<PAGE>

                                                                    EXHIBIT 10.8

                        50 MINUTEMAN LIMITED PARTNERSHIP
                              200 BRICKSTONC SQUARE
                          ANDOVER, MASSACHUSETTS 01810
                   TELEPHONE (978) 749-3000 FAX (978) 749-3009

                                      June 4, 1998


PICTURETEL CORPORATION
100 Minuteman Road
Andover, Massachusetts 01810

-and-

CABLETRON SYSTEMS, INC.
CABLETRON SYSTEMS SALES & SERVICE, INC.
35 Industrial Way
Rochester, New Hampshire 03867

     Re:   50 MINUTEMAN ROAD, ANDOVER, MASSACHUSETTS
           SUBLEASE (THE "SUBLEASE"), DATED AS OF JUNE 4, 1998, BETWEEN
           PICTURETEL CORPORATION ("TENANT") AND CABLETRON SYSTEMS
           SALES & SERVICE, INC. ("SUBTENANT")

Ladies and Gentlemen:

     In this letter agreement, the Amended and Restated Lease, dated June 4,
1998, between 50 Minuteman Limited Partnership ("Landlord") and Tenant, and all
existing and future extensions and amendments thereto, are referred to as the
"Main Lease." Unless otherwise defined, terms used in this letter agreement have
the same meanings as those used in the Main Lease. Pursuant to the Main Lease,
Tenant is leasing the Premises (located at 50 Minuteman Road, Andover,
Massachusetts) from Landlord. Pursuant to the Sublease, Tenant intends to
sublease the entire Premises to Subtenant, and the parties have asked for our
consent. Cabletron Systems, Inc. ("Guarantor") is guaranteeing the obligations
of Subtenant pursuant to a Continuing Guaranty of Sublease (the "Guaranty").

     Landlord hereby consents to the Sublease, subject to the following terms
and conditions:

     1. Notwithstanding anything to the contrary, by consenting to the Sublease
Landlord is not: consenting to any modifications of the Main Lease or enlarging
any of its obligations or liabilities thereunder; assuming or incurring any
duties, obligations or liabilities to Tenant or Subtenant; releasing Tenant (or
any other party liable) in any way under the Main Lease or modifying Tenant's
obligations or liabilities thereunder; approving any provisions of the Sublease;
waiving or electing its rights and remedies under the Main Lease, all of which
Landlord reserves; or consenting in advance to any other assignments, subleases
or other Transfers, or anything else.
<PAGE>

     2. Landlord is not and will not become liable or obligated in any way under
or in connection with the Sublease or for any defaults or non-compliance by any
party thereunder, and all such claims are hereby waived and released by Tenant,
Subtenant and Guarantor. Without limiting the generality of the foregoing,
Tenant, Subtenant and Guarantor acknowledge and agree that although Landlord was
involved in the preparation of the Sublease, the Guaranty and other related
documents (collectively, the "Sublease and Related Documents"), such involvement
was only as a matter of convenience for the parties and Landlord shall not be
liable or obligated in any way if any of the provisions of the Sublease and
Related Documents are mistaken or deficient in any manner (nor shall any
involvement of Landlord or its representatives in connection with the Sublease
and Related Documents create any privity between Landlord and Subtenant and/or
Guarantor), and all associated claims are hereby waived and released by Tenant
and Subtenant.

     Landlord and Subtenant have entered into that certain Non-Disturbance and
Attornment Agreement (the "Non-Disturbance Agreement"), dated as of the date
hereof, pursuant to which, under certain circumstances, Landlord and Subtenant
may enter into a direct lease relationship with one another with respect to the
Premises.

     Except as may be specifically set forth in this letter agreement with
respect to agreements, waivers, obligations, and liabilities made, undertaken or
assumed by Subtenant and/or Guarantor in favor of Landlord, there is no privity
of contract between Landlord, on the one hand, and Subtenant and/or Guarantor,
on the other hand, other than privity to the extent arising under the Non-
Disturbance Agreement. But, the foregoing shall not be deemed in any way to
restrict or diminish Landlord's ability to enforce the Main Lease or this letter
agreement or any terms of the Sublease and/or the Guaranty to the extent
benefiting Landlord,, or any rights and remedies which Landlord may have for any
default or violation thereunder.

     3. Tenant, Subtenant and Guarantor agree that Landlord is not responsible
for, and they jointly and severally shall indemnify and defend Landlord and its
Affiliates and hold them harmless from any and all costs, claims or liabilities
(including, without limitation, attorneys fees and costs) arising from or in
connection with claims for any brokerage commissions, fees, or other similar
consideration arising out of or in connection with the Sublease and Related
Documents, or the negotiations thereof or any other arrangements between Tenant
and Subtenant and/or Guarantor.

     4. Subtenant and Guarantor agree that (except as may be set forth in the
Non- Disturbance Agreement while it is in full force and effect): (a) the
termination of the Main Lease shall not constitute a merger of estates, but in
any event Landlord reserves the right to terminate any sublease if the Main
Lease terminates; and (b) on a termination of the Main Lease and the written
election of Landlord, Subtenant shall attorn to Landlord and recognize Landlord
as the sublessor under the Sublease (which shall then become a direct lease with
Landlord), or at Landlord's election, enter into a new direct lease with
Landlord on the same terms as the Sublease, and in any such event the
obligations of Sublessee shall continued to be guaranteed in full by Guarantor
pursuant to the Guaranty, which will be deemed to have been amended in favor of
Landlord, or at Landlord's election Guarantor shall enter into a new Guaranty of
Lease

                                      -2-
<PAGE>

in favor Landlord on the same terms as the Guaranty.

     5. Landlord and Tenant shall continue to carry (or cause to be carried)
insurance as required under the Main Lease, and, during the term of the
Sublease, Subtenant agrees that Tenant, Landlord and its general partners,
Landlord's Mortgagees and all property managers will be named as additional
insureds on all liability insurance policies that are carried by Subtenant with
respect to the Premises, and all casualty insurance policies carried by
Subtenant will contain waivers of subrogation in favor of Landlord and Tenant
(and Subtenant hereby waives subrogation). Subtenant agrees to provide Landlord
and Tenant with insurance certificates as evidence of the foregoing throughout
the term of the Sublease. During the Sublease term, Landlord agrees that all
applicable insurance policies carried by Landlord under the Main Lease will
contain waivers of subrogation in accordance with Section 8.3 of the Main Lease
in favor of Tenant and Subtenant. Furthermore, all of the parties hereto agree
that the provisions of Section 8.3 of the Main Lease and the waivers thereunder
shall apply with respect to all of them (and as to Subtenant, as if it were the
Tenant under the Main Lease). Subtenant and Guarantor hereby waive and release
Landlord and its Affiliates from all current and future claims of any type in
connection with or arising from: the Sublease and Related Documents and any
other sublease with Tenant (or any performance or failure to perform
thereunder); the Main Lease (or any performance or failure to perform
thereunder); or the Premises or the rest of the Project (or the condition,
operation or management thereof).

     6. Neither the Sublease nor the Guaranty shall be amended without
Landlord's prior written consent (and any amendments without such consent shall
be null and void) and Landlord shall concurrently receive a copy of any notices
between Tenant, on the one hand, and Subtenant or Guarantor, on the other hand.
Landlord acknowledges that pursuant to Section 15 of the Sublease, Sublessee may
communicate directly with and send notices to Landlord with respect to
Landlord's obligations under the Main Lease. However, Landlord's receipt of
communications or notices from or its correspondence or responsive actions to
Tenant, Subtenant or Guarantor, or its receipt of rent or other payments from
Subtenant or Guarantor, or its acceptance from Subtenant or Guarantor of
performance of Tenant's obligations or cure of Tenant's failure to perform under
of comply with the Main Lease (which Landlord agrees to accept if such failure
to perform or comply is susceptible of being cured by Subtenant or Guarantor and
such performance or cure is rendered in accordance with the Main Lease and the
applicable notice and cure periods, if any, thereunder), shall not in any way
establish privity of contract with Subtenant or Guarantor nor shall it affect
the Main Lease or the rights and obligations of the parties thereto. Landlord
shall attempt to concurrently deliver to Subtenant copies of any notices of
default it delivers to Tenant under the Main Lease, but Landlord shall have no
liability nor shall Subtenant or Tenant acquire any rights or be relieved of any
obligations if Landlord fails to deliver such notices to Subtenant or fails to
deliver them to Subtenant in a timely manner.

     7. Pursuant to the Sublease, Subtenant agrees to pay to Tenant a $1 Million
sum described as an "infrastructure payment" and, in years five through ten of
the Sublease term, base rent which is $5,060 per month in excess of the monthly
base rent now scheduled to be paid by Tenant under the Main Lease. Provided that
Tenant does not default under the Main Lease, Landlord waives its rights under
Section 18.5(a) of the Main Lease to share in this $1 Million "infrastructure
payment," or in this excess base rent (provided that all other rent is paid

                                      -3-
<PAGE>

to Landlord as and when due), and such amounts shall not be deemed to be part of
the base rent or Operating Costs for purposes of calculating the management fees
payable under the Main Lease.

     8. All waivers and releases of Subtenant hereunder also are deemed to have
been made by Guarantor on its own behalf, and all obligations and liabilities of
Subtenant hereunder also are deemed to be guaranteed by Guarantor under the
Guaranty in favor of Landlord and Tenant, as applicable, as if set forth
specifically in the Guaranty.

     9. Subtenant agrees to use the Premises only for the uses permitted under
the Main Lease, and for the demonstration of Subtenant's equipment (and such
latter use by Subtenant is hereby approved by Landlord and Tenant during the
Sublease term). Unless otherwise agreed by both Landlord and Tenant, Subtenant
shall pay rent under the Sublease in accordance with Section 3 of the Sublease
(in its present form).

     10. Subject to Landlord's prior written approval as to form and substance,
Tenant and Subtenant shall have the right to record a Notice of Sublease
satisfying the minimum Massachusetts statutory requirements for such Notices,
provided that, prior thereto, Landlord receives a Notice of Termination of
Sublease in recordable form and in form and substance satisfactory to Landlord,
executed by Tenant and Subtenant, that is sufficient to remove the Notice of
Sublease of record. Landlord shall have the right to record such Notice of
Termination of Sublease if the Sublease expires or terminates by operation of
law or otherwise. In addition, Tenant and Subtenant each hereby appoint Landlord
as its attorney-in-fact to execute, acknowledge and deliver on its behalf,
either in its name or in Landlord's name, the Notice of Termination of Sublease
(if required) and/or any other documents or instruments, and to take any other
action necessary, to remove the Notice of Sublease of record if the Sublease
expires or terminates. This appointment is irrevocable and is coupled with an
interest.

     11. The Sublease and Related Documents and all other subleases are subject
and subordinate in all respects to the Main Lease. Each of the parties
represents and warrants that it has the valid right and authority to sign this
letter agreement and perform the terms hereof, and that this letter agreement is
binding on it and its successors and assigns and inures to the benefit of the
parties hereto and their respective successors and assigns. This letter
agreement may be executed in counterparts. Landlord's consent in this letter
agreement will be effective only if and when Landlord receives at least two
counterparts of this letter agreement executed by Tenant, Subtenant and
Guarantor, and is conditioned on Landlord and Tenant promptly receiving copies
of the insurance certificates from Subtenant as described above. In any action
or proceeding to enforce or interpret this letter agreement, the prevailing
party or parties shall be entitled to reasonable attorneys' fees and costs. This
letter agreement is governed by the internal laws of Massachusetts and cannot be
amended without the written consent of the affected parties. Furthermore,
Tenant, Subtenant and Guarantor each represents and warrants, with respect to
each of the following documents (if it has executed such document), that such
document is binding on it and enforceable against it in accordance with the
terms of such document and has been authorized by all necessary corporate
action, and that its execution, delivery and performance of such document is not
prohibited by nor in conflict with its Articles of Incorporation or Bylaws or
any agreements by which it is bound: the Sublease, the Guaranty, the Notice of
Sublease, the Notice of Termination of Sublease, this letter agreement, the Non-

                                      -4-
<PAGE>

Disturbance Agreement, and all related documents and agreements.

     12. Landlord shall request that its current mortgagee execute and deliver
such mortgagee's standard form Subordination, Non-Disturbance and Attornment
Agreement in favor of Subtenant, but obtaining such an agreement is not a
condition to the Sublease and Related Documents, and the rights and obligations
of any party to the Sublease and Related Documents, the Main Lease or hereto
shall not be affected if for any reason such mortgagee (or Subtenant) refuses to
execute or deliver such an agreement.

                                Sincerely,

                                50 MINUTEMAN LIMITED PARTNERSHIP, a
                                Massachusetts limited partnership

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

                                By: /s/ Illegible
                                     ----------------------------
                                     Name: Illegible
                                     Title: Vice President
                                     Authorized Signature

AGREED:

PICTURETEL CORPORATION, a Delaware      CABLETRON SYSTEMS SALES & SERVICE,
CORPORATION                             INC.,  a Delaware corporation


By: /s/ Illegible                       By: /s/ David Kirkpatrick
Name:                                   Name: David Kirkpatrick
                                              -----------------
Title: Vice President                   Title: Chief Financial Officer
Authorized Signature                    Authorized Signature

                                CABLETRON SYSTEMS, INC. a Delaware
                                   corporation


                                        By:  /s/ Craig Benson
                                           ------------------------
                                           Name: Craig Benson
                                           Title:President
                                           Authorized Signature

                                      -5-
<PAGE>

                                50 MINUTEMAN ROAD
                             ANDOVER, MASSACHUSETTS



                                    SUBLEASE



SUBLESSOR:   PICTURETEL CORPORATION, a Delaware Corporation


SUBLESSEE:   CABLETRON SYSTEMS SALES & SERVICE, INC.,  a Delaware corporation


DATE:  June 4, 1998

                                      -6-
<PAGE>

                                    SUBLEASE

     THIS SUBLEASE, dated and effective as of June 4, 1998, is between
PICTURETEL CORPORATION, a Delaware corporation ("Sublessor"), and CABLETRON
SYSTEMS SALES & SERVICE, INC., a Delaware corporation ("Sublessee").

                                    RECITALS:

     A. Pursuant to that certain Amended and Restated Lease, dated as of June 4,
1998 (the "Main Lease"), between SO Minuteman Limited Partnership ("Landlord"),
as the landlord, and Sublessor, as the tenant, Sublessor is leasing from
Landlord the improved real property commonly known as 50 Minuteman Road in
Andover, Massachusetts, which is improved with, among other things, a building
of approximately 151,800 square feet. This improved real property is described
as the "Premises" in the Main Lease. Capitalized terms not otherwise defined
herein shall have the meanings set forth in the Main Lease.

     B. Sublessor has agreed to sublease to Sublessee, and Sublessee has agreed
to sublease from Sublessor, the entire Premises, for the Sublease Term, on the
terms and conditions stated herein.

                                   AGREEMENTS:

     In consideration of the mutual covenants herein contained and for Ten
Dollars ($10.00) and other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties agree as follows:

     B. Incorporation of Main Lease. Except to the extent inconsistent with or
modified by the terms and conditions of this Sublease, all terms and conditions
of the Main Lease are hereby incorporated into this Sublease and shall govern
Su6lessee's use and occupancy of the Premises and its rights, obligations and
liabilities with respect thereto, in the same manner as if Sublessee were the
Tenant and Sublessor were the Landlord under the Main Lease, and the Sublease
Term were the term under the Main Lease: provided, however, that Sublessor shall
not be obligated to pay for or provide any services to Sublessee or to or for
the benefit of the Premises, or to repair or maintain the Premises or to pay for
or perform the obligations of Landlord under the :Main Lease, and whenever the
obligations of Sublessor to Sublessee hereunder derive from the obligations of
Landlord to Sublessor (including, without limitation, any consent or approval of
Landlord or the provision of any services by Landlord under the Main Lease), the
sole obligation of Sublessor shall be to use reasonably diligent efforts to
obtain appropriate action on the part of Landlord (or omission to take action)
in accordance with the terms of the Main Lease, but Sublessor shall not be
liable to Sublessee if it fails to obtain such consent or approval or if
Landlord takes any action or fails to take such appropriate action. However, if
Landlord defaults under the Main Lease Sublessee shall have the right to avail
itself of the "Right of Self Help" as set forth in Section 14.4 of the Main
Lease (except that, in accordance with Section 1(h) hereof, the parenthetical at
the end of Section 14.4 of the Main Lease shall be deemed deleted and shall not
apply with respect to Sublessee). Subject to the foregoing, Sublessor and
Sublessee each shall comply with and perform the terms and provisions of the
Main Lease as if they were Landlord and Tenant, respectively, thereunder, to the
extent

                                      -7-
<PAGE>

the same are not inconsistent with or modified by the terms and provisions of
this Sublease (including, without limitation, obtaining approval or consent from
Sublessor hereunder where such approval would be required under the Main Lease,
and, in addition, obtaining such approval or consent from Landlord). The
following provisions of the Main Lease shall not be incorporated into this
Sublease (or shall be incorporated in modified form as set forth below):

     1. Sections 1.1(a) and 1.1(b). The Commencement Date of this Sublease is
the date first set forth above, and the Sublease Term begins on the Commencement
Date and ends ten (10) Lease Years thereafter, unless terminated earlier per
this Sublease or the Main Lease.

     2. Section 1.1(g).

     3. Section 1.1(1).

     4. Section 2.

     5. The first sentence of Section 4(a).

     6. The last three sentences of Section 5(a) starting with the words
"Notwithstanding the foregoing, if and for so long as...," and Section 5(b).

     7. Sections 7.1(c) and 7.1(d), and the words "until the end of the ninth
Lease Year," in the first and second lines of Section 7.1(b).

     8. Addenda # 2, 3 and 4, and all references to any of them, including,
without limitation, all references to Extension Options and Net Proceeds.

     9. Section 9.3.

     10. All of Section 18.4 after the words "other obligations under this
Lease," in the fourth line thereof, and all references to a Released Assignor.

     11. Sections 19.4 and 19.5.

     12. Section 22.2(g).

     13. The first sentence of Section 24.9 after the words "agreements or
understandings" in the third line thereof.

     14. Section 24.17 and all references to the Letter of Credit and the Letter
of Credit Loan.

     15. Exhibits "C", "D", "DD", "L" and "M".

     C. Demise of Premises: Sublease Term. Sublessor hereby leases to Sublessee,
and Sublessee hereby leases from Sublessor, the Premises on the terms and
conditions set forth herein, TO HAVE AND TO HOLD for the Sublease Term as
defined in Section 1(a) hereof, except that this Sublease shall terminate when
and if the Main Lease terminates. Sublessee has no right to extend the Sublease
Term.

                                      -8-
<PAGE>

     This Sublease is and shall remain subject and subordinate in all respect to
the Main Lease and to all extensions, modifications, consolidations and
replacements thereof. It is the intention of the parties that Landlord shall
retain all of its rights and remedies under the Main Lease and that Sublessee
shall cooperate in connection with the exercise thereof and take (or omit to
take) all actions as may be required of the Tenant under the Main Lease.

     D.  Rent.
         ----

     1. Subject to Section 3(b) below, all rent payable by Sublessee (including,
without limitation, Taxes, Operating Costs and utilities) shall be payable
beginning as of the Commencement Date of this Sublease, and the annual base rent
payable by Sublessee during the Sublease Term shall be as set forth below and
shall be payable in equal monthly installments in advance beginning on the
Commencement Date of this Sublease and thereafter on the first day of each month
during the Sublease Term, prorated for any portion of a month. Base rent and all
other rent payable by Sublessee shall be paid directly to or as directed by
Landlord under the Main Lease (except that on request of Landlord or Sublessor,
pursuant to Section 5(a) of the Main Lease, base rent shall be payable into the
collection account described in said Section 5(a)), and receipt of such payments
by Landlord or the collection account (as to base rent only) shall be deemed
receipt by Sublessor hereunder, except that if and to the extent that Landlord
or the collection account already has received from Sublessee for each month
during the fifth through tenth Lease Years base rent of One Hundred Ninety Six
Thousand and Seventy Five Dollars ($196,075), and Landlord receives all other
rent due for such month, base rent hereunder for each such month in excess of
$196,075 (i.e., $5,060) shall be paid directly to or as directed by Sublessor
for so long as Sublessor is not in default under the Main Lease. Otherwise, all
rent will be payable in accordance with Section 5(a) of the Main Lease.

               Lease Year        Annual Base Rent
               -----------       ----------------

               1-4               $2,352,900

               5-10               2,413,620

     2. Notwithstanding Section 3(a) above, Sublessee's obligation to pay base
rent, Taxes and Operating Costs shall be entirely abated until October 1, 19'98.

     E. Default by Sublessee. Notwithstanding anything in the Main Lease to the
contrary, for the purposes of determining applicable cure periods hereunder for
a default by Sublessee, Sublessee's cure period hereunder shall be two (2)
business days less than any such cure period granted to Sublessor as Tenant
under the Main Lease. In addition, a valid notice of default from Landlord under
the Main Lease that is delivered to Sublessee (whether or not it is addressed to
Sublessee) shall be deemed to be a valid notice of default delivered by
Sublessor to Sublessee hereunder,

     F. Quiet Enjoyment. Sublessor, with respect to the Sublease Term, covenants
and agrees with Sublessee, that upon Sublessee paying the rent and performing
the covenants of this Sublease, and subject to the terms and conditions of this
Sublease, Sublessee shall peacefully and quietly have, hold and enjoy the
Premises and all rights granted to Sublessee in this Sublease

                                      -9-
<PAGE>

throughout the Sublease Term without hindrance or molestation by anyone claiming
by or through Sublessor.

     G. Condition of the Premises. By its execution hereto, Sublessee agrees
that it accepts the Premises "as is" in all respects. Except as specifically set
forth in Section 13 hereof, Sublessor is not making and Sublessee has not relied
on any representations or warranties of any type, express or implied, in
connection with the condition of the Premises or its fitness for any particular
use. Sublessor shall have no obligation or duty to Sublessee regarding the
preparation of the Premises for occupancy by Sublessee or the payment of any
amounts in connection therewith.

     H. Infrastructure Payment. The Building will be delivered to Sublessee with
the existing above-standard finishes, Lucent switch, UPS system, generator and
cabling, which shall remain Sublessor's property to the extent that such items
are deemed to be "Tenant's Property" under the Main Lease, and Sublessee shall
not remove any of the foregoing items at the expiration of the Sublease Term or
otherwise. As payment for the use of these above-standard items during the
Sublease Term, which were originally paid for by Sublessor, concurrently with
its execution of this Sublease Sublessee shall pay to Sublessor the amount of
One Million Dollars ($1,000,000) by cashier's check or wire transfer in good
U.S. funds, which amount shall be in addition to, and shall not be credited
against or reduce, any base rent or other rent payable by Sublessee hereunder.
If and to the extent that Sublessee makes additions to these items during the
Sublease Term and such additions would be deemed to be "Tenant's Property" under
the Main. Lease if made by Tenant thereunder, the additions shall be and remain
Sublessee's property and may be removed by Sublessee at the end of the Sublease
Term, provided that Sublessee shall repair any damage to these items caused
thereby.

     I. Casualty and Condemnation. If the Premises or any part thereof are
damaged or destroyed by fire or other casualty or are Condemned, then: if and to
the extent that the rent payable by Sublessor as Tenant under the Main Lease is
abated as a result thereof, then rent under this Sublease shall be similarly
abated to the same extent for the same period. If the Condemnation, damage or
destruction is of the type which entitles either Landlord or Tenant to terminate
the Main Lease in whole or in part and either such party elects to terminate,
then this Sublease shall terminate to the same extent as of the same date. In
addition, if the Condemnation, damage or destruction is of the type that would
entitle Sublessor to terminate the Main Lease, then Sublessee shall have the
right to terminate this Sublease to the same extent, subject to and in
accordance with the terms and conditions of Article 17 or Section 16.2 of the
Main Lease, as applicable. Sublessee agrees that Sublessor shall not, in any
case, have any obligation whatsoever to rebuild or repair the Premises or pay
any amounts in connection therewith.

     J. Indemnification and Insurance. Sublessee acknowledges and agrees that:
(a) Sublessee's indemnification and defense obligations hereunder, whether set
forth-specifically in this document or by incorporation of the Main Lease, shall
also include the obligation to indemnify and defend Landlord and its Affiliates
to the same extent; (b) all waivers and releases by Sublessee in this Sublease,
whether set forth specifically in this document or by incorporation of the Main
Lease or in some other document (including, without limitation, the waiver of
subrogation required of Sublessee's insurers under Section 8.3 of the Main
Lease), shall apply with respect to Sublessor and Landlord and its Affiliates;
(c) all insurance required to be carried

                                      -10-
<PAGE>

by Sublessee as set forth in Section 8.1 of the Main Lease shall comply with
that Section and shall name as additional insureds Sublessor, Landlord and its
general partners, Landlord's Mortgagees and any property managers; (d) Sublessor
shall not be required to (although it may) carry any of the insurance required
to be carried by Landlord under the Main Lease nor does Sublessor make any
representations and warranties about the adequacy of any insurance to protect
Sublessee's interests; and (e) nothing in this Sublease is intended to, nor
shall it, affect any of the rights and obligations of Landlord and Sublessor
under the Main Lease.

     K. Signage. Subject to and in accordance with the terms and conditions of
the Main Lease, Sublessee shall have the right at its cost to replace
Sublessor's signage on and in the Building and to have its name placed on a
monument sign outside of the Building.

     L. Action with Respect to Main Lease . Sublessor shall not amend or modify
(nor agree to amend or modify) the Main Lease in any way that would maternally
increase Sublessee's obligations or materially diminish Sublessee's rights under
this Sublease without Sublessee's prior written consent. Sublessee shall not do
or permit to be done anything that would increase Sublessor's obligations under
the Main Lease nor shall Sublessor or Sublessee do or permit anything to be done
that would cause a default under the Main Lease prior to the end of the Sublease
Term.

     M. Sublessor's Rights and Remedies. If Sublessee defaults hereunder
Sublessor shall have all of the rights and remedies of Landlord under the Main
Lease with respect to Sublessee's default, to the extent same are applicable
thereto, provided, however, that notwithstanding anything contained in Exhibit
"H" to the Main Lease to the contrary, for the purposes of this Sublease, the
"Unamortized Costs" as shown in Exhibit "H" shall be reduced, as of any point in
time during the term hereof, by the amount of the "Unamortized Costs" as shown
in Exhibit "H" which are effective as of the date of the stated expiration date
of the Sublease.

     N. Representations and Warranties: (a) Sublessor hereby represents and
warrants that: (i) Sublessor is the Tenant under the Main Lease; (ii) the Main
Lease is in full force and effect, and attached hereto as Exhibit AA is a true,
correct and complete copy of the Main Lease; (iii) Sublessor has not received
any notice of default under the. Main Lease from Landlord relating to a default,
or alleged default, which, as of the date hereof, remains uncured or has not
been waived by Landlord; (iv) Sublessor is not insolvent and is able to pay its
debts and other obligations as they come due, has not declared bankruptcy or
filed a petition to take advantage of any law relating to bankruptcy,
insolvency, reorganization, winding up or composition or adjustment of debts,
and no such proceeding has been commenced against Sublessor seeking such relief,
and Sublessor has no knowledge that any such proceeding is threatened; (v) the
execution and delivery or this Sublease by Sublessor has been authorized by all
requisite corporate action; and (vi) to the best of Sublessor's knowledge,
Sublessor has not created, released or disposed of any hazardous or toxic
substances on, in or under the Premises in amounts that would require
remediation under any applicable Laws.

     (b) Sublessee hereby represents and warrants that: Sublessee is not
insolvent and is able to pay its debts and other obligations as they come due;
Sublessee has not declared bankruptcy or filed a petition to take advantage of
any law relating to bankruptcy, insolvency, reorganization, winding-up or
composition or adjustment of debts and no such proceeding has

                                      -11-
<PAGE>

been commenced against Sublessee seeking such relief, and Sublessor has no
knowledge that any such proceeding is threatened; and the execution and delivery
of this Sublease by Sublessee has been authorized by all requisite corporate
action.

     (c) Except as specifically set forth in this Sublease, the parties are not
making or relying on any representations or warranties of any kind, express or
implied.


     O. No Assignment or Sublease by Sublessee. Notwithstanding anything herein
or in the Main Lease to the contrary, Sublessee shall have no right, power or
authority to assign its rights under this Sublease or to sublease or sub-
sublease the Premises or to otherwise engage in a Transfer (and Sublessor shall
have no obligation to consent thereto), except for:

     1. A valid assignment of this Sublease in accordance with the terms of
Section 18 of the Main Lease, as modified by Section 1(j) hereof; or

     2. A valid sub-sublease of a portion of the Premises in accordance with the
terms of Section 18 of the Main Lease, as modified by Section 1(j) hereof,
provided that at all times Sublessee still continues to sublease and occupy at
least fifty percent (50%) of the Building, there shall be no more than one (1)
sub-sublease/sub-sublessee, and prior to termination of this Sublease Sublessee
shall, at its sole cost, remove any Alterations made in order to demise the
Premises for the sub-sublessee, repair all damage and restore the Premises to
the condition existing prior to such demising.

     P. Communication with Landlord. So long as Sublessee is not in default
hereunder, and subject to all of the terms and conditions of this Sublease,
Sublessee shall have the right, without the prior consent of Sublessor, to send
notices to and communicate directly with Landlord under the Main Lease with
respect to Landlord's obligations under the Main Lease, provided that copies of
all such notices given to or received from Landlord by Sublessee (including,
without limitation, requests for approvals, consents or waivers) are
concurrently delivered to Sublessor, and that such notices or other
communications shall not be deemed to modify the Main Lease or this Sublease or
a party's rights and obligations thereunder.

     Q. Notices. All notices required or permitted hereunder shall be given and
deemed effective in accordance with Section 24.16 of the Main Lease, and the
addresses of Sublessor and Sublessee shall be as follows:

     If to Sublessor:    PictureTel Corporation
                         100 Minuteman Road
                          Andover, Massachusetts 01810

     with a copy to:     PictureTel Corporation
                         100 Minuteman Road
                          Andover, Massachusetts 01810
                         Attention:  Vice President, Human Resources

     If to Sublessee:    (for notices other than invoices)
                          -------------------------------

                                      -12-
<PAGE>

                           c/o Cabletron Systems, Inc.
                         35 Industrial Way
                         Rochester, New Hampshire 03866
                           Attention: Legal Department

                         (for invoices)
                          ------------
                           c/o Cabletron Systems, Inc.
                         PO Box 5010
                         Rochester, New Hampshire 03866

Any of the parties named in this Section may change its address by written
notice sent to each of the other persons at the addresses as set forth herein.
Copies of all notices also shall be delivered to Landlord at the then-current
address for Landlord under the Main Lease, such delivery to be concurrent with
the delivery of notices to Sublessor and Sublessee.

     R. Brokerage. Within two (2) business days after receiving the One Million
Dollar ($1,000,000) infrastructure payment from Sublessee, Sublessor shall pay
as full and complete consideration $40,000 to Avalon Partners, Inc, (Sublessor's
broker), and $460,000 to Grubb & Ellis and R. M. Bradley & Co., Inc. by joint
check. Sublessee warrants and represents to Sublessor and Landlord that
Sublessee has not dealt with any agent, broker or finder in connection with this
Sublease or the Premises except Avalon Partners, Inc. and Grubb & Ellis and R.M.
Bradley & Co., Inc., and agrees to indemnify and defend Sublessor and Landlord
and hold them harmless from any loss, cost, damage, claims and liabilities of
any type, including, without limitation, reasonable attorneys' fees and costs,
incurred by Sublessor or Landlord for any breach of this representation and
warranty and any claims by anyone (other than Avalon Partners, Inc.) claiming
by, under or through Grubb & Ellis and R.M. Bradley & Co., Inc. for commissions
or consideration.

     S. Amendment. This Sublease (and this Section) shall not be amended,
altered or modified except by an instrument in writing executed by Sublessor and
Sublessee and consented to by Landlord.

     T. Contingent Effectiveness and Special Termination Conditions. This
Sublease shall be effective as of the date first set forth above but may be
terminated by Sublessor at any time, without Sublessor incurring any liability
to Sublessee, if the following conditions are not satisfied: (a) concurrently
with the delivery of this Sublease, Landlord, Sublessor, Sublessee and Cabletron
Systems, Inc. ("Guarantor") each execute and deliver a letter agreement whereby
Landlord consents to this Sublease (the "Consent Letter"); (b) concurrently with
delivery of this Sublease, Landlord and Sublessor each receive from Sublessee
Certificates of Insurance as required under this Sublease and the Consent
Letter; (c) concurrently with the delivery of this Sublease, Guarantor executes
and delivers a Continuing Guaranty of Sublease guarantying the payment and
performance of Sublessee's obligations under this Sublease (the "Guaranty"); and
(d) within fourteen (14) days after the date first set forth above, Landlord and
Sublessor each receive certified copies of Board of Directors' Resolutions
approving the execution and delivery of this Sublease, the Consent Letter and
related documents by Sublessee, and the execution and delivery of the Guaranty,
the Consent Letter and related documents by Guarantor. Sublessee also shall have
the right to terminate this Sublease at any time without incurring any liability
to

                                      -13-
<PAGE>

Sublessor if within fourteen (14) days after the date first set forth above
Sublessee has not received certified copies of the Board of Directors Resolution
approving the execution and delivery of this Sublease, the Consent Letter and
related documents by Sublessor.

     IN WITNESS WHEREOF, intending to be legally bound, the parties have
executed this Sublease under seal as of the date first above written.

                                          Sublessor

WITNESS:                                  PICTURTEL CORPORATION, a
                                          Delaware corporation

 /s/ William D. Kranson                   By: /s/ Lawrence M .Bornstein
---------------------------------            -------------------------------
Name Printed:  William D. Kranson            Name: Lawrence M .Bornstein
                                             Title: Vice President
                                             Authorized Signature

                                          Sublessee:

WITNESS:                                  CABLETRON SYSTEMS SALES &
                                          SERVICE, INC., a Delaware corporation

 /s/ Susan U. Kosko                       By: /s/ Craig Benson
                                             -------------------------------
Name Printed:  Susan U. Kosko                Name: Craig R. Benson
                                             Title: President
                                             Authorized Signature

                                      -14-
<PAGE>

                                   EXHIBIT AA

                                      -15-
<PAGE>

                             ANDOVER, MASSACHUSETTS

                           AMENDED AND RESTATED LEASE

     LANDLORD:   50 MINUTEMAN LIMITED PARTNERSHIP, A MASSACHUSETTS LIMITED
                 PARTNERSHIP

     TENANT:     PICTURETEL CORPORATION, A DELAWARE CORPORATION

     DATE:       June 4, 1988

                                      -16-
<PAGE>

                                TABLE OF CONTENTS

1.  BASIC LEASE PROVISIONS..................................................   1

2.  CONSTRUCTION OF PREMISES................................................   2

3.  POSSESSION AND SURRENDER OF PREMISES....................................   2

4.  TERM....................................................................   2

5.  RENT....................................................................   3

6.  TAXES...................................................................   3

7.  OPERATING COSTS.........................................................   4

8.  INSURANCE...............................................................   5

9.  MONTHLY PAYMENT OF TAXES AND OPERATING COSTS: AUDITS....................   6

10.  UTILITIES AND LANDLORD'S SERVICE"......................................   7

11.  USE OF PREMISES........................................................   7

12.  MAINTENANCE AND REPAIRS................................................   8

13.  ALTERATIONS............................................................   9

14.  INDEMNITY; SATISFACTION OF REMEDIES....................................  10

15.  PARKING................................................................  11

16.  DAMAGE OR DESTRUCTION..................................................  11

17.  CONDEMNATION...........................................................  13

18.  ASSIGNMENT AND SUBLETTING..............................................  14

19.  MORTGAGEE PROTECTION, UNPERMITTED FINANCING: LANDLORD'S LOAN DEFAULTS..  17

20.  ESTOPPEL CERTIFICATES; FINANCIAL STATEMENTS............................  19

21.  DEFAULT................................................................  19

22.  REMEDIES FOR DEFAULT...................................................  20

                                      -17-
<PAGE>

23.  BANKRUPTCY PROVISIONS [SEE EXHIBIT "F"]................................  21

24.  GENERAL PROVISIONS.....................................................  21

25.  HAZARDOUS SUBSTANCES...................................................  27

SIGNATURES..................................................................  28

                                      -18-
<PAGE>

                                  EXHIBIT LIST

"A" Project Site Plan
"B" Premises
"C" Workletter [INTENTIONALLY OMITTED]
"CC" PictureTel Initial Information [INTENTIONALLY OMITTED] "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 - Right of First Offer to
Purchase

                                      -19-
<PAGE>

                         INDEX TO CERTAIN DEFINED TERMS
                         ------------------------------

Term                                    Page     Section, Exhibit or Addendum
----                                    ----     ----------------------------

Affiliates..............................  26     24.18(a)
Alterations.............................   9     13
Bankruptcy.....................  Page 1 of 2     Exhibit "F"
Base Rent...............................   1     1.1(3)
Building................................   1     1/1(d)
Cash Proceeds..................  Page 1 of 3     Addendum #3
Commencement Date.......................   1     1.1(a)
Condemnation............................  13     17
Condemned...............................  13     17
Control Affiliates......................  26     24.18(b)
Costs..........................  Page 1 of 3     Addendum #3
Cure Payments...........................  19     19.5
Default.................................  27     24.18(g)
Existing Lease..........................   1     Third unnumbered paragraph
Extension Options..............  Page 1 of 1     Addendum #2
Fair Rental Value..............  Page 1 of 1     Exhibit "DD"
Financial Statements....................  19     20(b)
hazardous substances....................  27     25
Landlord................................  24     24.12
Landlord's Insurance Proceeds...........  11     16.1
Landlord's Mortgagee....................  17     19.1
Landlord's Services.....................   7     10(a)
Landlord's Work.........................   2     2
Laws....................................  26     24.18(c)
LC Advances.............................  26     24.17(f)
LC Note.................................  26     24.17(f)
LC Return......................  Page 3 of 3     Addendum #3
Lease...................................   1     First unnumbered paragraph
Lease Year..............................   2     4
Letter of Credit........................1,25     1.1(g),24.17
Liabilities.............................  26     24.18(d)
Liens...................................   9     13.4
Net Proceeds...................  Page 2 of 3     Addendum #3
Operating Costs.........................   4     7.1
Permitted Assignee......................  17     18.5(c)
Permitted Sublessee.....................  17     18.5(c)
Premises................................   1     1.1(c)
Reconstruction Costs....................  13     16.5
Related Entities........................  26     24.18(e)
Released Assignor.......................  15     18.4
rent....................................   3     5
Right of Self Help......................  11     14.4

                                      -20-
<PAGE>

Superior Leases and Mortgages...........  22     24.18(f)
Systems and Equipment...................  27     24.4
Tax Payments...................  Page 2 of 3     Addendum #3
Taxes...................................   3     6.1
Tenants Broker..........................   2     1.1(l)
Tenant's Percentage.....................   1     1.1(f)
Tenant's Property.......................   2     3
Tenant's Work...........................   2     2
Term....................................   1     1.1(b)
Transfer................................  14     18.1
Unamortized Costs.......................  20     22.2(a)

                                      -21-
<PAGE>

                           AMENDED AND RESTATED LEASE
                           --------------------------

     THIS AMENDED AND RESTATED LEASE (the "Lease"), dated and effective as of
June 4, 1998, 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:

     This Lease amends and restates in its entirety the following lease and
amendments between Landlord and Tenant (collectively, the "Existing Lease"):
Indenture of Lease, dated 8/26/98; Letter Agreement, dated 3/20/97; Amendment #1
to Lease, dated 3/19/97; Letter Agreement, dated 8/22/97; and Letter Agreement,
dated 9/2/97. Pursuant to the Existing Lease, Landlord constructed the Building
and the rest of the Premises for Tenant, and substantially completed its work as
of 8/15/97. The term of the Existing Lease began as of 8/25/97, and Tenant's
obligation to pay base rent, Taxes, Operating Costs and utilities began on
9/1/97. Tenant has been leasing the Premises pursuant to the Existing Lease.

1.  BASIC LEASE PROVISIONS.
    ----------------------

     1.1 Summary.
         -------

     (a) "Commencement Date": September 1, 1997.

     (b) Term: The term of this Lease began on August 25, 1997 and will end on
September 30, 2015, 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, agreed to contain 151,800 s.f., and associated
improvements constructed by Landlord on the land, as they may be subsequently
changed, enlarged or improved in the future.

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

     (f)  Tenant's Percentage: 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

                                      -22-
<PAGE>

                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.
                200 Brickstone Square Andover, Massachusetts 01810
                Attn: Martin Spagat

                With a Copy to:
                --------------
                c/o The Brickstone Companies
                The Plaza at Continental Park
                Suite 5252 2101 Rosecrans Avenue
                El Segundo, California 9024.5-4742
                Attn: John G. Baker, Esq.

      (k)       Guarantor: N/A.

      (1)       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 part of the Premises.

     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.

                                      -23-
<PAGE>

2.  CONSTRUCTION OF PREMISES.
    ------------------------

     The parties agree that Landlord has performed all of "Landlord's Work" and
Tenant has performed all of "Tenant's Work" (if any) as described in the
Workletter attached as Exhibit "C" to the Existing Lease.

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 Amendment and Restatement of Lease is effective as of the date
first set forth above, and the term is as set forth in Section 1.1(b). 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 Commencement Date. Tenant's failure to execute such an agreement will not
affect the actual Commencement Date or the expiration date of the initial Lease
term.

5.  RENT.
    ----

     (a) Tenant will pay the base rent as shown in Exhibit "D" in equal monthly
installments in advance beginning on the Commencement Date, 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, E1
Segundo, California 90245-4742 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

                                      -24-
<PAGE>

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 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 Commencement Date and continuing thereafter during the term, Tenant
will pay Tenant's Percentage of Taxes directly to Landlord as additional rent
within fifteen (l5) days after receipt of Landlord's bill. Taxes that are
assessed during the term of this Tease 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.

                                      -25-
<PAGE>

     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 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).

                                      -26-
<PAGE>

     (b) Subject to the other terms and conditions of this Lease, until the end
of the ninth (9th) Lease Year, Operating Costs also will nest 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 wi11 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 ( I 7th) 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, totaling 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 Commencement Date and continuing thereafter during the
term, Tenant will pay Tenant's 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 $TO Million combined single limit for each occurrence, with a
deductible not to exceed $10,000.00. 1f 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, the closest 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).

                                      -27-
<PAGE>

     (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 or on or before the date that Tenant or its
contractors or representatives first enter the Premises, 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. 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.

                                      -28-
<PAGE>

     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 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

                                      -29-
<PAGE>

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 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" to the Existing Lease.
Beginning as of the Commencement Date, 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,
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 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 nn
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 l :?.l 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

                                      -30-
<PAGE>

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.

     (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 ibis
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-of-business 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.

                                      -31-
<PAGE>

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 I-IVAC 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 hose 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 above-
standard 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,

                                      -32-
<PAGE>

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 anti encumbrances based on or arising from such claims ("Liens").
Tenant will indemnify Landlord for, and hold Landlord 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

                                      -33-
<PAGE>

MECHANICS', MATERIALMENS' OR OTHER LIENS SOUGHT ON THE PREMISES WILL 1N 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 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

                                      -34-
<PAGE>

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, Nit 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
(3()) days after a subsequent written notice from Tenant to Landlord (but if
more than thirty (30) days care reasonably required to cure, Landlord will be
deemed to have cured if it promptly begins to rare within the thirty (30)-day
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.)

                                      -35-
<PAGE>

15.  PARKING.
     -------

     All parking areas nn 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 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

                                      -36-
<PAGE>

than the insurance proceeds that are reasonably likely to he 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.

     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 (regardless of whether or not-Landlord has collected sufficient
insurance proceeds for such repairs), 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 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 (1 S)
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 (1 S) 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

                                      -37-
<PAGE>

substantially completed the repairs it is required to make (regardless of
whether or not Landlord has collected sufficient insurance proceeds for such
repairs) 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
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

                                      -38-
<PAGE>

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.

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 nn 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 he 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

                                      -39-
<PAGE>

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 he treated by them as confidential to the same extent as by
Landlord.

     18.3 Reasonable Consent. Landlord will nit unreasonably withhold or delay
its consent to an assignment or sublease by Tenant, but Landlord may withhold
its consent to any other Transfer (including, without limitation, any
hypothecation or assignment for security purposes) 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

                                      -40-
<PAGE>

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. 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 subleases)
aggregating more than fifty percent (SO%) 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 #? 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.
                ----------------

                                      -41-
<PAGE>

     (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 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
s>.iblease 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 arid
agreements for its protection from Tenant and the assignee or subtenant, each of
whom agrees to give such assurances and execute

                                      -42-
<PAGE>

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 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 he 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

                                      -43-
<PAGE>

succeeds to Landlord's interest tinder 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-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 thc. 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 [60J 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 a s 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
notices) 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, Landlord agrees not to use the Premises or any portion thereof to
secure any indebtedness other than:

                                      -44-
<PAGE>

     (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.

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 serviced 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
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

                                      -45-
<PAGE>

have been repaid in full. For purposes of this Section, Landlord's default under
the applicable loans) shall be deemed to be a breach of Landlord's obligations
under the applicable loans) which is not cured within applicable notice and cure
periods under such loans. Such loans shall provide that: (A) the lenders) shall
deliver notices of such defaults to Tenant concurrently with delivery to
Landlord; and (B) that the lenders) 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.
          -------

     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

                                      -46-
<PAGE>

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 "I-I" 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 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 hale rent to Landlord will be referred to as the "New Rent Payment Date."
Subject to the rest of this Subsection, Tenant will he 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

                                      -47-
<PAGE>

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 prig 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 (or its successor), plus all of the
unpaid expenses described in Sections 22.2(x) (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.

     (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 tile 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.

                                      -48-
<PAGE>

     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 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

                                      -49-
<PAGE>

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. The parties acknowledge and agree that
Landlord has paid all brokerage commissions and other compensation due to
Tenant's Broker under the Existing Lease, and that no brokerage commissions or
other compensation are owed by Landlord to Tenant's Broker in connection with
this Lease or the Existing Lease.

     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 Teases and Mortgages" means all present and future ground leases,
underlying 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 there>..mder, 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

                                      -50-
<PAGE>

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, belt 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 (IO) 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.

     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 frill 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 except for that certain Letter Agreement, dated 9/16/97,
regarding, among other things, a $234,864 net refund to Tenant, and except that
the Existing Lease shall be deemed to have been in effect until the effective
date of this Lease. 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

                                      -51-
<PAGE>

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 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 Tease 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 he 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

                                      -52-
<PAGE>

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 he 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 he 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.

     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 I. l 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.
                 ----------------

                                      -53-
<PAGE>

     (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 $7.3 Million, wilt be
issued initially by Bank of Boston (or its successor) 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 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, 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 $7.3
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 be a default under
this Lease, and 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

                                      -54-
<PAGE>

Credit for all or any portion thereof; provided, however, that if Tenant
delivers the required renewal of the Letter of Credit to the beneficiary before
the expiration of the existing Letter of Credit and before the beneficiary has
drawn under the existing Letter of Credit, then Tenant shall be deemed to have
cured such default.

     (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 loans) from its lender(s). If
Tenant defaults under this Lease or there is a default under such loans) 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 drawls) 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)  [INTENTIONALLY OMITTED]

     (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 Fetter 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.

     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.
             -------------------

                                      -55-
<PAGE>

     (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.

     (b) "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.

     (c) "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.

     (d) "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).

     (e) "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.

     (f) "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.

     (g) "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).

25.   HAZARDOUS SUBSTANCE.
      -------------------

     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

                                      -56-
<PAGE>

strictly in accordance with applicable Laws. 1f 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 Taws promulgated by the EPA,
OSI-IA 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.

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 Amended and Restated Lease as a sealed instrument as of the date first set
forth above.

                                      -57-
<PAGE>

                                   "LANDLORD"

Executed:      June 4, 1998                 50 MINUTEMAN LIMITED
                                            PARTNERSHIP, a Massachusetts limited
                                            partnership

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

/s/ Illegible                               By: /s/ Illegible
---------------------------                    ---------------------------
                                               Illegible     , President

                                    "TENANT"

Executed:      June 4, 1988                 PICTURETEL CORPORATION, a
                                            Delaware corporation

WITNESS:

/s/ Illegible                               Name: /s/ Lawrence M. Bornstein
---------------------------                       --------------------------
                                                  Name: Lawrence M. Bornstein
                                                  Title: Vice President
                                                  Authorized Signature


/s/ Illegible                               Name: /s/ Richard B. Goldman
---------------------------                       --------------------------
                                                  Name: Richard B. Goldman
                                                  Title: Vice President
                                                  Authorized Signature

                                      -58-
<PAGE>

                                  EXHIBIT "A"

                                      -59-
<PAGE>

                                   EXHIBIT "B"

                               PARCEL DESCRIPTION
                               ------------------

                                  PARCEL "c-2"
                                  ------------

A CERTAIN PARCEL OF LAND LOCATED IN ANDOVER, COUNTY OF ESSEX, ' MASSACHUSETTS,
SITUATED NORTHERLY OF RIVER ROAD, BEING SHOWN AS PARCEL " C-2 " ON A PLAN
ENTITLED, " PLAN OF LAND PREPARED FOR 1776 LIMITED PARTNERSHIP", ANDOVER, HA,
SCALE: 1'=100' DATED: APRIL 17, 1996 REVISED APRIL 25, 1996, PREPARED BY OWEN
HASKELL, INC.

SAID PARCEL " C-2 " BEING FURTHER BOUNDED AND DESCRIBED AS FOLLOWS:

BEGINNING AT THE MOST WESTERLY CORNER OF THE PARCEL HEREIN DESCRIBED AT A POINT
ON THE EASTERLY SIDELINE OF MINUTEMAN ROAD AND THE SOUTHERLY CORNER OF PARCEL
"A-1" AS SHOWN OF SAID PLAN; THENCE,

EASTERLY BY PARCEL " A-1", THE FOLLOWING SIX COURSES:

N 62/degrees/ 29' 10" E TWO HUNDRED THIRTY AND 00/100 FEET (230.00'), N
33/degrees/ 07' 37" E FOUR HUNDRED FIFTEEN AND 00/100 FEET (415.00'), N
12/degrees/ 18' 48" E ONE HUNDRED SEVENTY SIX AND 00/100 FEET (176 . 00' ) , N
14/degrees/ 03' 17" W EIGHTY THREE AND 40/100 FEET (83.40'), BY A CURVE TO THE
RIGHT HAVING A RADIUS OF ONE HUNDRED SIXTY AND 00/100 FEET
               (160.00') A LENGTH OF ONE HUNDRED THIRTEEN AND 93/100 FEET
               (113.93'), TO A POINT AT THE WESTERLY CORNER OF PARCEL "B-1" AS
               SHOWN ON SAID PLAN; THENCE,

S                         30/degrees/ 53' 06" E NINE HUNDRED THIRTY TWO AND
                          82/100 FEET (932.82') ALONG PARCEL " B-1 " AND THE
                          LAND OF NOW OR FORMERLY OF JOHN PAPPAS TO A POINT ON
                          THE WESTERLY SIDELINE OF RIVER ROAD; THENCE,

BY THE WESTERLY SIDELINE OF RIVER ROAD THE FOLLOWING TWO COURSES:

S 41/degrees/ 08' 17" W   ONE HUNDRED NINE`S FIVE AND 96/100 FEET (195.96')
                          AND
BY                        A CURVE TO THE LEFT HAVING A RADIUS OF NINETEEN
                          HUNDRED EIGHTY THREE-AND 05/100 FEET (1983.05') A
                          LENGTH OF FOUR HUNDRED FIFTY TWO A.ND 34/100 FEET
                          (452.34'), TO A POINT ON THE EASTERLY SIDELINE OF
                          MINUTEMAN ROAD; THENCE,

BY THE EASTERLY SIDELINE OF MINUTEMAN ROAD THE FOLLOWING  SIX
COURSES:

S 55/degrees/ 31' 54" W, TWENTY THREE AND 20/100 FEET (23.20'), BY A CURVE TO
THE RIGHT HAVING A RADIUS OF EIGHTY SIX AND 00/100

                                      -60-
<PAGE>

               FEET (86.00') A LENGTH OF SIXTY AND 04/100 FEET (60.04'),

BY A CURVE TO THE RIGHT HAVING A RADIUS OF ONE HUNDRED EIGHTY SIX AND 00/100
               FEET (186.00') A LENGTH OF SIXTY EIGHT AND 17/100 FEET (68.17'),

N 63/degrees/  28' 05" W   ONE HUNDRED FORTY AND 73/100 FEET (140.73') TO A
               STONE BOUND,

BY             A CURVE TO THE RIGHT HAVING A RADIUS OF FOUR HUNDRED TWENTY EIGHT
               AND 00/100 FEET (428.00') A LENGTH OF TWO HUNDRED THREE AND
               71/100 FEET (203 .71') TO A STONE BOUND, AND

N              36/degrees/ 11' 50" W TWO HUNDRED NINETY TWO AND 00/100 FEET
               (292.00'), TO THE SOUTHERLY CORNER OF PARCEL " A-1 " AND THE
               POINT OF.BEGINNING.

     PARCEL " C-2 " CONTAINING 598,051 SQUARE FEET OR 13.729
          ACRES, MORE OR LESS.

                                      -61-
<PAGE>

                                   EXHIBIT "C"

                                   WORKLETTER

                             [INTENTIONALLY OMITTED]

                                      -62-
<PAGE>

                                  EXHIBIT "CC"

                         PICTURETEL INITIAL INFORMATION

                             [INTENTIONALLY OMITTED]

                                      -63-
<PAGE>

                                   EXHIBIT "D"

                                    BASE RENT

     1. [INTENTIONALLY OMITTED]

     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(h) OF THE LEASE FOR POSSIBLE RENT CREDITS IN CONNECTION WITH THE
-------------------------------------------------------------------------------
LETTER OF CREDIT.]
------------------

                                      -64-
<PAGE>

                                  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. 1f 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 (S) years' experience in the appraisal of office property in the area in
which the Premises is located and he members of professional organizations such
as the American Institute of Real Estate Appraisers or the equivalent.

     Landlord and Tenant will instruct the appraisers) 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
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.

                                      -65-
<PAGE>

     (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).

                                      -66-
<PAGE>

                                   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 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.

                                      -67-
<PAGE>

     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.

                                      -68-
<PAGE>

                                   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 and 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.

     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

                                      -69-
<PAGE>

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 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.

                                      -70-
<PAGE>

     23.4 Construction. The terms of this Article will he 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 "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 compactors) (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).

                                      -71-
<PAGE>

                                    EXHIBIT H

                                UNAMORTIZED COST

                                    EXHIBIT H
                                UNAMORTIZED COST


<TABLE>
<CAPTION>

 MONTH (STARTING AFTER MONTH IN WHICH COMMENCEMENT DATE    MONTH (STARTING AFTER MONTH IN WHICH COMMENCEMENT DATE
 OCCURS) PRIOR TO COMMENCEMENT DATE THE UNAMORTIZED        OCCURS) PRIOR TO COMMENCEMENT DATE THE UNAMORTIZED COSTS
 COSTS SHALL BE $10.2 MILLION             AMOUNT           SHALL BE $10.2 MILLION             AMOUNT
----------------------------------------------------------------------------------------------------
<S>                          <C>                           <C>                           <C>
                                       10,200,000
----------------------------------------------------------------------------------------------------
            1                          10,180,983                         44               9,212,982
----------------------------------------------------------------------------------------------------
            2                          10,161,823                         45               9,186,562
----------------------------------------------------------------------------------------------------
            3                          10,142,519                         46               9,159,944
----------------------------------------------------------------------------------------------------
            4                          10,123,070                         47               9,133,126
----------------------------------------------------------------------------------------------------
            5                          10,103,476                         48               9,106,107
----------------------------------------------------------------------------------------------------
            6                          10,083,735                         49               9,078,886
----------------------------------------------------------------------------------------------------
            7                          10,063,845                         50               9,051,460
----------------------------------------------------------------------------------------------------
            8                          10,043,807                         51               9,023,828
----------------------------------------------------------------------------------------------------
            9                          10,023,618                         52               8,995,990
----------------------------------------------------------------------------------------------------
            10                         10,003,278                         53               8,967,942
----------------------------------------------------------------------------------------------------
            11                          9,982,785                         54               8,939,685
----------------------------------------------------------------------------------------------------
            12                          9,962,139                         55               8,911,215
----------------------------------------------------------------------------------------------------
            13                          9,941,337                         56               8,882,532
----------------------------------------------------------------------------------------------------
            14                          9,920,380                         57               8,853,633
----------------------------------------------------------------------------------------------------
            15                          9,899,265                         58               8,824,518
----------------------------------------------------------------------------------------------------
            16                          9,877,992                         59               8,795,185
----------------------------------------------------------------------------------------------------
            17                          9,856,560                         60               8,765,631
----------------------------------------------------------------------------------------------------
            18                          9,834,967                         61               8,735,856
----------------------------------------------------------------------------------------------------
            19                          9,813,212                         62               8,705,857
----------------------------------------------------------------------------------------------------
            20                          9,791,293                         63               8,675,634
----------------------------------------------------------------------------------------------------
            21                          9,769,211                         64               8,645,184
----------------------------------------------------------------------------------------------------
            22                          9,746,963                         65               8,614,505
----------------------------------------------------------------------------------------------------
            23                          9,724,547                         66               8,583,597
----------------------------------------------------------------------------------------------------
            24                          9,701,964                         67               8,552,456
----------------------------------------------------------------------------------------------------
            25                          9,679,211                         68               8,521,082
----------------------------------------------------------------------------------------------------
            26                          9,656,288                         69               8,489,473
----------------------------------------------------------------------------------------------------
            27                          9,633,193                         70               8,457,627
----------------------------------------------------------------------------------------------------
            28                          9,609,925                         71               8,425,542
----------------------------------------------------------------------------------------------------
            29                          9,586,482                         72               8,393,216
----------------------------------------------------------------------------------------------------
            30                          9,562,863                         73               8,360,648
----------------------------------------------------------------------------------------------------
            31                          9,539,067                         74               8,327,835
----------------------------------------------------------------------------------------------------
            32                          9,515,093                         75               8,294,777
----------------------------------------------------------------------------------------------------
            33                          9,490,938                         76               8,261,470
----------------------------------------------------------------------------------------------------
            34                          9,466,603                         77               8,227,914
----------------------------------------------------------------------------------------------------
            35                          9,442,085                         78               8,194,106
----------------------------------------------------------------------------------------------------
            36                          9,417,383                         79               8,160,044
----------------------------------------------------------------------------------------------------
            37                          9,392,496                         80               8,125,727
----------------------------------------------------------------------------------------------------
            38                          9,367,423                         81               8,091,153
----------------------------------------------------------------------------------------------------
            39                          9,342,161                         82               8,056,319
----------------------------------------------------------------------------------------------------
</TABLE>

                                      -72-
<PAGE>

<TABLE>
<CAPTION>

 MONTH (STARTING AFTER MONTH IN WHICH COMMENCEMENT DATE    MONTH (STARTING AFTER MONTH IN WHICH COMMENCEMENT DATE
 OCCURS) PRIOR TO COMMENCEMENT DATE THE UNAMORTIZED        OCCURS) PRIOR TO COMMENCEMENT DATE THE UNAMORTIZED COSTS
 COSTS SHALL BE $10.2 MILLION             AMOUNT           SHALL BE $10.2 MILLION             AMOUNT
----------------------------------------------------------------------------------------------------
<S>                          <C>                           <C>                           <C>
            40                          9,316,710                         83               8,021,224
----------------------------------------------------------------------------------------------------
            41                          9,291,068                         84               7,985,866
----------------------------------------------------------------------------------------------------
            42                          9,265,234                         85               7,950,242
----------------------------------------------------------------------------------------------------
            43                          9,239,205                         86               7,914,352
----------------------------------------------------------------------------------------------------
            87                          7,878,192                        136               5,730,511
----------------------------------------------------------------------------------------------------
            88                          7,841,761                        137               5,677,973
----------------------------------------------------------------------------------------------------
            89                          7,805,057                        138               5,625,040
----------------------------------------------------------------------------------------------------
            90                          7,768,077                        139               5,571,711
----------------------------------------------------------------------------------------------------
            91                          7,730,821                        140               5,517,981
----------------------------------------------------------------------------------------------------
            92                          7,693,284                        141               5,463,849
----------------------------------------------------------------------------------------------------
            93                          7,655,467                        142               5,409,310
----------------------------------------------------------------------------------------------------
            94                          7,617,365                        143               5,354,363
----------------------------------------------------------------------------------------------------
            95                          7,578,978                        144               5,299,003
----------------------------------------------------------------------------------------------------
            96                          7,540,303                        145               5,243,228
----------------------------------------------------------------------------------------------------
            97                          7,501,338                        146               5,187,035
----------------------------------------------------------------------------------------------------
            98                          7,462,081                        147               5,130,420
----------------------------------------------------------------------------------------------------
            99                          7,422,529                        148               5,073,381
----------------------------------------------------------------------------------------------------
            100                         7,382,681                        149               5,015,914
----------------------------------------------------------------------------------------------------
            101                         7,342,533                        150               4,958,016
----------------------------------------------------------------------------------------------------
            102                         7,302,085                        151               4,899,684
----------------------------------------------------------------------------------------------------
            103                         7,261,333                        152               4,840,914
----------------------------------------------------------------------------------------------------
            104                         7,220,276                        153               4,781,703
----------------------------------------------------------------------------------------------------
            105                         7,178,910                        154               4,722,049
----------------------------------------------------------------------------------------------------
            106                         7,137,235                        155               4,661,947
----------------------------------------------------------------------------------------------------
            107                         7,095,247                        156               4,601,394
----------------------------------------------------------------------------------------------------
            108                         7,052,944                        157               4,540,387
----------------------------------------------------------------------------------------------------
            109                         7,010,323                        158               4,478,923
----------------------------------------------------------------------------------------------------
            110                         6,967,384                        159               4,416,997
----------------------------------------------------------------------------------------------------
            111                         6,924,122                        160               4,354,607
----------------------------------------------------------------------------------------------------
            112                         6,880,535                        161               4,291,750
----------------------------------------------------------------------------------------------------
            113                         6,836,622                        162               4,228,420
----------------------------------------------------------------------------------------------------
            114                         6,792,379                        163               4,164,616
----------------------------------------------------------------------------------------------------
            115                         6,747,804                        164               4,100,333
----------------------------------------------------------------------------------------------------
            116                         6,702,896                        165               4,035,568
----------------------------------------------------------------------------------------------------
            117                         6,657,650                        166               3,970,318
----------------------------------------------------------------------------------------------------
            118                         6,612,065                        167               3,904,578
----------------------------------------------------------------------------------------------------
            119                         6,566,138                        168               3,838,345
----------------------------------------------------------------------------------------------------
            120                         6,519,867                        169               3,771,615
----------------------------------------------------------------------------------------------------
            121                         6,473,248                        170               3,704,385
----------------------------------------------------------------------------------------------------
            122                         6,426,280                        171               3,636,650
----------------------------------------------------------------------------------------------------
            123                         6,378,960                        172               3,568,408
----------------------------------------------------------------------------------------------------
            124                         6,331,285                        173               3,499,653
----------------------------------------------------------------------------------------------------
            125                         6,283,252                        174               3,430,383
----------------------------------------------------------------------------------------------------
            126                         6,234,859                        175               3,360,594
----------------------------------------------------------------------------------------------------
            127                         6,186,103                        176               3,290,281
----------------------------------------------------------------------------------------------------
            128                         6,136,982                        177               3,219,441
----------------------------------------------------------------------------------------------------
            129                         6,087,492                        178               3,148,069
----------------------------------------------------------------------------------------------------
            130                         6,037,630                        179               3,076,162
----------------------------------------------------------------------------------------------------
            131                         5,987,395                        180               3,003,716
----------------------------------------------------------------------------------------------------
</TABLE>

                                      -73-
<PAGE>

<TABLE>
<CAPTION>

 MONTH (STARTING AFTER MONTH IN WHICH COMMENCEMENT DATE    MONTH (STARTING AFTER MONTH IN WHICH COMMENCEMENT DATE
 OCCURS) PRIOR TO COMMENCEMENT DATE THE UNAMORTIZED        OCCURS) PRIOR TO COMMENCEMENT DATE THE UNAMORTIZED COSTS
 COSTS SHALL BE $10.2 MILLION             AMOUNT           SHALL BE $10.2 MILLION             AMOUNT
----------------------------------------------------------------------------------------------------
<S>                          <C>                           <C>                           <C>
            132                         5,936,783                        181               2,930,727
----------------------------------------------------------------------------------------------------
            133                         5,885,792                        182               2,857,190
----------------------------------------------------------------------------------------------------
            134                         5,834,418                        183               2,783,101
----------------------------------------------------------------------------------------------------
            135                         5,782,659                        184               2,708,457
----------------------------------------------------------------------------------------------------
            185                         2,633,253
----------------------------------------------------------------------------------------------------
            186                         2,557,485
----------------------------------------------------------------------------------------------------
            187                         2,481,149
----------------------------------------------------------------------------------------------------
            188                         2,404,240
----------------------------------------------------------------------------------------------------
            189                         2,326,755
----------------------------------------------------------------------------------------------------
            190                         2,248,688
----------------------------------------------------------------------------------------------------
            191                         2,170,036
----------------------------------------------------------------------------------------------------
            192                         2,090,794
----------------------------------------------------------------------------------------------------
            193                         2,010,957
----------------------------------------------------------------------------------------------------
            194                         1,930,522
----------------------------------------------------------------------------------------------------
            195                         1,849,484
----------------------------------------------------------------------------------------------------
            196                         1,767,837
----------------------------------------------------------------------------------------------------
            197                         1,685,579
----------------------------------------------------------------------------------------------------
            198                         1,602,703
----------------------------------------------------------------------------------------------------
            199                         1,519,206
----------------------------------------------------------------------------------------------------
            200                         1,435,083
----------------------------------------------------------------------------------------------------
            201                         1,350,329
----------------------------------------------------------------------------------------------------
            202                         1,264,939
----------------------------------------------------------------------------------------------------
            203                         1,178,908
----------------------------------------------------------------------------------------------------
            204                         1,092,233
----------------------------------------------------------------------------------------------------
            205                         1,004,907
----------------------------------------------------------------------------------------------------
            206                           916,927
----------------------------------------------------------------------------------------------------
            207                           828,286
----------------------------------------------------------------------------------------------------
            208                           738,981
----------------------------------------------------------------------------------------------------
            209                           649,006
----------------------------------------------------------------------------------------------------
            210                           558,356
----------------------------------------------------------------------------------------------------
            211                           467,026
----------------------------------------------------------------------------------------------------
            212                           375,012
----------------------------------------------------------------------------------------------------
            213                           282,307
----------------------------------------------------------------------------------------------------
            214                           188,907
----------------------------------------------------------------------------------------------------
            215                            94,806
----------------------------------------------------------------------------------------------------
            216                                 0
----------------------------------------------------------------------------------------------------
</TABLE>

                                      -74-
<PAGE>

                                   EXHIBIT "I"

                             [INTENTIONALLY OMITTED]

                                      -75-
<PAGE>

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

          Square Footage: Approximately 151,800 s.f.

                                      -76-
<PAGE>

          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 punch1ist 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.

          (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.

                                      -77-
<PAGE>

                                Very truly yours,


                                Tenant: PictureTel Corporation

                                By:
                                   ------------------------------
                                Title:
                                      ---------------------------

                                Date:
                                     ----------------------------

                                      -78-
<PAGE>

                                    EXHIBIT J

RECORDING REQUESTED BY
AND WHEN RECORDED MAIL TO:

--------------------------------------------------------------------------------
                    Space Above This Line for Recorder's Use

            SUBORDINATION, NON-DISTURBANCE AND ATTORNMENT AGREEMENT

     THIS AGREEMENT, is made this day of , 199 by

     having its principal office and place of business located at

     ("Tenant"), and John Hancock Mutual Life Insurance Company, having is
principal place of business located at 200 Clarendon Street, John Hancock Place,
P.O. Box 111, Boston, MA 02117 ("Lender"), with reference to the following
facts:

                                    RECITALS

     A.  On ,                                                  ("Landlord")
     and Tenant entered into a certain lease ("Lease") covering certain apace
("Premises") in the building located at , which property is more particularly
described in the Mortgage (as hereinafter defined) ("Property");

     U. Lender has agreed to make a loan ("Loan") to Landlord, which Loan is to
be evidenced by a note and secured, inter alia, by a first [deed of
trust/mortgage] in favor of Lender and upon the terms and conditions described
therein, which shall be recorded in the Official Records of (said mortgage and
all amendments, modifications, renewals, substitutions, extensions,
consolidations and replacements are hereinafter collectively referred to as
"Mortgage");

     V. It is a condition precedent to obtaining the Loan that (i) the Mortgage
unconditionally be and remain at all times a first lien or charge upon the
Property prior and superior to the Lease; (11) Tenant specifically and
unconditionally subordinate the Lease to the lien or charge of the Mortgage and
(iii) Tenant attorn to Lends: and its successor and assigns in the event of the
foreclosure or other proceeding to enforce the Mortgage;

     NOW, THEREFORE, in consideration of the mutual benefits accruing to the
parties hereto. and other valuable consideration, the receipt and sufficiency of
which are hereby acknowledged, and in order to induce Lender to enter into the
above-referenced Loan, Lender and Tenant hereby agree as follows:

     1. Subordination. The Mortgage is and shall unconditionally be and remain
at all times a lien or charge upon the Property prior and superior to the Lease,
the leasehold estate created thereby and all rights and privileges of Tenant or
any other tenant thereunder, and the Lease, the leasehold estate created thereby
and all rights and privileges of Tenant or any other tenant thereunder are
hereby unconditionally subjected and made subordinate to the lien or charge of
the Mortgage.

                                      -79-
<PAGE>

     2. Lender's Exercise of-Remedies. In the event of (a) the institution of
any foreclosure, trustee's sale or other like proceeding, (b) the appointment of
a receiver for the Landlord or the Property, (c) the exercise of rights to
collect rents under the Mortgage or an assignment of rents, (d) the recording by
Lender or its successor or assignee of a deed in lieu of foreclosure for the
Property, or (e) any transfer or abandonment of penasasioa of the Property to
Leader or its successor or assigns in connection with any proceedings affecting
Landlord under the Bankruptcy Code, 11 U.S.C. (S) 101 et seq. (any such
foreclosure, recording of a deed in lieu of foreclosure, or transfer or
abandonment of the Property referred to in the preceding clauses (a) through (e)
is hereinafter called a "Transfer", and Lender or any successor or assignee of
Lender taking title to the Property in connection with a Transfer is hereinafter
called the "Transferee"), such Transferee shall not: (i) be liable for any
damages (including, without limitation, consequential damages) or other relief
or be subject to any offers, defenses or counterclaims of any kind attributable
to any act, omission or waiver (express or implied) of Landlord or any prior
landlord under the Lease, or otherwise; (11) be obligated to complete any
construction or improvements at the Property, Premises or elsewhere agreed to be
done by Landlord or any prior landlord under the Lease, or otherwise, or to
reimburse Tenant for any prior construction work done by Tenant, or be subject
to any offsets, defenses or counterclaims therefor, (iii) be bound by any
prepayment by Tenant of more than one month's installment of rent unless such
prepayment has been specifically approved in writing by Lender, or be liable or
responsible for any security deposit or other sums which Tenant may have paid
under the Lease unless such deposit or other sums have been physically delivered
to Transferee, (iv) be bound by any modification of or amendment to the Lease,
unless such amendment or modification shall have been approved in writing by
Lender, (v) be bound by any notices given by Tenant to Landlord unless a copy
thereof vas then simultaneously given to Lender, (vi) be required after a fire,
casualty or condemnation of the Property or Premises to repair or rebuild the
same to the extent that such repair or rebuilding requires funds in excess of
the insurance or condemnation proceeds specifically allocable to the Premises
and arising out of each fire, casualty or condemnation which have actually been
received by Transferee, and then only to the extent required by the terms of the
Lease, (vii) be responsible to provide any additional apace at the Property or
elsewhere for which Tenant has any option or right under the Lease, or
otherwise, unless Transferee at its option elects to provide the same, and
Tenant hereby releases Transferee from any obligation to provide the same, and
agrees that Tenant shall have no right to cancel the Lease and shall possess no
right to any claim against Transferee as a result of the failure to provide any
such additional apace, or (viii) be liable for or incur any obligation with
respect to any , representations or warranties of any nature set forth in the
Lease or otherwise, including, but not limited to, representations or warranties
relating to any latent or patent defects in construction with respect to/ the
Property or the Premises, Landlord's title or compliance of the Property or
Premises with applicable environmental, building, zoning or other laws,
including, but not limited to, the Americans with Disabilities Act and
regulations pursuant thereto.

     3. Attornment and Non-Disturbance. Except as set forth in Paragraph Z
above, provided (a) Tenant complies with this Agreement, (b) Tenant is not in
default under the terms of the Lease and no event has occurred which, with the
passage of time or the giving of notice or both, would constitute a default
under the Lease, (c) the Lease is in full force and effect, both as of the date
Lender files a lis pendena, or otherwise commences a foreclosure action, or at
any

                                      -80-
<PAGE>

time thereafter, and (d) Tenant shall be in possession of the Premises, no
default under the Mortgage and no proceeding to foreclose the same will disturb
Tenant's possession under the Lease end the Lease will not be affected or cut
off thereby, and notwithstanding any such foreclosure or other Transfer of the
Property to Transferee, the Lease will be recognized as a direct lease from
Transferee to Tenant upon the Transfer for the balance of the term thereof.

     Tenant shall attorn to Transferee, Including Lender if Lender becomes a
Transferee, as the landlord under the Lease. Said attornment is subject to the
limitation of Transferee's obligations set forth in Paragraph 2 above and shall
be effective and self-operative without the execution of any further instruments
upon Transferee succeeding to the interest of the landlord under the Lease.
Within ten (10) days after receipt of a written request therefor from
Transferee, Tenant agrees to provide Transferee a written confirmation of its
attornment to Transferee and any other matter set forth in this Agreement.
Failure to provide such written confirmation shall at Transferee's sole option,
constitute a default under the Lease, but failure to receive such written
confirmation from Tenant shall not derogate from Tenant's obligations to
Transferee hereunder.

     4. Miscellaneous.

     (a) This Agreement shall inure to the benefit of the parties hereto their
successors and assigns; provided, however, that in the event of the assignment
or transfer of the interest of Transferee, all obligations and liabilities of
Transferee under this Agreement shall terminate, and thereupon all such
obligations and liabilities shall be the responsibility of the party to whom
Transferee's interest is assigned or transferred; and provided further that the
interest of Tenant under this Agreement may not be assigned or transferred
except to the extent the assignment of Tenant's interest in the Lease is
permitted under the Lease.

     (b) Tenant acknowledges that it has notice that the Lease and the rent and
all other sums due thereunder have been assigned to the Lender as part of the
security for the note secured by the Mortgage and upon written notice from
Lender of a default under the Mortgage, Tenant shall pay its rent and all other
sums due under the Lease directly to Lender,

     (a) Tenant covenants and acknowledges that it has no right or option of any
nature whatsoever, whether pursuant to the Lease or otherwise, to purchase the
Property or the real property of which the Property is a part, or any portion
thereof or any interest therein and to the extent that Tenant has had, or
hereafter acquires any such right or option, the same is hereby acknowledged to
be subject and subordinate to the Mortgage and is hereby waived and released as
against Transferee.

     (b) Anything herein or in the Lease to the contrary notwithstanding, in the
event that Transferee shall acquire title to the Property, Transferee shall have
no obligation, nor incur any liability, beyond Transferee's then interest 1n the
Property, and Tenant shall look exclusively to such interest of Transferee in
the Property for the payment and discharge of any obligations imposed upon
Transferee hereunder or under the Lease, or otherwise, subject to the limitation
of Transferee's obligations provided for in Paragraph 2 above.

     (c) This Agreement is the whole and only agreement between the parties
hereto with regard to the subordination of the Lease to the lien or charge of
the Mortgage, and shall

                                      -81-
<PAGE>

supersede end cancel all other subjection or subordination agreements including,
but not limited to, those provisions, If any, contained in the Lease which
provide for the subjection or subordination of said Lease to a deed of trust or
to a mortgage or mortgagee. This Agreement may not be modified in any manner or
terminated except by an instrument in writing executed by the parties hereto.

     (d) This Agreement shall be deemed to have been made in the state where the
Property is located and the validity, interpretation and enforcement of this
Agreement shall be determined in accordance with the laws of such state.

     (e) In the event any legal action or proceeding is commenced to interpret
or enforce the terms of, or obligations arising out of, this Agreement, or to
recover damages for the breach thereof, the party prevailing in any such action
or proceeding shall be entitled to recover from the non-prevailing party all
reasonable attorneys' fees, costs and expenses incurred by the prevailing party.

     (c) Any notices or communications required or permitted to be given or made
hereunder shall be deemed to be so given or made when in writing and delivered
in person or sent by United States registered or certified mail, postage
prepaid, or by nationally recognized overnight courier service, directed to the
parties at the following addresses or such other addresses as they may from time
to time designate in writing:

     Lender:   John Hancock Mutual Life Insurance Company
               Real Estate Investment Group
               Attention: Mortgage Investments, T-53
               John Hancock Place
               P.0. Box 111

     (f)       Boston, MA 02117
               Reference Loan No.  ___________

     Tenant:
              ---------------------------------

     Notices or communications mailed in the U.S. mail shall be deemed to be
served on the third business day following mailing, notices or communication
served by hand or by overnight courier shall be deemed served upon receipt.

     The parties hereto represent and warrant that their respective signatories
to this Agreement have been duly authorized by the Tenant and Lender, as
applicable.

                                      -82-
<PAGE>

             SUBORDINATION, NON-DISTRUBANCE AND ATTORNMENT AGREEMENT
             -------------------------------------------------------

     THIS AGREEMENT, is made this 10th day of July, 1996 by PICTURETEL
CORPORATION. a Delaware corporation, having its principal office and place of
business located at The Toner at NorthWoods, 7.22 Rosewood Drive, Danvers,
Massachusetts 01923 ('Tenant') and Life Investors Insurance Company of America,
an Iowa corporation, having its principal place of business located at 6333
Edgewood Road, N.E., Cedar Rapids, Iowa 52499 "Lender"), with reference to the
following facts:

                                    RECITALS
                                    --------

     A. 100 Minuteman Limited Partnership, a Massachusetts limited partnership
("Landlord'), and Tenant entered into a certain lease, dated as of October 10,
1995, and amended by Amendment #1 to Lease dated July 10, 1996 (collectively,
together with any extensions, renewals of replacements thereof the "Least"),
covering land and a building, and other improvements thereon located in Andover,
Massachusetts, which property is more particularly described in the Mortgage (as
hereinafter defined ('Property');

     B. Lender has agreed to make a loan ('Loan') to Landlord, which Loan is to
be evidenced by a note and secured, inter alia, by a first mortgage and security
agreement in favor of Lender and upon the terms and conditions described
therein, which shall be recorded in the Registry of Deeds, Essex county (said
mortgage and security agreement, and all amendments, modifications, renewals,
substitutions, extensions, consolidation and replacements are hereinafter
collectively referred to as 'mortgage*);

     C. It is a condition precedent to obtaining the Loan that ii) the Mortgage
unconditionally be and remain at all times a first lien oz change upon the
Property prior and superior to the Lease aid to any rights of offsets, defenses
or credits that Tenant may have under Section 19.5 of the Lease in connection
with that certain Letter of Credit issued by Bank of Boston, dated October 10,
1995, in the original fact amount of $10,000,000 and may renew". replacements or
amendments thereof (the 'Letter of Credit') ; (ii) Tenant specifically and
unconditionally subordinate the Lease and its rights under the Letter of Credit
to the lieu or charge of the Mortgage; and (iii) Tenant attorn to Lender and its
successor and assigns in the event of the foreclosure or other proceeding to
enforce the Mortgage:

     NOW, THEREFORE, in consideration of the mutual benefits accruing to the
parties hereto and other valuable consideration, the-- receipt and sufficiency
of which axe hereby acknowledged, and in order to induce Lender to enter into
the shave-referenced Loan, Lender and Tenant hereby agree as follow:

     1. Subordination. The Mortgage is and shall unconditionally be and remain
at all times a lien or charge upon the Property prior and superior to the Lease
and any rights of offset, credit, deduction. reimbursement or payment that
Tenant may have in connection with the Letter of Credit under section 19.5 of
the Lease and/or the 'LC Note' (as defined in the Lease), the leasehold estate
created thereby and all rights and privileges of Tenant or any other tenant
thereunder, and tile Lease, the leasehold estate created thereby and ail rights
dad privileges of tenant or any other tenant under the Lease, including, without
limitation, in connection with the

                                      -83-
<PAGE>

Letter of Credit under Section, 19.5 of the Lease and/or the LC !Tote, are
hereby unconditionally subjected and made subordinate to the lien or charge of
the Mortgage.

     2. Lender's Exercise of Remedies . In the event of (a) the institution of
any foreclosure, trustee's sale or other like proceeding, (b) the appointment of
a receiver for the Landlord or the Property, (c) the exercise of rights to
collect rents under tae mortgage or an assignment of rents, (d) the recording by
Lender or its successor or assignee of a deed in lieu of foreclosure for the
property, or (e) any transfer or abandonment of possession of the Property to
Lender or its successor or assigns in connection with any proceedings affecting
Landlord under the Bankruptcy Code, 11 U.3.C. 3 201 et seg. (any each
foreclosure, recording of a deed in lieu of foreclosure, or transfer or
abandonment of the Property referred to in the preceding clauses (a) through W
is hereinafter called a 'Transfer', and Lender of any successor or assignee of
Lender taking title to the Property in connection with a Transfer is hereinafter
called the `Transferee , such Transferee shall ant: (i) be liable far any
damages (including, without limitation, consequential damages) or other relief
or be subject to any offsets, defenses or counterclaims of any kind attributable
Co any act,, omission or waiver (express or implied) of Landlord or any prior
landlord under the Lease, including, without limitation, in connection rites the
Letter of Credit wader Section 19.5 of the Lease and/or the LC Rote, or
otherwise; (ii) be obligated to complete any construction or improvements at the
Property, Premises or elsewhere agreed to he dune by Landlord or any prior
landlord under the Lease, including, without limitation, Landlord's obligations
under that certain Agency Agreement between Landlord and Tenant dated October
10, 1995. and Landlord's obligation of construction contained in Exhibit C to
the Lease, or otherwise, or to reimburse Tenant far any prior construction work
done by Tenant, or be subject to any offsets, defenses or counterclaims
therefor, (iii) be bound by say prepayment by Tenant of more than one month's
installment of rent unless such prepayment has been specifically approved in
writing by Leader, or be liable or responsible for any security deposit or other
sums which Tenant may have paid under the Lease =leas such deposit or other sum
have been physically delivered to Transferee, (iv) be bound by any modification
of or amendment to the Lease, unless such amendment or modification shall have
been approved in writing try Lender. (v) he bound by any notices given by Tenant
to Landlord, (vi) be required after a fire, casualty or condemnation of the
Property or Premise to repair or rebuild the same to the extent that such repair
or rebuilding requires funds in excess of the insurance or condemnation proceeds
specifically allocable to the Premises and arising out of such fire, casualty or
condemnation which have actually been received by Transferee, and then only to
the extent required by the lean of the Lodge. (vii) be responsible to provide
any additional space at the I>roperty oz elsewhere for which Tenant has say
option or right under the Lease. or otherwise, unless Transferee at its option
elects to provide the same, and Tenant hereby releases Transferee from guy
obligation to provide the same, and agrees that Tenant shall have no right to
cancel the Lease and shall possess no right to any claim against Transferee as a
result of the failure to provide any such additional apace, (viii) be liable for
or incur any obligation with respect to any representations or warranties of any
nature set forth in the Lease or otherwise, including, but not limited to,
representations or warranties relating to any intent or patent defects in
construction with respect to the Property or the Premises, Landlord's title or
compliance of the Property or Premises with applicable environmental, building,
zoning or other lays, including, but not limited to, the American with
Disabilities Act and say regulations pursuant thereto, ox (ix) be subject to the
obligation to reimburse or credit against, rent three amounts paid by Tenant to
the issuer of the Letter of Credit, which right in sec forts in Section S(b) of
the Lease:

                                      -84-
<PAGE>

     3. Attornment and Non-Disturbance. Except as set forth in Paragraph 7
above, provided (a) Tenant complies with this Agreement, (b) Tenant is not in
default under the terms of the Lease and no event has occurred which, rich the
passage of time or the giving of notice or both, would constitute a default
cooler the Lease, (c) the Lease is in full force and effect, both as of the date
Lender files a lie ere, or otherwise commences a foreclosure action, or at any
time thereafter, and (d) Tenant shall be is possession of the Premises, no
default under the Mortgage and no proceeding to foreclose the sine rill disturb
Tenant's possession under the Lease and the Lease rill not be affected or cut
off thereby, and notwithstanding any such foreclosure oz other Transfer of the
Property to Transferee, the Lease rill be recognized as a direct lease from
Transferee to Tenant upon the Transfer for the balance of the term thereof. i

     Tenant shall attorn to Transferee, including Lender if Leader became a
Transferee, as the landlord under the Lease. Said attornment is subject to the
limitation of Transferee's obligations set forth in Paragraph 2 above slid shall
be effective and "If-operative without the exception of say farther instruments
upon Transferee succeeding to the interest of the landlord under the Lease.
within ten (10) days after receipt of a written request therefor from
Transferee, Tenant agrees to provide Transferee a written conformation of its
attornment to Transferee and any other matter act forth in this Agreement.
Failure to provide such written confirmation shall, at Transferee's sole option,
constitute a default under the Lease, but failure to receive arch a mitten
confirmation from Tenant shall sot derogate from Tenant's obligations to
Transferee hereunder.

     4. Miscellaneous.

     (a) This Agreement shall inure to the benefit of the parties hereto, their
successors and assigns; provided, however, that in the sorest of the assignment
or transfer of the interest of Transferee, all obligations and liabilities of
Transferee nudes this agreement shall terminate, and theztupan all such
obligations sad liebilitiea shall be the respoRlsibility of the patty to wham
Transferee's ince~est is assigned or transferred: and pzorided further that the
in t sees t o f Tmaat under this Agreement affil not be : e a f gacd or tuns f
esz ed except to the extent the assigmtat of Tenant's interest in the Lease is
permitted under the Lease.

     (b) Tenant acknowledges that is has notice that the Lease and the rent era
all other nuns due thereunder gave been assigned to the Lender as part. of the
security for the note secured by the Mortgage and upon written notice from
Lender of a default under the Mortgage, Tenant shall pay its rent and all other
sums due under the Lease directly to Lewder.

     (c) Tenant covenants and acknowledges that it has certain rights and
options to purchase the Property or the real property of which the Property is a
part, as set forth in Addendum's 4 and 5 of the Lease and elsewhere in the
Lease, and Tenant hereby expressly agrees that such rights shall be subject and
subordinate to the Mortgage and such rights are hereby relived and released as
against Transferee.

     (d) Anything herein or in the Lease to the contrary notwithstanding, in the
event that Transferee shell acquire title to the Property, Transferee shall have
no obligation, nor incur any liability, beyond Transferee's then interest in the
Property, and Tenant shall look exclusively to

                                      -85-
<PAGE>

such interest of Transferee is the Property for the payment sad discharge of any
obligations imposed upon Transferee hereunder or under the Lease, or otherwise,
subject to the limitation of Transferee's obligations provided for in Paragraph
a above.

     (e) This Agreement is the whole cad only agreement between the parties
hereto with regard to the subordination of the Lease to the lien or charge of
the Mortgage, and shall supersede and cancel all other subjection or
subordination agreements, including, but not limited to, those provisions, if
any, contained in the Lease which provide for the subjection or subordination of
said Lease to a deed of trust or to a mortgage or mortgagee. This Agreement may
not be modified is any manner or terminated except by do instrument in writing
executed by the parties hereto.

     (f) This Agreement shall be deemed to have been mace in the state there the
property is located and the validity, interpretation and enforcement of this
Agreement &hall he determined in accordance with the lava of such state.

     (g) In the event any legal action or proceeding is commenced to interpret
or enforce the terms of, or obligations arising oat of, this 1greement, or to
recover damages for the breach thereof, the party prevailing in any such action
or proceeding shall be entitled to recover fray the non-prevailing party all
reasonable attorneys' fees, casts and expenses incurred by the prevailing part;.

     (h) Any notices or communications required or permitted to be given or made
hereunder or under the Lease rich respect to or involving the Lender as a
Landlord's Mortgagee shall be governed by this provision, and the parties hereto
expressly acknowledge that this provision shall control the Lender's obligation
to provide notice. Tenant agrees that Section 19.5(11) of the Lease is amended
as follows: Leader rill asks a good faith effort to provide notice to Tenant in
the treat of default by Landlord, and shall is the Loan Documents list Tenant as
an additional party to receive a courtesy copy of any default notice sent by
Lender to Landlord, but Lender shall not be obligated to provide such notice and
Lender will not be liable for the failure to provide notice to Tenant, nor rill
such failure be a default under the Lease, Notice shall be deemed to be so given
or made when in writing and delivered in person or sent by United States
registered or certified mail, postage prepaid, or by nationally recognized
overnight courier service, directed to the parties at the following addresses or
such other addressee as they may from time to time designate in writing:

     Lender:  AEGON USA Realty Advisors, Inc.
              Attention: Gary Whittington, Esq.
              4333 Edgewrood Road, Y. B .
              Cedar Rapids, TA 57499

     Tenant:  PictureTel Corporation
              Attention: Chief Financial Officer
              The Tower at Northwoods
              222 Rosewood Drive
              Danvers, MA 01973

                                      -86-
<PAGE>

     Notices or communications mailed in the U.S. Mail shall be deemed to be
served on the third business day following mailing, notices or communications
served by hand or by overnight courier shall he deemed served upon receipt.

     The parties hereto represent and warrant that their respective signatories
to this Agreement have been duly authorized by tae Tenant and Lender, as
applicable. i

     (i) In the event Landlord exercises its option to repair the Property in
the event of damage pursuant to Section 16.7 of the Lease. Tenant hereby agrees
to provide an additional estoppel letter to Lender confirming Tenant's
obligation to continue to perform in accordance with the Lease.

     (j) Tenant agrees to establish the collection accost required by section
S(a) of the Lease, at the written request of Lender, so sang as the Loan is
encumbering the Property,

     (k) Tenant also agrees to furnish to Leader all financial information it
must provide to Landlord under section ZO(b) of the Lease.

                                      -87-
<PAGE>

     IN WITNESS WHEREOF, this Agreement has been signed and delivered an of date
and year first above set forth.


                          TENANT:

                          PICTURETEL CORPORATION

                          ------------------------------
                          By: /s/ Lawrence M. Bornstein
                               -------------------------
                          Its: Vice President
                               ---------------

                          LENDER:

                            LIFE INVESTORS INSURANCE
                          COMPANY OF AMERICA

                          ------------------------------
                          By:
                          Its:

                            Consented to by Landlord:

                        100 MINUTEMAN LIMIED PARTNERSHIP

                          By NIUMA - MINUTEMAN, INC.
                          Its General Partner

                          ------------------------------
                          By: /s/ Illegible
                              -------------
                          Its: Illegible
                               ---------

                                      -88-
<PAGE>

STATE OF MASSACHUSETTS  )
                        ) ss.
COUNTY OF Essex         )

     Before me personally appeared the above-named Lawrence M. Bornstein, of
PictureTel corp, as aforesaid, and acknowledged the foregoing instrument to be
his free act and deed as Vice President of Picturetel Corp. and the free act and
deed of Lawrence B. Bornstein.


                                  /s/ Illegible
                                ---------------------------
                                Notary Public
                                My Commission Expires:

STATE OF MASSACHUSETTS  )
                        ) ss.
COUNTY OF Essex         )

     Before me personally appeared the above-named John Kusmiersky, of
Nuna-Minuteman, Inc., as aforesaid, and acknowledged the foregoing instrument to
be his free act and deed as President of Niuro-Minuteman, Inc. and the free act
and deed of John Kusmiersky.


                                  /s/ Illegible
                                ---------------------------
                                Notary Public
                                My Commission Expires:

                                      -89-
<PAGE>

                           TENANT ESTOPPEL CERTIFICATI

                                       OF

                                 [TENANT'S NAME)

T0:  John Hancock Mutual Life Insurance Company ("John Hancock")

RE:   Lease Between and at J.H. Loan No.      [Landlord
      and                                     [Tenant] for space located
      at                                      [Suite No.   ] ("Leased Premises")

Ladies and Gentlemen:

For good and valuable consideration and as an inducement to the making of a
mortgage/deed of trust loan by John Hancock to (Name of Borrower) covering the
Leased Premises, the undersigned, as Lessee under that certain lease ("Lease")
dated [Fill In) made with , as Lessor, hereby certifies that (1) the undersigned
has entered into occupancy of the Lcase4 Premises on contain which Leased
Premises is acknowledged to [rentable/usable] square feet; (2) said Lease is in
full force and effect and has not been modified, supplemented or amended in any
way (except by agreements dated (Fill 1nJ); (3) the same represents the entire
agreement between the panics as to this leasing; (4) the term of the Lease
expires on ; (S) there are no options to extend the term except as follows: ;
(6) there arc no options to purchase the Leased Premises or any rights of first
refusal except as follows: (7) all conditions under the Lease to be performed by
the Lessor prerequisite to the full effectiveness of the Lease have been
satisfied; (8) all of the construction, repair and improvements contemplated by
the Lease to be performed by Lessor have been performed by Lessor and have been
completed satisfactorily in accordance with the terms of the Lease, and that no
other construction, repair and improvements are contemplated under the Lease;
(9) there arc no sums or credits due Lessee from Lessor under the Lease; (10) on
this date there exists no factual circumstance or condition which, with notice
or the lapse of time, or both, would give rise to any obligation on the part of
Lessor, would constitute as a default on the part of Lessor, would constitute a
defense to the enforcement of the Lease by Lessor or an offset against the rents
or other charges due the Lessor under the Lease, or would constitute the basis
for a claim or cause of action against the Lessor-, (11) the minimum rental
obligation under the Lease in effect is SS , the minimum and additional rental
to advance; (12) a security deposit in the amount of S per annum, the current
monthly additional rental is has been paid, and no rental has been paid in was
paid by Lessee to Lessor on , 19 ; (13) the Tenant is not using the Leased
Premises in violation of any applicable laws, rules, ordinance or regulations,
including, but not limited to, any applicable - environmental laws, rules or
regulations (collectively "Laws"), there are no regulatory actions or other
claims pending or threatened against the Tenant in connection with any such
Laws, Tenant has not received any notice from any third party or governmental
authority alleging a violation of any such Laws, and Tenant shall immediately
notify Lessor and John Hancock in writing of any exiseing, pending or threatened
action by any local, state or federal governmental authority and of any third
party claims of which Tenant is aware arising out of the violation or alleged
violation of any Laws; (14) there has not been filed by or against the Tenant
nor, to the best knowledge and belief of Tenant, is there threatened against or
contemplated by Tenant, a petition in bankruptcy,

                                      -90-
<PAGE>

voluntary or otherwise, any assignment for the benefit of creditors, any
petition socking reorganization or arrangement under bankruptcy laws of the
United States or of any state thereof, or any other action brought under said
bankruptcy laws; and (15) to the best of Tenant's knowledge, there has riot been
any assignment, hypothecation or pledge of Lessor's interest in the Lease or
rents accruing under the Lease, other than to John Hancock.

The undersigned, as Lessee, hereby agrees that from this date forward it (i)
will not pay any rent due under the Least more than thirty (30) days in advance
of its due daft; (ii) agrees to give prompt, written notice to John Hancock, as
holder of a mortgage/deed of trust covering the Leased Premises, of any default
of the Lessor in the obligations of Lessor under said Lease, if such default is
of such a nature as to give the Lessee a right to terminate the Lease, to reduce
rent thereunder, or to credit or offset any amounts against future rents, (iii)
will not sock to terminate the Lease or claim a partial or total eviction until
giving such notice and providing John Hancock at (ease sixty (60) days fronvthe
date of such notice to remedy such default, or such reasonable additional time
if the default is of such a nature that it cannot be cured within such sixty
(60) day period, provided John Hancock has commenced the curing of such within
such sixty (60) day period and is diligently pursuing the cure of such default,
provided, however, Lessee hereby acknowledges that John Hancock shall be under
no obligation to remedy such default, (iv) agrees that if John Hancock succeeds
to the interest of the Lessor under the Lease shat John Hancock shall not be
liable for any act or omission of the Lessor or subject to any offset or
defenses which the Lessee might have against the Lessor and shall have no
obligation, nor incur any liability, beyond John Hancock's then interes; in the
Leased Premises and (v) will not modify, amend or cancel the Lease without the
prior written consent of John Hancock.

All notices to John Hancock shall be by certified mail, return rcrcipt requested
addressed to: John Hancock Mutual Life insurance Company, John Hancock Place,
P.O. Box 1 11, Rcal Estate Investment Group, Attention: Mortgage Investments, T-
53, Boston, MA 02117.

The Tenant acknowledges having read this Certificate and understands the
cerlUtcations and representations made herein, and hereby executes this
Certificate, which shall take effect as a sealed instrument, intending reliance
here. ,. by John Hancock. The undersigned signatory represents and warrants that
he or she Is duly authorized to execute this Certificate on behalf of the
Tenant.

                                      -91-
<PAGE>

     IN WITNESS WHEREOF, this Agreement has been signed and delivered as of the
date and year first above set forth.

                         TENANT:

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

                         By:  _______________________________
                              Its:



                         LENDER:


                         JOHN HANCOCK MUTUAL LIFE INSURANCE COMPANY


                         By:  _______________________________
                                 Its:  ___________________________
                                        duly authorized


STATE OF     )
             )  ss.
COUNTY OF    )


     On this ______ day of , ________________ 19 , before me, the undersigned, a
Notary Public in and for the said _____________________, residing therein, duly
commissioned and sworn, personally appeared ____________________, to me
personally known, who by me duly sworn, did say that he/she is a of
_____________________________ (that the seal affixed to the foregoing instrument
is the corporate seal of said corporation, and that said instrument was signed
and sealed in behalf of said corporation-by authority of its Board of Directors)
and as the free act and deed of said corporation.

     IN WITNESS WHEREOF, I have hereunto set my hand and affixed my official
seal in said County the day and year in this certificate first above written.

                                              ------------------------------
                                               Notary Public in and for said
                                              ------------------------------
My commission expires:

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

                                      -92-
<PAGE>

STATE OF       )
               )  ss.
COUNTY OF      )


         On this _______ day of , _________________ 19 , before me, the
undersigned, a Notary Public in and for the said ______________________ ,
residing therein, duly commissioned and sworn, personally appeared
_______________________, to me personally known, who by me duly sworn, did say
that he/she is a of _______________________________ (that the seal affixed to
the foregoing instrument is the corporate seal of said corporation, and that
said instrument was signed and sealed in behalf of said corporation-by authority
of its Board of Directors) and as the free act and deed of said corporation.

         IN WITNESS WHEREOF, I have hereunto set my hand and affixed my official
seal in said County the day and year in this certificate first above written.

                                                ------------------------------
                                                 Notary Public in and for said
                                                ------------------------------
My commission expires:

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

                                      -93-
<PAGE>

TENANTS NAME:



BY: _______________________________          Date:  __________________
    Name:

_________________________________________
Title; Its _____________________President



STATE OF      )
              )  ss.
COUNTY OF     )


         On this ________ day of , ______________ 19 , before me, the
undersigned, a Notary Public in and for the said ____________________, residing
therein, duly commissioned and sworn, personally appeared _____________________,
to me personally known, who by me duly sworn, did say that he/she is a of
______________________________ (that the seal affixed to the foregoing
instrument is the corporate seal of said corporation, and that said instrument
was signed and sealed in behalf of said corporation-by authority of its Board of
Directors) and as the free act and deed of said corporation.

         IN WITNESS WHEREOF, I have hereunto set my hand and affixed my official
seal in said County the day and year in this certificate first above written.

                                               ------------------------------
                                                Notary Public in and for said
                                               ------------------------------
My commission expires:

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

                                      -94-
<PAGE>

                                    EXHIBIT K

                               THE "PROJECT AREA"

                                      -95-
<PAGE>

$7,300,000                                                Andover, Massachusetts
                                                                 August 26, 1996
                                 PROMISSORY NOTE

         This Promissory Note is entered into pursuant to Section 24.17(fj of
that certain Lease, dated as of August 26, 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, up to a maximum of $7.3 Million, 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 The Bank of Nova Scotia or one of the Undersigned's
other 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 nn 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 the same rate payable on the
first mortgage loan encumbering the "Premises" (as defined in the Lease);
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 shill 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 !he amount payable by it under the

                                      -96-
<PAGE>

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
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) above still will apply. .

         The Undersigned may prepay the principal amount outstanding in whole or
in part without penalty. The Undersigned 21aj 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.

                                      -97-
<PAGE>

         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.

         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: /s/ John Kusmiersky
                                    -----------------------------
                                    John Kusmiersky, President
                                    Hereunto Duly Authoirzed

                                      -98-
<PAGE>

                                   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 .

                                      -99-
<PAGE>

                                   EXHIBIT "M"

     8.15 PictureTe1 Letter of Credit. Notwithstanding anything to the contrary
contained herein, it is understood and agreed with respect to the PictureTel
Letter of Credit that:

     (a) if the PictureTel Letter of Credit is not renewed at least thirty (30)
days prior to its expiration date, Lender soall always be entitled to draw on
the whole amount thereofand hold the proceeds thereof in escrow as substitute
collateral, drawable under the same circumstances that Lender is permitted to
draw under the PictureTel Letter of Credit, except that if, within thirty (30)
days after Lender notifies Borrower that Lender has so drawn upon the PictureTel
Letter of Credit, a substitute letter of credit from an issuer and in amount,
form and substance satisfactory to Lender has been deposited with the Lender,
then Lender shall return such proceeds to Key Tenant;

     (b) prior to Permanent Commitment Approval and Final Plan Approval, Lender
shall be entitled to draw on the PictureTel (.otter of Credit upon the
occurrence on any Event of Default (except as otherwise provided in Section
2.06(a) of the Mortgage with respect to an Event of Default under 7.01(j) of
this Agreement) and to apply the proceeds thereof tc) the Secured Obligations in
such order as fender determines;

     (c) prior to Permanent Commitment Approval and Final Plan Approval if all
Loan proceeds that the bender is obligated to advance pursuant to Section ?.04
prior to Permanent Commitment Approval and Final Plan Approval have been
advanced, then lender shall be entitled to draw on the Picture gel letter of
Credit and use the proceeds thereon to complete the Improvements in the same
manner and in progress payments as the Loan Advances under this Agreement would
have been disbursed-,

     (a) upon Permanent Commitment Approval and Final Plan Approval and provided
there exists no Event of Default or Potential Default, Subject to the terms and
conditions hereof generally governing the making of Loan Advances, Borrower
shall have the right to requisition and Lender shall be obliged to fund
available Loan proceeds for the purpose of refunding to Key Tenant such amounts
previously drawn under the PictureTel Letter of Credit as may have been applied
in lieu of Loan proceeds to complete the Improvements as otherwise provided in
this Agreement. In connection with any such disbursement to repay Key Tenant and
subject to the terms and conditions hereof generally governing the making of
Loan Advances, Borrower may draw upon the Interest Reserve category of the
Project Budget and Lender shall be obliged to fund available Loan proceeds
(subject to any adjustments to the Interest Reserve as provided in Section 2.05
above) in order to pay to the Key Tenant interest on any such refunded amount at
a rate equal to the EIJRO Rate Option under the Note for the period that such
refunded funds were outstanding;

     (b) after Permanent Commitment Approval and Final Plan Approval should the
Permanent Commitment he later terminated or amended without Lender's prior
written consent or should the Permanent Lender fail or refuse to fund the
Permanent Commitment in accordance with its terms and the Tri-Party Agreement,
Lender shall he entitled to draw upon 'he PictureTel Letter of Credit and apply
the proceeds thereof to complete the Improves,,ents in the same r inner and in
Progress Payments as the Loan Proceeds under this Agreement would have been

                                     -100-
<PAGE>

disbursed it the Permanent Commitment had been in force (provided, however, that
if the Permanent Commitment shall be terminated by the Borrower or if Borrower
shall tail to satisfy any condition to the funding of the Permanent Commitment
on or before the Maturity Date, then Lender may also elect to draw and apply the
proceeds of the PictureTel Letter of Credit to reduce the principal balance of
the Loan to $13,000,000) to $11,400,000);

     (c) except as provided to the contrary in (e) above, after Permanent
Commitment Approval and Final Plan Approval, provided that there shall exist no
default of Borrower under the Permanent Commitment, and prior to completion of
the Improvements, Lender shall be entitled tc draw upon the PictureTel Letter of
Credit and apply the proceeds to the Secured Obligations in such order as Lender
determines only upon a default by Key Tenant under the Key Lease after notice
thereof and lapse of applicable cure periods thereunder;

     (d) before Permanent Commitment Approval and Final Plan Approval and before
completion of the Improvements, the face amount of the PictureTel Letter of
Credit shall be reduced from time to time by an amount equal to each draw under
said Letter of Credit. Upon Permanent Commitment Approval and Final Plan
Approval and provided Key Tenant has been reimbursed for previous draws under
the Picture Tel Letter of Credit as set forth in subsection (d) above, the
PictureTel Letter of Credit Shall be increased to $7,800,000 subject only to the
reductions provided under subsection (h) below; and

(e) after Permanent Commitment Approval and Final Plan Approval and after
completion of the improvements, the face amount of the PictureTel Letter of
Credit shall he subject to reduction on an annual basis as set forth in Exhibit
8.15 attached hereto and Lender shall be entitled to draw upon the Picture-Fel
fetter of Credit and apply the proceeds thereof to the Secured Obligations in
such order as lender determines only upon a default by Key Tenant under the Key
Lease after notice thereof and lapse of applicable cure periods thereunder or
upon the occurrence 4an Event of Default.

                                     -101-
<PAGE>

                                  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.

                                     -102-
<PAGE>

                                   ADDENDUM #2

                                EXTENSION OPTIONS

     2. 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. 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 (1 _5) 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 my 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 he 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: (a) 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); and (b) on the date
that Tenant validly exercises the first Extension Option Tenant is in full
occupancy of and conducting material business from the Building, at such time
there is no sublease of the Premises (except to a Permitted Soblessee), and
together with its exercise notice Tenant delivers to Landlord an unconditional
and irrevocable written waiver of its right to sublease all or any portion of
the Premises (except to a Permitted Sublessee) or to enter into any agreement
regarding any sublease (except with a Permitted Sublessee) for the balance of
the initial term of this Lease. 1f the conditions in the previous sentence have
not been satisfied with respect to any particular Extension Option, that
Extension Option and all subsequent Extension Options shall, at Landlord's
election, lapse and become null and void. Tl ME 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.

                                     -103-
<PAGE>

                                  ADDENDUM #3

                                  NETPROCEEDS

     3. 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 nit 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 pail by Tenant or its Affiliates; amounts drawn under the
Letter of Credit or the applications) 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 Net Proceeds distributed or distributable to Landlord pursuant to Section
3 below.

     4. 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
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 these 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

                                     -104-
<PAGE>

"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 (I%), 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.

     5. 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 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 ftlll; 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 ('/~) of all Net Proceeds available for distribution at the same times
as Net

                                     -105-
<PAGE>

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 he 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 he conducted at Tenant's cost and expense and shall be
conducted only by Tenant or its designated professional representatives.

     6. 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 bona fide sale or other conveyance by Landlord of
all or any portion of the Premises, or any interest therein (which shall not he
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 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 or
a sale associated with an "LC Return" as defined in Subsection (d) below).

     (d) The sale or other conveyance by Landlord of all or any portion of the
Premises or any interest therein, which sale or conveyance is not prohibited
under this Lease, provided that prior to or on or about the closing of such sale
or conveyance, the Letter of Credit is returned to Tenant undrawn (or if drawn
upon, with any outstanding LC Advances repaid in full) and with no obligation on
the part of Tenant to supply additional Letters of Credit under this Lease, and
in such event Tenant shall not have any continuing rights nor shall Landlord
have any continuing obligations with respect to Net Proceeds, whether received
by Landlord in connection with such

                                     -106-
<PAGE>

sale or conveyance or otherwise. The return of the Letter of Credit to Tenant as
described above is called the "LC Return."

     4. Unaffected Parties. Notwithstanding anything to the contrary, Tenant's
rights and Landlord's obligations under this Addendum will not he 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 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.

     5. 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 exectited 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.

                                     -107-
<PAGE>

                                  ADDENDUM #4

                        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 initial Lease term (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 sixty (60) days after delivery of the Offer Notice, Tenant shall
notify Landlord in writing that it unconditionally elects one of the two (2)
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) [INTENTIONALLY OMITTED]

         (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 Existing Lease Election. At
Landlord's election, all of Tenant's rights and Landlord's obligations under or
in connection with this Addendum 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.

     2. Purchase Election. If Tenant validly exercises the Purchase Election,
then Landlord shall sell and Tenant shall purchase the Premises on the following
terms and conditions:

     (d) The Offer Price for the Premises shall be as specified in the Offer
Notice, and 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,

                                     -108-
<PAGE>

as of the closing Tenant shall, as and to the extent set forth in the Offer
Notice, either repay in full all mortgage loans) 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
lenders) 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.

     (e) The closing will occur at a location in Massachusetts and on a date
specified by Landlord pursuant to written notice to Tenant, which date will be
at least three (3) months but no more than six (6) months after the Purchase
Election. 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).

     (f) 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 sub ~
ject 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
(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 buildings) or the
enlargement of the Building per this Lease, will nest be deemed to be violations
of this restriction). If this restriction is violated after the exercise of the
Purchase Election, Tenant shall have the right to terminate that Purchase
Election without liability and receive any deposit back. Notwithstanding the
foregoing, even if Tenant has validly exercised a Purchase Election, Tenant
shall have the right to terminate that Purchase Election without liability
(except for Landlord's out-of-pocket costs) and shall not be required to close
the

                                     -109-
<PAGE>

purchase if, after the exercise of the Purchase Election 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 judgment 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 Election: Landlord will continue the process of repairing
or rebuilding as otherwise required in this Lease until the closing date under
the Purchase Election; Tenant will be deemed to have waived its right to
terminate this Lease under Article 16, and its right to terminate the Purchase
Election 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.

     (g) 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 tinder or in connection with this Lease and/or the Premises (except
as set forth in the last sentence of Subsection (e) 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 and after the closing, Tenant shall indemnify, defend anc:
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 (e) below).

     (h) Time is of the essence in this Addendum. If Tenant defaults hereunder
after the closing under a Purchase Election 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 Election or any closing
as a result thereof shall not relieve Tenant or Landlord from any Liabilities
for any defaults under this Lease, nor will

                                     -110-
<PAGE>

they extinguish Liabilities for any indemnities or other obligations that
survive pursuant to the terms of the rest of this Lease or this Addendum.

3.  [INTENTIONALLY OMITTED]

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

     (i) 1f Tenant validly elects (or is deemed to have elected) the Existing
Lease Election, then for the next twelve (I2) 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 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
Existing Lease Election in accordance with the procedures established in Section
1 above, except that Tenant will have forty-five (45) days, and not sixty (60)
days, within which to respond to Landlord's new Offer Notice. If within twelve
(12) months after Tenant validly elects (or is deemed to have elected) the
Existing Lease Election in accordance with this Section 3 Landlord has not
executed a binding agreement to so] l 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.

     (j) If Tenant validly elects (or is deemed to have elected) 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 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:

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

                                     -111-
<PAGE>

     (l) 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

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

     (n) At the end of the initial Lease term.

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, VTEL Corp., and Sony.

7. [INTENTIONALLY OMITTED]

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 onl~: if Tenant has not become a Released Assignor in connection with its
valid assignment of this Lease.

                                     -112-
<PAGE>

                         CONTINUING GUARANTY OF SUBLEASE

     1. Definitions. "Guarantors" means CABLETRON SYSTEMS, INC., a Delaware
corporation. "Sublease" means the Sublease, dated N 4 , 1998, between Sublessor
and Sublessee with respect to any part of or space in the project now commonly
known as 50 MINUTEMAN ROAD located in ANDOVER, MASSACHUSETTS, and all existing
and future amendments to that Sublease and agreements related thereto and any
other sublease of 50 MINUTEMAN ROAD between Sublessor and Sublessee. "Sublessee"
means CABLETRON SYSTEMS SALES AND SERVICE INC., and its successors, assignees,
sublessees, other transferees, heirs and representatives. "Sublessor" means
PICTURETEL CORPORATION and its successors, assigns and other transferees. Other
terms used in this Guaranty have the same meanings as those used in the
Sublease.

     2. Guaranty. For Ten Dollars ($10.00) and other good and valuable
consideration, the receipt and sufficiency of which is acknowledged, Guarantors
irrevocably and unconditionally guaranty the timely payment, performance and
observance of all of Sublessee's obligations, liabilities, representations and
warranties under the Sublease, and agree to pay all amounts due under the
Sublease to the party or parties entitled thereto (whether by acceleration or
otherwise) and indemnify and defend Sublessor and any other parties entitled
thereto and hold Sublessor and any other parties entitled thereto harmless from
all other costs, damages, claims and liabilities of any type (including, without
limitation, attorneys' fees and costs) arising from or in connection with
Sublessee's default under the Sublease, Guarantors' breach of this Guaranty, and
any disputes, suits or actions among Guarantors and any other persons or
entities. Payment and performance due from Guarantors shall be rendered
immediately without offset, deduction or counterclaim.

     3. Continuing Guaranty. This is a continuing guaranty of payment and
performance, not merely of collection, and is an agreement of surety.
Guarantors' obligations are separate and distinct from Sublessee's obligations
under the Sublease and Guarantors' obligations under any other guaranties that
have been or may be made by Guarantors in favor of Sublessor, and are primary
and direct. All Guarantors (if more than one) are jointly and severally liable.
Guarantors' obligations will continue and will not be diminished, affected or
discharged in any way, whether or not: (a) Sublessor or Sublessee sells,
assigns, sub-subleases or otherwise Transfers all or any portion of the Premises
or its interest under the Sublease; (b) the Sublease terminates or expires or is
amended or extended or the Premises is vacated or surrendered; (c) either party
grants extensions or waivers under the Sublease or exercises or exhausts any
rights or remedies under the Sublease; (d) Sublessor obtains additional
guarantors hereunder or otherwise or security for the obligations of Sublessee
or Guarantors, or releases or discharges any of the Guarantors, any other
guarantors or any security, or proceeds or fails to proceed against Sublessee,
any of the Guarantors, any other guarantors, any other person or entity~ or any
security, in any manner or priority; (e) Guarantors' obligations are larger or
more burdensome than Sublessee's; or (f) Sublessee is relieved of any liability
or obligation under the Sublease or all or any part of the Sublease is or
becomes void, invalid, or unenforceable or is terminated, by agreement,
operation of law or otherwise, including, without limitation, by reason of
bankruptcy, insolvency, reorganization, assignment, arrangement, readjustment,
composition, liquidation, receivership or other similar proceeding, disability
or incompetency, lack of authority or capacity, impossibility, illegality,
duress, coercion or otherwise.

                                     -113-
<PAGE>

     4. Waivers. Guarantors waive and will not assert or claim: (a) demand,
presentment and protest; (b) notice of any kind, including, without limitation,
notice of default under or the amendment of the Sublease and notice of any of
the other matters in Article 3 above; (c) any right to require Sublessor or any
other party to proceed in any manner, or exercise, fail to exercise or exhaust
any rights and remedies, under the Sublease, this Guaranty or any other
agreements, or against Sublessee, any of the Guarantors, any other guarantors,
any security, or any other person or entity; (d) any defense arising out of the
absence, impairment, election of remedies or loss of any rights or remedies of
Guarantors, including, without limitation, rights of reimbursement or
subrogation, whether resulting from Sublessor's conduct or otherwise; (e) any
deduction, counterclaim or offset, any defense based on the statute of
limitations, and any claim or defense based on any of the matters described in
Article 3 hereof; and (f) any other remedies, defenses or benefits Guarantors
may derive from any law or decision benefiting or protecting a guarantor or
surety, to the extent waivable.

     5. Sublessor's Reliance. Any obligations created by or on behalf of
Sublessee or those purporting to act on Sublessee's behalf may be relied on by
Sublessor and are guaranteed under this Guaranty. Guarantors are solely
responsible for informing themselves about Sublessee's financial condition, the
likelihood of Sublessee's default, the terms of the Sublease, and all other
matters.

     6. Miscellaneous. To be effective, all waivers by Sublessor must be in
writing, specify the act or omission waived, and be signed by Sublessor, and all
amendments to this Guaranty must be signed by Sublessor and Guarantors and
consented to by the Landlord under the Main Lease. This Guaranty is the entire
agreement between Guarantors and Sublessor regarding this subject matter and
supersedes all prior agreements and understandings, oral or written, except for
the Consent Letter, dated as of the date hereof, among Sublessor, Sublessee,
Guarantors and 50 Minuteman Limited Partnership and the "Non-Disturbance
Agreement" (as defined therein). Each Guarantor represents and warrants that all
information, financial or otherwise, that has been or will be furnished to
Sublessor by or on behalf of Guarantor will be true and accurate in all material
respects and not incomplete or misleading in any way, and that he, she or it is
gaining a material benefit from the Sublease. Until and unless all of
Sublessee's obligations and liabilities under the Sublease and all of
Guarantors' obligations and liabilities hereunder have been fully paid and
performed, Guarantors will have no right of subrogation against Sublessee,
Guarantors subordinate all present and future obligations and liabilities due to
them from Sublessee to Guarantors obligations and liabilities hereunder, and
Guarantors will not enforce any rights or remedies they may have against
Sublessee. Sublessor has not made and Guarantors are not relying on any
representations or warranties of any type. This Guaranty will be governed and
enforced under Massachusetts law. As a further inducement to Sublessor to enter
into the Sublease, Guarantors waive trial by jury in any action or proceeding in
connection with this Guaranty. Guarantors irrevocably submit to and agree not to
contest the personal and other jurisdiction of the state and federal courts
located in Massachusetts to adjudicate all matters in connection with the
Sublease or involving Sublessor or Guarantors in any way, and Guarantors agree
not to seek a change of venue or to bring any claim, action or proceeding in any
other courts. If any portion of this Guaranty is invalid or unenforceable, the
remainder of this Guaranty will not be affected and it will be valid and
enforceable to the greatest extent permitted by law. Time is of the essence. If
Sublessor elects or is required to give a notice to a Guarantor, notice may be
given by personal delivery, mail, overnight courier

                                     -114-
<PAGE>

or electronic means (such as telecopier), or in any other manner as may be
permitted by law, and will be deemed given upon delivery (or, if mailed, four
days after it is deposited with the U. S. Mail) to that Guarantor's address as
set forth below, or to such other address as that Guarantor may previously have
specified in writing to Sublessor. Each Guarantor specifically waives personal
service of any summons, complaint or other process and agrees that service may
be made by Registered Mail, Return Receipt Requested, postage pre-paid, directed
to it in care of the address below, or by any other method if such other method
is permitted under applicable laws. This Guaranty is binding on Guarantors and
their successors, assigns, transferees, heirs, representatives and estates, and
inures to Sublessor's benefit. This Guaranty may be executed in counterparts.

     IN WITNESS WHEREOF, intending to be legally bound hereby, Guarantors have
executed this Guaranty under seal, and this Guaranty is effective as of the date
of the Sublease.

ADDRESS:                                     "GUARANTORS"

35 Industrial Way Rochester,                  CABLETRON SYSTEMS, INC.
New Hampshire 03866
Attn: Legal Department                        By: /s/ Craig R. Benson
                                                 --------------------------
                                                 Name: Craig R. Benson
                                                 Title: President
                                                 Authorized Signature


                                              By:  /s/ David Kirkpatrick
                                                  ---------------------------
                                                  Name: David Kirkpatrick
                                                  Title: Chief Financial Officer
                                                  Authorized Signature

                                     -115-