<PAGE>

                                                                    EXHIBIT 10.1

                                    SUBLEASE

     THIS SUBLEASE (the "Sublease") is dated as of the twentieth (20/th) day
of December 2002, by and between NaviPath, Inc., a Delaware corporation and
formerly known as NaviNet, Inc. ("Sublandlord"), and NaviSite, Inc., a Delaware
corporation ("Subtenant").

                                    RECITALS

     WHEREAS, pursuant to that certain Lease dated as of November 30, 1999, by
and between William J. Callahan and William J. Callahan Jr., as they are
trustees of Andover Park Realty Trust ("Prime Landlord"), as landlord, and
Sublandlord, as tenant, (the "Prime Lease"), a copy of which Prime Lease is
attached hereto as Exhibit A, Sublandlord leased from Prime Landlord certain
premises located in the building commonly known as 800 Federal Street, Andover,
MA (the "Building") containing approximately 52,234 rentable square feet of
space, as more fully described in the Prime Lease (the "Original Premises");
and

     WHEREAS, Subtenant desires to sublease from Sublandlord a portion of the
Original Premises described in the Prime Lease containing approximately 16,500
rentable square feet and more particularly shown on the floor plan attached
hereto as Exhibit B (the "Subleased Premises"), and Sublandlord is willing to
sublease the Subleased Premises to Subtenant on the provisions, covenants and
conditions hereinafter set forth.

                                    AGREEMENT

     NOW, THEREFORE, in consideration of Ten and 00/100 Dollars ($10.00), the
mutual covenants made herein, and other consideration, the receipt and
sufficiency of which are hereby acknowledged and agreed, Sublandlord hereby
subleases to Subtenant and Subtenant hereby takes and hires from Sublandlord the
Subleased Premises, on the terms and conditions set forth below:

     1. Defined Terms. All terms defined in the Prime Lease and used herein
shall, unless otherwise defined herein, have the meanings ascribed to such terms
in the Prime Lease.

     2. Term. The term of this Sublease (the "Sublease Term") shall commence on
the later of (i) January 31, 2003 and (ii) the date an occupancy certificate is
received (the "Sublease Term Commencement Date"), and shall continue until March
31, 2006, unless sooner terminated in accordance with the provisions of this
Sublease. Notwithstanding the foregoing sentence, if an occupancy certificate is
not received prior to February 17, 2003, Subtenant shall have the right to
terminate this Sublease by delivering written notice thereof to Sublandlord
prior to receipt of the occupancy certificate (the "Sublease Termination
Notice") and if the occupancy certificate is obtained prior to January 31, 2003,
then Subtenant can move into and occupy the Subleased Premises on or any time
after the date the occupancy certificate is obtained. Sublandlord shall exercise
commercially reasonable efforts to obtain an occupancy certificate prior to
January 31, 2003. In the event Subtenant delivers the Sublease Termination
Notice to Sublandlord, neither of the parties shall have any liability to the
other party whatsoever with respect to this Sublease or matters relating to this
Sublease. Subject to first receiving Prime Landlord's written consent to the
Sublease as described in Section 18(1) hereof, Sublandlord hereby grants to
Subtenant the right to enter the Subleased Premises (i) to install equipment as
early as January 1, 2003 and (ii) to move

<PAGE>

office supplies and files prior to the Sublease Term Commencement Date, but not
earlier than January 24, 2003. Subtenant shall be responsible for such equipment
and office supplies and files and any damage or loss thereto.

     3. Delivery. The Subleased Premises shall be delivered to Subtenant,
broom-clean and free of all occupants but otherwise "as-is, where-is and with
all faults", without representation or warranty, express or implied, other than
those contained in the Prime Lease and Subtenant hereby waives, disclaims and
renounces any representation or warranty other than those contained in the Prime
Lease.

     4. Sublandlord's Improvements. Sublandlord, at Sublandlord's cost, shall
provide for the construction of a full-height demising wall separating the
Subleased Premises from the adjacent area and the construction of a multi-tenant
lobby (collectively, "Sublandlord's Improvements"). Each of Sublandlord and
Subtenant acknowledges that the Basic Rent described in Section 5 below includes
amounts for the reimbursement of Sublandlord for the full cost of Sublandlord's
Improvements, such amounts being fully amortized over the Sublease Term. If
Subtenant commits a default (as defined in section 17 below) under this Sublease
and does not cure such default during the applicable cure or grace period, if
any, the amounts paid by the Sublandlord for Sublandlord's Improvements and not
yet recovered by Sublandlord through receipt of Basic Rent payments shall be
fully and immediately accelerated, due and payable in cash by Subtenant to
Sublandlord; provided, however, Sublandlord shall have the right in its sole
discretion to offset the total accelerated amounts outstanding against any
amounts owed by Sublandlord's parent company, CMGI, Inc., to Subtenant under
that certain SiteHarbor Services Agreement, with an effective date of March 7,
2000, by and between CMGI, Inc. and NaviSite (as amended from time to time and
any successor agreements thereto relating to web hosting and other such services
provided by Subtenant to CMGI, Inc. in the ordinary course of business, the
"SiteHarbor Agreement"). Subtenant agrees and covenants that after the date
hereof, it will not request or require any change orders with respect to the
Sublandlord's Improvements and that it will not take any action or fail to take
any actions which would cause a delay in the completion of the Sublandlord's
Improvements.

     5. Basic Rent. Subtenant shall pay to Sublandlord, in advance, in monthly
installments, without withholding, offset or reduction, Basic Rent at the rate
of $9.00 per rentable square foot per year (i.e., $12,375 per month) from the
Sublease Term Commencement Date through the end of the Sublease Term. Basic Rent
for any partial calendar months at the beginning or end of the Sublease Term
shall be prorated on a daily basis. Subtenant acknowledges that Sublandlord's
payments of Basic Rent under the Prime Lease are paid to Prime Landlord on the
first day of each calendar month during the Term and Subtenant therefore
covenants and agrees that its payments of Basic Rent hereunder shall be paid to
Sublandlord at least three (3) business days prior to the first day of each
calendar month. Subtenant shall deliver to Sublandlord upon execution of this
Sublease first month's rent for February 2003 in the amount of $12,375. In the
event the Subtenant delivers the Sublease Termination Notice in accordance with
Section 2, Sublandlord shall promptly return the first month's Basic Rent to
Subtenant.

     6. Additional Rent. Subtenant acknowledges that pursuant to the Prime
Lease, Sublandlord is obligated to pay to Prime Landlord additional rent on
account of Common Expenses (as defined in the Prime Lease), which includes,
among other things, common area maintenance and electricity. In lieu of
Subtenant paying or being responsible to pay any share or part of any Common
Expenses, taxes, betterments, assessments, utilities, water, sewer or other
charges,

                                       -2-

<PAGE>

including those items specifically excluded from Common Expenses which are due
or may become due by the Sublandlord as tenant under the Prime Lease, Subtenant
shall pay to Sublandlord, in advance, in monthly installments, without
withholding, offset or reduction, Additional Rent at the rate of $6.00 per
rentable square foot per year (i.e. $8,250 per month) for the period from the
Rent Commencement Date through the end of the Sublease. Additional Rent for any
partial calendar months at the beginning or end of the Sublease Term shall be
prorated on a daily basis. Subtenant acknowledges that Sublandlord's payments of
additional rent under the Prime Lease are paid to Prime Landlord on the first
day of each calendar month during the Term and Subtenant therefore covenants and
agrees that its payments of Additional Rent hereunder shall be paid to
Sublandlord with the Basic Rent at least three (3) business days prior to the
first day of each calendar month. Subtenant shall deliver to Sublandlord upon
execution of this Sublease first month's Additional Rent for February 2003 in
the amount of $8,250. In the event the Subtenant delivers the Sublease
Termination Notice in accordance with Section 2, Sublandlord shall promptly
return the first month's Additional Rent to Subtenant.

     7. Use. The Subleased Premises shall be used for those uses described in
Section 5 of the Prime Lease and for no other uses.

     8. Prime Lease. Subtenant agrees that it will do nothing in, on or about
the Subleased Premises which would result in the breach by Sublandlord of its
undertakings and obligations under the Prime Lease. Except for the following
provisions, this Sublease shall be subject to and on all of the terms and
conditions as are contained in the Prime Lease and the provisions of the Prime
Lease are hereby incorporated into this Sublease as if Sublandlord were the
landlord thereunder and Subtenant the tenant thereunder with regard to the
Subleased Premises only:

          (a) The defined economic terms in the Prime Lease for "Basic Rent,"
     "Additional Rent", "Security Deposit" and the like are inapplicable;

          (b) Section 3 off the Prime Lease (relating to Construction by
     Landlord) is inapplicable;

          (c) Section 6 of the Prime Lease (relating to Basic Rent and
     Additional Rent) is inapplicable;

          (d) Section 7 of the Prime Lease (relating to Taxes) is inapplicable;

          (e) Section 9 of the Prime Lease (relating to Utilities) is
     inapplicable;

          (f) Section 24 of the Prime Lease (relating to Extension of Term) is
     inapplicable;

          (g) Section 35 of the Prime Lease (relating to Security Deposit) is
     inapplicable;

          (h) Except as set forth in Section 16 below, Section 36 of the Prime
     Lease (relating to Signage) is inapplicable; and

          (i) Section 37 off the Prime Lease (relating to Y2K) is inapplicable.

     Where appropriate, references to "Landlord" in the Prime Lease shall be
deemed to mean "Sublandlord" hereunder, references to "Tenant" in the Prime
Lease shall be deemed to mean

                                       -3-

<PAGE>

"Subtenant" hereunder and references to the "Premises" in the Prime Lease shall
be deemed to mean "Subleased Premises" hereunder, it being understood and agreed
that Sublandlord will not be acting as, or assuming any of the responsibilities
of, Prime Landlord, and all references in the Prime Lease to Landlord-provided
services or Landlord insurance requirements, and any other references which by
their nature relate to the owner or operator of the Building, rather than to a
tenant of the Building subleasing space to a subtenant, shall continue to be
references to Prime Landlord and not to Sublandlord.

     9. Subtenant's Covenants. Except as otherwise provided in this Sublease,
Subtenant covenants to Sublandlord to perform all of the covenants and
obligations to be performed by Sublandlord as Tenant under the Prime Lease as
the same relate to the Subleased Premises and to comply with this Sublease and
the applicable provisions of the Prime Lease, as modified by this Sublease, in
all respects. If Subtenant shall fail to make any payment or perform any act
required to be made or performed by Sublandlord under the Prime Lease pursuant
to Subtenant's assumption of Sublandlord's obligations thereunder as they relate
to the Subleased Premises, and such default is not cured by Subtenant within two
(2) days prior to the expiration of such Prime Lease cure period, Sublandlord,
without waiving or releasing any obligation or default hereunder, may (but shall
be under no obligation to) make such payment or perform such act for the account
and at the expense of Subtenant, and may take any and all such actions as
Sublandlord in its sole discretion deems necessary or appropriate to accomplish
such cure. If Sublandlord shall reasonably incur any expense in remedying such
default, Sublandlord shall be entitled to recover such sums upon demand from
Subtenant as Additional Rent under this Sublease. Subtenant shall not make,
install, construct, remove, demolish or otherwise alter the Subleased Premises
without first receiving the written consent of the Prime Landlord and the
Sublandlord.

     10. Sublandlord's Covenants. Sublandlord covenants to Subtenant to perform
all of the covenants, obligations, terms and provisions required of it under the
Prime Lease and to promptly pay when due all Basic Rent, Additional Rent or
other charges due and accruing to Prime Landlord under the Prime Lease.
Sublandlord will use reasonable efforts to enforce on behalf of Subtenant
Sublandlord's rights under the Prime Lease. Nothing contained in this Sublease
shall be construed as a guarantee by Sublandlord of any of the obligations,
covenants, warranties, agreements or undertakings of Prime Landlord in the Prime
Lease. If Sublandlord shall fail to make any payment or perform any act required
to be made or performed by Sublandlord under the Prime Lease, and such default
is not cured by Sublandlord prior to the expiration of such Prime Lease cure
period, Subtenant, without waiving or releasing any obligation or default
hereunder, may (but shall be under no obligation to) make such payment or
perform such act for the account and at the expense of Sublandlord, and may take
any and all such actions as Subtenant in its sole discretion deems necessary or
appropriate to accomplish such cure. If Subtenant shall reasonably incur any
expense in remedying such default, Subtenant shall be entitled to recover such
sums along with any payment made pursuant to the Prime Lease upon demand from
Sublandlord as an offset against payments due Sublandlord under this Sublease.

     11. Indemnification. Subtenant shall indemnify Sublandlord and hold
Sublandlord harmless from and against any and all claims, demands suits,
judgments, liabilities, costs and expenses, including reasonable attorneys'
fees, arising out of or in connection with Subtenant's use and possession of the
Subleased Premises, or arising out of the failure of Subtenant, its agents,
contractors or employees to perform any covenant, term or condition of this
Sublease or of the Prime Lease to be performed by Subtenant hereunder.
Sublandlord shall indemnify Subtenant and

                                      -4-

<PAGE>

hold Subtenant harmless from and against any and all claims, demands suits,
judgments, liabilities, costs and expenses, including reasonable attorneys'
fees, arising out of or in connection with Sublandlord's use and possession of
the Premises, Building and Property excluding the Subleased Premises, and/or
arising out of the failure of Sublandlord, its agents, contractors or employees
to perform any covenant, term or condition of the Prime Lease as it relates to
the Premises, Building and Property excluding the Subleased Premises, and/ or
this Sublease to be performed by Sublandlord hereunder.

     12. Assignment and Subletting. Subtenant shall not assign this Sublease or
sublet the Subleased Premises in whole or in part without Prime Landlord's and
Sublandlord's prior written consent, which consent shall not be unreasonably
withheld or delayed, nor shall Subtenant participate in any transaction which
would constitute an assignment or sublet under the terms of Section 19 of the
Prime Lease. In connection with a sub-sublease consented to by Prime Landlord
and Sublandlord, Subtenant will pay to Sublandlord 50% of the amount by which
the sub-sublease rent and other consideration paid or payable exceeds the amount
of Basic Rent and Additional Rent paid to Sublandlord for such same space by
Subtenant under this Sublease.

     13. Security Deposit. Sublandlord and Subtenant agree that Subtenant shall
not be required to deliver to Sublandlord a security deposit. Upon the
occurrence of a default by Subtenant, after expiration of any applicable grace
or cure periods, Sublandlord shall have the right in its sole discretion to
offset the total amounts then due by Subtenant to Sublandlord as a result of the
default against any amounts owed by CMGI, Inc. to Subtenant under the SiteHarbor
Agreement. In the event amounts owed by CMGI, Inc. to Subtenant under the
SiteHarbor Agreement are not sufficiently large enough to offset all amounts
potentially owed by Subtenant to Sublandlord hereunder, Subtenant and
Sublandlord shall negotiate in good faith to provide Sublandlord with
additional security against a Subtenant default.

     14. Brokers. Subtenant represents and warrants to Sublandlord that it has
not dealt with and does not have an agreement with any broker in connection with
this Sublease and agrees to indemnify, defend and hold Sublandlord harmless from
and against any breach of this representation and warranty. Sublandlord agrees
to indemnify, defend and hold Subtenant harmless from and against any payment or
obligation to pay any broker fee, commission or expense associated with this
Sublease from Cornerstone Advisory Services LLC and any other broker with which
Sublandlord or CMGI, Inc. has an agreement.

     15. Insurance. Subtenant shall comply with all insurance requirements of
the Prime Lease, including the provisions of Section 8 thereof. Subtenant shall
deliver to Sublandlord certificates which evidence such insurance prior to the
Sublease Term Commencement Date, and thereafter as required under the Prime
Lease, and shall name in all such insurance policies both the Prime Landlord and
Sublandlord as additional insureds thereunder.

     16. Signage. Subject to the prior written approval from Prime Landlord and
Sublandlord, Subtenant, at Subtenant's sole cost and expense, shall be allowed
to place signage on the Subleased Premises, the property and/or Building.
Sublandlord hereby acknowledges that it presently intends to sublease to a third
party or third parties that portion of the Original Premises not subleased
hereunder. Sublandlord hereby grants to Subtenant the right to Sublandlord's
signage rights pursuant to Section 36 of the Prime Lease subject to the
following: If a party (a "New Subtenant") subleases all or a portion of the
Original Premises not subleased hereunder by

                                      -5-

<PAGE>

Subtenant with more square footage than included in the Subleased Premises, then
Sublandlord shall have the right (but not the obligation) to offer such signage
rights to the New Subtenant and have included in its sublease agreement such
rights to signage. In the event New Subtenant obtains Sublandlord's signage
rights, then Subtenant shall have no rights whatsoever to Sublandlord's signage
rights pursuant to Section 36 of the Prime Lease and any of Subtenant's rights
to Sublandlord's rights under Section 36 of the Prime Lease shall automatically
terminate. In the event New Subtenant does not obtain the signage rights or in
the event that no single New Subtenant subleases more square footage of the
Original Premises than is included in the Subleased Premises, then Sublandlord
shall grant its rights under Section 36 of the Prime Lease to Subtenant without
additional consideration.

     17. Default. In the event that (a) Subtenant shall fail to make payment of
any installment of Basic Rent, Additional Rent or other sum herein specified and
such failure shall continue for three (3) business days after notice from
Sublandlord (provided, however, that Sublandlord shall only be obligated to
provide Subtenant with one (1) notice of late payment during any twelve (12)
month period of the Sublease Term, and upon the second occurrence of late
payment during such twelve (12) month period of the Sublease Term, the same
shall be immediately deemed a default hereunder, even though no notice has been
given); (b) other than as set forth in (a) above, Subtenant shall fail to
observe or perform any other of Subtenant's covenants, agreements, or
obligations hereunder and such failure shall not be corrected within five (5)
business days after written notice thereof, including the failure to perform any
of the Sublandlord's obligations under the Prime Lease with respect to the
Subleased Premises that are assumed hereunder by Subtenant; or (c) a default by
Subtenant under the Prime Lease occurs; then Subtenant shall be deemed in
default hereunder and Sublandlord shall have the right thereafter to (i) declare
the term of this Sublease ended upon written notice to Subtenant, and accelerate
and collect from Subtenant the present value (computed at a capitalization rate
based upon the so-called corporate "Base Rate" then in effect at The First
National Bank of Boston) of all Basic Rent and Additional Rent and other sum due
hereunder that remain to be paid over the remaining Sublease Term and to remove
Subtenant's effects, (ii) elect not to terminate this Sublease and continue to
collect Basic Rent and Additional Rent and other sums due hereunder as they
come due; or (iii) exercise any and all rights and remedies as is accorded the
Prime Landlord for a default of Sublandlord under the Prime Lease, all in
accordance with applicable law. Subtenant shall indemnify Sublandlord against
all loss of Basic Rent and Additional Rent and all other payments which
Sublandlord may incur by reason of such termination during the remainder of the
Sublease Term, it being agreed that upon any termination of this Sublease due to
Subtenant's default, Sublandlord shall use reasonable efforts to mitigate its
damages, but the foregoing shall in no way require Sublandlord to lease the
Subleased Premises prior to leasing any other vacant space within the Original
Premises.

     18. Miscellaneous.

          (a) Counterparts. This instrument may be signed in counterpart
     originals, which, taken together, shall constitute a single original
     instrument.

          (b) Notices. Notices to Sublandlord or Subtenant required or permitted
     hereunder shall be sent in the manner prescribed in the Prime Lease.
     Notices to Sublandlord shall be to: NaviPath, Inc., c/o CMGI, Inc.,
     Attention: General Counsel, 100 Brickstone Square, Andover, MA 01810, with
     a copy to Thomas B. Rosedale, Browne Rosedale & Lanouette LLP, 100
     Brickstone Square, First Floor, Andover, MA 01810. Notices to

                                      -6-

<PAGE>

     Subtenant shall be to: NaviSite, Inc. at 800 Federal Street, Andover MA
     01810 Attention: General Counsel.

          (c) Amendments. This Sublease may not be changed or terminated orally
     but only by an agreement in writing signed by both Sublandlord and
     Subtenant.

          (d) Estoppel Certificates. Sublandlord and Subtenant each agree to
     furnish within ten (10) days after written request therefor by the other, a
     certificate stating (i) that this Sublease is in full force and effect and
     has not been amended or modified (or describing such amendment or
     modification, if any); (ii) the amounts of Basic Rent and Additional Rent
     and the dates through which Basic Rent and Additional Rent have been paid
     hereunder; (iii) that there are no defaults under this Sublease known to
     the signer of the certificate (or specifying such defaults, if known); and
     (iv) that Subtenant to its knowledge has no claims against Sublandlord
     hereunder except for the continuing obligations under this Sublease (or if
     Subtenant has any such claims, specifying the same).

          (e) No Waiver. The failure of either party to insist on strict
     performance of any covenant or condition hereof, or to exercise any option
     contained herein, shall not be construed as a waiver of such covenant,
     condition or option in any other instance.

          (f) Memorandum of Lease. Subtenant shall not record this Sublease or
     any memorandum hereof.

          (g) Governing Law. This Sublease has been negotiated, executed and
     delivered in the Commonwealth of Massachusetts, and the parties agree that
     the rights and obligations of the parties under this Sublease shall be
     governed and construed in accordance with the laws of the Commonwealth of
     Massachusetts.

          (h) Severability. The invalidity of any of the provisions of this
     Sublease will not impair or affect in any manner the validity,
     enforceability or effect of the rest of this Sublease.

          (i) Entire Agreement. All understandings and agreements, oral or
     written, heretofore made between the parties hereto with respect to the
     sublease of the Subleased Premises are merged in this Sublease, which alone
     fully and completely expresses the agreement between Sublandlord and
     Subtenant.

          (j) Relationship Between the Parties. This Sublease does not create
     the relationship of principal and agent, nor does it create any
     partnership, joint venture, or any association or relationship between
     Sublandlord and Subtenant other than as and to the extent specifically
     provided in this Sublease, the sole relationship of Sublandlord and
     Subtenant being that of sublandlord and subtenant as provided in this
     Sublease.

          (k) Remedies Cumulative. Except as specifically provided herein, all
     rights and remedies of a party under this Sublease shall be cumulative and
     none shall exclude any other rights and remedies allowed by law.

                                      -7-

<PAGE>

          (l) Condition Precedent. The effectiveness of this Sublease is
     expressly subject to and conditional upon obtaining (a) consent of the
     Subtenant's Board of Directors, and (b) Prime Landlord's written consent to
     this Sublease pursuant to Section 19 of the Prime Lease.

          (m) Termination of Prime Lease. If either Prime Landlord or
     Sublandlord terminates the Prime Lease pursuant to its terms or the Prime
     Lease otherwise terminates or expires, this Sublease shall likewise and
     simultaneously terminate.

          (n) Late Charges. In the event that any payment due by Subtenant
     hereunder is not paid within five (5) days after such payment is due, then
     Subtenant shall pay to Sublandlord a late charge equal to 5% of such
     overdue amount.

          (o) Holding Over. If Subtenant fails to surrender the Subleased
     Premises upon the expiration or sooner termination of the Sublease Term,
     this Sublease shall nevertheless terminate as of the expiration or
     termination date, and Subtenant shall become a tenant at sufferance, with
     Basic Rent increasing to $18 per rentable square foot plus Additional Rent.
     Subtenant shall indemnify and hold Sublandlord harmless from any holdover
     rent or other charges, penalties, damages or costs charged to, imposed
     upon, suffered or incurred by Sublandlord, including, without limitation,
     claims made against Sublandlord by Prime Landlord or any parties claiming
     under or through Prime Landlord, as a result of Subtenant's failure to
     surrender on time.

          (p) Attorneys' Fees. If either party employs an attorney to enforce,
     construe, or declare rights or obligations under this Sublease, the
     prevailing party shall be entitled to receive from the losing party
     reimbursement for all reasonable attorneys' fees and costs incurred in such
     proceeding, and such reimbursement shall be included in any judgment or
     final order issued in that proceeding. The "prevailing party" means the
     party determined by the trying authority to most nearly prevail.

          (q) Furniture. Prior to the Sublease Term Commencement Date, Subtenant
     and Sublandlord shall agree in writing to a sufficiently described list of
     the furniture presently located in the Subleased Premises. Subtenant shall
     be permitted to use said furniture during the Sublease Term, provided that
     it shall be returned to Sublandlord upon expiration or termination of the
     Sublease Term in the same condition as it is received from Sublandlord,
     normal wear and tear excepted.

     19. Guaranty. The parties acknowledge that as of the effective date of this
Sublease, the Sublandlord has filed for dissolution of its existence as a
corporation, therefore, in the event that Sublandlord fails to perform any of
its obligations under this Sublease, including but not limited to, its
obligations set forth in Sections 10 and 11, CMGI, Inc. shall promptly and fully
perform those obligations of the Sublandlord. Additionally, in the event that
any notice to or consent by the Sublandlord is required under the Prime Lease or
this Sublease, Subtenant may provide notice to or obtain consent from CMGI, Inc.
in place of Sublandlord and said notice and/or consent shall be effective
against Sublandlord.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

                                      -8-

<PAGE>

     IN WITNESS WHEREOF, the parties have executed this Sublease as an
instrument under seal as of the date first written above.

                                           SUBLANDLORD:

                                           NAVIPATH, INC.,
                                           a Delaware corporation


                                           By: /s/ Peter L. Gray
                                               ---------------------------------
                                               Name: Peter L. Gray
                                               Title: Secretary


                                           SUBTENANT:

                                           NAVISITE, INC.,
                                           a Delaware corporation


                                           By:  /s/ Illegible
                                               ---------------------------------
                                               Name: Illegible
                                               Title: Illegible

For the purposes of Section 19 only:                ---------------
                                                     NaviSite. Inc.
CMGI, INC.                                              APPROVED
a Delaware corporation                                As To Form
                                                    Legal Dept. RmD
                                                    Dated: 12/18/02
By: /s/ Peter L. Gray                               ---------------
    ---------------------------------
    Name: Peter L. Gray
    Title: E.V.P. and General Counsel

                                      -9-

<PAGE>

                                   EXHIBIT A

                                  PRIME LEASE

                                 [See Attached]

<PAGE>

                                      Lease
                                       By
                      Trustees of Andover Park Realty Trust
                                       To
                                  NaviNet, Inc.

                               800 Federal Street
                                  Woodland Park
                                   Andover, MA

                                Table of Contents

                                                                            Page
                                                                            ----
1.    Identifications                                                         1

2.    Lease; the Premises                                                     1

3.    Construction by Landlord                                                2

4.    Term                                                                    5

5.    Use of the Premises; Licenses and Permits                               6

6.    Basic Rent; Additional Rent                                             6

7.    Taxes                                                                  10

8.    Insurance; Waivers of Subrogation                                      12

9.    Utilities                                                              14

10.   Repairs                                                                14

11.   Compliance with Laws and Regulations                                   15

12.   Alterations by Tenant                                                  16

13.   Landlord's Access                                                      17

14.   Indemnities                                                            18

15.   Casualty Damage                                                        19

16.   Condemnation                                                           20

<PAGE>

                                Table of Contents
                                   (Continued)

                                                                            Page
                                                                            ----

17.   Landlord's Covenant of Quiet Enjoyment; Title                          22

18.   Tenant's Obligation to Quit                                            23

19.   Assignment and Subletting                                              23

20.   Transfers of Landlord's Interest                                       26

21.   Mortgagees' Rights                                                     26

22.   Tenant's Default Landlord's Remedies                                   28

23.   Remedies Cumulative; Waivers; Attorney's Fees                          31

24.   Extension of Term                                                      32

25.   Brokers                                                                33

26.   Notices                                                                34

27.   Recording                                                              34

28.   Estoppel Certificates                                                  35

29.   Bind and Inure; Limited Liability of Landlord                          35

30.   Captions                                                               36

31.   Integration                                                            36

32.   Hazardous; Toxic Substances                                            36

33.   Severability; Choice of Law                                            39

34.   Financial Statements                                                   39

35.   Security Deposit                                                       40

36.   Signage                                                                40

37.   Y2K                                                                    41

38.   Roof Rights                                                            41

<PAGE>

                                      LEASE

1.   Identifications

     This LEASE made as of the 30TH day of November 1999, by and between William
J. Callahan and William J. Callahan, Jr., as they are trustees of Andover Park
Realty Trust under a declaration of trust dated June 25, 1986 and filed with the
Essex County (North District) Registry of Deeds in Book 2226, Page 284 (the
"Landlord"), having an address c/o P.O. Box 269, Bedford, Massachusetts 01730,
and NaviNet, Inc. (the "Tenant"), a Delaware corporation having an address at
600 Federal Street (prior to occupancy of the Premises) and at 800 Federal
Street (after occupancy), Andover, Massachusetts, 01810. The Guarantor of the
Lease shall be CMGI, Inc., a Delaware corporation.

2.   Lease; the Premises

     In consideration of the Basic Rent, Additional Rent, and other payments and
covenants of the Tenant hereinafter set forth, and upon the following terms and
conditions, the Landlord hereby leases to the Tenant and the Tenant hereby
leases from the Landlord approximately 52,234 square feet on floor l as shown in
the floor plans attached hereto as Exhibit A-1 and more particularly described
in the 1/16" scaled floor plans initialed by Landlord and Tenant (excluding
therefrom only the entrance area(s), loading dock(s), elevator(s), stairway(s),
telephone, sprinkler, machine, and electrical rooms and other common areas,
being hereinafter called (the "Premises"), in that certain building (as defined
in Paragraph 3 hereof, the "Building") now under construction by the Landlord on
that certain parcel of land (the "Property") located at 800 Federal Street in
Woodland Park, Andover, Massachusetts, said parcel, as more particularly
described in Exhibit A attached hereto, consisting of approximately 22.758 acres
of land.

                                       1

<PAGE>

     The Premises leased together with reasonable rights, in common with the
Landlord and all others (including any other tenant or tenants of the Building
or the Property, claiming under the Landlord or otherwise) from time to time
lawfully entitled thereto, to use: (i) the first floor entrance area(s), loading
dock(s), elevator(s), stairways, and all other such common areas of the Building
for their intended purposes; (ii) the appurtenant right to use for their
intended purpose: the pipes, conduits, utility lines, wires, sewage system and
other appurtenant fixtures and equipment servicing the Premises; (iii) the
driveways, walkways, parking area and other common areas of the Property (all
currently located substantially as shown on the Site Plan referred to in
Paragraph 3) for their intended purposes (Tenant shall be granted use of 172
parking spaces on the Property for use by its employees and visitors of which 11
parking spaces shall be designated for use by visitors) in the parking area in
front of the main entrance to the Building; and (iv) Federal Street for all
purposes for which public ways may now or hereafter be used in the Town of
Andover.

3.   Construction by Landlord

     The Landlord shall, at its cost and expense except as otherwise expressly
agreed in this Lease, complete construction of the building (the "Building")
containing approximately 158,655 rentable square feet of floor space now under
construction on the Property substantially in accordance with Building plans
prepared by Spagnolo/Gisness & Associates, Inc.; the interior "fitup" of the
Premises substantially in accordance with plans therefor (the "Tenant's Interior
Plans") dated 9/15/99 prepared for the Tenant by Visnick & Caulfield Associates,
Inc. and attached hereto as Exhibit B to be consistent with the Building plans
(said Building plans and Tenant's Interior Plans, as from time to time amended
with the approval of the Tenant, being hereinafter collectively called the
"Plans"); and the driveway(s), walkway(s), parking area(s) and other
improvements to the

                                        2

<PAGE>

Property substantially as shown on the Site Plan dated 11/6/98 (the "Site
Plan"). Said Building, the interior work on the Premises and the driveway(s),
walkway(s) and parking area(s) are hereinafter collectively called the
"Improvements". The Tenant shall not unreasonably withhold or delay approval of
any changes or amendments to the Plans which the Landlord may from time to time
propose, provided, however, that the Tenant need not approve any such proposed
change or amendment which will materially adversely affect the value or quality
or the Tenant's anticipated use of the Premises or the suitability and utility
of the layout of the Premises for such use.

     The Landlord shall cause the Improvements to be so constructed in
accordance with the Tenant's Interior Plans in a good and workmanlike manner
using new first-class materials and, except as otherwise permitted under
variances or other deviations duly obtained, in compliance with all applicable
laws, by-laws, ordinances, codes, rules, regulations, orders and other lawful
requirements of governmental bodies having jurisdiction, it being the obligation
of the Landlord, at its cost and expense, to obtain from such bodies all
permits, licenses, certificates or other approvals required for construction of
the Improvements and for the initial occupancy of the Premises by the Tenant.

     Without regard to the commencement of the Term, the Tenant shall reimburse
Landlord, as and when the same are incurred or the applicable items of work are
completed and within thirty (30) days after receipt of itemized invoices from
the Landlord, for the actual costs of all change orders specifically requested
by Tenant, and with any work incorporated into the Premises (pursuant to the
Tenant's Interior Plans or otherwise requested or required by Tenant) in excess
of the cost of the work provided for in the Tenant's Interior Plans and "Outline
Specifications for NaviNet" dated September 21, 1999 such reimbursement to be
made at the Landlord's cost plus thirteen percent

                                       3

<PAGE>

(13%) for administration/general conditions. Landlord shall promptly pay all
contractors for whom Landlord has requested reimbursement from Tenant.

     The Landlord shall exercise all commercially reasonable efforts to cause
the Improvements to be Substantially Complete (as hereinafter defined) by March
1, 2000, as such date shall be automatically extended for the periods of: (a)
any delays on the part of the Tenant in providing to the Landlord the final
construction plans necessary to apply for a building permit by December 15,
1999; (b) any delays caused by change orders requested by Tenant; (c) any other
delays which are in whole or in part the responsibility of the Tenant, including
delays on the part of the Landlord in completing work which could have been
completed but for the delayed completion of other work for reasons in whole or
in part the responsibility of the Tenant (such items (a) through (c), "Tenant
Delays"); (d) and any delays which result from strikes, inability to obtain
materials (or substitutes acceptable to the Tenant at comparable cost), fire or
other casualty and from any other causes beyond the commercially reasonable
control of the Landlord ("Force Majeure Delays") (such date as so extended being
hereinafter called the "Date for Substantial Completion").

     The Improvements shall be deemed to be "Substantially Complete" when (i)
the same are complete (with all building electrical, mechanical and plumbing
systems operational) in accordance with the Plans and other provisions hereof
except only for items of work specified in a so-called "punch list" signed by
the Landlord and the Tenant the delayed completion of which items will not
substantially interfere with the use and enjoyment of the Premises by the Tenant
as contemplated hereby; and (ii) all temporary or permanent certificates and
permits necessary for initial occupancy of the Premises by the Tenant for
purposes permitted under Paragraph 5 hereof have been issued by the appropriate
governmental bodies having jurisdiction and copies thereof provided to the
Landlord.

                                       4

<PAGE>

The Landlord shall finish any such "punch list" items of work within thirty (30)
days after the Date for Substantial Completion. In addition, the Landlord shall
remedy any substantial defect of materials or workmanship in or affecting the
Premises of which the Tenant gives notice to the Landlord within twelve (12)
months after the commencement of the Term and shall, to the extent legally
possible, assign to the Tenant the benefit of all warranties and guarantees from
manufacturers, vendors, suppliers and subcontractors whose products or services
are incorporated into the Premises.

4.   Term

     The Term of this Lease shall commence on the later of (i) March 1, 2000 or
(ii) the earlier of the date the Improvements are Substantially Complete or the
date the Improvements would have been Substantially Complete except for Tenant
Delays (the "Term Commencement Date") and shall expire, unless earlier
terminated in accordance with the terms hereof, at midnight on the last day of
the calendar month after the expiration of six (6) years from the Term
Commencement Date. Landlord hereby grants Tenant the right to enter the Premises
and install fixtures and equipment prior to the Term Commencement Date and the
Tenant and Landlord shall coordinate such work with the Improvements. The Tenant
shall be responsible for such fixtures and equipment and any damage or loss
thereto. If the Improvements are not Substantially Complete as so defined on or
before July 15, 2000 as automatically extended for periods of any Tenant Delays,
or Force Majeure, the Tenant may, by written notice to Landlord within five (5)
days after such date, terminate this Lease; provided, further, that if the
Improvements are not Substantially Complete on or before September 15, 2000, as
so automatically extended for any Tenant Delays, Tenant may by written notice to
Landlord within five (5) days after such date, terminate this Lease.

                                       5

<PAGE>

5.   Use of the Premises; Licenses and Permits

     The Tenant shall use the Premises only for offices, computer room, research
and development, on uninterrupted power sources, training rooms, data center and
related storage as permitted under applicable laws, by-laws, ordinances, codes,
rules, regulations, orders and other lawful requirements of governmental bodies
having jurisdiction. The Tenant, its subtenants, licensees, invitees and any
other users of the Premises shall apply in their own names for and obtain at
their own expense any and all licenses, permits and other approvals which may be
required from such governmental bodies in connection with Tenant's particular
use of the Premises during the term except as set forth above. Tenant shall have
access to the Premises 24 hours a day, seven days a week, 365 days a year.

6.   Basic Rent; Additional Rent

     From and after the Term Commencement Date, the annual Basic Rent for the
Premises during the Term shall be due in accordance with the following schedule:

                 ANNUAL BASIC RENT   MONTHLY BASIC RENT

Years l and 2:      $705,159.00          $58,763.25
Years 3 and 4:      $757,396.00          $63,116.08
Years 5 and 6:      $809,627.00          $67,468.92

     Basic Rent shall be payable in advance on the first day of each month in
equal installments (except in the case of a partial month at the beginning of
the Term, in which event the Tenant shall pay an appropriate pro rata proportion
of such installment) to the Landlord at the address set forth above or such
other address as the Landlord may thereafter specify by the notice to the
Tenant,

                                       6

<PAGE>

without counterclaim, set off, deduction, abatement or defense, except as
otherwise expressly provided herein.

     This Lease is intended by the parties hereto to be a so-called "net" lease
and, to that end, the Basic Rent shall be received by the Landlord net of all
costs and expenses related to the Property, the Building and the Premises as
expressly set forth herein. Tenant agrees to pay to the Landlord, during the
Term hereof, Tenant's Percentage (herein defined) of Common Expenses
(hereinafter defined) within thirty (30) days of demand thereof. Landlord shall
bill Tenant for such common expenses no more often than monthly during the Term
hereof and within 120 days of the expiration or earlier termination of this
Lease. The Landlord shall, in each case, at the time demand for payment by the
Tenant of any Common Expenses, provide the Tenant with a computation of the
Common Expenses, and evidence of the payment or liability for any such charges,
costs, expenses and obligations. "Common Expenses" shall mean any and all
charges, costs and expenses which the Landlord may from time to time actually
incur-during the Term, in good faith, with respect to the operation and
maintenance of the Premises, Building and the Property, including, without
limitation, (i) making repairs to and undertaking maintenance of the Building
and the Property, including the common areas of the Building; (ii) providing
cleaning and utilities, including heat and air conditioning, to the common areas
of the Building; (iii) providing watering, landscaping and lawn care for the
Property; (iv) sanding, plowing and removal of snow and ice from the driveways,
walkways and parking areas on the Property; (v) Landlord's prorata share based
on its ownership of the Property of the maintenance and repair to the Woodland
Park common areas and Federal Street (including cleaning, landscaping, snow
removal, and lighting); (vi) maintaining the insurance required to be maintained
by the Landlord pursuant to Paragraph 8 hereof; and (vii) a commercially

                                       7

<PAGE>

reasonable management fee. Common Expenses shall not include (a) interest or
amortization payments on any mortgage or deed of trust affecting the Building or
on any loan made to Landlord; (b) leasing commissions, advertising expenses and
other costs incurred in leasing or attempting to lease any portion of the
Building; (c) the costs of repairs, improvement, special cleaning or other
special services performed for tenants to the extent that such items are
separately charged and payable by such tenants; (d) any cost or expense which
Landlord has the right to recover from any third party, including any insurance
carrier; (e) repairs or other work occasioned by fire, windstorm or other
casualty or by the exercise of eminent domain; (f) renovating or otherwise
improving, decorating, painting or redecorating space for other occupants of the
Building; (g) Landlord's cost of electricity and other services that are sold to
tenants and for which Landlord is entitled to be reimbursed by tenants as an
additional charge or rental over and above the basic rent, tax escalation, and
operating expense escalation payable under Landlord's lease with such tenant;
(h) costs incurred due to violation by Landlord or any other tenant of the terms
and conditions of any lease; (i) overhead and profit increment paid to
subsidiaries or affiliates of Landlord for services on or to the real property,
to the extent only that the cost of such services exceed competitive costs of
such services were they not so rendered by a subsidiary or affiliate; (j)
Landlord's general overhead except as it directly relates to the operation and
management of the Building, Tenant hereby acknowledging that operating costs
shall include a competitive management fee; (k) any compensation paid to clerks,
attendants or other persons in commercial concessions operated by Landlord; (1)
advertising and promotional expenditures; (m) any fines or penalties incurred
due to violations by Landlord or any governmental rules; (n) any costs incurred
by Landlord in the event that the building does not comply with governmental
rules in effect as of the execution date of this Lease; (o) costs for

                                       8

<PAGE>

sculpture, painting or other objects of art; (p) wages, salaries, or other
compensation paid to any executive employees above the grade of building
superintendent, except that if any such employee performs a service which would
have been performed by an outside consultant, the compensation (to the extent
allocable to service performed for the Building) paid to such employee for
performing such service shall be included in operating costs, to the extent only
that the cost of such service does not exceed competitive cost of such service
had such service been rendered by an outside consultant; (q) construction or
other work performed by Landlord for another tenant(s), whether or not Landlord
is entitled to be reimbursed for the cost of such work; (r) depreciation; (s)
costs related to a capital expenditure; provided that Common Expense shall
include the cost of Capital Expenditure(s) amortized over their useful life in
accordance with generally accepted industry practices at a 10% interest rate;
(t) any architects' fees, accountants' fees or any professional fees not
directly related to the maintenance of the Premises; or (u) any costs whatsoever
related to any expansion of the Building or the other park in which the
Building is located. "Tenant's Percentage" shall mean 32.9% which represents
that proportion that the rentable floor area of the Premises bears to the
rentable floor area of the Building. In any calendar year when the Building has
an average annual occupancy rate of less than 95% then, for the purposes of
Section 6 of this Lease, Common Expenses for the Property shall be extrapolated
as though the Building were 95% occupied, and Tenant's Percentage of Common
Expenses shall mean the same proportion of Common Expenses for the Property as
the rentable floor area of the Premises bears to 95% of the rentable floor area
of the Building. To the extent that any charge, cost or expense incurred by
Landlord for Common Expenses shall be such that it related to materials or
services furnished for periods after expiration or termination of the Term, then
such charge, cost or expense shall be appropriately adjusted or pro rated to
take into

                                       9

<PAGE>

effect only periods during the Term.

     If any payment of Basic Rent or Additional Rent is not paid to the Landlord
when due or within any applicable grace period, then at Landlord's option,
without notice and in addition to all other remedies hereunder, Tenant shall pay
upon demand to Landlord as Additional Rent interest thereon at an annual rate
equal to the corporate rate of the Fleet Bank from time to time in effect plus
two (2) percent, such interest to be computed from the date such Basic Rent or
Additional Rent was originally due through the date paid in full.

7.   Taxes

     The Tenant shall pay or cause to be paid to the Landlord (or, where
appropriate, directly to the authority by which the same are assessed or
imposed, with evidence of such payment to the Landlord) as Additional Rent not
later than ten (10) days prior to the date the same are due or twenty-one (21)
days after written notice thereof to the Tenant, whichever is later, all taxes
and excises upon the personal property and equipment of the Tenant located at
the Premises or the Property and the Tenant's Percentage of any and all real
estate taxes, betterments and special assessments (which the Landlord agrees
shall be paid over the longest period allowed by law) or amounts in lieu or in
the nature thereof and any water rents or sewer use charges (and the entire
amount of any interest, penalties and costs attributable to delayed payment of
Tenant's portion thereof where such delay is the fault of the Tenant) which may
now or hereafter be levied, assessed or imposed by the United States of America,
the Commonwealth of Massachusetts, the Town of Andover or any other authority,
or become a lien, upon all or any part of the Property, the Building, the
Premises, the use or occupation thereof, or upon the Landlord and the Tenant in
respect thereof, or upon the basis of rentals thereof or therefrom (except for
the Landlord's income, estate, gift or

                                       10

<PAGE>

transfer taxes), or upon the estate hereby created or upon the Landlord by
reason of ownership of the reversion. All payments by the Tenant on account of
Taxes shall be appropriately pro rated in connection with any tax bills received
by Landlord covering periods which are not within the Term.

     The Tenant shall, upon written notice from the Landlord, prepay to
Mortgagee or the Landlord monthly as Additional Rent, in the same manner as
Basic Rent, one-twelfth (1/12) of the total of all such amounts as the Landlord
may from time to time reasonably estimate will be payable annually by the Tenant
under this Paragraph 7, which prepayments the Landlord agrees shall be applied,
without interest to such amounts as actually become payable. As soon as any such
amounts so payable are actually determined appropriate adjustment of any
overpayments of underpayments shall be made but in no event later than 30 days
after the close of the fiscal year for taxes immediately following the
expiration or earlier termination of this Lease.

     Subject to the rights of any Mortgagees, the Landlord shall, at the request
of the Tenant or any other tenant or tenants of the Building, use reasonable
efforts to obtain an abatement of or to contest or review by legal proceedings
or otherwise any such tax, levy, charge or assessment described in the first
paragraph of this Section 7. In such event the Tenant and such other tenants
shall either pay such tax, levy, charge or assessment (under protest, if
necessary) or shall, if requested, deposit with the Landlord in trust (or
provide an indemnity bond in) an amount sufficient to cover the contested item
together with any interest, penalties or costs as the Landlord may reasonably
require. The Tenant and any such other tenants, jointly and severally, shall
defend, indemnify and save the Landlord harmless from and against and shall pay
as Additional Rent the Tenant's Percentage of (i) any such tax, levy, charge or
assessment that may be determined to be due and (ii) any and all costs or
expenses (including reasonable attorney's fees) the Landlord may incur

                                       11

<PAGE>

in connection with any such proceedings. When any such contested item shall have
been settled or paid, the balance of any sums deposited with the Landlord in
trust shall be repaid to the Tenant. The Tenant shall be entitled to share in
any refund or abatement, net of such costs and expenses, which may be made of
any tax, levy, charge or assessment in the same proportion that the same was
paid by the Tenant or with the Tenant's funds.

8.   Insurance; Waivers of Subrogation

     The Tenant shall, at its own cost and expense, obtain prior to the
commencement of the Term and throughout the Term shall maintain, with companies
qualified to do business in Massachusetts and acceptable to any first Mortgagee,
insurance for the benefits as additional insureds of the Landlord and any
Mortgagees as their respective interests may appear, commercial general
liability insurance against claims for bodily injury, death or property damage
occurring to, upon or about the Premises, the Building or the Property, in
limits of $1,000,000 for bodily injury or death and $500,000 for property damage
or in such higher or lower limits as any Mortgagee may reasonably require with
respect to comparable premises, buildings and property in suburban Boston.

     The Landlord shall obtain and throughout the Term shall maintain, with
companies qualified to do business in Massachusetts and acceptable to any first
Mortgagee, insurance for the benefit as named insureds of the Landlord and any
Mortgagees as their respective interests may appear, with losses first payable
to such Mortgagees under standard mortgagee endorsements, as follows; (i)
insurance against lost rentals from the Building for a period of at least one
year and so-called "casualty" insurance against loss or damage to the Building
such as may result from fire and such other casualties as are normally covered
by an "extended coverage" endorsement, such casualty insurance to be without
deductible and in an amount equal to the full replacement cost of the

                                       12

<PAGE>

Building; (ii) in reasonable amounts, boiler and machinery insurance on any
Building steam boilers, pressure vessels and pressure piping, rotating
electrical machines, and miscellaneous electrical apparatus, engines, pumps, and
compressors, fans and blowers, with so-called "standard blanket coverage" (15 HP
and over); and (iii) such other insurance coverages in such additional amounts,
as any Mortgagee may reasonably require or as a prudent and reasonable owner
would from time to time carry on similar premises in view of any new risks
arising or changes of conditions (e.g. inflation) occurring during the Term.

     Neither the Landlord nor the Tenant shall be liable to the other for any
loss or damage to the Building, the Premises or other property or injury to or
death of persons occurring on the Property or in the Building or the Premises or
in any manner growing out of or connected with the Tenant's use and occupation
of the Premises, the Building or the Property or the condition thereof, whether
or not caused by the negligence or other fault of the Landlord, the Tenant or
their respective agents, employees, subtenants, licensees, invitees or
assignees; provided, however, that this release (i) shall apply only to the
extent that such loss or damage to the Building or other property or injury to
or death of persons is covered by (x) insurance which protects the Landlord or
the Tenant or both of them as the case may be, or (y) insurance required to be
carried by either party under this Lease; (ii) shall not be construed to impose
any other or greater liability upon either the Landlord or the Tenant than would
have existed in the absence hereof; and (iii) shall be in effect only so long as
the applicable insurance policy contains a clause providing that this release
shall not affect the right of the insureds to recover under such policies, which
clauses shall be obtained by the parties hereto whenever available. All property
of the Tenant in, and any other contents of, the Premises shall be at the
Tenant's sole risk and the Tenant shall be responsible for insuring the same.

                                       13

<PAGE>

9.   Utilities

     The Tenant shall pay the Tenant's Percentage of water and sewer use charges
with respects to normal water usage for Tenant's domestic use of the Building
(except that either the Landlord or the Tenant may arrange to have the Premises
separately metered at its own expense, in which event the Tenant shall be billed
for such water and sewer use charges imposed in respect of the usage indicated
by such meter and in which case shall not pay any Tenant's Percentage of Common
Expense with respect to water and sewer) and shall, at its own cost and expense,
pay for all other utilities provided to the Premises during the Term, including,
without limitation, electricity (including electricity for heat and air
conditioning), water beyond such normal usage for Tenant's domestic use (in the
absence of such a meter), telephone service, security and fire protection,
cleaning and trash removal. Landlord shall, at its own expense, install a meter
to measure Tenant's electric consumption.

10.  Repairs

     From and after the commencement of and during the Term, the Tenant shall,
except to the extent it is Landlord's responsibility or caused by the negligence
of the Landlord, at its own cost and expense, make all interior nonstructural
repairs, replacements and renewals necessary except to the extent covered by
builder or vendor warranties to keep the Premises in as good condition, order
and repair as the same are at the commencement of the Term reasonable wear and
use and damage by fire or other casualty, taking by eminent domain only
excepted, and keep and maintain all portions of the Premises in a clean and
orderly condition, free of accumulation of dirt, rubbish, and other debris, it
being understood that the foregoing exception for reasonable wear and use shall
not relieve the Tenant from the obligation to keep the Premises in good order,
repair and condition.

                                       14

<PAGE>

     From and after the commencement of and during the Term, the Landlord shall
make all necessary repairs, replacement and renewals, interior and exterior,
structural and nonstructural as Common Expenses as in Paragraph 6 defined, to:
keep the Building and all its electrical, mechanical, heating, ventilating and
air conditioning, plumbing and other building systems and the parking areas,
sprinklers and other improvements on the Property in good condition, order and
repair as the same are at the commencement of the Term or thereafter may be put,
damage by fire or other casualty only excepted; keep all driveways, walkways,
parking areas and other improvements on the Property free of snow and sanded;
keep all lawns and landscaped areas of the Property watered, fertilized and
neatly trimmed; provide cleaning services and utilities to the common areas of
the Building at a quality level similar to first class office buildings in
suburban Boston; and otherwise to keep the common area of the Building and the
Property in compliance with all applicable laws, by-laws, ordinances, codes,
rules, regulations, orders or other lawful requirement.

     Notwithstanding, the Landlord shall, at its own cost and expense, and not
as a Common Expense make all repairs necessary to keep the structural support
elements of the Building in structurally good condition, order and repair,
damage resulting from any act (not consented to in writing by the Landlord) and
any omissions of the Tenant or its agents, contractors and employees, from
reasonable wear and use and from fire or other casualty only excepted.

11.  Compliance with Laws and Regulations

     The Tenant agrees that its obligations to make payment of the Basic Rent,
Additional Rent and all other charges on its part to be paid, and to perform all
of the covenants and agreements on its part to be performed during the Term
hereunder shall not, except as set forth in Paragraph 16 in the event of
condemnation by public authority, be affected by any present or future law,
by-law,

                                       15

<PAGE>

ordinance, code, rule, regulation, order or other lawful requirement regulating
or affecting the use which may be made of the Premises or the Property.

     During the Term the Tenant shall comply, at its own cost and expense, with:
all applicable laws, by-laws, ordinances, codes, rules, regulations, orders and
other lawful requirements of the governmental bodies having jurisdiction (other
than such as are the obligation of the Landlord under Paragraphs 3 and 10
hereof), whether or not foreseeable, and whether or not they involve any changes
in governmental policy, which are applicable to the Tenant's particular use of
the Premises, the fixtures and equipment therein; the order, rules and
regulations of the National Board of Fire Underwriters, or any other body
hereafter constituted exercising similar functions, which may be applicable to
the Tenant's particular use of the Premises, the fixtures and equipment therein
or the use thereof; and the reasonable requirements of all policies of public
liability, fire and all other types of insurance at any time in force with
respect to the Tenant's particular use of the Premises, the Building or the
Property and the fixtures and equipment therein and thereon.

12.  Alterations by Tenant

     The Tenant shall make no alterations or improvements in or to any portion
of the Premises or any portion of the Building or the Property without the
Landlord's prior written consent and without first providing the Landlord with
suitable assurance of the Tenant's obligation to complete the same at no expense
to the Landlord and without any mechanics' or materialmen's lien upon the
Property. The Landlord agrees that its consent shall not be withheld for
interior, non-structural alterations, additions and improvements to the Premises
consistent with the use of the Premises as contemplated hereby; any such
consents to interior, non-structural alterations, additions and improvements
may, if it is special in nature and adversely affects the value of the Premises
and if

                                       16

<PAGE>

the Landlord reasonably advises the Tenant as part of or by notice at the time
of any such consent, be conditioned upon the Tenant's being obligated to remove
the same at the expiration or termination of this Lease and to restore the
Premises to their condition prior to such alterations, additions and
improvements. Landlord acknowledges that Tenant will not be required to remove
Tenant's initial improvements as set forth in Tenant's Interior Plans.
Notwithstanding the foregoing, Tenant may make alterations costing no more than
$10,000 and not affecting the exterior appearance of the Building, structural
components, or Building systems without Landlord's approval, provided that
Tenant gives Landlord at least 10 days prior notice of the alterations to be
made in reasonable detail. If Landlord does not give notice to Tenant within
such ten day period to the effect that the alterations must be removed at the
expiration of the Term, Landlord shall be deemed to have agreed that such
alterations need not be removed at the expiration of the Term.

13.  Landlord's Access

     The Tenant agrees to permit the Landlord and any Mortgagees and their
authorized representatives to enter the Premises at all reasonable times during
usual business hours after reasonable oral notice and accompanied by Tenant's
representative for the purposes of inspecting the same, exercising such other
rights as it or they may have hereunder or under any mortgagees and at any time
without notice in the event of emergency. Such rights of access shall not
unreasonably interfere with Tenant's business operations. Landlord agrees not to
show the Premises to prospective tenants until less than nine (9) months remain
in the Term. Landlord acknowledges that Tenant's business at the Premises
involves sensitive information and operations and the Tenant has security
requirements to protect such information and operations. Landlord and any person
entering the Premises with, at the direction of or under the authority of,
Landlord shall follow Tenant's security

                                       17

<PAGE>

requirements, which include the requirement that all persons entering the
Premises be attended by a representative of Tenant, Tenant shall make a
representative available upon 24-hours prior notice by Landlord. In the event of
an emergency that could cause damage to health, safety or property Landlord
shall use good faith efforts to follow Tenant's security requirements and in
such event Landlord will be required to give only such notice that it in good
faith believes is feasible under the circumstances and need not wait to be
accompanied by Tenant or its employees or representatives (although these
parties may still accompany Landlord if they are available and wish to do so).

14.  Indemnities

     The Tenant shall and does hereby agree to protect, defend, indemnify and
save the Landlord harmless from and against any all claims (other than claims
arising from any omission, fault, negligence or other misconduct of the Landlord
or its agents, contractors or employees of the Landlord in or about the
Premises, the Building or the Property) arising: (i) from the conduct or
management of or from any work or thing whatsoever done in or about the Premises
during the Term; (ii) from any condition existing, or any injury to or death of
persons or damage to property occurring during the Term, or resulting from an
occurrence during the Term, in or about the Premises; and (iii) from any breach
or default on the part of the Tenant in the performance of any covenant or
agreement on the part of the Tenant to be performed pursuant to the terms of
this Lease or from any negligent act or omission on the part of the Tenant or
any of its agents, employees, subtenants, licensees, invitees or assignees; the
Tenant further agrees to indemnify the Landlord from and against all costs,
expenses, including reasonable attorneys' fees, and other liabilities incurred
in connection with any such indemnified claim or action or proceeding brought
thereon, any and all of which costs, expenses and liabilities, if reasonably
suffered, paid or incurred by the Landlord, the

                                       18

<PAGE>

Tenant shall repay upon demand to the Landlord as Additional Rent.

     The Landlord shall and does hereby agree to protect, defend, indemnify and
save the Tenant harmless from and against any and all claims (other than claims
arising from any omission, fault, negligence or other misconduct of the Tenant
or its agents, contractors or employees of the Tenant in or about the Premises,
the Building or the Property) arising from any breach or default on the part of
the Landlord in the performance of any covenant or agreement on the part of the
Landlord to be performed pursuant to the terms of this Lease or from any
negligent act or omission on the part of the Landlord or any of its agents,
contractors or employees; the Landlord further agrees to indemnify the Tenant
from and against all costs, expenses, including reasonable attorney's fees and
other liabilities incurred in connection with any such indemnified claim or
action or proceeding brought thereon. Tenant's agreement to indemnify and hold
Landlord harmless, the exclusion from Tenant's indemnity, Landlord's agreement
to indemnify and hold Tenant harmless pursuant to this Section 14 and otherwise
in this Lease are not intended to and shall not relieve any insurance carrier of
its obligations under policies required to be carried by Landlord or Tenant,
respectively, pursuant to the Lease to the extent that such policies cover the
results of such acts, omissions or willful misconduct.

15. Casualty Damage

     Except as otherwise provided below, in the event of partial or total
destruction of the Premises during the Term by fire or other casualty, the
Landlord shall, after receipt of any insurance proceeds available as a result of
such casualty, as promptly as practicable repair, reconstruct or replace the
portions of the Premises destroyed as nearly as possible to their condition
prior to such destruction, except that in no event shall the Landlord be
obligated to expend more for such repair, reconstruction or replacement than the
amounts of any such insurance proceeds actually received

                                       19

<PAGE>

unless such proceeds are inadequate by reason of the failure of the Landlord to
obtain or maintain the insurance required by Paragraph 8 (i) hereof. During the
period of such repair, reconstruction and replacement there shall be an
equitable abatement of Basic Rent hereunder in proportion to the nature and
extent of the destruction.

     If the Building is so extensively destroyed by fire or other casualty that
the Premises are not susceptible of repair, reconstruction or replacement within
nine (9) months from the date of such destruction, or if such destruction
resulted from causes or risks not required to be insured against by the Landlord
hereunder, or if any Mortgagee refuses to agree to release net insurance
proceeds to the Landlord, or if the insurance proceeds actually received by the
Landlord are inadequate to repair the Premises to a condition reasonably
tenantable for the intended use unless such proceeds are inadequate by reason of
the failure of the Landlord to obtain or maintain the insurance required by
Paragraph 8(i) hereof, the Landlord or the Tenant may terminate this Lease by
giving written notice to the other within thirty (30) days after the date of
such destruction unless, in the case of notice from the Tenant, within ten (10)
days after receipt of any such notice by the Landlord, the Landlord gives notice
to the Tenant that the Landlord will make the necessary additional funds
available for such repair, reconstruction or replacement and complete such
repair, reconstruction or replacement within nine (9) months from the date of
such destruction, in which event this Lease shall nevertheless remain in effect.
In the event of termination as aforesaid this Lease shall terminate as of, and
Basic Rent and Additional Rent shall be appropriately apportioned through and
abated from and after, the date of the notice of termination.

16. Condemnation

     If (a) more than ten percent (10%) of the rentable floor area of the
Premises, or (b) more than

                                       20

<PAGE>

twenty percent (20%) of the parking area then available for use by the Tenant or
of access to the Premises, or (c) in Tenant's reasonable opinion a material
element of the Premises necessary for the operation of Tenant's business shall
be taken by eminent domain or appropriated by public authority, or (d) if access
to the parking of the Premises is materially affected by any such taking the
Landlord or the Tenant may terminate this Lease by giving written notice to the
other within thirty (30) days after such taking or appropriation. In the event
of such a termination, this Lease shall terminate as of the date the Tenant
actually surrenders possession, and the Basic Rent and Additional Rent reserved
shall be apportioned and paid to and as of such date.

     If all or any part of the Premises, the parking or access to either is
taken or appropriated by public authority as aforesaid and this Lease is not
terminated as set forth above, the Landlord shall, subject to the rights of any
Mortgagees, apply any such damages and compensation awarded (net of the costs
and expenses, including reasonable attorney's fees, incurred by the Landlord in
obtaining the same) to secure and close so much of the Improvements or other
buildings, structures and improvements constituting a part of the Premises as
remain and shall, to the extent possible, repair all damage and replace any part
so taken or appropriated by a suitable structure or parking area or addition of
similar size and design to that portion so taken or appropriated, except that in
no event shall the Landlord be obligated to expand more for such replacement
than the net amount of any such damages, compensation or award which the
Landlord may have received as damages in respect of the Building and any
improvements situated on the Property as they existed immediately prior to such
taking or appropriation; in such event there shall be an equitable abatement of
Basic Rent in proportion to the loss of useable floor area in the Premises after
giving effect to such replacement or an equitable abatement of Basic Rent due to
the loss of any parking or access to parking or the

                                       21

<PAGE>

Premises, from and after the date the Tenant must surrender possession or, if
later, the date the Tenant actually surrenders possession.

     The Landlord hereby reserves, and the Tenant hereby assigns to the
Landlord, any and all interest in and claims to the entirety of any damages or
other compensation by way of damages which may be awarded in connection with any
such taking or appropriation, except those awards which may be granted
separately to Tenant for its leasehold improvements and/or relocation expenses.

17.  Landlord's Covenant of Quiet Enjoyment; Title

     The Landlord represents it has the right to enter into this Lease and to
lease the Premises to the Tenant free of the claims of any third party, there
are no encumbrances to title which prohibit the permitted use, and the Building
and Property are not in violation of any easement of record. The Landlord
covenants that the Tenant, upon paying the Basic Rent and Additional Rent and
performing and observing all of the other covenants and provisions hereof, may
peaceably and quietly hold and enjoy the Premises for the Term as aforesaid,
subject, however, to all of the terms and provision of this Lease.

     In the event Landlord fails to perform any of its obligations under this
Lease within thirty (30) days after written notice from Tenant to Landlord and
to the holder of any mortgage on the Property of which Tenant has notice
specifying the nature of such obligations or if any such failure to perform such
obligations is of the type which cannot be cured within such thirty (30) days,
then if Landlord or the holder of any such mortgage (at the option of such
mortgagee) fails to (i) commence performing the cure thereof within thirty (30)
days after such written notice from Tenant and (ii) thereafter prosecute same to
completion with due diligence given the nature of same, then

                                       22

<PAGE>

thereafter at any time prior to Landlord's commencing same, Tenant may, but need
not, perform such obligations and may make a demand on Landlord for payment of
the reasonable out of pocket cost thereof actually incurred by Tenant. Tenant
need not wait for the expiration of any of the foregoing cure periods to expire
in the case of emergency. If, within thirty (30) days of receipt of any such
demand, Landlord shall not have paid same, then Tenant shall have the right to
bring suit in court of competent jurisdiction in the Commonwealth of
Massachusetts seeking payment of the sum claimed in Tenant's applicable demand.

18.  Tenant's Obligation to Quit

     The Tenant shall, upon expiration of the Term or other termination of this
Lease, leave peaceably and quietly surrender and deliver to the Landlord the
Premises and any replacements or renewals thereof in the order, condition and
repair required by Paragraph 10 hereof and the other provisions of this Lease,
except however, that the Tenant shall first remove any trade fixtures and
equipment (including but not limited to computer room equipment and fixtures
desired to be removed by Tenant) and any alterations, additions and improvements
which the Landlord has required be removed pursuant to the terms of Paragraph 12
hereof. Also, Tenant shall remove any alterations, additions, and improvements
which it has installed without seeking Landlord's consent pursuant to Paragraph
12 if the Landlord so requests. Tenant specifically agrees to repair any damage
caused by removal of any additional alterations or improvements.

19.  Assignment and Subletting

     The Tenant shall not assign, transfer, mortgage or pledge this Lease or to
grant a security interest in Tenant's rights hereunder, or to sublease (which
term shall be deemed to include the granting of concessions and licenses and the
like) or permit anyone other than Tenant to occupy all

                                       23

<PAGE>

or any part of the Premises or suffer or permit this Lease or the leasehold
interest hereby created or any other rights arising under this Lease to be
assigned, transferred or encumbered, in whole or in part, whether voluntarily,
involuntarily or by operation of law, unless, in each instance (i) the prior
written consent of Landlord thereto shall have been obtained, which consent
shall not be unreasonably withheld or delayed, (ii) any defaults then existing
with respect to the obligations of Tenant under this Lease shall have been
cured, and (iii) in the case of a proposed assignment, sublease or occupancy by
another, the proposed assignee, sublessee, or occupant is qualified to do
business in the state in which the Premises are located and in the case of a
proposed assignment, such assignee executes and delivers to Landlord an
agreement satisfactory to Landlord by which such assignee shall be bound by and
shall assume all the obligations of Tenant under this Lease. Notwithstanding the
foregoing, Tenant may assign this Lease or sublet any portion or all of the
Premises to any corporation, partnership, trust, association or other business
or organization (x) directly or indirectly controlling Tenant,(y) directly or
indirectly controlled by Tenant, (z) or under common control with Tenant, or to
any successor of Tenant by merger, consolidation or acquisition of substantially
all of the stock or assets of Tenant, without the prior written consent of
Landlord as required in (i) above, provided that (a) Tenant shall deliver to
Landlord at least 15 days' advance notice of such proposed assignment or
sublease, (b) in the case of a merger, consolidation or sale, the net worth of
Tenant's successor (determined in accordance with generally accepted accounting
principles) immediately after such merger, consolidation or sale shall be at
least equal to the greater of (1) the net worth of Tenant (similarly determined)
immediately prior to such merger, consolidation or sale or (2) the net worth of
Tenant (similarly determined) on the date hereof.

     If for any assignment or sublease or occupancy by another, Tenant receives
rent or other

                                       24

<PAGE>

consideration, either initially or over the term of the assignment, sublease or
occupancy, in excess of rent called for hereunder, or in case of sublease of
part of the Premises, in excess of such rent fairly allocable to the part so
subleased, after appropriate adjustments to assure that all other payments
called for hereunder are appropriately taken into account and after deducting
the reasonable costs of attorney, brokerage and renovation costs relating to the
sublease or assignment, Tenant shall pay to Landlord, as Additional Rent, 50% of
the excess of each such payment of rent or other consideration received by
Tenant promptly after its receipt.

     For the purposes of this Section 19, the transfer in the aggregate in any
twelve-month period of over 50% or more in interest in Tenant (whether stock,
partnership interest or other form of ownership or control) by any person or
persons having an interest in ownership or control of Tenant shall be deemed an
assignment of this Lease. The preceding sentence shall not apply to the Tenant
named herein if such Tenant is a corporation and the outstanding voting stock
thereof is listed on a recognized securities exchange nor shall such sentence
apply to an initial public offering of the stock of the initial Tenant provided
the outstanding stock thereof is listed on a recognized securities exchange.

     Any attempted assignment, transfer, mortgage, pledge, grant of security
interest, sublease or other encumbrance, except as permitted by this Section 19,
shall be void. No assignment, transfer, mortgage, grant of security interest,
sublease or other encumbrance, whether or not approved, and no indulgence
granted by Landlord to any assignee, sublessee or occupant shall in any way
impair Tenant's continuing primary liability (which after an assignment or
subletting shall be joint and several with the assignee or sublessee) of Tenant
hereunder, and no approval in a particular instance shall be deemed to be a
waiver of the obligation to obtain Landlord's approval in any other case.

                                       25

<PAGE>

20.  Transfers of Landlord's Interest

     The Landlord shall have the right from time to time to sell or mortgage its
interest in the Property, the Building and the Premises, to assign its interest
in this Lease, or to assign from time to time the whole or any portion of its
entitlement to receive the Basic Rent, Additional Rent or other sums and charges
at any time paid or payable hereunder by the Tenant to the Landlord, to any
Mortgagees or other transferees designated by the Landlord in duly recorded
instruments, and in any such case the Tenant shall pay the Basic Rent,
Additional Rent and such other sums and charges so assigned, subject to the term
of the Lease, upon demand to such Mortgagees and other transferees at the
addresses mentioned in and in accordance with the terms of such instruments
provided the Tenant has been notified of such transfer and provided with such
addresses, and further provided, that any such assignment shall not relieve
Landlord of any of its obligations hereunder.

21.  Mortgagees' Rights

     The Tenant hereby agrees that this Lease is and shall be subject and
subordinate to any mortgage (and to any amendments, extensions, increases,
refinancing or restructuring thereof) of the Property, the Building or the
Premises, whether or not such mortgage is filed subsequent to the execution,
delivery or the recording of this Lease or any notice hereof (the holder from
time to time of any such mortgage being in this Lease sometimes called the
"Mortgagee"). The foregoing subordination shall be self-operative and
automatically effective as to any mortgage filed subsequent to the execution and
delivery hereof but only if either the Mortgagee agrees in writing or such
mortgage provides that, for so long as there exists no default under this Lease
by the Tenant not cured within applicable periods of notice and grace, the
Mortgagee will be bound by the terms of this Lease and will not, in foreclosing
against or taking possession of the Premises or otherwise

                                       26

<PAGE>

exercising its rights under such mortgage, disturb the Tenant's possession of
the Premises hereunder or words of similar import. The Tenant hereby agrees to
execute, acknowledge and deliver in recordable form such instruments confirming
and evidencing the foregoing subordination as the Landlord or any such Mortgagee
may from time to time reasonably require.

     Provided that the Tenant has been provided with notice of such mortgage and
appropriate addresses to which notice should be sent, no notice from the Tenant
of any default by the Landlord in its obligations shall be valid, and the Tenant
shall not attempt to terminate this Lease, withhold Basic Rent or Additional
Rent or exercise any other remedy which may arise by reason of any such default,
unless the Tenant first gives such notice to all Mortgagees (which have provided
Tenant with notice of its mortgage) and provides such Mortgagees with reasonable
time after such notice to cure such default, provided that, such Mortgagees
shall be bound by any applicable cure periods specified in this Lease. The
Tenant shall and does hereby agree, upon default by the Landlord under any
mortgage, to attorn to and recognize the Mortgagee or anyone else claiming under
such mortgage, including a purchaser at a foreclosure sale so long as such
mortgagee or other party agrees to be bound by the Landlord's obligations under
this Lease, at its request as successor to the interest of the Landlord under
this Lease, to execute, acknowledge and deliver in recordable form such evidence
of this attornment, which shall nevertheless be self-operative and automatically
effective, as the Mortgagee or such successor may request and to make payments
of Basic Rent and Additional Rent hereunder directly to the Mortgagee or any
such successor, as the case may be, upon request. Any Mortgagee may, at any
time, by giving written notice to, and without further consent from, the Tenant,
subordinate its mortgage to this Lease, and thereupon the interest of the Tenant
under this Lease shall automatically be deemed to be prior to the lien of such
mortgage without regard to the

                                       27

<PAGE>

relative dates of execution, delivery or recording thereof or otherwise.
Landlord shall, within 60 days of the date hereof or the date of a new mortgage
(as the case may be), obtain from any current or future mortgagee a
non-disturbance and attornment agreement in form customary for mortgagee and
reasonably satisfactory to Tenant.

22.  Tenant's Default Landlord's Remedies

     If the Tenant shall default in the payment of any Basic Rent or Additional
Rent and such default shall continue for ten (10) days after written notice from
the Landlord; or if the Tenant shall default in the performance or observance of
any of the other covenants contained in these presents and on the Tenant's part
to be performed or observed and shall fail, within thirty (30) days after
written notice from the Landlord of such default, to cure such default or if
such default is not susceptible of cure within said thirty (30) day period,
promptly to make provision for such cure and thereafter to pursue such cure
diligently to completion; or if the estate hereby created shall be taken on
execution, or by other process of law; or if the Tenant shall be involved in
financial difficulties as evidenced:

     (1)  by its commencement of a voluntary case under Title 11 of the United
          States Code as from time to time in effect, or by its authorizing, by
          appropriate proceeding of trustees or other governing body the
          commencement of such voluntary case,

     (2)  by its filing an answer or other pleading admitting or failing to deny
          the material allegations of a petition filed against it commencing an
          involuntary case under said Title 11, or seeking, consenting to or
          acquiescing in the relief therein provided, or by its failing to
          controvert timely the material allegations of any such petition,

                                       28

<PAGE>

     (3)  by the entry of an order for relief in any involuntary case commenced
          under said Title 11,

     (4)  by its seeking relief as a debtor under any applicable law, other than
          said Title 11, or any jurisdiction relating to the liquidation or
          reorganization of debtors or to the modification or alteration of the
          rights of creditors, or by its consenting to or acquiescing in such
          relief,

     (5)  by the entry of an order by a court of competent jurisdiction (i)
          finding it to be bankrupt or insolvent, (ii) ordering or approving its
          liquidation, reorganization or any modification or alteration of the
          right of its creditors, or (iii) assuming custody of, or appointing a
          receiver or other custodian for, all or a substantial part of its
          property, or

     (6)  by its making an assignment for the benefit of, or entering into a
          composition with, its creditors, or appointing or consenting to the
          appointment of a receiver or other custodian for all or a substantial
          part of its property;

then and in any of said cases, the Landlord may, to the extent permitted by law,
immediately or at any time thereafter so long as such default remains incurred
and with reasonable demand and notice, terminate this Lease and enter into and
upon the Premises, or any part thereof in the name of the whole, and repossess
the same as of the Landlord's former estate, and expel the Tenant and those
claiming through or under the Tenant and remove its effects without being deemed
guilty of any manner of trespass, and without prejudice to any remedies which
might otherwise be used for arrears of rent or preceding breach of covenant.

     No termination or repossession provided for in this Paragraph 22 shall
relieve the Tenant or

                                       29

<PAGE>

any guarantor of the obligations of the Tenant under this Lease of its
liabilities and obligations under this Lease, all of which shall survive any
such termination or repossession. In the event of any such termination or
repossession, the Tenant shall pay to the Landlord either (i) in advance on the
first day of each month, for what would have been the entire balance of the
Term, one-twelfth (1/12) (and a pro rata portion thereof for any fraction of a
month) of the Basic Rent, Additional Rent and all other amounts for which the
Tenant is obligated hereunder, less, in each case, the actual net receipts by
the Landlord by reason of any reletting of the Premises after deducting the
Landlord's reasonable expenses in connection with such reletting, including,
without limitation, removal, storage and repair costs and reasonable brokers'
and attorneys' fees, or (ii) at the option of the Landlord exercisable by the
Landlord's giving notice to the Tenant within thirty (30) days after any such
termination, the present value (computed at a capitalization rate based upon the
so-called corporate "Base Rate" then in effect at The First National Bank of
Boston) of the amount by which the payments of Basic Rent and the Additional
Rent reasonably estimated to be payable for the balance of the Term after the
date of the exercise of said option would exceed the payments reasonably
estimated to be the fair rental value of the Premises on the terms and
conditions of this Lease over such period, determined as of such date. Landlord
shall use reasonable efforts to relet the Premises for the reasonable rental
value thereof and to collect the rent under such reletting but Landlord shall
not be liable for failure to relet the Premises or in the event that the
Premises are relet for failure to collect the rent under such reletting.

     Without thereby affecting any other right or remedy of the Landlord
hereunder, the Landlord may, at its option, cure for the Tenant's account any
default by the Tenant hereunder which remains uncured, after the end of cure
period provided for in this Lease, and the cost to the Landlord of such

                                       30

<PAGE>

cure shall be deemed to be Additional Rent and shall be paid to the Landlord by
the Tenant with the installment of Basic Rent next accruing.

     In the event that the Landlord fails to perform any of its obligation under
this Lease within thirty (30) days after notice of such default from the Tenant,
then Tenant may cure such default and any reasonable costs incurred by Tenant in
connection with such default shall be promptly reimbursed by Landlord upon
presentation with appropriate invoices.

23.  Remedies Cumulative; Waivers; Attorney's Fees

     The specific remedies to which the Landlord or the Tenant may resort under
the terms of this Lease are cumulative and are not intended to be exclusive of
any other remedies or means of redress to which the Landlord or the Tenant may
be lawfully entitled under any provision of this Lease or otherwise. The failure
of the Landlord or the Tenant to insist in any one or more cases upon the strict
performance of any of the covenants of this Lease, or to exercise any option
herein contained, shall not be construed as a waiver or relinquishment for the
future of such covenant or option. A receipt by the Landlord, or payment by the
Tenant, of Basic Rent or Additional Rent with knowledge of the breach of any
covenant hereof shall not be deemed a waiver of such breach, and no waiver,
change, modification or discharge by the Landlord or the Tenant of any provision
in this Lease shall be deemed to have been made or shall be effective unless
expressed in writing and signed by an authorized representative of the Landlord
or the Tenant as appropriate. In addition to the other remedies in this Lease
provided, the Landlord or the Tenant shall be entitled to the restraint by
injunction of the covenants, conditions or provisions. If either party brings an
action to enforce the terms hereof or declare rights hereunder, the prevailing
party in such action, on trial or appeal, shall be entitled to its reasonable
attorney's fees to be paid by the losing party as fixed by the court.

                                       31

<PAGE>

24.  Extension of Term

     The Tenant shall have the right, at its sole option, by in each instance
giving notice thereof to the Landlord at least nine (9) months prior to the
expiration of the then existing Term, to extend the Term of this Lease for one
(1) additional successive period of five (5) years (commencing upon the
expiration of the initial Term) on the same terms and conditions, except Basic
Rent, as herein set forth except that it is understood and agreed that such
extensions shall be exercisable only if at the time of exercise in each case (i)
there exists no default on the part of the Tenant under this Lease which has not
been cured within the time provided for cure hereunder and (ii) the party then
obligated under this Lease is one or more of the following: the Tenant
originally named herein, any other tenant that is a parent, a subsidiary of, a
corporation or other entity controlling or under common control with, or a
successor by reason of a merger, consolidation or sale of stock or assets of,
the Tenant originally named herein or any entity controlled by, or under common
control with Tenant. The failure to give such notice in a timely fashion shall
be deemed an irrevocable election on the part of the Tenant not to exercise such
extension option.

     The Basic Rent during such extended period shall be the fair market net
rental for the Premises (not including special computer room improvements
installed by Tenant at its expense) under the terms and conditions of this Lease
for a period of five years determined as of the commencement of such extended
period. Tenant shall notify Landlord not sooner than nine (9) months prior to
the expiration of the then existing Term of its desire to enter into
negotiations to determine Basic Rent for the extended period. If the Landlord
and the Tenant are unable to agree upon the Basic Rent for such extended period
at least eight (8) months prior to its commencement, the Basic Rent for such
period shall be determined by appraisal as hereinafter provided. Within ten

                                       32

<PAGE>

(10) days after the date for commencement of appraisal proceedings pursuant to
the provisions of this Paragraph 24, the Landlord and the Tenant shall each
simultaneously give written notice to the other setting forth its "best offer"
for such annual rate of Basic Rent and designating an Appraiser (as that term is
hereinafter qualified and defined). The two Appraisers so designated shall,
within ten (10) days after their designation, select a third Appraiser and give
notice to both the landlord and the Tenant identifying the third Appraiser. The
three Appraisers shall within thirty (30) days after the selection of the third
Appraiser report to the Landlord and the Tenant in writing, informing them of
the annual rate of Basic Rent determined by them, or by a majority of them, to
be payable by the Tenant to the Landlord for the Premises during such 5-year
extended period. The Appraiser's report shall be accompanied by an explanation
of the method used to arrive at the value or values assigned and the pertinent
data (or a summary thereof) considered by the Appraisers in reaching their
decision. All expenses of the appraisal process (including Appraisers' fees)
shall be payable by the party whose "best offer" set forth in the notice as
above provided varied the most from the annual rate of Basic Rent established in
the Appraisers' report. The Appraisers shall advise the parties which is
responsible for the expenses. An "Appraiser" shall be a person who is an MAI
(Member of the Appraisal Institute) designation, is independent of the Landlord
and the Tenant, and has at least eight (8) years' experience in appraising
commercial and industrial real estate in the metropolitan Boston area.

     Notwithstanding the foregoing procedure, in no event will the Basic Rent be
less than $809,627 per year.

25.  Brokers

     Tenant represents and warrants that it has had no dealings with any broker
or agent in

                                       33

<PAGE>

connection with this Lease, other than Meredith & Grew and CRF Partners, Inc.
(collectively, the "Brokers") and shall indemnify and hold harmless Landlord
from any claims for any brokerage commission other than that of the Brokers as a
result of the failure of this warranty. Landlord represents and warrants that it
has had no dealing with any broker or agent in connection with this Lease other
than the Brokers and shall indemnify and hold harmless Tenant from any claims
for any brokerage commission (including from Brokers) as a result of the failure
of this warranty. Landlord covenants and agrees that any and all brokerage fees
due to the Brokers are its sole and exclusive obligation.

26.  Notices

     Any notices, approvals, specifications or consents required or permitted
hereunder shall be in wiring and mailed, postage prepaid, by registered or
certified mail, return receipt requested, if to the Landlord or to the Tenant at
100 Brickstone Square, Andover, MA 01810 Attention: General Counsel for each, a
copy of any notice to Tenant shall be sent to Hale and Dorr LLP, 60 State
Street, Boston, MA 02109 - Attn: Pamela Coravos and if to any Mortgagee at such
address as it may specify by such notice to the Landlord and the Tenant, or at
such other address as any of them may from time to time specify by like notice
to the others. Any such notice shall be deemed given when received or, if
earlier, when postal records indicate delivery was first attempted.

27.  Recording

     The Landlord and the Tenant hereby agree, each at the request of the other
or of any Mortgagee, promptly to execute, acknowledge and deliver in recordable
from short forms or notices of lease and notices of assignments or rents and
profits containing the date of commencement of the Term and such other
information as may from time to time be necessary under the applicable statutes

                                       34

<PAGE>

for the protection of any interest of the Landlord, the Tenant or any Mortgagee
in the Premises of this Lease.

28.  Estoppel Certificates

     The Landlord and the Tenant hereby agree from time to time, each within ten
(10) days prior written notice from the other or any Mortgagee, to execute,
acknowledge and deliver, without charge, to the other party, the Mortgagee or
any other person designated by the other party, a statement in writing
certifying: that this Lease is unmodified and in full force and effect (or if
there have been modifications, identifying the same by the date thereof and
specifying the nature thereof); that to the knowledge of such party there exist
no defaults (or if there be any defaults, specifying the same); the amount of
the Basic Rent, the dates to which the Basic Rent, Additional Rent and other
sums and charges payable hereunder have been paid; and that such party to its
knowledge has no claims against the other party hereunder except for the
continuing obligations under this Lease (or if such party has any such claims,
specifying the same).

29.  Bind and Inure; Limited Liability of Landlord

     All of the covenants, agreements, stipulations, provisions, conditions and
obligations herein expressed and set forth shall be considered as running with
the land and shall extend to, bind and inure to the benefit of the Landlord and
the Tenant, which terms as used in this Lease shall include their respective
successors and assigns where the context hereof so admits.

     The Landlord shall not have any individual or personal liability for the
fulfillment of the covenants, agreements and obligations of the Landlord
hereunder, the Tenant's recourse and the Landlord's liability hereunder being
limited to the Property and the Building. The term "Landlord" as used in this
Lease shall refer only to the owner or owners from time to time of the Property
or the

                                       35

<PAGE>

Building, it being understood that no such owner shall have any liability
hereunder for matters arising from and after the date such owner ceases to have
any interest in the Property or the Building.

     In no event shall either party be liable to the other for any special,
consequential or indirect damages suffered by the other party, whether arising
in contract or tort.

30.  Captions

     The captions for the numbered Paragraphs of this Lease are provided for
reference only, and they do not constitute a part of this agreement or any
indication of the intentions of the parties hereto.

31.  Integration

     The parties acknowledge that all prior written and oral agreements between
them and all prior representations made by either party to the other have been
incorporated in this instrument or otherwise satisfied prior to the execution
hereof.

32.  Hazardous, Toxic Substances

     The term "Hazardous Substances", as used in this Paragraph, shall include,
without limitation, flammables, explosives, radioactive materials, asbestos,
polychlorinated biphenyls (PCBs), chemicals known to cause cancer or
reproductive toxicity, pollutants, contaminants, hazardous wastes, toxic
substances or related materials, petroleum and petroleum products, and
substances declared to be hazardous or toxic under any law or regulation now or
hereafter enacted or promulgated by any governmental authority.

Tenant shall not cause or permit to occur:

     (a)  Any violation of any federal, state, or local law, ordinance, or
          regulation now or hereafter enacted, related to environmental
          conditions, under, or about the Premises

                                       36

<PAGE>

          arising from Tenant's use or occupancy of the Premises, including, but
          not limited to, soil and ground water conditions; or

     (b)  The use, generation, release, manufacture, refining, production,
          processing, storage, or disposal (including, without limitation, any
          by-products of Tenant's manufacturing operations) of any Hazardous
          Substance on, under, or about the Premises, or the transportation to
          or from the Premises of any Hazardous Substance, except for such
          substances and materials which are used in connection with the
          operations of the Tenant permitted under this Lease and which shall be
          used, stored, handled and disposed of both individually and in the
          aggregate solely in accordance with all Laws.

In furtherance of Tenant's obligations under this Lease and not in limitation
thereof, Tenant covenants and agrees as follows:

     (a)  Tenant shall, at Tenant's expense, comply with all laws regulating its
          use, generation, storage, transportation, or disposal of Hazardous
          Substances (the "Laws").

     (b)  Tenant shall, at Tenant's expense, make all submissions to, provide
          all information required by, and comply with all requirements of all
          governmental authorities (the "Authorities") under the Laws related to
          Tenant's use and occupancy of the Premises.

     (c)  If a clean-up is required under any Law because of any deposit, spill,
          discharge, or other release of Hazardous Substances that occurs during
          the Term, at or from the Premises which is caused by Tenant's action
          or omission, then Tenant shall, at Tenant's expense, prepare and
          submit the required plans and all related bonds and other financial
          assurances; and Tenant shall carry out all work required by such

                                       37

<PAGE>

          clean-up plans under the Laws.

     (d)  Tenant shall promptly provide all information regarding the use,
          generation, storage, transportation or disposal of Hazardous
          Substances that is reasonably requested by Landlord. If Tenant fails
          to fulfill any duty imposed under this Paragraph, within a reasonable
          time, Landlord may do so; and in such case, Tenant shall reasonably
          cooperate with Landlord in order to prepare all documents Landlord
          deems reasonably necessary or appropriate to determine the
          applicability of the Laws to the Premises and Tenant's use thereof,
          and for compliance therewith, and Tenant shall execute all documents
          which are deemed reasonably satisfactory by Tenant's legal counsel
          promptly upon Landlord's request. No such action by Landlord and no
          attempt made by Landlord to mitigate damages under any Law shall
          constitute a waiver of any of Tenant's obligations under this
          Paragraph.

     Tenant shall indemnify, defend, and hold harmless Landlord and its
officers, directors, shareholders and all of their respective agents and
employees from all fines, suits, procedures, claims, and actions of every kind
and all costs, associated therewith (including attorneys and consultants fees)
arising out of or in any way connected with any deposit, spill, discharge, or
other release of Hazardous Substances caused by Tenant's action or omission that
occurs during the Term at or from the Premises, or from Tenant's failure to
provide all information, make all submissions, and take or refrain from taking
all actions required by all Authorities under the Laws and all other
environmental laws relating to Tenant's use and occupancy of the Premises.
Landlord shall give Tenant prompt written notice of any claim or suit which it
has a right to indemnification hereunder. Landlord shall (at Tenant's expense)
render Tenant all reasonable assistance requested by Tenant

                                       38

<PAGE>

in the defense or settlement of any such claim or suit. Neither party shall pay
any such claim, or settle any such suit, without the prior written consent of
the other party, which shall not be unreasonably withheld. Tenant's obligations
and liabilities under this Paragraph shall survive the expiration or termination
of this Paragraph.

     Landlord, to the best of its knowledge, is not aware of any Hazardous
Substances which have been released on the Property.

     There shall be excluded from Common Expenses any costs arising from
management, abatement, removal or remediating any lead paint, asbestos or PCBs
and costs arising from the presence of Hazardous Substances in the air, soil,
surface waters or groundwater of the Premises except to the extent caused by
Tenant acts.

     Landlord has no knowledge of the presence of Hazardous Substances in the
Building or at, on, or about the Premises or on the property abutting the
Premises.

     Tenant shall not be responsible under this Lease in any respect whatsoever
for any condition involving Hazardous Substances which may exist as of the date
of execution and delivery of this Lease or which was not caused by Tenant.

33.  Severability; Choice of Law

     If any provision of this Lease shall be declared to be void or
unenforceable either by law or by a court of competent jurisdiction, the
validity or enforceability of the remaining provisions shall not thereby be
affected.

34.  Financial Statements

     If requested by Landlord in connection with a financing or sale, Tenant
shall furnish to Landlord and to any holder of a mortgage on the Premises as
Landlord may designate by notice to

                                       39

<PAGE>

Tenant, a copy of its most recent annual report(s) and/or quarterly reports.

35.  Security Deposit

     At the time of the execution hereof, Tenant shall pay to Landlord a
security deposit in the amount of $58,763.25 which may be an irrevocable letter
of credit drawn on a bank and in a form reasonably satisfactory to the Landlord.
The Landlord may apply the deposit from time to time against outstanding
obligations of Tenant hereunder. Tenant shall have no right to require the
Landlord to so apply said deposit, nor shall Tenant be entitled to credit the
same against rents or other sums payable hereunder. If and to the extent that
the Landlord makes such use of the security deposit, or any part thereof, the
sum so applied by Landlord shall be restored to the security deposit by Tenant
upon ten (10) days written notice from Landlord, and failure to pay to Landlord
the amount to be so restored shall be a default hereunder giving rise to all of
the Landlord's rights and remedies applicable to a default in the payment of
rent*. Provided Tenant is not then in default beyond any applicable notice and
cure periods, Landlord shall return the security deposit within 30 days of the
termination or earlier expiration of the Lease.

*    Tenant shall have no obligation to restore any Substitute Credit as defined
     in the Lease Guaranty.

36.  Signage

     Tenant shall, at its sole cost and expense, have the right to install
signage in an area not to exceed 50 square feet upon the exterior of the
Building (as shown on Exhibit S). If Landlord, at its expense, constructs a
pylon sign for the Building, Tenant shall have the right to install a strip
thereon identifying the Tenant, at its cost and expense. If Landlord installs,
at Landlord's expense, a Building directory, Landlord shall provide for the
inclusion of Tenant's name. All signage is subject to Landlord's prior approval
taking into account the overall appearance of the Building and the management of
the Building and Park and which shall not be unreasonably withheld. All such

                                       40

<PAGE>

signage shall comply with applicable laws, ordinances, regulations and
requirements of governmental bodies having jurisdiction.

37.  Y2K

     Landlord warrants to Tenant that base Building equipment, software and
appliances, including but not limited to elevators, heating, ventilating and air
conditioning systems, card key access systems, door locks, energy management
systems, sprinkler systems, fire detection and life safety systems and other
building systems will remain fully functional and perform their normal
operations on and after January 1, 2000, without interruptions or malfunctions
as a result of the passage from the year 1999 to the year 2000. If any repairs,
alternations or replacements must be made to any of the aforesaid equipment,
software or appliances in order to prevent or eliminate any such interruptions
or malfunctions in the services or operations provided thereby, Landlord will
cause any such repairs, alterations or replacements will be paid by Landlord.
Landlord further agrees that any interruption or malfunction of any of the
aforesaid building systems which may occur as a result of the passage from the
year 1999 to the year 2000 will not be deemed to constitute a "force majeure"
event or an event the occurrence of which is beyond the reasonable control of
the Landlord to prevent or avoid.

38.  Roof Rights

     Subject to Article 12 of the Lease, Tenant shall have the right to install
telecommunications equipment on the roof of the Building in a location mutually
agreeable to Landlord and Tenant taking into account good engineering practice
and overall management of the Building.

     This Lease is made under, and shall be construed in accordance with, the
laws of the Commonwealth of Massachusetts.

                                       41

<PAGE>

     IN WITNESS WHEREOF, the parties hereto have caused this instrument to be
executed in duplicate under seal as of the date first above written.

     Landlord


     /s/ William J. Callahan
     ---------------------------------------------
     William J. Callahan, Trustee as aforesaid
     and not individually


     /s/ William J. Callahan, Jr., Trustee
     ---------------------------------------------
     William J. Callahan Jr., Trustee as aforesaid
     and not individually


     Tenant
     NaviNet, Inc.


     By: Illegible
         -----------------------------------------
                     Name and Title

                                       42

<PAGE>

                                                                       Exhibit A

                                 [Map] SITE MAP

<PAGE>

                                                                     Exhibit A-1

                              [GRAPHIC] FLOOR PLAN

800 FEDERAL STREET                                              FIRST FLOOR PLAN
================================================================================
Woodland Park, Andover, MA.              Andover Park Realty Trust, Andover, MA.

<PAGE>

                                                                       Exhibit B

[GRAPHIC]

                         WILLIAMS CONSTRUCTION CO., INC.
--------------------------------------------------------------------------------
  2 SKY MEADOW DRIVE, NASHUA, NH 03062 * (603) 891-1054 * FAX (603)891-1186

                         Outline Specification "NAVINET"

                               800 FEDERAL STREET

                                ANDOVER, MA 01810

                               September 21, 1999

BUILDING SPECIFICATION:

We propose to complete the following tenant improvement work for Navinet. This
work to be done in conformance with all local, state and other agencies having
jurisdiction. The building will meet the requirements of the A.D.A. This outline
specification is based on drawings F-1 Dated 9/15/99 by Visnick & Caulfield
Associates. The building common loading area will remain as base building plan.

OFFICE PARTITIONS:

Shall be constructed of 3 5/8" screwable 25 gauge galvanized metal stud, and all
required metal track, with 1/2" drywall, taped and sanded, ready to paint.

Supply and install nineteen hundred and eighty (1,980) lineal feet of wall type
1. 9'6" Partition (6" above ceiling).

Supply and install eleven hundred and ten (1,110) lineal feet of

<PAGE>

wall type 2. Full height partition to the underside of deck.

Supply & install 3 1/2" batt insulation to all new walls listed above.

CEILINGS:

To be suspended type with Class "A" 2' x4' x5/8" fissured tile.

Supply and install all necessary wall angle and cuts for walls that extend
through ceiling.

FLOORS:

Building standard carpet is a 26 oz., Olefin, installed, directly glued down on
the concrete floor. Color to be selected by Tenant. Provide a supplied and
installed carpet allowance for five thousand three hundred and fifty yards
(5,350 yd) of carpet at eighteen ($18.00sq.yd) dollars per square yard.

Supply and install 1/8" Standard Excelon vinyl composition tile manufactured by
Armstrong, color to be selected by Tenant.

Supply all necessary carpet to tile reducers.

4" Vinyl base Manufactured by Johnsonite Shall be 4" cove. Color shall be
selected by Tenant.

DOORS, FRAMES, AND HARDWARE:

One hundred and seven (107) new 3'x0"-7'x0" doors, manufactured by Weyerhaeuser
or equal, shall be solid core premium grade birch doors.

Two (2) new 6'x0'-7'xO' doors, manufactured by Weyerhaeuser or equal, shall be
solid core premium grade birch doors.

Frames shall be 16 gauge metal of knock down construction. All hardware shall
include Falcon "F" series brushed chrome passage, or Lock lever sets. Sixteen
(16) Norton 8500 series door closures are figured, coat hooks per door schedule.
Wall or floor stops shall be provide for all doors.

Hollow Metal side lifts:

Supply and install the following:
   Eighty seven (87)  3'-0" x 7'-0"
   Two           (2) 12'-0" x 7'-0"

                                       2

<PAGE>

   One           (1) 18'-0" x 7'-0"

GLASS & GLAZING:

Supply and install the following:
   Eighty seven (87) 1/4" tempered sidelites.
   Forty two    (42) lineal feet of 1/4" tempered glass for
                     conference rooms.

PAINTING:

1.   All interior walls shall receive two coats of eggshell latex paint. Paint
     shall be Benjamin Moore, color to be White Dove.

2.   All interior door frames shall receive two coats of Alkyd semi-Gloss,
     color to be White Dove.

3.   All interior solid core birch doors shall receive two coats of
     polyurethane.

MILLWORK:

Provide closet pole and shelf for two closet.

Provide one hundred and forty two (142') lineal feet laminate cabinets and
countertops

All other millwork shall be provided by Tenant.

Blocking:

Supply and install all necessary fire rated wood blocking.

APPLIANCES:

Provide three (3) Whirlpool refrigerators with ice makers.

Provide two (2) Whirlpool dishwashers.

ELECTRIC:

1.   Provide two outlet per office.

2.   Supply power wiring to added V.A.V. Boxes

3.   Add two (2) 75 kva transformers, two (2) 225 amp 120/208 volt double tub
     panels, 42 circuits per tub.

4.   Provide 120 volt 20 amp. power to cubicles per plan. No more

                                       3

<PAGE>

     than eight (8) cubicles on a three (3) circuit, 4 wire feed (MC cable).

5.   Each enclosed room to have separate switch.

6.   Lighting fixtures will be 18 cell parabolics with t-8, 3 lamps and
     electronic ballast. Supply and install ninety three (93) additional 18 cell
     parabolics for tenant improvement work.

7.   Provide exit signs, emergency lighting, strobes, and horns as required by
     code.

8.   No special electrical requirements have been figured for interior
     conference rooms or labs.

9.   Refer to Page 5 - Additional Electrical Specifications

HEATING, VENTILATION, AND AIR CONDITIONING:

1.   Provide engineering, vav boxes, ductwork, diffusers and control wiring and
     balancing for a variable air volume system.

2.   Space above the suspended ceiling is utilized as an Open plenum return.

3.   400 sq ft per ton of A/C is provided for open areas.

4.   No special HVAC requirements have been figured for interior conference
     rooms or labs.

PLUMBING:

1.   All plumbing work shall be performed in compliance with the Massachusetts
     State Plumbing Codes as well as the Plumbing codes required by the town of
     Andover.

2.   Supply and install three (3) 33x22 SS kitchen sink.

3.   Supply and install two (2) 1/2 hp disposals.

Fire Protection:

Relocate or add all necessary sprinkler heads per NFPA 13 ordinary hazard.

Supply and install ten (10) Larsen's recessed cabinets model #2409-2 and 10 LB
ABC fire extinguishers and triangular signs.

                                       4

<PAGE>

Additional Electrical Specifications:

MAIN SERVICE-

1.   Two (2) 3000 amp, 3 phase 4 wire 277/480 volts with (6) six 600 amp and (1)
     one 400 amp distribution breaker.

DISTRIBUTION-

1.   The building is designed to be divided into seven (7) separate areas
     including metered section. Six (6) meters for tenant areas and one (1)
     meter for common area.

2.   Each section has a 600 amp distribution panel for all 277/480 volt
     requirements and 225 amp panel feed by a 75 KVA transformer for all 120/208
     volt requirements.

3.   The house panel is 400 amp 40 volts and has a 150 amp 120/208 panel feed by
     a 45 KVA transformer.

Exclusions:

power wiring - distribution or equipment connections process piping - drainage,
gas, water, air, steam, oil, etc. fire suppression system for computer rooms.

curtains, blinds, and all other window treatments.

special non slip or static proof floor finishes other than specified above.

raised computer room flooring wall covering other than specified above fire
alarm system for data center security system and card reader access system
smoke or draft curtains telephone/data equipment, wiring or receptacles computer
equipment, wiring or receptacles special electrical equipment other than
specified above exterior and interior signs public address system no desk,
cabintry, or millwork has been figured for reception area.


-----------------                                       ------------------------
CMGI Accepted By:                                       Williams Const. Co., Inc

                                       5

<PAGE>

                                                                       Exhibit B

                               [GRAPHIC] BUILDOUT

<PAGE>

                                                                       Exhibit S

                             [GRAPHIC] SIGN LOCATION

<PAGE>

                                 LEASE GUARANTY

     CMGI, Inc. (the "Guarantor") is a Delaware corporation having a business
address at 100 Brickstone Square, Andover, MA 01810. The Guarantor's wholly
owned subsidiary, NaviNet, Inc. (the "Tenant") is a corporation which has
entered into a lease (the "Lease") dated as of Nov. 30,1999, with William J.
Callahan and William J. Callahan, Jr., as they are trustees of Andover Park
Realty Trust under a declaration of trust dated June 25, 1986 and filed with the
Essex County (North District) Registry of Deeds in Book 2226, Page 284 (the
"Landlord"), having an address c/o P.O. Box 269, Bedford, Massachusetts 01730
with respect to the leased Premises at 800 Federal Street, Woodland Park,
Andover, Massachusetts.

     For good and valuable consideration, the Guarantor hereby unconditionally
guarantees the payment when due of all Basic Rent, Additional Rent and other
amounts from time to time due under the Lease and the Performance of all of the
Tenant's obligations and undertaking under the Lease and the prompt
reimbursement to Landlord of all costs and expenses of enforcement or collection
incurred by Landlord with respect to the Lease or under this Guaranty (together
called the "Obligations"). In the case of rental payments due under the Lease,
this Guaranty is a guarantee of payment and is absolute and in no way
conditional or contingent. Notwithstanding the foregoing, in connection with the
enforcement of this Guaranty by the Landlord, the Guarantor may assert any
defense against the Landlord which is available to the Tenant under the Lease.
In case any of the Tenant's covenants and agreements under the Lease have not
been performed or any rental payments shall not have been paid by the Tenant
when due, the Guarantor will, not later that five(5) business days after written
notice by the Landlord, perform the same and/or pay the same or cause the same
to be performed and/or paid to the Landlord.

     This Guaranty shall continue in effect during the initial term and any
extended or renewal term or terms (collectively the "Term") under the Lease and
with respect to those Obligations of the Tenant under the Lease which survive
the termination of the Lease, this Guaranty shall continue in effect until said
obligations have been satisfied in full. The Guarantor's obligation to pay the
rental payments when due under the Lease shall continue notwithstanding the fact
that the collection or enforcement thereof against the Tenant may be stayed or
enjoined under Title 11 of the United States Code, as from time to time in
effect, or other similar law. The Guarantor hereby acknowledges that the
Landlord has entered into the Lease in reliance on this Guaranty being a
continuing agreement and the irrevocability of the Guaranty hereunder and agrees
that this Guaranty may not be revoked in whole or in part except as specifically
provided in the last paragraph hereof.

     The Guarantor's obligations under this Guaranty shall not be affected by
any action taken by the Landlord to waive compliance with, consent to or enter
into any amendment or change of any of the terms of, or grant any other
indulgence under, the Lease without prior notice to the Guarantor.

     Guarantor agrees: that the liability of Guarantor hereunder is direct and
unconditional and may be enforced without requiring Landlord first to resort to
any other right or remedy against Tenant or its successors or assigns or any
other guarantor of any of the Obligations, or to resort to any security for any
of the Obligations, and Guarantor hereby waives any right which it would or
might have at law, in equity or by statute to require Landlord first to resort
to any such right or remedy or to any such security, that this Guaranty shall be
construed as an absolute, unconditional, continuing and unlimited obligation of
Guarantor without regard to the regularity, validity or enforceability of any of
the Obligations; that the Guarantor shall have not right of subrogation,
reimbursement or indemnity nor any right of recourse to security for any of the

                                       1

<PAGE>

Obligations until the Term of the Lease has expired, Tenant has vacated the
premises, and all of the Obligations have been fully paid and performed; that
any and all present and future debts and obligations of Tenant to Guarantor are
hereby subordinated and postponed to the full payment, performance and
observance of all of the Obligations; and that nothing shall discharge or
satisfy the liability of Guarantor except the full payment, performance and
observance of all of the Obligations.

     The Guarantor, by its execution hereof (i) hereby irrevocably submits to
the nonexclusive jurisdiction of the Commonwealth of Massachusetts and to the
nonexclusive jurisdiction of the United States District Court for the District
of Massachusetts for the purpose of any suit, action or other proceedings
arising out of or based upon this Guaranty, brought by the Landlord and (ii)
hereby waives, to the extent not prohibited by law, and agrees not to assert, by
way of motion, as a defense or otherwise, in any proceeding, any claim that the
Guarantor is not subject personally to the jurisdiction of the above-named
courts, that the Guarantor's property is generally exempt or immune from
attachment or execution, that any such proceeding brought in one of the
abovenamed courts is brought in an inconvenient forum, that the venue of any
such proceeding brought in any one of the above-named courts is improper, or
that this Guaranty may not be enforced in or by such court.

     This Guaranty shall be binding upon the Guarantor and its successors and
assigns and shall inure to the benefit of the Landlord and its successors and
assigns.

     Any sums paid and all cost and expenses, including reasonable attorney's
fee, incurred by the Landlord in connection with the enforcement of this
Guaranty and/or the Lease, shall be reimbursed by the Guarantor to the Landlord
immediately upon demand thereof, accompanied by reasonable documentation.

     Notwithstanding the foregoing provisions of this Guaranty, Guarantor shall
have no greater liability under this Guaranty than Tenant has under the Lease.

     Notwithstanding anything to the contrary contained herein, this Guaranty
and all of Guarantor's obligations and agreements hereunder shall terminate and
be of no further force or effect immediately upon either (a) the closing of the
sale of shares of common stock of NaviNet, Inc. in a public offering pursuant to
an effective registration statement under the Securities Act of 1933, as amended
resulting in a net worth (determined in accordance the GAAP) in excess of
$55,000,000 or (b) deposit with Landlord an additional amount either in cash or
in the form of an irrevocable letter of credit drawn on a bank and in a form
reasonably satisfactory to Landlord to be held and applied in compliance with
terms and conditions of article 35 of the Lease as modified by the terms of this
Guaranty (the "Substitute Credit") so that the Substitute Credit shall be as
follows:

                       1-2 months of Term -    $1,000,000;
                       13-24 months of Term -  $1,000,000;
                       25-36 months of Term -  $  925,000;
                       37-48 months of Term -  $  850,000;
                       49-60 months of Term -  $  775,000;
                       61-72 months of Term -  $  700,000;
                       Any extension of Term - $  700,000.

Within thirty days of the commencement of each year of the Term of the Lease
after the Substitute Credit has been deposited with Landlord, Landlord shall
forthwith refund to Guarantor an appropriate amount of such Substitute Credit
if the same is in the form of cash to be in compliance with the Substitute
Credit defined for each year of the Term or if it is in the form of a

                                       2

<PAGE>

letter of credit, the renewal of the letter of credit shall be in an amount to
be in compliance with the Substitute Credit defined for each year of the Term.
Such Substitute Credit shall be held and applied by Landlord as security deposit
under the Lease. Under no circumstances shall Guarantor have any obligations
whatsoever to replenish such Substitute Credit if the Landlord has drawn down
any portion of the letter of credit and/or applied any portion of a Substitute
Credit in the form of cash. Further, if there is a draw and/or application (the
"Draw Amount"), and there is subsequent decrease in the required amount of the
Substitute Credit (the "Burn Down Amount"), the required Substitute Credit
amount shall be decreased in the amount by which the Draw Amount exceeds the
Burn Down Amount. By way of example, assume in the 24th month there is a draw in
the amount of $100,000. The Burn Down from month 24 to month 25 is $1,000,000
minus $925,000, which equals $75,000. The difference between the Burn Down
Amount and the Draw Amount is $25,000. There would be a one-time credit for
$25,000 so that the required Substitute Credit amount for months 25 through 36
would be $900,000, not $925,000.

     IN WITNESS WHEREOF, the Guarantor has caused this Guaranty to be executed
as a sealed instrument by its duly authorized officer on this 3rd day of
December 1999.

                                              CMGI, Inc.


                                              By /s/ Andrew Hajducky
                                                 -------------------------------
                                              Name: Andrew Hajducky
                                              Title: CFO

                                       3

<PAGE>

                                   EXHIBIT B

                                 FLOOR PLAN OF
                               SUBLEASED PREMISES

                                 [See Attached]

<PAGE>

                              [GRAPHIC] FLOOR PLAN