CGPM
  Total Make-up = Rate + Cycles                                38.25 TMup
  Hourly Evaporation rate=E rate x 60 min.                   2295.00 HMup
  #1 Load Tonage x Hourly E rate=Make-Up Rate                   2295 LMup

Water & Sewage charges:
  Water is supplied by City of Fairfax. Cooling towers have to be
  metered to qualify for the water only (no sewer) rate:
  1,000 gallons = 1 unit charge     = $2.33
  One gallon =                                 $0.002330
  LMup / 1 unit=Unit x Cost=Cost per/hr.            $5.35

Total Water Make-up Unit Cost:                                 $5.35 Hr

Step Three: Equipment Depreciation

Equipment cost:
Package A/C Units (12 total):                           $ 291,666.67
Cooling Towers (2 total):                               $  50,000.00
Condenser Pumps (2 total):                              $   8,333.33
Tower and Pump Piping:                                  $  40,000.00
VAV Boxes:                                              $ 428,000.00

    1. Equipment Cost:                                  $ 818,000.00
    2. Estimated Life:                                            20 Yrs
    3. Annual Run Time:                                         3208 Hrs

Total Equipment Depreciation Cost:                            $12.75 Hr

                                   EXHIBIT F
                                  Page 6 of 7
<PAGE>

                                                                       Exhibit F

Step Four: Equipment Maintenance Cost
<TABLE>
<S>                                                                    <C>
E.M.C. = Maintenance Cost divided by Annual operating hours.           Total Cost per Year
  Maintenance Cost:
   1. Air Filters                                   $4,000.00               $3,333.33
   2. Water Treatment & Supplies                    $4,500.00               $3,750.00
   3. HVAC Supplies                                 $4,200.00               $3,500.00
   4. MISC. Supplies                                $1,500.00               $1,250.00
      Annual Operating Hours:                 3208
Total Cost:                                                                $11,833.33

Total Equipment Maintenance Cost:                                               $3.07  Prhr




Step Five: Calculation Totals Per Condition                            Total Cost Per Hour

   1. Electrical Cost:                                            =           $105.62  E.C.
   2. Water Cost:                                                 =             $5.35  W.C.
   3. Equipment Depreciation Cost:                                =            $12.75  EDC
   4. Equipment Maintenance Cost:                                 =             $3.07  EMC

Total Cost Per Hour:                                              =           $126.79  Prhr


Step Six: Operating Cost per Floor:                               =           $126.79  PrHr

Maintenance Engineering Costs                                     =            $29.25

Total Operating Cost Per Hour:                                    =           $156.04

Per Floor Cost Per Hour (five floors in operation):               =            $31.21
</TABLE>

                                   EXHIBIT F
                                  Page 7 of 7

<PAGE>

                                   EXHIBIT "G"
                                   -----------

                             CLEANING SPECIFICATIONS
                             -----------------------
<TABLE>
<CAPTION>

JANITORIAL SPECIFICATIONS                                              FREQUENCY

           Main Lobbies, Elevator Lobbies, Public Areas And Corridors
<S><C>
Dust & clean lobby directory                                             Nightly
Dust & clean all walls,  from floor to 72"
above floor. Do not clean marble walls.                                  Nightly
Dust all window ledges & frames                                          Nightly
Empty all waste  baskets and reline                                      Nightly
Clean tile and floor (sweep and wash)                                    Nightly
Dust and spot clean reception desk                                       Nightly
Vacuum all carpeted areas and spot clean if necessary.                   Nightly
Vacuum all lobby  furniture                                              Nightly
Dust clean and spot clean all pictures,  wall  hangings,
and display cases from base to top.                                      Nightly
Sweep,  mop and spray buff marble  floor  areas.                         Nightly
Detail/edge  vacuum all  carpeted  areas                                  Weekly
Dust and clean all  ventilating louvers.                                  Weekly
Dust and clean all window  blinds.                                       Monthly
Dust and clean all recessed  light  fixtures  (outside  surface).        Monthly
Clean  and  vacuum  all ventilating  louvers.                          Quarterly
Sweep  and wet mop all  floors  at  entrances.                           Nightly
Dust all  unobstructed  furniture, file
cabinets and library shelves.                                            Nightly
Dust all fire extinguisher lockers, annunciator
panels and pull stations.                                                Nightly
Damp wipe with  non-abrasive  detergent all brass  entrances.            Nightly
Clean and polish brass  thresholds.                                      Nightly
Wipe with damp cloth metal trim work, doors, door frames,
walls and light switches, and tenant signage, remove
finger prints, smudges, water and other marks.                           Nightly
Detail clean andpolish drinking  fountains.                              Nightly
Wash all glass doors at entrances.                                       Nightly
Wax lobby  attendant's  desk,  if any.                                    Weekly
Dust  overhead  pipes in elevator lobbies, corridors, stairwells.        Monthly
Dust ceiling in lobby Monthly Vacuum and
clean all furniture, including upholstered chairs.                    Bi-monthly
Wash all cove base moldings                                            As Needed
Dust all ceiling light fixtures,  grids or lenses.                     As Needed
Loading dock and trash areas to be kept neat and clean                     Daily
Wipe and polish planters.                                              As Needed
Service corridors should be spray
buffed, stripped and refinished.                                          Weekly
Shampoo all mats and common area  carpets.                Quarterly or As Needed
</TABLE>
<PAGE>

<TABLE>
<CAPTION>

JANITORIAL SPECIFICATIONS                                              FREQUENCY

                                    Elevators
<S><C>
Clean and polish tracks, plates and grooves.                               Daily
Maintain hard surface floors in a manner consistent with
process used in main lobby area. Appearance shall be
consistent  and free of traffic wear  patterns.                            Daily
Damp wipe,  dust,  and/or thoroughly clean, using
the appropriate chemicals and polishes, all exterior
and interior doors, cab walls, door frames, and indicator panels.          Daily
All service elevator  areas must have  protective
floor and wall  coverings used to protect areas in front
of freight  elevator from spillage  resulting from trash removal.        Nightly



Dust ceilings, light fixtures and ceiling finishes thoroughly.            Weekly
Dust inside of telephone cabinets                                         Weekly
Spot clean carpeted floors                                             As Needed
</TABLE>
                                  Tenant Areas

Spot clean all interior partitions,
glass windows, glass entrance doors.                                     Nightly
Clean doors, door frames, walls and switch plates
to remove fingerprints, spills and other markings.                       Nightly
Clean all counters and counter tops in kitchen areas.
Remove dust from all spaces up to 72" above floor.                       Nightly
Edge vacuum all carpeted areas.                                           Weekly
Spray buff all non-carpeted areas.                                        Weekly
Spot clean walls and metal trim work.                                     Weekly
Strip and refinish all non-carpeted areas.                  Monthly or As Needed
Spot clean all walls from ceiling to floors.                             Monthly
Dust all picture frames and wall hangings.                               Monthly
Dust all lighting and ventilation fixtures.                              Monthly
Remove hand marks and keep polished all brass handles.                   Nightly
Wipe off all counter tops, cabinet fronts,
and appliances in kitchen areas.                                         Nightly
Clean all glass furniture tops.                                          Nightly
Vacuum all carpeted tenant areas.
Spot clean all carpets as needed.                                        Nightly
Vacuum, dust, spot clean interior tenant stairways.                      Nightly
Clean all interior partition glass including glass doors.                 Weekly
Maintain all composition hard surface floors to ensure a
scuff-free, gloss, clean appearance.                                      Weekly
Pile lift all reception and hallway floor surfaces to remove
embedded dirt and restore pile to a uniform condition.                    Weekly
<PAGE>

JANITORIAL SPECIFICATIONS                                              FREQUENCY

                                    Restrooms

Fill floor drain with sufficient water to preclude
sewer gas from escaping.                                                 Nightly
Dust ventilating diffusers and light lenses.                             Nightly
Partitions - wash to remove streaks, stains
and smudges with proper combination lavatory cleaner
disinfectant and deodorizer (odor free) and fungicide.                   Nightly
Sweep and wash all tile floors.                                          Nightly
Empty, remove and clean waste receptacles, replace
plastic liners.                                                          Nightly
Floors - remove all litter, wet mop with proper combination
lavatory cleaner, disinfectant deodorizer (odor free) and fungicide.
Rinse and mop with plain water. Remove all stains from underneath
sinks, toilets and urinals.                                              Nightly
Vacuum all carpet, if applicable.                                        Nightly
Refill all toilet tissue and toilet seat cover
dispensers (if any).                                                 Twice Daily
Check, refill if necessary, all soap and lotion dispensers.              Nightly
Clean diffusers and light lenses.                                         Weekly
Walls - wash completely (floor to ceiling) with
proper combination cleaner,disinfectant, deodorant
(odor free) and fungicide (no streaking).                                Monthly
Thresholds - clean and brighten.                                          Weekly
Damp wipe all baseboards.                                                 Weekly
Machine scrub all tile floors.                                           Monthly
Strip and seal all floors.  No wax.  Slight gloss.
Maintain a clean, scuff-free appearance.                               Quarterly



Damp wipe with mild non-abrasive detergent all doors,
kick plates, door frames, walls, light
switches, glass and partitions.                                          Nightly
Clean and polish towel and toilet dispensers,
flush O-meters, shelves, piping, tampon machines, toilet hinges
and other material surface to remove all stains
and fingerprints.  Refill all machines as necessary.                     Nightly
Clean glass mirrors and vanity tops, removing
all fingerprints, streaks, smudgesand splash marks,
sink elbow plumbing.                                                     Nightly
Empty and damp wash all waste containers using
proper disinfectant, deodorant and germicide
combination cleaner.                                                     Nightly
Clean toilets, toilet seats and urinals with
proper combination of lavatory cleaner, disinfectant and
deodorizer removing all streaks, stains and deposits,  Clean
and polish all chrome work.  Add deodorizer in all toilet bowls.         Nightly
Wash and disinfect both sides of toilet seats.                           Nightly
Clean and organize janitorial closets.                                   Nightly
<PAGE>

JANITORIAL SPECIFICATIONS                                              FREQUENCY

                             Stairways and Landings

Police and remove all debris.                                              Daily
Sweep, damp mop and/or vacuum all floors
on the garage elevator landings.                                         Nightly
Spot clean, dust walls and handrails.                                     Weekly
Sweep, damp mop and/or vacuum all flooring and stairs.                    Weekly
Damp wipe with non-abrasive detergent and clean all
doors, light switches, glass, hand rails, etc.                            Weekly
Wash and clean from floor to ceiling all light
fixtures, ledges, moldings, walls, grills, vents, piping, etc.           Monthly
Dust mop and damp mop landings and stairs.                             As Needed
Damp mop to remove spills.                                             As Needed

                              Exterior Maintenance

Maintain exterior grounds.                                         3 Times Daily
Remove litter from planters                                        3 Times Daily
Clean all lobby glass areas.                                               Daily
Clean curb and gutter areas.                                               Daily
Polish all thresholds and door handles.                         3 Times Per Week
Power wash sidewalks.                                       Monthly or As Needed
Remove gum from sidewalks.                                             As Needed
Remove graffiti.                                                       As Needed
Empty exterior garbage and ash trays                                       Daily
Clean exterior facade from base to 72".                                As Needed
<PAGE>

                                   EXHIBIT "H"
                                   -----------

                         TENANT'S SIGNAGE SPECIFICATIONS
                         -------------------------------

                                 (see attached)
<PAGE>

                             [GRAPHIC OF SIGNAGE]

Subject to the terms of Paragraph 2.3 of the Lease, Tenant to install two (2)
signs of this general depiction on the exterior facades of the Building; the
total allowable signage square footage for both signs combined shall not exceed
one hundred eighty five (185) square feet.

                                   Exhibit H
<PAGE>

                     [Letterhead of Creative Sign Systems]

January 4, 2000

MicroStrategy
8000 Crescent Drive
Vienna, VA 22182
Attn: Bill Painter

RE:  Signage

Dear Mr. Painter:

Please find the attached drawing of the main site sign identification, which
consists of the logo in channel letters, fabricated from a stain finished
stainless steel. The face of each letter is #2283 red acrylic. Each letter is
internally illuminated with neon tubing. The face side tubing is clear red while
the back side tubing is white. The letter faces are illuminated in red while the
wall is haloed in a soft white.

Should you have any questions or require any additional information, please do
not hesitate to call.

Sincerley,

/s/ John B. Mayer

John B. Mayer,
President

lar

                                    Exhibit H
<PAGE>

                   [graphic of building exterior-view No. 1]

Subject to the terms of Paragraph 2.3 of the Lease, Tenant to install two (2)
signs of this general depiction on the exterior facades of the Building; the
total allowable signage square footage for both signs combined shall not exceed
one hundred eighty five (185) square feet.

                                   Exhibit H
<PAGE>

                   [graphic of building exterior-view No. 2]

Subject to the terms of Paragraph 2.3 of the Lease, Tenant to install two (2)
signs of this general depiction on the exterior facades of the Building; the
total allowable signage square footage for both signs combined shall not exceed
one hundred eighty five (185) square feet.

                                   Exhibit H


<PAGE>

                                  Larger Sign

          [photograph of building with sign-1861 International Drive]

                                   Exhibit H
<PAGE>

                                 Smaller Sign
                               Initial Location

          [photograph of building with sign-1861 International Drive]

                                   Exhibit H


<PAGE>

                                 Smaller Sign
                               Initial Location

          [photograph of building with sign-1861 International Drive]

                                   Exhibit H



<PAGE>

                             [graphic of signage]

                                   Exhibit H
<PAGE>

                                   EXHIBIT "I"
                                   -----------

                          TENANT'S GENERATOR EQUIPMENT
                          ----------------------------
                (Preliminary location, plans and specifications)
                 ----------------------------------------------

                                 (see attached)
<PAGE>


                              [blocking diagram]

                                   Exhibit I

<PAGE>

                                   EXHIBIT "J"
                                   -----------

                         TENANT'S TRANSFORMER EQUIPMENT
                         ------------------------------
                (Preliminary location, plans and specifications)
                 ----------------------------------------------

                                 (see attached)
<PAGE>

                [SCHEMATIC FOR P-2 PARKING LEVEL PLAN -- POWER]

                                   Exhibit J
<PAGE>

                                   EXHIBIT "K"
                                   -----------

                      TENANT'S ROOFTOP MECHANICAL EQUIPMENT
                      -------------------------------------

                (Preliminary location, plans and specifications)
                 ----------------------------------------------

                                 (see attached)
<PAGE>

                        [SCHEMATIC FOR ROOF PLAN HVAC]

                                   Exhibit K


<PAGE>

                                   EXHIBIT "L"
                                   -----------

                GUIDELINES AND LIMITATIONS REGARDING IMPROVEMENTS
                -------------------------------------------------

The  parties  acknowledge  that the  Building  is a "Class A' office  project in
Tyson's Corner, Virginia. Tenant's plans for the Improvements will be consistent
with Class A office space in the Tyson's  Corner  market.  Tenant (and  Tenant's
design  consultants) are aware of the Landlord's  interest in maintaining a high
level of quality and finish throughout the Building,  including the Premises, to
reflect the level of design and finish of a Class A office building.

As of the date of this Lease, all of Tenant's detailed space plans have not been
completed,  The basic  configuration  of the planned  Premises is anticipated to
include a  combination  of  enclosed  offices  and  conference  rooms  along the
perimeter of each floor and open plan office space utilizing  systems  furniture
cubicles/workstations  in the interior areas of each floor (around the core). It
is  anticipated  that the planned  Premises  will be designed to  accommodate  a
typical  tenant  occupancy  load of up to 150  people per floor or an average of
approximately one (1) person per one hundred seventy five (175) square feet.

The  anticipated  design/layout  for the planned  Premises  is also  expected to
include  interior  offices,  work areas and support  spaces  such as  conference
rooms, copy and file rooms,  break rooms,  kitchenettes and coffee areas,  which
are typically included in local market office configurations. The plans will not
include  an  employee  cafeteria.  The  design is also  expected  to  include on
medium-sized  computer/network  room not  greater  than  15,000 sq. ft. with the
potential  for raised  computer  flooring.  This room is  intended  for use as a
central computer and telecommunications  systems center for the entire Premises.
The computer room  improvements  which are eligible for  reimbursement  from the
Improvement  Allowance  will not include  computer  equipment or other  personal
property.

The typical  level of interior  finish  expected for the planned  Premises  will
include standard and upgraded  interior carpets,  standard  interior  acoustical
ceilings and grid,  interior paint and stains,  and possibly vinyl and/or fabric
wall coverings in areas of higher traffic, higher finish and emphasized interior
design (lobbies, reception areas, conference rooms, executive suites, etc.)

The planned Improvements will include a typical level of tenant electrical power
and lighting  distribution as well as tenant mechanical  ductwork  distribution,
connections and controls throughout all levels of the planned Premises. Upgraded
mechanical and electrical equipment  (lighting,  HVAC, etc.) may be installed by
Tenant as required to service certain specialized Tenant spaces and functions.

The Improvements  will not include any  specialty design or  decorative  feature
or  element  involving  water,  for  example,  or  other such  features  in  the
Premises.  The  Improvements  also  will not include  unusually large conference
facilities or modifications to elevator doors or restrooms.
<PAGE>

                                   EXHIBIT "M"
                                   -----------

                        TENANT'S COMMUNICATIONS EQUIPMENT
                        ---------------------------------

                (Preliminary location, plans and specifications)
                 ----------------------------------------------

                                 (see attached)
<PAGE>

               [SCHEMATIC FOR PROPOSED SATELLITE ARRAY LOCATION]

                                   Exhibit M
<PAGE>

                                   EXHIBIT "N"
                                   -----------

                    PRELIMINARY CONCEPTUAL FOURTH FLOOR PLANS
                    -----------------------------------------

                                 (see attached)
<PAGE>

                     [SCHEMATIC OF 4TH FLOOR MASTER PLAN]

                                   Exhibit N

<PAGE>

PROPOSED DESIGN FOR THE 4TH FLOOR

MicroStrategy at 1861 International Drive
January 3, 2000

Approximately one half of the 4th floor will have special areas as shown on the
reduced floor plan. The special areas will include several data centers, the
main telephone room, the Network Operation Center for Strategy.com and several
additional mechanical & electrical rooms to serve these special areas. All of
these areas will have a raised access floor (raf) at different heights above the
slab. In the conditions where the raf abuts the glass curtain wall of the
building, there will also be a metal handrail attached to the raf, mecho shades
that screen the interior and a metal trim at the curtain wall sill that matches
the existing metal frames.

The other areas on this floor will be general office areas similar to the 3rd
and 5th floors.

Network Operation Center (NOC)
------------------------------

The NOC for Strategy.com has a 6" raf, a rear projection room, observation room
with a glass wall and operator consoles to house the many computer monitors.
The windows that occur in the projection room will be required to have a
black-out window treatment. This area will also have special lighting and a
special ceiling system for acoustical purposes. The walls will have a special
wall treatment and the flooring will be carpet tiles.

Data Centers, Main Telephone Room and Mechanical Rooms
------------------------------------------------------

These areas will have a 16" raf that provides under floor cooling generated in
the new mechanical rooms specifically designed for the computer equipment heat
loads. The ceiling systems and lighting will be the same as the general office
areas. The flooring will have a laminated floor tile on the raf and the walls
will be painted drywall with 4" vinyl base.

Mechanical System
-----------------

The NOC and Data Centers will be served by a Computer Room AC System consisting
of three (3) 150-ton roof mounted Evaporative Fluid Coolers and approximately 11
down-flow glycol cooled computer grade units mounted on a 16" raf. An
architectural screen, visually consistent with the base building penthouse with
the modified parapet height, will be added on the roof to hide the new
mechanical units. The new mechanical units will also require steel supports
attached to the roof as designed by the base building structural engineer. One
of the fluid coolers, one of the associated pumps and part of the distribution
piping were designed as part of the 3rd and 5th floor fit-out. This system will
ultimately provide cooling for all of MicroStrategy's critical areas and will
include N+1 redundancy throughout. The remainder of the 4th floor (approximately
half) will remain on the base building system.

                                   Exhibit N
<PAGE>

PROPOSED DESIGN FOR THE 4TH FLOOR (continued)
Page 2


Electrical System
-----------------

Power for the lighting, receptacles and VAV boxes in the office area of the 4th
floor will be derived from the base building power distribution system. This
consists of a buss mounted disconnect switch, high voltage distribution for the
VAV and lighting and step down transformers for the receptacle load.

Normal power for the NOC and Data Centers will be derived from the supplemental
electrical service. This electrical service was designed and specified under the
3rd and 5th floor documents. It consists of a 3000 amp, 480 volt service with
main switches for different usage's. One main switch will power the generator
backed up loads and one main switch will control the generator and UPS backed up
loads. A single automatic transfer switch will transfer power from the normal
service to the generators.

Standby power generators will provide standby power to the un-interruptible
power supplies. Since multiple standby power generators will be used, they will
be linked with paralleling gear. The un-interruptible power supplies, associated
paralleling gear and distribution equipment will be located in the parking
garage. The power distribution units for the Data Center and the NOC will be
located in the individual spaces. The mechanical equipment associated with the
Data Center and the NOC will be powered by the utility and the standby power
generators. A blocking plan has been submitted as part of the 3rd and 5th floor
documents. The plan shows preliminary layouts for the generators, UPS's and new
electrical room.

                                   Exhibit N
<PAGE>

MicroStrategy at 1861 International Drive
Revised 1/3/2000

PROPOSED ELECTRICAL SYSTEM FOR THE 4TH FLOOR

Power for the lighting, receptacles and VAV boxes in the office area of the
fourth floor will be derived from the base building power distribution system.
This consists of a buss mounted disconnect switch, high voltage distribution for
the VAV and lighting and step down transformers for the receptacle load.

Normal power for the NOC and Data center will be derived from the supplemental
electrical service. This electrical service was designed and specified under the
third and fifth floor project. It consists of a 3000 amp, 480 volt service with
main switches for different usage's. One main switch will power the generator
backed up loads and one main switch will control the generator and UPS backed up
loads. A single automatic transfer switch will transfer power from the normal
service to the generators.

A maximum of (3)-600KVA standby power generators will provide standby power to
the un-interruptible power supplies. The generator muffler exhausts will be run
from the generator to the building exterior. Routing and location to be
coordinated with landlord. Since multiple standby power generators will be used,
they will be linked with paralleling gear. The un-interruptible power supplies
will also be linked with paralleling gear. The standby power generators,
un-interruptible power supplies, associated paralleling gear and distribution
equipment will be located in the parking garage. The power distribution units
for the Data room and the NOC room will be located in the individual spaces. The
Mechanical equipment associated with the Data room and the NOC room will be
powered by the utility and the standby power generators. A blocking plan has
been submitted as part of the third and fifth floors. The plan shows preliminary
layouts for the generators, UPS's and new electrical room.


PROPOSED MECHANICAL SYSTEM FOR THE 4TH FLOOR

The 4th floor Network Operations Center (NOC) and data centers will be served by
a computer room AC system consisting of three (3) 150-ton roof mounted
evaporative fluid coolers and approximately 11 downflow glycol cooled computer
grade units mounted on a 16" raised access floor. One of the fluid coolers, one
of the associated pumps and part of the distribution piping are designed as part
of MicroStrategy's 3rd and 5th floor tenant fit-out. This system will ultimately
provide cooling for all of MicroStrategy's critical areas and will include N+l
redundancy throughout. The remainder of the 4th floor office space will remain
on the base building HVAC system.

Two fuel tanks and pumps shall be located on the lowest parking level (P3), in a
4 hour rated room. Fuel tanks shall provide fuel for emergency generators. A
fill box shall be located where a fuel truck can fill the tanks. Final location
shall be coordinated with landlord. A shaft will be required for the radiator
exhaust for the generators. Size and location of shaft shall also be coordinated
with landlord.

                                   Exhibit N
<PAGE>

                                   EXHIBIT "O"
                                   -----------

                   PRELIMINARY CONCEPTUAL ELEVATOR LOBBY PLANS
                   -------------------------------------------

                                 (see attached)






















































<PAGE>

                                                                       Exhibit O

PROPOSED DESIGN DESCRIPTION OF FLOORS 2 THRU 6 PUBLIC AREAS

MicroStrategy at 1861 International Drive
December 30, 1999

Floors 2, 3, 5 and 6
--------------------

These floors will all be similar in design intent and finishes. The elevator
lobbies will have carpeted flooring, with border and inlay pattern coppered
drywall ceiling with indirect cove lighting with recessed down lights and slot
diffeners, wall covering or special paint finish (Portex or other approved
Applor) on the walls and stained wood for headboard and trim. The elevator doors
and frames will remain an brushed stainless steel.

The public corridors will have carpet, acoustical tile ceiling with 9/16" grid,
swooped down lights, 3' x 8' wood vencor doors with aluminum facets and brushed
stainless steel hardware, wall covering or special paint finish on the walls and
stained wood headboard. Some doors may be wider than 3 feet for moving computer
equipment.

4th Floor
---------

This floor will be upgraded in design and finishes from the typical floor public
areas. The design intent for the elevator lobby is to have something that is
similar in the ground floor lobby design. The finishes will include a
combination stone and carpet flooring, wood, metal and/ or stone walls, cover
drywall ceiling with recessed down lights and/or special lighting fixtures and
stained wood for trim. The elevator doors and frames will remain as brushed
stainless steel.

The public corridors on the 4th floor may also be upgraded from the typical
floor. The finishes in the elevator lobby will continue in the reception area
and the corridor that leads to the Network Operation Center. Finishes in the
other public corridors on that floor may be more similar to the typical floor.

                                   Exhibit O
<PAGE>

                            1861 INTERNATIONAL DRIVE
                             McLean, Virginia 22102
--------------------------------------------------------------------------------
                               BUILDING STANDARDS

ARCHITECTURAL:
-------------

PARTITIONS:    Floor to ceiling partitions within the Tenant Space shall be
               constructed using 2-1/2' thick, 25 gauge steel studs at 16 on
               center with 5/6' thick gypsum wallboard.

               Demising partitions between suites and public corridors shall be
               constructed using 2-1/2" thick (min), 20 gauge slab-to-slab steel
               studs at 16" on center with 5/8" thick gypsum wallboard. The
               demising partitions shall be sound insulated and comply with one
               (1) hour fire rating UL assembly requirements.

               All partitions shall be taped, speckled, sanded and finished with
               one coat of latex primer and one coat of latex eggshell finish
               paint.

               All partitions shall receive 4" straight vinyl base at carpeted
               floor areas and 4" vinyl cove base at all resilient flooring.


DOORFRAMES:    All lobby, public corridor and office doorframes shall be factory
               finished Aluminum frames with 1/4" X 1/4" reveal trim and mitered
               corners. Factory primed knocked down hollow metal doorframes may
               be used at storage, utility rooms/closet doors.


DOORS:         Glass doors may be used at Suite Entries. The use of glass doors
               at suite entries is subject to landlord review and approval of
               all submittals/shop drawings.

               Tenant doors shall be 3'-0" X 6'-0", solid core, stain grade,
               maple wood veneered doors. Hardwood edge bands to match face
               veneers. The doors may be finished at the job site.


HARDWARE:      All hardware shall be satin chromium plated finish #626.

               Lock / latch sets shall be SCHLAGE, L-Series heavy-duty mortise
               sets, Style #07, Escutcheon style L concealed.

               All hardware sets to include floor mounted stops with black
               resilient inserts. Location to be coordinated with Architect.

               All door closers shall be LCN.

               All floor stops, flush bolts and dust proof strikes shall be
               IVES.

CEILING GRID:  The suspended acoustical ceiling grid shall be Armstrong
               Silhouette XL 9/16", Bolt-Slot, white grid with 1/4" reveal.
               Typical ceiling height shall be 9'-0" AFF.

                                   Exhibit O
<PAGE>

                                                        1861 INTERNATIONAL DRIVE
                                                              BUILDING STANDARDS
                                                                     Page 2 of 3

CEILING TILE:       The acoustical ceiling tile shall be Armstrong Cortega,
                    24" x 24", white tile, Item #2195

                    All gypsum wallboard ceilings shall be 1/2" thick gypsum
                    wallboard on 25 gauge, 2-1/2" thick metal studs at 16" on
                    center. The gypsum wallboard shall be finished as described
                    at partitions sections.

VCT:                The vinyl composite floor tile shall be 12" x 12" x 1/8"
                    standard commercial grade tile. Tenant shall select the
                    color.

CARPET:             The carpet shall be direct glue down, commercial grade, min.
                    30 oz. Cut pile, made of 100% nylon with a 10 (ten) year
                    warranty. Tenant shall select the pattern and color.

PAINT:              All gypsum wallboard surfaces shall receive one coat of
                    latex primer and one coat of latex eggshell finish paint.

                    All interior wood and metal surfaces shall receive one coat
                    of latex primer and two coats of latex semi-gloss paint.


ELECTRICAL:
-----------

LIGHT FIXTURES:     The general lighting at the tenant space shall be 2' x 4'
                    Fluorescent 277V lite fixture with high efficiency
                    electronic ballast, cool white F32/T8 lamps and chrome 18
                    cell parabolic lenses. (LIGHTOLIER DPA2-G18LS-340277-SO).

                    The lighting at the public lobbies and corridors shall be
                    2' x 2' Fluorescent 277V light fixture with high efficiency
                    electronic ballast, cool white F32/T8 lamps and chrome 9
                    cell parabolic lenses. (LIGHTOLIER DPA2-G9LA-2U4277-SO).

EXIT LIGHTS:        All exit light fixtures shall be LED, with white steel
                    housing and red letters as manufactured by Self-Powered
                    Lighting, Inc., Model CLC-AC-1/2-R-W-W-CC.

FIRE ALARM:         Notifier fully addressable Fire Alarm System with XP Series
                    Transponder. All connections to building fire alarm panels
                    must be performed by the Landlord's fire alarm contractor.

                                                        (continued on next page)

                                   Exhibit O
<PAGE>

                                                        1861 INTERNATIONAL DRIVE
                                                              BUILDING STANDARDS
                                                                    Page: 3 of 3


MECHANICAL & PLUMBING:
---------------------


SPRINKLER PIPING: All sprinkler piping shall be manufactured to comply with ASTM
                  standards A53 and/or Al35. Fittings shall be class 250
                  threaded cast iron or grooved-end type iron fittings, style 77
                  as manufactured by Victaulic Corporation or accepted equal.


SPRINKLER HEADS:  All sprinkler heads shall be fully --recessed heads at 165F
                  with painted off white escutcheon plates. All sprinkler heads
                  shall be located at the center of the tile in acoustical
                  ceilings.


FIRE DAMPERS:     The fire dampers shall be as manufactured by Ruskin, type IBD2
                  with a 165F fusible link, UL approved.

                  Style A -- directly behind registers, Style B -- for
                  rectangular duct, and Style B -- for round duct,


REGISTERS / GRILLES / DIFFUSERS:

                  Perimeter diffusers shall be TITUS plenum slot diffusers.
                  Model #N-1-D or equal

                  Supply air diffusers shall be TITUS Modu-Bloc Series, 24"X24",
                  Model MBR-30 with 3/4" slots, with integral building standard
                  ceiling tile.

VAV BOXES:        The VAV Boxes shall be;

                      .   TRANE, Fan Powered, Variable Air Volume Terminal Units
                          with Electric Re-Heat for perimeter applications,
                      .   TRANE Variable Air Volume Single Duct Terminal Units
                          for interior applications.

                  All VAV boxes to be equipped with DDC Controller and
                  Temperature Sensor compatible with the Base Building System.

                                      *****

                            End of Building Standards

                                   Exhibit O