Document:

<PAGE>

                                                                    Exhibit 10.7
                                                                    ------------

                                     LEASE
                                       BY
                YVON CORMIER, TRUSTEE OF Y-CEE INVESTMENT TRUST
                                       TO
                               AVICI SYSTEMS INC.

                               TABLE OF CONTENTS
                               -----------------
<TABLE>
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                                                                Page
                                                                ----
<C>  <S>                                                          <C>
 1.  Identifications.............................................  3
 2.  Lease; the Premises.........................................  3
 3.  Tenant Fit-Up; Costs and Reimbursement......................  5
 4.  Term........................................................  8
 5.  Use of the Premises; Licenses and Permits...................  8
 6.  Basic Rent; Additional Rent.................................  9
 7.  Taxes....................................................... 14
 8.  Insurance; Waivers of Subrogation........................... 15
 9.  Utilities................................................... 17
10.  Repairs..................................................... 18
11.  Compliance with Laws and Regulations........................ 20
12.  Alterations by Tenant....................................... 21
13.  Landlord's Access........................................... 22
14.  Indemnities................................................. 23
15.  Casualty Damage............................................. 24
16.  Condemnation................................................ 26
17.  Landlord's Covenant of Quiet Enjoyment; Title............... 29
18.  Tenant's Obligation to Quit................................. 29
19.  Transfers of Tenant's Interest.............................. 30
20.  Transfers of Landlord's Interest............................ 31
21.  Mortgagees' Rights.......................................... 32
22.  Tenant's Default; Landlord's Remedies....................... 34
23.  Remedies Cumulative; Waivers................................ 38
24.  Notices..................................................... 39
</TABLE>
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<TABLE>
<C>  <S>                                                          <C>
25.  Recording................................................... 39
26.  Estoppel Certificates....................................... 40
27.  Hazardous Materials and Compliance with Environmental Laws.. 40
28.  Other Utilities............................................. 42
29.  Option to Extend Term and to Request Additional Space....... 42
30.  Security Deposit............................................ 45
31.  Brokerage................................................... 46
32.  Bind and Inure; Limited Liability of Landlord............... 46
33.  Authority................................................... 47
34.  Captions.................................................... 47
35.  Integration................................................. 47
36.  Severability; Choice of Law, and Forum...................... 48
</TABLE>

                                      -2-
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                                     LEASE
1.   Identifications:
     ----------------

     This LEASE made as of the second day of _________ 1998, by and between the
following parties:
                                  THE PARTIES:
                                  ------------

     (a)  The name and address of the Landlord is:
          Yvon Cormier, Trustee of Y-CEE INVESTMENT TRUST
          59 Chandler Circle
          Andover, MA  01810

     (b)  The name and address of the Tenant is:
          Avici Systems Inc.
          12 Elizabeth Drive
          Chelmsford, MA 01824

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, it being the intent of the parties hereto that this instrument be
deemed a "triple net lease" except as hereinafter provided, the Landlord hereby
leases to the Tenant and the Tenant hereby leases from the Landlord certain
premises comprising 47,000 sq. ft. the total rentable area in the Building ("The
Premises"), known and otherwise numbered Building 6 of Billerica Office Park
("Building"), the same more definitively described in a Floor Plan attached
hereto as Exhibit A ("Floor Plan"), on a parcel of land (the "Property") in
Billerica Office Park, so-called, in the Towns of Billerica, and Tewksbury
Middlesex County, Massachusetts, together with the right to use other
improvements

                                      -3-
<PAGE>

constructed on the Property, including the exclusive right to use 141 parking
areas adjacent to the Building based upon a ratio of 3 spaces per 1,000 rentable
sq. ft. in the Premises. In addition, the Tenant shall be allowed to use non-
designated parking spaces until such time as they are assigned by the Landlord
to future Tenants at the building.

     The Premises are leased together with the right, in common with the
Landlord and all others claiming under the Landlord or otherwise from time to
time lawfully entitled thereto, to use Billerica Park Drive (together with any
additional and substitute ways now or hereafter laid out in Billerica Park for
common use, the "Common Drives") for all purposes for which public ways may now
or hereafter be used in the Towns of Billerica and Tewksbury.  The Landlord
reserves the rights to relocate the Common Drives and to install, maintain,
repair, replace and grant easements for utility lines, pipes and conduits in the
Common Drives and across the Property for the benefit of other properties, all
without any measurable interference with or, any interruption of the use and
enjoyment of access to the Premises by the Tenant as contemplated hereby subject
to the same conditions as Landlord's right to relocate common drives and place
and grant easements for utility lines.  Landlord further reserves the right at
any time to submit all or a portion of the Common Drives to a declaration of
common easements for the benefit of the Property and the other properties in
Billerica Park serviced by the Common Drives, in which event the Tenant shall,
if (i) all such other properties in Billerica Park are afforded substantially
the same rights and benefits in the Common Drives, (ii) the expenses of
Maintenance, landscaping, plowing and sanding are fairly and reasonably
allocated among the Property and such other properties and (iii) such
declaration shall not adversely affect the rights of Tenant hereunder
(specifically including the Tenant's exclusive rights to use the 141 parking
areas adjacent to the Building) be bound by the same and shall pay as Additional
Rent hereunder its

                                      -4-
<PAGE>

pro-rata (as defined hereafter) share of such expenses as are from time to time
allocable to the Property under such declaration, provided those charges are
typical of those assessed to similar properties at Billerica Park. The Tenant's
Pro-Rata Share of expenses as delineated aforesaid shall be based on a fraction
the numerator of which shall be the total amount of square feet leased to the
Tenant at the Building and the denominator of which shall be the aggregate total
of rentable square feet in Building 6.

3.   Tenant Fit-Up; Costs and Reimbursement:
     ---------------------------------------

     Upon execution of this Lease, the Tenant shall be allowed access to the
Premises for purposes of undertaking and completing a fit-up of the interior
portion of the Premises in order to accommodate its proposed business
operations.  To facilitate the Tenant commencing the fit-up, the Landlord shall
deliver the Premises, Building, and Property, including but limited to the roof,
foundations, beams, girders, mullions, exterior runoff water and related
drainage systems, exterior walls, parking lot and sidewalk areas, HVAC systems,
electrical and plumbing systems, loading doors, entrance doors, interior walls,
floors, ceilings, and the exterior and interior portion of all windows, window
frames, doors, door frames and all other glass and plate glass in good and
normal operating order and repair, free from all defects.

     Prior to the Tenant being allowed access to the Building to begin work on
the fit-up, however, it shall be required to submit to the Landlord for approval
all plans and/or specifications related to the contemplated work, it being
agreed, however, that the Landlord will not unreasonably withhold, condition, or
delay such approval.  If Landlord shall fail to approve the plans and/or
specifications within three business days from receipt of the same from the
Tenant, it shall be conclusively presumed that the Landlord has approved the
plans as presented.  If the Landlord shall disapprove the plans and
specifications, he shall set forth in writing the

                                      -5-
<PAGE>

basis for the same. In connection with the approval of such plans and
specifications, the parties agree to cooperate with one another and to work
together in good faith so that plans and specifications submitted by the Tenant
in a timely manner are approved and/or accepted by the Landlord within thirty
(30) days from execution of this instrument.

     All such plans and specifications shall be drawn in accordance with good
engineering practices.  In addition thereto, the Tenant shall assure that all
work done at the Building is completed in a good and workmanlike manner and that
only first class materials are used by any contractor(s) hired by the Tenant to
perform the fit-up.  Any contractors hired by the Tenant to perform the fit-up
shall use materials in connection with the fit-up that are comparable in quality
to those already existing materials used in the construction of the Building.

     The Tenant shall bear all costs of preparing all plans, drawings and
specifications and in addition thereto, the Tenant shall be solely exclusively
liable to all contractors hired to perform work for the fit-up including without
limitation all costs of labor and materials.  Barring an instrument signed by
the Landlord, the Landlord shall have no liability whatsoever for costs,
expenses and/or fees due contractors hired by the Tenant.  In connection
therewith, should the Tenant breach this obligation and should the Landlord be
joined in any action brought by any third party against the Tenant asserting
damages for goods sold and delivered and/or for services rendered (including but
not limited to any action to perfect and/or to record a mechanic's or
materialman's lien against the Premises), then in such event (i) the Tenant
shall have thirty (30) days from commencement of such litigation to cause the
same to be Dismissed or to cause such lien to be removed by the posting of a
bond or such other means at the Tenant shall in its sole discretion implement
failing which the same shall be deemed an event of default thereby entitling the
Landlord, without further notice other than that required by law, to avail
itself of the remedies

                                      -6-
<PAGE>

described in (S)22 hereafter (ii) the Tenant shall indemnify and shall otherwise
hold the Landlord harmless from and against any and all such claims including
but not limited to reimbursement to the Landlord for all reasonable legal
fees/costs it might incur in connection with defense of any such action.

     During the period of the fit-up, the Tenant shall pay all utilities for the
Premises based on readings from meters, submeters or check meters.  In
connection herewith, the Tenant acknowledges that failure to complete the fit-up
shall not delay the Commencement Date of the Lease as defined in (S)4 and the
accompanying responsibility of the Tenant to begin payment of both basic and
additional rent effective on the Commencement Date unless such delay is caused
by Landlord, including without limitation, Landlord's failure to timely approve
Tenant's plans.

     Furthermore, and in conjunction with the Tenant's fit-up, it shall be the
sole and exclusive responsibility of the Tenant to obtain any permits necessary
for it to begin work as may be required by either the towns of Billerica or
Tewksbury and likewise, it shall be the sole and exclusive responsibility of the
Tenant to assure that all final inspections which may be required by either
municipality take place in a timely fashion so as not delay issuance of any
occupancy permit which might be required.

     In addition thereto, it shall be the sole and exclusive responsibility of
the Tenant to assure, effective with its execution of this Lease, that all
insurance required by (S)8 has been obtained and is full force and effect.

     In conjunction with the fit-up, and prior to any contractor commencing work
at the Building, the Tenant shall deliver in form suitable to the Landlord, if
requested, evidence that each of such contractors has in full force and effect
Workmen's Compensation for the benefit of its employees.  In any all event,
however, the Landlord shall bear no liability for any person

                                      -7-
<PAGE>

injured while on the Premises during the process of the fit-up except if such
injury or damage is caused by the negligence or other misconduct of the
Landlord, its agents, servants, employees or contractors.

4.   Term:
     -----

     The Term of this Lease (the "Term"), shall begin on the date of execution
of this instrument and shall end on July 31, 2001 ("Expiration Date") unless (i)
sooner terminated in accordance with the terms and provisions of this Lease;
(ii) or extended pursuant to the provisions of (S)29 hereafter.  The
Commencement Date ("Commencement Date") shall be August 1, 1998 (subject to
delays in completion of Tenant's work caused by Landlord) or the date on which
the Tenant begins to conduct business from the Premises, whichever first occurs.

5.   Use of the Premises; Licenses and Permits:
     ------------------------------------------

     The Tenant shall use the Premises only for offices, general engineering,
research and development, light manufacturing, warehousing, (collectively
"Permitted Uses") and such other uses as are or may be permitted by the Zoning
By-Laws for the towns of Billerica and Tewksbury all to the extent now and
hereafter from time to time permitted under applicable laws, by-laws,
ordinances, codes, rules, regulations, orders and other lawful requirements of
governmental bodies having jurisdiction.  The Landlord represents that as of the
date of this Lease the Premises may be used for all Permitted Uses under the
Billerica and Tewksbury Zoning By-laws applicable to the Building and that the
Premises, Property and Building conform with all applicable laws, codes, by-
laws, rules, ordinances, statutes and regulations including but not limited to
`the Americans With Disabilities Act.  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

                                      -8-
<PAGE>

governmental bodies solely in connection with operation of the Tenant's business
at the Premises during the Term.

6.   Basic Rent; Additional Rent:
     ----------------------------

     Effective with the Commencement Date, and for the term of this Lease as
defined by (S)4 above (except as provided for in the second paragraph of this
clause), the Tenant shall pay to the Landlord as Basic Rent, the sum of Three
Hundred Seventy Six Thousand ($376,000.00) Dollars per year in monthly
installments of Thirty One Thousand Three Hundred Thirty Three and 33/100
(31,333.33) Dollars, the same calculated at the rate of $8.00 per square foot
for 47,000 rentable square feet of area at the Building more particularly
described on Exhibit A.

     As more specifically set forth hereafter, each yearly amount of Basic Rent
is to be Triple Net.  Basic Rent shall be payable without counterclaim,
deduction, defense setoff or abatement, except as otherwise expressly provided
herein, 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 the appropriate pro rata proportion of such installment) to the
Landlord at the address set forth above or to such other party or such other
address as the Landlord may thereafter from time to time specify by notice to
the Tenant.  If the name or address of the party entitled to receive Basic Rent
and Additional Rent shall be changed, the Tenant may, until ten (10) days after
receipt of such notice or such change, continue to pay Basic Rent and Additional
Rent to the party and the address to which, and in the manner in which, the
preceding installment of Basic Rent was paid.

     To the end this Lease is Triple Net, Basic Rent shall be received by the
Landlord net of all costs and expenses related to the Premises other than as
expressly set forth herein.  The Tenant agrees to pay, for that area leased to
it and exclusively dedicated to its use, its proportionate share

                                      -9-
<PAGE>

(initially 47% except in the case of real estate taxes for which the Tenant
shall pay 100% of the tax bill issued from the town of Billerica and 35.4% of
the tax bill issued from the town of Tewksbury) of real estate taxes, insurance
premiums of the Landlord, costs of common area utilities, costs of repairs and
maintenance,* specifically including ordinary maintenance of the parking lot and
walkways, costs of snow plowing other costs which are specifically set forth
herein and any and all charges, costs, expenses, and obligations of every kind
and nature whatever with regard to the Building or the use, operation or
maintenance thereof,** except as otherwise expressly agreed in this Lease
("Additional Rent"), to the Landlord upon demand as Additional Rent, in the same
manner as Basic Rent. The Landlord shall in each case, at the time of demand for
payment, provide the Tenant with evidence of the payment for any such charges,
costs, expenses and obligations. In connection with the Tenant's obligation to
pay Additional Rent, the Landlord shall provide an annual statement to the
Tenant prepared in accordance with generally accepted accounting principles and
certified by an officer of the Landlord no later than ninety days after the end
of each year.

     Any adjustment(s) to Additional Rent shall be based on the annual statement
subject to the Tenant's audit rights as described in the Lease.  Notwithstanding
anything in this Lease to the contrary, the Tenant shall have no liability for
the Landlord's mortgage debt service or other financing costs, any brokerage
expenses of the Landlord or any repairs which are the obligation of the Landlord
under Paragraph 10 or any capital improvements or assessments prior to the
Commencement Date of the Lease or within the last year of the term and last year
of any Option Period.

------------------------------------
*  of common areas and facility
**  incurred by Landlord

                                      -10-
<PAGE>

     Specifically excluded from Additional Rent are:

     1.  The cost of correcting defects (other than defects in Tenant's work),
except conditions (not occasioned by construction effects) resulting from
ordinary wear and tear shall not be deemed effects for this purpose;

     2.  Salaries of officers and executives of the Landlord not connected with
the Operation of the Property;

     3.  The initial cost of tools and equipment used in the operation of the
Property;

     4.  Depreciation;

     5.  Expenses relating to tenants' alterations, including, without
limitation, the construction of initial leasehold improvement for tenant spaces;

     6.  Interest, fees or principal on indebtedness and any ground lease rents;

     7.  Expenses for which the Landlord, by the terms of this Lease or any
other lease, makes a separate charge;

     8.  Real estate taxes, other than as provided for by the Lease;

     9.  The cost of any electric current furnished to Tenant and other Building
tenants exclusive of the lobby which is to be a common area and outside lighting
for the parking lot;

     10.  The cost of any services or systems for that portion of the Building
occupied by the Landlord or affiliates of the Landlord (exclusive of space
occupied by the Landlord or affiliates of the landlord in connection with the
operation of the Building) and which are not provided generally to other tenants
in the Building;

     11.  Leasing fees or commissions, advertising and promotional expenses, and
legal fees incurred in connection with leasing space in the Building;

                                      -11-
<PAGE>

     12.  Costs incurred in performing work or furnishing services for any
tenant (including Tenant), whether at such tenant's or Landlord's expense, to
the extent that such work or service is in excess of any work or service that
Landlord is obligated to furnish to Tenant at Landlord's expense (e.g., if
Landlord agrees to provide extra cleaning to another tenant, the cost thereof
would be excluded since Landlord is not obligated to furnish extra cleaning to
Tenant);

     13.  The cost of repairs or replacements incurred by reason of fire or
other casualty or condemnation;

     14.  Association fees and dues;

     15.  Expenses for painting and redecorating for other tenants;

     16.  Legal expenses in enforcing the terms of the Lease for the Tenant and
any other tenant;

     17.  Penalties and interest for late payment of real estate taxes, water
and sewer charges, or any other obligation of Landlord;

     18.  Water rents and sewer charges to any tenant on a direct meter basis
which are paid by the tenant;

     19.  The cost of any item or service to the extent to which Landlord is
entitled to be reimbursed or compensated by insurance, any tenant, or any third
party, or would have been entitled to reimbursement or compensation if Landlord
maintained the insurance which it is required to maintain hereunder;

     20.  Expenses due to Landlord's default under any lease or other agreement
relating to the Building, the Lot, or the Premises, and

     21.  All other items that, under generally accepted accounting principles,
are properly classified as capital expenditures, except as expressly otherwise
provided in this Lease.

                                      -12-
<PAGE>

     The Tenant shall pay to the Landlord upon demand as Additional Rent
interest on any payments of Basic Rent or Additional Rent not paid within 10
(ten) days after the same are due) at a rate (herein called the "Lease Interest
Rate") equal to five percent (5%) per annum computed from the date such payment
was due until such payment is made, each of such payment(s) of interest being
payable as Additional Rent with the payment of Basic Rent next coming due.
Notwithstanding the foregoing, if no such demand is made in writing delivered in
hand to the Tenant within the period of thirty (30) days following the date any
payment of Basic Rent or Additional Rent was due, the Landlord shall be deemed
to have waived the right to be paid any interest on such payment in respect of
periods prior to such demand.

     Rent for any partial month shall be equitably pro-rated.  Rent shall be
paid by check mailed by the first business day of each month to the Landlord at
the above address or any other address provided to Tenant by Landlord in
accordance with this Lease.

     The Tenant shall have ninety (90) days from receipt of any year end
statement described above to dispute the inclusion or amount of any item or
items in any such statement provided to it.  In such event, the Tenant shall pay
the Operating Expense Payment and the Tax Payment excluding the items or amounts
in dispute.  If the parties are unable to settle the dispute between themselves
within sixty (60) days of notice by the Tenant to the Landlord, such dispute
shall be settled by a firm of real estate audit professionals mutually
acceptable to both parties ("Audit Professionals").  If the Landlord and Tenant
cannot agree on the Audit Professionals within thirty (30) days, then each party
shall, within fifteen (15) days thereafter, select one independent firm of
auditors and the two then selected shall chose a third independent Audit
Professional.  The third firm thereupon shall settle the dispute and both the
Landlord and Tenant shall be bound its decision.  If the Landlord fails to
select its Audit Professional within the 15 day period as

                                      -13-
<PAGE>

aforesaid, then to the extent the Tenant has previously paid the Landlord for
items in Dispute, the Tenant shall have the right to deduct such amount from any
installments of basic or additional rent or other charges due or becoming due
under the Lease ("Set Off Rights.") If the Tenant fails to select its auditor
within such 15 day period, it shall be conclusively deemed that the Tenant has
waived its right to audit and/or to contest the validity of applicable Year End
Statements.

     Audit Professionals shall be entitled to review all records relating to the
disputed items.  All costs for the Audit Professionals shall be borne by the
party against whom a decision is rendered, subject to the following:  if more
than one item is disputed, the expenses shall be apportioned equitably according
to the number of items decided against each party taking into consideration the
amount(s) involved.

     If the Audit Professionals determine that the Tenant has made an
underpayment, Tenant shall reimburse Landlord for the amount of the same within
thirty (30) days following such determination.  If the Audit Professionals
determine that the Tenant has made an overpayment, the Landlord shall reimburse
the Tenant for the same likewise within thirty (30) days of such determination.

     Should the Landlord fail to pay the overpayment as described aforesaid, the
Tenant shall have the remedy of the Set Off Rights.  If the Tenant fails to pay
the Landlord the underpayment, the same shall be deemed a default of non-payment
under the Lease.

7.   Taxes.   (Deleted)
     ------
8.   Insurance; Waivers of Subrogation;
     ----------------------------------

     The Landlord shall carry appropriate general liability insurance as well
property and casualty insurance on the Premises, Building, Property and
Improvements with the same limits of coverage as set forth for the Tenant
herein.  The Landlord shall further obtain insurance for the

                                      -14-
<PAGE>

Building and Improvements, with full replacement cost as determined by its
Insurer. 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 reasonably acceptable to the
Landlord and to any Mortgagee(s), for the benefit as named insureds of the
Landlord, the Tenant and any Mortgagees as their respective interests may
appear, the following:

     (i)   comprehensive general liability and property insurance (with
           contractual liability rider) against claims for bodily injury, death
           or property damage occurring to, upon or about the Premises in limits
           of $2,000,000.00 per occurrence for bodily injury or death and
           property damage or such higher limits as may result from the
           operation of clause (iv) below, the risk of loss to all Tenant's
           contents of, and personal property and trade fixtures located in, the
           Premises being upon the Tenant, and the Landlord having no liability
           with respect thereto;

     (ii)  deleted

     (iii) so called "property" or "casualty" insurance, with losses payable to
           the Landlord or any first Mortgagee, against loss or damage to the
           presently existing (prior to Tenant's occupation) interior
           Improvements and to any other buildings, structures and improvements
           from time to time constituting a part of the Premises, such as may
           result from fire and such other casualties as are normally covered by
           "extended coverage" and "difference in conditions" endorsements, such
           casualty or property insurance to be in an amount equal to the
           replacement cost of the Improvements and any other buildings,
           structures or improvements from time to time constituting part of the
           Premises and to include lost rentals coverage for a period of at
           least one year.

                                      -15-
<PAGE>

           Replacement cost shall be redetermined as frequently as the Landlord
           or any Mortgagee may from time to time reasonably request; and

     (iv)  at the written request of the Landlord, such other insurance
           coverages and such additional coverage amounts as any Mortgagee may
           reasonably require the Landlord to obtain provided such coverage is
           customary and usual with respect to commercial buildings similar to
           the subject property.

     At the commencement of the Term and thereafter not less than ten (10) days
prior to the expiration dates of the policies theretofore furnished originals or
duplicates or certificates (contractually binding upon the insurer and not
merely informational) thereof issued by the insurers, shall be delivered to the
Landlord.  All such policies and certificates shall provide that they are non-
cancellable without at least thirty (30) days' prior written notice to the
Landlord and any Mortgagees.  Tenant shall have the right to substitute
insurance policies of equal coverage.

     The Landlord and the Tenant each hereby release the other from any
liability for any loss or damage to the Premises or other property and for
injury to or death of persons occurring on or about the Premises or in any
manner growing out of or connected with the Tenant's use and occupation of the
Premises or the condition thereof, whether or not caused by the negligence or
other fault of the Landlord, the Tenant or other respective agents, employees,
subtenants, licensees, invitees or assignees; provided, however, that this
release (i) shall apply notwithstanding the indemnities set forth in Paragraph
14, but only to the extent that such loss or, damage to the Premises or other
property or injury to or death of persons is covered by insurance which protects
the Landlord or the Tenant or both of them as the case may be; (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 to the extent and so

                                      -16-
<PAGE>

long as the applicable insurance policies provide 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.

9.   Utilities;
     ----------

     The Landlord represents and warrants that all building systems at the
Premises, Building and Property are in good condition and repair, without
defects, at the time of commencement of the Lease; the Premises, Building and
Property contain in-place utilities for the Tenant to operate its business which
the Tenant has inspected; and all permits required therefor have been obtained
and are and will remain in full force and effect.  In connection with the in-
place utilities, the Tenant shall be solely liable and responsible for
installation of such other utilities which may be needed to operate its business
should the same not be in existence on the date of execution of this Lease.  The
Tenant expressly acknowledges that its intended use of the Premises is for
commercial purposes and the Landlord shall have no duty to furnish to the Tenant
with utility services of any kind, except as to water, sewer, gas, telephone
[subject to telephone company], electric and HVAC services.  Separate gas and
electrical meters shall be provided for the Tenant and the Tenant in turn agrees
to be billed directly by the applicable utility company.

10.  Repairs:
     --------

     The Landlord shall, at its own cost and expense, and during the term of the
Lease, maintain and make all necessary repairs to the roof, foundations, beams,
girders, and other structural elements of the Building, mullions, exterior
runoff water and related drainage systems, all exterior areas, including Parking
Lots and walkways (subject to the Tenant paying for those ordinary repairs as
Additional Rent per the terms contained on Page 11 of the Lease), all other
Common Areas and facilities (subject to assessment of the same as an element of
Additional

                                      -17-
<PAGE>

Rent) and exterior walls of the Premises only (exclusive of signs which may be
installed by the Tenant). However, the Landlord shall have no obligation to
repair any damage resulting from negligent acts of the Tenant, its agents,
employees, contractors, and invitees unless covered by Landlord's insurance
policy.

     In connection herewith, the Landlord represents (i) The property shall be
maintained consistent with generally accepted practices associated with a first
class research and development building (ii) it shall provide snow plowing for
the parking areas (iii) it shall remove snow and ice from walkways (iv) it shall
provide landscaping services so that the property is maintained in a neat and
clean condition.  The same, however, shall be deemed a common area maintenance
charge subject to inclusion as Additional Rent.

     From and after the commencement of and during the Term, the Tenant shall,
at its own cost and expense:  make all other repairs, non-structural, interior
and exterior, necessary to keep the Premises, including all electrical other
than common systems, mechanical, heating, ventilating and air conditioning,
plumbing (other than in common areas) and other building systems [excluding ewer
and gas systems and all capital repairs and replacements] serving the Premises,
in as good condition, order and repair as the same are at the commencement of
the Term or thereafter may be put, reasonable wear and use, damage by fire or
other casualty caused by the Landlord and repairs which are expressly the
obligation of the Landlord hereunder only excepted (it being understood,
however, 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).

[Deleted]
 -------

                                      -18-
<PAGE>

     If the Landlord shall fail to cure any default by the Landlord in its
obligations under this Paragraph 10, thirty (30) days after notice from the
Tenant to the Landlord of such default (or, in the event of imminent danger of
injury to persons or damage to property, after telephone notice of such default)
or to commence such cure and diligently prosecute the same to completion, in the
absence of any Terminable Default on the part of the Tenant hereunder, the
Tenant may, at its option, cure such default for the Landlord's account as was
specified in such notice, in which event the Tenant may offset against the Basic
Rent next accruing under this Lease, cumulatively until exhausted, the
reasonable costs and expenses it can demonstrate were incurred in good faith in
the cure of such default plus interest thereon at the Lease Interest Rate, but
in no event shall any such offset reduce the amount of Basic Rent payable below
the amount from time to time necessary for the Landlord to make payments of
principal, interest and other expenses payable under any first Mortgage
perfected against the Premises, including any real estate taxes or other
expenses which are or could become a lien upon the Premises, except to the
extent such taxes and other expenses are actually paid by the Tenant.  The
Landlord shall provide the Tenant with evidence of such payments as the Tenant
may reasonably require.  Notwithstanding the foregoing, if the Landlord disputes
the Tenant's allegation of default or the Tenant's right to take any action
under this paragraph, any action taken by the Tenant under this paragraph or the
costs and expenses incurred in any action taken by the Tenant under this
paragraph, shall not afford the Tenant the right to offset any amounts due the
Landlord until (i) the parties in good faith attempt to meet and resolve any
such dispute within 10 days after notice from the Landlord to the Tenant (ii)
determination of such dispute by a court of appropriate jurisdiction.

     Notwithstanding anything to the contrary as contained in this Paragraph,
the Landlord shall be solely and exclusively liable for ill repairs and
replacements which are capital in nature.

                                      -19-
<PAGE>

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

     During the Term, the Tenant and Landlord shall comply, each 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
hereunder), whether or not foreseeable, and whether or not they involve any
changes in governmental policy, which are applicable to the Premises, the
fixtures and equipment therein and thereon, or the Tenant's particular use
thereof; the orders, rules and regulations of the New England Fire Insurance
Rating Association or any other body hereafter constituted exercising similar
functions, which may be applicable to the Premises, the fixtures and equipment
therein or thereon or the use thereof; and the requirements of all policies of
public liability, fire and all other types of insurance at any time in force
with respect to the Premises and the fixtures and equipment therein and thereon.
Notwithstanding the foregoing, the Tenant shall not be responsible for future
laws, by-laws, ordinances, codes, rules, regulations, orders and other lawful
requirements of governmental bodies having jurisdiction that require a
structural change to the Premises, Building or Property or other capital outlay.

                                      -20-
<PAGE>

12.  Alterations by Tenant:
     ----------------------

     The Tenant shall erect no signs (other than one at the driveway to the
Building and on the facade of the Building, subject to approval of the Landlord
(which approval shall not be unreasonably withheld, conditioned or delayed] and
subject to any applicable ordinances related to signs as promulgated by either
the towns of Billerica or Tewksbury) and shall make no alterations, additions or
improvements in or to any portion of the Premises without the Landlord's prior
written consent subject to the provisions of this Paragraph 12, which consent
shall not be unreasonably withheld, conditioned or delayed.  In connection
therewith, the Landlord shall have ten days, from receipt of written notice from
the Tenant detailing the proposed alterations, to approve or reject the same.
The Landlord shall be deemed to have given his approval to any proposed
alterations unless he shall have objected to the same within the time set forth
herein.  As part of any request for such consent, the Tenant shall provide the
Landlord with plans and specifications drawn in accordance with good engineering
practice (only if it would be usual and appropriate to prepare plans and
specifications given the nature and extent to the proposed alterations,
additions or improvements), reasonable evidence of suitable insurance and, lien
bonds or other suitable assurances of the Tenant's obligation and wherewithal to
complete the same at no expense to the Landlord and without failure to pay any
contractor engaged to do the work.

     The Landlord agrees that in the absence of a Terminable Default on the part
of the Tenant hereunder, its consent shall not be required for interior, non-
structural alterations to the Building from time to time constituting a part of
the Premises if the same are consistent with the use of the Premises as
contemplated hereby and with the heating, ventilating and air conditioning and
other engineering and mechanical systems in the building.  (Deleted)  At the
                                                            -------
time Tenant requests

                                      -21-
<PAGE>

Landlord's consent to any future alterations, installations, removals, additions
or improvements, Landlord agrees it will only require Tenant to remove such
alteration, installment, removal, addition or improvement at the end of the
Lease Term provided the Landlord, in his sole discretion, determines such
improvements will impair his ability to re-let the Premises to another tenant.

13.  Landlord's Access:
     ------------------

     The Tenant agrees to permit the Landlord Purchasers and any Mortgagees and
their authorized representatives to enter the Premises (i) at all reasonable
times during usual business hours after not less than two business days' prior
oral or written notice for the purposes of inspecting the same, exercising such
other rights as it or they may have hereunder or under any mortgages (provided
such rights are consistent with the Landlord's rights hereunder) and, during the
last six (6) months of the Term or after any Terminable Default (inclusive of
any applicable notice period) hereunder on the part of the Tenant, to show the
Premises to other prospective tenants, and (ii) at any time and without notice
in the event of emergency (in which event the Landlord shall attempt to give
oral notice by telephone.)  In connection therewith, Landlord shall use all
commercially reasonable efforts to protect Tenant's property and personnel from
loss and injury and to avoid interfering with conduct of Tenant's business.

14.  Indemnities:
     ------------

     The Tenant and Landlord agree as follows:  each shall indemnify and save
the other harmless from and against any and all losses, claims, liability,
expenses and damages (other than consequential damages) which either directly or
indirectly, in whole or in part arise out of or result from (i) the negligence
or

                                      -22-
<PAGE>

willful misconduct of either party, its agents, servants and employees (ii) any
act or occurrence in or about the Premises, unless caused by the negligence or
willful misconduct of the applicable party, its agents, servants, contractors or
employees (iii) the breach of any provision of this Lease by either party or any
of its agents, servants, employees or contractors (iv) judgments, citations,
fines or other penalties rendered or assessed against one or the other (with the
exception of any claims under the applicable party's workmen's compensation
insurance policy) as a result of one of the party's failure to comply with all
federal, state and local laws, safety and health regulations relating to either
party's use or occupation of the Premises. In connection herewith, both the
Landlord and Tenant agree to give the other prompt notice of any such violation
which may be asserted by a governmental agency.

     The Landlord and Tenant further agree to indemnify the other from and
against all costs, expenses (including reasonable attorneys' fees) and other
liabilities incurred in connection with any such indemnified claim or action
and/or proceeding brought thereon.  If the Landlord shall breach this covenant
and fail to reimburse the Tenant for such costs and expenses after written
demand, the Tenant shall be allowed to offset the same against basic or
additional rent.  If the Tenant shall breach this covenant and fail to reimburse
the Landlord for such costs and expenses after written demand, the Landlord may
declare a Default under this Lease based upon non-payment of rent.

     Nothing contained above is intended to require indemnification for any
property claim for which insurance is required to be maintained under the terms
this Lease.  The rights and obligations of the Landlord and Tenant under this
Paragraph 14 shall survive the expiration and/or earlier termination of this
Lease.

15.  Casualty Damage:
     ----------------

     a.  Tenant's Right to Terminate:  if the Premises or the Building shall be
damaged or destroyed by fire, windstorm or any other insured casualty, the
Tenant shall immediately give

                                      -23-
<PAGE>

written notice thereof to Landlord and unless this Lease is terminated as
hereinafter provided, the Landlord, at his own expense, shall repair or rebuild
the same so as to restore the Premises to substantially the same condition they
were in immediately prior to such damage or destruction, subject however, to
zoning and building laws then in existence, provided that the Landlord shall not
be responsible for any delay in such repair or reconstruction which may result
from any cause beyond its reasonable control, and provided further that the
Landlord shall not be required to expend more than the net amount of insurance
proceeds, if any received, by Landlord for such purposes, plus the amount of any
deductible, so long as the Landlord maintains the insurance required of it under
this Lease. Notwithstanding the foregoing, the Landlord within 30 days after
receipt of said written notice of damage, shall inform the Tenant if said damage
can be repaired within 120 days, based upon a reasonable estimate of the
Landlord's architect and Engineer. If the Landlord notifies the Tenant it cannot
repair or rebuild the Premises so as to restore the same to substantially the
same condition they were in immediately prior to the destruction within said 120
days, or if in fact the Premises is not restored within 120 days, then in either
of such event, the Tenant may elect to cancel this Lease upon notice to the
Landlord.

     b.  Landlord's Right to Terminate:  If the Premises or the Building are
substantially damaged by fire or casualty (the term "substantially damaged"
meaning damage of such character that the same cannot, in the ordinary course,
reasonably be expected to be repaired within 120 days from the time that repair
work would commence or if either the Premises or Building shall be damaged or
destroyed to the extend of 25% or more on a square footage basis by my cause,
(whether insured against by the Landlord or not) the Landlord may elect by
written notice to the Tenant, to be provided to Tenant within 30 days of
Landlord's receipt of said damage, either to terminate this Lease or to repair
or rebuild on the conditions set forth in the above clause.  The

                                      -24-
<PAGE>

Tenant shall likewise be afforded the right to terminate the Lease if more than
25% of either the Premises or Building shall be damaged or destroyed.

     c.  Tenant's Obligations to Repair:  In the event that the remises or
Building is damaged or destroyed by any cause, then, unless this Lease is
terminated as provided above, the Tenant at its own expense (but in no event
beyond the limits of its insurance less any applicable deductible) and
proceeding with all reasonable dispatch shall repair or replace all trade
fixtures, equipments, signs or other property installed by or belonging to the
Tenant which shall be damaged to destroyed.

     d.  Abatement of Rent:  If the Premises shall be damaged by fire or
casualty, the Basic Rent and Additional Rent payable by the Tenant shall abate
or be reduced proportionately for the period in which, by reason of such damage,
there is substantial interference with the operation of the Tenant's use of the
Premises, having regard to the extent to which Tenant may be required to
discontinue its use of the Premises, but such abatement or reduction shall end
if and when Landlord shall have substantially restored the Premises (exclusive
of any of Tenant's fixtures, furnishings, equipment and the like or work
performed therein by Tenant) to substantially the condition in which the
Premises were in prior to such damage, so long as Tenant has been provided 120
days from the date it is afforded access to the Premises to complete the
Tenant's repairs.  In no event shall Landlord be obligated in connection with
the restoration of the Premises, as stated herein, to expend an amount in excess
of the proceeds of insurance recovered with respect thereto.  In the event the
Premises shall be damaged by fire or other casualty resulting from negligence of
the Tenant, its agents, contractors, employees or invitees, and this Lease shall
not be terminated as a result of such damage, Tenant shall not be released

                                      -25-
<PAGE>

from any of its obligations hereunder including, without limitation, its duty to
pay the Basic Rent and Additional Rent payable by Tenant without abatement or
reduction.

     e.  Award:  Landlord shall have and hereby reserves and accepts and Tenant
hereby grants and assigns to Landlord, all rights to recover damages to the
Premises, Building or Property and the leasehold interest hereby created, from
Landlord's insurance and to compensation accrued or hereafter to accrue by
reason of such damage or destruction, as aforesaid, and by way of confirming the
foregoing, Tenant hereby grants and assigns, and covenants with Landlord, to
grant and assign to Landlord all rights to such damages or compensation from
Landlord's insurance.  Nothing contained herein shall be construed to prevent
Tenant from prosecuting in any proceedings a claim for the value of the Tenant's
inventory, furnishings, equipment or usual trade fixtures installed in the
Premises by Tenant and at Tenant's expense, provided that such action shall not
affect the amount of compensation otherwise recoverable by Landlord.

16.  Condemnation:

     If a substantial portion of the useable floor areas of the building, or of
the parking area, from time to time constituting part of the Premises shall be
taken, such that the same shall materially and adversely interfere with the
Tenant's ability to conduct business on the Premises, or if the Tenant's access
to the Premises shall be deprived for three (3) months or more, by eminent
domain or appropriated by public authority, the Tenant may terminate this Lease
by giving written notice to the Landlord within thirty (30) days after such
taking or appropriation becomes final.  In the event of any such termination,
this Lease shall terminate a s of the date the Tenant must surrender possession
or, if later, the date the Tenant actually surrenders possession,

                                      -26-
<PAGE>

or the date Tenant's access is deprived 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 improvements or any other improvements from time
to time constituting part of the Premises 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
attorneys' fees, incurred by the Landlord in obtaining the same) to secure,
close and restore so much of the Improvements or other improvements constituting
part of the Premises as remain to an architectural whole except that in no event
shall the Landlord be obligated to expend 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 to the Improvements and any other improvements
from time to time constituting part of the Premises 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 Improvements after giving effect to such replacement, from and after
the date the Tenant must surrender possession (or access is deprived) or, if
later, the date the Tenant actually surrenders possession and except further,
that if, in such event, for any reason any Mortgagee retains any portion of such
damages or award and the Landlord fails within thirty (30) days after a request
by notice from the Tenant to agree to secure and close the remaining
improvements as aforesaid, then the Tenant shall have an additional period of
sixty (60) days after the expiration of such thirty (30) day period within which
to terminate this Lease, in which event, this Lease shall thereupon be void and
without recourse to the parties as to obligations thereafter accruing.  The
Tenant agrees that the foregoing rights shall be its sole remedies, both at law
and in equity, for

                                      -27-
<PAGE>

the failure of any Mortgagees and the Landlord to fulfill its obligations to
secure and close the remaining improvements as aforesaid.

     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 so much of such damages or award as is
specifically and separately awarded to the Tenant and expressly attributable to
Improvements constructed and/or made by the Tenant as well as to the Tenant's
trade fixtures, personal property or moving expenses.  Nothing contained herein
shall prohibit the Tenant from making claim in its own name against the
municipality for damages including but not limited to loss of business and an
amount equal to its unamortized costs of leasehold improvements on condition
such application does not interfere with the Landlord's paramount right to claim
damages in connection with any such taking.  Notwithstanding anything to the
contrary set forth above, if the Tenant is deprived of access to the Property,
an abatement of rent, effective on the date of deprivation, shall take effect.
In addition thereto, in the event of Condemnation, all Basic and Additional Rent
shall be abated.

17.  Landlord's Covenant of Quiet Enjoyment; Title:
     ----------------------------------------------

     The Landlord covenants that the Tenant, upon paying the Basic Rent and
Additional Rent provided for hereunder 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 provisions of this Lease.  The Landlord warrants that as Trustee of Y-CEE
INVESTMENT TRUST, u/d/t dated January 12, 1979 and recorded with the Middlesex
Northern District Registry of Deeds at Book 2348, Page 327, that he has the
right and lawful authority to enter Into this Lease and further that the
Landlord is the owner of the fee in

                                      -28-
<PAGE>

the Premises subject to no liens or encumbrances of record except those which
are required by Lexington Savings Bank to secure a mortgage on said )remises. In
connection herewith, the Landlord, upon request, shall furnish to the Tenant
evidence sufficient to establish that it owns the Premises, including a list of
encumbrances, if any, perfected and recorded against the same.

18.  Tenant's Obligation to Quit:
     ----------------------------

     The Tenant shall, upon expiration of the Term or other termination of this
Lease, leave and peaceably and quietly surrender and deliver to the Landlord the
Premises and any alterations, additions and improvements which have been made by
the Tenant to the Premises, and any replacements 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 and any alterations, additions and Improvements which the Landlord
has required be removed pursuant to the terms of Paragraph 12 hereof and Tenant
if so requested by the Landlord pursuant to the terms of Paragraph 12 hereof,
restoring the Premises in each case to substantially their condition prior to
the Installation of such fixtures or the undertaking of such alterations,
additions or improvements, as the case may be reasonable wear and tear and
casualty excepted.  The provisions of this Paragraph 18 shall expressly survive
the termination or expiration of the Term of this Lease.

19.  Transfers of Tenant's Interest:
     -------------------------------

     a.  Subletting:  Tenant shall have the right, subject to approval of the
Landlord which consent shall not be unreasonably withheld, conditioned or
delayed, to sublet all or any portion of the Premises or grant a license
therein, provided:  (i) Tenant is not in default of the Lease beyond any
applicable cure period (ii) Tenant provides Landlord with prior written notice
of the Sublease or license, at least thirty (30) days prior to the commencement
date of the sublease or license

                                      -29-
<PAGE>

(iii) Tenant delivers to Landlord an executed copy of the sublease or license by
the commencement date of the sublease or license (iv) Tenant remains liable
under the Lease.

     Notwithstanding the provisions of (S)26 hereafter, Landlord shall, at
Tenant's Request, provide Tenant with (i) an Estoppel Certificate stating
whether Landlord knows of any Default under the Lease at the time of the
proposed subletting [or assignment as hereinafter provided]

     b.  Assignment:  Should the Tenant desire to assign its interest in the
Lease to a third party, it shall be required to notify the Landlord of the same
in writing and to furnish the Landlord timely any and all materials it might
reasonably request concerning the proposed Assignee's financial condition and a
detailed description of such entity's business operations and proposed use of
the Premises.  The Landlord shall be required to notify the Tenant in writing of
its decision whether to agree to or reject the proposed Assignment within thirty
(30) days of its receipt of all documentation it might request be supplied to it
from either the Tenant and/or proposed Assignee.  In connection therewith,
Landlord shall not unreasonably withhold, condition or delay its consent.

     Any attempted assignment without the consent of the Landlord and without an
executed Assumption Agreement between it, the Tenant and the Assignee, shall be
deemed void.

     Notwithstanding anything to the contrary, the Landlord shall not withhold,
its consent to an assignment by the Tenant, upon reasonable notification to the
Landlord, to a subsidiary, parent or affiliate of Tenant or to a successor to
Tenant by means of merger, consolidation, corporate reorganization or the
purchase of all or substantially all of the Tenant's assets or stock condition
such Assignee shall demonstrate its financial ability to comply with all terms
under the Lease including but not limited to the fact that its net worth is not
less than that of the Tenant and the transferee assumes the terms of this Lease
by execution of a separate writing. in addition thereto,

                                      -30-
<PAGE>

any other transfer, pledge, sale or other disposition and/or power to vote the
outstanding shares of *corporate stock of the Tenant shall not be deemed an
Assignment. In the event of any Assignment,** Tenant shall remain liable under
the provisions of the Lease jointly and severally with Assignee.

20.  Transfers of Landlord's Interest:
     ---------------------------------

     The Landlord shall have the right from time to time to sell or mortgage its
interest in the Building and Property, to assign its interest in this Lease, or
to assign from time to time the whole or any portion of 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 (or, in the case of any purchasers at foreclosure sales or
grantees under deeds in lieu of foreclosure, by any Mortgagee) by duly recorded
instruments and after receipt of copies of such instruments, the Tenant shall
pay the Basic Rent, Additional Rent and

     *   less than the majority of

     **  under this clause (b)

such other sums and charges so assigned, subject to the terms of the Lease, upon
demand to such Mortgagees and other transferees, purchasers and grantees at the
addresses mentioned in and in accordance with the terms of such instruments.
Each foreclosing Mortgagee or other transferee, purchaser or grantee shall, in
writing, assume the obligations of the Landlord under this Lease, subject,
however, to the limitations upon liability of the Landlord as set forth in
Paragraph 27.

     Within ten (10) days following any transfer by Landlord of its ownership
interest in the property, Landlord shall provide Tenant with written notice of
such transfer and the name and address of the successor Landlord to whom Tenant
should send future rent payments and notices (the "Transfer Notice").  In the
event that the Landlord fails to provide the Transfer Notice,

                                      -31-
<PAGE>

(a) the Tenant shall not be liable to any successor Landlord for rent payments
paid to the former (predecessor) Landlord and (b) any successor Landlord shall
be bound by any notice sent to the former (predecessor) Landlord by the Tenant.

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,
refinancings or restructurings thereof) of 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 a recordable writing or such mortgage provides
that, for so long as there exists no Terminable Default under this Lease on the
part of the Tenant, the Mortgagee, in Foreclosing against or taking possession
of the Premises or otherwise Exercising its rights under such mortgage, will not
join the Tenant in any foreclosure proceedings (except to the extent required by
law) and will not terminate this Lease (except as provided herein) or disturb
the Tenant's possession of the Premises hereunder in customary form or words of
similar import and will make insurance proceeds available as and to the extent
provided in Paragraph 8.  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.

     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

                                      -32-
<PAGE>

first gives such notice to all Mortgagees of whom Tenant has been given notice
and provides such Mortgagees with the same period(s) for cure as are available
to the Landlord after such notice within which to cure such default. 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, 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. In such event, the Tenant shall not be liable to
the Landlord for any payment made to such Mortgagee. By any such request, such
Mortgagee or successor shall be deemed and construed without further agreement
to have assumed and agreed to carry out and perform all covenants and
obligations of the Landlord under this Lease thereafter arising, subject,
however, to the provisions of Paragraph 27. Any Mortgagee may, at any time, by
giving written notice to and without any 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 relative dates of execution, delivery or
recording thereof or otherwise.

     In connection herewith, the Tenant acknowledges that any Mortgagee reserves
the right to use whatever reasonable format of a non-disturbance agreement it
might elect to employ and therefore the Landlord does not warrant or otherwise
represent what the precise provisions of that instrument might be or what the
same might provide.  Notwithstanding the foregoing, any Subordination and
Nondisturbance Agreement prepared by the Mortgagee and presented to the

                                      -33-
<PAGE>

Tenant for execution shall include a provision that the Tenant's possession
shall not be disturbed and the Mortgagee shall abide by the terms and conditions
of this Lease if the Tenant is then in compliance with the terms of this
instrument [to wit: not in default beyond applicable notice and cure periods)
and continues to abide by the terms and conditions of the same. The costs of
recording any such non-disturbance agreement shall be borne by the Tenant.

22.  Tenant's Default; Landlord's Remedies:
     --------------------------------------

     If (a) the Tenant shall default in the payment of any Basic Rent or
Additional Rent and such default shall continue for fourteen (14) days after
notice from the Landlord of such default without cure; or (b) the Tenant shall
default in the performance or observance of any of the other covenants contained
in this Lease and on the Tenant's part to be performed or observed and shall
fail, within thirty (30) days after notice from the Landlord of such default to
cure such default, or if it is beyond the reasonable control of the Tenant to
cure such default within thirty (30) days, promptly to commence such cure and
thereafter to pursue such cure diligently to completion; or (c) 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 proceedings 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.

                                      -34-
<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, of 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 rights
     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 (a), (b), or (c) (each of which, subject to the
following sentence is herein sometimes called a ("Terminable Default"), the
Landlord may, to the extent permitted by law, immediately or at any time
thereafter and without demand or notice, terminate this Lease and enter onto and
upon the Premises, or any part thereof, repossess the same as 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, of its obligations and liabilities 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

                                      -35-
<PAGE>

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 broker's 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 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. In connection with reletting the Premises as
provided for herein, Landlord agrees to use all reasonable efforts in connection
with the same.

     Without thereby affecting any other right or remedy of the Landlord
hereunder, in the event of (i) any default on the part of the Tenant in the
performance or observance of any non-monetary covenant contained in this Lease
and on the Tenant's part to be performed or observed and the failure of the
Tenant, within thirty (30) days after notice from the Landlord of such default,
to cure such default or if it is beyond the reasonable control of the Tenant to
cure such default within thirty (30) days or promptly to commence such cure and
thereafter to pursue such cure diligently to completion or (ii) any default on
the part of the Tenant which results in jeopardy to the Landlord's title to the
Premises or to the Landlord's interest under any mortgage of the Premises and
which remains uncured for two (2) business days after notice of such default

                                      -36-
<PAGE>

from the Landlord to the Tenant (or if it is beyond the reasonable control of
the Tenant to cure such default within two (2) business days, if the Tenant
shall not promptly commence such cure and thereafter diligently pursue such cure
to completion) or (iii) imminent danger of injury to persons or damage to
property as a result of any default on the part of the Tenant as to which the
Landlord has given telephone notice to the Tenant, or (iv) any Terminable
Default on the part of the Tenant hereunder, then in any of such events the
Landlord may, at its option, cure such default or Terminable Default for the
Tenant's account and the cost to the Landlord of such cure, together with
interest thereon at the Lease Interest Rate, 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.

     If the Landlord shall be required to commence proceedings to enforce its
remedies as provided for herein, it shall, in addition to damages, be entitled
to receive all its costs and its reasonable attorney's fees incurred by it in
any such action.

23.  Remedies Cumulative; Waivers:
     -----------------------------

     The specific remedies to which the Landlord or 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 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 shall not be construed as a
waiver or relinquishment for the future of such covenant.  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 of
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

                                      -37-
<PAGE>

representative of the Landlord or the Tenant as appropriate. In addition to the
other remedies provided for in this Lease, the Landlord and the Tenant shall be
entitled to the restraint by injunction of the covenants, conditions or
provisions of this Lease, or to a decree compelling performance of or compliance
with any of such covenants, conditions or provisions. In connection herewith,
the prevailing party, should litigation be initiated, shall entitled to an award
of its costs and its reasonable attorney's fees.

24.  Notices:
     --------

     Any notices, requests, approvals, specifications, demands or consents
required or permitted hereunder shall be in writing and mailed, postage prepaid,
by registered or certified mail, return receipt requested, if to the Landlord or
to the Tenant at the address set forth herein for each, with copies of such
notice(s) sent to respective counsel for both the Landlord and Tenant, as
follows: if to the Landlord, Robert L. Marder, Esquire, 23 Central Avenue, Suite
408, Lynn, Ma. 01901; if to the Tenant to: Melvin R. Shuman, Esq., Hale and
Dorr, 60 State Street, Boston, MA 02109; 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.  When this Lease provides for any period to commence after notice, such
period shall be deemed to commence one day after postal records indicate
delivery of such notice was first sent as attested to by Post Office Stamped
Receipt.  When this Lease requires that notice be given on or before a certain
date or within a certain period, such notice shall be deemed given on the date
mailed as in this Paragraph 24 provided.  Time shall be of the essence of all
notice provisions of this Lease.

                                      -38-
<PAGE>

25.  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 a recordable
form or notice of lease, notices of any assignments of rents and profits,
notices of any amendments to this Lease and of such other information as may
from time to time be necessary under G.L. (Ter. ed.) Chapter 183, Section 4 or
under similar additional or successor statutes for the protection of any
Interest of the Landlord, the Tenant or any Mortgagee having a perfected
interest in the Premises.  The party which seek preparation of any such
document(s) listed herein shall bear the cost(s) of recording the same.

26.  Estoppel Certificates:
     ----------------------

     The Landlord and the Tenant hereby agree from time to time, but not more
than twice during any calendar year, each after not less than twenty (20) 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).

                                      -39-
<PAGE>

27.  Hazardous Materials and Compliance with Environmental Laws:
     -----------------------------------------------------------

     (a) The Landlord represents that the Property, Premises and Building and
its existing uses to the best of his knowledge and belief (after due
investigation and familiarity with previous uses) comply with, and Landlord is
not in violation of, and has not violated, in connection with his ownership,
use, maintenance or operation of the Property, Premises and Building and the
conduct of business related thereto, any applicable federal, state, county or
local statutes, laws, regulations, rules, ordinances, codes, standards, orders,
licenses and permits of any governmental authorities relating to environmental,
health or safety matters (including without limitation Hazardous Materials as
defined hereafter) [collectively "Environmental Laws"].  Landlord and Tenant
shall at their own expense promptly observe and comply with all present and
future Environmental Laws including without limitation the Clean Air Act
Amendments of 1990 and any regulations (as amended) and all regulations and
standards as are or may be promulgated thereunder.

     (b) Without limiting the foregoing, Landlord represents that it, its
agents, servants, contractors and employees have (i) operated the Property
Premises and Building and have at all times received, handled, used, stored,
treated, transported and disposed of any chemical, material or substance,
exposure to which is prohibited, limited or regulated by any federal, state,
country, regional, or local authority or which even if not so prohibited,
limited or regulated, poses a hazard to the health and safety of the occupants
of the Property, Premises and Building (collectively "Hazardous Materials") in
strict compliance with Environmental Laws and (ii) removed (or will remove prior
to the Commencement Date) from the Property all Hazardous Materials.

                                      -40-
<PAGE>

     (c) Landlord represents there is no fact pertaining to the physical
condition of the Property, Premises and Building known to him which (i)
materially and adversely affects or materially and adversely will affect the
Property, Premises and Building or the use, enjoyment or value thereof or
Landlord's ability to perform his obligations contained in this Lease and (ii)
which Landlord has not disclosed to Tenant in writing prior to this Lease.

     (d) Landlord represents it has received no notices of any violation or
claimed violation of any of the matters referred to above including notices
related to any pending investigation, lawsuit or other action relating thereto.
In addition thereto, Landlord hereby agrees to indemnify and hold tenant
harmless from and against any and all "Remediation Costs" (as hereafter defined)
sustained or incurred by Tenant in the event that Tenant is required by any
state or federal agency to affect a Remediation of any Hazardous Substances
which may be located on the Property and the Building as of the date of this
Lease, unless such Hazardous Substances are present or released as the result of
the acts or omissions of Tenant or any of Tenant's agents, servants, employees,
contractors or invitees.

     As used herein, the term "Remediation Costs" shall mean the cost of
remediation and clean-up of the Hazardous Substances which Tenant may incur as
the result of any order of the DEP, the U.S. Environmental Protection Agency or
any State or Federal Court of competent jurisdiction requiring that Tenant
affect a remediation of any Hazardous Substances.

     (e) The provisions of this (S)27 shall survive the expiration or earlier
termination of this Lease.

28.  Other Utilities:
     ----------------

     [Deleted] Subject to approval from the Landlord, which approval shall not
be unreasonably withheld, conditioned or delayed, the Tenant, at its sole cost
and expense, shall

                                      -41-
<PAGE>

have right to introduce into the Premises such other utilities as it may be deem
necessary for the conduct of its business. The Tenant shall pay the cost of all
such other utilities directly to the applicable utility supplier.

29.  Option to Extend Term and to Request Additional Space:
     ------------------------------------------------------

     A.  Provided that no Terminable Default exists, then, in such event, the
Tenant shall have the option of notifying the Landlord not later than one
hundred eighty (180) days prior to the expiration of the Lease Term, as defined
by (S)4 above, of its intent to extend the term of this Lease for a period of
three (3) years ("Option Period").

     During the term of the Option Period, the Tenant shall pay to the Landlord
as basic rent the sum of $399,500.00 per year in monthly installments of
$33,291.67, the same calculated at the rate of $8.50 per square foot for the
47,000 square feet of area at Building 6.

     In addition thereto, all obligations of the Tenant with respect to the
triple net provision of the Lease, as defined in (S)6 above and in other
applicable portions of this instrument, shall remain in full force and effect
during the Option Period as well as all other terms, conditions and covenants of
such Lease without necessity that any other writing be executed by the parties.

     B.  Provided that no Terminable Default exists, then in such event, the
Tenant shall have the following additional options:

          (i) Lease of Remaining Building:  The Tenant shall have the right at
              ---------------------------
any time during the base or initial term of this Lease, to notify the landlord
of its intent to lease all of the then remaining uncommitted space at the
Building on the same terms and conditions applicable to the base term; in such
event, the Landlord and Tenant shall first be required to execute a Letter of
Intent in the same format as that which was executed by the parties on or about
April 28, 1998, subject (in the case of  a lease for the entire Building) to
terms and conditions applicable to a

                                      -42-
<PAGE>

true net lease for the entire building (other than payment of capital repairs or
replacements which shall continue to be governed by Section 6 hereof) it being
understood, however, that if the Tenant should exercise this right, the term of
said lease applicable to the entire building, or 100,000 square feet of the
Premises, shall be three years in duration from the date on which any lease
modification is executed.

     Reservation:  The ability of the Tenant to exercise this right shall
     -----------
terminate automatically with respect to a portion or all of the uncommitted
space at the Building, when the Landlord shall have executed a Letter of Intent
with any third party for a lease of such portion or all of the remaining
uncommitted space at the Building and thereafter a lease is entered into between
the Landlord and that other Third Party.  Barring execution of a Lease, the
Tenant's right as aforesaid to lease the remaining space or a portion thereof at
the Building shall be revived.  In connection with the Tenant's rights set forth
in this clause (i), the Landlord agrees he shall not execute any Letter of
Intent or lease with any third party for lease of any portion of the then
remaining leasable space in the Building unless Landlord has previously notified
Tenant in writing of the potential interest of such third party (provided that
such notice shall not be required to include any confidential information) and
has afforded the Tenant five business days within which to exercise its first
right to lease all the then remaining leasable space in the Building.

     (ii) Lease of Additional Space: After the initial lease-up of the entire
          --------------------------
Building, the Landlord agrees as follows: the Tenant shall have the first option
to lease additional space ("Additional Space") at the Building once any tenant
for such Additional Space shall have vacated the same.

     In connection therewith,

                                      -43-
<PAGE>

          [1]  the Landlord shall promptly notify the Tenant in writing when it
receives notice that any Tenant for that adjacent contiguous space has given
notice of its intent not to renew any lease for that area;

          [2]  the Tenant shall have ten (10) days from receipt of said notice
to advise the Landlord in writing whether it intends to exercise such option for
the Additional Space;

          [3]  should the Tenant notify the Landlord of its intent to exercise
the option for Additional Space, the parties shall thereupon meet, and within
five days from receipt of the Tenant's notice, shall execute a letter of intent
in the same format as that which was executed by them on or about April 28,
1998, it being understood that the amount of base rent for the Additional Space
shall be market rental as determined by the Landlord;

          [4]  failing notice by the Tenant as described in (S)[2] above, the
Landlord shall have the right to market the Additional Space and to execute a
Letter of Intent with any third party for the same.

30.  Security Deposit:
     ----------------

     To secure the Tenant's performance to pay Basic and Additional Rent under
the terms, conditions and covenants of this Lease, the Tenant, upon execution of
this instrument, shall pay to the Landlord six months Basic Rent in advance
("Security Deposit") or $188,000.00. Such Security Deposit may be paid in cash,
surety bond or irrevocable letter of credit.

     If paid in cash [to include check], the Security Deposit shall be deposited
into an escrow account.("Escrow") by the Landlord and all interest earned
thereon shall accrue to the Tenant.

     In connection with the preceding paragraph, the Landlord shall provide the
Tenant with the name of the Bank, title of the account, and account number into
which the Security Deposit has been deposited.  Prior to opening the Escrow, the
Tenant shall furnish the Landlord with its

                                      -44-
<PAGE>

tax identification number to assure any tax due on interest earned is reported
as earnings of the Tenant.

     Upon a monetary default of the Tenant, after notice and expiration of
applicable cure periods, as defined by (S)22 or should the Tenant commit damage
or waste to the Premises which is not repaired prior to the date it shall Quit
and Deliver up possession of the Premises to the Landlord, the Landlord shall
have the right of set-off against the Escrow and shall account to the.  Tenant
for the same.

     It is agreed between the Landlord and Tenant, since the Lease between them
is commercial, that the provisions of G.L. c. 186, (S)15B shall not be
applicable to the terms of this clause.

31.  Brokerage:
     ----------

     The Brokers named herein, Meredith & Grew Incorporated and Spaulding Slye,
by execution hereafter, each certifies that it is duly licensed as a broker by
the Commonwealth of Massachusetts and hereby joins in this Agreement and becomes
a party hereto insofar as any provisions of this instrument expressly apply to
it.

32.  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 Premises, Property and Building. In

                                      -45-
<PAGE>

connection therewith, the Landlord agrees it shall not cause the Premises,
Property or Building to be mortgaged beyond 85% of its fair market value
determined by an Appraisal to be performed by an applicable lender. The term
"Landlord" as used in this Lease shall refer only to the owner or owners from
time to time of the Premises who shall be deemed and construed without further
agreement to have assumed and agreed to carry out and perform all covenants and
obligations of the Landlord arising under this Lease during the period of such
ownership (and, except in the case of foreclosing Mortgagees, purchasers at
foreclosure sales, grantees under deeds in lieu of foreclosure and their
successors and assigns, prior to such period if not carried out and performed by
the prior owner), subject, however, to the provisions of this Paragraph 31, it
being understood that no such owner shall have any liability hereunder for
matters rising from and after the date such owner ceases to have any interest in
the remises. In no event shall the Landlord be liable to the Tenant for any
special consequential or indirect damages suffered by the Tenant or any other
person or entity by reason of a default by the Landlord under any provisions of
this Lease. Likewise, the  Tenant shall not be liable to the Landlord or any
special, consequential or indirect damages suffered by the Landlord   any other
person or entity by reason of a default by the Tenant under any revisions of
this Lease.

33.  Authority:
     ----------

     The Landlord represents he has been specifically authorized by the
beneficiaries of Y-CEE INVESTMENT TRUST to execute this instrument.

     The Tenant represents its duly authorized officer, identified hereafter, as
been authorized to execute this instrument by the Board of Directors of Avici
Systems Inc.

                                      -46-
<PAGE>

34.  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.

35.  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.

36.  Severability; Choice of Law, and Forum:
     ---------------------------------------

     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 remaining provisions shall not thereby be
affected.

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

     In addition thereto, and should either the Landlord or Tenant initiate
litigation to seek enforcement of the terms, conditions and/or covenants of the
within Lease, in such event the parties agree that Jurisdiction, other than for
Summary Process proceedings, shall vest solely and exclusively with Essex County
Superior Court Department for the Commonwealth of Massachusetts, each signatory
hereafter having agreed to the within forum selection clause.

                                      -47-
<PAGE>

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

                              Landlord,
                              TRUSTEE OF Y-CEE INVESTMENT TRUST

                              /s/ Yvon Cormier
                              --------------------------------------------------
                              Yvon Cormier, as Trustee as aforesaid and not
                              individually

                              Tenant,
                              AVICI SYSTEMS, INC.
                              By:

                              /s/ Surya Pandit
                              --------------------------------------------------
                              6/1/98

Broker,                       Broker,
SPAULDING & SLYE              MEREDITH & GREW INCORPORATED
By:                           By:

/s/ Roy Hirshland             /s/ David L. Pergola
---------------------------   --------------------------------------------------

                           [Graphic of Office Space]

                               AMENDMENT TO LEASE
                               ------------------

     This Amendment is attached hereto and is incorporated by reference, as if
fully set forth therein, to a Lease ("Lease") dated June 2, 1998 by and between
Yvon Cormier, Trustee of Y-CEE Investment Trust, u/d/t dated January 12, 1979
and recorded with the Middlesex County (Northern District) Registry of Deeds at
Book 2348, Page 327, 59 Chandler Circle, Andover, Middlesex County ("Lessor")
and Avici Systems, Inc., a corporation organized in accordance with law, having
its principal place of business at Building 6, 101 Billerica Avenue, Billerica,
Middlesex County ("Lessee").

                                      -48-
<PAGE>

     In consideration of One ($1.00) Dollar, the parties hereby agree the Lease
more particularly described above be and is hereby amended effective as follows:

     (a) By deleting the following designated clauses ("Deleted Clause") from
(S)6 of the Lease which is entitled Basic Rent; Additional Rent and substituting
therefore the following new clause ("Amended Clause"):

          Deleted Clause:  "To the end this Lease is Triple Net, Basic Rent
          ---------------
shall be received by the Landlord net of all costs and expenses related the
Premises other than as expressly set forth herein.  The Tenant agrees to pay,
for that area leased to it and exclusively dedicated to its use, its
proportionate share (initially 47% except in the case of real estate taxes for
which the Tenant shall pay 100% of the tax bill issued from the town of
Billerica, and 35.4% of the tax bill issued from the town of Tewksbury) of
leased space, of real estate taxes, insurance premiums of the Landlord, costs of
utilities, costs of repairs and maintenance, specifically including ordinary
maintenance of the parking lot and walkways, costs of snow plowing other costs
which are specifically set forth herein and any and all charges, costs,
expenses, and obligations of every kind and nature whatever with regard to the
Premises or the use, operation or maintenance thereof, except as otherwise
expressly agreed in this Lease ("Additional Rent"), to the Landlord upon demand
as Additional Rent, in the same manner as Basic Rent.  The Landlord shall in
each case, at the time of demand for payment, provide the Tenant with evidence
of the payment for any such charges, costs, expenses and obligations.  In
connection with the Tenant's obligation to pay Additional Rent, the Landlord
shall provide an annual statement to the Tenant prepared in accordance with
generally accepted accounting principles and certified by an officer of the
Landlord no later than ninety days after the end of each year.

<PAGE>

          Any adjustment(s) to Additional Rent shall be based on the annual
statement subject to the Tenant's audit rights as described in the Lease.
Notwithstanding anything in this Lease to the contrary, the Tenant shall have no
liability for the Landlord's mortgage debt service or other financing costs, any
brokerage expenses of the Landlord or any repairs which are the obligation of
the Landlord under Paragraph 10 or any capital improvements or assessments prior
to the Commencement Date of the Lease or within the last year of the Term and
last year of any Option Period."

          Amended Clause:  "To the end this Lease is Triple Net, Basic Rent
          --------------
shall be received by the Landlord net of all costs and expenses related to the
Premises other than as expressly set forth herein.  The Tenant agrees to pay,
for that area leased to it and exclusively dedicated to its use, its
proportionate share (initially 47% except in the case of real estate taxes for
which the Tenant shall pay 100% of the tax bill issued from the town of
Billerica and 35.4% of the tax bill issued from the town of Tewksbury) of (i)
real estate taxes, (ii) insurance premiums billed to the Landlord for Building 6
of Billerica Office Park and (iii) costs of repairs and maintenance,
specifically including ordinary maintenance of the parking lot and walkways,
landscaping, costs of snow plowing, common area utilities and other costs which
are specifically set forth herein (collectively "Maintenance Costs") [those
costs delineated in (S)(iii) calculated at the rate of  $.75 per square foot of
leased space (to wit:  47,000 sq. ft.), such rate fixed for the Basic Term of
the Lease and Option Period so long as and only so long as the original Landlord
named herein (the "Original Landlord") remains the Landlord, which totals
$35,250.00 per year, payable in monthly installments of $2,937.50] as
"Additional Rent," to the Landlord upon demand and in the same manner as Basic
Rent.  The Landlord shall in each case, at the time of demand for payment,
provide the Tenant with evidence of the payment for real estate taxes and

<PAGE>

insurance and if the Original Landlord is no longer the Landlord, Maintenance
Costs. In connection with the Tenant's obligation to pay that portion of the
Additional Rent for real estate taxes and insurance, the Landlord shall provide
the Tenant a copy of the relevant real estate tax bill(s) and insurance bill,
certified by an officer of the Landlord, no later than ninety (90) days from
receipt of the same and including therewith a calculation of the Tenant's Pro
Rata share determined as aforesaid. In connection with Tenant's obligation to
pay Maintenance Costs, if the original Landlord is no longer the Landlord,
Landlord shall provide an annual statement to the Tenant, prepared in accordance
with generally accepted accounting principles and certified by an officer of the
Landlord, setting forth all Maintenance Costs for the previous year, no later
than ninety (90) days after the end of each year included in the Term. The
Tenant shall thereafter have those audit rights to dispute such charges as more
specifically delineated hereafter in this Section 5.

     Notwithstanding anything in this Lease to the contrary, the Tenant shall
have no liability for the Landlord's mortgage debt service or other financing
costs, any brokerage expenses of the Landlord, any management fee or fees paid
or payable by or to Landlord, or any repairs which are the obligation of the
Landlord under Paragraph 10 or any capital improvements or assessments prior to
the Commencement Date of the Lease or within the last year of the Term and last
year of any Option Period."

     Except as otherwise amended by this instrument, the Lessor and Lessee by
execution hereafter hereby ratify and otherwise reaffirm all terms, conditions,
covenants, obligations and representations set forth and otherwise contained in
the Lease more particularly described above.

     Signed Under Seal this 29th Day of October 1998
     -----------------------------------------------

                                Y-CEE Investment Trust,
                                By:

                                /s/ Yvon Cormier
                                --------------------------
                                Yvon Cormier, Trustee

                                Avici Systems Inc.
                                By:

                                /s/ John Colorusso
                                --------------------------
                                John Colorusso, Controller<PAGE>

                                  Exhibit 10.1

<TABLE>
<CAPTION>
==================================================================================================================================
HEADLANDS MORTGAGE                                                SERVICING CERTIFICATE
==================================================================================================================================
<S>                                                                <C>                                        <C>
Revolving Home Equity Loan    LIBOR:                               6.13000%     Current Collection Period:    04/01/00-04/30/00
Asset-Backed Notes            Margin:                              0.65000%     P&S Agreement Date:                12/1/98
Series 1998-2                 Class A-1  Note Rate:                6.78000%     Original Closing Date:            12/29/98
                              Class A-2  Note Rate:                6.51000%     Distribution Date:                 5/15/00
                              Class A-3  Note Rate:                6.67000%     Record Date:                       5/14/00
                              Interest Period 04/17/00 thru           28        Pool Factor:                     60.2601791%
                              05/14/00:
                              Servicing Fee Rate:                  0.50000%     Initial Class A-1 O/C Amt:       2,041,531.37
                              Class A-1 Premium Fee Rate:          0.19000%     Initial Class A-2 O/C Amt:       2,430,777.93
                              Class A-2 Premium Fee Rate:          0.22000%     Initial Class A-3 O/C Amt:       3,312,404.71
                              Class A-3 Premium Fee Rate:          0.40000%     Class A-1 O/C Amt as of Pmt      4,763,573.17
                                                                                Date
                              Trustee Fee:                         0.00750%     Class A-2 O/C Amt as of Pmt      5,973,741.07
                                                                                Date:
                              Class A-1 Weighted Avg Loan Rate:   11.94457%     Class A-3 O/C Amt as of Pmt      6,419,345.67
                                                                                Date:
                              Class A-2 Weighted Avg Loan Rate:   11.00090%     Class A-1 WAM:
                              Class A-3 Weighted Avg Loan Rate:   13.44380%     Class A-2 WAM:
                              Total Management Fee                 1,000.00     Class A-3 WAM:
==================================================================================================================================
</TABLE>

<TABLE>
<CAPTION>
<S>                                                                                                  <C>
BALANCES
     Beginning HELOC Pool Balance                                                                    85,299.956.62
     Beginning Second Lien Pool Balance                                                              52,424,991.71
     Beginning HLTV Pool Balance                                                                     38,607,927.54

     Beginning Class A-1 Note Balance -- CUSIP 422093AG9                                             80,536,383.45
     Beginning Class A-2 Note Balance -- CUSIP 422093AH7                                             46,625,488.79
     Beginning Class A-3 Note Balance -- CUSIP 422093AJ3                                             32,379,863.88
     Overcollateralization Amount                                                                     1,660,198.04
     Overcollateralization Loan Amount                                                                        0.00

     Ending HELOC Pool Balance                                                                       82,849,577.69
     Ending Second Lien Pool Balance                                                                 50,908,801.02
     Ending HLTV Pool Balance                                                                        38,064,091.28

     Ending Class A-1 Note Balance -- CUSIP  422093AG9                                               78,086,004.52
     Ending Class A-2 Note Balance -- CUSIP  422093AH7                                               44,935,059.95
     Ending Class A-3 Note Balance -- CUSIP  422093AJ3                                               31,644,745.61

     Additional Balances  Class A-1                                                                   1,962,889.15

     Number of all Retransferred Mortgage Loans (Current Retransfer Date)                                        0
     Retransferred Mortgage Loan Trust Balances (Current Retransfer Date)                                     0.00
     Cumulative Number of all Retransferred Mortgage Loans (From Previous Distributions)                         0
     Cumulative Retransferred Mortgage Loan Trust Balances (From Previous Distributions)                      0.00
     Number of all Subsequent HELOC Mortgage Loans (Current Date)                                                0
     Subsequent HELOC Mortgage Loan Asset Balance (Current Date)                                              0.00
     Number of all SubsequentSecond Lien Mortgage Loans (Current Date)                                           0
     Subsequent Second Lien Mortgage Loan Asset Balance (Current Date)                                        0.00
     Number of all Subsequent HLTV Mortgage Loans (Current Date)                                                 0
     Subsequent HLTV Mortgage Loan Asset Balance (Current Date)                                               0.00
     Cumulative Number of ALL Subsequent Mortgage Loans                                                      1,830
     Cumulative Subsequent Mortgage Loan Asset Balance                                               64,876,717.43

     Beginning Loan Count                                                                                    5,071
     Ending Loan Count                                                                                       4,950
</TABLE>

<PAGE>

<TABLE>
<S>                                                                                                                  <C>
COLLECTION AMOUNTS Class A-1
 1   Aggregate of All Mortgage Collections (Gross)                                                                   5,170,063.64
 2   Total Mortgage Interest Collections (Gross)                                                                       756,795.56
     Servicing Fees (current collection period)                                                                         35,541.65
     Deferred Interest Transfer (DI)                                                                                         0.00
  3a    Mortgage Principal Collections                                                                               4,413,268.08
  3b    Pre-Funded Balance                                                                                                   0.00
  3c    Net Liquidation Proceeds                                                                                             0.00
 3    Total Mortgage Principal Collections                                                                           4,413,268.08
      Aggregate of Transfer Deposits                                                                                         0.00
      Investor Loss Amount                                                                                                   0.00
      Aggregate Investor Loss Reduction Amount                                                                         391,810.36

COLLECTION AMOUNTS Class A-2
 1   Aggregate of All Mortgage Collections (Gross)                                                                   1,974,361.50
 2   Total Mortgage Interest Collections (Gross)                                                                       458,170.81
     Servicing Fees (current collection period)                                                                         21,843.75
     Deferred Interest Transfer (DI)                                                                                         0.00
  3a    Mortgage Principal Collections                                                                               1,516,190.69
  3b    Pre-Funded Balance                                                                                                   0.00
  3c    Net Liquidation Proceeds                                                                                             0.00
 3   Total Mortgage Principal Collections                                                                            1,516,190.69
     Aggregate of Transfer Deposits                                                                                          0.00
     Investor Loss Amount                                                                                                    0.00
     Aggregate Investor Loss Reduction Amount                                                                          184,263.08

COLLECTION AMOUNTS Class A-3
 1   Aggregate of All Mortgage Collections (Gross)                                                                     942,350.11
 2   Total Mortgage Interest Collections (Gross)                                                                       398,513.85
     Servicing Fees (current collection period)                                                                         16,086.64
     Deferred Interest Transfer (DI)                                                                                         0.00
  3a    Mortgage Principal Collections                                                                                 543,836.26
  3b    Pre-Funded Balance                                                                                                   0.00
  3c    Net Liquidation Proceeds                                                                                             0.00
 3   Total Mortgage Principal Collections                                                                              543,836.26
     Aggregate of Transfer Deposits                                                                                          0.00
     Investor Loss Amount                                                                                                    0.00
     Aggregate Investor Loss Reduction Amount                                                                          644,659.08

TOTAL COLLECTION
AMOUNT
 1   Aggregate of All Mortgage Collections (Gross)                                                                   8,086,775.25
 2   Total Mortgage Interest Collections (Gross)                                                                     1,613,480.22
     Servicing Fees (current collection period)                                                                         73,472.03
     Deferred Interest Transfer (DI)                                                                                         0.00
  3a    Mortgage Principal Collections                                                                               6,473,295.03
  3b    Insurance Proceeds                                                                                                   0.00
  3c    Net Liquidation Proceeds                                                                                             0.00
 3   Total Mortgage Principal Collections                                                                            6,473,295.03
     Aggregate of Transfer Deposits                                                                                          0.00
     Investor Loss Amount                                                                                                    0.00
     Aggregate Investor Loss Reduction Amount                                                                        1,220,732.52
</TABLE>

<PAGE>

<TABLE>
 <S>                                                                                                                <C>
     Class A-1 Net Interest Collection                                                                                721,253.91
     Class A-2 Net Interest Collection                                                                                436,327.06
     Class A-3 Net Interest Collection                                                                                382,427.21

DISTRIBUTION AMOUNTS Class A-1
     Class A-1 Note  Interest 8.6 (d)(iv)                                                                             424,695.20
     Class A-1 Note  Unpaid Interest Shortfall (current cycle)                                                              0.00
     Class A-1 Note  Reserve Fund Amount                                                                              282,781.45
     Investor Loss Amount                                                                                                   0.00
     Previous Investor Loss Amount                                                                                          0.00
     Monthly Credit Enhancer Premium 8.6 (d)(ii)                                                                       12,751.59
     Credit Enhancer Reimbursement                                                                                          0.00
     Accelerated Principal Distribution Amount                                                                              0.00
     Spread Account Deposit                                                                                                 0.00
     Indenture Trustee Fee 8.6 (d)(i)                                                                                     503.35
     Management Fee 8.6 (d)(iii)                                                                                          522.32
     Payment to Servicer                                                                                                    0.00
     Deferred Interest                                                                                                      0.00
     Remaining Amount to Transferor                                                                                         0.00
     Total Certificateholders Distribution Allocable to Interest                                                      721,253.91

     Maximum Principal Payment                                                                                      2,450,378.93
     Scheduled Principal Collection Payment ((x)the excess of Max Prin Pymt (y) the HELOC Pool O/C Redctin                  0.00
     Amt) 8.6(d)(v)
     Accelerated Principal Distribution Amount                                                                              0.00
     Loan Loss                                                                                                              0.00
     HELOC Overcollateralization Deficit 8.6 (d)(vi)                                                                        0.00
     Total Certificateholders Distribution Allocable to Principal                                                   2,450,378.93

DISTRIBUTION AMOUNTS Class A-2
     Class A-2 Note  Interest 8.6 (d)(iv)                                                                             252,943.28
     Class A-2 Note  Unpaid Interest Shortfall (current cycle)                                                              0.00
     Class A-2 Note  Reserve Fund Amount                                                                                    0.00
     Investor Loss Amount                                                                                                   0.00
     Previous Investor Loss Amount                                                                                          0.00
     Monthly Credit Enhancer Premium 8.6 (d)(ii)                                                                        8,548.01
     Credit Enhancer Reimbursement                                                                                          0.00
     Accelerated Principal Distribution Amount                                                                        174,238.15
     Spread Account Deposit                                                                                                 0.00
     Indenture Trustee Fee 8.6 (d)(i)                                                                                     291.41
     Management Fee 8.6 (d)(iii)                                                                                          306.22
     Payment to Servicer                                                                                                    0.00
     Deferred Interest                                                                                                      0.00
     Remaining Amount to Transferor                                                                                         0.00
     Total Certificateholders Distribution Allocable to Interest                                                      436,327.06

     Maximum Principal Payment                                                                                      1,516,190.69
     Scheduled Principal Collection Payment ((x)the excess of Max Prin Pymt (y) the Second Pool O/C Redctin                 0.00
     Amt) 8.6(d)(v)
     Accelerated Principal Distribution Amount                                                                        174,238.15
     Loan Loss                                                                                                              0.00
     Second Lien Overcollateralization Deficit 8.6 (d)(vi)                                                                  0.00
     Total Certificateholders Distribution Allocable to Principal                                                   1,690,428.84
</TABLE>

<PAGE>

<TABLE>
<S>                                                                                            <C>
DISTRIBUTION AMOUNTS Class A-3
     Class A-3 Note  Interest 8.6 (d)(iv)                                                        179,978.08
     Class A-3 Note  Unpaid Interest Shortfall (current cycle) 5.01(i)                                 0.00
     Class A-3 Note  Reserve Fund Amount                                                               0.00
     Investor Loss Amount 5.01(iii)                                                                    0.00
     Previous Investor Loss Amount 5.01(iv)                                                            0.00
     Monthly Credit Enhancer Premium 8.6 (d)(ii)                                                  10,793.29
     Credit Enhancer Reimbursement 5.01(vi)                                                            0.00
     Accelerated Principal Distribution Amount 5.01(vii)                                         191,282.01
     Spread Account Deposit 5.01(viii)                                                                 0.00
     Indenture Trustee Fee 8.6 (d)(i)                                                                202.37
     Management Fee 8.6 (d)(iii)                                                                     171.46
     Payment to Servicer per Section 7.03 5.01 (x)                                                     0.00
     Deferred Interest 5.01 (xi)                                                                       0.00
     Remaining Amount to Transferor 5.01 (xii)                                                         0.00
     Total Certificateholders Distribution Allocable to Interest                                 382,427.21

     Maximum Principal Payment                                                                   543,836.26
     Scheduled Principal Collection Payment                                                            0.00
     Accelerated Principal Distribution Amount                                                   191,282.01
     Loan Loss                                                                                         0.00
     HLTV Lien Overcollateralization Deficit 8.6 (d)(vi)                                               0.00
     Total Certificateholders Distribution Allocable to Principal                                735,118.27

TOTAL DISTRIBUTION AMOUNT
     Class A Note  Interest 8.6 (d)(iv)                                                          857,616.55
     Class A Note  Unpaid Interest Shortfall (current cycle) 5.01(i)                                   0.00
     Class A Note  Reserve Fund Amount                                                           282,781.45
     Investor Loss Amount 5.01(iii)                                                                    0.00
     Previous Investor Loss Amount 5.01(iv)                                                            0.00
     Monthly Credit Enhancer Premium 8.6 (d)(ii)                                                  32,092.89
     Credit Enhancer Reimbursement 5.01(vi)                                                            0.00
     Accelerated Principal Distribution Amount 5.01(vii)                                         365,520.16
     Spread Account Deposit 5.01(viii)                                                                 0.00
     Indenture Trustee Fee 8.6 (d)(i)                                                                997.14
     Management Fee 8.6 (d)(iii)                                                                   1,000.00
     Payment to Servicer per Section 7.03 5.01 (x)                                                     0.00
     Deferred Interest 5.01 (xi)                                                                       0.00
     Remaining Amount to Transferor 5.01 (xii)                                                         0.00
     Total Certificateholders Distribution Allocable to Interest                               1,540,008.18

     Maximum Principal Payment                                                                 4,510,405.88
     Scheduled Principal Collection Payment                                                            0.00
     Accelerated Principal Distribution Amount                                                   365,520.16
     Loan Loss                                                                                         0.00
     Overcollateralization Deficit 8.6 (d)(vi)                                                         0.00
     Total Certificateholders Distribution Allocable to Principal                              4,875,926.04

LOSSES/RETRANSFERS
     Unpaid Class A-1 Note  Interest Shortfall Due (From Previous Distributions)                       0.00
     Unpaid Class A-2 Note  Interest Shortfall Due (From Previous Distributions)                       0.00
     Unpaid Class A-3 Note  Interest Shortfall Due (From Previous Distributions)                       0.00
     Interest Earned on Shortfall @ applicable Certificate Rate                                        0.00
     Investor Loss Reduction Amount (From Previous Distributions)                                      0.00
</TABLE>
<PAGE>

<TABLE>
<CAPTION>
DISTRIBUTION TO CERTIFICATEHOLDERS  (PER CERTIFICATE WITH A $1,000 DENOMINATION)
Class A-1
         <S>                                                                                         <C>
         Total Class A-1 Note Distribution Amount Allocable to Interest                                 3.1679354
         Interest Distribution Amount                                                                   3.1679354
         Unpaid Note Interest Shortfall Included in Current Distribution                                0.0000000
         Unpaid Note Interest Shortfall Remaining after Current Distribution (Carryover)                0.0000000

         Total Class A-1 Note Distribution Amount Allocable to Principal                               18.2781493
         Maximum Principal Payment                                                                     18.2781493
         Scheduled Principal Collections Payment                                                        0.0000000
         Loan Loss                                                                                      0.0000000
         Accelerated Principal Distribution Amount                                                      0.0000000

Class A-2
         Total Class A-2 Note Distribution Amount Allocable to Interest                                 3.2183063
         Interest Distribution Amount                                                                   3.2183063
         Unpaid Note Interest Shortfall Included in Current Distribution                                0.0000000
         Unpaid Note Interest Shortfall Remaining after Current Distribution (Carryover)                0.0000000

         Total Class A-2 Note Distribution Amount Allocable to Principal                               21.5080546
         Maximum Principal Payment                                                                     19.2911475
         Scheduled Principal Collections Payment                                                        0.0000000
         Loan Loss                                                                                      0.0000000
         Accelerated Principal Distribution Amount                                                      2.2169071

Class A-3
         Total Class A-3 Note Distribution Amount Allocable to Interest                                 4.0896986
         Interest Distribution Amount                                                                   4.0896986
         Unpaid Note Interest Shortfall Included in Current Distribution                                0.0000000
         Unpaid Note Interest Shortfall Remaining after Current Distribution (Carryover)                0.0000000

         Total Class A-3 Note Distribution Amount Allocable to Principal                               16.7043242
         Maximum Principal Payment                                                                     12.3577628
         Scheduled Principal Collections Payment                                                        0.0000000
         Loan Loss                                                                                      0.0000000
         Accelerated Principal Distribution Amount                                                      4.3465614

         Reimbursed Investor Loss Reduction Amounts Included in Current Distribution                    0.0000000
         Investor Loss Reduction Amounts after Current Distribution (carryover)                         0.0000000

         Total Interest Amount Distributed to Class A Certificateholder                                10.4759403
         Total Principal Amount Distributed to Class A Certificateholder                               56.4905281

         Credit Enhancement Draw Amount                                                                      0.00

DELINQUENCIES/FORECLOSURES

Class A-1
         Number of Mortgages 30 to 59 Days Delinquent                                                          39
         Aggregate Principal Balances of Mortgages 30 to 59 Days Delinquent                          1,671,349.95
         Number of Mortgages 60 to 89 Days Delinquent                                                           7
         Aggregate Principal Balances of Mortgages 60 to 89 Days Delinquent                            216,742.90
         Number of Mortgages 90 to 179 Days Delinquent                                                          2
         Aggregate Principal Balances of Mortgages 90 to 179 Days Delinquent                           103,148.30
         Number of Mortgages 180 or more Days Delinquent                                                        3
</TABLE>
<PAGE>

<TABLE>
         <S>                                                                                         <C>
         Aggregate Principal Balances of Mortgages 180 or more Days Delinquent                         265,589.21
         Number of Mortgage Loans in Foreclosure                                                                5
         Aggregate Principal Balances of Mortgage Loans in Foreclosure                                 121,951.19

         Book Value of Real Estate Acquired Through Foreclosure or Grant of a Deed                           0.00
         Aggregate Trust Balances of any Liquidated Loans in the Current Month                               0.00

Class A-2
         Number of Mortgages 30 to 59 Days Delinquent                                                          40
         Aggregate Principal Balances of Mortgages 30 to 59 Days Delinquent                          1,521,988.49
         Number of Mortgages 60 to 89 Days Delinquent                                                           4
         Aggregate Principal Balances of Mortgages 60 to 89 Days Delinquent                            102,257.75
         Number of Mortgages 90 to 179 Days Delinquent                                                          5
         Aggregate Principal Balances of Mortgages 90 to 179 Days Delinquent                           144,080.82
         Number of Mortgages 180 or more Days Delinquent                                                        1
         Aggregate Principal Balances of Mortgages 180 or more Days Delinquent                          40,000.00
         Number of Mortgage Loans in Foreclosure                                                                7
         Aggregate Principal Balances of Mortgage Loans in Foreclosure                                 367,088.07

         Book Value of Real Estate Acquired Through Foreclosure or Grant of a Deed                      67,861.30
         Aggregate Trust Balances of any Liquidated Loans in the Current Month                               0.00

Class A-3
         Number of Mortgages 30 to 59 Days Delinquent                                                          43
         Aggregate Principal Balances of Mortgages 30 to 59 Days Delinquent                          1,546,375.56
         Number of Mortgages 60 to 89 Days Delinquent                                                          14
         Aggregate Principal Balances of Mortgages 60 to 89 Days Delinquent                            593,460.87
         Number of Mortgages 90 to 179 Days Delinquent                                                         12
         Aggregate Principal Balances of Mortgages 90 to 179 Days Delinquent                           430,987.61
         Number of Mortgages 180 or more Days Delinquent                                                        8
         Aggregate Principal Balances of Mortgages 180 or more Days Delinquent                         299,168.96
         Number of Mortgage Loans in Foreclosure                                                               20
         Aggregate Principal Balances of Mortgage Loans in Foreclosure                                 710,893.31

         Book Value of Real Estate Acquired Through Foreclosure or Grant of a Deed                           0.00
         Aggregate Trust Balances of any Liquidated Loans in the Current Month                               0.00

TOTAL DELINQUENCIES/FORECLOSURES

         Number of Mortgages 30 to 59 Days Delinquent                                                         122
         Aggregate Principal Balances of Mortgages 30 to 59 Days Delinquent                          4,739,714.00
         Number of Mortgages 60 to 89 Days Delinquent                                                          25
         Aggregate Principal Balances of Mortgages 60 to 89 Days Delinquent                            912,461.52
         Number of Mortgages 90 to 179 Days Delinquent                                                         19
         Aggregate Principal Balances of Mortgages 90 to 179 Days Delinquent                           678,216.73
         Number of Mortgages 180 or more Days Delinquent                                                       12
         Aggregate Principal Balances of Mortgages 180 or more Days Delinquent                         604,758.17
         Number of Mortgage Loans in Foreclosure                                                               32
         Aggregate Principal Balances of Mortgage Loans in Foreclosure                               1,199,932.57

         Book Value of Real Estate Acquired Through Foreclosure or Grant of a Deed                      67,861.30
         Aggregate Trust Balances of any Liquidated Loans in the Current Month                               0.00
=================================================================================================================

PRE-FUNDED ACCOUNT ACTIVITY

         Beginning Balance Pre-Funded Account                                                                0.00
         Remaining Amount for Distribution to Classes                                                        0.00
         Withdrawal for Subsequent Loan Purchase:                                                            0.00
         Ending Balance Pre-Funded Account                                                                   0.00
         Pre-Funding Period:  From Closing Date thru the 2/15/99
</TABLE>
<PAGE>

<TABLE>
<CAPTION>
RESERVE FUND ACTIVITY
         <S>                                                                                          <C>
         Class A-1 Reserve Fund  Beginning Balance                                                    3,600,103.75
         Class A-1 Reserve Fund  Deposit/Withdrawal                                                     282,781.45
         Class A-1 Reserve Fund  Ending Balance                                                       3,882,885.20

         Class A-2 Reserve Fund  Beginning Balance                                                            0.00
         Class A-2 Reserve Fund  Deposit/Withdrawal                                                           0.00
         Class A-2 Reserve Fund  Ending Balance                                                               0.00

         Class A-3 Reserve Fund  Beginning Balance                                                            0.00
         Class A-3 Reserve Fund  Deposit/Withdrawal                                                           0.00
         Class A-3 Reserve Fund  Ending Balance                                                               0.00

CROSSOVER ACTIVITY
         Class A-1 Activity This Distribution                                                                 0.00
         Class A-2 Activity This Distribution                                                                 0.00
         Class A-3 Activity This Distribution                                                                 0.00

         OFFICER'S CERTIFICATE
         All Computations reflected in this Servicer Certificate were made
         In conformity with the Pooling and Servicing Agreement.

         The Attached Servicing Certificate is true and correct in all material respects.

         ________________________________________________________
         A Servicing Officer  Teri Martine
</TABLE>
<PAGE>

<TABLE>
<CAPTION>
------------------------------------------------------------------------------------------------------------------------------------
HEADLANDS                                STATEMENT TO NOTEHOLDERS
MORTGAGE
====================================================================================================================================
<S>                           <C>                              <C>           <C>                             <C>
Revolving Home Equity Loan    LIBOR:                           6.13000%      Current Collection Period:      04/01/00-04/30/00
Asset-Backed Notes            Margin:                          0.65000%      P&S Agreement Date:                   12/1/98
Series 1998-2                 Class A-1  Note Rate:            6.78000%      Original Closing Date:               12/29/98
                              Class A-2  Note Rate:            6.51000%      Distribution Date:                    5/15/00
                              Class A-3  Note Rate:            6.67000%      Record Date:                          5/14/00
                              Interest Period  4/17/00 thru         28       Pool Factor:                       60.2601791%
                              5/14/00:
===================================================================================================================================

        BALANCES
        Beginning HELOC Pool Balance                                                                         85,299,956.62
        Beginning Second Lien Pool Balance                                                                   52,424,991.71
        Beginning HLTV Pool Balance                                                                          38,607,927.54

        Beginning Class A-1 Note Balance -- CUSIP  422093AG9                                                 80,536,383.45
        Beginning Class A-2 Note Balance -- CUSIP  422093AH7                                                 46,625,488.79
        Beginning Class A-3 Note Balance -- CUSIP  422093AJ3                                                 32,379,863.88

        Ending HELOC Pool Balance                                                                            82,849,577.69
        Ending Second Lien Pool Balance                                                                      50,908,801.02
        Ending HLTV Pool Balance                                                                             38,064,091.28

        Ending Class A-1 Note Balance -- CUSIP  422093AG9                                                    78,086,004.52
        Ending Class A-2 Note Balance -- CUSIP  422093AH7                                                    44,935,059.95
        Ending Class A-3 Note Balance -- CUSIP  422093AJ3                                                    31,644,745.61

        Additional Balances  Class A-1                                                                        1,962,889.15

        Number of all Retransferred Mortgage Loans (Current Retransfer Date)                                             0
        Retransferred Mortgage Loan Trust Balances (Current Retransfer Date)                                          0.00
        Cumulative Number of all Retransferred Mortgage Loans (From Previous Distributions)                              0
        Cumulative Retransferred Mortgage Loan Trust Balances (From Previous Distributions)                          0 .00
        Number of all Subsequent HELOC Mortgage Loans (Current Date)                                                     0
        Subsequent HELOC Mortgage Loan Asset Balance (Current Date)                                                   0.00
        Number of all SubsequentSecond Lien Mortgage Loans (Current Date)                                                0
        Subsequent Second Lien Mortgage Loan Asset Balance (Current Date)                                             0.00
        Number of all Subsequent HLTV Mortgage Loans (Current Date)                                                      0
        Subsequent HLTV Mortgage Loan Asset Balance (Current Date)                                                    0.00
        Cumulative Number of ALL Subsequent Mortgage Loans                                                            1830
        Cumulative Subsequent Mortgage Loan Asset Balance                                                    64,876,717.43

        Beginning Loan Count                                                                                         5,071
        Ending Loan Count                                                                                            4,950

COLLECTION AMOUNTS Class A-1
        Aggregate of All Mortgage Collections                                                                 5,134,521.99
        Total Mortgage Interest Collections                                                                     756,795.56
        Servicing Fees (current collection period)                                                              (35,541.65)
        Mortgage Principal Collections                                                                        4,413,268.08
        Pre-Funded Balance                                                                                            0.00

       Total Mortgage Principal Collections                                                                   4,413,268.08
</TABLE>
<PAGE>

<TABLE>
<S>                                                                                   <C>
COLLECTION AMOUNTS Class A-2
      Aggregate of All Mortgage Collections                                           1,952,517.75
      Total Mortgage Interest Collections                                               458,170.81
      Servicing Fees (current collection period)                                        (21,843.75)
         Mortgage Principal Collections                                               1,516,190.69
         Pre-Funded Balance                                                                   0.00

      Total Mortgage Principal Collections                                            1,516,190.69

COLLECTION AMOUNTS Class A-3
      Aggregate of All Mortgage Collections                                             926,263.47
      Total Mortgage Interest Collections                                               398,513.85
      Servicing Fees (current collection period)                                        (16,086.64)
         Mortgage Principal Collections                                                 543,836.26
         Pre-Funded Balance                                                                   0.00

      Total Mortgage Principal Collections                                              543,836.26

TOTAL COLLECTION AMOUNT
      Aggregate of All Mortgage Collections                                           8,086,775.25
      Total Mortgage Interest Collections                                             1,613,480.22
         Mortgage Principal Collections                                               6,473,295.03
         Pre-Funded Balance                                                                   0.00

      Total Mortgage Principal Collections                                            6,473,295.03

DISTRIBUTION AMOUNTS Class A-1
      Class A-1 Note    Interest                                                        424,695.20
      Class A-1 Note    Unpaid Interest Shortfall  (current cycle)                            0.00
      Class A-1 Note    Reserve Fund Amount                                             282,781.45

      Maximum Principal Payment                                                       2,450,378.93
      Scheduled Principal Collection                                                          0.00
      Accelerated Principal Distribution Amount                                               0.00
      Loan Loss                                                                               0.00
      HELOC Overcollateralization Deficit                                                     0.00
      Total Certificateholders Distribution Allocable to PrincipaL                    2,450,378.93

DISTRIBUTION AMOUNTS Class A-2
      Class A-2 Note    Interest                                                        252,943.28
      Class A-2 Note    Unpaid Interest Shortfall  (current cycle)                            0.00
      Class A-2 Note    Reserve Fund Amount                                                   0.00

      Maximum Principal Payment                                                       1,516,190.69
      Scheduled Principal Collection                                                          0.00
      Accelerated Principal Distribution Amount                                         174,238.15
      Loan Loss                                                                               0.00
      HELOC Overcollateralization Deficit                                                     0.00
      Total Certificateholders Distribution Allocable to PrincipaL                    1,690,428.84

DISTRIBUTION AMOUNTS Class A-3
      Class A-3 Note    Interest                                                        179,978.08
      Class A-3 Note    Unpaid Interest Shortfall (current cycle)                             0.00
      Class A-3 Note    Reserve Fund Amount                                                   0.00

      Maximum Principal Payment                                                         543,836.26
      Scheduled Principal Collection Payment                                                  0.00
      Accelerated Principal Distribution Amount                                         191,282.01
</TABLE>
<PAGE>

<TABLE>
<S>                                                                                                               <C>
           Loan Loss                                                                                                      0.00
           HLTV Lien Overcollateralization Deficit                                                                        0.00
           Total Certificateholders Distribution Allocable to Principal                                             735,118.27

TOTAL DISTRIBUTION AMOUNT
           Class A Note Interest                                                                                    857,616.55
           Class A Note Unpaid Interest Shortfall (current cycle)                                                         0.00
           Class A Note Reserve Fund Amount                                                                         282,781.45

           Maximum Principal Payment                                                                              4,510,405.88
           Scheduled Principal Collection Payment/bal                                                                     0.00
           Accelerated Principal Distribution Amount                                                                365,520.16
           Overcollateralization Deficit                                                                                  0.00
           Total Certificateholders Distribution Allocable to Principal                                           4,875,926.04

 LOSSES/RETRANSFERS

           Unpaid Class A-1 Note Interest Shortfall Due (From Previous Distributions)                                     0.00
           Unpaid Class A-2 Note Interest Shortfall Due (From Previous Distributions)                                     0.00
           Unpaid Class A-3 Note Interest Shortfall Due (From Previous Distributions)                                     0.00
           Interest Earned on Shortfall @ applicable Certificate Rate                                                     0.00
           Investor Loss Reduction Amount (From Previous Distributions)                                                   0.00

DISTRIBUTION TO CERTIFICATEHOLDERS (PER CERTIFICATE WITH A $1,000 DENOMINATION)

Class A-1
           Total Class A-1 Note Distribution Amount Allocable to Interest                                            3.1679354
           Interest Distribution Amount                                                                              3.1679354
           Unpaid Note Interest Shortfall Included in Current Distribution                                           0.0000000
           Unpaid Note Interest Shortfall Remaining after Current Distribution (Carryover)                           0.0000000

           Total Class A-1 Note Distribution Amount Allocable to Principal                                          18.2781493
           Maximum Principal Payment                                                                                18.2781493
           Scheduled Principal Collections Payment                                                                   0.0000000
           Loan Loss                                                                                                 0.0000000
           Accelerated Principal Distribution Amount                                                                 0.0000000

Class A-2
           Total Class A-2 Note Distribution Amount Allocable to Interest                                            3.2183063
           Interest Distribution Amount                                                                              3.2183063
           Unpaid Note Interest Shortfall Included in Current Distribution                                           0.0000000
           Unpaid Note Interest Shortfall Remaining after Current Distribution (Carryover)                           0.0000000

           Total Class A-2 Note Distribution Amount Allocable to Principal                                          21.5080546
           Maximum Principal Payment                                                                                19.2911475
           Scheduled Principal Collections Payment                                                                   0.0000000
           Loan Loss                                                                                                 0.0000000
           Accelerated Principal Distribution Amount                                                                 2.2169071

Class A-3
           Total Class A-3 Note Distribution Amount Allocable to Interest                                            4.0896986
           Interest Distribution Amount                                                                              4.0896986
           Unpaid Note Interest Shortfall Included in Current Distribution                                           0.0000000
           Unpaid Note Interest Shortfall Remaining after Current Distribution (Carryover)                           0.0000000
</TABLE>
<PAGE>

<TABLE>
<S>                                                                                                               <C>
           Total Class A-3 Note Distribution Amount Allocable to                                                    16.7043242
           Principal
           Maximum Principal Payment                                                                                12.3577628
           Scheduled Principal Collections Payment                                                                   0.0000000
           Loan Loss                                                                                                 0.0000000
           Accelerated Principal Distribution Amount                                                                 4.3465614

           Reimbursed Investor Loss Reduction Amounts Included in Current Distribution                               0.0000000
           Investor Loss Reduction Amounts after Current Distribution (carryover)                                    0.0000000

           Total Interest Amount Distributed to Class A Certificateholder                                           10.4759403
           Total Principal Amount Distributed to Class A Certificateholder                                          56.4905281

           Credit Enhancement Draw Amount                                                                                    0

DELINQUENCIES/FORECLOSURES
Class A-1
           Number of Mortgages 31 to 60 Days Delinquent                                                                     39
           Aggregate Principal Balances of Mortgages 31 to 60 Days Delinquent                                     1,671,349.95
           Number of Mortgages 61 to 90 Days Delinquent                                                                      7
           Aggregate Principal Balances of Mortgages 61 to 90 Days Delinquent                                       216,742.90
           Number of Mortgages 91 to 180 or more Days Delinquent                                                             2
           Aggregate Principal Balances of Mortgages 91 to 180 or more Days Delinquent                              103,148.30
           Number of Mortgages 181 or more Days Delinquent                                                                   3
           Aggregate Principal Balances of Mortgages 181 or more Days Delinquent                                    265,589.21
           Number of Mortgage Loans in Foreclosure                                                                           5
           Aggregate Principal Balances of Mortgage Loans in Foreclosure                                            121,951.19

           Book Value of Real Estate Acquired Through Foreclosure or Grant of a Deed                                      0.00
           Aggregate Trust Balances of any Liquidated Loans in the Current Month                                          0.00

Class A-2
           Number of Mortgages 31 to 60 Days Delinquent                                                                     40
           Aggregate Principal Balances of Mortgages 31 to 60 Days Delinquent                                     1,521,988.49
           Number of Mortgages 61 to 90 Days Delinquent                                                                      4
           Aggregate Principal Balances of Mortgages 61 to 90 Days Delinquent                                       102,257.75
           Number of Mortgages 91 to 180 or more Days Delinquent                                                             5
           Aggregate Principal Balances of Mortgages 91 to 180 or more Days Delinquent                              144,080.82
           Number of Mortgages 181 or more Days Delinquent                                                                   1
           Aggregate Principal Balances of Mortgages 181 or more Days Delinquent                                     40,000.00
           Number of Mortgage Loans in Foreclosure                                                                           7
           Aggregate Principal Balances of Mortgage Loans in Foreclosure                                            367,088.07

           Book Value of Real Estate Acquired Through Foreclosure or Grant of a Deed                                 67,861.30
           Aggregate Trust Balances of any Liquidated Loans in the Current Month                                          0.00

Class A-3
           Number of Mortgages 31 to 60 Days Delinquent                                                                     43
           Aggregate Principal Balances of Mortgages 31 to 60 Days Delinquent                                     1,546,375.56
           Number of Mortgages 61 to 90 Days Delinquent                                                                     14
           Aggregate Principal Balances of Mortgages 61 to 90 Days Delinquent                                       593,460.87
           Number of Mortgages 91 to 180 or more Days Delinquent                                                            12
           Aggregate Principal Balances of Mortgages 91 to 180 or more Days Delinquent                              430,987.61
           Number of Mortgages 181 or more Days Delinquent                                                                   8
           Aggregate Principal Balances of Mortgages 181 or more Days Delinquent                                    299,168.96
           Number of Mortgage Loans in Foreclosure                                                                          20
           Aggregate Principal Balances of Mortgage Loans in Foreclosure                                            710,893.31

           Book Value of Real Estate Acquired Through Foreclosure or Grant of a Deed                                      0.00
           Aggregate Trust Balances of any Liquidated Loans in the Current Month                                          0.00

TOTAL DELINQUENCIES/FORECLOSURES
</TABLE>
<PAGE>

<TABLE>
<S>                                                                                                               <C>
           Number of Mortgages 31 to 60 Days Delinquent                                                                    122
           Aggregate Principal Balances of Mortgages 31 to 60 Days Delinquent                                     4,739,714.00
           Number of Mortgages 61 to 90 Days Delinquent                                                                     25
           Aggregate Principal Balances of Mortgages 61 to 90 Days Delinquent                                       912,461.52
           Number of Mortgages 91 to 180 or more Days Delinquent                                                            19
           Aggregate Principal Balances of Mortgages 91 to 180 or more Days Delinquent                              678,216.73
           Number of Mortgages 181 or more Days Delinquent                                                                  12
           Aggregate Principal Balances of Mortgages 181 or more Days Delinquent                                    604,758.17
           Number of Mortgage Loans in Foreclosure                                                                          32
           Aggregate Principal Balances of Mortgage Loans in Foreclosure                                          1,199,932.57

           Book Value of Real Estate Acquired Through Foreclosure or Grant of a Deed                                 67,861.30
           Aggregate Trust Balances of any Liquidated Loans in the Current Month                                          0.00
==============================================================================================================================

           Class A-1 Note Rate For Next Distribution       LIBOR    tbd

PRE-FUNDED ACCOUNT ACTIVITY
           Beginning Balance Pre Funding Account                                                                          0.00
           Remaining Amount for Distribution to Classes                                                                   0.00
           Withdrawal for Subsequent Loan Purchase:                                                                       0.00
           Ending Balance Pre Funding Account                                                                             0.00
           Pre-Funding Period:  From Closing Date thru the 2/15/99

RESERVE FUND ACTIVITY

           Class A-1 Reserve Fund  Beginning Balance                                                              3,600,103.75
           Class A-1 Reserve Fund  Deposit/Withdrawal                                                               282,781.45
           Class A-1 Reserve Fund  Ending Balance                                                                 3,882,885.20

           Class A-2 Reserve Fund  Beginning Balance                                                                      0.00
           Class A-2 Reserve Fund  Deposit/Withdrawal                                                                     0.00
           Class A-2 Reserve Fund  Ending Balance                                                                         0.00

           Class A-3 Reserve Fund  Beginning Balance                                                                      0.00
           Class A-3 Reserve Fund  Deposit/Withdrawal                                                                     0.00
           Class A-3 Reserve Fund  Ending Balance                                                                         0.00
</TABLE>

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