<PAGE>   1








                             ANDOVER, MASSACHUSETTS



                                      LEASE




LANDLORD:         50 MINUTEMAN LIMITED PARTNERSHIP,
                  a Massachusetts Limited Partnership



TENANT:           PICTURETEL CORPORATION, a Delaware corporation




DATE:             August 26, 1996




<PAGE>   2

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

<S>      <C>                                                                     <C>
  1.     BASIC LEASE PROVISIONS .................................................- 1 -
         ----------------------
  2.     CONSTRUCTION OF PREMISES ...............................................- 2 -
         ------------------------
  3.     POSSESSION AND SURRENDER OF PREMISES ...................................- 3 -
         ------------------------------------
  4.     TERM ...................................................................- 3 -
         ----
  5.     RENT ...................................................................- 3 -
         ----
  6.     TAXES ..................................................................- 4 -
         -----
  7.     OPERATING COSTS ........................................................- 5 -
         ---------------
  8.     INSURANCE ..............................................................- 6 -
         ---------
  9.     MONTHLY PAYMENT OF TAXES AND OPERATING COSTS; AUDITS ...................- 7 -
         ----------------------------------------------------
  10.    UTILITIES AND LANDLORD'S SERVICES ......................................- 8 -
         --------------------------------- 
  11.    USE OF PREMISES ........................................................- 8 -
         ---------------
  12.    MAINTENANCE AND REPAIRS ................................................- 9 -
         ----------------------- 
  13.    ALTERATIONS ...........................................................- 10 -
         -----------
  14.    INDEMNITY; SATISFACTION OF REMEDIES ...................................- 11 -
         -----------------------------------
  15.    PARKING ...............................................................- 12 -
         -------
  16.    DAMAGE OR DESTRUCTION .................................................- 13 -
         ---------------------
  17.    CONDEMNATION ..........................................................- 15 -
         ------------
  18.    ASSIGNMENT AND SUBLETTING .............................................- 15 -
         -------------------------                                                                                
  19.    MORTGAGEE PROTECTION; UNPERMITTED FINANCING; LANDLORD'S LOAN
         ------------------------------------------------------------
         DEFAULTS ..............................................................- 19 -
         --------
  20.    ESTOPPEL CERTIFICATES; FINANCIAL STATEMENTS ...........................- 21 -
         -------------------------------------------
  21.    DEFAULT ...............................................................- 21 -
         -------
  22.    REMEDIES FOR DEFAULT ..................................................- 21 -
         --------------------
  23.    BANKRUPTCY PROVISIONS [SEE EXHIBIT "F"] ...............................- 23 -

  24.    GENERAL PROVISIONS ....................................................- 23 -
         ------------------
  25.    HAZARDOUS SUBSTANCES ..................................................- 29 -
         --------------------
  SIGNATURE PAGE................................................................- 30 -
</TABLE>

                        EXHIBIT LIST
                        ------------

                                      (ii)


<PAGE>   3



"A"      Project Site Plan
"B"      Premises
"C"      Workletter
"CC"     PictureTel Initial Information
"D"      Base Rent
"DD"     Base Rent During Extension Options
"E"      Rules and Regulations
"F"      Bankruptcy Provisions
"G"      Landlord's Services
"H"      Unamortized Cost Schedule
"I"      [INTENTIONALLY OMITTED]
"J"      Forms of Estoppel Certificate and Subordination, Non-disturbance and
          Attornment Agreement
"K"      Map
"L"      LC Note
"M"      Beneficiary's Rights
Addendum #1 - Rooftop Communications Equipment
Addendum #2 - Extension Options
Addendum #3 - Net Proceeds 
Addendum #4 - Purchase Options 
Addendum #5 - Right of First Offer to Purchase 
Addendum #6 - [INTENTIONALLY OMITTED] 
Addendum #7 - Budget Savings (with Schedule 7AAA attached)

                                      (ii)

<PAGE>   4

                         INDEX TO CERTAIN DEFINED TERMS
                         ------------------------------
<TABLE>
<CAPTION>

TERM                                           SECTION              PAGE
----                                           -------              ----
<S>                                            <C>                   <C>     
Affiliates                                     24.18(a)              28      
Alterations                                    13                    10
Bankruptcy Code                                                      Exhibit "F"
base rent                                      1.1(e)                 1
Building                                       1.1(d)                 1
Commencement Date                              1(aa)                  1
Condemnation                                   17                    15
Control Affiliates                             24.18(aa)             28
Cure Payments                                  19.5                  20
Excess Refinancing Proceeds                    Add. #5                3
Existing Loans                                 2(a)                  Add. #4
Extension Options                              1                     Add. #2
Guarantor                                      1.1(k)                 2
Hazardous Substances                           25                    29
Landlord's Insurance Proceeds                  16.1                  13
Landlord's Mortgagees                          19.1                  19
Landlord's Work                                2                      3
Laws                                           24.18(b)              28
Letter of Credit Advances                      24.17(f)              28
Letter of Credit Loan                          24.17(b)              28
Lease Year                                     4                      3
Letter of Credit                               24.17                 26
Liabilities                                    24.18(c)              29
Liens                                          13.4                  11
No-sale Election                               Add. #5                2
Occupancy Date                                 1.1(a)                 1
Operating Costs                                7.1                    5
Permitted Assignee                             18.5(c)               18
Permitted Sublessee                            18.5(c)               18
Phase                                          1.1(dd)                1
Premises                                       1.1(c)                 1
Purchase Options                                                     Add. #4
Reconstruction Costs                           16.5                  14
Related Entities                               24.18(cc)             29
Released Assignor                              18.4                  16
Rent                                           5                      4
Right of Self Help                             14.4                  12
Systems and Equipment                          24.18(d)              29
Superior Leases and Mortgages                  24.4                  24
Taxes                                          6.1                    4
Tenant's Broker                                1.1(l)                 2
Tenant's Percentage                            1.1(f)                 1
Tenant's Property                              3                      3
Tenant's Work                                  1.1                   Exh. C
Transfer                                       18.1                  15
Unamortized Costs                                                    Exhibit "H"
Unpermitted Financing                          19.4                  19
</TABLE>

                                                                             
                                      (iii)

<PAGE>   5


                                      LEASE
                                      -----

     THIS INDENTURE OF LEASE, dated as of August 26, 1996, is between 50
MINUTEMAN LIMITED PARTNERSHIP, a Massachusetts limited partnership ("Landlord"),
and PICTURETEL CORPORATION, a Delaware corporation ("Tenant").

     Landlord leases the Premises to Tenant and Tenant leases the Premises from
Landlord on the following terms and conditions:

1.   BASIC LEASE PROVISIONS.
     ----------------------
         
     1.1  Summary.
          -------

          (a) Occupancy Date: when all of Landlord's Work is deemed to be
substantially completed (as described in Article 2) or when Tenant occupies the
Building, whichever is earlier. If Landlord's Work is subdivided into Phases,
the Occupancy Date for each Phase will be when Landlord's Work for that
particular Phase is deemed to be substantially completed (as described in
Article 2) or Tenant occupies that Phase, whichever is earlier.

          (aa) "Commencement Date": The later of August 1, 1997; or the
Occupancy Date (or on the last Occupancy Date if Landlord's Work is subdivided
into Phases).

          (b) Term: The term of this Lease will begin on the Occupancy Date (or
on the first Occupancy Date if Landlord's Work is subdivided into Phases) and
will end eighteen (18) Lease Years after the Commencement Date, unless extended
or terminated earlier per this Lease.

          (c) Premises: The land located in Andover, Massachusetts, legally
described in Exhibit "B," and all improvements now or hereafter constructed on
the land.

          (d) Building: The building of approximately 150,000 s.f. and
associated improvements to be constructed by Landlord on the land, designated as
the "Building" in Exhibit "A," as it may be initially constructed and
subsequently changed, enlarged or improved in the future pursuant to Landlord's
Work or otherwise.

          (dd) Phase: The parties acknowledge that Landlord's Work for the
Building may be subdivided into one or more different areas, each of which may
have a different Occupancy Date due to the differing nature of Landlord's Work
necessary to meet the requirements of Tenant's employees who ultimately will
occupy those different areas. If Landlord's Work is so subdivided, each of these
separate areas will be called a "Phase." The parties acknowledge that these
areas may change during Landlord's Work, and that performing Landlord's Work in
Phases and/or getting separate Certificates of Occupancy for each Phase may be
impractical or unlawful.

          (e) Base Rent: (see Exhibit "D").

                                      -4-

<PAGE>   6



          (f) Tenant's Percentage: If Landlord's Work is subdivided into Phases,
Tenant's Percentage for each Phase will be a fraction, expressed as a
percentage, determined by dividing the rentable area of that Phase by the
rentable area of the entire Building as if Landlord's Work was completed. If the
rentable area of the entire Building is not known when a particular Phase is
completed, then the rentable area of the Building shall be based on Landlord's
reasonable determination at the time, with a retroactive adjustment when the
rentable area of the Building is determined. Notwithstanding anything to
contrary, the rentable area shall be determined in each case by Landlord's
architect or representative in a consistent fashion, and upon the occurrence of
the Occupancy Date (or the Occupancy Date for all of the Phases, if Landlord's
Work is subdivided into Phases), Tenant's Percentage shall be 100%.

          (g) Letter of Credit: (See Section 24.17).

          (h) Use of Premises: For general office purposes, engineering,
research and development, light manufacturing, demonstration of video
teleconferencing systems, training rooms, customer demonstrations, repairs,
distribution and warehousing, and uses incidental thereto.

     (i)  Notice to Tenant:
          -----------------

                           PictureTel Corporation
                           100 Minuteman Road
                           Andover, Massachusetts  01810
                           Attn:  Chief Financial Officer

                           With a Copy to:
                           --------------
                           PictureTel Corporation
                            100 Minuteman Road
                           Andover, Massachusetts  01810
                           Attn:  Vice President, Human Resources

     (j)  Notice to Landlord:
          ------------------
                           c/o Brickstone Properties, Inc.
                           300 Brickstone Square
                           Andover, Massachusetts 01810
                           Attn:  Martin Spagat

                           With a Copy to:
                           --------------
                           c/o U.S. Managers Realty, Inc.
                           The Plaza at Continental Park
                           Suite 5252
                           2101 Rosecrans Avenue
                           El Segundo, California  90245-4709
                           Attn:  John G. Baker, Esq.


                                      -5-

<PAGE>   7

          (k) Guarantor: N/A. 
                        -----
          (l) Tenant's Broker: Avalon Partners, Inc..

          (m) Certain Other Defined Terms: [See Section 24.18]

If there is a conflict between this summary and the rest of this Lease, the rest
of this Lease will control.

     1.2 SITE PLAN. Exhibit "A" is the general site plan of the land, the
Building and the other principal improvements that are planned as part of the
Premises. The parties acknowledge and agree that the site plan may change as a
result of changes in the Building or other improvements or Landlord's Work, and
so the parties agree that Landlord will have the right to substitute for Exhibit
"A" another general site plan, if necessary, to depict the Premises more
accurately upon such substantial completion.

     1.3 PREMISES. Subject to and in accordance with the terms and limitations
in this Lease (including any regarding prior notice, entry and the
non-disturbance of Tenant's business), Landlord reserves the right to install,
maintain, repair and replace Systems and Equipment within or serving the
Building or the rest of the Premises or otherwise modify the Premises in
emergencies or in order to comply with its obligations or exercise its rights
under this Lease or to comply with Laws or insurance requirements or to protect
health, safety or property or to provide access, drainage, utilities and
services (including cabling), and associated improvements in accordance with
easements that are or may be granted for adjacent properties, and in so doing
Landlord will endeavor not to interrupt Tenant's uses of the Premises or the
services Landlord is required to provide under this Lease more than reasonably
necessary. Landlord will not otherwise have the right to materially modify the
Premises unless it obtains Tenant's approval, which will not be unreasonably
withheld or delayed.

2.   CONSTRUCTION OF PREMISES.
     ------------------------
        
     Landlord will perform "Landlord's Work" and Tenant will perform "Tenant's
Work" (if any) as described in the Workletter attached as Exhibit "C." The good
faith written certification by Landlord's architect of the substantial
completion of Landlord's Work and the issuance of a temporary or final
certificate of occupancy by the Town of Andover will be binding on the parties
as to the date of substantial completion of Landlord's Work (in its entirety or
for each Phase, as applicable). Except for Tenant delays and force majeure,
Landlord will diligently attempt to substantially complete Landlord's Work on or
before October 1, 1997. Landlord's Work (in its entirety or for each Phase, as
applicable) will be deemed substantially completed even if Landlord has not
completed "punch list" or other minor items, as long as Landlord agrees to
complete these items diligently. Tenant's final punch list for Landlord's Work
(in its entirety or for each Phase, as applicable) will be submitted to Landlord
within fifteen (15) days after Landlord notifies Tenant that Landlord's Work is
substantially completed. Subject to scheduling requirements for the completion
of Landlord's Work, Tenant's contractors may have access to the Premises prior
to the completion of Landlord's Work as described in Exhibit "C," and to the


                                      -6-
<PAGE>   8
extent that conflicts with the scheduling for Landlord's Work can reasonably be
avoided, Landlord and its contractors will attempt to cooperate reasonably with
Tenant's contractors so that Tenant's Work can be completed in a timely manner.


3.   POSSESSION AND SURRENDER OF PREMISES.
     ------------------------------------

     When this Lease terminates, Tenant will remove from the Premises all of its
signs, movable trade fixtures and equipment, inventory and other personal
property, whether owned by Tenant or its Affiliates ("Tenant's Property").
Tenant's Property remaining more than five (5) business days after delivery of
written notice from Landlord after such termination will be deemed abandoned and
Landlord may keep, sell, destroy or dispose of it without any Liabilities to
Tenant or its Affiliates. Tenant will repair all damage and surrender the
Premises broom clean and in good order, condition and repair, reasonable wear
and tear, damage by fire and casualty and taking by eminent domain excepted.

4.   TERM.
     ----
         
     (a) This Lease is effective as of the date first set forth above, and the
term begins on the Occupancy Date (or on the first Occupancy Date for a Phase if
Landlord's Work is subdivided into Phases) and ends eighteen (18) Lease Years
after the Commencement Date, unless terminated earlier or extended in accordance
with this Lease. A "Lease Year" is a period of twelve (12) consecutive calendar
months during the Lease term, starting with the Commencement Date. However, the
first Lease Year is the first twelve (12) full calendar months plus the partial
month (if any) after the Commencement Date if the Commencement Date is not the
first day of the month, and the last Lease Year may be less than twelve (12)
months. In addition to the rent payable for the first Lease Year, Tenant will
pay rent for the partial calendar month (if any) after the Commencement Date.
Within ten (10) days after Landlord's request in each instance, Tenant will
execute an agreement confirming the Occupancy Date (or the Occupancy Date for
each Phase, if applicable) and/or the Commencement Date. Tenant's failure to
execute such an agreement will not affect the actual Occupancy Date(s) or the
actual Commencement Date.

     (b) If necessary, the initial term of this Lease shall be deemed extended
(but not shortened) so that the initial term of this Lease will expire eighteen
(18) years (plus any partial month) after the closing and funding of the initial
permanent mortgage loan (as opposed to any loan that provides for construction
financing) that is secured by the Premises; provided, however, that the initial
term of this Lease shall not be extended by more than nine (9) months by reason
of this clause. Promptly upon Landlord's request after Tenant receives written
notification that such closing and funding has occurred, Tenant will execute an
agreement confirming the new expiration date of the initial Lease term. Tenant's
failure to execute such an agreement will not affect the actual extended
expiration date of the initial Lease term.

                                      -7-

<PAGE>   9


5.   RENT.
     ----
         
     (a) Tenant will pay the base rent as shown in Exhibit "D" in equal monthly
installments in advance beginning on the later of August 1, 1997, or the
Occupancy Date (or if Landlord's Work is subdivided into Phases, on the
Occupancy Date for each Phase), and thereafter on the first day of each month
during the term (except as otherwise shown in Exhibit "D"), prorated for any
portion of a month. The term "rent" includes base rent, additional rent and all
other amounts to be paid by Tenant under this Lease, whether or not specifically
described as rent. All rent will be paid without demand, deduction, counterclaim
or offset of any type (except as may be specifically provided otherwise
elsewhere in this Lease) in lawful U.S. legal tender at The Plaza at Continental
Park, Suite 5252, 2101 Rosecrans Avenue, El Segundo, California 90245-4707 or to
such other person or place as Landlord may from time to time designate.
Notwithstanding the foregoing, if and for so long as there is a mortgage loan
encumbering the Premises or a loan that is secured by the Letter of Credit, at
the written request of Landlord or Tenant, Landlord and Tenant will establish a
collection account for the receipt and disbursement of base rent. In such event,
Tenant, will pay the base rent as and when required each month into this
collection account, and the collection agent promptly will disburse from such
amount an amount sufficient to pay debt service and any other amounts owed to
the mortgage lender and the lender of the loan secured by the Letter of Credit,
with the balance being disbursed first to Tenant (but only if and to the extent
necessary to pay current debt service to Tenant under the LC Note per Section
24.17(f) if any amounts are then owed under the LC Note) and then to Landlord.
The collection agent and the terms of this collection account will be subject to
the mutual written approval of Landlord and Tenant, which approval will be based
on customary terms for such agreements and will not be unreasonably withheld or
delayed.

     (b) If Tenant provides and continues to provide the Letter of Credit in
accordance with Section 24.17 and otherwise does not default under this Lease,
within thirty (30) days after payment by Tenant and delivery to Landlord of an
invoice therefor and reasonable evidence of Tenant's payment (but not earlier
than the date that Tenant pays its first full month of base rent under this
Lease), Landlord either will reimburse to Tenant, or credit against rent owed by
Tenant, the actual amounts paid by Tenant to the issuer of the Letter of Credit
for such issuance, up to an annual amount equal to one percent (1%) of the face
amount of the Letter of Credit from time to time.

6.   TAXES.
     -----

     6.1 DEFINITION OF TAXES. "Taxes" means all taxes, assessments, levies,
charges and fees imposed against, for or in connection with all or any portion
of: the Premises; the use, ownership, leasing, occupancy, operation, management,
repair, maintenance, demolition or improvement of the Premises; the amount of,
or Landlord's right to receive or the receipt of, rent, profit or income from
the Premises (but specifically excluding Landlord's net income taxes);
improvements, utilities and services, whether because of special assessment
districts or otherwise; the value of Landlord's interest in the Premises; and
fixtures, equipment and other real or personal property used in connection with
the Premises. Taxes also include, without limitation, license fees, sales, use,
capital and value-added taxes, penalties (but only if Tenant

                                       -8-

<PAGE>   10


does not pay its share of Taxes as and when required), interest and costs
incurred in contesting taxes, and any charges or taxes in addition to, in
substitution or in lieu of, partially or totally, any taxes or charges
previously included within this definition, including taxes or charges
completely unforeseen by the parties and collected from whatever source. TAXES
DO NOT INCLUDE: Landlord's federal or state net income, franchise, excise,
inheritance, gift or estate taxes, and any deed stamps or documentary or
transfer taxes payable upon the Transfer of the Premises to any of Landlord's
Control Affiliates.

     6.2 PAYMENT OF TAXES. Subject to and in accordance with Article 9, starting
as of the Occupancy Date (or if Landlord's Work is subdivided into Phases, as of
the first Occupancy Date for a Phase) and continuing thereafter during the term,
Tenant will pay Tenant's Percentage of Taxes directly to Landlord as additional
rent within fifteen (15) days after receipt of Landlord's bill. Taxes that are
assessed during the term of this Lease and also cover any periods prior to or
after the term of this Lease will be appropriately prorated.

     6.3 TENANT'S TAXES. Tenant will pay all taxes assessments, license fees and
charges levied, assessed or imposed on Tenant, Tenant's business operations and
Tenant's Property, and Tenant will indemnify and hold Landlord and its
Affiliates harmless from any Liabilities in connection therewith or in
connection with any non-payment thereof.

     6.4 CONTEST. Subject to the terms of the pre-existing agreement entered
into by Landlord and Digital Equipment Corporation with respect to the tax
fiscal years ending June 30, 1995 and June 30, 1996, Tenant will have the right
to contest the amount or validity of any Taxes with the appropriate governmental
authorities, provided that: Tenant pays all Taxes when due and complies with all
applicable rules, regulations and other Laws in connection with such contest;
Tenant pays all costs and expenses in connection with such contest and neither
Landlord nor the Premises will, as a result of such contest or any nonpayment of
Taxes, become subject to any cost, loss, claim, liability, lien or encumbrance
of any type. Tenant will indemnify and hold Landlord and its Affiliates harmless
from any Liabilities in connection with any such contest or any nonpayment of
Taxes. Landlord also will have the right to contest Taxes. A pro rata share of
any refund of Taxes obtained, net of all bona fide costs and expenses incurred
in connection with the contest resulting in such refund, shall be refunded to
Tenant in proportion to the amount of the Taxes paid by Tenant to which such
refund relates.


7.   OPERATING COSTS.
     ---------------

     7.1  Definition of Operating Costs.
          -----------------------------

          (a) "Operating Costs" are all costs and expenses incurred in
connection with the Premises and for its ownership, operation, management,
maintenance, repair, restoration and replacement, including, without limitation,
costs for: services, costs and utilities not otherwise directly paid or
reimbursed by Tenant; materials, supplies and equipment; premiums for Landlord's
insurance policies and deductibles thereunder; wages and payroll, including
bonuses, fringe benefits, workers compensation and payroll taxes (but excluding
the foregoing payable to Landlord's partner or chief executive charged with the
operation and management of the Premises, currently Martin Spagat); professional
and consulting fees; management fees at the

                                      -9-
<PAGE>   11



rate of 3.5% of all scheduled base rent, Taxes and Operating Costs payable by
Tenant (without giving effect to any abatements or reductions) and utilities and
services payable by Tenant (other than those payable by Tenant directly to
third-party providers), or at prevailing rates, whichever is greater, or if no
managing agent is retained, an amount in lieu thereof not in excess of the
greater of the foregoing amounts; complying with any Laws and insurance
requirements; environmental matters, including, without limitation, costs of
investigations, disclosures, preventive measures, remediation, disposal, audits,
monitoring, maintenance and responsive actions; roadway maintenance; costs
payable in connection with any easements that benefit or burden the Premises;
capital expenditures (excluding those incurred for repairs or rebuilding
resulting from a casualty, but INCLUDING an amount thereof equal to any
deductibles under Landlord's casualty insurance policies); an annual audit of
Landlord's books and records relating to the Premises and the preparation of
Landlord's annual financial statements (but not its tax returns); and
snowplowing and landscaping. OPERATING COSTS DO NOT INCLUDE: Taxes; depreciation
of the Premises structures and improvements; Landlord's loan or ground lease
payments (including principal payments); costs of negotiating and enforcing
leases; brokerage commissions; costs of any items otherwise includable in
Operating Costs to the extent that they are reimbursed under warranties or by
insurance proceeds or condemnation awards; costs for Landlord's California
corporate office; costs of Landlord's Work; and costs directly paid or
specifically reimbursed by Tenant (other than by an allocation of Operating
Costs).

          (b) Subject to the other terms and conditions of this Lease, until the
end of the ninth (9th) Lease Year, Operating Costs also will not include, and
Landlord will be responsible at its cost for, the replacement of the Building's
roof and major structural members (as opposed to the cost of the repair and
maintenance thereof, which WILL be included as part of Operating Costs), unless
such replacement is required due to the acts or omissions of Tenant or its
Affiliates, in which case Tenant will be solely responsible for all costs in
connection therewith.

          (c) The costs for such replacement WILL be included as part of
Operating Costs starting as of the beginning of the tenth (10th) Lease Year and
ending as of the beginning of the seventeenth (17th) Lease Year.

          (d) If the first Extension Option is exercised, or Tenant otherwise
agrees to extend the Lease term or the Lease term is otherwise deemed to have
been extended pursuant to the specific terms of this Lease, or if Tenant or any
of its Related Entities has entered into any agreements or exercised any rights
to lease additional space in a new building or buildings, or an enlargement of
the Building after completion of Landlord's Work, totalling more than 25,000
feet to be constructed on the Premises or to purchase or otherwise acquire all
or any portion of the Premises or any interest in Landlord, then the cost for
such replacement WILL be included as part of Operating Costs for the seventeenth
(17th) and eighteenth (18th) Lease Years and thereafter if this Lease is
extended. If none of the events described in the preceding sentence occur, then
the terms of Section 7.1(b) again will apply during the seventeenth (17th) and
eighteenth (18th) Lease Years.

     7.2 PAYMENT OF OPERATING COSTS. Subject to and in accordance with Article
9, starting as of the Occupancy Date (or if Landlord's Work is subdivided into
Phases, as of the first Occupancy Date for a Phase) and continuing thereafter
during the term, Tenant will pay Tenant's
 
                                      -10-

<PAGE>   12

Percentage of Operating Costs to Landlord as additional rent within thirty (30)
days after receipt of Landlord's bills.

8.   INSURANCE.
     ---------

     8.1 Tenant's Insurance.
         ------------------     
                  
          (a) Tenant will maintain during the term:

               (i) Commercial general liability insurance (Broad Form CGL, or if
this insurance is not then commercially available, the closest equivalent), with
contractual liability (including indemnities made by Tenant in this Lease), 
cross-liability endorsements (or the equivalent) and fire legal liability 
endorsements, and automobile liability insurance. The amount of this insurance 
will be at least $10 Million combined single limit for each occurrence, with a 
deductible not to exceed $10,000.00. If this policy includes a "general 
aggregate" limit, the limit will be at least two (2) times the combined single 
limit per occurrence.

               (ii)"All risk" casualty insurance (or if this insurance is not
then commercially available, theclosest equivalent), covering all of Tenant's 
Property and all Alterations made by or for the benefit of Tenant (excluding 
Landlord's Work). This insurance will be for full replacement cost (which may 
be subject to standard exclusions in such policies).

               (iii) Employer's liability insurance of not less than 
$1,000,000.00, and worker's compensation insurance in statutory limits.

          (b) Tenant's commercial general liability policy must: name Landlord
and the following parties as additional insureds - Landlord and its general
partners, Landlord's Mortgagees, and the property managers; be written on an
"occurrence" basis; be from insurers licensed to do business in Massachusetts
and who also maintain a Best's rating of at least A+; and state with respect to
both liability and casualty policies that the insurers will not cancel, fail to
renew or modify the coverage without first giving Landlord at least thirty (30)
days prior written notice (provided, however, that notice of modification will
not be required with respect to modifications which neither reduce the policy
limits or materially restrict or reduce the coverage provided by a policy). No
more than once every five (5) years during the term, upon Landlord's written
request the limits of Tenant's insurance policies shall be increased to amounts
as reasonably determined by Landlord based upon customary practices of other
prudent landlords.

          (c) Tenant will supply copies of each paid-up policy or a certificate
from the insurer certifying that the policy has been issued and complies with
all of the terms of this Article. This insurance must be in effect and the
policies or certificates delivered to Landlord on or before the

                                      -11-

<PAGE>   13

first Occupancy Date for a Phase, or on or before the date that Tenant or its
contractors or representatives first enter the Premises, whichever is earlier,
and renewals provided not less than thirty (30) days before the expiration of
the coverage. Landlord always may inspect and copy any of the policies.

     8.2  Landlord's Insurance.
          --------------------

          (a) Landlord will maintain during the Lease term the following
insurance policies (or if any of them are not commercially available, the
closest equivalents): an "all risk" casualty insurance policy for the full
replacement cost (or the highest amount not in excess thereof that is reasonably
commercially available) of the Building (which may be subject to standard
exclusions in such policies and to exclusion for foundations and footings),
rental loss insurance providing coverage for two (2) years (or the longest
period not in excess thereof that is reasonably commercially available) of base
rent and estimated Taxes and Operating Costs, commercial general liability
insurance (Broad Form CGL) of at least $10 Million combined single limit for
each occurrence, with a deductible not to exceed $10,000.00, and other insurance
policies with commercially reasonable carriers in such amounts, with such
deductibles and providing protection against such perils as Landlord determines
to be necessary in its reasonable discretion. All losses on all policies
maintained pursuant to this Article will be settled in Landlord's name (or as
otherwise designated by Landlord) and proceeds will belong and be paid to
Landlord except if and to the extent specifically set forth in Addendum #3 and
Addendum #4 or by reference in Addendum #5. Landlord makes no representations or
warranties as to the adequacy of any insurance to protect Landlord's or Tenant's
interests. Upon Tenant's written request, Landlord will provide Tenant with
certificates of Landlord's insurance.

          (b) Tenant and its Affiliates will not undertake, fail to undertake or
permit any acts or omissions which will increase the cost of, violate, void or
make voidable all or any portion of any insurance policies maintained by
Landlord, unless Landlord gives its specific written consent and Tenant pays all
increased costs to Landlord on demand.

     8.3  Waiver of Subrogation.
          ---------------------

          Landlord shall cause each casualty insurance policy required to be
carried under this Lease (or actually carried by Landlord) to be written in such
a manner as to provide that the insurer waives all right of recovery by way of
subrogation against Tenant in connection with any loss or damage covered by that
policy, even if such loss or damage may have been caused by the act, omission,
negligence or strict liability of Tenant, its subtenants or assignees or any of
their officers, directors, agents, employees, contractors, licensees, invitees
or suppliers. Tenant shall cause each casualty insurance policy required to be
carried by Tenant under this Lease (or actually carried by Tenant) to be written
in such a manner as to provide that the insurer waives all right of recovery by
way of subrogation against Landlord and any other additional insureds in
connection with any loss or damage covered by that policy, even if such loss or
damage may have been caused by the act, omission, negligence or strict liability
of Landlord or the additional insureds or their respective general or limited
partners, officers, directors, agents, employees, contractors, licensees,
invitees, suppliers, successors or assigns and neither party shall be liable to
the other for any loss or damage to the property of the other party caused by
fire or any of the 

                                      -12-


<PAGE>   14

casualties covered by the casualty insurance policies required to be maintained
under this Lease (or actually maintained) by the other party even if such loss
or damage is caused by the party or any of the other persons or entities
described above in this clause and even if the cost of the loss or damage is
below the deductible amount on the applicable policy or policies maintained.

9.   MONTHLY PAYMENT OF TAXES AND OPERATING COSTS; AUDITS.
     ----------------------------------------------------

     9.1 MONTHLY PAYMENTS. At any time and from time to time, and subject to
later change, Landlord may elect to have Tenant pay its share of Taxes and
Operating Costs (or either of them) in monthly installments, in advance on the
first of each month, based on amounts reasonably estimated by Landlord (as
revised from time to time). If these estimated monthly payments are required,
after the end of each tax fiscal year, Lease Year or other relevant periods
selected by Landlord, Landlord will deliver to Tenant a statement of the actual
amounts due for the period. Any additional amounts due from Tenant will be
payable as additional rent within thirty (30) days (fifteen [15] days for Taxes)
after receipt of Landlord's statement, and any overpayment by Tenant will be
refunded by Landlord or deducted from the next monthly installments due for that
particular payment category. At any time or from time to time, Landlord may
deliver a bill to Tenant for Tenant's share of Taxes and Operating Costs (or
either of them), and Tenant will pay the amount due to Landlord as additional
rent within thirty (30) days (fifteen [15] days for Taxes) after receipt of
Landlord's bill. Tenant will receive a credit for any estimated monthly payments
already paid by Tenant for the period covered by that bill.

     9.2 TENANT'S AUDIT OF TAXES AND OPERATING COSTS. Upon Tenant's written
request in each instance, Landlord will furnish Tenant reasonable backup
information for its itemized statements. During the Lease term (and after the
Lease term, but within ninety (90) days after Landlord's last invoice to
Tenant), and upon at least fourteen (14) days' prior written notice to Landlord,
not more than once in each calendar year Tenant may audit Landlord's records of
Taxes and Operating Costs for the prior calendar year in order to verify the
accuracy of the Taxes and Operating Costs charged to Tenant. Such audit will be
conducted only during regular business hours where Landlord maintains its
records (which Landlord agrees will be in Massachusetts or California) and
Tenant will deliver a copy of the results of the audit to Landlord within
fifteen (15) days after receipt by Tenant. All audits will be conducted at
Tenant's cost and expense and no subtenant will have the right to conduct an
audit, and no assignee will have the right to conduct an audit for any period
when the assignee was not in possession of the Premises.

     9.3 LANDLORD'S AUDIT. In addition to providing the information described in
Addendum #3, Landlord shall arrange for an annual audit to be made of its books
and records relating to this Lease (including with respect to Net Proceeds under
Addendum #3). Landlord shall deliver a copy of this annual audit to Tenant
within ten (10) days after it is received in final form by Landlord. Tenant
shall have the right, at its sole cost and expense, at any time during the term
of this Lease and for six (6) months thereafter, to consult with Landlord's
auditors regarding such audit. If the results of an annual audit made by
Landlord's auditors show an

                                      -13-

<PAGE>   15

underpayment or overpayment with respect to Net Proceeds, the shortfall or the
excess, as applicable, will be paid or refunded within thirty (30) days after
the final results of such audit have been delivered to Landlord and Tenant.

10.  UTILITIES AND LANDLORD'S SERVICES.
     ---------------------------------

          (a) Landlord will initially be responsible for bringing utility
services (including electricity and hot and cold running water) to the Building
to the extent provided as part of Landlord's Work in Exhibit "C." Beginning as
of the Occupancy Date (or if Landlord's Work is subdivided in Phases, as of the
Occupancy Date for each Phase), Tenant will pay when due to the furnishing
parties all fees and costs associated with utilities and communication services
provided to or for the benefit of Tenant or the Premises (or for that Phase, if
applicable), including, without limitation, electricity, water, sewer, gas,
heat, telephone, trash and waste removal and disposal, and all other utilities
and services provided, whether or not separately metered. If and to the extent
that an Occupancy Date has occurred for a Phase but Landlord's Work is
continuing with respect to other Phases, if necessary there shall be reasonable
proration between Landlord and Tenant of utilities and services consumed for
Landlord's Work, so that Landlord bears the cost for such utilities and
services. If utilities and services payable by Tenant are not charged to Tenant
directly by a public utility, Tenant will pay the charges therefor (as
determined by meter or submeter, or if there is no meter or submeter as
reasonably determined by Landlord) directly to Landlord as additional rent,
either monthly when base rent is due, or within fifteen (15) days after receipt
of Landlord's bill, at Landlord's option. Landlord will not be responsible for
any Liabilities incurred by Tenant or Tenant's Affiliates nor may Tenant abate
rent, terminate this Lease or pursue any other right or remedy against Landlord
or Landlord's Affiliates, as a result of any termination or malfunction of any
utilities or systems except as specifically provided otherwise in this Lease,
although this will not be deemed to limit in any way Landlord's repair and
maintenance obligations under Section 12.1 or its repair and/or restoration
obligations under Articles 16 and 17 if and to the extent applicable.

          (b) During the Lease term, Landlord shall provide the services
("Landlord's Services") set forth in Exhibit "G."

11.  USE OF PREMISES.
     ---------------

     Tenant will use the Premises for the purposes described in Section 1.1(h),
but for no other purpose. Tenant will:

          (a) Not permit any objectionable or unreasonable noises, vibrations,
odors or fumes in or to emanate from the Premises, nor commit or permit any
waste, improper, immoral or offensive use of the Premises, any public or private
nuisance or anything that disturbs the quiet enjoyment of neighboring owners or
tenants. All deliveries and pickups must be conducted at reasonable times and in
a reasonable manner. All trash and waste products must be stored, discharged,
processed and removed in a reasonable manner and in compliance with applicable
Laws and so as not to be visible to neighboring owners or tenants or create any
health or fire hazard.

                                      -14-
<PAGE>   16

          (b) [INTENTIONALLY OMITTED]

          (c) Not: permit any coin or token operated vending, pinball, gaming or
other mechanical devices on the Premises, except for telephones and vending
machines solely for use by Tenant's employees and its business invitees; permit
governmental or quasi-governmental agencies to occupy the Premises; use or
operate the Premises for retail sales to the general public or as a messenger,
answering or employment service, doctors' offices, for banking or mortgage
broker or mortgage banking purposes (but a credit union of not more than 1,800
square feet serving only Tenant's employees will not be deemed excluded by this
clause), a restaurant or food-service facility (other than for Tenant's
employees and its business invitees), a school or educational institution
(although training and demonstration rooms for Tenant's employees and customers
are permitted), or living or sleeping quarters; store, sell or distribute
obscene, lewd or pornographic materials or engage in related businesses in or
from the Premises; or conduct any auction, distress, fire, bankruptcy or
going-out-ofbusiness sale (except that Tenant may conduct such a sale once each
calendar year in the Premises of its equipment and products, provided that each
such sale is in accordance with applicable Laws and lasts no more than three (3)
days).

          (d) Comply with: Laws and insurance requirements affecting the
Premises or any use and occupancy thereof, including, without limitation, making
required alterations to the Premises; and Landlord's rules and regulations and
reasonable changes to those rules and regulations made by Landlord from time to
time (provided that such reasonable changes are not materially more adverse to
Tenant than the current rules and regulations). Tenant will, at its expense,
obtain and maintain all licenses, approvals and variances necessary to conduct
its business and occupy the Premises (other than the initial temporary or final
Certificates of Occupancy to be obtained in connection with Landlord's Work),
but none of those licenses, permits or variances will be binding on or in any
way affect or restrict Landlord or the Premises itself.

          (e) If it wishes, install exterior signage on the Building, as well as
a limited number of monument signs, which shall be subject to compliance with
applicable Laws and Landlord's approval as to size, location, materials and
design, which approval shall not be unreasonably withheld. Subject to compliance
with applicable Laws, Tenant may install such interior signage as it may deem
necessary or advisable. Tenant will be responsible for the maintenance and
repair of its signage, and on or before the expiration of the term, it will
remove its signage and repair any damage to Landlord's reasonable satisfaction.

          (f) During the Lease term, unless Tenant's right to possession is
terminated pursuant to this Lease, Tenant and its employees will have access to
the Premises twenty-four (24) hours per day, three hundred sixty-five (365) days
per year, subject to emergencies, force majeure and necessary repairs,
maintenance or construction.

                                      -15-

<PAGE>   17

12.  MAINTENANCE AND REPAIRS.
     -----------------------

     12.1 LANDLORD'S OBLIGATIONS. Landlord will repair and maintain: the
roadways, sidewalks, parking lot and loading docks of the Premises, and provide
snow plowing and landscaping for the Premises; the roof, any elevators, the
structural elements of the Building (including structural elements of the
columns, stairwells, foundations, floors and exterior walls of the Building, but
not the interior surfaces of any walls, floors or ceilings); the plumbing
Systems and Equipment, but excluding any specialty plumbing Systems and
Equipment for Tenant's engineering, research and development or manufacturing
processes or any kitchen appliances or cafeteria equipment or installations; the
base building HVAC system (but excluding any special systems, such as special
computer-room cooling systems, etc.); the exterior windows and exterior glass of
the Premises (except as provided in Section 12.2 below); and the base building
life safety and sprinkler systems, and the base building electrical system (but
excluding for example Tenant's own security system and any special or
abovestandard systems, such as special computer-room systems, etc.) All of the
foregoing will be performed in a manner generally similar to the repair and
maintenance activities customarily undertaken by prudent owners of property
similar to the Building. However, subject to the terms in Section 8.3 of this
Lease regarding casualties and waivers of claims for damage, Tenant will be
responsible for all repairs and maintenance resulting from Tenant's Alterations
or the negligent or intentional acts or omissions of Tenant or its Affiliates.
Landlord will make its repairs within a reasonable time following Tenant's
notification that the repairs are required and once begun will proceed
diligently with such repairs. Landlord's obligations are subject to the
provisions of Articles 16 and 17 and the rest of this Lease. If requested by
Tenant, Landlord will provide a full-time or part-time building engineer on-site
on the Premises to help supervise and perform Landlord's repair, maintenance and
service obligations, and all costs for such personnel shall be deemed to part of
Operating Costs.

     12.2 TENANT'S OBLIGATIONS. Except for Landlord's obligations in Section
12.1, Tenant will maintain and repair the Building and the Systems and Equipment
serving the Building in a first-class manner, provide its own janitorial service
and keep the Building in good order and condition, including, without
limitation, Tenant's Property, all doors, windows (but only to the extent of
breakage or damage caused by Tenant or its Affiliates), window treatments, wall
coverings, floor coverings, non-structural portions of the ceiling, floor and
walls, and Tenant's Alterations (unless otherwise requested by Landlord),
reasonable wear and tear and damage by fire and casualty excepted. Landlord will
reasonably cooperate with Tenant to enforce any warranties that Landlord may
receive in connection with any equipment that Tenant is required to maintain.

13.  ALTERATIONS.
     -----------

     13.1 LANDLORD'S CONSENT. "Alterations" means Tenant's alterations,
additions, improvements, remodeling, repainting, decorations or other changes
(NOT including the tenant improvements made as part of Landlord's Work). Tenant
may make nonstructural Alterations to the interior of the Building WITHOUT
Landlord's consent provided that Tenant complies with this Article and the rest
of this Lease and the Alterations do not: affect the windows or the exterior of
the Building; increase any mezzanine areas of the Building; adversely affect the
strength,

                                      -16-
<PAGE>   18

structural integrity or load-bearing capacity of any portion of the Building; or
adversely affect the Systems and Equipment in the Building. All other
Alterations require Landlord's prior written consent, which may be withheld
arbitrarily. Whether or not Landlord's consent is required, Alterations are
subject to the rest of this Article.

     13.2 NOTICE. Tenant will notify Landlord at least fifteen (15) days before
beginning any Alterations (other than the initial Tenant's Work for each Phase).
Together with Tenant's notice, or if notice is not required then prior to
beginning the Alterations, Tenant will give Landlord copies of the necessary
permits and approvals and, if Landlord deems it necessary in its arbitrary
discretion, plans and specifications for the Alterations (but not for minor,
non-structural Alterations such as wall coverings, wall hangings, built-in
cabinetry, movable partitions, carpeting and painting). Landlord's review or
approval of Tenant's plans and specifications is solely for Landlord's benefit
and will not be considered a representation or warranty to Tenant as to safety,
adequacy, efficiency, compliance with Laws or any other matter, or a waiver of
any of Tenant's obligations. Except for items of Tenant's Property, and unless
otherwise specifically agreed by Landlord in writing in response to Tenant's
specific written request in each instance with respect to each Alteration, at
the end of this Lease all Alterations will be removed and the Premises restored
to its condition prior to the Alterations, unless otherwise requested in writing
by Landlord prior to the end of this Lease, in which case they will be
surrendered with the Premises at the end of this Lease and will be deemed to be
Landlord's property (except for moveable partitions, which will remain Tenant's
Property).

     13.3 COMPLIANCE WITH LAWS. Alterations will comply in all respects with
this Lease and applicable Laws and insurance requirements. Alterations will be
done in a first-class manner, using first quality materials, and so as not to
interfere with Landlord or other tenants in the Premises, cause labor disputes,
disharmony or delay, or impose any Liabilities on Landlord. Alterations will be
performed only by experienced, licensed and bonded contractors and
subcontractors approved in writing by Landlord (except that Tenant need not
obtain Landlord's approval for contractors who perform a non-structural
Alteration with an aggregate cost of less than $100,000.00). Tenant will cause
its contractors and subcontractors to carry workmen's compensation insurance in
statutory limits, and commercial general liability insurance (Broad Form CGL, or
if such insurance is not then commercially available, the closest equivalent) in
an amount not less than $1,000,000.00 or such higher amount as then may be
customarily demanded by prudent landlords, and such liability insurance shall
contain cross-liability endorsements or the equivalent (if Landlord is to be
named as an additional insured hereunder) and automobile liability insurance in
the same amount, and if such work is reasonably estimated to cost more than
$75,000.00 in any instance, Landlord and its general partners, Landlord's
Mortgagees and the property managers shall be named as additional insureds on
such policies.

     13.4 LIENS. Tenant will pay when due all claims for labor, materials and
services claimed to be furnished for Tenant or Tenant's Affiliates or for their
benefit and keep the Building and the Premises free from all liens, security
interests and encumbrances based on or arising from such claims ("Liens").
Tenant will indemnify Landlord for, and hold Landlord 

                                      -17-


<PAGE>   19

harmless from, all Liens, the removal of all Liens and any related actions or
proceedings, and all Liabilities incurred by Landlord in connection therewith.
NOTICE IS HEREBY GIVEN TO ALL PERSONS FURNISHING LABOR OR MATERIALS TO TENANT
THAT NO MECHANICS', MATERIALMENS' OR OTHER LIENS SOUGHT ON THE PREMISES WILL IN
ANY MANNER AFFECT LANDLORD'S RIGHT, TITLE OR INTEREST.

14.  INDEMNITY; SATISFACTION OF REMEDIES.
     -----------------------------------

     14.1 INDEMNIFICATION. Notwithstanding Section 24.11 or any other provision
of this Lease, but subject to the next sentence, Tenant will NOT be required to
indemnify Landlord for or hold it harmless from Liabilities if and to the extent
that they arise directly from Landlord's negligence or willful misconduct or the
negligence or willful misconduct of Landlord's employees, agents, contractors
and subcontractors (if and to the extent that those contractors and
subcontractors are performing work under contracts or agreements with Landlord).
Notwithstanding anything to the contrary, for all purposes in connection with
this Lease and the Premises, Landlord and its employees, agents, contractors and
subcontractors and their respective Affiliates never will be deemed to have been
negligent or to have engaged in willful misconduct because of any failure to
properly supervise Tenant or Tenant's Affiliates or to prevent, discover,
disclose, correct or cure any acts or omissions of Tenant or Tenant's
Affiliates. Except as otherwise specifically provided in Section 8.3, Tenant
will indemnify Landlord for and hold Landlord harmless from Liabilities arising
from or in connection with: acts or omissions of Tenant and its Affiliates on,
about or in connection with the Premises, and/or agreements or alleged
agreements involving Tenant and any third parties, and/or the conduct of
Tenant's business; Tenant's breach of or default under this Lease; and claims by
Tenant's Affiliates or persons other than Tenant if Landlord declines to consent
to any act, event or document requiring Landlord's consent under this Lease
(but, subject to the terms of this Lease, this will NOT prevent Tenant from
bringing an action against Landlord if Landlord declines to consent if Landlord
is required to consent by the terms of this Lease or if Landlord's decision not
to consent is unreasonable where Landlord is required to be reasonable).

     14.2 DAMAGE TO PERSONS OR PROPERTY. Subject to the rest of this Section and
the rest of this Lease, Landlord will be liable for injuries to persons and
damages to property to the extent caused by its own negligence or willful
misconduct or the negligence or willful misconduct of Landlord's employees,
agents, contractors and subcontractors (if and to the extent that those
contractors and subcontractors are performing work under contracts or agreements
with Landlord), but Landlord will not be liable for any special, indirect,
consequential, punitive or similar damages (including, without limitation, any
loss of use or revenue by Tenant or any other person) under any circumstances,
or for any Liabilities arising from or in connection with: acts or omissions of
Tenant, any third parties, or their Affiliates, including, without limitation,
burglary, vandalism, theft, or criminal or illegal activity; explosion, fire,
steam, electricity, water, gas, rain, pollution, contamination, hazardous
substances, motor vehicles or any casualties; breakage, cracking, leakage,
malfunction, obstruction or other defects in Systems and Equipment or the roof,
walls, floors, surfaces or structure, or of any services or utilities; any work,
demolition, maintenance or repairs permitted under this Lease; any exercise of
Landlord's rights under any Laws or under this Lease, including any entry by
Landlord or its Affiliates on the Premises and/or the Building as permitted by
and in accordance with this Lease; any loss of or damage to 

                                      -18-

<PAGE>   20

Tenant's Property; or the requirements of any Laws or any of the matters
described in Section 24.5. Tenant waives all claims against Landlord in
connection therewith, but the foregoing is not meant to imply that Tenant will
be liable therefor, or be required to indemnify Landlord against any loss,
damage or liability incurred by Landlord as a result thereof, unless such
liability or indemnity is otherwise provided for by the terms of this Lease, nor
to release Landlord from its repair and maintenance obligations under Section
12.1 or Landlord's obligations to repair and/or restore in Articles 16 and 17 if
and to the extent applicable. Tenant also waives any Laws or rights that would
permit Tenant to terminate this Lease, perform repairs or maintenance in lieu of
Landlord (or on Landlord's behalf), or offset or withhold any amounts due
because of damage to or destruction of the Premises, any repairs or maintenance,
or for any other reason (unless specifically permitted in this Lease [for
example, in Section 14.4 below]). This exculpation of Landlord and all of
Tenant's waivers in this Lease will apply to all of Tenant's Affiliates to the
greatest extent possible.

     14.3 SATISFACTION OF REMEDIES. Notwithstanding anything in this Lease or
elsewhere to the contrary: Tenant will look solely to Landlord's interest in the
Premises and, subject to the terms of this Lease, Landlord's interest in
liability insurance proceeds, casualty insurance proceeds and eminent domain
awards if and to the extent that such proceeds or awards are not paid to or
retained by Landlord's Mortgagees or applied in accordance with this Lease, to
satisfy any claims, rights or remedies, and Landlord and its partners and their
respective Affiliates, at every level of ownership and interest, have no
personal or individual liability of any type, whether for breach of this Lease
or otherwise, their assets will not be subject to lien or levy of any type, nor
will they be named individually in any suits, actions or proceedings of any
type.

     14.4 Tenant's Self Help.
          ------------------

          (a) Tenant shall have the right, but not the obligation, to perform an
obligation that Landlord is otherwise required to perform under this Lease (the
"Right of Self Help") under the circumstances set forth below:

               (i) If Landlord fails to perform such obligation as and when
required under this Lease, such failure materially interferes with Tenant's
business activities in the Premises, and such failure continues without cure for
thirty (30) days after a subsequent written notice from Tenant to Landlord (but
if more than thirty (30) days are reasonably required to cure, Landlord will be
deemed to have cured if it promptly begins to cure within the thirty (30)-day

                                      -19-

<PAGE>   21

period and then diligently completes the cure as soon as reasonably possible),
and Tenant provides an additional notice to Landlord and Landlord's Mortgagees
that it intends to perform such obligation and Landlord and Landlord Mortgagees
fail to perform such obligation within a reasonable time after receiving
Tenant's notice of its intention to so perform.

               (ii) If the failure to perform such obligation would result in an
emergency condition if not remedied promptly (i.e., an imminent and substantial
risk of significant additional property damage, or personal injury or death) and
Landlord fails to perform such obligation within a reasonable period of time
after receiving Tenant's notice of such emergency condition and Tenant's
intention to exercise the Right of Self Help (and in such case Tenant shall
exercise its Right of Self Help only if and to the extent reasonably necessary
to remedy the emergency condition, and as soon as there no longer is an
emergency condition, Tenant shall not have the right to continue to exercise the
Right of Self Help pursuant to this Subsection (ii)).

(See Section 3 of Addendum #3, which addresses Tenant's recovery of the
reasonable costs and expenses incurred by Tenant in exercising its Right of Self
Help.)

15.  PARKING.
     -------

     All parking areas on the Premises shall be available to Tenant and its
Affiliates. Except for Tenant's share of Taxes and Operating Costs associated
with the parking areas, Tenant will not be charged for parking. If necessary in
Landlord's reasonable judgement to protect property, permit adequate security,
prevent unauthorized use or entry, increase safety or promote the orderly or
efficient flow of traffic, Landlord may: change signs, lanes and the direction
of traffic within the parking areas; change, eliminate or add parking spaces or
areas devoted to parking (provided that Tenant's parking is not reduced); allow
parking with a validation, valet, sticker or other system; promulgate reasonable
rules and regulations that do not materially adversely affect any of Tenant's
parking rights; and take any other actions deemed necessary by Landlord, as long
as such actions conform with this Lease.

16.  DAMAGE OR DESTRUCTION.
     ---------------------

     16.1 REPAIRS. Subject to the rest of this Article and the rest of this
Lease, Landlord will repair damage to the Premises and the Building caused by
fire or other casualties to the extent insured against under standard "all risk"
casualty policies. However, Landlord is not obligated to repair damage for which
Landlord has no liability if and to the extent specifically so provided under
other provisions of this Section or the rest of this Lease or to undertake
repairs unless insurance proceeds are available, spend more than the net
insurance proceeds it actually receives and is permitted to retain for any
repair or replacement ("Landlord's Insurance Proceeds") (except if and to the
extent that Tenant agrees in writing to advance, and in fact advances as needed,
all costs in such repairs), or repair or replace any damage to Tenant's Work,
Tenant's Property or any Alterations (except to the extent that damage to such
Alterations is covered by Landlord's 

                                      -20-

<PAGE>   22

casualty insurance policy). Except as may otherwise be required by then
applicable Laws or as provided in this Lease, Landlord will attempt to restore
the damaged portions to their prior condition. Landlord will proceed diligently
to complete repairs within a reasonable time after receiving notice of the
damage, required approvals, building permits and licenses and the insurance
proceeds payable on account of the damage, all of which Landlord will pursue
diligently, but in no event will this diligent pursuit be deemed to require any
legal action by or on behalf of Landlord, except if and to the extent that
Tenant agrees in writing to advance, and in fact advances as needed, all costs
in connection with such legal action and such legal action does not result in
any Liabilities to Landlord.

     16.2 ELECTION TO TERMINATE. Landlord has the option either to (a) repair
the casualty damage, or (b) terminate this Lease by delivering written notice
within ninety (90) days after the damage occurs, if: (i) the damage occurs
during the last two (2) years of the term, as the term already may have been
extended pursuant to this Lease, and in Landlord's reasonable determination the
repairs would take more than one hundred fifty (150) days or one-third (1/3) of
the remaining term, whichever is less, to complete (unless Tenant validly
exercises a previously unexercised Extension Option in accordance with this
Lease within thirty (30) days after receipt of written notice from Landlord that
Landlord intends to terminate this Lease in accordance with this Subsection (i)
or unless Tenant within such 30-day period agrees in writing to advance, and in
fact advances as needed, all costs in excess of Landlord's Insurance Proceeds in
order to complete such repairs); or (ii) Tenant is in default; or (iii) in
Landlord's reasonable judgement the repairs would take more than two (2) years
from the date of the damage to complete or cost more than the insurance proceeds
that are reasonably likely to be made available as a result of such casualty
(unless within thirty (30) days after receipt of written notice from Landlord
that it intends to terminate this Lease in accordance with this Subsection (iii)
Tenant agrees in writing to advance, and in fact advances as needed, all costs
in excess of Landlord's Insurance Proceeds in order to complete such repairs; or
(iv) Tenant already has exercised the Cancellation Option; or (v) if the damage
occurs during the eighth (8th) or ninth (9th) Lease Year and in Landlord's
reasonable determination the repairs would take more than one hundred fifty
(150) days or 1/3 of the remaining period until the end of the ninth (9th) Lease
Year, whichever is less, to complete, and within thirty (30) days after
Landlord's written request. Tenant agrees to advance and in fact advances as
needed, all costs in excess of Landlord Insurance Proceeds in order to complete
such repairs.

          Tenant also has the right to terminate this Lease for such damage if:
(x) the damage denies Tenant access to the Premises, or causes more than thirty
percent (30%) of Tenant's parking spaces to become unusable (and Landlord cannot
replace those lost spaces reasonably promptly and in reasonable proximity to the
Premises, whether by the use of valet parking, or otherwise), or causes at least
85% of the useable area of the Building to become entirely untenantable,
Landlord elects or is required under this Lease to repair the damage, and except
for delays for which Tenant is responsible under this Lease, Landlord fails to
substantially complete the repairs it is required to make (or restore access or
restore or replace parking spaces, as applicable) within two (2) years after the
damage occurs, Tenant delivers its written termination notice to Landlord within
fifteen (15) days after the end of Landlord's two (2)-year repair period and
Landlord fails to substantially complete those repairs (or restore access or
restore or replace parking spaces, as applicable) within sixty (60) days after
receiving such notice. If Landlord's repairs are deemed to be substantially
completed (or Landlord has restored 

                                      -21-

<PAGE>   23

access or restored or replaced parking spaces, as applicable) within this sixty
(60)-day period, Tenant's termination notice will be null and void and this
Lease will continue in existence; or (y) the damage denies Tenant access to the
Premises, or causes more than thirty percent (30%) of Tenant's parking spaces to
become unusable (and Landlord cannot replace those lost spaces reasonably
promptly and in reasonable proximity to the Premises, whether by the use of
valet parking, or otherwise) or causes at least 85% of the useable area of the
Building to become entirely untenantable, Landlord notifies Tenant specifically
and in writing that the repairs that Landlord is required to make probably will
take longer than two (2) years to substantially complete (or that Landlord
cannot restore access or restore or replace parking spaces, as applicable,
within two (2) years) and Tenant delivers to Landlord a written termination
notice within fifteen (15) days after receiving Landlord's notice; or (z) the
damage occurs during the last two (2) years of the term (as it may have been
extended) and the damage denies Tenant access to the Premises, or causes more
than thirty percent (30%) of Tenant's parking spaces to become unusable (and
Landlord cannot restore or replace those lost spaces reasonably promptly and in
reasonable proximity to the Premises, whether by the use of valet parking, or
otherwise) or causes at least 85% of the useable area of the Building to become
entirely untenantable, Landlord notifies Tenant specifically and in writing that
the repairs that Landlord is required to make probably will take longer than one
hundred fifty (150) days or one-third (1/3) of the remaining period until the
expiration of the term, whichever is less, to substantially complete (or that
Landlord cannot restore access or restore or replace parking spaces, as
applicable, within such period) and Tenant delivers to Landlord a written
termination notice within fifteen (15) days after receiving Landlord's notice.

     16.3 ABATEMENT OF RENT. If the Building or any portion thereof is damaged
by casualty so that it is untenantable for more than two (2) consecutive
business days, base rent and Taxes and Operating Costs will abate in proportion
to the degree to which Tenant's use of the Premises is impaired, as reasonably
determined by Landlord, from the date of the damage until Landlord has
substantially completed the repairs it is required to make and gives Tenant
access to the Premises, or Tenant reoccupies or can reoccupy the damaged part of
the Premises, whichever is earlier. The abatement of base rent, Taxes and
Operating Costs will not exceed the net amount of rental loss insurance
collected by Landlord for or by reason of such casualty. The abatement of base
rent, Taxes and Operating Costs described above is Tenant's sole remedy and
compensation in connection with any damage, destruction or repairs, except for
Tenant's right to terminate as permitted in this Article, or unless Landlord
willfully fails to attempt to complete with diligence the repairs it is required
or elects to make.

     16.4 CONSEQUENCES OF TERMINATION. If this Lease is terminated per this
Article 16 or Article 17 but Tenant holds over in the Premises, then despite the
second to last sentence of Section 24.1, the most recent annual base rent will
not be doubled, and any abatement of rent that applied prior to the termination
will continue to apply to the same extent and for the same period that it would
have absent the termination. However, the rest of Section 24.1 will continue to
apply. Notwithstanding anything to the contrary, after a termination of this
Lease per this Article 16 or Article 17: Tenant shall remove Tenant's Property
from the Premises as quickly as reasonably practicable, but in any event within
sixty (60) days after such termination; Tenant assumes all risk of loss and/or
damage to Tenant's Property from any source, and waives against Landlord and its
Affiliates all Liabilities in connection therewith; Tenant shall cooperate with

                                      -22-

<PAGE>   24

Landlord at Tenant's expense to minimize any interference with Landlord's
activities on the Premises; and upon Landlord's request, Tenant shall
immediately remove (or relocate to an unaffected part of the Building, if any,
or the Premises) the items of Tenant's Property specified by Landlord if, in
Landlord's good faith belief, such removal or relocation is necessary to avoid
the risk of additional damage, injury or death or to comply with applicable
Laws, and if Tenant does not so remove or relocate those items of Tenant's
Property as so required, those items shall be deemed abandoned by Tenant and
Landlord shall have all of the rights set forth in the second sentence of
Article 3.

     16.5 RECONSTRUCTION COSTS. "Reconstruction Costs" means the costs advanced
by Tenant, if any, to perform Landlord's repairs up to the same level of fit and
finish that existed immediately prior to the casualty damage if and to the
extent that Tenant specifically has been granted the right in this Article 16 to
advance such costs. Reconstruction Costs shall not include any costs to repair
or replace Tenant's Work, Tenant's Property or any Alterations, nor any advances
that are subsequently repaid to Tenant (whether by insurance or otherwise).

17.  CONDEMNATION.
     ------------

          (a) If all or substantially all of the Premises is condemned, taken or
appropriated by any public or quasi-public authority under the power of eminent
domain, police power or otherwise, or if there is a conveyance in lieu thereof
("Condemned" or a "Condemnation"), this Lease will terminate as of the day
before the Condemnation.

          (b) If more than twenty-five percent (25%) of the usable area of the
Building is Condemned, either Landlord or Tenant may terminate this Lease as of
the day prior thereto by delivering written notice to the other within fifteen
(15) days after the Condemnation. Tenant also will have the right to terminate
this Lease subject to the terms of and in the manner described in Section (16.2
(x), (y) and (z) if the Condemnation denies Tenant access to the Building or
effectively renders the Building untenantable in the same manner, to the same
extent and for the same periods as a casualty as described in those Sections, or
at least thirty percent (30%) of Tenant's parking spaces are Condemned and are
not restored or replaced by Landlord and the ratio of the number of Tenant's
parking spaces Condemned compared to the rentable area of the Building Condemned
at the same time (if any) is materially greater than the ratio of Tenant's total
initial parking spaces compared to the initial rentable area of the Building, in
each case effective as of the date of Condemnation.

          (c) If part of the Premises is Condemned and this Lease is not
terminated, Landlord will make the necessary repairs so that, to the extent
reasonably possible, the remaining part of the Premises will be a complete
architectural unit. Otherwise, Landlord's restoration will be conducted as
described in Section 16.1, MUTATIS MUTANDIS, except that Landlord will not be
required to begin repairs until a reasonable time after it receives any
necessary approvals, building permits and licenses and substantially all of the
proceeds of any awards granted for the Condemnation, and then will proceed
diligently with the repairs. As of the date of Condemnation, base rent will
abate in proportion to the area of the Building Condemned.

                                      -23-
<PAGE>   25

Except for Tenant's rights to receive its share of Net Proceeds as set forth in
Addendum #3, all proceeds, income, rent, awards and interest in connection with
any Condemnation will belong to Landlord, whether awarded as compensation for
diminution of value to the leasehold improvements, or the unexpired portion of
this Lease, or otherwise. Except for Tenant's right to receive Net Proceeds as
set forth in Addendum #3, Tenant waives all claims against Landlord and the
condemning authority with respect thereto, and in connection with a
Condemnation, but nothing in this Section prevents Tenant from bringing a
separate action against the condemning authority for moving costs or for lost
goodwill (as long as this separate action does not diminish Landlord's
recovery).

18.  ASSIGNMENT AND SUBLETTING.
     -------------------------

     18.1 LANDLORD'S CONSENT REQUIRED. Tenant will not, and does not have the
right or power to, voluntarily, involuntarily or by operation of any Laws, sell,
convey, mortgage, subject to a security interest, license, assign, sublet or
otherwise transfer or encumber all or any part of Tenant's interest in this
Lease or the Premises, or allow anyone other than Tenant's employees (or
employees of Tenant's current or future joint venturers or development partners
who are temporarily working on joint projects with Tenant and who will not, in
the aggregate, occupy more than 25,000 square feet of space in the Building) to
occupy the Building or the Premises (singularly or collectively, "Transfer"),
without in each instance first obtaining Landlord's prior written consent
(unless Landlord's consent specifically is not required per Section 18.5(c)) and
complying with this Article and any attempt to do so without this consent (which
may be withheld arbitrarily unless otherwise specifically set forth in this
Article) and compliance will be null and void and a default, unless otherwise
specifically elected by Landlord in writing.

     18.2 NOTICE. Tenant will notify Landlord in writing at least thirty (30)
days before any proposed or pending Transfer (or as soon as reasonably possible
in the case of the Transfer pursuant to Section 18.5 (c) if thirty (30)-day
advance notice is not possible, but in any case before such a Transfer) and will
deliver to Landlord such information as Landlord may reasonably request in
connection with the proposed or pending Transfer and the proposed Transferee,
including, without limitation, a copy of the final executed Transfer documents,
current financial statements prepared or reviewed by an independent certified
public accountant, a current Dun & Bradstreet report (if available) and other
reasonably available financial information about and banking references for the
proposed Transferee, and information as to the type of business and business
history of the proposed Transferee. All of this information must be certified as
true and correct by a senior, responsible officer of the party providing the
information. The financial information received by Landlord from the Transferee
will be treated as confidential information, unless the information is otherwise
publicly available or is obtained by Landlord from other sources, and in any
event Landlord may disclose it to Landlord's lenders, attorneys, accountants,
prospective purchasers and their agents, to be treated by them as confidential
to the same extent as by Landlord.

                                      -24-

<PAGE>   26

     18.3 REASONABLE CONSENT. Landlord will not unreasonably withhold or delay
its consent to an assignment or sublease by Tenant. Landlord may withhold its
consent to any hypothecation, assignment for security purposes or other Transfer
arbitrarily and in its sole discretion. Tenant agrees that Landlord's
withholding of consent to a proposed sublease or assignment will be deemed
reasonable if Tenant is in default or any of the other material terms and
conditions of this Article have not been complied with, or if any of the
following conditions are not satisfied: (a) the subtenant or assignee will use
the Building and the Premises only for the uses permitted in Section 1.1(h) and
otherwise in accordance with this Lease, and the business and reputation of the
subtenant or assignee are reasonably acceptable to Landlord and Landlord'
Mortgagees (and Landlord's Mortgagees will not unreasonably withhold or delay
their consent); (b) the subtenant or assignee is reputable and creditworthy and
has the independent financial ability to perform its obligations under its
assignment or sublease without undue financial burden in Landlord's reasonable
judgment (which reasonable judgment shall be deemed satisfied if the subtenant
or assignee has a net worth, credit rating and financial capability at least
equal to Tenant's when Tenant executed this Lease), and it is not then subject
to any bankruptcy or reorganization plan, proceeding or order, and no receiver
is managing its affairs or assets; and (c) there will be no more than an
aggregate of six (6) subleases of the Premises at any one time. These conditions
are not exclusive and Landlord may consider other factors deemed to be relevant
in determining if Landlord should grant or reasonably withhold its consent.

     18.4 NO RELEASE OF TENANT. Whether or not Landlord consents, no Transfer
will release or alter any of the Transferor's or Tenant's Liabilities hereunder,
including, without limitation, the joint and several obligations of the
Transferor and Tenant to pay rent and perform all of Tenant's other obligations
under this Lease, except that, provided that there is then no default by Tenant
under this Lease, but notwithstanding any other provisions of this Lease to the
contrary, an assignor will be released (a "Released Assignor") from further
obligations under this Lease as of the date that the following conditions are
satisfied:

          (a) There is a valid assignment of this Lease by the assignor in
accordance with the terms of this Article to an assignee who has a net worth,
Moody's or Standard & Poor's credit rating and financial capability at least
equal to those possessed by PictureTel Corporation when PictureTel Corporation
executed this Lease or equal to those possessed by the assignor just prior to
the assignment (whichever are better), or the assignor validly assigns this
Lease to and merges into or consolidates with a Permitted Assignee and thereby
ceases to exist. PictureTel Corporation's, credit rating as of the date of its
execution of this Lease is deemed to be Baa2 (Moody's) and BBB (Standard &
Poor's).

          (b) The assignee (including a Permitted Assignee) unconditionally
assumes in writing for Landlord's benefit this Lease and all of the assignor's
and Tenant's Liabilities including, without limitation, those that arose prior
to the assignment, and notwithstanding any other provision of this Lease, upon
such assignment and assumption the assignor shall have no further obligations
under this Lease and may cease its existence without any violation of any
provision of this Lease. 
                                      -25-

<PAGE>   27

The acceptance of rent by Landlord from any person other than Tenant is not a
waiver by Landlord. Consent to one Transfer will not be deemed to be consent to
any subsequent Transfer. If Tenant or any Transferee defaults under this Lease,
Landlord may proceed directly against the Transferee and/or against Tenant
and/or against the Transferor without proceeding or exhausting its remedies
against the other. After any assignment, or after sublease(s) aggregating more
than fifty percent (50%) of the area of the Building with an initial term
(including options) of at least seventy-five percent (75%) of the remaining term
of this Lease at the time of such Transfer, Landlord may consent in its
arbitrary discretion to subsequent Transfers of or amendments to this Lease
without notifying Tenant or any other person, without obtaining consent thereto,
and without relieving Tenant or a Transferor of its Liabilities under this Lease
(as it may be amended), provided that unless Tenant or a Transferor consents in
writing, Tenant or such Transferor (as applicable), will not become liable by
reason of any such Transfer or amendment to the extent of any increase in
Tenant's or such Transferor's (as applicable) aggregate obligations and
liabilities under this Lease as set forth in such Transfer or amendments, or for
increases in the scope of any indemnities owed to Landlord (e.g., an additional
act or omission requiring indemnification, as opposed to an increase in the
potential liability under an existing indemnity), or for any increase in the
Lease term, except for: (a) Extension Options exercised pursuant to and in
accordance with Addendum #2 hereto or otherwise agreed to by Tenant or
Transferor (as applicable); or (b) other extensions agreed to by a Transferee,
in each case if such other extension is permitted in accordance with the terms
of a written agreement between Tenant or the transferor and such Transferee,
provided that within thirty (30) days after such extension has been entered into
Tenant receives notice, or in fact otherwise becomes aware, that such extension
has been entered into. Subject to the following, but notwithstanding anything
else to the contrary, Tenant and a Transferor will not be relieved of any
Liabilities under this Lease if and to the extent that Landlord grants or
consents to any waivers under this Lease to or for the benefit of any Transferee
(but if, prior to a breach by Tenant or any Transferee, Landlord waives in
writing the performance by the Transferee of any obligation that Tenant
otherwise would be required to perform under this Lease, that waiver also shall
apply with respect to Tenant [or such Transferor, as applicable]). Landlord's
waivers with respect to a Transferee will not affect the rights (if any) of
Tenant or the Transferor (as applicable) against the Transferee for any breach
of this Lease or any assignment, sublease or other agreement (as applicable) by
the Transferee. However, all of such rights against the Transferee will be
subject and subordinate to Landlord's rights under this Lease against the
Transferee in the event of a default under this Lease.

     18.5 Additional Terms.
          ----------------

          (a) Tenant will pay Landlord's reasonable attorneys' fees and other
costs in connection with any request for Landlord's consent to a Transfer. This
Article is binding on and will apply to every Transferee, at every level. The
surrender of this Lease or its termination will not be a merger, but Landlord
will have the right in its arbitrary discretion to terminate all subleases and
the occupancy rights of all Transferees. Tenant will pay to Landlord as
additional rent: all consideration paid or payable for or by reason of any
assignment of this Lease (other than an assignment to a Permitted Assignee), and
in the case of a sublease, the amount by which the sublease rent and other
consideration paid or payable exceeds the base rent, Taxes and Operating Costs
payable by Tenant under this Lease for the sublease term (prorated if the area
subleased is less than the entire area of the Building), in each case after
Tenant first recovers its 

                                      -26-

<PAGE>   28

bona fide, reasonable out-of-pocket costs paid to third parties unaffiliated
with Tenant or the subtenant or assignee to obtain the subtenant or assignee
(including without limitation, attorneys fees, brokerage commissions, new tenant
improvements made solely for the subtenant or assignee), and Tenant recovers any
free rent granted. At Landlord's option, Landlord may collect all or any part of
this additional rent directly from the payor. Tenant will promptly deliver to
Landlord copies of all executed transfer documents, all collateral agreements
and all later amendment.

          (b) An assignee will be deemed to have assumed all of Tenant's
Liabilities under this lease and will be deemed to be bound by this Lease, and
Tenant and the assignee will indemnify Landlord and hold it harmless from all
Liabilities in connection with the assignment, although this indemnity will not
affect any liability that Landlord owes to Tenant or others if and to the extent
specifically set forth in the terms of this Lease, and it is also understood
that Tenant's and any assignee's Liabilities and indemnities relating to the use
and occupancy of the Premises will remain as set forth in this Lease and any
amendments thereto. To confirm the foregoing, a prospective assignee will be
required to execute and deliver to Landlord an unconditional written assumption
of Tenant's Liabilities under this Lease and the indemnity described above.
Tenant and the assignee will be deemed to be jointly and severally liable for
all Liabilities of the Tenant under this Lease. A sublease will be deemed to be
subject and subordinate to this Lease in all respects; Tenant and the subtenant
will indemnify Landlord and hold it harmless from all Liabilities in connection
with the sublease (although this indemnity will not affect any liability that
Landlord owes to Tenant or others if and to the extent specifically set forth in
the terms of this Lease, and it is understood that Tenant's Liabilities and
indemnities relating to the use and occupancy of the Premises remain as set
forth in this Lease and any amendments thereto); the subtenant will acquire no
rights or claims against Landlord or its Affiliates; if this Lease is terminated
or Landlord rightfully reenters or repossesses the Premises, Landlord may
terminate the sublease, or at its option, become the sublessor under the
sublease and the subtenant will attorn to Landlord, but Landlord will not be
liable for Tenant's acts or omissions, subject to any existing defenses or
offsets against Tenant or bound by any amendment to the sublease made without
Landlord's prior written consent. Sublessees will not have the right or power to
make further Transfers, and any attempt to do so will be null and void and a
default unless otherwise specifically elected by Landlord in writing. Tenant
will make each prospective Transferee aware of the terms of this Article and
will deliver to each prospective Transferee a true and correct copy of this
Lease prior to any Transfer. Each document of assignment, sublease or other
Transfer, at every level, must include or explicitly incorporate the terms of
this Article. Landlord may require confirming and/or additional assurances and
agreements for its protection from Tenant and the assignee or subtenant, each of
whom agrees to give such assurances and execute such agreements, in each case
consistent with the terms of this Lease. Notwithstanding anything to the
contrary, except for a valid assignment or sublease to a Permitted Assignee or a
Permitted Sublessee, respectively, Tenant will not, and will not have the right
or power to, assign or convey to, or sublease or otherwise Transfer more than
20,000 square feet in the Building to, any then-current tenant that leases more
than 20,000 square feet in any project which lies within 

                                      -27-

<PAGE>   29

the "Project Area" as depicted in Exhibit "K" hereto, and of which, at such
time, Landlord or any of its Control Affiliates is the owner, or a general
partner in the Owner, or a shareholder (in a closely held corporation) of at
least forty percent (40%) of the issued and outstanding voting shares of the
owner or a general partner in the owner, and Landlord may arbitrarily withhold
its consent to such a Transfer.

          (c) If Tenant is a corporation, the Transfer, directly or indirectly,
by one or more transactions of more than forty percent (40%) of Tenant's capital
stock (but if Tenant is a public corporation whose stock is regularly traded on
a national stock exchange or in the over-the-counter market and quoted on
NASDAQ, stock purchases in the ordinary course of business on the open market
will not be deemed to be Transfers of stock for purposes of this Subsection
(c)), or any dissolution, merger, consolidation or other reorganization of
Tenant, or if Tenant becomes a subsidiary or division of another entity, or the
Transfer of substantially all of Tenant's assets, will be deemed to be an
assignment of this Lease. Notwithstanding anything to the contrary herein
contained, an assignment or sublease by Tenant to an entity that is controlled
by, controls or is under common control with Tenant, or to an entity resulting
from a merger, consolidation or reorganization with Tenant, or to a purchaser of
substantially all of the assets or shares of Tenant, will be deemed to be a
permitted assignment or sublease, as applicable, that does not require
Landlord's or Landlord's Mortgagees' consent provided that the rest of this
Article is complied with, the Transferee (if an assignee) unconditionally
assumes this Lease and all of Tenant's Liabilities (including, without
limitation, those arising before the assignment) in writing, and the Transferee
has a net worth, Moody's or Standard & Poor's credit rating, and financial
capability at least equal to PictureTel Corporation's when PictureTel
Corporation executed this Lease as set forth in Section 18.4(a) (and such
Transferee will be a "Permitted Assignee" or a "Permitted Sublessee," as
applicable). As a material inducement to Landlord, Tenant agrees that it will
make each potential Transferee contemplated by this clause (including any
potential purchasers or candidates for merger, consolidation or reorganization)
aware of this clause and the rest of this Lease, deliver a copy of this clause
and the rest of this Lease to such party prior to entering into such an
agreement with such party and make the written assumption described herein and
the compliance with this Article a condition to the effectiveness of such an
agreement.

          (d) An assignee pursuant to a valid assignment and assumption of this
Lease in accordance with the terms of this Article shall be regarded as the
Tenant under this Lease with all of the rights and Liabilities of the Tenant,
except as otherwise specifically provided in this Lease, but this shall not
affect the assignor's continuing liability under this Lease as set forth in
Section 18.4.

19.  MORTGAGEE PROTECTION; UNPERMITTED FINANCING; LANDLORD'S LOAN DEFAULTS.
     ---------------------------------------------------------------------

     19.1 SUBORDINATION AND ATTORNMENT. This Lease is subordinate to all
Superior Leases and Mortgages (defined in Section 24.4), and Tenant will attorn
to each person or entity that succeeds to Landlord's interest under this Lease,
provided that such person or entity agrees in writing not to disturb Tenant's
rights under this Lease as long as Tenant is not in default. This Section is
self-operative, but if requested to confirm a subordination and/or attornment or
non-

                                      -28-

<PAGE>   30

disturbance, Tenant will execute subordination and/or attornment and/or
non-disturbance agreements furnished by Landlord or Landlord's lessor or
mortgagee under any of the Superior Leases and Mortgages (a "Landlord's
Mortgagee") within twenty (20) days after request and provided that such
agreements: materially substantively conform to typical institutional forms of
agreements then in use and do not result in a material adverse change in any of
the material terms of this Lease, and provided that any such subordination
agreements shall provide that the lender shall agree to concurrently deliver to
Tenant any notices of Landlord's default delivered to Landlord and to accept
from Tenant a cure of such defaults (if and to the extent that such defaults are
curable by Tenant) within the cure periods for such defaults granted to Landlord
under such loans; or materially substantively conform to one or more of the
forms attached as Exhibit "J" hereto. However, if Landlord or Landlord's
Mortgagee elects in writing, this Lease will be superior to the Superior Leases
and Mortgages specified, regardless of the date of recording, and Tenant will
execute an agreement confirming this election on request.

     19.2 MORTGAGEE'S LIABILITY. The obligations and Liabilities of Landlord,
Landlord's Mortgagees or their successors under this Lease will exist only if
and for so long as each of these respective parties owns fee title to the
Premises or is the lessee under a ground lease of the Premises. Tenant will be
liable to Landlord's Mortgagees or their successors if any of those parties
become the owner of the Premises for any payment of base rent made more than
thirty (30) days in advance of the due date for such payment as set forth in
this Lease. Landlord's Mortgagees and their successors will not be liable for:
(a) acts or omissions of prior owners; (b) the return of any security deposit
not delivered to them; or (c) amendments to this Lease made without their
consent (if their consent is required under a Superior Lease or Mortgage).

     19.3 MORTGAGEE'S RIGHT TO CURE. No act or omission (if any) which otherwise
entitles Tenant under the terms of this Lease or by any Laws to be released from
any Lease obligations or to terminate this Lease will result in such a release
or termination unless Tenant first gives written notice of the act or omission
to Landlord and Landlord's Mortgagees and those parties then fail to correct or
cure the act or omission within a reasonable time thereafter (which will not be
less than sixty [60] days and which, in any case, will be long enough to allow
the Landlord's Mortgagees sufficient time within which to complete such a
correction or cure in a commercially reasonable and diligent manner). Nothing in
this Section or the rest of this Lease obligates Landlord's Mortgagees to
correct or cure any act or omission or is meant to imply that Tenant has the
right to terminate this Lease or be released from its obligations except as may
otherwise be permitted in this Lease (although if Landlord or Landlord's
Mortgagees fail to cure as set forth above, then nothing in this clause shall
prevent Tenant from exercising any of its rights and remedies as specifically
set forth in this Lease). Landlord will (and upon Tenant's written request
shall), and/or Landlord's Mortgagees may, give notice to Tenant in writing of
the identity of any mortgagee of the Premises and Tenant may rely on such
notice(s) in complying with this Article.

     19.4 UNPERMITTED FINANCING. So long as Tenant is not in default and is
entitled to continue to receive a share of Net Proceeds in accordance with
Addendum #3 and/or to exercise a Purchase Option in accordance with Addendum #4,
Landlord agrees not to use the Premises or any portion thereof to secure any
indebtedness other than:

                                      -29-

<PAGE>   31

          (a) The initial acquisition, construction/development, and/or
permanent financing in connection with the Premises and any additional advances
thereunder and any extensions, renewals, consolidations, replacements or
modifications thereof, so long as the proceeds thereof are used for the purposes
set forth in Subsection (b) below; or

          (b) Financing, the proceeds of which are: used to repay all or part of
the financing described in Subsection (a) above; or used to benefit the Premises
or pay any Liabilities in connection therewith or as required under this Lease;
or are included in Cash Proceeds; or used to pay for any development fees,
management fees or fees in lieu thereof payable to Landlord or its Affiliates
pursuant to this Lease or in connection with Landlord's Work or in connection
with the construction of any additional buildings on the Premises or the
enlargement of or other modification of the Building or the rest of the
Premises.

In any case, any such permitted financing that is placed on the Premises on or
before the end of the eighteenth (18th) Lease Year shall, by its terms, be
amortized and repaid entirely on or before the end of the Lease term (as it may
have been extended prior to the date that such financing encumbers the Premises,
and assuming no early terminations of the term), unless Tenant consents thereto
or Landlord agrees to reduce the cash portion of the purchase price of the third
(3rd) Purchase Option under Addendum #4 by the outstanding principal balance of
such financing as of the end of such Lease term (assuming no early terminations
thereof).

Secured financing that is prohibited pursuant to this Section 19.4 is called the
"Unpermitted Financing."

     19.5 Landlord's Loan Defaults. If either:
          ------------------------

          (a) Landlord defaults under any loans the lender of which is the
beneficiary under the Letter of Credit, and as a result of Landlord's default
such lender/beneficiary draws under the Letter of Credit (not including any
draws of the type described in Sections 24.17(b) or (e)), and Landlord's default
did not arise as a result of Tenant's breach of its obligations under this Lease
(e.g., Tenant's failure to pay rent in full when due hereunder) and at the time
of Landlord's default Tenant is not in default under this Lease; or

          (b) Landlord defaults under any mortgage loan secured by the Premises
or any portion thereof and the Letter of Credit is not drawn as a result
thereof, and Landlord's default did not arise as a result of Tenant's breach of
its obligations under this Lease and at the time of Landlord's default Tenant is
not in default under this Lease (e.g., Tenant's failure to pay rent in full when
due hereunder), and Tenant exercises its rights to cure Landlord's default; or

          (c) The beneficiary of the Letter of Credit draws under the Letter of
Credit and such draws are deemed to be LC Advances under Section 24.17(f);

THEN, if and to the extent that Landlord does not reimburse Tenant for the
amounts drawn under the Letter of Credit as set forth in Subsection (a) above
and/or the amounts paid by Tenant to the mortgagee to cure Landlord's default as
set forth in Subsection (b) above and/or pay to Tenant as and when required
amounts due under the LC Note (including for purposes of this Section only

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<PAGE>   32

amounts, if any, that remain due under the LC Note after funds from a permanent
loan have been received by Landlord and used to prepay Tenant as provided under
the LC Note) as described in Section 24.17(f) (collectively, the "Cure
Payments"), notwithstanding anything to the contrary in this Lease: (i) as
described in Section 3 of Addendum #3, Net Proceeds first will be distributed to
Tenant to repay the unrepaid Cure Payments; and (ii) if there are any unrepaid
Cure Payments as of the date that the loan secured by the Letter of Credit and
the mortgage loan and any refinancing thereof are fully paid, Tenant may offset
against base rent an amount equal to the difference between the monthly base
rent due from Tenant, less the monthly debt service (multiplied by 1.2) due to
any then-existing Landlord's Mortgagees, until the Cure Payments have been
repaid in full. For purposes of this Section, Landlord's default under the
applicable loan(s) shall be deemed to be a breach of Landlord's obligations
under the applicable loan(s) which is not cured within applicable notice and
cure periods under such loans. Such loans shall provide that: (A) the lender(s)
shall deliver notices of such defaults to Tenant concurrently with delivery to
Landlord; and (B) that the lender(s) will accept a cure of such defaults by
Tenant (if and to the extent that such defaults are curable by Tenant) within
the cure periods for such defaults granted to Landlord under such loans.

20.  ESTOPPEL CERTIFICATES; FINANCIAL STATEMENTS.
     -------------------------------------------

          (a) Tenant will from time to time, within twenty (20) days after
written request by Landlord (which request will be made in accordance with
Section 24.16), execute and deliver an estoppel certificate in form satisfactory
to Landlord or its designees which will certify (except as may be truthfully and
accurately noted to the contrary by Tenant therein) such information that is
available to Tenant concerning this Lease or Tenant or its Affiliates as
Landlord or its designees may request. Tenant understands that Landlord's timely
receipt of these Estoppel certificates may be critical and Tenant agrees that if
it fails to execute and deliver estoppel certificates as required, Landlord's
good faith representations concerning the matters covered by the estoppel
certificate will conclusively be presumed to be correct and binding on Tenant
and its Affiliates.

          (b) Within ninety (90) days after the end of each fiscal year of
Tenant that falls within the term of this Lease, Tenant will prepare and/or
obtain, at no cost or expense to Landlord, annual audited financial statements
for Tenant and any assignee of this Lease and any sublessee of more than 30,000
square feet in the Building (including, without limitation, a balance sheet,
income statement and statement of sources and uses of funds) prepared in
accordance with generally accepted accounting principles and signed by an
independent certified public accountant (the "Financial Statements"). Within ten
(10) days after Landlord's written request from time to time, Tenant shall
deliver to Landlord (and if requested, to Landlord's Mortgagees) copies of the
most recent annual and quarterly Financial Statements, whether or not audited
(provided, however, that for so long as Tenant and/or the assignee and/or the
sublessee is a public company, such public company shall not be required to
release its Financial Statements to Landlord or Landlord's Mortgagees until it
releases them or is permitted to release them to the public, whichever is
earlier).

21.  DEFAULT.
     -------

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<PAGE>   33

     The occurrence of one or more of the following events will be a default by
Tenant under this Lease: (a) [INTENTIONALLY OMITTED]; (b) the failure to pay
rent or any other required amount within ten (10) days after written notice that
the payment is due, but even if Tenant has not paid in full within the first ten
(10)-day period, Tenant will not be in default unless it fails to pay in full
within ten (10) days after an additional written notice that payment is due
(except that no such ADDITIONAL notice will be required if Tenant has failed to
pay rent when due more than twice in any twelve (12)-month period); (c) as
provided in Articles 23 and 25; (d) a Transfer or attempted Transfer in
violation of Article 18; (e) the failure to maintain its required insurance
policies (unless such insurance policies are not generally offered by
responsible insurance companies, in which case Tenant must maintain the closest
form of policy then generally offered by responsible insurance companies, and in
which case Landlord's insurance obligations will be similarly modified); or (f)
the failure to observe or perform any other obligation, term or condition within
the time period specified in this Lease and if such failure continues for an
additional five (5) days after the expiration of such prior period and the
delivery of a subsequent written notice; if no time period is specified, it will
be a default if this failure continues for thirty (30) days after written notice
from Landlord to Tenant, but if more than thirty (30) days are reasonably
required to cure, Tenant will not be in default if Tenant promptly begins to
cure within the thirty (30)-day period and then diligently completes the cure as
soon as possible but within seventy-five (75) days after the notice of default
is given, or such longer period as may be otherwise permitted in this Lease.

22.  REMEDIES FOR DEFAULT.
     --------------------

     22.1 GENERAL. If Tenant defaults, Landlord may at any time thereafter, with
or without notice or demand, do any or all of the following in its arbitrary
discretion: (a) give Tenant written notice stating that the Lease is terminated,
effective on the giving of notice or on a date stated in the notice, as Landlord
may elect, in which event this Lease will terminate without further action; (b)
in any manner permitted by law or this lease, and with or without notice, and
with or without terminating this Lease, terminate Tenant's right of possession
and enter and repossess the Premises, and expel Tenant and Tenant's Affiliates,
and remove their property and effects, without being guilty of trespass; and (c)
pursue any other right or remedy now or hereafter available to Landlord under
this Lease or at law or in equity.

     22.2 Tenant's Obligations. If Tenant defaults:
          --------------------

          (a) All rent due at the time of the default will be paid immediately
and Tenant also will pay such costs as Landlord may incur for attorneys' fees
and reasonable costs, inspection fees, brokerage fees, putting the Premises in
good order, condition and repair (fire and casualty excepted), but not including
costs to improve the Premises for a new tenant, and, in addition, Tenant
specifically agrees to pay an amount equal to the amount (if any) set forth in
Exhibit "H" hereto applicable to the month in which the default occurs (the
"Unamortized Costs").

          (b) Landlord may, at its sole option and in its arbitrary discretion,
re-let all or any portion of the Premises on terms satisfactory to Landlord in
its arbitrary discretion, either in its own name or otherwise, for a term or
terms which may, at Landlord's option, be more or less 

                                      -32-

<PAGE>   34

than the balance of the term of this Lease and pursuant to one or more leases,
and Landlord may grant concessions, tenant allowances and/or free rent, among
other things.

          (c) Unless and until Landlord elects to accelerate the rent due
pursuant to Section 22.2(e) and Tenant pays all the amounts due thereunder,
whether or not the Premises are re-let, Tenant will pay punctually to Landlord
all of the rent and other sums and perform all of Tenant's obligations for the
entire Lease term (assuming the original expiration date, as extended) in the
same manner and at the same time as if this Lease had not been terminated.

          (d) If Landlord re-lets the Premises, the date that the new tenant
begins to pay base rent to Landlord will be referred to as the "New Rent Payment
Date." Subject to the rest of this Subsection, Tenant will be entitled to a
credit (the "Credit") against the amounts owed by Tenant in an amount equal to:
(a) the total rent stream payable by the new tenant to Landlord only for the
period starting on the New Rent Payment Date and ending on the original
expiration date of this Lease, as it may have been extended by Tenant prior to
the default (and if the amounts owed by Tenant to Landlord have been accelerated
pursuant to Subsection (e) below, then the total rent stream owed by the new
tenant will be discounted to the date of such acceleration or the New Rent
Payment Date, whichever is later, at the prime rate then charged by the Bank of
Boston on such date); less (b) the costs and expenses incurred by Landlord to
relet the Premises to such new Tenant (including, without limitation, marketing
fees, brokerage fees, legal fees and the costs to repair and improve the
Premises for such new tenant). The Credit to be received by Tenant will never
exceed the amounts actually owed by Tenant to Landlord and Landlord will not be
required to pay any amounts to Tenant by reason of the Credit. Neither the
Credit nor any other credit will be given to Tenant for any rent received or
projected to be received from any reletting for any period after the original
expiration date of this Lease, as it may have been extended by Tenant prior to
the default.

          (e) At Landlord's option, Landlord may, by written notice to Tenant at
any time after Tenant's default, elect to recover, and Tenant will thereupon
pay, as liquidated damages, an amount equal to the total rent stream which would
have accrued to Landlord under this Lease for the remainder of the Lease term as
accelerated (assuming the original expiration date, as extended) if the default
had not occurred, discounted to the date of Landlord's election at the then
prime rate charged by the Bank of Boston, plus all of the unpaid expenses
described in Sections 22.2(a) (except for the Unamortized Costs) and 22.2(f).

          (f) No action of Landlord in connection with any re-letting, or
failure to re-let or collect rent under such re-letting, will operate or be
construed to release or reduce Tenant's Liabilities hereunder. Without limiting
any of the foregoing provisions, and in addition to any other amounts that
Tenant is otherwise obligated to pay, Tenant agrees that Landlord may recover
from Tenant all costs and expenses, including reasonable attorneys' fees and
costs, incurred by Landlord in enforcing this Lease from and after Tenant's
default.

                                      -33-

<PAGE>   35

          (g) Any amount drawn under the Letter of Credit pursuant to Section
24.17(c) or any amount of the cash security deposit applied by Landlord pursuant
to Section 24.17(c) shall be credited against amounts owed by Tenant to Landlord
under this Section 22.2, whether for base rent, additional rent, Unamortized
Costs or liquidated damages, but among them as specified by Landlord.

     22.3 REDEMPTION. Tenant waives any and all rights of redemption granted by
or under any Laws if Tenant is evicted or dispossessed for any default by
Tenant, or if Landlord obtains possession of the Premises by reason of any
default by Tenant.

     22.4 PERFORMANCE BY LANDLORD. If Tenant fails to perform any of its
obligations under this Lease, Landlord, without waiving or curing the default or
failure, may, but will not be obligated to, perform Tenant's obligations for the
account and at the expense of Tenant. Landlord will attempt to provide Tenant
with oral or written notice before performing Tenant's obligations, but if
Landlord believes that such actions are necessary due to an emergency or to
prevent damage or injury or protect health, safety or property, Landlord need
not give notice before performing Tenant's obligations. Tenant will pay on
demand all reasonable costs and expenses incurred by Landlord in connection with
Landlord's performance of Tenant's obligations.

     22.5 POST-JUDGMENT INTEREST. The amount of any judgment obtained by
Landlord against Tenant in any legal proceeding arising out of Tenant's default
under this Lease will bear interest until paid at the Bank of Boston's (or its
successor's) prime rate plus three percent (3%), or the maximum rate permitted
by law, whichever is less. Notwithstanding anything to the contrary contained in
any Laws, with respect to any damages that are certain or ascertainable by
calculation, interest will accrue from the day that the right to the damages
vests in Landlord, and in the case of any unliquidated claim, interest will
accrue from the day the claim arose.

23.  BANKRUPTCY PROVISIONS [SEE EXHIBIT "F"].

24.  GENERAL PROVISIONS.
     ------------------

     24.1 HOLDING OVER. Tenant will not hold over in the Premises after the end
of the Lease term without the express prior written consent of Landlord, which
may be withheld arbitrarily. However, provided that Tenant is not in default,
Tenant may extend the Lease Term on the same terms and conditions provided that
Tenant delivers an unconditional extension notice to Landlord at least six (6)
months before the end of the term (or any extensions thereof) and specifies in
that notice the length of extension period, which cannot be more than three (3)
months. If Tenant validly exercises this extension right, the term will be
deemed extended for the period specified in Tenant's notice (but not for more
than three (3) months), and such extension will be part of the Lease term and
will not be considered a holding over by Tenant, but there will be no further
extension rights. This extension right is applicable only at the end of the
Lease term, as extended. Landlord will diligently attempt to include in its
lease with any succeeding or prospective tenant provisions disclaiming liability
for consequential damages (i.e., damages for lost business or revenue, as
opposed to actual damages or penalties) to any such tenant, and/or provisions
limiting such succeeding or prospective tenant's remedies solely to the
termination of the Lease, as a result of Landlord's failure to substantially
complete and deliver 

                                      -34-

<PAGE>   36

space to such tenant as required, but Tenant will indemnify Landlord for, and
hold Landlord harmless from, any and all Liabilities arising out of or in
connection with any holding over, including, without limitation, any claims made
by any succeeding or prospective tenant and any loss of rent suffered by
Landlord. If, despite this express agreement, any tenancy is created by Tenant's
holding over, except as specifically set forth in the next sentence, the tenancy
will be a tenancy at sufferance terminable immediately at Landlord's sole option
on written notice to Tenant, but otherwise subject to the terms of this Lease,
except that the most recent annual base rent will be doubled (except as
specifically set forth in Section 16.4). Nothing in this Article or elsewhere in
this Lease permits Tenant to hold over or in any way limits Landlord's other
rights and remedies if Tenant holds over (except as specifically set forth in
16.4).

     24.2 ENTRY BY LANDLORD. Landlord and its designated representatives at all
times shall have the right to enter the Premises, and Landlord will retain (or
be given by Tenant) keys to unlock all the doors to or within the Building,
excluding doors to Tenant's vaults and files. Landlord in good faith will
attempt to give Tenant reasonable advance (which will not require more than
twenty-four (24) hours prior) written notice to Tenant or to a responsible
officer of Tenant or Tenant's designated facilities manager, or oral notice to a
responsible officer of Tenant or Tenant's designated facilities manager, prior
to entering the Building and not to unreasonably disturb the conduct of Tenant's
business by such entry, but Landlord need not give prior notice and will have
the right to use any means necessary to enter the Building if Landlord believes
there is an emergency or that entry is necessary to prevent damage or injury or
protect health, safety or property. Entry to the Premises or the Building and
the exercise of Landlord's rights in accordance with this Lease will not, under
any circumstances, be deemed to be a default, a forcible or unlawful entry into
or a detainer of the Premises or the Building or an eviction of Tenant from the
Premises or the Building or any portion thereof, nor will it subject Landlord to
any Liabilities or entitle Tenant to any compensation, abatement of rent or
other rights and remedies.

     24.3 BROKERS. Tenant represents and warrants that it has had no dealings
with any agent, broker, finder or other person who is or might be entitled to a
commission or other fee from Landlord in connection with this or any related
transaction, except for Tenant's Broker. Landlord will incur Liabilities for
brokerage commissions or other compensation to Tenant's Broker only pursuant to
a written agreement (if any) executed and delivered by Landlord and Tenant's
Broker.

     24.4 QUIET ENJOYMENT. So long as Tenant pays all rent and pays and performs
its other Liabilities as and when required, Tenant may quietly enjoy the
Premises without hindrance or molestation by Landlord or any person lawfully
claiming through or under Landlord, subject to the terms of this Lease and the
terms of any Superior Leases and Mortgages and other agreements or matters of
record or to which this Lease is subordinate. As used in this Lease, the term
"Superior Leases and Mortgages" means all present and future ground leases,
underlying 

                                      -35-

<PAGE>   37

leases, mortgages, deeds of trust or other encumbrances, and the documents and
agreements in connection therewith, and all renewals, modifications,
consolidations, replacements or extensions thereof and advances made thereunder,
affecting all or any portion of the Premises, but not including any of the same
securing or relating to an Unpermitted Financing.

     24.5 SECURITY. Tenant is solely responsible for providing security for the
Premises and Tenant's personnel within the Premises. Without limiting the
generality of this Section, Tenant agrees that: (a) Landlord may, but will not
be required to, supply security personnel and systems for the Building or the
Premises or Tenant's personnel, and remove or restrain unauthorized persons and
prevent unauthorized acts; (b) Landlord will incur no Liabilities for failing to
provide security personnel or systems or, if provided, for acts, omissions or
malfunctions of the security personnel or systems (although this is not meant to
imply that Tenant will have liability therefor or be required to indemnify
Landlord therefor, unless Tenant is otherwise liable therefor or required to
indemnify Landlord therefor pursuant to the other terms of this Lease); and (c)
Landlord and its Affiliates make no representations or warranties of any kind in
connection with the security or safety of the Premises or the Building. Subject
to the terms and conditions in this Lease, Tenant will have the right to install
a security system for the Building at Tenant's sole cost and expense. Tenant
will keep Landlord fully apprised and give to Landlord's designated
representatives the means necessary to bypass the security system and enter the
Building in the event of an emergency.

     24.6 OBLIGATIONS; SUCCESSORS; RECORDATION. If Tenant consists of more than
one person or entity, the obligations and liabilities of those persons or
entities are joint and several. Time is of the essence of this Lease. Subject to
the restrictions in Article 18 or elsewhere in this Lease, this Lease inures to
the benefit of and binds Landlord, Tenant and their respective successors and
assigns and anyone who acquires an interest in this Lease, or in the case of
Landlord anyone who acquires title to the Premises. Tenant will not record this
Lease, but each party agrees on the written request of the other, to execute a
notice of lease in recordable form and in customary form reasonably satisfactory
to Landlord's attorney.

     24.7 LATE CHARGES. If any rent or other amounts payable by Tenant are not
received within five (5) days after the due date more than twice in any calendar
year, Tenant will pay to Landlord on demand a late charge equal to five percent
(5%) of the overdue amount, and if not received within ten (10) days after the
due date, the amounts also will bear interest from the due date until paid at
the interest rate in Section 22.5. Notwithstanding the previous sentence, for
the first and second times in any calendar year that any rent or other amounts
payable by Tenant are not received within five (5) days after the due date, if
Landlord accordingly incurs late charges from one or more of its lenders, then
Tenant shall pay such late charges up to a maximum of five percent (5%) of the
amount overdue from Tenant. Collection of these late charges and interest will
not: be a waiver or cure of Tenant's default or failure to perform; be deemed to
be liquidated damages, an invalid penalty or an election of remedies; or prevent
Landlord from exercising any other rights and remedies.

                                      -36-

<PAGE>   38

     24.8 ACCORD AND SATISFACTION. Payment by Tenant or acceptance by Landlord
of less than the full amount of rent due is not a waiver (unless such acceptance
is accompanied by a written waiver signed by Landlord specifying that such
acceptance is a waiver and specifying the amount being waived), but will be
deemed to be on account of amounts next due, and no endorsements or statements
on any check or any letter accompanying any check or payment will be deemed an
accord and satisfaction or binding on Landlord. Landlord may accept the check or
payment without prejudice to any of Landlord's rights and remedies, including,
without limitation, the right to recover the full amount due.

     24.9 PRIOR AGREEMENTS; AMENDMENTS; WAIVER. This Lease is an integrated
document and contains all of the agreements of the parties with respect to any
matter covered or mentioned in this Lease, and supersedes all prior agreements
or understandings.

This Lease may not be amended except by an agreement in writing signed by
Landlord and Tenant. All waivers must be in writing, specify the act or omission
waived and be signed by the party charged with the waiver. No other alleged
waivers will be effective, including, without limitation, Landlord's acceptance
of rent (except as specifically provided otherwise in Section 24.8), collection
of a late charge or application of a security deposit. Landlord's waiver of any
specific act, omission, term or condition will not be a waiver of any other or
subsequent act, omission, term or condition.

     24.10 REPRESENTATIONS; INABILITY TO PERFORM. Except as may be specifically
set forth as representations and warranties in this Lease, Landlord and its
Affiliates have not made, and Tenant is not relying on, any representations or
warranties of any kind, express or implied, with respect to the Premises or this
transaction. Landlord will not be in default nor incur any Liabilities if it
does not fulfill any of its obligations, or is delayed in doing so, because of
accidents, breakage, strike, labor troubles, war, sabotage, governmental
regulations or controls, inability to obtain materials or services, acts of God,
or any other cause, whether similar or dissimilar, beyond Landlord's reasonable
control, but will not be deemed to limit in any way Landlord's repair and
maintenance obligations under Section 12.1 or its repair and/or restoration
obligations under Articles 16 and 17, except to the extent that such repair,
maintenance or restoration activities are affected by such events or causes.

     24.11 LEGAL PROCEEDINGS. In any action or proceeding involving or relating
in any way to this Lease, the court or other person or entity having
jurisdiction in such action or proceeding will award to the party in whose favor
judgment is entered the actual attorneys' fees and costs incurred. Subject to
Article 14, Tenant also will indemnify Landlord for, and hold Landlord harmless
from and against, all Liabilities incurred by Landlord if Landlord becomes or is
made a party to any proceeding or action: (a) brought AGAINST any person or
entity (other than a permitted Assignee under Section 18.5(c) or any assignee
pursuant to an assignment that caused the assignor to become a Released
Assignor) holding any interest under this Lease or using the Premises by license
of or agreement with Tenant (provided that Tenant's indemnity obligations in
this case will not exceed the indemnity obligations that Tenant would have had
under Article 14 if Tenant "stood in the shoes" of such other person or entity
and the action or proceeding was brought against Tenant); or (b) brought by any
person or entity (other than an assignee under a valid assignment of this Lease
if and to the same extent that Tenant would have had the right to 

                                      -37-

<PAGE>   39

bring such action or proceeding against Landlord under the same circumstances)
holding any interest under this Lease or using the Premises by license of or
agreement with Tenant; or (c) necessary to protect Landlord's interest under
this Lease in a proceeding under the Bankruptcy Code or in connection with the
matters described or contemplated in Exhibit "F" hereto. Unless prohibited by
law, Tenant waives the right to trial by jury in all actions involving or
related to this Lease, the Premises or any collateral or subsequent agreements
between the parties, and any right to impose a counterclaim in any proceeding
brought for possession of the Premises as a result of Tenant's default (although
this waiver of counterclaim will not be deemed to prohibit Tenant from bringing
any claims in a separate non-consolidated action). Tenant also submits to and
agrees not to contest the sole and exclusive jurisdiction of the state and
federal courts located in Massachusetts to adjudicate all matters in connection
with this Lease or involving Landlord or Landlord's Affiliates in any way, and
Tenant agrees that it will bring all suits and actions only in such
Massachusetts courts and not to seek a change of venue. In any circumstance
where a party is obligated to indemnify or hold harmless the other party under
this Lease, that obligation also will include the obligation to protect the
other party and defend it with counsel acceptable to the other party or, at the
other party's election, the other party may employ its own counsel and the
indemnifying party will pay when due all attorneys' fees and costs. These
obligations to indemnify, hold harmless, protect and defend will survive the
expiration or termination of this Lease.

     24.12 OWNERSHIP; INVALIDITY; REMEDIES; CHOICE OF LAW. As used in this
Lease, the term "Landlord" means only the current owner or owners of the fee
title to the Premises. Upon each conveyance (whether voluntary or involuntary)
of fee title, the conveying party will be relieved of all Liabilities and
obligations contained in or derived from this Lease or arising out of any act,
occurrence or omission occurring after the date of such conveyance. Landlord may
Transfer all or any portion of its interests in this Lease or the Premises
without affecting Tenant's obligations and Liabilities under this Lease. Tenant
has no right, title or interest in the name of the Building or of the Premises,
and may use these names only to identify its location. Any provision of this
Lease which is invalid, void or illegal will not affect, impair or invalidate
any of the other provisions and the other provisions will remain in full force
and effect. Landlord's rights and remedies are cumulative and not exclusive.
This Lease is governed by the laws of Massachusetts applicable to transactions
to be performed wholly therein.

     24.13 TRIPLE NET LEASE; CONSENT. The parties acknowledge and agree that
this is intended to be, to the fullest extent possible, a "triple net" lease,
and all costs and expenses in connection with the Premises in addition to the
base rent are intended to be paid or reimbursed by Tenant unless otherwise
stated in this Lease (but this shall not be deemed to affect Landlord's
obligations to pay portions of the Net Proceeds to Tenant to the extent set
forth in Addendum #3). Notwithstanding anything to the contrary, Landlord will
not be required under any circumstances to agree to any amendments,
modifications, waivers, increases or decreases in any of the terms of this Lease
or any of the rights and obligations of the parties hereunder, whether or not
such agreement would be reasonable under the circumstances. In any dispute
involving Landlord's withholding of consent or approval or its exercise of
judgement, the sole right and remedy of Tenant and its Affiliates is declaratory
relief (i.e., that such consent or approval should be granted), and Tenant and
its Affiliates waive all other rights and remedies, including, without
limitation, claims for damages.

                                      -38-

<PAGE>   40

     24.14 PRESUMPTIONS; EXHIBITS; SUBMISSION. This Lease will be construed
without regard to any presumption or other rule requiring construction or
interpretation for or against the party drafting the document. The titles to the
Articles and Sections of this Lease are not a part of this Lease and will have
no effect on its construction or interpretation. Whenever required by the
context of this Lease, the singular includes the plural and the plural includes
the singular, and the masculine, feminine and neuter genders each include the
others, and the word "person" includes individuals, corporations, partnerships
or other entities. All exhibits, addenda and riders attached to this Lease are
incorporated in this Lease by this reference. The submission of this Lease to
Tenant or its broker, agent or attorney for review or signature is not an offer
to Tenant to lease the Premises or the grant of an option to lease to Premises.
This Lease will not be binding unless and until it is executed and delivered by
both Landlord and Tenant.

     24.15 COOPERATION. If Landlord finds it necessary to enter the Building to
perform its obligations or exercise its rights under this Lease, Tenant will
cooperate reasonably with Landlord, and this cooperation will include moving
machinery, equipment or Alterations within the Building and allowing Landlord
sufficient space within the Premises to enable Landlord to perform any work that
Landlord has the right or is required to perform under this Lease.

     24.16 NOTICES. Unless otherwise specifically stated in this Lease, all
notices, demands or communications required or permitted under this Lease (the
"Notices") will be in writing and personally delivered (by messenger or
recognized national overnight carrier), or sent by certified mail, return
receipt requested, postage prepaid. Notices to Tenant prior will be delivered to
the address for Tenant in Section 1.1 or to such other address as may be
specified by Tenant to Landlord in writing. Notices to Landlord will be
delivered to the addresses for Landlord in Section 1.1 or to such other address
as may be specified by Landlord to Tenant in writing. Notices will be effective
on the earlier of: delivery; or, if mailed, four (4) days after they are mailed
in accordance with this Section.

     24.17 Letter of Credit.
           ----------------

          (a) Upon the execution and delivery of this Lease, Tenant will obtain
and deliver to Landlord an irrevocable, unconditional standby letter of credit
in accordance with the terms and conditions of this Section (the "Letter of
Credit"). The Letter of Credit will be in the amount of $7.8 Million, will be
issued initially by Bank of Boston or Chemical Bank and subsequently by any
issuer that meets the criteria in Section 24.17(e), will name Landlord (or, at
Landlord's request from time to time, a current lender to Landlord) as the
beneficiary thereof and will have an initial term of at least one (1) year and,
with renewals, an aggregate term (as renewed) as set forth below. The terms of
the Letter of Credit shall be as set forth in this Section 24.17 and in form
reasonably acceptable to the beneficiary thereof. The beneficiary shall have the
right to draw under the Letter of Credit on one or more occasions from time to
time during its term and in accordance with the terms hereof simply upon
presentation to the issuer of a sight draft executed by the beneficiary or its
authorized representative and without further condition, and the issuer shall
pay upon presentation of such draft without deduction or offset of any type. The
Letter of Credit shall be assignable in whole but not in part, and at Landlord's
request from time to time, it shall be reissued in favor of a new beneficiary in
accordance with the terms of this 
                                      -39-
<PAGE>   41

Lease. Provided that Tenant is not in default and is entitled to continue to
receive a share of Net Proceeds in accordance with Addendum #3 and/or to
exercise a Purchase Option in accordance with Addendum #4, Landlord agrees not
to request that any of its lenders be named as a beneficiary under the Letter of
Credit with respect to any Unpermitted Financing supplied by such lenders.

          (b) Each loan obtained from time to time by Landlord in compliance
with this Lease which is secured by the Letter of Credit (other than the initial
mortgage construction loan) sometimes is referred to as the "Letter of Credit
Loan." Until and unless the Letter of Credit is drawn upon, starting as of one
(1) year after the Commencement Date, and on each annual anniversary thereafter
(or, if the Letter of Credit Loan has not funded within one (1) year after the
Commencement Date, then starting as of fifteen (15) months and fifteen (15) days
after the Commencement Date, and on each annual anniversary thereafter), the
face amount of the Letter of Credit shall be reduced in an amount equal to the
annual principal reduction that would result from a direct reduction loan
amortization schedule, assuming an interest rate equal to the interest rate used
to calculate principal amortization under the Letter of Credit Loan (such
schedule to be provided or approved by the lender of the Letter of Credit Loan),
which will have the effect of reducing the Letter of Credit to zero over the
initial term of the Lease (as it may be extended pursuant to Section 4(b)) .
However, subject to the foregoing but notwithstanding anything else to the
contrary, even if the Letter of Credit has been drawn upon, if and to the extent
that those amounts are repaid to Tenant, Tenant shall thereupon cause the face
amount, and the amount that may again be drawn, under the Letter of Credit to be
increased by an amount equal to the amount so repaid. (For example, if $2
Million were to be drawn under the Letter of Credit pursuant to Section
24.17(f), and if that $2 Million were then repaid, the face amount and the
amount that could be drawn under the Letter of Credit again would be $7.8
Million.) Tenant shall cause the Letter of Credit to be renewed continuously on
the same terms as described above for successive one (1)-year terms (or longer
terms) so that the Letter of Credit is continuously maintained for a term
expiring at the end of the initial term of the Lease (as it may be extended
pursuant to Section 4(b)). Each succeeding Letter of Credit shall be effective
on or before the date that the then-existing Letter of Credit expires. Tenant's
failure to deliver these renewals of the Letter of Credit to the beneficiary at
least thirty (30) days prior to each expiration date shall not in and of itself
be a default under this Lease, but at the beneficiary's option, and
notwithstanding anything to the contrary, the beneficiary shall have the
immediate right thereon and thereafter to draw under the Letter of Credit for
all or any portion thereof, and the cash proceeds thereof shall be held and, if
necessary, applied, by the beneficiary in the same manner as set forth in
Subsection (d) below.

                                      -40-

<PAGE>   42


                  (c) The Letter of Credit is security for the timely payment
and performance of all of Tenant's Liabilities in connection with this Lease,
including, without limitation, Tenant's obligation to pay base rent, additional
rent and any amounts due under any Addendum hereto, and the Unamortized Costs if
Tenant defaults, and the obligations under Landlord's loan(s) from its
lender(s). If Tenant defaults under this Lease or there is a default under such
loan(s) or if otherwise permitted under the loan documents, the beneficiary may,
but shall not be obligated to, draw under the Letter of Credit on one or more
occasions, and the beneficiary's draw(s) under or failure to draw down all or
any portion of the Letter of Credit in any particular instance will not be
deemed to be a waiver or election of any rights and remedies of any type, a
limitation on Landlord's or the beneficiary's right to damages, a payment of
liquidated damages or an accord or satisfaction.

          (d) Until and unless the Letter of Credit is drawn upon, Tenant may,
at any time, substitute for the Letter of Credit cash in an amount equal to the
then-current face amount of the Letter of Credit. If Tenant does so substitute
cash, then the amount thereof will be deemed to be a security deposit hereunder,
and will be deemed to be security for the same obligations and Liabilities as
are set forth in Section 24.17(c). Landlord (and/or the beneficiary under the
former Letter of Credit) will have the right to apply all or any portion of that
security deposit in the same manner and subject to the same terms as are set
forth in Section 24.17(c), and until and unless the security deposit is applied
in accordance with this Lease, the amount of that security deposit shall reduce
in the manner and at the times set forth in the first sentence of Section
24.17(b). Until applied, the cash security deposit shall be kept in a separate,
interest-bearing account or in another form of investment reasonably acceptable
to Tenant and the secured party, and until and unless it is applied, interest
earned thereon shall be payable annually to Tenant, and the security deposit
shall be used for no other purpose other than as security for the payment and
performance of the obligations and Liabilities as set forth in Section 24.17(c).

          (e) Tenant shall cause the Letter of Credit to be replaced by a Letter
of Credit issued by another recognized bank located and in good standing in the
United States that meets the financial criterion described below and is
otherwise reasonably acceptable to the beneficiary: (i) on demand by the
beneficiary if the issuer ever fails to meet the financial criterion described
below; or (ii) if Tenant wishes to replace the Letter of Credit with a Letter of
Credit issued by another bank. The financial criterion referred to above is the
requirement that the issuer will maintain ratings from Moody's and Standard &
Poor's at least equal to those enjoyed by the initial issuer of the Letter of
Credit on the date that the Letter of Credit is issued. The beneficiary shall
have the immediate right thereon and thereafter to draw under the Letter of
Credit for all or any portion thereof if the Letter of Credit is not replaced as
and when required by an issuer meeting the financial criterion referred to
above, and the cash proceeds thereof shall be held and, if necessary, applied,
by the beneficiary in the same manner as set forth in Subsection (d) above.

          (f) In addition to the other circumstances set forth in this Lease
pursuant to which the beneficiary of the Letter of Credit may draw thereunder,
the beneficiary may draw under the Letter of Credit in accordance with the terms
of Exhibit "M" or terms substantially similar thereto.

                                      -41-

<PAGE>   43

               Any amounts drawn by the beneficiary under the Letter of Credit
(not including draws of the type described in Sections 24.17(b) and (e), or
draws resulting from Tenant's default under this Lease or any other agreements
between Tenant and the beneficiary or Landlord's default under a loan arising as
a result of Tenant's breach of its obligations under this Lease) shall be
referred to as the "LC Advances," and shall be treated as a loan made by Tenant
to Landlord, which shall be repayable on the terms set forth in a promissory
note executed by Landlord in favor of Tenant in the form attached as Exhibit "L"
hereto (the "LC Note").

     24.18 Other Defined Terms.
           -------------------

          (a) "Affiliates" means: a party's internal partners, and the
directors, officers, agents, employees, parent, subsidiaries, invitees,
customers, licensees, concessionaires, contractors, subcontractors, successors,
assigns, subtenants, and representatives of the party or its internal partners.

          (aa) "Control Affiliates" means a party's internal partners, and the
directors, officers, employees, parent, subsidiaries, successors or assigns of
the party or its internal partners, or an entity in which any of them owns at
least 20% of the outstanding interests or voting shares.

          (b) "Laws" means: laws, codes, decisions, ordinances, rules,
regulations, any CC&R's or deed restrictions (or the equivalent) to which the
Premises may be subject, licenses, permits (including without limitation the
Andover Site Plan Special Permit and any amendments thereto), and directives of
governmental and quasi-governmental officers, including, without limitation,
those relating to building and safety, fire prevention, health, energy
conservation, Hazardous Substances and environmental protection.

          (c) "Liabilities" means: obligations, costs, damages, claims,
injuries, liens, liabilities and judgments, including, without limitation,
attorneys' fees and costs (whether or not suit is commenced or judgment
entered).

          (cc) "Related Entities" means a party's successors, assigns, parent or
subsidiaries, or any person that controls, is controlled by or is under common
control with that party, and the successors or assigns of such person.

          (d) "Systems and Equipment" means: all HVAC, plumbing, mechanical,
electrical, lighting, water, gas, sewer, safety, sanitary and any other utility
or service facilities, systems and equipment, and all pipes, ducts, poles,
stacks, chases, conduits and wires.

          (e) "Default," when applied to Tenant, and whether or not used with an
initial capital, will have the meaning set forth in Section 21.

     24.19 NO PARTNERSHIP. Notwithstanding anything to the contrary, neither
this Lease nor the performance of any of the terms and conditions thereof are
intended to create or imply, nor shall they create or imply, any partnership,
joint venture, trust, fiduciary relationship or agency relationship between
Landlord and Tenant (or any of their respective Affiliates).

                                      -42-

<PAGE>   44

25.  HAZARDOUS SUBSTANCES.
     --------------------

     Without limiting the generality of any portion of this Lease, Tenant and
its Affiliates will:

          (a) Not store, handle, transport, use, process, generate, discharge or
dispose of any hazardous, toxic, corrosive, dangerous, explosive, flammable or
noxious substances, gasses or waste, whether now or hereafter defined under any
Laws or otherwise (collectively, "hazardous substances"), from, in or about the
Building or the rest of the Premises, or create any release of any hazardous
substances, nor permit any of the foregoing to occur, except for customary and
reasonable amounts of office supplies and other supplies reasonably used in the
conduct of Tenant's permitted research and development, light manufacturing and
warehousing activities which may contain or consist of reasonable amounts of
hazardous substances, and then only strictly in accordance with applicable Laws.
If any of the foregoing prohibited activities occur, or if Landlord in good
faith believes that any of the foregoing prohibited activities have occurred or
are likely to occur or that Tenant and its Affiliates are not complying fully
with the requirements of this Article, in addition to any other rights and
remedies of Landlord, Tenant and its Affiliates immediately will cease the acts
or omissions and in addition to any other rights and remedies (all of which are
cumulative), at Landlord's request Tenant will take such actions as may be
required by Laws and as Landlord may in good faith direct to cure or prevent the
problem. Tenant and its Affiliates will comply fully with all Laws and insurance
requirements in connection with or related to hazardous substances, whether now
or hereafter existing, including, without limitation, CERCLA, SARA, RCRA, TSCA,
CWA, Chapter 21E of Massachusetts General Laws and any other Laws promulgated by
the EPA, OSHA or Commonwealth of Massachusetts.

          (b) Immediately pay, and indemnify Landlord and its Affiliates for and
hold them harmless from, all Liabilities in connection with or arising directly
or indirectly from any breach by Tenant or its Affiliates of their obligations
in this Article, including, without limitation, Liabilities to any lenders and
the costs of any of the following, whether required by Landlord, any lenders,
applicable Laws or insurance requirements or otherwise: any "response actions"
or "responses"; any surveys, "audits", inspections, tests, reports or procedures
deemed necessary or desirable by Landlord or governmental or quasi-governmental
authorities to determine the existence or scope of any hazardous substances or
Tenant's compliance with this Article, and any actions recommended to be taken
in connection therewith; compliance with any applicable Laws and insurance
requirements; any requirements, directives or plans for the prevention,
containment, processing, storage, clean-up or disposal of hazardous substances;
the release and discharge of any resulting liens; and any other injury or
damage. On the expiration or earlier termination of this Lease, Tenant will
leave the Building and the Premises free of hazardous substances stored,
handled, transported, used, processed, generated, discharged or disposed of in,
on, from or about the Building, or the Premises by Tenant or its Affiliates.

          (c) Immediately deliver to Landlord copies of any notices,
information, reports, and communications of any type received or given in
connection with hazardous substances, including, without limitation, notices of
violation and settlement actions from or with governmental or quasi-governmental
authorities.

                                      -43-

<PAGE>   45

Tenant's failure to comply with the requirements of this Article will be a
material default under this Lease, but if the failure was not intentional, then
if Tenant immediately begins to cure the failure and diligently begins and
completes all required remediation, disposal and other responsive actions in
accordance with the Lease and applicable Laws and guidelines and all necessary
repairs to the Building or the Premises, Tenant will be deemed to have cured the
default (although Tenant's indemnity obligations and other Liabilities still
will remain). All of Tenant's obligations and Liabilities under this Article
will survive the expiration or earlier termination of this Lease.

     IN WITNESS WHEREOF, intending to be legally bound, each party has executed

this Lease as a sealed instrument as of the date first set forth above.

                                       "LANDLORD"

Executed:                      , 1996
         ----------------------
                                        50 MINUTEMAN LIMITED PARTNERSHIP,
                                        a Massachusetts limited partnership

WITNESS:                                By:  NIUNA-50 MINUTEMAN, INC.,
                                             a general partner

                                        By:
-------------------------                  ---------------------------------
Name Printed:                                 John Kusmiersky, President

                                        "TENANT"
Executed:                      , 1996
         ----------------------
                                        PICTURETEL CORPORATION,
WITNESS:                                a Delaware corporation

                                        By:
                                           ---------------------------------
Name Printed:                                         (Signature)

                                        Name:
                                        Title:

WITNESS:                                Authorized Signature

                                        
                                        By:
-------------------------                  ---------------------------------
Name Printed:                                         (Signature)

                                        Name:
                                        Title:
                                        Authorized Signature

                                      -44-
<PAGE>   46


                                   EXHIBIT "A"

                           INITIAL PREMISES SITE PLAN



                     [SITE PLAN OF PREMISES TO BE ATTACHED]












                                   EXHIBIT "A"

<PAGE>   47


                                   EXHIBIT "B"


                                LEGAL DESCRIPTION







                                   EXHIBIT "B"

<PAGE>   48


                                   EXHIBIT "C"

                                   WORKLETTER

1.   General Conditions.
     ------------------

     1.1 Landlord will construct Landlord's Work in accordance with applicable
Laws in effect at the time, except that Landlord makes no agreements,
representations or warranties concerning compliance with the Americans with
Disabilities Act or any rules, regulations, guidelines or additional legislation
issued in connection therewith. (The previous sentence is not meant to change
the obligations of the parties pursuant to Section 11(d).) Landlord conclusively
shall be deemed to have complied with all applicable Laws in effect at the time
with respect to Landlord's Work when and if Landlord obtains a Certificate of
Occupancy for the Building. Subject to Section 2(a), Tenant and its contractors
may have access to the Building for the purpose of preparing the Building for
Tenant's occupancy before Landlord's Work has been substantially completed, but
only with Landlord's prior written approval. After any entry by Tenant or its
contractors, all of Tenant's Lease obligations will be immediately effective
except for the obligation to pay base rent, Taxes and Operating Costs. All
construction, materials, services, licenses, approvals, costs, installations and
equipment to or for the Premises other than Landlord's Work are called "Tenant's
Work," and will be performed by Tenant at Tenant's sole cost and in a good and
workmanlike manner and subject to the rest of the terms of this Lease. Subject
to Section 2(a), Tenant will not interfere in any way with Landlord's Work,
whether in connection with Tenant's Work or otherwise. If Landlord's Work is
delayed or made more expensive due to: any act or omission of Tenant or its
Affiliates (including, without limitation, any delay of or failure to complete
Tenant's Work [subject to Section 2(a)], any requested or required changes to
Exhibit "C" agreed to by Landlord, or any failure or delay in submitting the
information in Exhibit "CC" or other plans, specifications, drawings,
requirements, information or approvals, or changes or inaccuracies in any of the
foregoing that are or are supposed to be submitted by or on behalf of or
approved by Tenant); or the inclusion in Exhibit "C" or other Tenant
specifications of "long lead" items or services that cannot reasonably be
obtained in sufficient time to be incorporated in Landlord's Work in the normal
course of Landlord's construction schedule (and Tenant's failure to delete or
substitute for those items or services), then Tenant will be responsible for the
delays and additional cost, Landlord's Work will be deemed substantially
completed when it would have been completed but for the delays (and at minimum
any delays will be subtracted from the date of actual substantial completion in
determining when substantial completion will be deemed to have occurred), and
Tenant will pay any additional cost to Landlord as additional rent within
fifteen (15) days after receipt of Landlord's bill. Furthermore, if a delay for
which Tenant is responsible results in an increased interest rate on Landlord's
loans, then Tenant will pay as additional rent the increased amounts payable by
Landlord as and when Landlord is obligated to pay such amounts. Within ten (10)
days after Landlord's request, Tenant will execute and deliver to Landlord a
certificate confirming the date of substantial completion of Landlord's Work.
Tenant's certificate is for purposes of confirmation only and will not affect
the actual date of substantial completion.

         1.2 Landlord intends that: Gilbane Building Company (or an affiliated
entity) will act as the construction manager, or in an equivalent capacity, with
respect to Landlord's Work; and that Gilbane Building Company (or an affiliated
entity) will guaranty the maximum price for 

                                  EXHIBIT "C"

<PAGE>   49

Landlord's Work. With respect to Landlord's Work, at least the "major trades"
will be competitively bid to subcontractors, and Landlord will award those
subcontracts to the lowest bidder, except that Landlord may award a subcontract
to any of the bidding subcontractors if: (a) the lowest bidder takes exception
to the bid documents; or (b) the initial bid or subsequent revised bid of the
subcontractor chosen by Landlord is within 5% of the lowest responsive and
timely bid received.

     1.3 Notwithstanding anything to the contrary, Landlord's Work will not
include, and Landlord will not be responsible for, any labor or services in
connection with Tenant's security or alarm systems, and Tenant's data,
telecommunications, audio, visual, computer, cafeteria or fitness-related
equipment or installations or any piping, wiring, cabling or conduits associated
with any of the foregoing or any hookups thereof.

     1.4 The rest of this Workletter is attached and is incorporated herein by
this reference.

                                   EXHIBIT "C"
<PAGE>   50
                                   EXHIBIT "C"
                      50 MINUTEMAN ROAD, ANDOVER, MA 01810
                              PICTURETEL WORKLETTER
                           BURT HILL PROJECT 96622.00
                             REVISED AUGUST 20, 1996


1.   INTRODUCTION

     A.   The Landlord will construct a new 151,800+/- square foot
          office/research and development building, with associated driveways,
          parking areas and utility infrastructure during a period of
          approximately 14 months beginning August, 1996.

     B.   The site address is 50 Minuteman Road, Andover, MA 01810. The land
          area is 598,051 square feet, comprising 13.729 acres which are zoned
          Industrial D according to the Andover Town Zoning Bylaw. The new
          3-story building will contain 53,000 square feet on the Ground Floor
          and 49,400 square feet on each of the Second and the Third Floors. The
          new building will face northwest toward the visitor entrance of 100
          Minuteman Road.

     C.   The site is identified in the Essex North Registry public records as
          Parcel C-2, situated immediately to the south of Parcel A-1, a
          37.856-acre parcel with building and other site improvements, commonly
          known as 100 Minuteman Road. The eastern section of Parcel C-2 is a
          former softball field, to be removed in order to accommodate the new
          building and approximately 300 parking spaces to be located
          immediately around the building. A landscaped earthen berm along the
          perimeter of the site will screen the parking from vehicles and the
          adjacent residents along River Road. A landscaped berm will also be
          created along Minuteman Road to screen approximately 200 cars to be
          parked adjacent to the road. A retention pond will be constructed on
          the west side of the new building on the north side of the front entry
          to accommodate storm water.

2.   GENERAL INTENT

     A.   It is the intent of this Workletter to describe the new building
          improvements for the use by the Tenant. Certain plans and
          specifications for the new building, a list of which is attached to
          this Workletter, which have been prepared by the Landlord's architect
          and engineers, are intended to be incorporated herein by this
          reference. In the event any inconsistency or other irreconcilable
          difference is found between the provisions of this Workletter and
          information contained in the plans and specifications, the provisions
          of this Workletter are intended to govern.

     B.   The quality standard of finish tenant improvements, unless otherwise
          specified to the contrary, will be equal to the standard at Tenant's
          100 Brickstone Square, Andover facilities. For unit quantities of
          finish Tenant Improvements, see 3.4 below. Also under this Workletter,
          the new base building and core systems and equipment will be
          constructed by the Landlord in good working condition 

                                   EXHIBIT "C"
<PAGE>   51

          conforming with applicable building codes, otherwise to perform equal
          to those at Tenant's 100 Brickstone Square facilities, unless
          specified to the contrary herein.

     C.   Any changes from the standards established above requested by the
          Tenant as to the quality or quantity of construction and/or
          installation provided under this Workletter by the Landlord shall be
          at the Tenant's sole cost and may be undertaken at the Landlord's
          discretion, due regard being given to consideration of their impact
          upon construction and occupancy schedules, the availability of Tenant
          funding, and similar issues which may affect the performance of the
          Landlord under the Workletter.

3.   NEW BUILDING AREA USES

     A.   Shipping, receiving, and support spaces; approximately 600 square
          feet.

     B.   Cafeteria, kitchen and seating area, approximately 5,800 square feet,
          which is included in the area described in 3.4 below. Tenant will
          supply and install all equipment, appliances and millwork; Landlord
          will provide rough-in and final hook-up.

     C.   Lobby and entry vestibule, approximately 3,600 square feet.

     D.   Office and conference/training rooms to be constructed throughout the
          balance of the new building, except for space dedicated to elevator
          shafts, bathroom cores, stairwells and mechanical shafts, in a ratio
          of enclosed-to-open space equal to the ratio at Tenant's 100
          Brickstone Square, Andover, facilities.

     E.   Recap of new building areas:

                    53,000 sf           Ground Floor
                    49,400 sf           Second Floor
                    49,400 sf           Third Floor
                    ------

                    151,800+/- SF       TOTAL NEW BUILDING

4.   SITE

     A.   Site features will include bituminous paved parking areas, striped to
          accommodate 506 parking spaces, including 10 handicap, 15 visitor, and
          481 all-day parking spaces.

     B.   Building entry stairs and plazas will be granite pavers with thermal
          finish and sidewalks will be brick/concrete with broom finish.

     C.   Parking lot lighting mounted on lamp posts and exterior entrance
          lighting will be operational with photo-electric sensor controls.

                                  EXHIBIT "C"
<PAGE>   52



     D.   Landscaping surrounding the new building and ornamental trees and
          shrubbery at the entry areas and throughout the site will be installed
          and enhanced at the Landlord's discretion, the budget for which will
          be approximately $130,000.

     E.   Foundation and underslab drainage will be provided as required by site
          conditions and the Andover Conservation Commission.

5.   STRUCTURE

     A.   Building foundations will be cast-in-place concrete spread footings
          and foundation walls. The ground floor slab will have continuous
          perimeter insulation.

     B.   The primary structure will be steel columns on a 30' by 30' grid with
          composite steel girders, beams, and composite (steel deck and
          concrete) floor slabs on the second and third floors and a
          steel-reinforced concrete slab on grade.

     C.   The structural capacity of the ground floor = 100 lb/sf and the
          structural capacity of the second and the third floors = 80 lb/sf live
          load plus 20 lb/sf partition load for a total of 100 lb/sf; the roof
          structural capacity = 30 lb/sf.

6.   BUILDING EXTERIOR

     A.   The new building exterior will be a curtain-wall system with fixed,
          insulated, thermally broken windows and aluminum insulated
          sandwich-type panels with a premium paint finish.

     B.   The stair towers will be exposed concrete construction with a light
          sandblast finish. 

     C.   The ground floor will be an aluminum and insulated glass storefront
          system constructed on a concrete knee wall with a light sandblast
          finish.

7.   ROOF

     A.   The roof will be a single ply ballasted rubber roof over rigid
          insulation on steel deck, with roof structural members sloped to
          internal drains.

     B.   Natural daylight in the atrium will be supplemented by south-facing
          clerestory windows built on the atrium roof.

8.   LIGHTNING PROTECTION SYSTEM

     A.   A lightning protection system equivalent to that existing at 100
          Minuteman Road will be provided for the building and all rooftop
          equipment.

                                  EXHIBIT "C"

<PAGE>   53

9.   ELEVATORS AND CENTRAL CORE

     A.   Three elevators will be provided: two hydraulic passenger elevators
          and one hydraulic combination passenger and freight elevator. Each
          passenger elevator will be 3,500 lb. capacity, minimum 6' 8" wide by
          5' 5" deep car. The freight elevator will be 4,500 lb. capacity,
          minimum 5' 8" wide by 7' 9 1/2" deep car.

     B.   The new building will have a central core consisting of an elevator
          lobby and a three-story atrium. Finishes at the ground floor of the
          atrium and the elevator lobby will include a slate floor and a
          concrete accent wall with a light sandblast finish. Finishes at the
          upper level elevator lobbies will be carpeting and painted gypsum
          wallboard. On either side of the elevator lobbies will be a service
          core accommodating toilet rooms, employee kitchen/coffee stations, and
          electrical/data rooms. On the ground floor, a security guard
          station/fire command center will be located adjacent to the elevator
          lobby.

10.  LOADING DOCKS

     A.   A two-bay loading dock will be constructed at the exterior of the
          northeast side of the new building, with an adjacent interior
          shipping/receiving area.

     B.   A concrete pad will be poured adjacent to the loading dock, sized to
          accommodate one full-size dumpster.

     C.   The loading dock area will be screened by earth berming and shrubbery.

11.  HVAC SYSTEM

     A.   The Landlord will provide a complete heating, ventilating and air
          conditioning (HVAC) system for the Tenant's use. Heat loads consistent
          with those at the Tenant's facilities at 100 Brickstone Square,
          Andover, will be provided by the Tenant to facilitate the Landlord's
          design of the HVAC system.

     B.   All HVAC equipment will be controlled by an automatic temperature
          control ATC system located at a terminal in the building engineer's
          office within the new building.

     C.   The Landlord will consider design input from the Tenant's engineers in
          connection with the ATC system, which input is to give due regard to
          schedule and cost implications.

                                   EXHIBIT "C"
<PAGE>   54

12.  ELECTRIC SYSTEM

     A.   The Landlord will provide power supply from Massachusetts Electric
          Company, including distribution panels, transformers, wiring, devices,
          and an emergency power system, including an emergency generator and
          fuel supply equipment, as required by applicable building codes for
          life safety purposes.

     B.   The Landlord will provide ceiling-mounted 277-volt two-lamp deep cell
          parabolic light fixtures with electronic ballasts.

     C.   The Landlord will provide emergency lighting in the new building, as
          required by building code, including exit corridors leading to fire
          stairs.

     D.   The Landlord will provide standard wall outlets for data and
          telecommunications. The standard outlet consists of a rough box
          plaster ring and pull string to the ceiling plenum above. The Tenant
          is responsible for all other Tenant system components from the point
          of connection at the base building telephone closet to the final point
          of use devices. The data/telephone system and cabling will be
          furnished and installed by the Tenant.

     E.   All security systems will be furnished and installed by the Tenant.

13.  LIFE SAFETY

     A.   The Landlord will provide a code-required fire alarm system (and
          suppression system in the cafeteria, if required by applicable
          building codes) and associated equipment as required for and
          consistent with the described occupancy.

     B.   The new building will have three fire exit stair towers and one open
          monumental stair in the west atrium. The east fire exit stair tower
          will extend to the roof. The fire exit stair towers will consist of
          painted, exposed concrete masonry units on the interior, with
          concrete-filled steel pan-type stairs with rubber tread covers and
          vinyl composition tile on the floors and landings. Stair railings will
          be 1 1/2" diameter tubular steel, painted. The monumental stair will
          be a steel stair with granite treads and landings and a painted steel
          plate balustrade.

14.  PLUMBING SYSTEM

     A.   Two toilet rooms per gender per floor will be provided, containing
          water closets, lavatories and (in the men's room) urinals. The number
          of fixtures will comply with building code requirements based on a new
          building maximum occupant load of 500 people. Toilet room finishes
          will be 2"x2" ceramic mosaic tile on the floors and walls, plastic
          laminate-covered lavatory countertops, metal toilet 

                                   EXHIBIT "C"

<PAGE>   55


          partitions, all in manufacturer's standard colors. Ceilings will be
          gypsum wallboard, painted. Toilet fixtures and finishes, including
          tile and lighting, will be consistent with the quality at the Tenant's
          100 Brickstone Square facilities.

     B.   Two coffee stations per floor will be provided, and will include
          plastic laminate-covered base and overhead built-in cabinetry, with a
          single bowl stainless steel sink. Floors will be finished with vinyl
          composition tile, and walls and ceilings will be gypsum wallboard,
          painted.

     C.   Plumbing, piping and other fixtures will be supplied as required by
          applicable building codes to accommodate the needs of the base
          building central equipment, such as floor drains, rain water drains,
          leaders, risers and connections to the public water supply and sewage
          and storm drain systems.

     D.   An ADA-accessible water fountain will be provided outside each set of
          toilet rooms.

     E.   Accessible toilet fixtures will be provided as required by ADA.

15.  FIRE SUPPRESSION

     A.   The Landlord will provide fire suppression system components, as
          required by code, including all central equipment, piping and controls
          (stand pipe risers, hose valves, enunciator, etc.), sprinkler
          distribution piping, and sprinkler heads in building common areas,
          including lobbies, toilet rooms, penthouses, mechanical rooms,
          electrical closets, etc.

     B.   Sprinkler heads will be provided in Tenant areas in a regular grid
          pattern per high-density open plan configuration. Drops will not be
          uniformly centered in the ceiling tile unless the Tenant directs so at
          the Tenant's own cost. The Landlord will coordinate sprinkler drops to
          avoid interference with the lighting pattern, HVAC diffusers and other
          ceiling mounted components that are being provided by the Landlord.
          The Landlord will also modify sprinkler locations in enclosed spaces,
          such as offices, in order to coordinate with partitions, light
          fixtures and diffusers.

16.  FINISHES

     A.   The new building office and conference/training rooms, and related
          support spaces, will be improved with ceiling, wall and floor finishes
          equal to those at Tenant's 100 Brickstone Square, Andover, facilities.

     B.   The typical ceiling heights will be at 9 feet throughout the second
          and third floors and 10'2" throughout the ground floor, except the
          lobby atrium, which will be to the roof.


                                   EXHIBIT "C"


<PAGE>   56

     C.   All exterior windows will be provided with new, building-standard
          blinds equal to those at Tenant's 100 Brickstone Square, Andover,
          facilities.

     D.   Landlord will provide a kitchen, cafeteria and seating area on the
          first floor. The kitchen will include equipment as required to allow a
          full service type of operation (kitchen equipment, appliances and
          millwork to be furnished and installed by the Tenant; Landlord will
          provide rough-in and final hook-up). The kitchen area will be finished
          with ceramic tile walls and floors and gypsum wallboard ceilings.

NOTE:     THE TENANT'S SPACE PLANNER AND DESIGN ARCHITECT WILL PROVIDE THE 
          LAYOUT AND SPECIFICATIONS FOR TENANT IMPROVEMENTS PER EXHIBIT "CC" 
          OF THE LEASE WORKLETTER. THE FIT AND FINISH WILL BE CONSISTENT WITH 
          THAT AT THE TENANT'S 100 BRICKSTONE SQUARE, ANDOVER, FACILITIES. THE
          LANDLORD'S ARCHITECT WILL PROVIDE CADD DRAWING DISKS OF THE BASE 
          BUILDING TO THE TENANT'S DESIGN ARCHITECT FOR USE IN PLANNING THE 
          SPACE LAYOUT.

                                   EXHIBIT "C"
<PAGE>   57

                                  EXHIBIT "CC"

                         PICTURETEL INITIAL INFORMATION


     1. PictureTel will deliver the following information to Landlord on or
about September 30, 1996: detailed floor plans/layouts for the Building,
including the size and location of all offices, conference rooms, training rooms
and other areas, prepared to 1/8" scale, with architectural features included
(e.g., high wall versus low wall); equipment loads, BTU requirements, amperage
requirements, and similar requirements for all areas; PictureTel's choices and
specifications for hardware, floor and wall finishes, and other design elements
and other information and specifications sufficient to enable Landlord to
produce final plans, drawings and specifications for Landlord's Work.

     2. The goal of Landlord's design team is to produce GMP pricing documents
on or about December 1, 1996. Therefore, in addition to the information to be
delivered as described above, Tenant will direct its professionals to deliver to
Landlord's design team design documents on a weekly basis or otherwise as often
as practicable, and to deliver sufficient information for all of the Building to
Landlord's design team in sufficient time so that Landlord's design team can
reasonably attempt to meet the December 1, 1996 target date.

                                  EXHIBIT "CC"

<PAGE>   58


                                   EXHIBIT "D"

                                    BASE RENT

     1. Subject to Paragraph 2 below, if Landlord's Work is subdivided into
Phases, then for each Phase, starting on the later of August 1, 1997, or the
Occupancy Date for that Phase, the annual base rent for that Phase shall be
Tenant's Percentage of Two Million Three Hundred and Fifty-two Thousand Nine
Hundred Dollars ($2,352,900), which will be payable in equal monthly
installments in advance as set forth in Section 5(a) of the Lease. If Tenant's
Percentage is retroactively adjusted as set forth in Section 1.1(f), then if any
amounts are owed by Tenant they shall be paid within fifteen (15) days after
such adjustment, and if any amounts are owed by Landlord they shall be paid
within fifteen (15) days after such adjustment, or, at Landlord's election, the
amounts owed to Tenant shall be credited against the next rental payments due
from Tenant.

     2. AS OF THE COMMENCEMENT DATE, THE ANNUAL BASE RENT FOR THE PREMISES WILL
BE TWO MILLION THREE HUNDRED AND FIFTY-TWO THOUSAND NINE HUNDRED DOLLARS
($2,352,900) PER ANNUM, WHICH WILL BE PAYABLE IN EQUAL MONTHLY INSTALLMENTS IN
ADVANCE AS SET FORTH IN SECTION 5(a) OF THE LEASE. The annual base rent during
the Extension Options shall be determined in accordance with Exhibit "DD"
hereto.

     3. Base rent payable for any other space leased by Tenant from Landlord
shall be in addition to and at rates different from the base rent set forth
above, unless otherwise specifically agreed in writing by Landlord and Tenant.

[SEE SECTION 5(b) OF THE LEASE FOR POSSIBLE RENT CREDITS IN CONNECTION WITH THE
LETTER OF CREDIT.]

                                   EXHIBIT "D"

<PAGE>   59


                                  EXHIBIT "DD"

                       BASE RENT DURING EXTENSION OPTIONS

     The annual base rent for each year of each Extension Option will be the
"Fair Rental Value" of the Premises determined as follows separately for each
Extension Option, but not less than the scheduled annual base rent under the
Lease for the year immediately preceding the applicable Extension Option term
(without giving effect to any abatements or reductions in that rent):

          (a) If Landlord and Tenant can't agree on the annual base rent for
each Lease Year of the applicable Extension Option term at least eight (8)
months before the beginning of that Extension Option term, then unless otherwise
agreed in writing by Landlord and Tenant, Landlord and Tenant will try to agree
in writing on a single appraiser at least seven (7) months before the beginning
of that Extension Option term. If Landlord and Tenant can't agree on a single
appraiser within this time period, then Landlord and Tenant each will appoint,
in writing, one appraiser not later than six (6) months before the beginning of
the that Extension Option term. Within fifteen (15) days after their
appointment, the two appointed appraisers will appoint a third appraiser. If the
two appraisers can't agree, a third appraiser will be appointed by the American
Institute of Real Estate Appraisers (or if this organization refuses to act or
no longer exists, then by an organization deemed by Landlord to be reasonably
equivalent) not later than five (5) months before the beginning of that
Extension Option term. If either Landlord or Tenant fails to appoint its
appraiser within the prescribed time period, the single appraiser appointed will
determine the Fair Rental Value. If both parties fail to appoint appraisers
within the prescribed time periods, then the first appraiser validly appointed
by a party will determine the Fair Rental Value. Appraisers must have at least
five (5) years' experience in the appraisal of office property in the area in
which the Premises is located and be members of professional organizations such
as the American Institute of Real Estate Appraisers or the equivalent.

          Landlord and Tenant will instruct the appraiser(s) to complete and
submit their determination of the Fair Rental Value not later than four (4)
months before the beginning of that Extension Option term.

          (b) For purposes of this Lease, the term "Fair Rental Value" means:
ninety-five percent (95%) of the annual net base rent that a ready and willing
tenant would pay for the Premises during each year of that Extension Option term
to a ready and willing landlord of the Premises, taking into account free
parking and other economic benefits of this Lease in determining that rent,
assuming that the Premises was exposed for lease on the open market for a
reasonable period of time, could be used for any lawful use and was improved to
its then-existing 

                                   EXHIBIT "E"
<PAGE>   60

level, and assuming the following factors, among others, also are taken into
account and given effect: improvements, if any, agreed to be made by Landlord,
the location of the Premises, the Lease term, and tenant improvement and other
leasing concessions then being given by other landlords of comparable space. If
only a single appraiser is appointed as described above, then that appraiser
will determine the Fair Rental Value. Otherwise, the Fair Rental Value will be
the arithmetic average of the two (2) of the three (3) appraisals which are
closest in amount, and the third appraisal will be disregarded.

          (c) If for some reason the Fair Rental Value is not determined before
the beginning of that Extension Option period, then Tenant will pay to Landlord
base rent at the scheduled rate most recently payable until the Fair Rental
Value is determined. When the Fair Rental Value is determined, Landlord will
notify Tenant, and Tenant will pay to Landlord, within thirty (30) days after
receipt of such notice, any difference between the base rent actually paid by
Tenant to Landlord and the new base rent determined hereunder (if the new base
rent is higher).

                                   EXHIBIT "E"

<PAGE>   61
                                   EXHIBIT "E"
                              RULES AND REGULATIONS

          1. Any person whose presence on the Premises at any time shall, in the
reasonable judgment of the Landlord, be prejudicial to the safety, character,
reputation and interests of the Premises may be denied access to the Premises or
may be ejected therefrom. In case of invasion, riot, public excitement or other
commotion the Landlord may prevent all access to the Premises or the Building
during the continuance of the same, by closing the doors or otherwise, for the
safety of Tenant or protection of property. The Landlord shall in no way be
liable to Tenant or its Affiliates for damages or loss arising from the
admission, exclusion or ejection of any person to or from the Premises under the
provisions of this rule, as long as Landlord acts reasonably under the
circumstances as they appear to Landlord at the time.

          2. No awnings or other projections over or around the windows shall be
installed by Tenant, and all window blinds used or installed by Tenant or its
Affiliates shall be of the same type in order to provide a uniform exterior
appearance.

          3. Tenant shall not encumber or obstruct, or permit the encumbrance or
obstruction of, or store or place any materials, outside of the Building, or in
any entrances, corridors, elevators, fire exits or stairways of the of the
Building so as to create any unsafe or unlawful condition.

          4. Nothing shall be done or permitted by Tenant which would impair or
interfere with any of the Systems or Equipment or the proper and economic
servicing of the Building or the Premises, nor shall there be installed by
Tenant any Systems or Equipment or other equipment of any kind which, in
Landlord's reasonable judgment, could result in such impairment or interference.
No dangerous, inflammable, combustible or explosive object or material shall be
brought into the Building or onto the Premises by Tenant or with the permission
of Tenant, except strictly in accordance with this Lease.

          5. Whenever Tenant shall submit to Landlord any plan, agreement or
other document for Landlord's consent or approval, Tenant agrees to pay Landlord
as additional rent, on demand, a processing fee in a sum equal to the reasonable
fees payable to any architects, contractors, engineers and attorneys engaged by
Landlord to review said plan, agreement or document, and costs, expenses or fees
required to be paid by Landlord to or at the direction of Landlord's Mortgagees
in order to secure approval of said plan, agreement or document, if and to the
extent that their approval is required.

          6. No acids, vapors, hazardous or other materials shall be discharged
or permitted to be discharged into the waste lines, ducts, vents or flues which
may damage them or any other portions of the Building or the Premises. The water
and wash closets and other 

                                   EXHIBIT "E"

<PAGE>   62
plumbing fixtures in or serving the Building shall not be used for any purpose
other than the purpose for which they were designed or constructed, and no
sweepings, rubbish, rags, acids or other foreign substances shall be deposited
therein. All damage resulting from any misuse of the fixtures shall be borne by
Tenant, if it shall have caused the same, subject to Section 8.3 of the Lease.

          7. Landlord shall have the right to prohibit any advertising by Tenant
which impairs the reputation of the Building or the Premises, and upon written
notice from Landlord, Tenant shall refrain from or discontinue such advertising.

          8. All third party movers used by Tenant shall be appropriately
licensed and shall maintain reasonable insurance coverage (proof of such
coverage shall be delivered to Landlord prior to movers providing service in, on
or to the Premises.

          9. The Premises shall not be used for lodging or sleeping or for any
immoral or illegal purposes.

                                   EXHIBIT "E"

<PAGE>   63

                                   EXHIBIT "F"

                              BANKRUPTCY PROVISIONS

     This Article is incorporated into the Lease as Article 23:

23.  BANKRUPTCY OR INSOLVENCY.
     ------------------------

     23.1 TENANT'S INTEREST NOT TRANSFERABLE. Neither Tenant's interest in this
Lease nor any estate hereby created in Tenant nor any interest herein or therein
will pass to any trustee or receiver or assignee for the benefit of creditors or
otherwise by operation of law except as may specifically be provided pursuant to
the Bankruptcy Code, 11 U.S.C. Section 101 ET SEQ. (the "Bankruptcy Code").

     23.2 Default and Termination. If:
          -----------------------

          (a) Tenant or Tenant's Guarantor, if any, or its executors,
administrators, or assigns, will generally not pay its debts within a reasonable
and customary time after they become due or will admit in writing its inability
to pay its debts, or will make a general assignment for the benefit of
creditors; or

          (b) Tenant or Tenant's Guarantor, if any, will commence any case,
proceeding or other action seeking reorganization, arrangement, adjustment,
liquidation, dissolution or composition of it or its debts under any law
relating to bankruptcy, insolvency, reorganization or relief of debtors, or
seeking appointment of a receiver, trustee, custodian or other similar official
for it or for all or any substantial part of its property; or

          (c) Tenant or Tenant's Guarantor, if any, will take any corporate,
partnership or other action to authorize or in furtherance of any of the actions
set forth above in subsection (a) or (b); or

          (d) Any case, proceeding or other action against Tenant or Tenant's
Guarantor, if any, will be commenced seeking to have an order for relief entered
against it as debtor, or seeking reorganization, arrangement, adjustment,
liquidation, dissolution or composition of it or its debts under any law
relating to bankruptcy, insolvency, reorganization or relief of debtors, or
seeking appointment of a receiver, trustee, custodian or other similar official
for it or for all or any substantial part of its property, and such case,
proceeding or other action remains undismissed or unstayed for a period of sixty
(60) days, then it will be a default hereunder and this Lease and all rights of
Tenant hereunder will automatically cease and terminate as if the date of such
event were the original expiration date of this Lease and Tenant will vacate and
surrender the Premises but will remain liable as herein provided.

                                  EXHIBIT "F"
                                      -2-

<PAGE>   64

     23.3 Rights and Obligations Under the Bankruptcy Code.
          ------------------------------------------------

(a) Upon the filing of a petition by or against Tenant under the Bankruptcy
Code, Tenant, as debtor and as debtor in possession, and any trustee who may be
appointed agree as follows: (i) to perform all obligations of Tenant under this
Lease, including, but not limited to, the covenants regarding the operations and
uses of the Premises until such time as this Lease is either rejected or assumed
by order of the United States Bankruptcy Court; (ii) to pay monthly in advance
on the first day of each month as reasonable compensation for use and occupancy
of the Premises an amount equal to all base rent and other rent otherwise due
pursuant to this Lease; (iii) to reject or assume this Lease within sixty (60)
days of the filing of a petition under any Chapter of the Bankruptcy Code or
under any Law relating to bankruptcy, insolvency, reorganization or relief of
debtors (any such rejection being deemed an automatic termination of this
Lease); (iv) to give Landlord at least thirty (30) days prior written notice of
any proceeding relating to any assumption of this Lease; (v) to give at least
thirty (30) days prior written notice of any abandonment of the Premises (any
such abandonment being deemed a rejection and automatic termination of this
Lease), unless the Bankruptcy Court has otherwise extended the period for
acceptance or rejection; (vi) to all other things of benefit to Landlord
otherwise required under the Bankruptcy Code or under any Law relating to
bankruptcy, insolvency, reorganization or relief of debtors; (vii) to be deemed
to have rejected this Lease in the event of the failure to comply with any of
the above; and (viii) to have consented to the entry of an order by an
appropriate United States Bankruptcy Court providing all of the above, except
that if and to the extent that any of the above provisions, if enforced, would
violate the Bankruptcy Code then in existence, then such provisions shall be
conformed to the Bankruptcy Code then in existence.

          (b) No default under this Lease by Tenant, either prior to or
subsequent to the filing of such petition, will be deemed to have been waived
unless expressly done so in writing by Landlord.

          (c) Included within and in addition to any other conditions or
obligations imposed upon Tenant or its successor in the event of assumption
and/or assignment are the following: (i) the cure of any monetary defaults and
the reimbursement of pecuniary loss by the time of the entry of the order
approving such assumption and/or assignment (pecuniary loss will include,
without limitation, any attorneys' fees and costs and expert witness fees
incurred by Landlord in protecting its rights under this Lease, including
representation of Landlord in any proceeding commenced under the Bankruptcy Code
or under any Law relating to bankruptcy, insolvency, reorganization or relief of
debtor); (ii) the deposit of an additional sum equal to three (3) months' base
rent; (iii) the use of the Premises only as set forth in this Lease; (iv) the
reorganized debtor or assignee of such debtor in possession or of Tenant's
trustee demonstrates in writing that it has sufficient background including, but
not limited to, substantial experience in operating businesses in the manner
contemplated in this Lease and meet all other reasonable criteria of Landlord as
did Tenant upon execution of this Lease; (v) meet all other criteria of 11
U.S.C. Section 365(b)(3); and (v) the prior written consent of any mortgagee to
which this Lease 

                                   EXHIBIT "F"
                                       -2-
<PAGE>   65

has been assigned as collateral security; and (vi) the Premises at all times
remains a single unit and no Alterations or physical changes of any kind may be
made unless in compliance with the applicable provisions of this Lease, except
that if and to the extent that any of the above provisions, if enforced, would
violate the Bankruptcy Code then in existence, then such provisions shall be
conformed to the Bankruptcy Code then in existence.

          (d) Any person or entity to whom this Lease is assigned pursuant to
the provisions of the Bankruptcy Code will be deemed without further act or deed
to have assumed all of the obligations arising under this Lease on or after the
date of such assignment. Any such assignee will upon demand execute and deliver
to Landlord an instrument confirming such assumption.

     23.4 CONSTRUCTION. The terms of this Article will be in addition to, but
not exclusive of, any rights or remedies of Landlord in Article 22 and elsewhere
in this Lease or otherwise available at law or in equity, and will not be deemed
to limit Landlord, except as may be required by law.

                                   EXHIBIT "F"
                                       -2-

<PAGE>   66

                                   EXHIBIT "G"

                               LANDLORD'S SERVICES

     In addition to Landlord's obligations in Article 12 and the rest of this
Lease, Landlord shall furnish (as part of Operating Costs) the following
services during the term of the Lease and any renewals:

I.   Outside Maintenance:
     -------------------

     A.   All parking areas and access ways will be plowed of snow and ice and
          sanded as reasonably required and practicable. All paths and walkways
          will be shoveled of snow and sanded as reasonably required and
          practicable.
     B.   All landscaped areas and exterior grounds shall be kept in a neat
          appearance.
     C.   Lighting of all parking areas and roadways.

II.  Miscellaneous Services:
     ----------------------

     A.   Render pest control services as reasonably required.
     B.   Wash exterior windows at least once per year.

III. Janitorial Services: None, Tenant responsible for all Janitorial Services.
     -------------------

IV.  TRASH: Tenant will have access to trash compactor(s) (or the equivalent)
     for standard office-usage trash disposal. Landlord provides hauling from
     compactor.

     Landlord will provide or hire the personnel necessary to provide the
     services set forth herein, including, if necessary, on-site personnel (and
     the costs related to all of such personnel shall be part of Operating
     Costs).

                                   EXHIBIT "G"
                                       -1-

<PAGE>   67

                                   EXHIBIT "I"

                             [INTENTIONALLY OMITTED]
--------------------------------------------------------------------------------



                                   EXHIBIT "I"

<PAGE>   68

                                   EXHIBIT "J"

                              ESTOPPEL CERTIFICATE


The Bank of Nova Scotia
Real Estate Banking
New York Agency
One Liberty Plaza
New York, New York 10006 ("Lender")

     RE:  Proposed Loan to 50 Minuteman Limited Partnership (the "Landlord")
          Secured by a $7.8 Million Letter of Credit issued by The First
          National Bank of Boston (the "Letter of Credit') delivered by
          PictureTel Corporation (the "Tenant")

Dear Sir or Madam:

     We are the tenant under the terms of a certain lease (together with any
amendments, options, extensions and renewals listed below, the "Lease") demising
premises which comprise all of the property located at 50 Minuteman Road,
Andover, Massachusetts (the "Real Property"). We understand that you, Lender,
will rely on this Certificate in connection with a proposed $     Million loan
(the "Loan) to Landlord. The Letter of Credit will be Lender's security for the
Loan.

     Tenant certifies that:

     (a)  It occupies the premises demised by the Lease.

     (b)  The material business terms of the Lease are as follows:

          Landlord: 50 Minuteman Limited Partnership.

          Lease Date:

          Lease Commencement Date:

          Subleases (if any): N/A

          Amendments and Modifications (if any):

          Current Monthly Base Rent:

          Current Expense Reimbursement: The Lease is triple net, and operating
          costs,


                                   EXHIBIT "J"
                                      -2-
<PAGE>   69

          insurance and real estate taxes are payable by Tenant per the terms of
          the Lease.

          Square Footage: Approximately 150,000 s.f.

          Expiration Date:

          Renewals or Extension Options (if any): Seven 10-year extension
          options.

          Security or other Deposit: The Letter of Credit.

          Uncompleted Tenant Improvements (if any): Landlord's Work has been
          substantially completed, subject to minor punchlist items.

          Unpaid Tenant Allowances (if any): N/A.

          Other Financial Obligation of Landlord (if any): N/A

     (c)  The Lease is Tenant's entire agreement with the Landlord.

     (d)  Tenant has accepted and currently occupies the leased premises, is
          paying full rent under the Lease, and neither (i) presently asserts
          any Landlord default, claim against Landlord, matured right of setoff,
          or right to pay reduced rent nor (ii) knows of any fact which, with
          the giving of notice or the passage of time, or both, could give rise
          to any such default claim or right.

     (e)  Tenant neither (i) presently asserts any matured right to terminate or
          to cancel the Lease nor (ii) knows of any fact which, with the giving
          of notice or the passage of time or both, could give rise to any such
          right.

     (f)  Tenant does not presently intend to vacate its premises any time prior
          to the lease's expiration date and knows of no fact which could give
          rise to any such intent.

     (g)  Tenant is not the debtor in any bankruptcy or state insolvency case
          and is not the subject of any receivership, winding up, liquidation or
          similar proceeding.

                                  EXHIBIT "J"
                                      -2-

<PAGE>   70

     (h)  Tenant agrees that no future modification or amendment of the Lease
          relating to the Letter of Credit will be enforceable unless the
          modification or amendment has been consented to in writing by the
          Lender.

                                             Very truly yours,

                                             Tenant: PictureTel Corporation

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

                                             Title:
                                                   -----------------------------

                                             Date:
                                                  ------------------------------
                                   EXHIBIT "L"

$7,800,000                                                Andover, Massachusetts
                                                          ________________, 1996
                                                          
                                 PROMISSORY NOTE

     This Promissory Note is entered into pursuant to Section 24.17(f) of that
certain Lease, dated as of________________ , 1996, between PictureTel
Corporation and the Undersigned (the "Lease"), and is the "LC Note" referred to
therein.

     FOR VALUE RECEIVED, the Undersigned, 50 Minuteman Limited Partnership, a
Massachusetts limited partnership, promises to pay to PictureTel Corporation
("PictureTel"), or to its order, at such address as may be designated by
PictureTel, the sum of all amounts which shall have been drawn by the
beneficiary under any Letter of Credit issued by the First National Bank of
Boston or any other entity on behalf of PictureTel in favor of the Undersigned
or one of the Undersigned's lenders pursuant to the Lease and which amounts are
treated as "LC Advances" pursuant to Section 24.17(f) of the Lease (and if no
such amounts are drawn, then no amounts shall be due under this Promissory
Note), with interest on any such amounts accruing from the date of the draw to
the date the first payment is due PictureTel hereunder, at the Interest Rate or
Interest Rates specified herein below, with such accrued interest as of the date
the first payment is due hereunder converting to principal as of the date such
first payment is due, in monthly installments with interest as provided herein
or as otherwise provided herein.

     The applicable Interest Rate at any time with respect to any such amounts
drawn under the Letter of Credit shall be:

     (a) for the period that the initial construction loan to the Undersigned
remains

                                  EXHIBIT "J"
                                      -2-
<PAGE>   71

outstanding, the average interest rate of all borrowings under that initial
construction loan (hereafter the "Construction Rate"), provided however, that if
the Undersigned does not obtain a permanent loan within 15-1/2 months after the
Commencement Date, or if the Undersigned has obtained a permanent loan and
amounts remain due PictureTel under this Note, the applicable Interest Rate
shall be the Construction Rate plus 75 basis points, unless there is a material
adverse change to PictureTel's financial condition, in which case the applicable
Interest Rate shall be the same rate payable on the first mortgage loan
encumbering the Premises,

     (b) after the date that the initial construction loan is no longer
outstanding, the same rate payable on the first mortgage loan encumbering the
Premises;

provided however, that if at any time there is no first mortgage loan
encumbering the Premises, then during such period the Interest Rate shall be the
stated rate of the first mortgage loan most recently encumbering the Premises.

     Notwithstanding anything to the contrary, payments otherwise due hereunder
shall be subject to the following:

     (a) All such payments shall be subject and subordinate in all respects to
the prior payment in full of all amounts then due under the first mortgage loan.

     (b) The amount of each such payment, when added to the monthly amounts
payable under the first mortgage loan, shall not exceed the base rent paid by
PictureTel under the Lease for that month, and each such payment shall be
reduced if necessary so as not to exceed such limit.

     (c) Any deficits or reductions in or failure to pay such payments resulting
from the operation of clauses (a) or (b) immediately above shall not be deemed
defaults hereunder, but the unpaid amounts shall be added to the principal
balance due hereunder as of the date they otherwise would have been due from the
Undersigned.

     (d) If there is a "default" (as defined in the Lease) under the Lease, in
addition to any rights under the Lease, the Undersigned may offset and deduct
against the amounts payable by it hereunder the amounts due to the Landlord
under the Lease. The "Tenant" (as defined in the Lease) shall not have the right
to offset or deduct against the amount payable by it under the Lease any amounts
due to PictureTel hereunder except as may be specifically set forth in the Lease
with respect to amounts drawn under the Letter of Credit.

     The first monthly installment payable to PictureTel pursuant to this
Promissory Note shall be due beginning the first day of the first full month for
which PictureTel is obligated to pay base rent to the Undersigned under the
Lease. The amount of the principal payable on the first such installment and
each subsequent installment shall be that monthly amount which is necessary to
fully amortize the then outstanding principal balance due PictureTel hereunder
(including any interest which has accrued prior to the date the first such
installment is due) in equal monthly installments over the initial term of the
Lease, assuming an interest rate of nine percent (9%) per annum. The amount of
interest payable each month shall be calculated by applying the applicable
Interest Rate to the then remaining principal balance. If after the first

                                  EXHIBIT "L"
                                      -2-
<PAGE>   72

installment is due additional amounts are drawn under the Letter of Credit and
treated as "LC Advances" or principal is prepaid by the Undersigned, the amount
of principal due in each monthly installment from that date forward shall be
determined in the same manner as set forth above but using the increased or
decreased principal amount, as the case may be, and assuming amortization over
the then remaining initial term of the Lease at the same assumed nine percent
(9%) interest rate.

     This Note shall be due and payable in full without further notice or demand
if: (i) the Undersigned shall fail within fifteen (15) days after written notice
from PictureTel to make any payment when due hereunder, unless Tenant is then in
default under the Lease; or (ii) if the Undersigned defaults under the first
mortgage loan encumbering the Premises and the lender successfully completes a
foreclosure thereunder, provided that such default did not arise as a result of
Tenant's breach of its obligations under the Lease and provided that the Tenant
is not then in default under the Lease. However, in any such event the
provisions of Subsections (a), (b), (c) and (d) in the last full paragraph
starting on Page 1 of this Note still will apply.

     The Undersigned may prepay the principal amount outstanding in whole or in
part without penalty. The Undersigned shall partially or entirely prepay the
principal amount outstanding and all accrued interest if and to the extent that
the Undersigned receives proceeds from the funding of a permanent loan that are
in excess of all amounts due under any first mortgage loan then encumbering the
Premises. Payments under this Note will be applied first against interest due
and any excess to the principal amount outstanding.

     Amounts due hereunder shall be payable in lawful money of the United States
of America, in immediately available funds, at the place PictureTel may
designate from time to time in writing to the Undersigned.

     In case any payment herein provided for shall not be paid when due, the
Undersigned promises to pay all reasonable cost of successful collection and
enforcement of this Note, including all reasonable attorneys' fees.

     This Note shall be governed by, and construed in accordance with, the laws
of the Commonwealth of Massachusetts.

     The Undersigned and all endorsers of this Note hereby waive presentment,
demand, notice of nonpayment, protest and all other demands and notices in
connection with the delivery, acceptance, performance or enforcement of this
Note.

                                   EXHIBIT "L"
                                      -2-
<PAGE>   73

     This Note is not negotiable and may not be assigned or pledged by
PictureTel, except that this Note may be assigned to a permitted assignee under
the Lease.

     This Note will take effect as a sealed instrument.

                                   50 Minuteman Limited Partnership

                                   By: Niuna-50 Minuteman, Inc., general partner

                                       By:
                                          ---------------------------------
                                          John Kusmiersky, President
                                          Hereunto Duly Authorized

                                   EXHIBIT "L"
                                       -2-

<PAGE>   74

                                   EXHIBIT "M"

                              BENEFICIARY'S RIGHTS

     The lender of the Letter of Credit Loan, as beneficiary under the Letter of
Credit, may draw under the Letter of Credit from time to time on one or more
occasions on the occurrence of an event of default as defined in the Loan
Agreement, and any amendments thereto, between Landlord and such lender.

                                   EXHIBIT "M"

<PAGE>   75

                                   ADDENDUM #1

                        ROOFTOP COMMUNICATIONS EQUIPMENT

     Subject to the following and the rest of this Article and this Lease,
Tenant may install satellite dishes and other communications equipment and
antennas of reasonable size on the roof of the Building in a mutually agreeable
location, or in another mutually agreeably location. Notwithstanding anything to
the contrary, Tenant will be responsible for all Liabilities in connection with
these satellite dishes and antennas and associated Systems and Equipment,
including, without limitation, installation, removal, operation, maintenance,
insurance, taxes and other costs and fees, and any necessary alterations or
improvements to the Building or the rest of the Premises. Tenant also will be
solely responsible for securing all federal, state and local permits in
connection with the installation and operation of these satellite dishes and
antennas prior to installation and for complying with all applicable Laws. If
these satellite dishes and antennas are on a roof, Tenant will secure from the
membrane roofing manufacturer certification that the installation is compatible
with all design requirements and that this installation will not void the
existing roof warranty. This certification must be delivered to Landlord before
installation begins. Tenant also will use only a manufacturer-authorized roofing
contractor for any work that requires the penetration of the existing membrane
roofing system. Upon the expiration or earlier termination of this Lease,
Tenant, at its expense, will remove these satellite dishes or antennas and all
associated Systems and Equipment and repair all damage. Notwithstanding anything
to the contrary, Landlord will have no Liabilities in connection with these
satellite dishes or antennas and associated Systems and Equipment, and Tenant
will indemnify Landlord for and hold it free and harmless from all Liabilities
arising out of or in connection with these satellite dishes or antennas and all
associated Systems and Equipment.

                                   ADDENDUM #1
                                       -1-

<PAGE>   76

                                   ADDENDUM #2

                                EXTENSION OPTIONS

     1. GRANT OF EXTENSION OPTIONS. Landlord grants to Tenant seven (7) options
(the "Extension Options") to extend the Lease term for additional terms of ten
(10) years each on the same terms and conditions as this Lease, except that
there will be no further right to extend and except as set forth below. Except
as specifically set forth in Section 4 below, the Extension Options can be
exercised only by Tenant delivering unconditional written notice of exercise to
Landlord on or before the later of: two (2) years before the expiration of the
then-current term; or fifteen (15) days after Landlord's written notice to
Tenant of Tenant's failure to exercise, which notice may be given at any time
after two (2) years before the expiration of the then-current term. If for ANY
REASON Landlord does not actually receive Tenant's unconditional written notice
of exercise when required, at Landlord's election the Extension Options will
lapse and become null and void and there will be no further right to extend the
Lease term. If Tenant does not validly exercise an Extension Option, that
Extension Option and all subsequent Extension Options shall, at Landlord's
election, lapse and become null and void. The Extension Options are personal to
the Tenant originally named in this Lease and may not be exercised by anyone
else (except for an assignee pursuant to a valid assignment of this Lease, and
then only if prior to the date for exercise set forth in this Lease the assignor
and the assignee deliver to Landlord a jointly executed and unconditional
written notice stating that the specific Extension Option may be exercised by
the assignee; provided that notwithstanding anything to the contrary, if there
is a valid assignment of this Lease then thereafter ONLY the assignee will have
the right to exercise any Extension Options and such exercise shall be subject
to the terms above). The Extension Options are granted to and may be exercised
by Tenant on the express condition that, at the time of the exercise and at all
times before the beginning of each Extension Option period, Tenant is not in
default (and has not committed acts which would constitute a default with the
passage of time or the giving of notice). TIME IS ABSOLUTELY OF THE ESSENCE.

     2. NO ADDITIONAL WORK. Landlord will not be required to perform or pay for
any work or other improvement to the Premises, and subject to the other terms of
this Lease Tenant will accept the Premises in its then "as is" condition in all
respects. The annual base rent for each Lease Year of each Extension Option
period will be as set forth in Exhibit "DD."

     3. CANCELLATION. Tenant shall not have the right or power to exercise any
Extension Options if this Lease has expired or been terminated pursuant to its
terms.

     4. SPECIAL EXTENSION OPTION. If pursuant to Addendum #4 Tenant exercises
the third (3rd) Purchase Option at the end of the sixteenth (16th) Lease Year
and thereafter Landlord fails to close on the sale of the Premises to Tenant due
to Landlord's default under Addendum #4, or if Landlord commences any case,
proceeding or other action seeking reorganization, arrangement, adjustment,
liquidation, dissolution or composition of it or its debts under any law
relating to bankruptcy, insolvency, reorganization or relief of debtors, or
seeking appointment of a receiver, trustee, custodian or similar official for it
or for all or any substantial part of its property, or any 

                                  ADDENDUM #2
                                      -1-


<PAGE>   77

such case, proceeding or action is commenced against Landlord and is not stayed
or dismissed before the closing and Landlord fails to close as a result thereof
(the "Landlord Bankruptcy"), THEN, the Extension Options granted to Tenant in
accordance with this Addendum #2 shall be exercisable by Tenant in accordance
with this Addendum #2, except that Tenant may exercise the first (1st) Extension
Option by giving Landlord written notice thereof in accordance with Section 1
above within thirty (30) days after the earlier of the scheduled closing date or
the date of the Landlord Bankruptcy, but in any case prior to the expiration of
the initial Lease term, and otherwise in accordance with this Addendum. Exercise
of the first (1st) Extension Option by Tenant as provided in this Section 4
shall in no manner affect or extinguish the rights and obligations of Landlord
and Tenant under or in connection with Tenant's exercise of the third (3rd)
Purchase Option.

                                   ADDENDUM #2
                                      - 1 -

<PAGE>   78

                                   ADDENDUM #3

                                  NET PROCEEDS

     1. CASH PROCEEDS. "Cash Proceeds" means: all cash proceeds actually
received by or on behalf of Landlord that Landlord is permitted to retain (for
example, if Landlord must refund an overpayment to Tenant or a third party, the
amount refunded will not be deemed to be "retained" by Landlord nor shall it be
a part of Cash Proceeds hereunder) from the sale, leasing (including base rent
and additional rent), assignment, subleasing, initial financing (including,
without limitation, the initial financing secured by the Premises and any
financing secured by the Letter of Credit, but subject, however, to Addendum
#7), refinancing, encumbrance, Condemnation or other disposition of all or any
portion of the Premises or any interest therein (including any additional
buildings constructed on the Premises), and any casualty and rental insurance
proceeds received by or on behalf of Landlord that Landlord is permitted to
retain in connection with all or any portion of the Premises, any loans,
advances or capital contributions made to Landlord, indemnities paid by Tenant
to Landlord and any interest or investment income received by Landlord on such
cash proceeds. Notwithstanding the foregoing, Cash Proceeds do not include any
amounts paid to or receivable by Landlord for, as a result of or in connection
with: an exercise of any Purchase Options; Tenant's defaults, or any judgments,
settlements or awards paid by Tenant or its Affiliates; amounts drawn under the
Letter of Credit or the application(s) of any cash security deposit, or any late
charges or interest payable by Tenant; the Transfer of any interest in Landlord
or in any of its partners or other Control Affiliates; or development fees,
management fees or fees in lieu thereof payable to Landlord or its Affiliates
pursuant to this Lease or in connection with Landlord's Work or in connection
with the construction of any additional buildings on the Premises or the
enlargement or other modification of the Building or the rest of the Premises;
or any Excess Refinancing Proceeds as described in Section 3 of Addendum #5; or
any Net Proceeds distributed or distributable to Landlord pursuant to Section 3
below.

     2. COSTS. "Costs" means: all bona fide costs and expenses of any type paid
by Landlord or its Affiliates, or reasonably anticipated by Landlord to be
payable by Landlord or its Affiliates, for, as a result of or in connection with
all or any portion of the Premises or any interest therein or any ownership,
operation, management, maintenance, repair, restoration, replacement,
improvement, leasing (other than the payment of Net Proceeds hereunder),
financing, refinancing or Transfer by Landlord thereof (whether or not included
as part of Operating Costs, but not including any sale or conveyance to any of
Landlord's Control Affiliates), or the establishment and maintenance of
Landlord's existence in good standing as an entity, or any rights or Liabilities
in connection with any of the foregoing, including, without limitation, costs
and expenses for: the acquisition, sale or other disposition of all or any
portion of the Premises and any rights appurtenant thereto (including, without
limitation, all costs for due diligence, investigations, remedial work, closing
costs, escrow and title fees, legal fees, professional fees and commissions);
Landlord's Work and all other labor, services and materials supplied to or for
the benefit of the Premises (including any additional buildings constructed on

                                   ADDENDUM #3
                                      - -

<PAGE>   79

the Premises) and/or Tenant under or in connection with this Lease (including,
without limitation, costs for designers, architects, engineers, draftsmen,
supervision, permits and approvals, development fees (other than those payable
to Landlord or its Affiliates which are excluded from Cash Proceeds as set forth
in Section 1 above), fees, profit and savings payable to construction managers,
contractors and subcontractors, and all other reasonably related "hard" and
"soft" costs); financing, refinancing and encumbrance of the Premises or any
interest therein (including, without limitation, payment of all principal,
interest, fees, commissions, appraisals, escrow and title fees, other closing
costs, interest rate hedges, "caps" or "floors," and other costs in connection
therewith and other amounts owed under any of the loan documents); the repayment
of all bona fide capital contributions, loans or advances made by Landlord or
its partners or their respective Affiliates (including, without limitation, the
repayment of such amounts and commercially reasonable interest on such loans and
a commercially reasonable rate of return on such contributions or advances,
which in any case will be at least equal to the Bank of Boston's (or its
successor's) prime rate plus one percent (1%), or the maximum rate permitted by
law, whichever is less, and commercially reasonable closing costs, commissions
and/or loan fees or similar fees in order to obtain such loans, contributions or
advances); the payment and performance of all of Landlord's Liabilities and the
exercise of Landlord's rights under or in connection with this Lease or the
Premises or agreements in connection therewith (including, without limitation,
costs for Taxes, Operating Costs, amounts in connection with Hazardous
Substances and environmental protection, compliance will all Laws, indemnity and
defense costs, and other costs in connection therewith and other amounts owed
under any of the loan documents); attorneys' fees and other costs in connection
with the defense or prosection of any litigation, proceedings, claims or
counterclaims or as otherwise deemed necessary by Landlord; judgments, claims,
awards or settlements, whether due to the fault of Landlord or its partners or
otherwise; an amount per calendar year equal to forty percent (40%) of an amount
(the "Tax Payments") equal to: Landlord's taxable income (if any) in the prior
calendar year (other than the taxable income resulting solely from the sale or
the conveyance of the Premises) less the amounts paid to Landlord for that prior
calendar year pursuant to this Subclause of this Section 2, and if in any year
the Tax Payments are not fully paid, then the unpaid Tax Payments shall cumulate
and be paid as Costs as soon as there are sufficient Cash Proceeds; the
preparation of Landlord's annual audited financial statements and any other
information to be provided by Landlord under this Lease (including audits of Net
Proceeds) and tax returns; corporate or partnership license fees, filing fees,
business and franchise taxes and fees, and similar charges; and reserves deemed
reasonably necessary by Landlord in connection with any of the foregoing. Unless
otherwise specifically agreed and set forth in this Lease (e.g., with respect to
the interest rate on loans or the return on capital, or with respect to
management fees or fees in lieu thereof, or budgeted development fees), amounts
payable as Costs by Landlord to any of its Affiliates for services rendered
shall not exceed the prevailing rates that would be payable to unaffiliated
third parties in an arms-length transaction. Costs do not include any of the
above amounts which are directly paid by Tenant or which are funded by
insurance.

     3. PAYMENT OF NET PROCEEDS. "Net Proceeds" means, from time to time, an
amount equal to the positive amount, if any, obtained by taking an amount equal
to the current amount of Cash Proceeds and deducting therefrom an amount equal
to the current amount of Costs. Prior to

                                   ADDENDUM #3
                                      - -

<PAGE>   80

any distribution of Net Proceeds to any of Landlord's Control Affiliates,
Landlord first will pay to Tenant Net Proceeds in amount equal to: the unrepaid
Reconstruction Costs (if any) until the Reconstruction Costs have been repaid in
full; and the unrepaid Cure Payments (if any) until the unrepaid Cure Payments
have been repaid in full; and the reasonable costs and expenses incurred by
Tenant in good faith to third parties in validly exercising its Right of Self
Help as set forth in Section 14.4, but excluding therefrom any of such costs and
expenses that otherwise would qualify as Operating Costs under Article 7.
Thereafter, Landlord will pay to Tenant one-half (1/2) of all Net Proceeds
available for distribution at the same times as Net Proceeds are distributed by
Landlord to its Control Affiliates. These payments to Tenant will be deemed to
be a reduction in Tenant's rent already paid from time to time under this Lease
(although they may not be credited, offset or deducted against Tenant's current
or future rent payments owed). Payments of Net Proceeds to Tenant during any
year shall be subject to an annual reconciliation for that year (which shall
occur after the end of that year), and any amounts overpaid to Tenant or owed by
Landlord shall be adjusted in cash between the parties within thirty (30) days
after such annual reconciliation is delivered. Upon Tenant's written request in
each instance, Landlord will furnish to Tenant reasonable backup information for
its annual reconciliations, including copies of Landlord's most recent financial
statements. Within ninety (90) days after delivery of each of Landlord's annual
reconciliations, and upon at least fourteen (14) days' prior written notice to
Landlord, not more than once in each calendar year Tenant may audit Landlord's
books and records applicable to the period after the last annual reconciliation
in order to verify the accuracy of Landlord's calculation of Net Proceeds. Such
audit will be conducted only during regular business hours where Landlord
maintains its books and records (which Landlord agrees will be in Massachusetts
or California) and Tenant will deliver a copy of the audit to Landlord within
fifteen (15) days after receipt by Tenant. All audits will be conducted at
Tenant's cost and expense and shall be conducted only by Tenant or its
designated professional representatives.

     4. TERMINATION OF RIGHTS. Notwithstanding anything to the contrary, as of
the date of the first occurrence of any or all of the following, at Landlord's
election all of Tenant's rights and Landlord's obligations under or in
connection with this Addendum will terminate and lapse completely, except that
the entity that is the Landlord immediately prior to the occurrence of any or
all of the following shall remain obligated to pay to Tenant (or at such
entity's election credit against amounts owed by Tenant to such entity) Tenant's
share of undistributed Net Proceeds (if any) existing as of the date of such
occurrence:

          (a) The termination or expiration of this Lease in accordance with its
terms.

          (b) A default by Tenant under this Lease.

          (c) The closing of any Purchase Option or, unless the No-sale Election
first has been validly elected and still is in full force and effect, another
bona fide sale or other conveyance by Landlord of all or any portion of the
Premises, or any interest therein (which shall not be deemed to include an
interest in Landlord), which sale or conveyance is not prohibited under this
Lease, but Tenant's rights and Landlord's obligations with respect to Net
Proceeds shall continue with respect to the portions of the Premises or
interests therein, if any, still 

                                   ADDENDUM #3
                                      - -


<PAGE>   81

retained by Landlord and with respect to any Net Proceeds received by Landlord
in connection with such sale or other conveyance (except with respect to a sale
pursuant to a Purchase Option).

     5. UNAFFECTED PARTIES. Notwithstanding anything to the contrary, Tenant's
rights and Landlord's obligations under this Addendum will not be binding on and
will not affect or otherwise apply in any way to:

          (a) Any party that, in a bona fide transaction, purchases or otherwise
acquires all or any portion of the Premises or any interest therein, or its
successors, assigns and purchasers, or their respective Affiliates (unless the
No- sale Election first has been validly elected and still is in full force and
effect or unless any such sale or conveyance is prohibited under this Lease); or

          (b) Landlord's Mortgagees, whether or not they take title to or
acquire all or any portion of the Premises or any interest therein, and their
successors, assigns and purchasers, or their respective Affiliates.

     6. PERSONAL RIGHTS. Notwithstanding anything to the contrary, the rights
granted to Tenant under or in connection with this Addendum are granted to and
may be exercised only by the Tenant originally named in this Lease, and they may
not be exercised by anyone else (other than by an assignee to whom such rights
have been entirely assigned pursuant to a valid assignment of this Lease, if at
the time of such assignment the assignor and the assignee deliver to Landlord a
jointly executed written notice stating unconditionally that the assignee has
the right to exercise such rights), and Tenant shall not, and shall not have the
right or power to, otherwise assign or Transfer any of these rights. If at the
time of a valid assignment the assignor and the assignee deliver to Landlord a
jointly executed written notice directing Landlord to pay a portion of the Net
Proceeds otherwise payable to the assignee instead to the assignor, then
Landlord will continue to pay that portion of the Net Proceeds to the assignor
until and unless Landlord receives from the assignor and the assignee a jointly
executed written notice changing such direction to Landlord and then Landlord
shall pay in accordance with the new direction.

                                   ADDENDUM #3
                                      - -

<PAGE>   82

                                   ADDENDUM #4

                                PURCHASE OPTIONS


     1. GRANT AND EXERCISE. Provided that this Lease is in full force and effect
and Tenant first has validly exercised one of its purchase options in accordance
with the terms of the Lease, dated as of October 10, 1995, between Tenant and
100 Minuteman Limited Partnership, as amended (the "100 Minuteman Lease") and
subject to the terms hereof, Landlord grants to Tenant three (3) options (the
"Purchase Options") to purchase the Premises from Landlord, which Purchase
Options must be exercised during the following periods:

          (a) The first (1st) Purchase Option can be exercised only during the
first month of the fifth (5th) Lease Year.

          (b) The second (2nd) Purchase Option can be exercised only during the
first month of the tenth (10th) Lease Year.

          (c) The third (3rd) Purchase Option can be exercised only during the
last month of the sixteenth (16th) Lease Year.

The Purchase Options can be exercised only by Tenant delivering unconditional
written notice of exercise to Landlord as and when required together with a
cashier's check or the wire transfer of funds to Landlord in an amount equal to
five percent (5%) of the total purchase price under the applicable Purchase
Option. These funds shall be placed by Landlord into a separate interest-bearing
account or other mutually agreeable investment instrument and these funds and
all interest earned thereon collectively are called the "Deposit." When and if
the closing under the applicable Purchase Option occurs, the Deposit shall be
credited against the cash portion of the purchase price payable by Tenant
thereunder. If the Deposit is in excess of the cash portion of the purchase
price payable by Tenant, the excess shall be returned to Tenant as of the
closing. If for ANY REASON Landlord does not actually receive this unconditional
written notice of exercise and the Deposit as and when required, at Landlord's
option the applicable Purchase Option will lapse and become null and void.

          At Landlord's election, the Purchase Options and all of Tenant's
rights and Landlord's obligations under this Addendum and Addendum #5 shall
lapse and become null and void if: (i) Tenant defaults under the rest of this
Lease at any time prior to the exercise of a Purchase Option or any closing
thereunder; or (ii) Tenant defaults under this Addendum, or defaults in
connection with any closing under, or fails to close as required after the
exercise of, a Purchase Option (a "Purchase Option Default"). If Tenant commits
a Purchase Option Default Tenant also shall waive as against Landlord and its
Affiliates all Liabilities and defaults (if any) of or by any of them under this
Lease that directly arise from or in connection with the Purchase Option
Default, and Landlord shall retain the Deposit as its sole and liquidated
damages for the Purchase Option Default, and if Tenant commits more than one
Purchase Option Default, at Landlord's election the Purchase Options and all of
Tenant's rights and Landlord's obligations 

                                  ADDENDUM #4
                                      - -

<PAGE>   83

under this Addendum and Addendum #5 shall lapse and become null and void. (A
Purchase Option Default is not the same as a default described in Section 4(c)
of this Addendum.)

     2. Purchase Price.
        --------------
       
          (a) The cash portion of the purchase price for the Premises shall be
payable by cashier's check or wire transfer of immediately available funds to or
at the direction of Landlord and will be payable in full on or before the
scheduled closing date. In addition to the cash portion of the purchase price,
as of the closing Tenant shall either repay in full all mortgage loan(s) secured
by the Premises, and any other loan secured by the Letter of Credit (if separate
from such mortgage loan(s)) , other than those that are Unpermitted Financing
(the "Existing Loans") (including, without limitation, any prepayment or
"breakage" fees or similar charges) or assume the Existing Loans, and in any
case Tenant will cause the lender(s) to release Landlord and its Affiliates as
of the closing from all Liabilities in connection with the Existing Loans and
Tenant shall indemnify and hold Landlord and its Affiliates harmless from all
further Liabilities in connection with the Existing Loans. In addition to the
purchase price, Tenant shall pay all closing costs of any type (other than

Landlord's attorneys' fees and costs), including, without limitation,
commissions (if any) and the costs of deed stamps and documentary and transfer
taxes and fees, surveys, title insurance, escrows, recording and other similar
fees and costs. Base rent will be prorated between the parties as of the closing
date, but there will be no other prorations or adjustments.

          (b) The cash portion of the purchase price for the Premises shall be
never be less than zero, but otherwise shall be equal to the following amounts:

             (i) For the first (1st) Purchase Option, an amount equal to:(x) ten
(10) times the "Current Base Rent Amount" (defined below); less (y) the
"Existing Mortgage Balance" (as defined below). The "Current Base Rent Amount"
means the scheduled annual base rent payable under this Lease as of the date of
closing, without any deductions, offsets or abatements of any type, and
including, without limitation, scheduled annual base rent payable in connection
with any other space leased or agreed to be leased from Landlord in a new
building or new buildings, or an enlargement of the Building, on the Premises.
If an agreement has been entered into to lease such other space or a right to
lease such other space has been exercised prior to closing but the full base
rent applicable thereto has not commenced or cannot be accurately determined as
of the closing, then the scheduled annual base rent applicable to that Purchase
Option shall be reasonably estimated by Landlord. (As a hypothetical example, if
the scheduled annual base rent at the closing is $2,352,900.00, the Current Base
Rent Amount for the first (1st) Purchase Option would be $23,529,000.00.) The
"Existing Mortgage Balance" means the outstanding principal balance (not
including any prepayment or "breakage" fees or similar charges) as of the
closing date under an exercised Purchase Option of any Existing Loans.

             (ii) For the second (2nd) Purchase Option, an amount equal to: (x)
eight and one-half (8 1/2) times the Current Base Rent Amount; less (y) the 
Existing Mortgage Balance.

                                  ADDENDUM #4
                                      - -

<PAGE>   84

             (iii) For the third (3rd) Purchase Option, an amount equal to: (x)
five (5) times the Current Base Rent Amount; less (y) one-half (1/2) of any
Excess Refinancing Proceeds distributed to Landlord or its Control Affiliates;
and less (z) the outstanding principal balance of any Unpermitted Financing
secured by the Premises (and Tenant shall then either repay in full or assume
such Unpermitted Financing, and if and to the extent that the deduction of such
outstanding principal balance otherwise would reduce the Purchase Price below
zero, Landlord shall pay to Tenant at the Closing cash an amount equal to the
amount by which the Purchase Price otherwise would have been reduced below
zero).

As a hypothetical example, if the second (2nd) Purchase Option is validly
exercised, the Current Base Rent Amount is $2,352,900.00, and as of the closing
the Existing Mortgage Balance is $13,000,000.00, then the cash portion of the
purchase price payable to Landlord would be only $6,999,650 and Tenant would
repay or assume the existing $13,000,000.00 mortgage loan secured by the
Premises, for a total purchase price of $19,999,650.

     3. CLOSING. The closing under an exercised Purchase Option will occur at a
location in Massachusetts and on a date specified by Landlord pursuant to
written notice to Tenant, which date will be: during the last four (4) months of
the fifth (5th) Lease Year (for the first (1st Purchase Option); during the last
four (4) months of the tenth (10th) Lease Year (for the second (2nd) Purchase
Option); and during the ninth (9th), tenth (10th) or eleventh (11th) months of
the last Lease Year of the initial Lease term (for the third (3rd) Purchase
Option). At the closing, Landlord will execute and deliver to Tenant a
Massachusetts Quitclaim Deed (which will be subject to all matters of record and
all title and survey exceptions), an affidavit of Landlord stating Landlord's
U.S. taxpayer identification number and that Landlord is not a "foreign person"
within the meaning of Section 1445(f)(3) of the Internal Revenue Code of 1986,
as amended or Landlord shall provide the necessary forms if Landlord IS a
"foreign person") , and a blanket assignment to Tenant of all third party
guaranties, warranties, permits, certificates, consents and approvals pertaining
to the Premises that are assignable by Landlord, to the extent assignable at no
cost or Liabilities to Landlord (unless Tenant advances such costs and
discharges such Liabilities, in which case they shall be assigned to the extent
assignable by Landlord).

     4.   Additional Terms.
          ----------------

          (a) Tenant specifically acknowledges and agrees that Landlord will
sell and Tenant will purchase the Premises on an "as is with all faults" basis,
subject to all exceptions to and defects of title, whether or not of record (but
subject also to Tenant's rights and Landlord's obligations as set forth below),
and that Tenant will not rely on nor will Landlord or any of its Affiliates be
deemed to have made, any representations or warranties of any kind, express or
implied including, without limitation, those in connection with the physical
condition of the Premises (including, without limitation, any matters involving
Hazardous Substances or compliance with any Laws), or the nature of title to the
Premises, or the advisability of Tenant's purchase of the Premises). However,
until and unless Tenant otherwise agrees in writing or defaults Landlord will
not voluntarily execute any documents affecting title that materially adversely
affect Tenant's operations or that render title to the Premises unmarketable

                                  ADDENDUM #4
                                      - -

<PAGE>   85

(but easements, dedications or other documents for access, drainage, utilities
or services (including cabling), curb cuts, or as otherwise may be needed to
comply with applicable Laws or to enable Landlord to meet its obligations under
this Lease or in connection with the construction of any new building(s) or the
enlargement of the Building per this Lease, will not be deemed to be violations
of this restriction). If this restriction is violated after the exercise of a
Purchase Option, Tenant shall have the right to terminate that Purchase Option
without liability and receive the Deposit back. Notwithstanding the foregoing,
even if Tenant has validly exercised a Purchase Option, Tenant shall have the
right to terminate that Purchase Option without liability (except for Landlord's
out-of-pocket costs) and shall not be required to close the purchase if, after
the exercise of the Purchase Option but prior to closing, there is a casualty
that causes damage of the type and to the extent described in Section 16.2(b)(x)
such that Tenant otherwise would have the right to terminate this Lease, and in
the reasonable judgement of a qualified independent contractor hired by Landlord
it will take more than two (2) years from the date of the damage to restore
access or restore or replace the destroyed parking spaces or substantially
complete the repairs that Landlord would have been required to make, and Tenant
notifies Landlord of its intent to terminate within thirty (30) days after
receiving the notice from Landlord's contractor, which shall be provided as soon
as reasonably practicable after the damage occurs. If these circumstances occur,
the closing date shall be extended as necessary to accommodate this thirty
(30)-day period. If Tenant does not so terminate, or if Tenant is not permitted
to so terminate as a result of a casualty, as of the closing Landlord will
assign to Tenant all casualty insurance proceeds otherwise payable to Landlord
on account of the damage and all rights and claims in connection therewith
(other than those which Landlord was entitled to receive for the period and/or
for the work and services performed prior to the closing). Notwithstanding
anything to the contrary, if Landlord is in the process of repairing or
rebuilding casualty damage and Tenant subsequently validly exercises a Purchase
Option: Landlord will continue the process of repairing or rebuilding as
otherwise required in this Lease until the closing date under the Purchase
Option; Tenant will be deemed to have waived its right to terminate this Lease
under Article 16, and its right to terminate the Purchase Option in connection
with that casualty or any repairs or rebuilding in connection therewith;
Landlord will assign to Tenant as of the closing all casualty insurance proceeds
otherwise payable to Landlord on account of the damage and all rights and claims
in connection therewith (other than those which Landlord was entitled to receive
for the period and/or for the work and services performed prior to the closing),
and Landlord shall assign to Tenant and Tenant shall assume all rights and
Liabilities of Landlord under the contracts entered into in connection with the
repair or rebuilding to the extent assignable and Tenant shall indemnify
Landlord and its Affiliates for and hold them harmless from all Liabilities in
connection therewith; and Landlord shall be obligated to continue to repair or
rebuild after the closing date only if and to the extent actually agreed to by
Landlord and Tenant in good faith and in writing at the time.

          (b) As of the closing, Tenant and its Affiliates will be deemed to
have released and discharged Landlord and its Affiliates from, and to have
waived, all Liabilities of any type, known or unknown, including, without
limitation, Liabilities under or in connection with this Lease and/or the
Premises (except as set forth in the last sentence of Subsection (c) below). As
a condition to closing, Landlord may require that Landlord's Mortgagees release
Landlord and its Affiliates from Liabilities under or in connection with any
Superior Leases or Mortgages. From

                                  ADDENDUM #4
                                      - -


<PAGE>   86

and after the closing, Tenant shall indemnify, defend and hold Landlord free and
harmless from all Liabilities under or in connection with this Lease and/or the
Premises and/or the purchase thereof (except as set forth in the last sentence
of Subsection (c) below).

          (c) Time is of the essence in this Addendum. If Tenant defaults
hereunder after the closing under a Purchase Option or Tenant or Landlord
defaults under any of the documents delivered by it in connection therewith, in
addition to any rights and remedies available to each of the respective parties,
each party shall have all rights and remedies at law and in equity, all of which
are cumulative and not exclusive, including, without limitation, the right to
require specific performance. The exercise of a Purchase Option or any closing
as a result thereof shall not relieve Tenant or Landlord from any Liabilities
for any defaults under this Lease, nor will they extinguish Liabilities for any
indemnities or other obligations that survive pursuant to the terms of the rest
of this Lease or this Addendum.

          (d) Notwithstanding anything to the contrary, as of the date of the
first occurrence of any of the following, at Landlord's election all of Tenant's
rights and Landlord's obligations under or in connection with this Addendum will
lapse and become null and void upon:

              (i) The expiration of the Lease term (as validly extended) or
termination of this Lease in accordance with its terms prior to the exercise of
a Purchase Option any closing thereunder; or

              (ii) The bona fide purchase or other acquisition of all or
substantially all of the Premises by any person or entity (including, without
limitation, Tenant or its Affiliates) other than by any of Landlord's Control
Affiliates prior to the exercise of a Purchase Option and other than any sale or
conveyance which is prohibited under this Lease; or

              (iii)The failure by Tenant to have closed on and acquired title 
to the leased to Tenant under the 100 Minuteman Lease in accordance with the
terms thereof before the date that Tenant is required to close (or, if earlier,
actually closes) its purchase of the Premises following its exercise of a
Purchase Option hereunder, but only in the event that such failure is due to the
fault or delay of Tenant .

          (e) Notwithstanding anything to the contrary, Tenant's rights and
Landlord's obligations under or in connection with this Addendum will not be
binding on and will not affect or otherwise apply in any way to Landlord's
Mortgagees or their successors, assigns and purchasers, or their respective
Affiliates, whether or not they take title to or acquire all or substantially
all of the Premises.

     5. PERSONAL RIGHTS. Notwithstanding anything to contrary, the Purchase
Options are granted only to and may be exercised only by the Tenant originally
named in this Lease, and they may not be exercised by anyone else (other than by
an assignee to whom the right to exercise a Purchase Option has been assigned
pursuant to a valid assignment of this Lease, if at the time of such assignment
the assignor and the assignee deliver to Landlord a jointly executed written

                                  ADDENDUM #4
                                      - -

<PAGE>   87

notice stating unconditionally that the assignee has the right to exercise such
Purchase Option) and Tenant shall not, and shall not have the right or power to,
otherwise assign or otherwise Transfer any of the Purchase Options or any rights
in connection therewith. Tenant may assign this Lease without granting to the
assignee the right to exercise any or all of the Purchase Options, and in such
event Tenant will retain the rights to exercise any Purchase Options whose
exercise rights have not been validly assigned as set forth in this Addendum, IF
AND ONLY IF Tenant has not become a Released Assignor in connection with its
assignment of this Lease.

                                   ADDENDUM #4
                                       - -

<PAGE>   88

                                   ADDENDUM #5
                        RIGHT OF FIRST OFFER TO PURCHASE

     1.   Grant of Rights.
          ---------------
          
          (a) Subject to the terms of this Addendum, before Landlord sells or
conveys the Premises during the first eighteen (18) Lease Years (other than
pursuant to a sale or conveyance to any of Landlord's Control Affiliates)
Landlord shall notify Tenant in writing (the "Offer Notice") of the purchase
price and the terms of payment thereof (e.g., all cash, or cash and purchase
money financing or assumption of debt) that Landlord intends to accept for the
Premises (the "Offer Price").
          (b) Within ninety (90) days after delivery of the Offer Notice, Tenant
shall notify Landlord in writing that it unconditionally elects one of the three
(3) following alternatives:

               (i) To purchase the Premises for the applicable Offer Price and
otherwise on the terms of this Addendum. (Tenant's election of the alternative
described in this Subsection (I) is referred to as the "Purchase Election.")

               (ii) To cause Landlord not to sell the Property during the first
eighteen (18) Lease Years. (Tenant's valid election of the alternative described
in this Subsection (ii) is referred to as the "No-sale Election.")

               (iii) To permit Landlord to sell or convey the Premises in
accordance with this Addendum and to continue to lease the Premises on the terms
of this Lease. (Tenant's election of the alternative described in this
Subsection (iii) is called the "Existing Lease Election.")

          (c) TIME IS ABSOLUTELY OF THE ESSENCE. If for ANY REASON Landlord does
not actually receive Tenant's unconditional written notice of election as and
when required, Tenant shall be deemed to have elected the No-sale Election. At
Landlord's election, all of Tenant's rights and Landlord's obligations under or
in connection with this Addendum and Addendum #4 shall lapse and become null and
void if Tenant defaults hereunder or under the rest of this Lease at any time
prior to any closing hereunder, or if Tenant defaults in connection with any
closing hereunder or fails to close as required after its election of the
Purchase Election (an "Offer Default"). Any amounts payable under this Addendum
in connection with the Purchase Election are deemed to be amounts payable under
the Lease, and any default hereunder will be deemed to be a default under the
Lease and in such case Landlord shall be entitled to all rights and remedies
hereunder and under the rest of the Lease, including, without limitation, the
right to require specific performance from Tenant. If Tenant commits an Offer
Default, Tenant also shall indemnify and hold Landlord harmless from and against
all Liabilities incurred by Landlord that arise from or in connection with the
Offer Default.

                                  ADDENDUM #5
                                      - -


<PAGE>   89

     2. PURCHASE ELECTION. If Tenant validly exercises the Purchase Election,
then Landlord shall sell and Tenant shall purchase the Premises and the
following terms and conditions of Addendum #4 are incorporated herein and shall
apply with respect to this Addendum and such sale and purchase as if it were the
sale and purchase under an exercised Purchase Option: Section 2(a) (except that
the applicable purchase price and the terms of the payment thereof shall be as
set forth in the Offer Price, or if there is an outstanding mortgage or
mortgages on the Premises at such time Tenant shall assume the mortgage(s) and
the cash portion of the Offer Price shall be deemed reduced by the outstanding
principal balance of the mortgage(s) assumed); Section 3 (except that the
closing date will be a date specified by Landlord that will be at least three
(3) months but no more than six (6) months after Tenant's notice of election);
and Sections 4(a), (b), (c) and (e).

     3. NO-SALE ELECTION. If Tenant validly elects the No-sale Election, then:

          (a) Until and unless Tenant otherwise agrees in writing, or Tenant
defaults under this Lease or Tenant's rights under this Addendum #5 terminate,
or the 18th Lease Year expires (whichever is earliest), Landlord will not sell
or convey the Premises except to one of Landlord's Control Affiliates or to
Tenant or one of its Related Entities or pursuant to the exercise of a Purchase
Option; and

          (b) Notwithstanding anything to the contrary, all "Excess Refinancing
Proceeds" (defined below) shall belong solely to Landlord and no portion thereof
shall be deemed to be part of Cash Proceeds pursuant to Addendum #3 or otherwise
payable or distributable to Tenant. However, if Tenant validly exercises the
third (3rd) Purchase Option in accordance with Addendum #4, then Tenant shall
receive the credit against the purchase price payable by Tenant as described in
Section 2(b) (iii) of Addendum #4. "Excess Refinancing Proceeds" means all of
the net proceeds actually distributed to Landlord that are directly traceable to
and result from excess proceeds from mortgage refinancing first encumbering the
Premises after a No-sale Election if and to the extent that the disbursed
principal balance of each such refinancing exceeds: the outstanding principal
balance and all accrued and unpaid interest and other charges (including,
without limitation, prepayment and "breakage" fees and similar charges) under
loan(s) that were repaid by such refinancing; plus any other Liabilities and
reserves therefor that were paid with the proceeds of such refinancing. There
shall not be deemed to be any Excess Refinancing Proceeds arising from the
funding of the financing described in Section 19.4(a).

     4.   Existing Lease Election.
          -----------------------

          (a) If Tenant validly elects (or is deemed to have elected) the
Existing Lease Election, then for the next twelve (12) months after Tenant's
election, Landlord may not sell or convey the Premises (other than pursuant to a
sale or conveyance to any of Landlord's Control Affiliates) for a purchase price
which is less than ninety-seven percent (97%) of the applicable 

                                  ADDENDUM #5
                                      - -

<PAGE>   90

Offer Price without first delivering to Tenant a new Offer Notice with an Offer
Price equal to such new, lower purchase price. If Landlord delivers such a new
Offer Notice, then Tenant shall have the right to elect either the Purchase
Election or the No-sale Election or the Existing Lease Election in accordance
with the procedures established in Section 1 above, except that Tenant will have
forty-five (45) days, and not ninety (90) days, within which to respond to
Landlord's new Offer Notice. If within twelve (12) months after Tenant validly
elects the Existing Lease Election in accordance with this Section 3 Landlord
has not executed a binding agreement to sell or convey the Premises for a
purchase price which is equal to or greater than ninety-seven percent (97%) of
the new, lower Offer Price, or if Landlord has entered into such a binding
agreement within the twelve (12)-month period but fails to close thereunder,
then the terms and conditions in Section 1 above again will apply.

     (b) If Tenant validly elects the Existing Lease Election, then
Tenant will have the right, upon written request to Landlord, to participate
reasonably and in good faith with Landlord in the negotiations conducted by
Landlord to sell or convey the Premises, which negotiations will be subject to
Landlord's control and direction. Tenant acknowledges and agrees that the manner
and substance of these negotiations are critical to Landlord, and so Tenant will
support Landlord's negotiating positions (provided that, unless Tenant otherwise
agrees, such negotiating positions do not attempt to change Tenant's rights and
obligations under this Lease) and will not attempt to delay, obstruct or hinder
these negotiations. Landlord will have the right at any time and in its sole
discretion to suspend, terminate or continue such negotiations and, subject to
Subsection (a) above, Articles 6 and 7 of this Addendum and the parenthetical in
the preceding sentence, to accept or reject terms offered by prospective buyers
and to execute documents and agreements, binding or otherwise, in connection
with a sale or conveyance of the Premises. Tenant shall have not have the right
or power nor shall it attempt to bind Landlord in connection with a sale or
conveyance of the Premises or to deal directly or negotiate alone with any
prospective buyer or its agents without Landlord's prior written consent.

     5. Termination of Rights. Notwithstanding anything to contrary, at
Landlord's election all of Tenant's rights and Landlord's obligations under or
in connection with this Addendum will lapse and become null and void upon:

          (a) The termination or expiration of the Lease term in accordance with
its terms, prior to any closing hereunder; or

          (b) Unless the No-sale Election first has been validly elected and is
still in full force and effect, the bona fide purchase or other acquisition of
all or substantially all of the Premises other than by any of Landlord's Control
Affiliates prior to the valid exercise of the Purchase Election hereunder and
other than any sale or conveyance which is prohibited under this Lease; or

          (c) As set forth in Section 9 below; or

          (d) At the end of the eighteenth (18th) Lease Year.

                                  ADDENDUM #5
                                      - -
<PAGE>   91

     6. NO SALE TO DIRECT COMPETITORS. Unless and until Tenant's rights under
this Addendum have lapsed or terminated, Landlord shall not sell or convey the
Premises to: AT&T, Intel or Compression Laboratories, Inc.

     7. RESTRICTIONS ON LANDLORD'S SALE RIGHTS. Until and unless Tenant defaults
hereunder or the rest of the Lease, or the Lease expires or terminates, Landlord
agrees that it will not sell or convey the Premises to anyone other than Tenant
or any of its Control Affiliates or any of Landlord's Control Affiliates: for
the first five (5) Lease Years; or other than for cash or cash equivalents
(which will be deemed to include, without limitation, purchase money financing
and/or the purchaser assuming or taking subject to debt); or from the date that
Tenant validly elects the No-Sale Election until the end of the 18th Lease Year.

     8. UNAFFECTED PARTIES. Notwithstanding anything to the contrary, Tenant's
rights and Landlord's obligations under or in connection with this Addendum will
not be binding on and will not affect or otherwise apply in any way to
Landlord's Mortgagees or their successors, assigns and purchasers or their
respective Affiliates, whether or not they take title to or acquire all or
substantially all of the Premises.

     9. PERSONAL RIGHTS. Notwithstanding anything to contrary, the rights of
Tenant in this Addendum are granted only to and may be exercised only by the
Tenant originally named in this Lease, and they may not be exercised by anyone
else (other than by an assignee to whom such rights have been entirely assigned
pursuant to a valid assignment of this Lease pursuant to which Tenant has become
a Released Assignor, if at the time of such assignment the assignor and the
assignee deliver to Landlord a jointly executed written notice stating
unconditionally that the assignee has the right to exercise such rights) and
Tenant shall not, and shall not have the right or power to, otherwise assign or
otherwise Transfer any of its rights under or in connection this Addendum.
Tenant may assign this Lease without granting to the assignee the rights of
Tenant under this Addendum, and in such event: Tenant will retain those rights
IF AND ONLY IF Tenant has not become a Released Assignor in connection with its
valid assignment of this Lease; and Tenant no longer will have the right
thereafter to exercise the No-sale Election, and if Tenant fails to make its
written election as and when required it will be deemed to have elected the
Existing Lease Election.

                                   ADDENDUM #5
                                       - -

<PAGE>   92

                                   ADDENDUM #7

                                 BUDGET SAVINGS

     1. TOTAL PROJECT COSTS. "Total Project Costs" means all costs and expenses
of any type incurred or payable by Landlord or its Affiliates that arise from or
in connection with the acquisition of the Premises, the initial financing
(including without limitation any mortgage loans, loans secured by the Letter of
Credit and any permanent financing) of or for the Premises or Landlord's Work,
including, without limitation, costs and expenses for: the purchase price for
the Premises and any rights appurtenant thereto (including, without limitation,
all costs for due diligence, investigations, remedial work, closing costs,
escrow and title fees, legal fees, professional fees and commissions); all
labor, services and materials, designers, architects, engineers, draftsman,
supervision, permits and approvals, development fees, and other fees, profit and
savings payable to construction managers, contractors and subcontractors, and
all other "hard" and "soft" costs in connection with Landlord's Work; all loan
fees, commissions, appraisals, escrow and title fees, other closing costs,
interest rate hedges, "caps" or "floors," interest and principal (if any) during
the construction period and other costs in connection with the initial financing
of the Premises; and other Liabilities arising out of or in connection with any
of the foregoing or as set forth in Schedule 7AAA" to this Addendum. (The
parties acknowledge and agree that Schedule "7AAA" is for illustrative purposes
only, and is not binding in any way on the parties nor is it a representation
and warranty by Landlord of any type, express or implied.)

     2. APPLICATION OF SAVINGS. If and to the extent that the total amount that
Landlord is able to draw down and retain under the initial financing of the
Premises EXCEEDS the Total Project Costs (after the Total Project Costs are
finally determined), then those excess proceeds shall be used by Landlord for
any or all of the following uses: as an interest reserve; to purchase interest
rate protection for floating rate financing (including, without limitation, for
hedges, swaps, caps or floors); or to reduce the principal balance of any
financing, or capital contributions or advances made by or on behalf of Landlord
or its Control Affiliates.

                                   ADDENDUM #7