Document:

<PAGE>   1
                                                                   Exhibit 10.16

                                    SUBLEASE

     This Sublease ("Sublease"), dated for reference purposes as of December
13, 1999, by and between Advanced Radio Telecom Corp., a Delaware corporation
("Sublandlord") and Quintus Corporation, a California corporation
("Subtenant"), and is based upon the following facts and circumstances:

     A.   Sublandlord is the tenant under that certain Office Lease and Rider
to Office (collectively, "Master Lease"), dated December 18, 1996, with
EOP-Westbrook Corporate Center, L.L.C., successor in interest to LaSalle
National Trust, N.A. (the "Master Landlord"). A copy of that Master Lease is
attached to this Sublease and marked as Exhibit A.

     B.   Subtenant desires to sublease from Sublandlord the entirety of the
premises being leased by Master Landlord to Sublessor under the Master Lease,
namely the premises commonly known as Four Westbrook Corporate Center, Suite
620, Westchester, Illinois, consisting of approximately 5,878 square feet, as
more particularly described in the Master Lease (the "Premises").

     NOW, THEREFORE, in consideration of the mutual covenants contained in this
Sublease, and for valuable consideration, the receipt and sufficiency of which
are acknowledged by the parties, the parties agree as follows:

     1.   Sublease. Sublandlord subleases to Subtenant and Subtenant subleases
from Sublandlord the Premises, subject to the terms, covenants, and conditions
contained in this Sublease. Subtenant and Sublandlord hereby agree that any
statements of square footage (rentable, usable or otherwise) set forth in the
Master Lease or in this Sublease that may have been used in calculating the
rent, pro rata share of Operating Expenses or Taxes or any other matters, are
not subject to revision, whether or not the actual square footage is more or
less, and the rent, pro rata share of Operating Expenses or Taxes or any other
similar matters is not subject to revision. Subtenant hereby acknowledges and
agrees that, as of the start of this Sublease, the Premises are in good order
and condition, and Subtenant accepts the Premises on an "AS IS" basis, in the
condition existing as of the start of this Sublease, with any and all faults,
whether known or unknown, latent or patent. Subtenant shall, at Subtenant's
sole cost and expense, subject to compliance with the terms and conditions of
this Sublease and the Master Lease, perform any and all work of improvement
that may be necessary for Subtenant's use and occupancy of the Premises.

     2.   Term.

          2.1  Subject to the terms and conditions set forth herein, the
original term ("Original Term") of this Sublease shall commence on February 1,
2000 ("Commencement Date") and shall expire on December 31, 2003 ("Expiration
Date").

          2.2  The Master Landlord's written consent to this Sublease in
accordance with the terms of the Master Lease is a condition subsequent to the
validity of this Sublease. If the Master Landlord's consent has not been
obtained and a copy of that consent delivered to Subtenant by one (1) business
day prior to the Commencement Date, then either Sublandlord or Subtenant shall
thereafter each have the ongoing right, subject to the terms of this Section,
to terminate this Sublease pursuant to a notice ("Termination Notice") so
stating delivered to the other party. If either party gives the Termination
Notice, then this Sublease shall terminate effective ten (10) days following
receipt of the Termination Notice by the other party ("Termination Date"), in
which event, if the Termination Date is

                                       1
<PAGE>   2

on a date after the Commencement Date, then notwithstanding such Commencement
Date, Sublandlord shall have no obligation to deliver the Premises to Sublessee
on the Commencement Date; provided, however, if Subtenant gives the Termination
Notice, and Sublandlord delivers to Subtenant the consent of Master Landlord to
this Sublease before the Termination Date, then Subtenant's exercise of such
termination right shall be cancelled and be null and void, the condition
subsequent set forth in this Section shall be satisfied and this Sublease shall
continue in full force and effect, and the Commencement Date shall be the later
of the Commencement Date set forth above or the date of Master Landlord's
consent to this Sublease. If this Sublease is terminated pursuant to one
party's giving the Notice of Termination, then this Sublease shall
automatically terminate as of the Termination Date, Sublandlord shall return to
Subtenant the Security Deposit and any other sums, if any, paid by Subtenant to
Sublandlord upon the parties execution of this Sublease and the parties shall
be released from any further obligations under this Sublease. Subtenant agrees
to cooperate with the Sublandlord, at no cost or expense to the Sublandlord, in
obtaining the consent of the Master Landlord to this Sublease, which
cooperation shall include, but not be limited to, providing documents,
materials and information requested or required by the Master Landlord, such as
those set forth in Section 15 of the Master Lease.

     3.   Monthly Base Rent, Operating Expenses and Taxes.

          3.1  Subtenant shall pay Sublandlord $10,776.33 per month as Monthly
Base Rent during the Term of the Sublease. The Monthly Base Rent will increase
annually on the anniversary of the Commencement Date by three percent (3%) of
the Monthly Base Rent then currently in effect.

          3.2  If the Term of this Sublease begins or ends on a date that is
not the first day of a month, Monthly Base Rent shall be prorated as of that
date. All Monthly Base Rent shall be payable monthly in advance on the first day
of each month. Except as otherwise specifically set forth in the Sublease,
Monthly Base Rent and all other amounts payable by Subtenant hereunder shall be
paid without offset, deduction, counter-claim, abatement or notice.

          3.3  Subtenant hereby acknowledges and agrees that in addition to
Monthly Base Rent and any other amounts payable by Subtenant hereunder,
Subtenant shall pay Sublandlord's pro rata share of Operating Expenses and
Taxes over actual 1999 real Operating Expenses and Taxes as and when
Sublandlord is obligated to pay the same under the terms of the Master Lease.

          3.4  Notwithstanding the foregoing, in lieu of any tenant improvement
allowance, Sublandlord shall abate the Monthly Base Rent, Operating Expenses
and Taxes for the first three months of the Term.

     4.   Use. Subtenant shall use and occupy the Premises for general office
use in accordance with the provisions of the Master Lease and this Sublease,
and for no other use or purpose.

     5.   Master Lease.

          5.1  As applied to this Sublease, the words "Landlord" and "Tenant"
in the Master Lease shall mean and refer to Sublandlord and Subtenant,
respectively, under this Sublease. Except as otherwise expressly provided in
this Sublease, the covenants, agreements, provisions, and conditions of the
Master Lease are made a part of and incorporated into this Sublease as if
recited in full in this Sublease.

                                       2
<PAGE>   3
          5.2  Except as otherwise expressly provided in this Sublease, the
rights and obligations of the Master Landlord and the Tenant under the Master
Lease will be deemed the rights and obligations of Sublandlord and Subtenant,
respectively, under this Sublease, and will inure to the benefit of, and be
binding on, Sublandlord and Subtenant, respectively. As between the parties to
this Sublease only, in the event of a conflict between the terms of the Master
Lease and the terms of this Sublease, the terms of this Sublease will control.

          5.3  Subtenant recognizes that Sublandlord is not in a position to
render any of the services or to perform any of the obligations required of
Master Landlord by the terms of the Master Lease, including, but not limited to,
the services or obligations of Master Landlord under the following Sections of
the Master Lease: Sections 7(C), 7(D) and (E) (pertaining to Operating
Expenses), Section 9 (Services), Section 13A(ii) and 13A(iv) (Risk Allocation
and Insurance), 13(C) (Landlord's Insurance), (18A) Repairs and Compliance, 19
(Fire or Casualty), 20 (Eminent Domain), (R-8) Second Addendum to Section 9,
and (R-13) Addendum to Section 17(CC). Therefore, despite anything to the
contrary in this Sublease, Subtenant agrees that Sublandlord shall have no
obligation, responsibility or liability in the performance or non-performance of
Master Landlord's obligations, responsibilities or liabilities under the Master
Lease. Subtenant shall look solely to Master Landlord therefor, and Sublandlord
shall not be liable to Subtenant for any default of the Master Landlord under
the Master Lease.

          5.4  Subtenant shall not have any claim against Sublandlord based in
the Master Landlord's failure or refusal to comply with any of the provisions
of the Master Lease. Despite the Master Landlord's failure or refusal to comply
with any of those provisions of the Master Lease, this Sublease shall remain in
full force and effect and Subtenant shall pay the Monthly Base Rent and all
other charges provided for in this Sublease without any abatement, deduction or
setoff. Except as expressly provided in this Sublease, Subtenant agrees to be
subject to, and bound by, all of the covenants, agreements, terms, provisions,
and conditions of the Master Lease, as though Subtenant was the tenant under
the Master Lease.

          5.5  Whenever the consent of the Master Landlord is required under
the Master Lease, then the consent of Sublandlord shall also be required.

     6.   Variations from Master Lease. As between Sublandlord and Subtenant,
the terms and conditions of the Master Lease are modified as stated below in
this Section:

          6.1  The following Sections of the Master Lease shall not apply to
this Sublease:

               - In Section (1) Basic Lease Provisions, subparagraphs B
(Tenant's address), D (Lease Term), E (Commencement Date), G (Monthly Base
Rent), H (Payee of Rent), I (Address for Payment of Rent), N (Security Deposit)
and O (Broker);

               - (3) Term;

               - (4) Possession;

               - (13A(ii) and 13A(iv)) Risk Allocation and Insurance, 13(C)
                 Landlord's Insurance;

               - (15) Assignment or Subletting (see Paragraph 10 below);

                                       3
<PAGE>   4
               -(18A) Repairs and Compliance;

               -(35) Security Deposit;

               -(38) Brokerage (see Paragraph 6.2 below);

               -The following provisions of the Rider: (R-1) Addendum to
Section 1(G), (R-2) Addendum to Subsection 1(N), (R-3) First Addendum to
Section 4, (R-4) Second Addendum to Section 4, (R-6) Addendum to Section 9(B),
(R-10) Addendum to Section 12(P), (R-11) Addendum to Section 17(R), (R-16)
Addition Space, (R-17) Right to Terminate, (R-18) Moving Allowance, and (R-20)
Option to Extend; and

               -Exhibit C (Work Letter Agreement).

          6.2  Sublandlord and Subtenant each represents to the other (i) that
such party has had no dealings with any real estate broker or agent in
connection with the negotiation of this Sublease except for Amanda Cribari of
Cawley Chicago Commercial Real Estate Company, LLC, representing the Subtenant
("Subtenant's Broker") and Michael Fortuna of Cushman & Wakefield, representing
the Sublandlord ("Sublandlord's Broker") (collectively, the "Brokers"), and (ii)
that other than the Brokers, the parties know of no other real estate broker or
agent who is entitled to a commission or finders fee in connection with this
sublease. Each party shall indemnify, protect, defend and hold harmless the
other party against all claims, demands, losses, liabilities, lawsuits,
judgments and costs and expenses (including reasonable attorney's fees) for
any subleasing commission, finder's fee, or equivalent compensation alleged to
be owing on account of the indemnifying parties dealings with any real estate
broker or agent other than the Brokers. The terms of this section shall survive
the expiration or earlier termination of the sublease term. Sublandlord shall
pay a commission to the Brokers pursuant to a separate agreement with the
Brokers.

          6.3  Any notice that may or must be given by either party under this
Sublease shall be delivered (i) personally, (ii) by certified mail, return
receipt requested, or (iii) by a nationally recognized overnight courier,
addressed to the party to whom it is intended. Any notice given to Sublandlord
or Subtenant shall be sent to the respective address set forth on the signature
page below, or to such other address as that party may designate for service of
notice by a notice given in accordance with the provisions of this section. A
notice sent pursuant to the terms of this section shall be deemed delivered (A)
when delivery is attempted, if delivered personally, (B) three (3) business
days after deposit into the United States mail, or (C) the day following
deposit with a nationally recognized overnight courier.

          6.4  All amounts payable under this Sublease by Subtenant are payable
directly to Sublandlord. Subtenant shall make any and all such payments to
Advanced Radio Telecom Corp.

          6.5  Subtenant shall name Sublandlord as an additional insured under
all insurance policies Subtenant is required to obtain hereunder and pursuant
to the Master Lease, including but not limited to, those policies required
under Section 13(B) of the Master Lease.

     7.   Hazardous Material.

          7.1  Use of Hazardous Material. Subtenant shall not cause or permit
any Hazardous

                                       4
<PAGE>   5
Material (as hereafter defined) to be generated, brought onto, used, stored, or
disposed of in or about the Premises by Subtenant or its agents, employees,
contractors, subtenants, or invitees. If, during the Term hereof, Subtenant
becomes aware of (a) any actual or threatened release of any Hazardous Material
on, under, or about the Premises or (b) any inquiry, investigation, proceeding,
or claim by any government agency or other person regarding the presence of
Hazardous Material on, under, or about the Premises, Subtenant shall give
Sublandlord written notice of the release or investigation within five (5) days
after learning of it and shall simultaneously furnish to Sublandlord copies of
any claims, notices of violation, reports, or other writings received by
Subtenant that concern the release or investigation.

          7.2. Remediation Obligations. If the presence of any Hazardous
Material brought onto the Premises by Subtenant or Subtenant's employees,
agents, contractors, or invitees results in contamination of the Premises,
Subtenant shall promptly take all necessary actions, at Subtenant's sole
expense, to return the Premises to the condition that existed before the
introduction of such Hazardous Material. Subtenant shall first obtain approval
of the proposed remedial action from the Master Landlord and the Sublandlord.
This provision does not limit the indemnification obligation set forth herein.

          7.3 Definition of "Hazardous Material." As used herein, the term
"Hazardous Material" shall mean any hazardous or toxic substance, material, or
waste that is or becomes regulated by the United States, the State of Illinois,
or any local government authority having jurisdiction over the Building.
Hazardous Material includes any "hazardous substance," as that term is defined
in the Comprehensive Environmental Response, Compensation, and Liability Act of
1980 (CERCLA) (42 United States Code sections 9601-9675), "Hazardous waste," as
that term is defined in the Resource Conservation and Recovery Act of 1976
(RCRA) (42 United States Code sections 6901-6992k), any pollutant, contaminant,
or hazardous, dangerous, or toxic chemical, material, or substance, within the
meaning of any other applicable federal, state, or local law, regulation,
ordinance, or requirement (including consent decrees and administrative orders
imposing liability or standards of conduct concerning any hazardous, dangerous,
or toxic waste, substance, or material, now or hereafter in effect), petroleum
products, radioactive material, including any source, special nuclear, or
byproduct material as defined in 42 United States Code sections 2011-2297g-4,
and polychlorinated biphenyls (PCBs) and substances or compounds containing
PCBs.

     8. Indemnity. Subtenant shall, at Subtenant's sole expense and with
counsel reasonably acceptable to Sublandlord, indemnify, defend, protect and
hold harmless Master Landlord, Sublandlord and their respective shareholders,
directors, officers, employees, partners, affiliates and agents from and
against all claims, demands, losses, liabilities, lawsuits, judgments and
costs and expenses (including reasonable attorney's fees) caused by, arising
from or resulting from (a) the failure of Subtenant to perform any of the
covenants, agreements, terms, provisions, or conditions contained herein or in
the Master Lease that Subtenant is obligated to perform under the provisions of
this Sublease, (b) Subtenant's use or occupancy of the Premises, (c) the
release of any Hazardous Material in or about the Premises, or the violation of
any Environmental Law, by Subtenant or Subtenant's agent, contracts, or
invitees. This indemnification includes losses attributable to diminution in
the value of the Premises, loss or restriction of use of the Premises, adverse
effect on the marketing of any space on the Premises, and all other
liabilities, obligations, penalties, fines, claims, actions (including remedial
or enforcement actions of any kind and administrative or judicial proceedings,
orders, or judgments), damages (including consequential and punitive damages),
and reasonable costs (including attorney, consultant, and expert fees and
expenses) resulting from the release or violation. This indemnification shall
survive the expiration or termination of this Sublease.

                                       5
<PAGE>   6
      9.   Cancellation of Master Lease. In the event the Master Lease is
canceled or terminated for any reason, or involuntarily surrendered by operation
of law before the expiration date of this Sublease, then this Sublease shall
also terminate; provided, however, Subtenant agrees, at the sole option of the
Master Landlord, to attorn to the Master Landlord for the then balance of the
Term of this Sublease and on the then executory terms of this Sublease. That
attornment shall be evidenced by an agreement in form and substance reasonably
satisfactory to the Master Landlord. Subtenant agrees to execute and deliver
such an agreement at any time within ten (10) business days after request by
the Master Landlord. Subtenant waives the provisions of any law now or later in
effect that may provide Subtenant any right to terminate this Sublease or to
surrender possession of the Premises in the event any proceeding is brought by
the Master Landlord to terminate the Master Lease.

     10.  Assignment or Subleasing. Subtenant shall have no right to assign
this Sublease or to sublet all or any portion of the Premises without the prior
written consent of both Sublandlord and Master Landlord, which consents will
not be unreasonably withheld.

     11.  Security Deposit.

          11.1 Within five business days following Subtenant's execution of
this Sublease, Subtenant shall deposit with Sublandlord the amount of
$11,775.59 ("Security Deposit"). The Security Deposit shall be held by
Sublandlord as security for the faithful performance by Subtenant of all the
terms, covenants, and conditions of this Sublease to be kept and performed by
Subtenant during the Term. If Subtenant defaults with respect to any provision
of this Sublease, including, but not limited to, any provision relating to the
payment of rent, Sublandlord may (but shall not be required to) use, retain and
apply all or any part of the Security Deposit for the payment of any rent or
any other sum in default, or for the payment of any amount which Sublandlord
may spend or become obligated to spend by reason of Subtenant's default, or to
compensate Sublandlord for any other loss or damage which Sublandlord may
suffer as a result of Subtenant's default. If any portion of the Security
Deposit is so used or applied, Subtenant shall, within five (5) days after
written demand therefor, deposit with Sublandlord in cash or a cashier's check
an amount sufficient to restore the Security Deposit to its original amount,
and Subtenant's failure to do so shall constitute a material default under this
Sublease.

          11.2 No trust relationship is created between Sublandlord and
Subtenant with respect to the Security Deposit. Sublandlord shall not be
required to keep the Security Deposit separate from its general funds, and
Subtenant shall not be entitled to interest on the Security Deposit. If
Subtenant shall fully and faithfully perform every provision of this Sublease,
the Security Deposit, or any balance thereof, shall be returned to Subtenant
(or, at Sublandlord's option, to the last assignee of Subtenant's interest
hereunder) within fifteen (15) days following the expiration of the Sublease
Term or vacation of the Premises by Subtenant, whichever event occurs last. In
the event of a termination of Sublandlord's interest in this Sublease, the
Security Deposit, or any portion thereof not previously applied, may be
released by Sublandlord to Sublandlord's transferee and, if so released,
Subtenant agrees to look solely to such transferee for proper application of
the Security Deposit in accordance with the terms of this Section and the
return thereof in accordance herewith.

     12.  General Provisions.

          12.3 Severability. If any provision of this Sublease or the
application of any provision of this Sublease to any person or circumstance is,
to any extent, held to be invalid or unenforceable, the remainder of this
Sublease or the application of that provision to persons or

                                       6
<PAGE>   7
circumstances other than those as to which it is held invalid or unenforceable,
shall not be affected, and each provision of this Sublease shall be valid and
be enforced to the fullest extent permitted by law.

     12.4  Entire Agreement; Waiver. This Sublease constitutes the final,
complete and exclusive statement between the parties to this Sublease
pertaining to the Premises, supersedes all prior and contemporaneous
understandings or agreements of the parties, and is binding on and inures to
the benefit of their respective heirs, representatives, successors, and
assigns. No party has been induced to enter into this Sublease by, nor is any
party relying on, any representation or warranty outside those expressly set
forth in this Sublease. Any agreement made after the date of this Sublease is
ineffective to modify, waive, release, terminate, or effect an abandonment of
this Sublease, in whole or in part, unless that agreement is in writing, is
signed by the parties to this Sublease, and specifically states that agreement
modifies this Sublease.

     12.5  Captions. Captions to the sections in this Sublease are included for
convenience only and do not modify any of the terms of this Sublease.

     12.6  Further Assurances. Each party to this Sublease shall at its own
cost and expense execute and deliver such further documents and instruments and
shall take such other actions as may be reasonably required or appropriate to
evidence or carry out the intent and purposes of this Sublease.

     12.7  Governing Law. This Sublease shall be governed by and in all
respects construed in accordance with the laws of the State of Illinois.

     12.8  Capitalized Terms. All terms spelled with initial capital letters in
this Sublease that are not expressly defined in this Sublease shall have the
respective meanings given such terms in the Master Lease.

                                       7
<PAGE>   8
          12.9 Word Usage. Unless the context clearly requires otherwise, (a)
the plural and singular numbers shall each be deemed to include the other; (b)
the masculine, feminine, and neuter genders shall each be deemed to include the
others; (c) "shall," "will," "must," "agrees," and "covenants" are each
mandatory; (d) "may" is permissive; (e) "or" is not exclusive; and (f)
"includes" and "including" are not limiting.

     The parties have executed this Sublease as of the date specified above.

Sublandlord:                       ADVANCED RADIO TELECOM CORP., a Delaware
                                   corporation

                                   By: /s/ R. S. MCCAMBRIDGE
                                       ---------------------------------
                                           R. S. McCambridge

                                   Its: President & C.O.O.
                                        --------------------------------

Address of Sublandlord:            500-108th Avenue NE, Suite 2600
                                   Bellevue, Washington 98004
                                   Attention: General Counsel

Subtenant:                         QUINTUS CORPORATION, a California
                                   corporation

                                   By: [Signature Illegible]
                                       ---------------------------------

                                   Its: Business Admin Manager
                                        --------------------------------

Address of Subtenant:              Four Westbrook Corporate Center
                                   Suite 620
                                   Westchester, Illinois 60154
                                   Attention:
                                              --------------------------

                                       8

<PAGE>   9
                           WESTBROOK CORPORATE CENTER
                             WESTCHESTER, ILLINOIS

                                  OFFICE LEASE

                                    Between

                         LASALLE NATIONAL TRUST, N.A.,
                           AS SUCCESSOR TRUSTEE UNDER
                                TRUST NO. 115264

                                    LANDLORD

                                      and

                          Advanced Radio Telecom, Inc.

                                     TENANT

                            DATED: December 18, 1996

Lease Prepared by:  Sidney G. Saltz
                    Jenner & Block
                    One IBM Plaza
                    Chicago, Illinois 60611
                    (312) 222-9350

<PAGE>   10
                                     INDEX

<TABLE>
<CAPTION>
                                                                   Page
                                                                   ----
<S>                                                                <C>
 1.  Basic Lease Provisions                                           1

 2.  Lease                                                            1

 3.  Term                                                             2

 4.  Possession                                                       2

 5.  Purpose                                                          2

 6.  Rent                                                             2

 7.  Additional Rent                                                  2

 8.  Lock Box                                                         4

 9.  Services                                                         5

10.  Tenant's Obligations                                             5

11.  Quiet Enjoyment                                                  6

12.  Certain Rights Reserved To Landlord                              6

13.  Risk Allocation And Insurance                                    7

14.  Indemnity                                                        9

15.  Assignment Or Subletting                                         9

16.  Condition Of Premises                                           10

17.  Use of Premises                                                 10

18.  Repairs And Compliance                                          12

19.  Fire Or Casualty                                                12

20.  Eminent Domain                                                  12

21.  Surrender                                                       13

22.  Removal Of Tenant's Property                                    13

23.  Holding Over                                                    13

24.  Subordination Or Superiority                                    14

25.  Encumbering Title                                               14

26.  Liens And Rights To Content                                     14

27.  Defaults                                                        14

28.  Remedies                                                        15

29.  Opportunity To Cure                                             15

30.  Landlord's Right To Cure                                        15

31.  Remedies Cumulative                                             16

32.  Default Under Other Leases                                      16

33.  No Reinstatement                                                16
</TABLE>

                                       i

<PAGE>   11

<TABLE>
<S>                                                              <C>
34.  Alteration                                                  16

35.  Security Deposit                                            17

36.  Relocation Of Tenant                                        17

37.  Parking Areas                                               17

38.  Brokerage                                                   18

39.  Estoppel Certificates                                       18

40.  Tenant's Statement                                          18

41.  Notices And Consents                                        18

42.  Modification Of Lease                                       18

43.  Landlord Means Owner                                        18

44.  Miscellaneous Provisions                                    19

45.  Short Form Lease                                            19

46.  Binding On Successors                                       19

47.  Execution Of Lease By Landlord                              19

48.  Light And Air                                               19

49.  Force Majeure                                               19

50.  Landlord's Expenses                                         19

51.  Tenant's Authorization                                      19

52.  Exculpatory Clause                                          19
</TABLE>

                                       ii

<PAGE>   12
                                  OFFICE LEASE
                           WESTBROOK CORPORATE CENTER
                             WESTCHESTER, ILLINOIS

     THIS LEASE is made and entered into this 18th day of December 1996, by and
between, ______________________________________  but as Successor Trustee under
a Trust Agreement dated February 9, 1990, and known as Trust No. 115264
("Landlord") and Advanced Radio Telecom, Inc., a Delaware corporation,
qualified to transact business in Illinois _______________________________
("Tenant").

     1.   BASIC LEASE PROVISIONS.

          A.   Property Address: Four Westbrook Corporate Center, Westchester,
     Illinois 60154.

          B.   Tenant's Address until the Commencement Date: 1415 West 22nd
     Street, Oak Brook, Illinois 60521
     Thereafter, the Premises.

          C.   Agent of Beneficiaries of Landlord: Podolsky and Associates
     L.P., One Westbrook Corporate Center, Suite 400, Westchester, Illinois
     60154 ("Agent").

          D.   Lease Term: Seven (7) years

          E.   Commencement Date: January 1, 1997

          F.   Expiration Date: December 31, 2003

          G.   Monthly Base Rent: $12,245.83
               See Rider

          H.   Payee of Rent: Podolsky and Associates Management Account II

          I.   Address for Payment of Rent: Lock Box 72414, Chicago, Illinois
               60678

          J.   Suite Number of Premises: 620

          K.   Rentable Area of Premises: 5,878 square feet

          L.   Rentable Area of this Project: 1,101,920 square feet

          M.   Initial Tenant's Pro Rata Share: .5334 percent

          N.   Security Deposit: $48,983.32 (See Rider)

          O.   Broker: Podolsky and Associates L.P. and Chicago Realty Group

          P.   Base Operating Expenses: Operating Expenses per square foot paid
               or incurred in 1997.

          Q.   Base Taxes: Taxes per square foot paid in 1997 (assessed in
               1996).

          R.   Number of Parking Spaces: Nineteen (19)

          S.   Number of Parking Spaces to be located in Executive Parking
               Structure: Three (3)

          T.   Rider: Check if a Rider is attached. [X]

     2.  LEASE. Landlord, for and in consideration of the rents herein reserved
and of the covenants and agreements herein contained on the part of the Tenant
to be performed, hereby leases to the Tenant, and the Tenant accepts from the
Landlord, certain space as shown on Exhibit A attached hereto and made a part
hereof, designated as the Suite specified in Section 1(J) ("Premises") and
located in the office portion of one of the buildings (individually or
collectively, as the context requires, the "Building"), situated

<PAGE>   13
on and a part of the property (the "Property") legally described in Exhibit B
attached hereto and made a part hereof. The property is part of a larger
complex known as Westbrook Corporate Center which consists of a total of five
(5) office buildings (the "Project").

          3.   TERM. Subject to Section 4, the term of this Lease (hereinafter
"Term") shall commence on the date (hereinafter "Commencement Date") which is
the earlier to occur of:

               A.   The date specified in Section 1(E); or

               B.   The date Tenant first occupies all or part of the Premises.

The Term shall expire on the date ("Expiration Date") specified in Section 1(F)
unless sooner terminated as otherwise provided elsewhere in the Lease.

          4.   POSSESSION. Landlord agrees to perform the work, if any,
specified in the Work Letter Agreement attached hereto as Exhibit C and by this
reference made a part hereof. See Rider. The Work shall be deemed
"substantially completed" when the Work specified in the Work Letter Agreement
is fully completed except for so-called "punch list" items, none of which
interfere with Tenant's use and occupancy of the Premises for the conduct of
its business and a certificate of occupancy is issued (unless the issuance is
prevented by the act or omission of Tenant). Landlord shall notify Tenant as
soon as such Work is substantially completed. In the event that there is a
dispute as to whether such Work is substantially completed, the dispute shall
be resolved by the architect who prepared the plans and specifications. Taking
of possession by Tenant shall be deemed conclusively to establish that such
Work has been completed in accordance with the Work Letter Agreement, except
for any agreed "punch list" items. If the Premises are not substantially
completed on or before the date specified in Section 1(E) hereof, this Lease
shall remain in effect, the Landlord shall have no liability to Tenant as a
result of any delay in occupancy, but, unless the delay is occasioned by any
act or omission of Tenant, the Commencement Date determined in accordance with
Section 3 hereof shall be delayed to the date on which such work is
substantially completed, and the Expiration Date shall be delayed by a like
number of days. See Rider.

          5.   PURPOSE. The Premises shall be used and occupied only for the
purpose of general offices and related office uses.

          6.   RENT. Tenant agrees to pay the Monthly Base Rent to the Payee
specified in Section 1(H), at the address specified in Section 1(I), or to such
other payee or at such other address as may be designated by notice in writing
from Landlord to Tenant, without prior demand therefor and without any
deduction whatsoever. Unless otherwise provided to the contrary in this Lease,
Monthly Base Rent shall be paid monthly in advance on the first day of each
month of the Term, except that the first installment of Monthly Base Rent shall
be paid by Tenant to Landlord upon execution of this Lease by Tenant. Monthly
Base Rent shall be pro-rated for partial months at the beginning and end of the
Term. All charges, costs and sums required to be paid by Tenant to Landlord
under this Lease in addition to Monthly Base Rent shall be deemed "Additional
Rent," and Monthly Base Rent and Additional Rent hereinafter collectively be
referred to as "Rent." Tenant's covenant to pay Rent shall be independent of
every other covenant in this Lease. Rent not paid within five (5) days after
notice shall bear interest from the due date at a rate per annum equal to two
percent (2%) in excess of the announced base rate of interest of American
National Bank and Trust Company of Chicago, as of the date of such default
("Default Rate").

          7.   ADDITIONAL RENT. A. It is contemplated by Landlord that the
Project will be under unified management. If and so long as such unified
management shall continue, Additional Rent shall be payable pursuant to
Sections 7(B) and 7(C) hereof. If such unified management shall be
discontinued, then the provisions of Section 7(G) shall control. It is mutually
understood that the Monthly Base Rent does not anticipate any increase in the
amount of taxes on the Project or in the cost of operation and maintenance of
the Project. In order that the Rent payable hereunder shall reflect all such
increases, Tenant agrees to pay as Additional Rent, an amount calculated as
hereinafter set forth.

               B.   Definitions:

                    (i)  First Year: The calendar year in which the Lease
               commences.

                    (ii)  Subsequent Year: Any calendar year following the First
               Year.

                    (iii)  Taxes: All taxes and assessments of every kind and
               nature which the owner or owners of the Project ("Owners") shall
               pay or become obligated to pay in respect of a calendar year
               because of or in connection with the ownership, leasing and
               operation of the Project, subject to the following:

                                      -2-
<PAGE>   14

                        (a)   the amount of ad valorem real and personal
            property taxes against Owner's real and personal property to be
            included shall be the amount shown by the latest available tax
            bills on the last day of the calendar year in respect of which
            Taxes are being determined. There shall be deducted from Taxes, the
            amount of any refunds in Taxes relative to the Project, in the year
            received by Owners;

                        (b)   the amount of special taxes or special
            assessments to be included shall be limited to the amount of the
            installment (plus any interest (other than penalty interest)
            payable thereon) of such special tax or special assessment required
            to be paid during the calendar year in respect of which Taxes are
            being determined;

                        (c)   the amount of any excise, sales, income or
            privilege tax or any other tax of any kind levied by the State of
            Illinois or any political subdivision thereof, on rents or other
            income from the Project shall be included, without limitation, but
            shall not be greater than the amount which would have been payable
            on account of such tax by Owners during the calendar year in
            respect of which Taxes are being determined had the income received
            by Owners from the Project been the sole taxable income of Owners
            for such calendar year;

                        (d)   there shall be excluded from Taxes all federal
            income taxes, state and local net income taxes, federal excess
            profits taxes, franchise, capital stock and federal or state
            inheritance or estate taxes; however, if and to the extent that,
            due to a change in the method of assessment or taxation, any
            franchise, capital stock, income, profits or excess profits or
            other tax or charge shall be substituted for the Taxes or any part
            thereof now or hereafter imposed because of or in connection with
            the ownership, leasing and operation of the Project, such taxes,
            computed as if Owners owned or operated no property other than the
            Project, shall be deemed included in the term Taxes.

                        (e)   Taxes shall also include fees and costs incurred
            by Owners during or prior to the Lease term for the purpose of
            contesting or protesting tax assessments or rates, to the extent
            that such fees and costs relate to savings realized during the term
            of the Lease and any extensions thereof.

                        (f)   See Rider.

                  (iv)  Operating Expenses: All expenses, incurred or paid on
      behalf of Owners in respect of the ownership, management, operation,
      maintenance and repair of, and necessary replacements in, the Project
      which, in accordance with generally accepted accounting practice as
      applied to the operation and maintenance of first-class mixed use office
      and commercial buildings, are properly chargeable to the ownership,
      management, operation, maintenance and repair of, and necessary
      replacements in, the Project including, without limitation, the cost of
      window washing, scavenger service, repair or replacement of any heating,
      ventilating and air conditioning equipment, wages and union benefits of
      janitors, cleaning personnel, engineers and other employees (including
      the amount of any social security taxes, unemployment insurance
      contributions and "fringe benefits"), insurance premiums, fuel costs and
      utility costs and management fees (not to exceed three percent (3%) of
      gross receipts). Operating Expenses shall specifically include the costs,
      as reasonably amortized by Owners with interest at a rate per annum equal
      to two percent (2%) per annum in excess of the announced base rate of
      interest of American National Bank and Trust Company of Chicago in effect
      as of the completion of any capital improvement, on the unamortized
      amount of any capital improvement made after the First Year which reduces
      other Operating Expenses, but in an amount not to exceed in any one year
      the reduction of such expense for that year. Operating Expenses shall not
      include: (a) any interest expense on mortgages placed upon the Project;
      (b) franchise or income taxes imposed upon Owners; (c) the cost of any
      work or service performed in any instance for any tenant (including
      Tenant) at the cost of such tenant; (d) expenses incurred by Owners as a
      result of a fire or other casualty or as a result of a taking by way of
      eminent domain; (e) expenses incurred in leasing or procuring new
      tenants; (f) legal expenses in enforcing the terms of any leases; (g)
      wages, salaries or other compensation paid to any executive employee
      above the grade of building manager; (h) any expenses incurred solely due
      to one tenant (including Tenant) and paid for by that tenant; or (i) any
      uninsured casualty required herein to have been insured by Landlord. In
      the event any buildings are not fully occupied during the First year or
      any Subsequent Year, the variable Operating Expenses for that year shall
      be equitably adjusted to reflect the Operating Expenses as though the
      Building were fully occupied. Further, if Owners are not furnishing any
      particular work or service (the cost of which if performed by Owners
      would constitute an Operating Expense) to a tenant who had undertaken to
      perform such work or service in lieu of the performance thereof by
      Owners, Operating Expenses shall be deemed for the purposes of this
      Section to be increased by an amount equal to the additional Operating
      Expenses which would reasonably have been incurred during such period by
      Owners if they had at its own expense furnished such work or service to
      such tenant.

                                      -3-
<PAGE>   15
                    (v)  Tenant's Pro Rata Share: As of the date of this Lease,
          the percentage set forth in Section 1(M) Tenant's Pro Rata Share shall
          be adjusted from time to time so as to reflect the then current
          proportion (expressed as a percentage) of the rentable area of the
          Premises to the rentable area of all buildings on the Project;
          provided, however, that if and so long as any portion of the Project
          is leased to "stand-alone tenants" as hereinafter defined, the
          percentage set forth in Section 1(M) shall not be applicable to
          Tenant's Pro Rata Share of Operating Expenses. In such event, for the
          purposes of calculating Tenant's Pro Rata Share of Operating
          Expenses, there shall be excluded from the rentable area of all
          buildings on the Project, the rentable area of any portions of the
          Project leased to "stand-along tenants," which term shall mean major
          retail or service tenants occupying the commercial, rather than the
          office portion of the Project, whose leases do not provide for the
          payment of Operating Expenses on the same basis as the remaining
          commercial tenants on the Project.

               C.   As soon as practicable after January 1 in the first
     Subsequent Year and in each Subsequent Year thereafter during the Term of
     this Lease, and in the Subsequent Year following the year in which this
     Lease expires, Landlord shall deliver to Tenant a statement in writing
     setting forth the amount of Operating Expenses and Taxes during the
     immediately preceding year. Within thirty (30) days after the delivery of
     all such statements in each Subsequent Year, Tenant shall pay to Landlord
     as Additional Rent, (i) a portion of Operating Expenses calculated by (a)
     multiplying Tenant's Pro Rata Share of Operating Expenses by the amount of
     Operating Expenses shown in Landlord's statement, and (b) subtracting
     therefrom an amount calculated in turn by multiplying Base Operating
     Expenses specified in Section 1(P) hereof by the Rentable Area of the
     Premises; plus (ii) a portion of Taxes calculated by (a) multiplying
     Tenant's Pro Rata Share by the amount of Taxes shown in Landlord's
     statement, and (b) subtracting therefrom an amount calculated in turn by
     multiplying Base Taxes specified in Section 1(O) hereof by the Rentable
     Area of the Premises; minus (iii) the amount of Additional Rent paid by
     Tenant for such Subsequent Year pursuant to Sections 7(D) and (E) hereof.
     In the event that due to any payment made in accordance with said Sections
     7(D) and (E), the Additional Rent paid in the immediately preceding
     Subsequent Year exceeds the Additional Rent due from Tenant for such
     period, Landlord shall pay to Tenant the excess amount, without interest,
     within thirty (30) days after Landlord's statement. If the term ends other
     than on the last day of a Subsequent Year, Tenant's Additional Rent shown
     on the statement delivered after the end of the Term shall be reduced
     proportionately and the payment due from Landlord or Tenant shall also be
     apportioned and paid as aforesaid.

               D.   Landlord may make reasonable estimates, forecasts or
     projections ("Projection") of Operating Expenses and Taxes for any
     Subsequent Year. Landlord may deliver to Tenant a written statement
     setting forth a Projection and a calculation of a monthly amount of
     Additional Rent payable by Tenant by reason thereof, to become effective
     as of delivery of the Projection. Tenant shall pay to Landlord the monthly
     amount of Additional Rent determined pursuant to the Projection; provided,
     however, that the Additional Rent shall be adjusted when the actual amount
     of Additional Rent can be determined.

               E.   After delivery of Landlord's statement, as provided in
     Section 7(C), and determination of the amount of the payment of Additional
     Rent to be made to Landlord, or refunded to Tenant, as the case may be,
     the monthly installments of Additional Rent then being paid by Tenant
     (either by reason of Section 7(D) hereof or by reason of a prior
     readjustment pursuant to this Section 7(E)) shall (i) be increased by
     one-twelfth of the amount of such payment if it is made by Tenant to
     Landlord, or (ii) be decreased by one-twelfth of the amount of such refund
     made by Landlord to Tenant, subject, however, to Landlord's right under
     Section 7(D) to make other reasonable Projections.

               F.   Anything contained in this Section 7 to the contrary
     notwithstanding, the Rent shall not be adjusted or decreased below the
     amount of Monthly Base Rent otherwise provided for in this Lease.

               G.   If the unified management of the Project shall be
     discontinued, then Taxes and Operating Expenses shall be limited to Taxes
     and Operating Expenses of Landlord relative to the Property, except that
     Operating Expenses shall include any such expenses which are incurred or
     paid by Landlord pursuant to the Westbrook Corporate Center Declaration of
     Easements, Covenants and Restrictions dated April 11, 1988 and recorded
     April 13, 1988, in the office of the Recorder of Deeds of Cook County,
     Illinois as Document No. 88-153449, and shall exclude payments made by
     other Owners to Landlord for such expenses pursuant thereto. In such
     event, Tenant's Pro Rata Share shall be adjusted from time to time so as
     to reflect the then current proportion (expressed as a percentage) of the
     rentable area of the Premises to the rentable area of all buildings on the
     Property (subject to the adjustment for "stand-alone" tenants).

          8.   LOCK BOX. Landlord may from time to time designate a lock box
     collection agent for the collection of rents or other charges due
     Landlord. In such event, the date of payment shall be the date of receipt
     by the lock box collection agent of such payment (or the date of
     collection of any such sum if

                                      -4-
<PAGE>   16

payment is made in the form of a negotiable instrument thereafter dishonored
upon presentment); however, for the purposes of this Lease, no such payment or
collection shall be deemed "accepted" by Landlord if an Event of Default shall
have occurred, and if Landlord thereafter remits a check payable to Tenant in
the amount received by the lock box collection agent within twenty one (21)
days after the amount sent by Tenant is received by the lock box collection
agent or, in the case of a dishonored instrument, within twenty one (21) days
after collection. Neither the negotiation of Tenant's negotiable instrument by
the lock box collection agent, nor, the possession of the funds by Landlord
during the twenty one (21) day period, nor the return of any such sum to Tenant
shall be deemed to be inconsistent with the rejection of Tenant's tender of
such payment for all purposes as of the date of Landlord's lock box collection
agent's receipt of such payment (or collection), nor shall any of such events
be deemed to be a waiver of any breach by Tenant of any terms, covenant or
condition of this Lease nor a waiver of any of Landlord's rights or remedies.

          9.   SERVICES. Landlord shall provide the following services, the
cost of which shall be included in Operating Expenses:

               A.   Standard janitor service as furnished in first class office
     buildings in the Chicago area in and about the Premises, Saturdays,
     Sundays and holidays excepted. Tenant shall not provide any janitor
     service.

               B.   Heat and air conditioning of the Premises and common areas,
     daily from 8:00 A.M. to 6:30 P.M., Saturdays 8:00 A.M. to 1:00 P.M.,
     Sundays and holidays excepted (hereinafter "Business Hours"), whenever
     heat or air conditioning shall, in Landlord's judgment, be required to
     maintain comfortable temperature. In the event Landlord determines that,
     as a result of the use by Tenant in the Premises of electric power for
     lights and outlets in excess of 3.5 watts per square foot, or occupancy of
     the Premises by more than one person per 200 square feet of rentable area,
     supplementary air conditioning is required to maintain a comfortable
     temperature in the Premises, Landlord shall have the right to install
     supplementary air conditioning equipment in the Premises, and Tenant
     shall reimburse Landlord for the cost of such equipment and the
     installation thereof, promptly upon being billed therefor by Landlord, and
     Tenant shall thereafter, at its sole cost and expense, operate, and
     perform necessary repairs, maintenance and, if necessary, replacements
     relative to said supplementary equipment. See Rider. Without limiting
     Tenant's obligations relative to the repair and maintenance of said
     supplementary air conditioning equipment as set forth above, Tenant shall,
     at all times during the term of this Lease during which supplementary air
     conditioning equipment is installed and operating, have and keep in force
     a maintenance contract, in form and with a contractor satisfactory to
     Landlord, providing for inspection thereof at least once each calendar
     quarter (which inspection shall encompass the work described on Schedule I
     attached hereto and made a part hereof) and providing for necessary
     repairs thereto. Said contract shall provide that it will not be
     cancelable by either party thereto, except upon thirty (30) days' prior
     written notice to Landlord.

               C.   Lighting of common areas during appropriate hours, depending
     upon seasons of the year.

               D.   Water for drinking, lavatory and toilet purposes. Tenant
     shall pay, at rates fixed by Landlord, for water used for any purpose other
     than drinking, lavatory and toilet purposes.

               E.   Passenger elevator service in common with other tenants at
     all times. Any or all elevator service may be automatic. All special or
     construction elevator service shall be available to Tenant, at no
     additional charge to Tenant, but shall be subject to reasonable scheduling
     by Landlord.

               F.   Window washing of all windows in the Premises both inside
     and out, weather permitting, at intervals to be determined by Landlord, but
     no less than three (3) times per year.

Any additional work or services of the character described above and any
unusual amount of such work or service, including service furnished outside the
stipulated hours, required by Tenant, shall be paid for by Tenant at Landlord's
cost, plus 20% thereof for Landlord's overhead. See Rider. Landlord does not
warrant that any of the services above mentioned will be free from
interruptions caused by repairs, renewals, improvements, alterations, strikes,
lockouts, accidents, inability of Landlord to obtain fuel or supplies, or other
causes beyond the reasonable control of Landlord. Any such interruption of
service shall never be deemed an eviction or disturbance of Tenant's use and
possession of the Premises or any part thereof, or render Landlord liable to
Tenant for damages or relieve Tenant from performance of Tenant's obligation
under this Lease. See Rider. Landlord shall not be obligated to provide
ventilating and air conditioning after 10:00 p.m. Landlord's furnishing at its
expense of additional services or services at hours other than those specified
above shall be at Landlord's option and, if furnished, shall never be deemed a
continuing obligation of Landlord.

          10.  TENANT'S OBLIGATIONS. Tenant shall be responsible for, and shall
pay the following:

               A.   All utility costs, including without limitation, electric
     and other charges incurred in connection with lighting, and providing
     electrical power to the Premises. Tenant shall

                                      -5-
<PAGE>   17
     hold Landlord harmless from all costs or expenses Landlord may incur from
     Tenant's failure to pay utility bills or to perform any of its obligations
     with respect to the purchase of utilities.

               B.  All interior maintenance, repairs and replacements as to the
     Premises and its equipment, including, without limitation, equipment for
     fire protection, plumbing, sewage and drainage serving the Premises only,
     plus sprinkler heads, fixtures and appurtenances, the replacement of lamps
     and ballasts, as required, but excluding the heating, ventilation and air
     conditioning equipment serving the Premises. Such work shall be performed
     at Tenant's expense either by Agent's employees or contractors or by
     persons approved by Landlord.

          11.  QUIET ENJOYMENT. Landlord represents that it has full power and
authority to enter into this Lease. So long as Tenant is not in default in the
performance of its covenants and agreements in this Lease, Tenant's quiet and
peaceable enjoyment of the Premises shall not be disturbed or interfered with
by Landlord or by any person claiming by, through, or under Landlord.

          12.  CERTAIN RIGHTS RESERVED TO LANDLORD. Landlord reserves the
following rights:

               A.  To change the Building's name or street address upon 30 days'
     prior written notice to Tenant.

               B.  To install, affix and maintain all signs on the Property or
     on the exterior and/or interior of the Building.

               C.  To designate and/or approve prior to installation, all types
     of signs, window shades, blinds, drapes, awnings or other similar items,
     and all internal lighting that may be visible from the exterior of the
     Building, or from interior common areas of the Building.

               D.  On reasonable prior notice to Tenant, to exhibit the Premises
     to prospective tenants during the last twelve (12) months of the Term, and
     to others having a legitimate interest at any time during the Term.

               E.  To maintain "For Rent" signs on the Property or on the
     exterior and/or interior of the Building and upon the common areas.

               F.  To change the arrangement of entrances, doors and corridors
     in the Building.

               G.  To grant to any party the exclusive right to conduct any
     business or render any service on or to the Property, provided such
     exclusive right shall not operate to prohibit Tenant from using the
     Premises for the Purpose set forth in Section 5.

               H.  To approve the weight, size and location of safes, vaults and
     other heavy equipment and articles in and about the Premises and the
     Building (so as not to exceed the legal live load per square foot
     designated by the structural engineers for the Building).

               I.  To establish controls for the purpose of regulating all
     property and packages (both personal and otherwise) to be moved into or out
     of the Premises and Building.

               J.  To regulate delivery and service of supplies in order to
     insure the cleanliness and security of the Premises and to avoid congestion
     of the loading docks, receiving areas and freight elevators.

               K.  To have access for Landlord and other tenants of the Building
     to any mail chutes and boxes located in or on the Premises according to the
     rules of the United States Postal Service.

               L.  To close the Building after Business Hours, except that the
     Tenant and its employees and invitees shall be entitled to admission at all
     times, under such regulations and procedures as Landlord may prescribe for
     security purposes.

               M.  To take any and all reasonable measures, including
     inspections and repairs to the Premises or to the Building or Property, as
     may be necessary or desirable in the operation or protection thereof.

               N.  To retain at all times master keys or pass keys to the
     Premises.

               O.  To install, operate and maintain a building security system
     which monitors, by closed circuit television or otherwise, all persons
     entering and leaving the Building.

                                      -6-
<PAGE>   18
          P.   To install and maintain pipes, ducts, conduits, wires and
     structural elements located in the Premises which serve other parts of the
     Building or other tenants. See Rider.

          Q.   To schedule Tenant's move into and out of the Building.

          R.   During the last ninety (90) days of the Term, if during or prior
     to that time Tenant vacates the Premises, to decorate, remodel, repair,
     alter or otherwise prepare the Premises for reoccupancy.

          S.   To install within the Premises suitable controls so as to
     maintain a minimum air temperature of 50 degrees F in order to prevent the
     freezing of water pipes.

Landlord may enter upon the Premises for said purposes and may exercise any or
all of the foregoing rights hereby reserved without being deemed guilty of an
eviction or disturbance of Tenant's use or possession of the Premises and
without being liable in any manner to Tenant. Landlord shall give Tenant not
less than one (1) day's prior oral notice of any entry onto the Premises,
except that if an emergency exists, Landlord may enter without notice; if
Tenant is not available to admit Landlord in an emergency, Landlord may use
reasonable force commensurate with the circumstances, to enter the Premises.

     13.  RISK ALLOCATION AND INSURANCE.

          A.   Allocation of Risks. The parties desire, to the extent permitted
     by law, to allocate certain risks of personal injury, bodily injury or
     property damage, and risks of loss of real or personal property by reason
     of fire, explosion or other casualty, and to provide for the responsibility
     for insuring those risks. It is the intent of the parties that, to the
     extent any event is insured for or required herein to be insured for, any
     loss, cost, damage or expense arising from such event, including, without
     limitation, the expense of defense against claims or suits, be covered by
     insurance, without regard to the fault of Tenant, its officers, employees
     or agents ("Tenant Protected Parties"), and without regard to the fault of
     Landlord, its beneficiaries, Agent, their respective partners,
     shareholders, members, agents, directors, officers and employees ("Landlord
     Protected Parties"). As between Landlord Protected Parties and Tenant
     Protected Parties, such risks are allocated as follows:

               (i)  Tenant shall bear the risk of bodily injury, personal injury
          or death, or damage to the property, of third persons, occasioned by
          events occurring on or about the Premises, regardless of the party at
          fault. Said risks shall be insured as provided in Section 13(B)(i).

              (ii)  Landlord shall bear the risk of bodily injury, personal
          injury, or death or damage to the property, of third persons,
          occasioned by events occurring on or about the Property (other than
          premises leased to tenants), provided such event is occasioned by the
          wrongful act or omission of any of Landlord Protected Parties. Said
          risk shall be insured against as provided in Section 13(C)(i).

             (iii)  Tenant shall bear the risk of damage to Tenant's contents,
          trade fixtures, machinery, equipment, furniture and furnishings in
          the Premises arising out of loss by the events required to be insured
          against pursuant to Section 13(B)(ii).

              (iv)  Landlord shall bear the risk of damage to the Building
          arising out of loss by events required to be insured against pursuant
          to Section 13(C)(ii).

     Notwithstanding the foregoing, provided the party required to carry
     insurance under Section 13(B)(i) or Section 13(C)(i) hereof does not
     default in its obligation to do so, if and to the extent that any loss
     occasioned by any event of the type described in Section 13(A)(i) or
     Section 13(A)(ii) exceeds the coverage or the amount of insurance as is
     actually carried, or results from an event not required to be insured
     against or not actually insured against, the party at fault shall pay the
     amount not actually covered.

          B.   Tenant's Insurance. Tenant shall procure and maintain policies
     of insurance, at its own cost and expense, insuring:

               (i)  the Landlord Protected Parties (as "named insureds"), and
          Landlord's mortgagee, if any, of which Tenant is given written
          notice, and Tenant Protected Parties, from all claims, demands or
          actions made by or on behalf of any person or persons, firm or
          corporation and arising from, related to or connected with the
          Premises, for bodily injury to or personal injury to or death of any
          person, or more than one (1) person, or for damage to property in an
          amount of not less than $3,000,000.00 combined single limit per
          occurrence/aggregate. Said insurance shall be written on an
          "occurrence" basis and not on a "claims made" basis. If at any time
          during the term of this Lease, Tenant owns or rents

                                      -7-
<PAGE>   19

                more than one location, the policy shall contain an endorsement
                to the effect that the aggregate limit in the policy shall apply
                separately to each location owned or rented by Tenant. Landlord
                shall have the right, exercisable by giving written notice
                thereof to Tenant, to require Tenant to increase such limit if,
                in Landlord's reasonable judgment, the amount thereof is
                insufficient to protect the Landlord Protected Parties and
                Tenant Protected Parties from judgments which might result from
                such claims, demands or actions. If Tenant is unable, despite
                reasonable efforts in good faith, to cause its liability insurer
                to insure the Landlord Protected Parties as "named insureds",
                Tenant shall nevertheless cause the Landlord Protected Parties
                to be insured as "additional insureds" and in such event, Tenant
                will protect, indemnify and save harmless the Landlord Protected
                Parties from and against any and all liabilities, obligations,
                claims, damages, penalties, causes of action, costs and expenses
                (including without limitation reasonable attorney's fees and
                expenses) imposed upon or incurred by or asserted against the
                Landlord Protected Parties, or any of them, by reason of any
                bodily injury to or personal injury to or death of any person or
                more than one person or for damage to property, occurring on or
                about the Premises, caused by any party including, without
                limitation, any Landlord Protected Party, to the extent of the
                amount of the insurance required to be carried under this
                Section or such greater amount of insurance as is actually
                carried. Tenant shall cause its liability insurance to include
                contractual liability coverage fully covering the indemnity
                hereinabove set forth.

                                (ii) all contents and Tenant's trade fixtures,
                machinery, equipment, furniture and furnishings in the Leased
                Premises to the extent of at least ninety percent (90%) of their
                replacement cost under Standard Fire and Extended Coverage
                Policy and all other risks of direct physical loss as insured
                against under Special Form ("all risk" coverage). Said insurance
                shall contain an endorsement waiving the insurer's right of
                subrogation against any Landlord Protected Party, provided that
                such waiver of the right of subrogation shall not be operative
                in any case where the effect thereof is to invalidate such
                insurance coverage or increase the cost thereof (except that
                Landlord shall have the right, within thirty (30) days following
                written notice, to pay such increased cost, thereby keeping such
                waiver in full force and effect).

                        C. Landlord's Insurance. Landlord shall procure and
        maintain policies of insurance insuring:

                                (i) All claims, demands or actions made by or on
                behalf of any person or persons, firm or corporation and arising
                from, related to or connected with the Property, other than
                premises leased to tenants, for bodily injury to or personal
                injury to or death of any person, or more than one (1) person,
                or for damage to property in an amount of not less then
                $3,000,000.00 combined single limit per occurrence/aggregate.
                Said insurance shall be written on an "occurrence" basis and not
                on a "claims made" basis. If at any time during the term of this
                Lease, Landlord owns more than one location, the policy shall
                contain an endorsement to the effect that the aggregate limit in
                the policy shall apply separately to each location owned by
                Landlord.

                                (ii) The improvements at any time situated upon
                the Property against loss or damage by fire, lightning, wind
                storm, hail storm, aircraft, vehicles, smoke, explosion, riot or
                civil commotion as provided by the Standard Fire and Extended
                Coverage Policy and all other risks of direct physical loss as
                insured against under Special Form ("all risk" coverage). The
                insurance coverage shall be for not less than 90% of the full
                replacement cost of such improvements with agreed amount
                endorsement. Landlord shall be named as the insured and all
                proceeds of insurance shall be payable to Landlord. Said
                insurance shall contain an endorsement waiving the insurer's
                right of subrogation against any Tenant Protected Party,
                provided that such waiver of the right of subrogation shall not
                be operative in any case where the effect thereof is to
                invalidate such insurance coverage or increase the cost thereof
                (except that Tenant shall have the right, within thirty (30)
                days following written notice, to pay such increased cost,
                thereby keeping such waiver in full force and effect).

                                (iii) Landlord's business income, protecting
                Landlord from loss of rents and other charges during the period
                while the Premises are untenantable due to fire or other
                casualty (for the period reasonably determined by Landlord).

                                (iv) Such other risks as reasonably determined
                by Landlord.

                        D. Form of Insurance. All of the aforesaid insurance
        shall be in responsible companies. As to Tenant's insurance, the insurer
        and the form, substance and amount (where not stated above) shall be
        satisfactory from time to time to Landlord and any mortgagee of
        Landlord, and shall unconditionally provide that it is not subject to
        cancellation, material modification or non-renewal except after at least
        thirty (30) days prior written notice to Landlord and any mortgagee of
        Landlord. Originals of Tenant's insurance policies (or certificates
        thereof satisfactory to Landlord), together with satisfactory evidence
        of payment of the premiums thereon, shall be deposited with

                                      -8-
<PAGE>   20
     Landlord at the Commencement Date and renewals thereof not less than thirty
     (30) days prior to the end of the term of such coverage.

          14.  INDEMNITY. Tenant agrees to protect, indemnify and save Landlord
Protected Parties (as defined in Section 13) harmless from and against all
liabilities, obligations, claims, damages, penalties, causes of action, costs
and expenses (including, without limitation, reasonable attorneys' fees and
expenses) imposed upon or incurred by or asserted against Landlord Protected
Parties, or any of them, by reasons of (a) any failure on the part of Tenant to
perform or comply with any of the terms of this Lease; or (b) performance of any
labor or services or the furnishing of any materials or any property in respect
to the Premises or any part thereof. In case any action, suit or proceeding is
brought against Landlord by reason of any such occurrence, Tenant will, at
Tenant's expense, by counsel reasonably approved by Landlord, resist and defend
such action, suit or proceeding, or cause the same to be resisted and defended.

          15.  ASSIGNMENT OR SUBLETTING.

               A.   Tenant shall not, without Landlord's prior written consent
     (i) assign, convey or mortgage this Lease or any interest under it; (ii)
     allow any transfer thereof or any lien upon Tenant's interest by operation
     of law; (iii) sublet the Premises or any part thereof; or (iv) permit the
     occupancy of the Premises or any part thereof by anyone other than Tenant.
     If Tenant desires to assign the Lease or enter into any sublease of the
     Premises, Tenant shall deliver written notice thereof to Landlord, together
     with a copy of the proposed assignment or sublease agreement at least
     thirty (30) day's prior to the effective date of the proposed assignment,
     or the proposed commencement date of the term of the proposed sublease.

               B.   In making its determination as to whether to consent to any
     proposed assignment or sublease, Landlord may consider, among other things,
     the credit-worthiness and business reputation of the proposed assignee or
     subtenant, the intended manner of use of the Premises by the proposed
     assignee or subtenant, the estimated pedestrian and vehicular traffic in
     the Premises and to the Property which would be generated by the proposed
     assignee or subtenant, and any other factors which Landlord may deem
     relevant. Subject to the foregoing, Landlord's consent to any assignment or
     subletting shall not unreasonably be withheld. Any proposed assignment or
     sublease shall be expressly subject to the terms and conditions of the
     Lease. Any assignee shall expressly assume in writing all of Tenant's
     obligations under the Lease. Any sublease shall (a) provide that the
     sublease shall procure and maintain policies of insurance covering
     liability and covering all contents, sublessee's trade fixtures, machinery,
     equipment, furniture and furnishings in the Premises, each as required of
     Tenants' in accordance with the terms of Section 13(B)(ii) hereof, (b)
     provide for copy to Landlord of notice of default by either party, and (c)
     otherwise be reasonably acceptable in form to Landlord.

               C.   In the event that Tenant proposes to assign the Lease or to
     enter into a sublease of all or substantially all of the Premises,
     Landlord shall have the right to terminate this Lease, effective as of the
     effective date of the assignment or the commencement date of the proposed
     sublease, as the case may be. Landlord may exercise said right by giving
     Tenant written notice thereof within fifteen (15) days after receipt by
     Landlord of Tenant's notice of the proposed assignment or sublease. In the
     event that Landlord exercises such right, Tenant shall surrender the
     Premises on the effective date of the termination and this Lease shall
     thereupon terminate. Landlord may, in the event of such termination, enter
     into a lease with any proposed assignee or subtenant for the Premises.

               D.   In the event that Tenant proposes to sublease only a
     portion of the Premises, Landlord shall have the right to exclude from
     this Lease that portion of the Premises proposed to be sublet by Tenant,
     effective as of the Commencement Date of the proposed sublease. Landlord
     may exercise said right by giving written notice thereof to tenant within
     fifteen (15) days after receipt by Landlord of Tenant's notice of the
     proposed sublease, and Landlord may enter into a lease with the proposed
     subtenant for the portion of the Premises so excluded. In the event that
     Landlord exercises such right, Tenant shall surrender the portion of the
     Premises proposed to be sublet on the effective date of the exclusion, this
     Lease shall terminate with respect to that portion of the Premises so
     excluded, and Tenant shall reimburse Landlord, as additional rent, for any
     cost to Landlord of construction or installation of necessary walls and
     doors and relocation of utilities as required to divide the Premises
     (unless such cost is paid for by the subtenant, either in cash or expressly
     amortized in the Rent payable by such party). Effective as of the date that
     any portion of the Premises are excluded pursuant to this Section 15(D),
     the rent and Tenant's Pro Rata Share shall be reduced in the same
     proportion as the number of square feet of rentable area contained in the
     portion of the Premises so excluded bears to the number of square feet of
     rentable area contained in the Premises prior to such exclusion.
     Notwithstanding the exclusion of that portion of the Premises and the
     termination of the Lease as to said portion, the Lease shall continue in
     full force and effect, as so modified, as to the remaining portion of the
     Premises. If Landlord does not exercise its right under this section 15(D)
     to exclude from this Lease that portion of the Premises proposed to be
     sublet by Tenant, and if Tenant enters into the proposed sublease, Tenant
     shall pay to Landlord monthly, as additional rent hereunder, fifty percent
     (50%) of the amount calculated by subtracting from the rent and other
     consideration payable by the subtenant to Tenant for said space during any
     month, the amount of "Effective Rent" payable

                                      -9-

<PAGE>   21
      by Tenant to Landlord for such month, allocated to the subleased portion
      of the Premises. Effective Rent for any month shall mean a sum calculated
      by (a) determining the total of (i) Monthly Base Rent and Additional Rent
      under Section 7 theretofore abated, plus (ii) any cash allowances
      theretofore paid or thereafter to be paid to Tenant, plus (iii) any
      payments by Landlord under prior leases of Tenant, plus (iv) any above
      building standard construction, as reasonably determined by Landlord, (b)
      dividing said total by the total number of months in the Term, and (c)
      subtracting the quotient from the amount of Monthly Base Rent payable
      under this Lease for such month. For such purpose, Effective Rent shall
      be deemed allocated based on the relative rentable square foot area of
      the total Premises and of that portion of the Premises so subleased by
      Tenant.

                  E.    No permitted assignment shall be effective and no
      permitted sublease shall commence unless and until any default by Tenant
      hereunder shall have been cured. No permitted assignment or subletting
      shall relieve Tenant from Tenant's obligations and agreements hereunder
      and Tenant shall continue to be liable as a principal and not as a
      guarantor or surety to the same extent as though no assignment or
      subletting had been made.

            16.   CONDITION OF PREMISES. Except as expressly set forth in this
Lease or in the Work Letter Agreement, Landlord has made no promise to alter,
remodel or improve the Premises and has made no representations respecting the
condition of the Premises or the Property.

            17.   USE OF PREMISES. Tenant agrees to perform the following
covenants and to comply with all reasonable rules and regulations that Landlord
may hereafter from time to time make for the Property. Landlord shall not be
liable in any way for damage caused by the non-observance by any of the other
tenants of such similar covenants in their leases or of such rules and
regulations.

                  A.    Tenant shall occupy and use the Premises during the
      terms for the purpose specified in Section 5 hereof and none other, and
      shall not conduct itself, or permit its agents, employees or invitees to
      conduct themselves, in the Premises or in the Building, in a manner
      inconsistent with the character of the Building as a mixed use building
      of the highest class, or with the comfort or convenience of other tenants.

                  B.    Tenant shall not, without the prior written consent of
      Landlord, exhibit, sell, or offer for sale on the Premises or in the
      Building any article or thing except those articles and things
      essentially connected with the stated use of the Premises by Tenant.

                  C.    Tenant will not make or permit to be made any use of
      the Premises which, directly or indirectly, is forbidden by public law,
      ordinance or governmental regulation. Without limiting the generality of
      the foregoing, Tenant shall not use or intend to use the Premises, in any
      manner or part, to commit, or facilitate the commission of a violation of
      the Federal Comprehensive Drug Abuse Prevention and Control Act of 1970,
      as amended, or to subject the Property or any part thereof to forfeiture
      under the Illinois Controlled Substances Act, Cannabis Control Act or any
      similar statute.

                  D.    Tenant shall not sell or offer to sell, distribute or
      serve any alcoholic or other intoxicating beverage in or about the
      Premises.

                  E.    Any sign, lettering, picture, notice or advertisement
      installed within the Premises which is visible from the public areas
      within the Building shall be installed in such manner and be of such
      character and style as Landlord shall approve in writing prior to such
      installation. No sign, lettering, picture, notice or advertisement shall
      be placed on any outside window or in a position to be visible from
      outside the Building.

                  F.    Tenant shall not advertise the business, profession or
      activities of Tenant conducted in the Building in any manner which
      violates the letter or spirit of any code of ethics adopted by any
      recognized association or organization pertaining to such business,
      profession or activities, and shall not use the name of the Project or
      the Building for any purposes other than that of the business address of
      Tenant, and Tenant shall never use any picture or likeness of the Project
      or the Building in any circulars, notices, advertisements or
      correspondence without Landlord's prior written consent.

                  G.    Tenant shall not obstruct or use the public areas of
      the Building for storage, or for any purpose other than ingress and
      egress. Tenant shall not place any object against glass partitions, doors
      or windows in the corridor area.

                  H.    No additional locks or similar devices shall be
      attached to any door without Landlord's prior written consent and only
      upon the condition that Landlord shall have the keys to or combination of
      such additional locks or devices. No keys for any door other than those
      provided by Landlord shall be made. If more than one key for each lock is
      desired, Landlord will provide the same upon payment by Tenant.

                                      -10-
<PAGE>   22
            I.    All persons entering or leaving the Building may be required
to do so under such regulations and controls as Landlord may from time to time
impose. Without limiting the generality of the foregoing, all persons entering
or leaving the Building between the hours of 6 P.M. and 8 A.M. Monday through
Friday or at any time on Saturday, Sunday or holidays may be required to
identify themselves to a watchman by registration or otherwise and to establish
their right to enter or leave the Building.

            J.    All corridor doors shall remain closed at all times when not
in use.

            K.    Tenant assumes all responsibility for protecting the Premises
from theft, robbery and pilferage. Except during Tenant's normal business hours,
Tenant shall keep all doors to the Premises locked and other means of entry to
the Premises closed and secured.

            L.    Only machinery or mechanical devices of a nature directly
related to Tenant's ordinary use of the Premises shall be installed, placed or
used in the Premises and the installation and use of all such machinery and
mechanical devices is subject to the other covenants contained in this Section
17 and the other portions of this Lease.

            M.    Tenant shall not do or permit anything to be done, or keep or
permit anything to be kept, in the Premises, which would increase the fire or
other casualty insurance rate on the Building or the property therein, or which
would result in insurance companies of good standing refusing to insure the
Building or any such property on a standard risk basis. In the event that any
use of the Premises by Tenant so increases such cost of insurance, Tenant shall
pay such increased cost to Landlord on demand as Additional Rent, but such
demand, or acceptance of such payment shall not be construed as a consent by
Landlord to Tenant's such use, or limit Landlord's further remedies under this
Lease.

            N.    Tenant shall comply, and cause its employees, agents,
contractors and invitees to comply, with Landlord's restrictions relative to
smoking in the lobbies, corridors, elevators, links, lavatories or other common
areas on the Property, whether posted or otherwise communicated to Tenant.

            O.    Safes, furniture, equipment, machines and other large or bulky
articles shall be brought into and out of the Building and into and out of the
Premises only through designated service entrances, and only then at such times
and in such manner (including the proper protection of the Building and the
Premises) as the Landlord shall direct and at Tenant's sole risk and cost.

            P.    Tenant shall not in any manner deface or damage the Property,
the Building or the Premises.

            Q.    Tenant shall not permit inflammables such as gasoline,
kerosene, naphtha and benzene, or explosives or any other articles of an
intrinsically dangerous nature in the Building or the Premises.

            R.    Tenant shall ascertain from Landlord the maximum amount of
electrical current which can safely be used in the Premises, taking into account
the capacity of the electric wiring of the Building and the Premises and the
requirements of other tenants, and shall not use more than such safe capacity.
Landlord's consent to the installation of electrical equipment shall not relieve
Tenant from the obligation not to use more electricity than such safe capacity.
[SEE RIDER.]

            S.    To the extent permitted by law, Tenant shall not permit
picketing or other union activity involving its employees in the Building,
except in those locations and subject to time and other limitations to which
Landlord may give prior written consent.

            T.    Tenant shall not enter or permit to be entered into or upon
the roof of the Building or any storage, heating, ventilation, air conditioning,
mechanical or machinery housing areas.

            U.    Tenant shall not distribute literature, flyers, handouts or
pamphlets of any type in any of the common areas of the Property without the
prior written consent of Landlord.

            V.    Tenant shall not permit the use of any apparatus for sound
production or transmission in such manner that the sound so transmitted or
produced shall be audible or vibrations therefrom shall be detectable beyond the
Premises. Tenant shall not cause or permit to be caused by any electrical or
communication interference of any kind to any electrically operated equipment on
the Property resulting directly or indirectly from the installation and/or
operation of any of Tenant's equipment.

            W.    Tenant shall not permit objectionable odors or vapors to
emanate from the Premises.

                                      -11-
<PAGE>   23
                  X.   Tenant shall not contract for any work or service which
      might involve the employment of labor incompatible with the Building
      employees or employees of contractors doing work or performing services by
      or on behalf of Landlord or with the terms and conditions of any
      collective bargaining agreement to which Landlord or landlord's agents or
      contractors may be a party.

                  Y.   Tenant shall not bring or permit to be brought, any
      bicycles or other vehicles into the Building or the Premises.

                  Z.   Tenant shall not bring or permit to be brought, any
      animals (other than animals to assist disabled persons) onto the Property
      or into the Building or the Premises.

                  AA.  Tenant shall not waste water by tying, wedging or
      otherwise fastening open any faucets.

                  BB.   Tenant shall not fasten any carpeting to the floors
      other than by the method approved by Landlord. Tenant shall use protective
      mats under desks, chairs or equipment and shall take such additional
      precautions as may be necessary to protect the carpeting from damage other
      than reasonable wear and tear.

                  CC.   [SEE RIDER.]

            18.   REPAIRS AND COMPLIANCE.

                  A.    Landlord shall keep the elevators, outside walls, roof
      and all public areas of the Building in good order and repair, and shall
      perform all maintenance and repairs to the heating, ventilating and air
      conditioning equipment serving the Premises. Except to the extent tenants
      (including Tenant) are required to reimburse Landlord for such work, the
      cost thereof to Landlord shall be included in Operating Expenses.

                  B.    Tenant shall promptly pay for the repairs set forth in
      Section 10(B) hereof and Tenant shall, at Tenant's own expense, comply
      with all laws and ordinances, and all orders, rules and regulations of all
      governmental authorities and of all insurance bodies and their fire
      prevention engineers at any time in force, applicable to the Premises or
      to the Tenant's use thereof, except that Tenant shall not hereby be under
      any obligation to comply with any law, ordinance, rule or regulation
      requiring any substantial structural alteration of or in connection with
      the Premises, unless such alteration is required by reason of Tenant's use
      of the Premises, or a condition which has been created by or at the
      sufferance of Tenant, or is required by reason of a breach of any of
      Tenant's covenants and agreements hereunder. Without limiting the
      generality of the foregoing, Tenant shall make any Alterations to the
      Premises required under Title III of the Americans with Disabilities Act
      (the "ADA") by reason of Tenant's use thereof.

            19.   FIRE OR CASUALTY. If the Premises or the building of which the
Premises are a part (including machinery or equipment used in its operation)
shall be damaged or destroyed by fire or other cause and if the Premises or such
building may be repaired and restored within one hundred eighty (180) days after
such damage, then Landlord shall commence to restore the Premises or such
building within sixty (60) days after such damage, and shall repair and restore
the same with reasonable promptness. [SEE RIDER.] If the damage renders the
Premises or such building untenantable in whole or in part and cannot reasonably
be repaired or restored within one hundred eighty (180) days, or if Landlord
elects to demolish such building or cease its operation, then Landlord shall
have the right to cancel and terminate this Lease as of the date of such damage
by giving written notice thereof to Tenant at any time within fifty-five (55)
days after such damage shall have occurred. If Landlord does not elect to cancel
and terminate this Lease as herein provided, Landlord shall repair and restore
the Premises or such building with reasonable promptness. In the event any such
damage renders the Premises untenantable by reason of such damage, then Rent
shall abate during the period beginning with the date of such fire or other
casualty and ending with the date when the Premises are again rendered
tenantable by an amount bearing the same ratio to the total amount of Rent for
such period as the untenantable portion of the Premises bears to the entire
Premises.

            20.   EMINENT DOMAIN.

                  A.    Taking of the Whole. In the event that the whole or a
      substantial part of the Premises shall be condemned or taken in any manner
      for any public or quasi-public use, and as a result thereof, the Premises
      cannot be used for substantially the same purpose as prior to such taking,
      this Lease and the Term and estate hereby granted shall cease and
      terminate as of the date possession is taken, and Landlord shall be
      entitled to receive the entire award, Tenant hereby assigning to Landlord
      its interest in said award, but if Landlord elects to make comparable
      space available to the Tenant within the Building under comparable rent
      and terms as herein provided. Tenant shall accept such space and this
      Lease shall then apply to such space. [SEE RIDER.]

                                      -12-
<PAGE>   24

                B. Partial Taking. If less than the whole or a substantial part
      of the Premises shall be so condemned or taken, and after such taking the
      Premises can be used for substantially the same purpose as prior thereto,
      the Lease term shall cease only on the part so taken, as of the date
      possession shall be taken by such public authority, and Tenant shall pay
      full Rent up to that date (with appropriate refund by Landlord of such
      Rent as may have been paid in advance for any period subsequent to the
      date possession is taken) and thereafter the Rent shall be equitably
      adjusted. Landlord shall, at its expense, make all necessary repairs or
      alterations to the Building so as to constitute the Premises a complete
      architectural unit, provided that Landlord shall not be obligated to
      undertake any such repairs and alterations if the cost thereof exceeds the
      award resulting from such taking.

                C. Landlord's Right to Terminate. If more than fifty percent
      (50%) of the building of which the Premises are a part or more than
      twenty-five percent (25%) of the aggregate rentable area of the buildings
      taken in the aggregate in the Project shall be taken by the exercise or
      under the threat of the exercise of the power of eminent domain, Landlord
      may, by notice in writing to Tenant delivered on or before the day of
      surrendering possession to the public authority, terminate this Lease, and
      rent shall be paid or refunded as of the date of termination. Landlord
      shall be entitled to receive the entire award, Tenant hereby assigning to
      Landlord its interest in said award.

            21. SURRENDER. Upon the termination of this Lease, whether by
forfeiture, lapse of time or otherwise, or upon the termination of the Tenant's
right to possession of the Premises, Tenant will at once surrender and deliver
up the Premises, together with all improvements thereon, to Landlord in good
condition and repair, reasonable wear and tear excepted; conditions existing
because of Tenant's failure to perform maintenance, repairs or replacements as
required of Tenant under this Lease shall not be deemed "reasonable wear and
tear." Tenant shall surrender to Agent all keys to the Premises and make know to
Agent the explanation of all combination locks which Tenant is permitted to
leave on the Premises. Said improvements shall include all plumbing, lighting,
electrical, heating, cooling and ventilating fixtures and equipment and other
articles of personal property used in the operation of the Premises (as
distinguished from operations incident to the business of Tenant). Tenant may
remove any floor covering as to which Tenant paid the total cost of purchase and
installation; in such event, Tenant shall remove all fastenings, paper, glue,
bases and other vestiges thereof and restore the floor surface to its previous
condition, or shall pay to Landlord the cost of so restoring the floor surface
condition. Except as provided in the immediately preceding sentence, all
additions, hardware, non-trade fixtures and all improvements, in or upon the
Premises placed there by Tenant ("Alterations") shall become Landlord's property
and shall remain upon the Premises upon such termination without compensation or
allowance credit to Tenant, provided, however, that Landlord shall have the
right to require Tenant to remove any Alterations or any portion thereof,
including without limitation any floor covering purchased and installed at
Tenant's sole cost, and to restore the Premises to their condition prior to the
making thereof, repairing any damage occasioned by such removal and restoration.
Said right shall be exercised by Landlord's giving written notice thereof to
Tenant on or before twenty (20) days after any such termination. If Landlord
requires removal of any Alteration or portion thereof, and Tenant does not make
such removal in accordance with this Section at the time of such termination or
within ten (10) days after such request, whichever is later, Landlord may remove
the same (and repair any damage occasioned thereby), and dispose thereof, or at
its election, deliver the same to any other place of business of Tenant, or
warehouse the same. Tenant shall pay the costs of such removal, repair, delivery
and warehousing to Landlord on demand.

            22. REMOVAL OF TENANT'S PROPERTY. Upon the termination of this Lease
by lapse of time, Tenant shall remove Tenant's articles of personal property
incident to Tenant's business ("Trade Fixtures"); provided, however, that Tenant
shall repair any injury or damage to the Premises which may result from such
removal, and shall restore the Premises to the same condition as prior to the
installation thereof. If Tenant does not remove Tenant's Trade Fixtures from the
Premises prior to the expiration or earlier termination of the Least Term,
Landlord may, at its option, remove the same (and repair any damage occasioned
thereby and restore the Premises as aforesaid) and dispose thereof or deliver
the same to any other place of business of Tenant, or warehouse the same, and
Tenant shall pay the cost of such removal, repair, restoration, delivery or
warehousing to Landlord on demand, or Landlord may treat said Trade Fixtures as
having been conveyed to Landlord with this Lease as a Bill of Sale, without
further payment or credit by Landlord to Tenant.

            23. HOLDING OVER. Tenant shall have no right to occupy the Premises
or any portion thereof after the expiration of the Lease or after termination of
the Lease or of Tenant's right to possession pursuant to Section 28 hereof. In
the event Tenant or any party claiming by, through or under Tenant holds over,
Landlord may exercise any and all remedies available to it at law or in equity
to recover possession of the Premises, and for damages. For each and every month
or partial month that Tenant or any party claiming by, through or under Tenant
remains in occupancy of all or any portion of the Premises after the expiration
of Lease or after termination of the Lease or Tenant's right to possession,
Tenant shall pay, as minimum damages and not as a penalty, monthly rental at a
rate equal to double the rate of Monthly Base Rent and Additional Rent payable
by Tenant hereunder immediately prior to the expiration or other termination of
the Lease or of Tenant's right to possession. The acceptance by Landlord of any
lesser sum shall be construed as payment on account and not in satisfaction of
damages for such holding over.

                                      -13-

<PAGE>   25
                  24.       SUBORDINATION OR SUPERIORITY. If the mortgage or
trustee named in any mortgage or trust deed hereafter made ("Mortgagee") shall
agree that, if it becomes the owner of the Property by foreclosure or deed in
lieu of foreclosure, it will recognize the rights and interests of Tenant under
the Lease and not disturb Tenant's use and occupancy of the Premises if and so
long as Tenant is not in default under the Lease (which agreement may, at such
mortgagee's option, require attornment by Tenant), then all or a portion of the
rights and interests of Tenant under this Lease shall be subject and
subordinate to such mortgage or trust deed and to any and all advances to be
made thereunder, and to the interest thereon, and all renewals, replacements
and extensions thereof. Any such Mortgage may elect that, instead of making
this Lease subject and subordinate to its mortgage or trust deed, the rights
and interests of Tenant under this lease shall have priority over the lien of
the mortgage or trust deed, whichever alternative may be elected by the
Mortgagee. If Tenant fails to execute and deliver any such instrument, Tenant
does hereby make, constitute and irrevocably appoint Landlord as its attorney
in fact, in its name, place and stead so to do.

                  25.        ENCUMBERING TITLE. Tenant shall not do any act
which shall in any way encumber the title of Landlord in and to the Premises,
the Building or the Property, nor shall the interest or estate of Landlord in
the Premises, the Building or the Property be in any way subject to any claim
by way of lien or encumbrance, whether by operation of law or by virtue of any
express or implied contract by Tenant. Any claim to, or lien upon, the Premises,
the Building or the Property arising from any act or omission of Tenant shall
accrue only against the leasehold estate of Tenant and shall be subject and
subordinate to the paramount title and rights of Landlord in and to the
Premises, the Building and the Property.

                  26.        LIENS AND RIGHT TO CONTEST. Tenant shall not
permit the Premises, the Building or the Property to become subject to any
mechanics', laborers' or materialmen's lien on account of labor or material
furnished to Tenant or claimed to have been furnished to Tenant in connection
with work of any character performed or claimed to have been performed on the
Premises by, or at the direction or sufferance of, Tenant, provided, however,
that Tenant shall have the right to contest in good faith and with reasonable
diligence, the validity of any such lien or claimed lien if Tenant shall give
to Landlord such security as may be deemed satisfactory to Landlord to assure
payment thereof and to prevent any sale, foreclosure, or forfeiture of the
Premises, the Building or the Property by reason of non-payment thereof,
provided further, however, that on final determination of the lien or claim of
lien, Tenant shall immediately pay any judgment rendered, with all proper costs
and charges, and shall have the lien released and any judgment satisfied.

                  27.        DEFAULTS. Tenant further agrees that any one or
more of the following events shall be considered Events of Default as said term
is used herein, that is to say, if:

                             A.        Tenant shall be adjudged an involuntary
        bankrupt, or a decree or order approving, as properly filed, a petition
        or answer filed against Tenant asking reorganization of Tenant under
        the Federal bankruptcy laws as now or hereafter amended, or under the
        laws of any State, shall be entered, and any such decree or judgment or
        order shall not have been vacated or stayed or set aside within sixty
        (60) days from the date of the entry or granting thereof; or

                             B.        Tenant shall file, or admit the
        jurisdiction of the court and the material allegations contained in,
        any petition in bankruptcy, or any petition pursuant or purporting to
        be pursuant to the Federal bankruptcy laws now or hereafter amended, or
        Tenant shall institute any proceedings for relief of Tenant under any
        bankruptcy or insolvency laws or any laws relating to the relief of
        debtors, readjustment of indebtedness, reorganization, arrangements,
        composition or extension; or

                             C.        Tenant shall make any assignment for the
        benefit of creditors or shall apply for or consent to the appointment
        of a receiver for Tenant or any of the property of Tenant; or

                             D.        The Premises are levied on by any
        revenue officer or similar officer; or

                             E.        A decree or order appointing a receiver
        of the property of Tenant shall be made and such decree or order shall
        not have been vacated, stayed or set aside within sixty (60) days from
        the date of entry or granting thereof; or

                             F.        Tenant shall abandon the Premises or
        vacate the same during the Term hereof; or

                             G.        Tenant shall default in any payments of
        Rent required to be made by Tenant hereunder when due as herein
        provided and such default shall continue for five (5) days after notice
        thereof in writing to Tenant; or

                                      -14-
<PAGE>   26
          H.   Tenant shall default in securing insurance or in providing
     evidence of insurance as set forth in Section 13 of this Lease and such
     default shall continue for five (5) days after notice thereof in writing
     to Tenant; or

          I.   Tenant shall fail to contest the validity of any lien or claimed
     lien and give security to Landlord to assure payment thereof, or having
     commenced to contest the same and having given such security, shall fail
     to prosecute such contest with diligence, or shall fail to have the same
     released and satisfied and judgment rendered thereon, and such default
     continues for ten (10) days after notice thereof in writing to Tenant; or

          J.   Tenant shall default in any of the other covenants and
     agreements herein contained to be kept, observed and performed by Tenant,
     and such default shall continue for thirty (30) days after notice thereof
     in writing to Tenant or shall exist at the expiration of the Term; or

          K.   Tenant shall default in keeping, observing or performing any
     covenant or agreement herein contained to be kept, observed and performed
     by Tenant, which default may result in an imminent risk of damage to
     property (including without limitation the Property or the improvements
     thereon or injury to or death of persons, and such default shall not be
     cured immediately upon notice hereof to Tenant (which notice shall be
     oral); or

          L.   Tenant shall repeatedly be late in the payment of Rent required
     to be paid hereunder or shall repeatedly default in the keeping, observing
     or performing of any other covenants or agreements herein contained to be
     kept, observed or performed by Tenant (provided written notice of such
     payment or other defaults shall have been given to Tenant, but whether or
     not Tenant shall have timely cured any such payment or other defaults of
     which notice was given).

     28.  REMEDIES. Upon the occurrence of any one or more Events of Default,
Landlord may terminate this Lease. Upon termination of this Lease, Landlord may
re-enter the Premises with or without process of law using such force as may be
necessary, and may remove all persons, fixtures and chattels therefrom and
Landlord shall not be liable for any damages resulting therefrom. Such re-entry
and repossession shall not work a forfeiture of the Rent to be paid and the
covenants to be performed by Tenant during the full Term. Upon such
repossession of the Premises, Landlord shall be entitled to recover as
liquidated damages and not as a penalty a sum of money equal to the value of
the Rent provided herein to be paid by Tenant to Landlord for the remainder of
the Term, less the fair rental value of the Premises for said period. Upon the
happening of any one or more of the above-mentioned Events of Default, Landlord
may repossess the Premises by forcible entry or detainer suit, or otherwise,
without demand or notice of any kind to Tenant (except as hereinabove expressly
provided for) and without terminating this Lease, in which event Landlord may
relet all or any part of the Premises for such rent and upon such terms as
shall be satisfactory to Landlord (including the right to relet the Premises
for a term greater or lesser than that remaining under the Term, and the right
to relet the Premises as apart of a larger area, and the right to change the
character or use made of the Premises). For the purpose of such reletting,
Landlord may decorate or make any repairs, changes, alterations or additions in
or to the Premises that may be necessary or convenient. If Landlord does not
relet the Premises, Tenant shall pay to Landlord on demand as liquidated
damages and not as a penalty a sum equal to the amount of Rent herein to be
paid by Tenant for the remainder of the Term. If the Premises are relet and a
sufficient sum shall not be realized from such reletting after paying all of the
expenses of such decorations, repairs, changes, alterations, additions, the
expenses of such reletting and the collection of the rent accruing therefrom
(including but not by way of limitation, reasonable attorneys' fees and
brokers' commissions), to satisfy the Rent herein provided to be paid for the
remainder of the Term, Tenant shall pay to Landlord on demand any deficiency.
Landlord shall use reasonable efforts to mitigate its damages arising out of
Tenant's default; Landlord shall not be deemed to have failed to use such
reasonable efforts by reason of the fact that Landlord has leased or sought to
lease other vacant premises owned by Landlord in preference to reletting the
Premises, or by reason of the fact that Landlord has sought to relet the
Premises at a rental rate higher than that payable by Tenant under the Lease
(but not in excess of the then current market rental rate).

     29.  OPPORTUNITY TO CURE. If Tenant defaults under Section 27(J), and such
default cannot with due diligence be cured within a period of thirty (30) days,
and if notice thereof in writing shall have been given to Tenant, and if
Tenant, prior to the expiration of thirty (30) days from and after the giving
of such notice, commences to eliminate the cause of such default and proceeds
diligently and with reasonable dispatch to take all steps and do all work
required to cure such default and does so cure such default, then an Event of
Default shall not be deemed to have occurred; provided, however, that Tenant's
right to cure hereunder shall not extend beyond the expiration of the Term, and
provided further that the curing of any default in such manner shall not be
construed to limit or restrict Landlord's remedies for any other default which
becomes an Event of Default.

     30.  LANDLORD'S RIGHT TO CURE. Landlord may, but shall not be obligated
to, cure any default by Tenant specifically including, but not by way of
limitation, Tenant's failure to obtain insurance, make repairs, or satisfy lien
claims, after complying with the notice provisions established in Section 29
and whenever Landlord so elects, all costs and expenses paid by Landlord in
curing such default, including without limitation reasonable attorney's fees,
shall be so much Additional Rent due on the next rent

                                      -15-
<PAGE>   27

date after such payment together with interest (except in the case of said
attorney's fees) at the Default Rate, from date of advancement to the date of
repayment by Tenant to Landlord.

                31. REMEDIES CUMULATIVE. No remedy herein or otherwise
conferred upon or reserved to Landlord shall be considered to exclude or
suspend any other remedy but the same shall be cumulative and shall be in
addition to every other remedy given hereunder, or now or hereafter existing at
law or in equity or by statute, and every power and remedy given by this Lease
to Landlord may be exercised from time to time and as often as occasion may
rise or as may be deemed expedient. No delay or omission of Landlord to
exercise any right or power arising from any default, shall impair any such
right or power or shall be construed to be a waiver of any such default or any
acquiescence therein or affect the rights of Landlord with respect to any other
existing or subsequent defaults. Neither the rights herein given to receive,
collect, sue for or distrain for any Rent, or to enforce the terms, provisions
and conditions of this Lease, or to prevent the breach or non-observance
thereof, or the exercise of any such right or any other right or remedy
hereunder or otherwise granted or arising, shall in any way affect or impair or
toll the right or power of Landlord to declare the Lease Term hereby granted
ended, or to terminate this Lease as provided for in this Lease, or to
repossess without terminating the Lease, because of any default in or breach of
the covenants, provisions, or conditions of this Lease.

                32. DEFAULT UNDER OTHER LEASES. A default in this Lease, or in
any other lease made by Tenant for any other premises on the Project shall, at
the Option of Landlord, be deemed a default in this Lease, the other lease or
both leases.

                33. NO REINSTATEMENT. The acceptance by Landlord of any payment
of rent or other charges thereunder after the termination by Landlord of this
Lease of Tenant's right to possession hereunder shall not, in the absence of
agreement in writing to the contrary by Landlord, be deemed to restore this
Lease or Tenant's right to possession hereunder, as the case may be, but shall
be construed as a payment on account, and not in satisfaction of damages due
from Tenant to Landlord.

                34. ALTERATION.

                        A. Tenant shall not make any alterations in or additions
        to the Premises without Landlord's prior written consent in each and
        every instance. [SEE RIDER]. As to any interior, non-structural
        alteration, Landlord shall not unreasonably withhold its consent; as to
        any other alteration, Landlord's consent may be withheld in Landlord's
        discretion. In making its determination of whether to consent to any
        proposed alteration as to which its consent may not be unreasonably
        withheld, Landlord may consider, among other things, the remaining
        length of the Term, the effect of the proposed alteration on the ability
        of the Landlord to lease the Premises to a successor to Tenant, and any
        other factors which Landlord may deem relevant. If Landlord consents to
        any proposed alteration or addition (which alteration or addition
        consented to is herein referred to as the "Alteration"), Landlord may
        elect, alternatively and at Landlord's option, to either arrange and
        contract for the Alteration to be performed, or to permit Tenant itself
        to arrange and contract for the Alteration, each as hereinafter
        provided.

                        B. In the event that Landlord shall elect to permit
        Tenant to arrange and contract for the Alteration, then Tenant shall,
        before permitting commencement of the Alteration, furnish to Landlord
        for Landlord's review and approval all necessary plans and
        specifications in reasonable detail, names and addresses of proposed
        contractors, copies of contracts, and shall furnish necessary permits
        and indemnification in form and amount reasonably satisfactory to
        Landlord, against any and all claims, costs, damages, liabilities and
        expenses which may arise in connection with the Alteration, and
        certificates of insurance in form and amount reasonably satisfactory to
        Landlord from all contractors performing labor or providing materials,
        insuring Landlord against any and all liabilities which may arise out of
        or be connected in any way with the Alteration; Tenant shall pay all
        costs and expenses relative to the Alteration. Tenant shall permit
        Landlord to monitor the construction operations in connection with the
        Alteration and to restrict, as may reasonably be required, the passage
        of manpower and materials and the conducting of construction activity in
        order to avoid unreasonably disruption to Landlord or to other tenants
        of the Building or damage to the Property or the Premises. Tenant shall
        pay to Landlord, for Landlord's overhead in connection with monitoring
        the Alteration, a sum equal to ten percent (10%) of Tenant's costs for
        the Alteration. Promptly following completion of the Alteration, Tenant
        shall furnish to Landlord contractors' affidavits, full and final
        waivers of lien and receipted bills covering all labor and materials
        expended and used in connection with the Alteration. Whether or not
        Tenant shall furnish Landlord with all the foregoing, Tenant hereby
        agrees to indemnify Landlord and hold Landlord harmless from any and all
        liabilities of any kind and description which may arise out of or be
        connected in any way with any Alteration. Any Alteration performed by
        Tenant shall comply with all Landlord's insurance requirements and with
        all applicable laws, ordinances and regulations. Landlord's approval of
        plans and specifications or supervision of construction operations, if
        any, shall not imply Landlord's acknowledgment, opinion or belief that
        the Alteration complies with any such applicable laws, ordinances or
        regulations, nor relieve Tenant from any responsibility hereinabove
        imposed. Following the completion of the Alteration, Tenant shall also
        provide Landlord with "as-built" drawings showing in detail the full
        extent and nature of the Alteration.

                                      -16-
<PAGE>   28
                  C.    In the event that Landlord shall elect to directly
      arrange and contract for the Alteration on behalf of Tenant, Landlord
      shall assume full responsibility for the preparation of plans and
      specifications for the Alteration for the Tenant's approval, the
      contracting for all labor and materials required by the Alteration,
      compliance of the Alteration with all applicable laws, ordinances,
      regulations, insurance and other requirements, and monitoring of the
      Alteration. Tenant shall pay to Landlord the cost of the Alteration
      including, without limitation, the cost of preparing the plans and
      specifications, the cost of permits, fees, labor and materials required
      to complete the Alteration, and the cost, if any, to repair and/or
      redecorate the Premises as may be necessitated by the Alteration
      (collectively "Costs"). Landlord's charge to Tenant for Landlord's
      overhead in connection with Landlord's performance of the Alteration
      shall be computed at twenty percent (20%) of the total substantiated
      Costs. The Costs payable by Tenant to Landlord and Landlord's charge
      therefor shall be deemed to be Additional Rent and shall be paid by
      Tenant as the Alterations are performed, upon being billed by Landlord.

            35.   SECURITY DEPOSIT. To secure the faithful performance by
Tenant of all the covenants, conditions and agreements in this Lease set forth
and contained on the part of Tenant to be fulfilled, kept, observed and
performed including, but not by way of limitation, such covenants and
agreements in this Lease which become applicable upon the termination of the
same by re-entry or otherwise, Tenant has deposited with Agent the Security
Deposit as specified in Section 1(N) on the understanding that: (a) the
Security Deposit or any portion thereof not previously applied, or from time to
time, such one or more portions thereof, may be applied to the curing of any
default that may then exist, without prejudice to any other remedy or remedies
which Landlord may have on account thereof, and upon such application Tenant
shall pay Agent on demand the amount so applied which shall be added to the
Security Deposit so the same may be restored to its original amount; (b) should
the Property be conveyed by Landlord or should Agent cease to be the agent of
the beneficiaries of Landlord, the Security Deposit or any portion thereof not
previously applied may be turned over the Landlord's grantee or the new agent,
as the case may be, and if the same be turned over as aforesaid, Tenant hereby
releases Landlord and Agent from any and all liability with respect to the
Security Deposit and/or its application or return; (c) Landlord shall have no
personal liability with respect to said sum and Tenant shall look exclusively
to Agent or its successors for return of said sum when Tenant is entitled
hereunder to such return; (d) Agent or its successor shall not be obligated to
hold the Security Deposit as a separate fund, but on the contrary may commingle
the same with its other funds; (e) if Tenant shall faithfully fulfill, keep,
perform and observe all of the covenants, conditions and agreements in this
Lease set forth and contained on the part of Tenant to be fulfilled, kept,
performed and observed, the sum deposited or the portion thereof not previously
applied, shall be returned to Tenant without interest no later than thirty (30)
days after the expiration of the Term of this Lease or any renewal or extension
thereof, provided Tenant has vacated the Premises and surrendered possession
thereof to Landlord at the expiration of said Term or any extension or renewal
thereof as provided herein; (f) in the event that Landlord terminates the Lease
or Tenant's right to possession pursuant to Section 28 of this Lease, Agent may
apply the Security Deposit against damages suffered to the date of such
termination and/or may retain the Security Deposit to apply against such
damages as may be suffered or shall accrue thereafter by reason of Tenant's
default; (g) in the event any bankruptcy, insolvency, reorganization or other
creditor-debtor proceedings shall be instituted by or against Tenant, or its
successors or assigns, the Security Deposit shall be deemed to be applied first
to the payment of any Rent or Additional Rent due Landlord for all periods
prior to the institution of such proceedings, and the balance, if any, of the
Security Deposit may be retained or paid to Landlord in partial liquidation of
Landlord's damages.

            37.   PARKING AREAS. Tenant has been allocated a total number of
parking spaces in the Project as designated in Section 1(R). It is understood
by the parties hereto that parking on the Project is presently allocated to
tenants thereof on an unreserved basis, but that each tenant will be allocated
a certain number of parking spaces located in the executive parking structure,
on a designated basis. Landlord shall provide, for Tenant's use on a designated
basis, the number of parking spaces in the executive parking structure set
forth in Section 1(S). It is understood and agreed that the number of parking
spaces in the executive parking structure set forth in Section 1(S) is included
in the total number of parking spaces set forth in

                                      -17-
<PAGE>   29
Section 1(R), and is not in addition thereto. Landlord shall have no obligation
to Tenant to enforce the parking limits imposed on other tenants on the
Project or to enforce against third parties Tenant's right to the exclusive use
of its executive parking structure parking spaces. If, however, Tenant uses
parking in excess of that provided for herein or uses parking spaces designated
by Landlord for special use, and if such use occurs on a regular basis, and if
Tenant fails, after written notice from Landlord to reduce its excess use of the
parking areas or its use of parking spaces designated by Landlord for special
use, then such failure shall constitute a default under this Lease. Tenant
agrees that it shall, upon written request from Agent, provide Agent with
license numbers of automobiles used by its employees or require its employees to
affix a parking identification sticker to the window of the employee's
automobile, in a manner reasonably designated by Agent. Tenant shall cause its
personnel who have been designated by Tenant as the persons who are authorized
to use Tenant's allocated executive parking structure parking spaces to refrain
from parking their automobiles in the unreserved (surface) parking area of
Westbrook during the hours of 8:00 a.m. to 6:00 p.m. (or such other hours as may
be designated from time to time by Agent), Mondays through Fridays. If any such
personnel park in the unreserved parking area during such hours on a regular or
repeated basis and Tenant fails, after notice from Landlord, to cure such
breach, then Landlord shall have the right, at is option, exercisable by notice
in writing to Tenant, to reduce the number of parking spaces in the executive
parking structure allocated to Tenant in Section 1(S) by a number equal to the
number of Tenant's personnel who shall have breached said provision.

            38. BROKERAGE. Tenant warrants that it has had no dealings with any
broker or agent in connection with this Lease other than the Broker as specified
in Section 1(O) and covenants to pay, hold harmless and indemnify Landlord from
and against any and all costs (including reasonable attorneys' fees), expense or
liability for any compensation, commissions and charges claimed by any other
broker or other agent with respect to this Lease or the negotiation thereof.

            39. ESTOPPEL CERTIFICATES. Tenant shall at any time and from time to
time upon not less than 10 days' prior written notice from Landlord execute,
acknowledge and deliver to Landlord, in form reasonably satisfactory to Landlord
and/or Landlord's mortgagee, a written statement certifying that Tenant has
accepted the Premises, that this Lease is unmodified and in full force and
effect (or if there have been modifications, that the same is in full force and
effect as modified, and stating the modifications), that Landlord is not in
default hereunder, the date to which Rent has been paid in advance, if any, and
such other accurate certifications as may reasonably be requested by Landlord or
Landlord's mortgagee, and agreeing to give copies to any mortgagee of Landlord
of all notices by Tenant to Landlord. It is intended that any such statement
delivered by Tenant to Landlord pursuant to this Section may be relied upon by
any prospective purchaser of the Property and Premises, any mortgagee of the
Property and Premises and their respective successors and assigns. If Tenant
fails to provide such statement in the manner herein required, in addition to
any other remedy available to Landlord, Tenant shall be liable to Landlord for
all costs, expenses and damages resulting from such failure.

            40. TENANT'S STATEMENT. Tenant shall furnish to Landlord within ten
(10) days after written request therefor from Landlord (not more frequently than
once in any twelve (12) month period), a copy of Tenant's then most recent
audited and certified financial statement. It is mutually agreed that the
Landlord may deliver a copy of such statements to any mortgagees or prospective
mortgagee of Landlord, or any prospective purchaser of the Property, but
otherwise Landlord shall treat such statements and information therein as
confidential.

            41. NOTICES AND CONSENTS. All notices, demands, requests, consents
or approvals which may or are required to be given by either party to the other
shall be in writing and shall be deemed given when received or refused, if sent
by United States Registered or Certified Mail, postage prepaid, or if sent by
courier service, with receipt, (a) if for Tenant, addressed to Tenant at the
Premises or at such other place as Tenant may from time to time designate by
notice to the Landlord, or (b) if for Landlord, in care of the Agent, Attention:
Owner's Rep, or at such other place as Landlord may from time to time designate
by notice to Tenant. Tenant may rely upon any notice, consent or approval given
in writing by the Agent or from the attorneys for the Agent or for Landlord.

            42. MODIFICATION OF LEASE. All negotiations, considerations,
representations and understandings between Landlord and Tenant are incorporated
herein. This Lease may be modified or altered only by agreement in writing
between Landlord and Tenant.

            43. LANDLORD MEANS OWNER. The term "Landlord" as used in this Lease,
so far as covenants or obligations on the part of the Landlord are concerned,
shall be limited to mean and include only the owner or owners at the time in
question of the Premises and the Property, and in the event of any transfer or
transfers of title thereto, Landlord herein named (and in case of any subsequent
transfer or conveyances, the then grantor) shall be automatically freed and
relieved, from and after the date of such transfer or conveyance, of all
liability as respects the performance of any covenants or obligations on the
part of Landlord contained in this Lease thereafter to be performed, provided,
that any funds in the hands of such Landlord or the then grantor at the time of
such transfer, in which Tenant has an interest, shall be turned over to the
grantee, and any amount then due and payable to Tenant by Landlord or the then
grantor under any provisions of this Lease, shall be paid to Tenant.

            44. MISCELLANEOUS PROVISIONS. All of the covenants of Tenant
hereunder shall be deemed and construed to be "conditions" as well as
"covenants" as though the words specifically expressing

                                      -18-
<PAGE>   30
or importing covenants and conditions were used in each separate instance. Time
is of the essence of this Lease, and all provisions relating thereto shall be
strictly construed. Nothing contained herein shall be deemed or construed by
the parties hereto, nor by any third party, as creating the relationship of
principal/agent, or of partnership, or of joint venture by the parties hereto,
it being understood and agreed that no provision contained in this Lease nor
any acts of the parties hereto shall be deemed to create any relationship other
than the relationship of Landlord and Tenant. The captions of this Lease are
for convenience only and are not to be construed as part of this Lease and
shall not be construed as defining or limiting in any way the scope or intent
of the provisions hereof. If any term or provision of this Lease shall to any
extent be held invalid or unenforceable, the remaining terms and conditions of
this Lease shall not be affected thereby, but each term and provision of this
Lease shall be valid and be enforced to the fullest extent permitted by law.
The covenants of this Lease which, by their terms, require payment or
performance by Tenant after the expiration or earlier termination of the Lease
and the obligation to pay any liability accruing during the term of the Lease,
shall survive the expiration or earlier termination of the Lease. This Lease
shall be governed by and construed in accordance with the laws of the State of
Illinois.

     45.  SHORT FORM LEASE. This Lease shall not be recorded, but the parties
agree, at the request of either of them, to execute a Short Form Lease for
recording, containing the names of the parties, the legal description and the
Term.

     46.  BINDING ON SUCCESSORS. All of the covenants, agreements, conditions
and undertakings contained in this Lease shall extend and inure to and be
binding upon the heirs, executors, administrators, successors and assigns of
the respective parties hereto, the same as if they were in every case
specifically named, and whenever in this Lease reference is made to either of
the parties hereto, it shall be held to include and apply to wherever
applicable, the heirs, executors, administrators, successors and assigns of
such party. Nothing herein contained shall be construed to grant or confer upon
any person or persons, firm, corporation or governmental authority, other than
the parties hereto, their heirs, executors, administrators, successors or
assigns, any right, claim or privilege by virtue of any covenant, agreement,
condition or undertaking in this Lease contained.

     47.  EXECUTION OF LEASE BY LANDLORD. Submission of this instrument for
examination or signature by Tenant does not constitute a reservation of or
option for the Lease. This instrument becomes effective as a Lease upon
execution and delivery by both Landlord and Tenant.

     48.  LIGHT AND AIR. No rights to light or air over any real estate,
whether belonging to Landlord or any other party, are granted to Tenant by the
Lease.

     49.  FORCE MAJEURE. Landlord shall not be deemed in default with respect
to any of the terms, covenants and conditions of this Lease on Landlord's part
to be performed, if Landlord's failure to timely perform same is due in whole or
in part to any strike, lockout, labor trouble (whether legal or illegal), civil
disorder, failure of power, restrictive governmental laws and regulations,
riots, insurrections, war, shortages, accidents, casualties, acts of God,
delays caused directly by Tenant or Tenant's agents, employees and invitees, or
any other cause beyond the reasonable control of the Landlord.

     50.  LANDLORD'S EXPENSES. Tenant agrees to pay on demand Landlord's
expenses, including reasonable attorney's fees, expenses and administrative
hearing and court costs incurred either directly or indirectly in enforcing any
obligation of Tenant under this Lease, in curing any default by Tenant, in
connection with appearing, defending or otherwise participating in any action
or proceeding arising from the filing, imposition, contesting, discharging or
satisfaction of any lien or claim for lien, in defending or otherwise
participating in any legal proceedings initiated by or on behalf of Tenant
wherein Landlord is not adjudicated to be in default under this Lease, or in
connection with any investigation or review of any conditions or documents in
the event Tenant requests Landlord's agreement, approval or consent to any
action of Tenant which may be desired by Tenant or required of Tenant
hereunder. All such expenses shall be deemed to be Additional Rent.

     51.  TENANT'S AUTHORIZATION. If Tenant is a corporation, partnership,
association or any other entity, Tenant shall furnish to Landlord, within ten
(10) days after written request therefor from Landlord, certified resolutions
of Tenant's directors or other governing person or body authorizing execution
and delivery of this Lease and performance of Tenant of its obligations
hereunder, and evidencing that the person who physically executed the Lease on
behalf of Tenant was duly authorized to do so.

     52.  EXCULPATORY CLAUSE. This Lease is executed by LaSalle National Trust,
N.A., not personally but as Successor Trustee as aforesaid, in the exercise of
the power and authority conferred upon and vested in it as such Trustee, and
under the express direction of the beneficiary of a certain Trust Agreement
dated February 9, 1990, and known as Trust Number 115264. It is expressly
understood and agreed that nothing in this Lease contained shall be construed
as creating any liability whatsoever against said Trustee personally or said
beneficiaries or their agents, and in particular without limiting the generality
of the foregoing, there shall be no personal liability to pay any indebtedness
accruing hereunder or to perform any covenant, either express or implied,
herein contained, to keep, preserve or sequester any property of said Trust,
that said Trustee is not the agent of the beneficiaries and has no authority to
bind the beneficiaries to perform any covenant or agreement herein, and that
all personal liability of said Trustee (and said beneficiaries and

                                      -19-
<PAGE>   31
their agents to the extent permitted by law) of every sort, if any, is hereby
expressly waived by Tenant, and by every person now or hereafter claiming any
right or security hereunder; and that so far as the parties hereto are
concerned, the owner of any indebtedness or liability accruing hereunder shall
look solely to the Trust Estate from time to time subject to the provisions of
said Trust Agreement for the payment thereof. It is further understood and
agreed that the said Trustee has no agents or employees and merely holds naked
legal title to the property herein described, and has no knowledge respecting
rentals, leases, or other factual matter with respect to said premises, except
as represented to it by the beneficiaries of said Trust.

         The parties hereto have caused this Lease to be executed on the date
first above written.

                                    LANDLORD:
                                    LaSALLE NATIONAL BANK, successor Trustee To:

                                    LASALLE NATIONAL TRUST, N.A.,
                                    not individually but as Successor
ATTEST:                             Trustee as aforesaid

/s/ NANCY A. STACK                  By /s/ [SIGNATURE ILLEGIBLE]
-------------------------------        ------------------------------------
    Asst. Secretary                    Its Vice President
                                           --------------------------------

                                    TENANT:

ATTEST:                             Advanced Radio Telecom, Inc.

                                    By /s/ [SIGNATURE ILLEGIBLE]
-------------------------------        ------------------------------------
          Secretary                    Its VP and General Manager
                                           --------------------------------

                                      -20-
<PAGE>   32

                     RIDER TO OFFICE LEASE BETWEEN LA SALLE
                 NATIONAL TRUST, TRUST NO. 115264, AS LANDLORD,
                  AND ADVANCED RADIO TELECOM, INC., AS TENANT

        R-1. Addendum to Section 1(G). Effective January 1, 1998, Monthly Base
Rent shall be payable in accordance with the following schedule:

<TABLE>
<CAPTION>
    Period:                   Monthly Base Rent:
    -------                   ------------------
<S>                            <C>
1/1/98-12/31/98                 $ 12,490.75
1/1/99-12/31/99                   12,735.67
1/1/00-12/31/00                   12,980.58
1/1/01-12/31/01                   13,225.50
1/1/02-12/31/02                   13,470.42
1/1/03-12/31/03                   13,715.34
</TABLE>

        R-2. Addendum to Subsection 1(N). Provided that no Event of Default by
Tenant shall then exist, the amount of the Security Deposit shall be reduced,
upon the expiration of the third year of the Term, to $12,245.83.

        R-3. First Addendum to Section 4. If the cost of the Work exceeds the
sum of $171,000.00, Tenant shall deposit the excess with Agent promptly upon
receipt of written notice thereof from Agent.

        R-4. Second Addendum to Section 4. Landlord shall make a good faith
effort to give Tenant written notice of any delay occasioned by an act or
omission of Tenant, but Landlord shall not be deemed in default hereunder for
failing to give such notice.

        R-5. Addendum to Section 7(B)(iii)(f). There shall be excluded from
Taxes penalties incurred by Landlord due to Landlord's late payment of Taxes.

        R-6. Addendum to Section 9(B). Landlord represents that based upon the
use of the Premises as contemplated by Tenant's plans and specifications
referred to in Exhibit C and approved by Landlord, supplementary air
conditioning equipment will not be required.

        R-7. First Addendum to Section 9. If Tenant requires heat or air
conditioning in the Premises other than during Business Hours, the rate for such

<PAGE>   33
service during the initial Term (predicated on utility rates as they are in
effect as of the execution and delivery of this Lease), shall be $17.00 per hour
or fraction thereof for each wing or part thereof occupied by Tenant and
requiring such service. If utility rates increase, then Landlord shall have the
right to increase said hourly rate to compensate Landlord for the actual amount
of the additional costs of the utilities utilized to provide such service by
reason of said rate increases. After the expiration of the initial Term (i.e.,
during any additional term resulting from the exercise of an option to extend or
otherwise), Landlord shall have the right to charge the same rate for such
service as its usual and customary rate charged to other tenants on the Property
from time to time. Landlord's overhead charge shall not be made relative to said
service.

            R-8.  Second Addendum to Section 9. Anything in Section 9 to the
contrary notwithstanding, if Landlord's failure or inability to furnish any
service is the direct result of Landlord's negligence or willful misconduct, or
if Landlord is not proceeding diligently to correct such failure or inability to
furnish any service and, in either event, the Premises or any portion thereof is
rendered unusable by Tenant for a period of five (5) consecutive business days,
Tenant shall be entitled to an equitable abatement of Monthly Base Rent payable
hereunder with respect to the Premises or portion thereof rendered unusable
beginning on the sixth (6th) business day of such failure or inability of
Landlord to furnish such service until the date such service is rendered.

            R-9.  Addendum to Section 12(M). If because Landlord fails to
complete any inspections or repairs to the Premises, the Building or Property
with due diligence, the Premises become untenantable for a period in excess of
five (5) consecutive business days, Rent shall thereafter abate on a per diem
basis until the Premises are again tenantable by Tenant.

            R-10. Addendum to Section 12(P). Landlord shall not, in connection
therewith, materially interfere with Tenant's use and enjoyment of the Premises
or materially reduce the rentable area of the Premises. Unless otherwise agreed
to by Tenant, each of such items shall be located inside the walls, above
dropped ceilings or below the floor level of the Premises.

                                      -2-
<PAGE>   34
            R-11. Addendum to Section 17(R). Landlord represents to Tenant that
the capacity of the electric wiring in the Building and the Premises is
sufficient for Tenant's use as reflected in the plans and specifications
referred to in Exhibit C and approved by Landlord.

            R-12. Addendum to Section 17(CC). Tenant shall not operate any coin
or token operated vending machine or similar device for the sale of any goods,
wares, merchandise, food, beverages, or service, except for use by its
employees and their guests. Tenant agrees that it will afford other tenants in
the Project designated by Landlord a reasonable opportunity to bid to provide
such machines.

            R-13. Addendum to Section 19. If the damage renders the Premises or
such building untenantable in whole or in part and cannot reasonably be
repaired or restored within three hundred sixty-five (365) days after the event
causing such damage or destruction, Landlord shall promptly give Tenant written
notice thereof and Tenant shall have the right, exercisable by giving written
notice thereof to Landlord within twenty (20) days after receipt of such notice
from Landlord, to terminate this Lease as of the date of such damage. If
neither party elects to cancel and terminate this Lease as herein provided,
Landlord shall repair and restore the Premises or such building with reasonable
promptness.

            R-14. Addendum to Section 20(A). Tenant shall have the right to
claim and to retain any separate award for moving expenses or for the taking of
Tenant's trade fixtures, provided such separate award does not delay or reduce
the amount of Landlord's award.

            R-15. Addendum to Section 34(A). Anything in Section 34(A) to the
contrary notwithstanding, Landlord's prior written consent shall not be
required for (a) wall coverings or (b) interior, non-structural Alterations not
affecting the Building's heating, ventilating or air conditioning systems, or
the Building's electrical or plumbing systems, and costing, in each instance,
less than Five Thousand Dollars ($5,000.00), provided the cost of such
Alterations shall not in any twelve (12) month period aggregate more than Twenty

                                      -3-
<PAGE>   35
Thousand Dollars ($20,000.00). Tenant shall, however, give Landlord written
notice of such Alterations. Landlord's review and approval of plans and
specifications, names and addresses of proposed contractors, copies of contract,
indemnification and supervision shall not be required, but Tenant shall
otherwise comply, in connection with such Alterations, with the provisions of
Section 34(B).

      R-16. Additional Space. (a) It is understood that there are presently
1,334 square feet of unleased space on the sixth (6th) floor of Four Westbrook
Corporate Center, shown as "Additional Space" on Exhibit A. Landlord agrees that
Landlord will keep Tenant apprised of Landlord's leasing activity with respect
thereto and will, at Tenant's request, advise Tenant in writing of the terms and
conditions upon which Landlord is willing to lease said space. Landlord agrees
that if Landlord has been requested to provide a revised proposal or space plan
to a prospective third-party tenant, Landlord shall give written notice thereof
to Tenant. Unless Tenant requests that Landlord advise Tenant of the terms and
conditions upon which Landlord is willing to lease said space and reaches
agreement with Landlord as to terms and conditions for a lease for said space on
or before seven (7) business days after receipt of such notice from Landlord,
Landlord shall have the right to conclude its negotiations with and lease said
space to such third-party. Tenant's rights under this subsection are subject to
prior rights of Lawson Associates, Inc.

      (b)   In addition to the rights of Tenant under Section R-16(a), Tenant
shall have the following rights regarding further Additional Space: Tenant may,
from time to time, give Landlord written notice of its need for additional
space, which notice shall specify the amount of space then needed and when the
space is required. Landlord shall, within seven (7) business days after receipt
of Tenant's said notice, advise Tenant in writing of the spaces which are
available in the Building. Tenant shall have the right to request that Landlord
advise Tenant in writing of the terms and conditions upon which Landlord is
willing to lease any of said designated space as selected by Tenant. Landlord
agrees that if Landlord has been requested to provide a

                                      -4-
<PAGE>   36
revised proposal or space plan to a prospective third party tenant for such
space, Landlord shall give written notice thereof to Tenant. Unless Tenant
requests that Landlord advise Tenant of the terms and conditions upon which
Landlord is willing to lease said space and reaches agreement with Landlord as
to the terms and conditions for a lease for said space on or before seven (7)
business days after receipt of such notice from Landlord, Landlord shall have
the right to conclude its negotiations and lease said space to such third
party. Tenants rights under this subsection are subject to prior rights of
other tenants.

     R-17. Right to Terminate. Provided that Tenant shall timely and faithfully
perform all of its covenants and obligations under this Lease, and provided
Tenant shall not have leased additional space pursuant to Section R-16 hereof,
Tenant shall have the right to terminate this Lease, effective December 31,
2002, which right shall be exercised by Tenant giving written notice thereof to
Landlord at least one (1) year prior to said effective date. It shall be a
condition of the effectiveness of such notice that it be accompanied by a
payment of consideration for such termination in the amount of Thirty Three
Thousand Six Hundred Seventy Six and 04/100 Dollars ($33,676.04).

     R-18. Moving Allowance. Provided that Tenant is not then in default
hereunder with times to cure expired, Landlord shall pay to Tenant, upon
Tenant's occupancy of the Premises, the sum of Five Thousand Eight Hundred
Seventy Eight and no/100 Dollars ($5,878.00).

     R-19. Antennas. Tenant shall have the right to install radio dishes on the
roof of the Building. The number of dishes, the sign, location and the manner
of installation shall be made in accordance with plans and specifications first
approved in writing by Landlord. Nothing contained herein shall be construed to
permit Tenant to violate any applicable laws or ordinances or any of the
provisions of this Lease including, without limitation, the provisions of
Section 17(V) of this Lease. Tenant shall, in such instance, install lines
between said equipment and the Premises through existing risers; said work
shall be done at Tenant's sole cost and expense. In the event such installation
requires the making of any roof cuts or the performance of any other roofing

                                      -5-
<PAGE>   37
work, such roof cuts shall be made only as directed in writing by Landlord and
all roof cuts and other roofing work shall be performed at Tenant's sole cost
and expense by the roofing contractor designated by Landlord.  Tenant shall, at
its sole cost and expense, perform any and all necessary repairs and maintenance
to said equipment and all related facilities and lines. From and after the
commencement of the installation of said equipment, Tenant shall reimburse
Landlord for all fees or charges imposed upon Landlord by any governmental
agency or utility having the right to impose the same by reason of the
installation or use thereof, but Tenant shall not otherwise be obligated to pay
any rent for the installation or use of such equipment or line. Tenant shall
remove such equipment at the expiration or earlier termination of the Lease or
of Tenant's right to possession hereunder, and Tenant shall restore the Building
to the condition existing prior to such installation, such removal work to be
subject to the same provisions of this Section regarding roofing work as were
applicable in connection with the original installation.

     R-20. Option to Extend. Provided Tenant shall timely and faithfully
perform all of its obligations under this Lease during the original Term and
provided further that Tenant (and not a sublessee or assignee) shall then be in
occupancy of all of the Premises, Tenant shall have the right, exercisable by
giving written notice thereof to Landlord, not more than fifteen (15) months
nor fewer than twelve (12) months prior to the expiration of the original Term
(time being of the essence thereof) to extend the Term for an additional term of
five (5) years upon all of the terms, covenants and conditions contained in
this Lease, except that the Monthly Base Rent during the additional term
(hereinafter "Extension Monthly Base Rent") shall be equal to the rate of
Monthly Base Rent prevailing as of the commencement date of the Additional
Term, for new leases for space in buildings in Westchester, Oak Brook and
Oakbrook Terrace, Illinois which are first class, high rise, multi-use office
building having amenities similar to those in Westbrook Corporate Center.
Within seven (7) business days of Landlord's receipt of Tenant's notice
exercising the option to extend, Landlord shall advise Tenant in writing of
Landlord's good faith estimate of the rate of

                                      -6-
<PAGE>   38
Extension Monthly Base Rent in accordance with said standard. The parties shall
negotiate in good faith to reach agreement on the amount of the Extension
Monthly Base Rent but if they are unable to do so on or before nine (9) months
prior to the expiration of the original Term, then either party shall have the
right, exercisable by giving written notice thereof to the other, to terminate
the negotiations and in such event, Tenant's exercise of the option to extend
shall be deemed null and void.

                                      -7-
<PAGE>   39
                          (IF TENANT IS A CORPORATION)

STATE OF ILLINOIS  )
                   )     SS:
COUNTY OF COOK     )

          I, _______________________, a Notary Public in and for said County,
in the State aforesaid, DO HEREBY CERTIFY that _____________________,
personally known to me to be the _____ President of _____________________, a
____________ corporation, and __________________________, personally known to
me to be the ________________ Secretary of said corporation and personally
known to me to be the same persons whose names are subscribed to the foregoing
instrument, appeared before me this day in person and severally acknowledged
that they signed and delivered the said instrument as ____________ President
and ____________ Secretary of said corporation to be affixed thereto, pursuant
to authority given by the Board of Directors of said corporation, as their free
and voluntary act and as the free and voluntary act and deed of said
corporation, for the uses and purposes therein set forth.

          GIVEN under my hand and Notarial Seal this __ day of ______________,
19__.

                                        ____________________________
                                              Notary Public
<PAGE>   40
                                   (LANDLORD)

STATE OF ILLINOIS   )
                    )    SS:
COUNTY OF COOK      )

          I, [ILLEGIBLE], a Notary Public in and for said County, in the State
aforesaid, DO HEREBY CERTIFY that [ILLEGIBLE], personally known to me to be the
Vice President of LaSalle National Trust, N.A. and NANCY A. STACK, personally
known to me to be the Asst. Secretary thereof and personally known to me to be
the same persons whose names are subscribed to the foregoing instrument,
appeared before me this day in person and severally acknowledged that they
signed and delivered the said instrument as Vice President and Asst. Secretary
of said corporation to be affixed thereto, pursuant to authority given by the
Board of Directors of said corporation, as their free and voluntary act and as
the free and voluntary act and deed of said corporation, for the uses and
purposes therein set forth.

          GIVEN under my hand and Notarial Seal this 10th day of January, 1997.

                               ["OFFICIAL SEAL"]
                                  [ILLEGIBLE]
                       [NOTARY PUBLIC STATE OF ILLINOIS]
                        [MY COMMISSION EXPIRES __ __ __]

                                             /s/ [SIGNATURE ILLEGIBLE]
                                            --------------------------
                                                   Notary Public
<PAGE>   41
                                  EXHIBIT "A"

                                  [FLOOR PLAN]

<PAGE>   42
                                   EXHIBIT B

PARCEL 4 OF LOT 1 IN WESTBROOK CORPORATE CENTER P.U.D. BEING A SUBDIVISION OF
PART OF THE NORTHEAST 1/4 OF SECTION 30, TOWNSHIP 39 NORTH, RANGE 12 EAST OF
THE THIRD PRINCIPAL MERIDIAN, ACCORDING TO THE SURVEY ATTACHED AS EXHIBIT C TO
THE INSTRUMENT RECORDED JULY 27, 1990 AS DOCUMENT NUMBER 90-362917, IN COOK
COUNTY, ILLINOIS.

<PAGE>   43
                                   EXHIBIT C

                             WORK LETTER AGREEMENT

1.   The Tenant has specified certain improvements to be constructed within the
Premises (hereinafter the "Work"), substantially as shown on the space plan and
specifications to be prepared as provided in Paragraph 2 hereof, to be approved
in writing by the parties hereto.

2.   All Work shall be performed at Landlord's sole cost. In addition, Tenant
shall cause the preparation of a space plan and working drawings, causing them
to be completed and approved by Landlord and Tenant on or before November 12,
1996. Landlord shall reimburse Tenant for the cost of the space plan and
working drawings (exclusive of engineering), in an amount not to exceed $18,809.

3.   The Tenant may request work additional to the Work specified herein
("Additional Work"). Additional Work is subject to the Landlord's prior
approval, which shall not be unreasonably withheld, and if done shall be
performed by the Landlord at the Tenant's sole expense. Before starting any
Additional Work, the Landlord will provide the Tenant with a written statement
of the cost of the Additional Work. Tenant agrees to promptly provide Landlord
with a written authorization to proceed with the Additional Work and shall also
then pay to the Landlord the amount set forth on the Landlord's statement. If
Tenant delays in the providing of said authorization and payment, the Landlord
will proceed with the Work without performing the Additional Work.

4.   The Tenant may request access for its agents to enter the Premises prior
to the commencement of the Term in order to perform other work required by
Tenant. Landlord, in its reasonable discretion, may grant the Tenant and its
agents a license to enter the Premises upon conditions that:

     A.   Tenant shall give Landlord five (5) days' prior written notice of its
request to have such access, and the notice shall be accompanied by:

          1.   A reasonably detailed description of and schedule for the work to
     be performed;

          2.   Names and addresses of contractors and suppliers providing labor
     and material for the work;

          3.   Copies of contracts, plans and specifications for the work; and

          4.   Evidence of licenses, permits, insurance, and indemnification, if
     any, required for the work.

All of the above shall be subject to Landlord's approval, which shall not be
unreasonably withheld.

     B.   Such early access shall be the subject to Landlord's scheduling.

     C.   Tenant's agents shall work in harmony and not interfere with any Work
or Additional Work in the Premises or Building. If said agents cause or
threaten to cause any disharmony or interference (including labor disharmony),
Landlord may withdraw such license upon 24 hours prior written notice to the
Tenant.

Any such early entry shall be deemed to be under all of the terms, covenants
and conditions of the Lease, excluding only the covenant to pay Rent or
Additional Rent under Section 7 of the Lease. Tenant shall be responsible for
any damage to the Work, the Additional Work, the Premises, or the Building
caused by its agents.

5.   The terms and provisions of the Lease, insofar as they are applicable to
this Work Letter Agreement, are hereby incorporated by reference.

6.   All amounts payable by Tenant to Landlord hereunder shall be deemed to be
Additional Rent under the Lease.

7.   Tenant shall deliver to Landlord within ten (10) days after the execution
and delivery of the Lease, any and all information, in addition to the
attachments hereto which Landlord may require to cause the preparation of all
working drawings. In addition, when Landlord submits working drawings to Tenant
for Tenant's review, Tenant shall respond to Landlord within five (5) days after
receipt thereof, approving or disapproving (setting forth in writing the reasons
for disapproval) the same. If Tenant does not so respond within said five (5)
days, Tenant shall be deemed to have approved the same.<PAGE>   1
                            [BRIGHTWARE LETTERHEAD]

                                                                 EXHIBIT - 10.17

                   SECOND AMENDMENT TO OEM/RESELLER AGREEMENT

This second amendment ("Second Amendment") serves to amend that certain
OEM/Reseller Agreement dated December 22, 1998 (the "Agreement") by and
between Brightware, Inc., ("Brightware") having a place of business at 350
Ignacio Blvd., Novato, CA 94949 and Quintus Corporation ("Company") having a
place of business at 47212 Mission Falls Court, Fremont, CA 94539. This Second
Amendment is effective as of the Second Amendment Effective Date.

The parties agree as follows:

Unless otherwise defined herein, capitalized terms used in this First Amendment
shall have the same meaning as those used in the Agreement.

"Second Amendment Effective Date" means December 23, 1999.

SECTION 9 - TERM AND TERMINATION

Per Section 9.1 of the Agreement, both parties agree to extend the terms of
this Agreement for a period of ninety (90) days, commencing with the Second
Amendment Effective Date. Upon such termination, both parties shall negotiate
in good faith a new OEM agreement or a continuing extension of the terms of
this Agreement.

PRECEDENCE

In the event of conflict between this Second Amendment and the Agreement, this
Second Amendment shall take precedence over the Agreement. This Second
Amendment, the First Amendment and the Agreement are the entire agreement
between the parties concerning the subject matter hereof and may only be
modified by an amendment executed by the parties authorized representatives.

This Second Amendment is made as of the Second Amendment Effective Date.

LICENSEE                              BRIGHTWARE, INC.

/s/ MICHELLE E. FIELDS                /s/ [SIGNATURE ILLEGIBLE]
-----------------------               --------------------------
Authorized Signature                  Authorized Signature

Michelle E. Fields,
Business Admin Manager                CFO
-----------------------               --------------------------
Printed Name, Title                   Printed Name, Title

                                       1

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00001-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00001-of-00352.parquet"}]]