Document:

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                                                                    EXHIBIT 10.1

                                                                  EXECUTION COPY

                       COLLABORATION AND LICENSE AGREEMENT

                                     BETWEEN

                        GENOME THERAPEUTICS CORPORATION,

                                       AND

                       AMERICAN HOME PRODUCTS CORPORATION

                          DATED AS OF DECEMBER 20, 1999

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                       COLLABORATION AND LICENSE AGREEMENT

         THIS COLLABORATION AND LICENSE AGREEMENT (the "Agreement") is dated as
of December 20, 1999 (the "Effective Date") and is made by and between GENOME
THERAPEUTICS CORPORATION, a corporation organized and existing under the laws of
the Commonwealth of Massachusetts having its offices at 100 Beaver Street,
Waltham, Massachusetts 02154 ("GTC") and AMERICAN HOME PRODUCTS CORPORATION,
acting through its Wyeth-Ayerst Laboratories Division, a corporation organized
and existing under the laws of the State of Delaware having its offices at 555
East Lancaster Avenue, St. Davids, Pennsylvania 19087 ("AHP"). GTC and AHP are
sometimes referred to herein individually as a party and collectively as the
parties.

                                 R E C I T A L S

         WHEREAS, GTC is involved in research programs regarding the use of
positional cloning to discover human genes, an objective of which is to discover
potential biological targets for use in drug discovery; and

         WHEREAS, AHP is interested in funding and collaborating with GTC for
the development, manufacture and sale of novel human therapeutics relating to
bone disease, bone metabolism, bone pathology and bone repair in humans; and

         WHEREAS, GTC is willing to provide to AHP its proprietary technology
and know-how relating to such bone disorders and enter into such a collaboration
upon the terms and conditions set forth below;

         NOW THEREFORE, in consideration of the premises and of the covenants
herein contained, the parties hereto mutually agree as follows:

                             SECTION 1. DEFINITIONS

         For purposes of this Agreement, the terms defined in this Section 1
shall have the meanings specified below:

         1.1 "ACADEMIC COLLABORATORS" shall mean academic institutions,
including without limitation Creighton University, that have entered into a
Research Agreement with GTC related to Bone Disorders.

         1.2 "ADDITIONAL COLLABORATION" shall have the meaning set forth in
Section 3.5.

         1.3 "ADDITIONAL INFORMATION" shall have the meaning set forth in
Section 3.5.

         1.4 "AFFILIATE" shall mean any corporation or other entity which
directly or indirectly controls, is controlled by or is under common control
with a party to this Agreement. A corporation or other entity shall be regarded
as in control of another corporation or entity if it

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owns or directly or indirectly controls more than fifty percent (50%) of the
outstanding voting stock or other ownership interest of the other corporation or
entity, or if it possesses, directly or indirectly, the power to manage, direct
or cause the direction of the management and policies of the corporation or
other entity or the power to elect or appoint fifty percent (50%) or more of the
members of the governing body of the corporation or other entity. Any such other
relationship as in fact results in actual control over the management, business
and affairs of a corporation or other entity shall also be deemed to constitute
control. Notwithstanding the foregoing, the term Affiliate shall not include a
subsidiary in which a party or its Affiliates own a majority of the ordinary
voting power to elect a majority of the board of directors but is restricted
from electing such majority by contract or other express restriction, until such
time as any such restriction is no longer in effect. ***

         1.5 "AGENTS" shall have the meaning set forth in Section 8.1.2.

         1.6 "AHP PATENT RIGHTS" shall mean (a) the United States and foreign
patent applications filed covering the AHP Technology, (b) any United States
patents and foreign patents issuing from such patent applications and (c) any
continuations, continuations-in-part directed to subject matter specifically
described in such patent applications, divisionals, patents of addition,
renewals, registrations, confirmations, reexaminations, reissues, extensions or
provisional applications of any of the foregoing.

         1.7 "AHP PROGRAM TECHNOLOGY" shall mean, collectively, the AHP
Technology, the AHP Patent Rights, AHP's interest in the Joint Technology and
AHP's interest in the Joint Patent Rights.

         1.8 "AHP TECHNOLOGY" shall mean (i) all inventions (whether or not
patentable), results, discoveries, improvements, know-how, techniques,
materials, compounds, products, designs, processes or other technology or
intellectual property rights in the Bone Disorder Field owned or licensed (with
the right to sublicense) by AHP (excluding technology licensed hereunder) and
first developed, created, conceived or reduced to practice solely by AHP
employees or Third Parties acting on behalf of AHP or its Affiliates during the
course of the Research Collaboration, and (ii) all information and data in the
possession of AHP in the Bone Disorder Field that is not generally known or
created solely by AHP during the Research Collaboration, whether or not secret,
patentable or patented, relating to materials, methods, processes, procedures,
protocols, techniques, and formulae reasonably useful for the development,
regulatory approval, manufacture, sale or use of the Products.

         1.9 "ANNUAL RESEARCH PLAN" shall have the meaning set forth in Section
4.5.2.

1.10     "APPROVAL MILESTONES" shall have the meaning set forth in Section 6.2.3

         1.11 "APPROVAL" shall have the meaning set forth in Section 5.3.1.

         1.12 "BONE DISORDERS" shall mean disorders relating to bone disease,
*** in humans. Bone Disorders SHALL NOT INCLUDE *** any other subject matter,
disease or condition, including without limitation joint disease and
inflammatory processes such as osteoarthritis and rheumatoid arthritis.

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         1.13 "BONE DISORDER FIELD" shall mean the use in humans *** for the
purpose of treating or preventing Bone Disorders.

         1.14 "CLAIM" shall mean a claim of a patent application pending ***
that has not been disallowed or abandoned or a claim of an issued and unexpired
patent that has not been held permanently revoked, unenforceable or invalidated
by a decision of a court or other governmental agency of competent jurisdiction,
and which is not subject to appeal.

         1.15 "COMMERCIALLY REASONABLE EFFORTS" shall mean efforts and resources
normally used by a party for a compound or product owned by it or to which it
has rights, which is of similar market potential at a similar stage in its
product life, taking into account the competitiveness of the marketplace, the
proprietary position of the compound or product, the regulatory structure
involved, the profitability of the applicable products, and other relevant
factors.

         1.16 "CONTRACT YEAR" shall mean each twelve (12) month period starting
on January 1, 2000, and each successive calendar year thereafter.

         1.17 "CREIGHTON UNIVERSITY AGREEMENTS" shall mean the agreement between
GTC and Creighton University dated April 3, 1997, as amended, and any additional
agreements between GTC and Creighton University related to the Field.

         1.18 "DEVELOPMENT MILESTONES" shall have the meaning set forth in
Section 6.2.2.

         1.19 "DEVELOPMENT TRACK" shall mean the decision of the Wyeth-Ayerst
Research Development Operating Committee ("DOC", or any successor or substitute
body) to advance a product to pre-development stage ("Phase 0", or any successor
or substitute designation) pursuant to its internal criteria and procedures.

         1.20 "DEVELOPMENT TRACK PRODUCT" shall mean a product approved for
Development Track.

         1.21 "DIAGNOSTIC INFORMATION" shall mean the information or data ***
discovered during the course of the Research Collaboration.

         1.22 "DIAGNOSTIC INFORMATION FIELD" shall mean the use of *** .

         1.23 "DIAGNOSTIC PRODUCTS" shall mean any device, product, process,
substance, composition or service intended to predict, detect, identify or
monitor a disease or determine the presence of a pathologic condition in humans.

         1.24 "DIAGNOSTIC TECHNOLOGY" shall mean (i) all inventions (whether or
not patentable), results, discoveries, improvements, know-how, techniques,
materials, compounds, products, designs, processes or other technology or
intellectual property rights related to a Diagnostic Product owned or licensed
(with the right to sublicense) by GTC and first developed, created, conceived or
reduced to practice solely by GTC employees or Third Parties, including without
limitation Academic Collaborators, acting on behalf of GTC or its Affiliates
either prior to the Effective Date hereof or thereafter during the course of the
Research Collaboration or the

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course of GTC's development activities under Section 3.3.1, and (ii) all
information and data in the possession of GTC that is not generally known,
existing as of the Effective Date or created by GTC during the Research
Collaboration or in the course of GTC's development activities under Section
3.3.1, whether or not secret, patentable or patented, relating to materials,
methods, processes, procedures, protocols, techniques, and formulae reasonably
useful for the development, regulatory approval, manufacture, sale or use of the
Diagnostic Products.

         1.25 "DISEASE" shall mean each category of human disease, other than
Bone Disorders.

         1.26 "EVENT OF DEFAULT" shall have the meanings set forth in Section
11.4.

         1.27 "EXPANDED THERAPEUTIC FIELD" shall mean the use in humans of
therapeutic or prophylactic products *** .

         1.28 "FDA" shall mean the United States Food and Drug Administration.

         1.29 "FIELD" shall mean the Therapeutic Field and the Diagnostic
Information Field.

         1.30 "FIRST COMMERCIAL SALE" of a Product in a country shall mean the
first for profit sale for use or consumption by the general public of a Product
in such country after the required marketing and, if necessary, governmental
pricing approvals for such country have been obtained.

         1.31 "GTC PATENT RIGHTS" shall mean (a) the United States and foreign
patent applications filed covering the GTC Technology, (b) any United States
patents and foreign patents issuing from such patent applications and (c) any
continuations, continuations-in-part directed to subject matter specifically
described in such patent applications, divisionals, patents of addition,
renewals, registrations, confirmations, reexaminations, reissues, extensions or
provisional applications of any of the foregoing.

         1.32 "GTC PROGRAM TECHNOLOGY" shall mean, collectively, the GTC
Technology, the GTC Patent Rights, GTC's interest in the Joint Technology and
GTC's interest in the Joint Patent Rights.

         1.33 "GTC TECHNOLOGY" shall mean (i) all inventions (whether or not
patentable), results, discoveries, improvements, know-how, techniques,
materials, compounds, products, designs, processes or other technology or
intellectual property rights in the Bone Disorder Field owned or licensed (with
the right to sublicense) by GTC (excluding technology licensed hereunder) and
first developed, created, conceived or reduced to practice solely by GTC
employees or Third Parties, including without limitation Academic Collaborators,
acting on behalf of GTC or its Affiliates either prior to the Effective Date
hereof or during the course of the Research Collaboration, and (ii) all
information and data in the possession of GTC in the Bone Disorder Field that is
not generally known, existing as of the Effective Date or created by GTC during
the Research Collaboration, whether or not secret, patentable or patented,
relating to materials, methods, processes, procedures, protocols, techniques,
and formulae reasonably useful for the development, regulatory approval,
manufacture, sale or use of the Products.

         1.34 "*** GENE" shall mean *** .

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         1.35 "*** PATHWAY GENE" shall mean *** .

         1.36 "IND" shall mean an investigational new drug application or its
equivalent filed with the FDA and necessary for beginning clinical trials in
humans, or any comparable application filed with the regulatory authorities of a
country other than the United States prior to beginning clinical trials in
humans in that country, with respect to Products.

         1.37 "INTERIM CLINICAL EVALUATION" or "ICE" shall mean the decision of
the Wyeth-Ayerst Research Development Operating Committee (DOC, or any successor
or substitute body) pursuant to its internal criteria and procedures, which
designation indicates AHP's approval to continue development of the product
candidate based on AHP's evaluation of Phase I/IIa studies, including efficacy
data from at least one Phase II clinical trial.

         1.38 "JOINT PATENT COMMITTEE" shall have the meaning set forth in
Section 4.6.

         1.39 "JOINT PATENT RIGHTS" shall mean (a) the United States and foreign
patent applications filed covering Joint Technology, (b) any United States
patents and foreign patents issuing from such patent applications and (c) any
continuations, continuations-in-part directed to subject matter specifically
described in such patent applications, divisionals, patents of addition,
renewals, registrations, confirmations, reexaminations, reissues, extensions or
provisional applications of any of the foregoing.

         1.40 "JOINT RESEARCH COMMITTEE" shall have the meaning set forth in
Section 4.5.1.

         1.41 "JOINT TECHNOLOGY" shall mean all inventions (whether or not
patentable), results, discoveries, improvements, know-how, techniques,
materials, compounds, products, designs, processes or other technology or
intellectual property rights first developed, created, conceived or reduced to
practice jointly by employees of GTC, or its Affiliates or Third Parties or
Academic Collaborators acting on behalf of GTC, and AHP, or its Affiliates,
during the course of the Research Collaboration.

         1.42 "KIT PRODUCT" shall have the meaning set forth in Section 3.3.2.

         1.43 "MAJOR MARKET COUNTRY" shall mean one or more of the United
States, Japan, the United Kingdom, France, Germany, and Italy.

         1.44 "NDA" shall mean a new drug application or product license
application or its equivalent filed with the FDA after completion of human
clinical trials to obtain marketing approval for a Product, or any comparable
application filed with the regulatory authorities of a country other than the
United States, including, where applicable, any applications for governmental
pricing and marketing approval.

         1.45 "NET SALES" shall mean the gross invoice price for Products sold
by AHP or its Affiliates or sublicensees to a Third Party customer less the
reasonable and customary accrual-basis deductions from such gross amounts for:
(i) normal and customary trade, cash and other discounts, allowances and credits
actually allowed and taken directly with respect to sales of Products; (ii)
credits or allowances actually granted for damaged goods, returns or rejections
of

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Products; (iii) sales or similar taxes (including duties or other governmental
charges levied on, absorbed or otherwise imposed directly on the sales of
Products including, without limitation, value added taxes or other governmental
charges otherwise measured by the billing amount, which are included in billing
amount); (iv) freight, postage, shipping, customs duties and insurance charges
which are included in the billing amount not in excess of one percent (1%) of
the Net Sales to which such deductions relate; (v) charge back payments and
rebates granted to managed health care organizations or to federal, state and
local governments, their agencies, and purchasers and reimbursers or to trade
customers, including but not limited to, wholesalers and chain and pharmacy
buying groups; and (vi) rebates (or equivalents thereof) that are granted to or
charged by national, state, provincial or local governmental authorities in
countries other than the United States provided, however, that the aggregate of
the foregoing deductions shall be comparable to the aggregate of such deductions
taken by AHP with respect to products sold by AHP in the same class. The
transfer of Products by AHP or one of its Affiliates to (i) another Affiliate of
AHP or (ii) a sublicensee of AHP shall not be considered a sale; in such cases,
Net Sales shall be determined based on the invoiced sales price by the Affiliate
or sublicensee to its Third Party customer, less the deductions allowed under
this Section. Every other commercial use or disposition of Products by AHP or
its Affiliates or sublicensees of AHP in barter or similar transactions, not
including samples, shall be considered a sale of the Products at the weighted
average Net Sales price for Products during the preceding quarter.

         In the event that a Product is sold in the form of a combination
product containing such Product and one or more other active ingredients which
is not by itself a Product (a "Combination Product"), Net Sales for such
Combination Product will be calculated by multiplying actual Net Sales of such
Combination Product by the fraction A/(A+B), where A is the invoice price of the
Product if sold separately by AHP, an Affiliate or a sublicensee and containing
a Product as the only active ingredient and B is the invoice price of any other
active component or components in the Combination Product if sold separately by
AHP, an Affiliate or a sublicensee. In the event that the Product is sold in the
form of a Combination Product containing such Product and one or more other
active ingredients which is not by itself a Product and one or more of such
other active ingredients of the Combination Product are not sold separately,
then the above formula shall be modified such that A shall be the total
manufacturing cost to AHP, its Affiliate or sublicensee of the Product and B
shall be the total manufacturing cost to AHP, its Affiliate, sublicensee or
other supplier of any other active component or components in the Combination
Product. Notwithstanding the foregoing, (i) active ingredients shall not include
diluents, vehicles or adjuvants and (ii) in no event shall Net Sales for any
Combination Product calculated under this provision be less than fifty percent
of the invoice price of such Combination Product. For the avoidance of doubt,
the parties acknowledge that a Kit Product sold by AHP pursuant to Section 3.3.2
shall not be considered a Combination Product.

         In the event that AHP, its Affiliates or sublicensees sell Products
pursuant to an agreement with an independent customer specifying, for a
combination of products or services, a single price, other terms of purchase not
separately identifying either a price per product or the effective deductions
referred to above per product or a price for units of the Products which is
discounted below AHP's, its Affiliates' or its sublicensee's standard invoice
price per unit of the Products by at least three (3) percentage points more than
the amount that any other product or service included in the arrangement is
discounted below such other product's or service's

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standard invoice price, then GTC and AHP will determine a mutually agreeable
method of calculation so that a fair and reasonable portion of the aggregate
purchase price is allocated to the Product(s) included in any such arrangement.

         If a Product is sold in bulk (as distinguished from packaged in
pharmaceutical form) for resale in packaged or finished form, Net Sales shall be
calculated by determining the quantity of Product in packaged pharmaceutical
form that would reasonably be produced from the bulk quantity of Product so
sold, and by multiplying such quantity by the average price for such Product in
packaged pharmaceutical form during the applicable royalty reporting period.

         1.46 "OVERALL RESEARCH PLAN" shall mean the research plan agreed upon
by the Joint Research Committee pursuant to Section 4.5.1, as it may be
subsequently amended, improved or modified from time to time, the draft of which
is attached hereto as Exhibit A (the "Draft Overall Research Plan").

         1.47 "PRODUCT" shall mean *** . For the avoidance of doubt, it is
understood that Products shall not include nutraceuticals (i.e., any product not
requiring approvals from a regulatory authority normally required for
prescription legend pharmaceuticals), dietary supplements or Diagnostic
Products.

         1.48 "PRODUCT CATEGORY" shall mean *** .

         1.49 "PRODUCT PATENT RIGHTS" shall mean (a) the United States and
foreign patent applications filed covering a therapeutic or prophylactic
product, substance, biological target, or formulation or the manufacture of such
a therapeutic or prophylactic product discovered and/or developed based upon the
Research Collaboration or during the course of AHP's performance of its
development obligations under Section 5 of this Agreement, (b) any United States
patents and foreign patents issuing from such patent applications and (c) any
continuations, continuations-in-part directed to subject matter specifically
described in such patent applications, divisionals, patents of addition,
renewals, registrations, confirmations, reexaminations, reissues, extensions or
provisional applications of any of the foregoing.

         1.50 "RESEARCH AGREEMENTS" shall mean, collectively, the Creighton
University Agreements and any other agreement between GTC and an Academic
Collaborator that may be entered into after the Effective Date in furtherance of
the Research Collaboration.

         1.51 "RESEARCH COLLABORATION" shall mean the work described and/or
performed under the Overall Research Plan and any Annual Research Plan, as may
be modified in accordance with the procedures set forth in Section 4.

         1.52 "RESEARCH MILESTONES" shall have the meaning set forth in Section
6.2.1.

         1.53 "THERAPEUTIC FIELD" shall mean the Bone Disorder Field and the
Expanded Therapeutic Field.

         1.54 "THIRD PARTY" shall mean any entity other than GTC or AHP and
their respective Affiliates.

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         1.55 "VALIDATED PATHWAY" shall mean *** .

         1.56 "VALIDATED TARGET" shall mean the *** .

         1.57 "WYETH DISCOVERY BOARD" means the Wyeth-Ayerst Research division
of AHP's Discovery Board, a body of Wyeth-Ayerst Discovery Research, and any
successor or substitute body thereto.

                                    Article 2
                    SCOPE AND STRUCTURE OF THE COLLABORATION

         2.1 GENERAL. GTC and AHP wish to establish a collaborative alliance to
develop Products. This collaborative alliance will include a Research
Collaboration, during which the parties will work to validate the *** Gene and
to identify *** Pathway Genes that are associated with or implicated in Bone
Disorders. During the course of this collaboration, GTC and AHP shall
communicate regularly and shall assume different rights and responsibilities for
the development of Products, all as more specifically described below.

         2.2 EXCLUSIVITY; ACKNOWLEDGMENT OF OTHER COLLABORATIONS. AHP
acknowledges that GTC is currently engaged in certain research collaborations
with Third Parties and intends to enter into additional research collaborations
in the future ***; PROVIDED, HOWEVER, *** in the Therapeutic Field with such
Third Parties other than pursuant to Section 5.2 of this Agreement. GTC agrees
that, during the term of the Research Collaboration and provided that AHP is not
in breach of a provision of this Agreement, it will *** or except as otherwise
contemplated by this Agreement.

                                    Article 3
                        LICENSE GRANTS; MARKETING RIGHTS

         3.1 GRANT OF RIGHTS BY GTC TO AHP.

                  3.1.1 EXCLUSIVE GRANT OF RIGHTS. Subject to the terms of this
Agreement, GTC hereby grants to AHP the worldwide exclusive right in the Bone
Disorder Field and the Expanded Therapeutic Field, with the right to grant
sublicenses as set forth in Section 3.1.3, under the GTC Program Technology
(other than Diagnostic Information) to research, develop, use, manufacture, have
manufactured, market, promote, import, export, offer for sale, sell and have
sold Products in the Bone Disorder Field and the Expanded Therapeutic Field. The
rights granted to AHP in this Section 3.1.1 shall survive the termination or
expiration of the Research Collaboration and continue for the entire term of
this Agreement.

                  3.1.2 NON-EXCLUSIVE GRANT OF RIGHTS IN THE DIAGNOSTIC
INFORMATION FIELD. Subject to the terms of this Agreement, GTC hereby grants to
AHP the worldwide non-exclusive royalty-free right in the Diagnostic Information
Field, with the right to grant sublicenses as set forth in Section 3.1.3, to use
Diagnostic Information solely for the purpose of conducting human clinical
trials and obtaining governmental approvals of a Product.

                  3.1.3 SUBLICENSES. AHP shall have the right to grant
sublicenses under the GTC Program Technology and the Diagnostic Information to
Affiliates of AHP and, with the prior

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written consent of GTC which shall not be unreasonably withheld, to Third
Parties, PROVIDED, HOWEVER, that such GTC consent shall not be required for
sublicenses to Third Parties limited to the manufacturing and/or distribution of
Products; AND PROVIDED FURTHER that each Third Party sublicensee shall execute a
written agreement pursuant to which it assumes the applicable obligations of AHP
hereunder.

         3.2 RESERVATION OF RIGHTS. Notwithstanding the rights granted to AHP
under Article 3, GTC at all times reserves the right to use the GTC Program
Technology to research, develop, use, manufacture, have manufactured, and sell
products other than Products, including, subject to the provisions of this
Article 3, the right to grant licenses and/or sublicenses with respect to any
such intellectual property rights for such purpose.

         3.3 DIAGNOSTIC PRODUCTS.

                  3.3.1 GTC RIGHTS. Without limiting the generality of Section
3.2, GTC retains the right to make, use and sell Diagnostic Products related to
the Therapeutic Field. Subject to the terms of this Agreement, AHP hereby grants
to GTC the worldwide non-exclusive royalty-free right, with the right to grant
sublicenses as set forth below, under the AHP Program Technology solely to
research, develop, use, manufacture, have manufactured, market, promote, import,
export, offer for sale, sell and have sold Diagnostic Products. GTC shall have
the right to grant sublicenses under the AHP Program Technology to Affiliates of
GTC and, with the prior written consent of AHP which shall not be unreasonably
withheld, to Third Parties; PROVIDED, HOWEVER, that such AHP consent shall not
be required for sublicenses to Third Parties limited to the manufacturing and/or
distribution of a Diagnostic Product.

                  3.3.2 KIT PRODUCT.  In the event   ***  .

         3.4 NO GRANT OF OTHER TECHNOLOGY OR PATENT RIGHTS. Except as otherwise
expressly provided in this Agreement, under no circumstances shall a party
hereto, as a result of this Agreement, obtain any ownership interest in or other
right to any technology, know-how, patents, patent applications, genomic
sequence data, products, or biological materials of the other party, including
items owned, controlled or developed by the other party, or transferred by the
other party to said party, at any time pursuant to this Agreement. Any
compounds, technology or know-how derived, developed or acquired solely by
either party independent of the GTC Program Technology, the AHP Program
Technology, or the Research Collaboration shall be the property of such party.

         3.5 OTHER GTC RESEARCH ACTIVITIES. During the term of this Agreement,
GTC may undertake genomic research activities outside of the scope of this
Agreement that yield other genes, gene products, drug targets, cellular
molecular mechanisms or information that may have utility as a pharmaceutical
target or as pharmacogenetic information in the Bone Disorder Field
(collectively, "Additional Information"). *** .

                                    Article 4
                      CONDUCT OF THE RESEARCH COLLABORATION

         4.1 OBLIGATIONS OF THE PARTIES.

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                  4.1.1 REASONABLE EFFORTS. During the Research Collaboration
and thereafter, each of the parties agrees to use its respective Commercially
Reasonable Efforts to perform its obligations under the Overall Research Plan,
each Annual Research Plan and this Agreement in a timely manner.

                  4.1.2 COMPLETION OF SEQUENCING *** . Upon the discovery and
sequencing *** pursuant to the Overall Research Plan and the Annual Research
Plans, GTC shall provide to the Joint Research Committee, as described below, a
written statement *** supported by adequate documents providing reasonable
detail concerning the completion of such sequencing *** . Within thirty (30)
days following receipt by the Joint Research Committee of such written statement
from GTC, the Joint Research Committee shall in good faith using criteria
consistent with the Overall Research Plan deliver its written confirmation to
AHP or deliver to GTC a written statement describing in detail any respect in
which sequencing has not been achieved.

                  4.1.3 DELIVERIES BY GTC. *** following the completion of
sequencing *** , GTC shall deliver to AHP electronic and, if requested, paper
copies of the DNA sequence of such *** Pathway Gene, an outline of the
methodologies and procedures used to obtain such *** Pathway Gene and mutational
information in sufficient detail for patent filings. GTC shall deliver to AHP,
upon request, DNA sequences and/or cDNA clones of each completed *** Pathway
Gene.

         4.2 ACCESS TO DATA. AHP will have direct access to raw sequence data
that form part of the GTC Program Technology and to other work resulting from
the Research Collaboration. AHP's access shall be during normal business hours
and upon reasonable notice, granting AHP treatment and priority not less
favorable than granted to GTC's other collaborators.

         4.3 TERM OF RESEARCH COLLABORATION; RESOURCES. The term of the Research
Collaboration shall continue for the period set forth in Section 11.1. During
the term of the Research Collaboration, GTC will provide, *** . Within thirty
(30) days of the Effective Date, GTC will provide to AHP the names,
qualifications and percentage effort of all such scientists and will thereafter
update such information in the event of any changes. AHP will compensate GTC for
any mutually agreed additional level of effort that is provided by GTC hereunder
at a rate to be mutually agreed upon between the two parties.

         4.4 AVAILABILITY OF EMPLOYEES. GTC agrees to make its employees
reasonably available at their places of employment to consult with AHP on issues
arising during the Research Collaboration.

         4.5 JOINT RESEARCH COMMITTEE.

                  4.5.1 RESEARCH PLAN. Within sixty (60) days after the
Effective Date, a joint committee (the "Joint Research Committee") shall be
appointed and shall agree upon an overall written plan for the research and
development to be conducted by the parties during the Research Collaboration
(the "Overall Research Plan"). The Overall Research Plan shall be consistent
with the scope, scale and direction of Draft Overall Research Plan attached
hereto as EXHIBIT A and shall establish:

                  (i)   the scope of the Research Collaboration;

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                  (ii)  the research objectives, work plan activities and time
                        schedules with respect to identification of *** Pathway
                        Genes;

                  (iii) the responsibilities of each party with respect to the
                        work to be performed under the Research Collaboration;
                        and

                  (iv)  the projected annual budget of the Research
                        Collaboration.

The Overall Research Plan may be revised and updated from time to time as agreed
upon in writing by the Joint Research Committee.

                  4.5.2 ANNUAL RESEARCH PLANS. Within sixty (60) days after the
Effective Date, the Joint Research Committee shall agree upon a written plan for
the specific activities to be conducted in connection with the Research
Collaboration during the first Contract Year (the "Annual Research Plan"), which
plan shall be based on the Draft Overall Research Plan. Thereafter, by each
anniversary of the Effective Date of each year during the Research
Collaboration, GTC shall submit to the Joint Research Committee a written
proposed Annual Research Plan for the following Contract Year. The Joint
Research Committee shall review each such proposal as soon as practicable and
shall approve within forty-five (45) days of each such submission the final
Annual Research Plan for the next succeeding Contract Year.

                  4.5.3 PERIODIC REVIEWS. The Joint Research Committee shall
review the Overall Research Plan on an ongoing basis and may make changes to
clarify the Annual Research Plan then in effect; PROVIDED, HOWEVER, the Annual
Research Plan then in effect shall not be modified except as agreed in writing
by the Joint Research Committee.

                  4.5.4 MEMBERSHIP OF JOINT RESEARCH COMMITTEE. The Joint
Research Committee shall be comprised of three (3) representatives from each of
AHP and GTC, with each party's representatives to be selected by that party. GTC
and AHP may replace one or more of their respective representatives on the Joint
Research Committee at any time upon written notice to the other party. Unless
the parties otherwise agree, the chairmanship of the Joint Research Committee
shall rotate at the end of each Contract Year between a representative of GTC
and a representative of AHP, with a representative of AHP serving as chairman
during the first Contract Year. The chairman of the Joint Research Committee
shall be responsible for calling meetings, preparing agendas and preparing and
issuing minutes of each meeting within thirty (30) days thereafter. From time to
time the Joint Research Committee may establish subcommittees to oversee
particular projects or activities, and such subcommittees will be constituted as
the Joint Research Committee shall agree.

                  4.5.5 JOINT RESEARCH COMMITTEE MEETINGS The Joint Research
Committee shall meet quarterly during the term of the Research Collaboration, or
more often as agreed upon by both parties. The location of such meetings shall
rotate equally among the principal research offices of AHP and GTC. ***
representatives from each of AHP and GTC shall constitute a quorum, and no
decision of the Joint Research Committee shall be binding unless a quorum is
present. Regularly scheduled meetings or special meetings of the Joint Research
Committee may be in such form (E.G., in person, by telephone or by video
conference) as the members of the Joint Research Committee shall agree. To the
extent feasible, video conferencing shall be used.

                                       11
<PAGE>

If a representative of a party is unable to attend a meeting, such party may
designate an alternate to attend such meeting in place of the absent
representative. At least one (1) week prior to each meeting of the Joint
Research Committee, each of GTC and AHP shall provide to the other a written
progress report. Such progress reports shall describe relevant findings since
the last meeting and provide such other information as reasonably requested by
AHP and/or GTC relating to the progress of the goals or performance of the
Research Collaboration. At such meetings, the Joint Research Committee shall (i)
formulate and review the objectives of the Research Collaboration as expressed
in the Overall Research Plan, (ii) monitor the progress of the Annual Research
Plan toward those objectives, (iii) approve expenditures within the budget set
forth in the Draft Overall Research Plan, Overall Research Plan or Annual
Research Plan, (iv) allocate the research funding, staffing and other resources
under the Research Collaboration, and (v) take such other actions as may be
specified under this Agreement or as the parties may deem appropriate. *** .
With the consent of both parties, other representatives of GTC or AHP or their
respective Affiliates may attend the meetings of the Joint Research Committee as
nonvoting observers. Each party shall be responsible for all expenses of its
representatives on the Joint Research Committee. The Joint Research Committee
shall keep accurate minutes of its deliberations, which minutes shall record all
proposed decisions and all actions recommended or taken and which shall be
countersigned by one representative of each party. All records of the Joint
Research Committee shall be available to both parties.

                  4.5.6 DECISION MAKING. Except as otherwise provided herein or
agreed by the parties, all decisions, approvals, determinations and other
actions of the members of the Joint Research Committee or their respective
designees present at the relevant meeting shall be *** , and a decision,
approval, determination or other action made in accordance with Section 4.5
shall be binding on the entire Joint Research Committee. The Joint Research
Committee may delegate to one party or to a specific representative the
authority to make certain decisions. Disputes among the members of the Joint
Research Committee shall be resolved as set forth in Section 12.6.

         4.6 JOINT PATENT COMMITTEE. A joint committee comprised of *** (the
"Joint Patent Committee") shall be appointed and shall meet as needed. A party
may change its representative to the Joint Patent Committee at any time. Members
of the Joint Patent Committee may be represented at any meeting by a deputy.
Additional members of the Joint Patent Committee may be appointed on an AD HOC
basis upon the mutual consent of the parties. The Joint Patent Committee shall
formulate an intellectual property protection strategy with regard to the Joint
Patent Rights. In any instance in which AHP informs GTC in writing that it
objects to the filing of any patent application by GTC, the filing of such
application shall be subject to the prior written approval of the Joint Patent
Committee. The policies and procedures set forth in Section 4.5.6. shall apply
to the Joint Patent Committee and references to the Joint Research Committee
made therein shall be deemed to refer to the Joint Patent Committee for purposes
of this Section 4.6. Disputes among the members of the Joint Patent Committee
shall be resolved as set forth in Section 12.6.

         4.7 KEY GTC EMPLOYEE. If the GTC program coordinator for the Research
Collaboration ceases to be an employee of GTC during the term of the Research
Collaboration, then GTC shall *** notify AHP in writing of such fact and propose
a timetable for replacement of the employee. AHP may interview the final
candidate selected by GTC to fill the

                                       12
<PAGE>

position and make recommendations to GTC. GTC shall have sole and final
authority for all hiring decisions.

         4.8 ASSIGNMENT OF INVENTIONS. GTC shall cause its contractors and other
Third Parties (other than Academic Collaborators) that perform work on its
behalf for the Research Collaboration to enter into agreements pursuant to which
each such person or entity assigns inventions, discoveries and works of
authorship to GTC.

         4.9 DESIGNATION OF VALIDATED TARGETS AND VALIDATED PATHWAYS. With
respect to the determination of a gene or pathway as a Validated Target or
Validated Pathway, *** .

                                    Article 5
                      DEVELOPMENT AND MARKETING OBLIGATIONS

         5.1 DISCOVERY EFFORTS.

                  5.1.1 DISCOVERY EFFORTS BY AHP. AHP agrees, at its own
expense, to use Commercially Reasonable Efforts to use, either directly or
through its Affiliates or sublicensees, each Validated Target to attempt to
discover *** .

         5.2 DEVELOPMENT EFFORTS.

                  5.2.1 DEVELOPMENT EFFORTS BY AHP. AHP agrees, at its own
expense, to use Commercially Reasonable Efforts to develop and commercialize,
either directly or through its Affiliates or sublicensees, Development Track
Products discovered by it in accordance with Section 5.1. Such efforts shall
include, without limitation, the active conduct of IN VIVO toxicology trials
necessary to obtain approval for use of a compound in human clinical trials or
the active conduct of human clinical trials. Development of Development Track
Products to a Product will be conducted principally by AHP; PROVIDED, HOWEVER,
that AHP shall consult with GTC and provide GTC with access to AHP Program
Technology to the extent necessary to enable both parties to attempt to resolve
any development problems jointly. The selection of the form of Development Track
Products for development and commercialization shall be in the sole discretion
of AHP. AHP, its Affiliates and sublicensees may, but shall have no obligation
under this Agreement to, develop and commercialize more than *** at any time
during the term of this Agreement. If AHP discontinues development of a
Development Track Product, AHP will, to the extent commercially reasonable,
resume the Commercially Reasonable Efforts described in Section 5.1, with the
objective of selecting a replacement and maintaining *** under active
pre-clinical or clinical development *** .

         5.3 MARKETING AND DISTRIBUTION EFFORTS.

                  5.3.1 MARKETING AND DISTRIBUTION EFFORTS BY AHP. AHP shall
have the exclusive worldwide right to market and distribute the Products and
shall use Commercially Reasonable Efforts to (i) seek all regulatory and
governmental pricing approvals required for marketing the Product ("Approval")
in all Major Market Countries; and (ii) upon receipt of Approval, if applicable,
of a Product in any country, use Commercially Reasonable Efforts to launch,
promote, market and sell such Product in such country. Both parties recognize
that extenuating circumstances may arise that warrant a delay in launching a
Product in a particular

                                       13
<PAGE>

country, including but not limited to unfavorable pricing or labeling of the
Product in such country. The parties agree that such extenuating circumstances
shall be considered in connection with any determination concerning whether AHP
has fulfilled its obligation to use Commercially Reasonable Efforts to seek
Approvals, launch, promote, market and sell such Product in such country.

                  5.3.2 AHP FAILURE TO USE MARKETING AND DISTRIBUTION EFFORTS.
In the event that AHP fails to meet its obligations under Section 5.3.1 with
respect to a Product in a Major Market Country, then GTC shall so notify AHP.
Effective ninety (90) days thereafter, if AHP has not cured such failure, then,
notwithstanding any other provision of this Agreement, AHP's right to develop
and commercialize the Product in such Major Market Country (an "Abandoned
Market") shall terminate. With respect to each Abandoned Market,

                  (i) the rights and licenses granted to AHP pursuant to
Article 3 as to such Product shall be terminated,

                  (ii) if AHP has filed Product Patent Rights in any Abandoned
Market with respect to such Product, then AHP shall, to the extent legally
permissible, take all action reasonably necessary to grant GTC an exclusive
fully paid-up, non-royalty bearing license to all of its right, title and
interest in such Product Patent Rights with respect to that such Product (or an
undivided interest therein if such Product Patent Rights also cover Products as
to which AHP retains its license rights under this Agreement),

                  (iii) if AHP has obtained any Approvals for such Products in
any Abandoned Market then AHP shall, to the extent legally permissible, take all
additional action reasonably necessary to assign all of its right, title and
interest in, and transfer possession and control to GTC of, such Approvals, and

                  (iv) AHP will assign to GTC all of its right, title and
interest in any brand trademark under which AHP shall have registered for use
with such Product in such Abandoned Market together with the goodwill associated
therewith, as well as sublicenses granted by AHP pursuant to Section 3.1.3 with
respect to such Product in such Abandoned Market.

         5.4 DEVELOPMENT OF A PRODUCT IN A PRODUCT CATEGORY. In the event that
the Joint Research Committee (JRC) determines that a program to discover or
develop *** Development Track Product in a given Product Category should be a
significant effort within the Research Collaboration, and GTC reasonably
believes that AHP has failed to use Commercially Reasonable Efforts to commence
and maintain such a program within *** months after the JRC's determination,
then GTC may notify AHP of such alleged failure by AHP. AHP shall then have ***
months from such notification to commence and maintain, or demonstrate that it
has used Commercially Reasonable Efforts to commence and maintain, or to present
a plan reasonably acceptable by the JRC for the initiation of such discovery or
development efforts for at least one Development Track Product in such Product
Category. If AHP does not commence and maintain such Commercially Reasonable
Efforts in such Product Category of discovery and development nor submit a plan
thereof for consideration by the JRC, then all licenses to AHP hereunder with
respect to the Product Category for which AHP has failed to perform under the
Annual Research Plan shall terminate immediately upon written notice from GTC.

                                       14
<PAGE>

Notwithstanding the foregoing, AHP shall use Commercially Reasonable Efforts to
discover or develop *** Development Track Product at all times.

         5.5 REPORTS. After the expiration or termination of the Research
Collaboration, AHP shall provide GTC with reasonably detailed reports which
shall describe AHP's progress with respect to its discovery, development and
commercialization, and marketing efforts under this Agreement. Such reports
shall be furnished semi-annually until Approvals, as necessary, have been
obtained pursuant to Section 5.3.1, and, thereafter, annually until the
termination or expiration of this Agreement.

                                    Article 6
                                    PAYMENTS

         6.1 LICENSE AND OTHER FEES.

                  6.1.1 LICENSE FEE.  AHP shall pay to GTC a license fee in the
amount of   ***   following the execution of this Agreement.

                  6.1.2 REIMBURSEMENT OF INCURRED RESEARCH AND DEVELOPMENT
EXPENSES. AHP shall pay to GTC as partial reimbursement for incurred research
and development expenses the amount of *** following the execution of this
Agreement.

         6.2 MILESTONE PAYMENTS. AHP shall pay to GTC the milestone payments
described below as and when the corresponding milestones are achieved:

                  6.2.1 RESEARCH MILESTONE PAYMENTS. AHP will promptly notify
the Joint Research Committee upon the accomplishment of the research milestones
set forth in EXHIBIT B ("Research Milestones"), which notification shall be
accompanied by such supporting information as to allow the Joint Research
Committee to confirm the accomplishment of such Research Milestone. Subject to
the provisions of Section 4.9, of the Joint Research Committee shall, within ***
days of receipt of such notification, determine whether the Research Milestone
described in such notification has been accomplished and shall report its
findings to both parties. If the Joint Research Committee determines that a
Research Milestone has been accomplished, *** following the receipt of
notification by the Joint Research Committee of such accomplishment, AHP shall
make the corresponding milestone payment set forth in EXHIBIT B; *** . Any
determination of the Joint Research Committee pursuant to Section 4.1.2 shall
also serve as such determination of the Joint Research Committee for the
purposes of this Section.

                  6.2.2 DEVELOPMENT MILESTONE PAYMENTS. AHP will promptly notify
GTC upon the accomplishment of the development milestones ("Development
Milestones") as set forth in EXHIBIT B and, *** following the accomplishment of
each such milestone, AHP shall make the corresponding milestone payment set
forth in EXHIBIT B. The Development Milestone payments shall be made *** in the
Bone Disorder Field *** shall be paid in Development Milestones for each
Development Track Product. *** .

                  6.2.3 APPROVAL MILESTONE PAYMENTS. AHP will promptly notify
GTC upon the accomplishment of the approval milestones ("Approval Milestones")
as set forth in EXHIBIT B

                                       15
<PAGE>

and, *** following the accomplishment of each such milestone, AHP shall make the
corresponding milestone payment set forth in EXHIBIT B. *** .

         6.3 RESEARCH FUNDING.

                  6.3.1 ANNUAL FEES. AHP will pay GTC *** for each of the ***
Contract Years, payable quarterly in advance in four equal installments of *** ,
and, should the Research Collaboration be extended for additional Contract
Year(s), quarterly thereafter in an amount adjusted as set forth below (the
"Adjusted Quarterly Fee"). AHP shall pay the first quarterly payment within ***
business days following the execution of this Agreement.

         As used herein, the phrase "Adjusted Quarterly Fee" shall mean the
following:

            ***

         CPI =             *** (i) a fraction, the numerator of which shall be
                           the difference between the Consumer Price Index
                           (CPI-U; U.S. City Average for all items; 1982-84 =
                           100) as of the last month of the immediately
                           preceding quarter and the Consumer Price Index as of
                           the month immediately preceding the Effective Date
                           and the denominator of which shall be the Consumer
                           Price Index as of the month immediately preceding the
                           Effective Date, and (ii) *** per annum (uncompounded)
                           from the Effective Date.

                  6.3.2 RESEARCH AGREEMENTS. In support of research efforts
hereunder, AHP will pay to GTC during each of the first two Contract Years of
this Agreement, or in its discretion directly to Creighton University, an
amount up to $250,000 per year determined by the Joint Research Committee to
defray expenses incurred by GTC for research performed by Creighton
University; PROVIDED, HOWEVER, that in no event shall the amount paid by AHP
be less than $150,000 per year. In the event that the Joint Research
Committee approves additional Research Agreements and AHP approves the
funding of such Research Agreements, then AHP shall make such additional
payments to GTC, or make payments directly to the Academic Collaborator(s),
as the Joint Research Committee shall determine. AHP shall have the right to
review future Creighton University Agreements related to the Bone Disorder
Field or, as appropriate, the Expanded Therapeutic Field before GTC enters
into any such agreements.

         6.4 ROYALTIES PAYABLE BY AHP AND ITS AFFILIATES AND SUBLICENSEES.
Following the First Commercial Sale of any Product in any country, AHP will pay,
on a quarterly basis, a royalty in the amounts set forth below on Net Sales of
the Products during the previous quarter.

                  6.4.1 ROYALTIES ON NET SALES OF THE PRODUCTS.  In
consideration of the licenses granted to AHP, AHP shall pay to GTC a royalty
on annual Net Sales by AHP, its Affiliates and sublicensees as follows:

         ***

                  6.4.2 SUBLICENSES. AHP shall either (i) pay to GTC royalties
on Net Sales of the Products sold by any Third Party sublicensee, or (ii)
provide in such sublicense that such sublicensee shall pay to GTC royalties on
Net Sales of the Products sold by such sublicensee, in either case at the
royalty rate set forth in Section 6.4.1 that would be applicable had such sales

                                       16
<PAGE>

been made by AHP, and provided that in either case, AHP shall remain liable for
the timely payment of all such royalties.

                  6.4.3 ADJUSTMENTS FOR THIRD PARTY PAYMENTS. If AHP pays
royalties or license fees to Third Parties for rights under patents to make
or sell the Products, it may deduct an amount equal to up to fifty percent
(50%) of such royalties and/or license fees from the royalties due but not
yet paid to GTC pursuant to Section 6.4.1; PROVIDED, HOWEVER, that the
aggregate royalties due to GTC under this Agreement may not be reduced by
more than fifty percent (50%) in any given quarter by all deductions or
credits allowed under this Agreement.

                  6.4.4 ROYALTY REPORTS, EXCHANGE RATES. During the term of this
Agreement following the First Commercial Sale of any Product in any country, AHP
shall within sixty (60) days after each calendar quarter furnish to GTC a
written quarterly report showing: (i) the gross sales of the Products sold by
AHP and its Affiliates and sublicensees during the reporting period and the
calculation of Net Sales from such gross sales; (ii) the sublicense payments
received by AHP during the reporting period; (iii) the royalties and other
payments payable in United States dollars which shall have accrued hereunder in
respect of such sales and sublicense payments; (iv) withholding taxes, if any,
required by law to be deducted in respect of such royalties and sublicense
payments; (v) the dates of the First Commercial Sales of Products in any country
during the reporting period; and (iv) the exchange rates used in determining the
amount of United States dollars payable hereunder. Royalties payable on sales in
countries other than the United States shall be calculated by multiplying the
appropriate royalty rate times the sales in each currency in which they are made
and converting the resulting amount into United States dollars at the rates of
exchange used by AHP for reporting such sales for United States financial
statement purposes. If no royalty or payment is due for any royalty period
hereunder, AHP shall so report. AHP shall keep complete and accurate records in
sufficient detail to properly reflect all gross sales and Net Sales and to
enable the royalties payable hereunder to be determined.

                  6.4.5 AUDITS. Upon the written request of GTC, AHP shall
permit an independent certified public accountant selected by GTC and acceptable
to AHP, which acceptance shall not be unreasonably withheld, to have access
during normal business hours to such records of AHP as may be reasonably
necessary to verify the accuracy of the royalty reports described herein, in
respect of any fiscal year ending not more than twenty-four (24) months prior to
the date of such request. GTC and AHP shall use commercially reasonable efforts
to schedule all such verifications within forty-five (45) days after GTC makes
its written request. All such verifications shall be conducted at GTC's expense
and not more than once in each calendar year. In the event GTC's independent
certified public accountant concludes that additional royalties were owed to GTC
during such period, the additional royalty shall be paid by AHP within thirty
(30) days of the date GTC delivers to AHP such independent certified public
accountant's written report so concluding. In the event GTC's independent
certified public accountant concludes that there was an overpayment of royalties
to GTC during such period, the overpayment shall be repaid by GTC within thirty
(30) days of the date GTC received such independent certified public
accountant's written report so concluding. The fees charged by such independent
certified public accountant shall be paid by GTC unless the audit discloses an
underpayment of the royalties payable by AHP for the audited period of more than
five percent (5%), in which case AHP shall pay the reasonable fees and expenses
charged by such representative. AHP shall include in each Third Party sublicense
granted by it pursuant to this

                                       17
<PAGE>

Agreement a provision requiring the sublicensee to make reports to AHP, to keep
and maintain records of sales made pursuant to such sublicense and to grant
access to such records by GTC's independent certified public accountant to the
same extent required of AHP under this Agreement. GTC agrees that all
information subject to review under this Section 6.4.5 or under any sublicense
agreement is confidential and that GTC shall cause its independent certified
public accountant to enter in a confidentiality agreement with AHP obligating
such accountant to retain all such information in confidence. GTC's independent
certified public accountant shall only report to GTC as to the computation of
the royalties and other payments due to GTC under this Agreement and shall not
disclose to GTC any other information of AHP or its sublicensees.

                  6.4.6 ROYALTY PAYMENT TERMS. Royalties shown to have accrued
by each royalty report provided for under this Agreement shall be due sixty (60)
days after the end of each calendar quarter. Payment of royalties in whole or in
part may be made in advance of such due date. Royalties determined to be owing
with respect to any prior quarter shall be added, together with interest thereon
accruing under this Agreement from the date of the report for the quarter for
which such amounts are owing, to the next quarterly payment hereunder.

         6.5 WITHHOLDING TAXES. AHP shall *** . AHP shall not *** , including
but not limited to any such taxes or charges incurred as a result of an
assignment or sublicense by AHP to any Affiliate or any Third Party, *** . AHP
shall maintain official receipts of payment of any withholding taxes and forward
these receipts to GTC within sixty (60) days. The parties will exercise
reasonable efforts to ensure that any withholding taxes imposed are reduced as
far as possible under the provisions of any treaties applicable to any payment
made hereunder.

         6.6 INTEREST ON LATE PAYMENTS. Any payments by AHP to GTC that are not
paid on or before *** days after the date such payments are due under this
Agreement shall bear interest at a rate per month no greater than *** ,
calculated on the total number of days payment is delinquent; PROVIDED, HOWEVER,
that interest shall not accrue pursuant to this Section 6.6 on any amounts
payable under this Agreement with respect to which payment is disputed in good
faith; PROVIDED FURTHER that interest shall accrue pursuant to this Section 6.6
once such dispute has been resolved if payment is not made promptly thereafter.

         6.7 MANNER OF PAYMENT. Payments to be made by AHP to GTC under this
Agreement shall be payable in United States dollars and shall be paid by bank
wire transfer in immediately available funds to such bank account in the
Commonwealth of Massachusetts as is designated in writing by GTC from time to
time; PROVIDED, HOWEVER, that AHP may make payments due under Section 6.4 by
check.

         6.8 CURRENCY BLOCKAGE. Where payments are due hereunder for sales of
Products in a country where, by reason or currency regulations or taxes of any
kind, it is impossible or illegal for AHP to transfer payments to GTC in that
country, such payments shall be deposited by AHP in whatever currency is
allowable for the benefit or credit of GTC in an accredited bank in that country
that is reasonably acceptable to GTC, and AHP shall use its reasonable efforts
to obtain authorization to effect the remittance within the applicable period
set forth under this Article 6.

                                    Article 7
                              INTELLECTUAL PROPERTY

                                       18
<PAGE>

         7.1 OWNERSHIP OF INTELLECTUAL PROPERTY.

                  7.1.1 GTC OWNERSHIP. GTC shall own all GTC Technology and GTC
Patent Rights.

                  7.1.2 AHP OWNERSHIP. AHP shall own all AHP Technology and AHP
Patent Rights.

                  7.1.3 JOINT INVENTIONS. Notwithstanding Sections 7.1.1 and
7.1.2, and subject to the rights and licenses granted under this Agreement, GTC
and AHP shall jointly own all Joint Technology and Joint Patent Rights.

         7.2 MANAGEMENT OF JOINT PATENT RIGHTS.

                  7.2.1 FILING, PROSECUTION AND MAINTENANCE OF JOINT PATENT
RIGHTS. GTC shall be responsible for supervising the preparation, filing,
prosecution (including oppositions) and maintenance of the Joint Patent Rights
using patent counsel selected by the Joint Patent Committee. The Joint Patent
Committee shall be responsible for making all decisions regarding whether to
file, prosecute and maintain patents and patent applications, and in which
countries to do so.

                  7.2.2 EXPENSES. All expenses incurred in connection with the
activities performed in Section 7.2.1 shall be borne by AHP, *** .

                  7.2.3 FAILURE TO PAY; ABANDONMENT. In the event that (i) AHP
fails to make any payment to maintain a patent under the Joint Patent Rights in
a particular country after determination by the Joint Patent Committee to
maintain such patent, or (ii) either party desires to abandon such Joint Patent
Rights (in the case of either (i) or (ii), the "Abandoning Party"), then the
Abandoning Party shall assign, and hereby does assign all of its right, title
and interest in such abandoned Joint Patent Rights in such country to the other
party. The Abandoning Party shall provide reasonable prior written notice to the
other party of such intention to cease payment or abandon such Joint Patent
Rights (which notice shall be given sufficiently in advance of any filing dates
to enable the other party to preserve its rights), and such other party shall
have the right, at its expense, to prepare, file, prosecute, and maintain such
Joint Patent Rights. If the other party elects to continue the preparation,
filing, prosecution or maintenance such Joint Patent Rights, then such Joint
Patent Rights shall be considered either AHP Patent Rights if GTC was the
Abandoning Party or GTC Patent Rights if AHP was the Abandoning Party, and in
either case, shall be subject to the terms of this Agreement as AHP Patent
Rights or GTC Patent Rights, as applicable. Notwithstanding the foregoing,
neither party shall be considered an Abandoning Party for any failure to
prepare, file, prosecute, maintain, or bear the expenses relating to any of the
foregoing, with respect to any patent under a Joint Patent Right that the Joint
Patent Committee determines not to pursue.

         7.3 FILING, PROSECUTION AND MAINTENANCE OF GTC PATENT RIGHTS. GTC shall
be responsible for the preparation, filing, prosecution (excluding interferences
and oppositions except as set forth below) and maintenance of the GTC Patent
Rights. AHP shall bear all expenses *** in the preparation, filing, prosecution
(excluding interferences and oppositions except as set forth below) and
maintenance of GTC Patent Rights. GTC shall provide AHP with

                                       19
<PAGE>

an opportunity to review and comment on all prosecution documents for each
patent application subject to this Section 7.3 before the filing of such
prosecution document, but GTC shall have final authority to select patent
counsel and to determine the form and content of such prosecution documents and
for making all decisions regarding whether to file, prosecute and maintain
patents and patent applications, and in which countries to do so. In the event
that AHP does not intend to bear the expenses of a patent or patent application
in accordance with this Section 7.3, it shall promptly notify GTC and the patent
or patent application shall cease to be a part of the GTC Program Technology.

         If either party becomes aware of an interference or opposition with
respect to a GTC Patent Right in the U.S. Patent and Trademark Office or a
comparable office in a country or region other than the United States, the party
will notify the other party and the Joint Patent Committee shall first determine
whether to proceed with the interference or opposition and such decision shall
not be subject to Section 12.6. If the Joint Patent Committee determines to
proceed with an interference or opposition proceeding with respect to a GTC
Patent Right, GTC shall be responsible for such interference or opposition
proceeding, using counsel selected by GTC, and AHP shall bear all expenses
reasonably incurred in such proceeding. If the Joint Patent Committee decides
not to proceed with an interference or opposition proceeding with respect to a
GTC Patent Right, GTC shall be free to proceed with the interference or
opposition at its own expense and the patent or patent application shall cease
to be a part of the GTC Program Technology.

         7.4 INFRINGEMENT.

                  7.4.1 NOTIFICATION. Each party shall promptly report in
writing to the other party during the term of this Agreement any known
infringement or suspected infringement of any of the Product Patent Rights,
Joint Patent Rights or GTC Patent Rights, and shall provide the other party with
all available evidence supporting said infringement or suspected infringement.

                  7.4.2 PROSECUTION BY AHP. Except as provided in Section 7.4.3
below, AHP shall have the right to initiate an infringement or other appropriate
suit against any third party who at any time has infringed, or is suspected of
infringing, any of the Joint Patent Rights or GTC Patent Rights. AHP shall give
GTC sufficient advance notice of its intent to file said suit and the reasons
therefor, and shall provide GTC with an opportunity to make suggestions and
comments regarding such suit. AHP shall keep GTC promptly informed, and shall
from time to time consult with GTC regarding the status of any such suit and
shall provide GTC with copies of all documents filed in, and all written
communications relating to, such suit.

         AHP shall *** , pay all expenses of the suit, including without
limitation attorneys' fees and court costs. GTC, in its sole discretion, may
elect, within sixty (60) days after the commencement of such litigation, to
contribute to the costs incurred by AHP in connection with such litigation and,
if it so elects, any damages, royalties, settlement fees or other consideration
received by AHP or any of its Affiliates for infringement as a result of such
litigation shall be shared by AHP and GTC pro rata based on their respective
sharing of the costs of such litigation. In the event that GTC elects not to
contribute to the costs of such litigation, AHP and/or its Affiliates shall be
entitled to retain any damages, royalties, settlement fees or other
consideration

                                       20
<PAGE>

for infringement resulting therefrom. If necessary, GTC shall join as a party to
the suit but shall be under no obligation to participate except to the extent
that such participation is required as the result of being a named party to the
suit. GTC shall offer reasonable assistance to AHP in connection therewith at
AHP's expense. GTC shall have the right to participate and be represented in any
such suit by its own counsel at its own expense.

                  7.4.3 PROSECUTION BY GTC. In the event that AHP elects not to
initiate an infringement or other appropriate suit pursuant to Section 7.4.2
above, AHP shall promptly advise GTC of its intent not to initiate such suit,
and GTC shall have the right, at the expense of GTC, of initiating an
infringement or other appropriate suit against any third party who at any time
has infringed, or is suspected of infringing, any of the Joint Patent Rights or
GTC Patent Rights. GTC shall have the sole and exclusive right to select counsel
for any such suit and shall, except as provided below, pay all expenses of the
suit including without limitation attorneys' fees and court costs. AHP, in its
sole discretion, may elect, within sixty (60) days after the commencement of
such litigation, to contribute to the costs incurred by GTC in connection with
such litigation and, if it so elects, any damages, royalties, settlement fee or
other consideration received by GTC or any of its Affiliates for infringement as
a result of such litigation shall be shared by GTC and AHP pro rata based on
their respective sharing of the costs of such litigation. In the event that AHP
elects not to contribute to the costs of such litigation, GTC and/or its
Affiliates shall be entitled to retain any damages, royalties, settlement fees
or other consideration for infringement resulting therefrom. If necessary, AHP
shall join as a party to the suit but shall be under no obligation to
participate except to the extent that such participation is required as a result
of being a named party to the suit. At GTC's request, AHP shall offer reasonable
assistance to GTC in connection therewith at GTC's expense.

         7.5 COOPERATION OF THE PARTIES. Each party agrees to cooperate fully in
the preparation, filing, and prosecution of any GTC Patent Rights or Joint
Patent Rights under this Agreement. Such cooperation includes, but is not
limited to: executing all papers and instruments, or requiring its employees or
agents, to execute such papers and instruments, so as to effectuate the
ownership of patent rights and technology set forth in Section 7.1 and to enable
the other party to apply for and to prosecute patent applications in any
country, including, without limitation, executing an appropriate assignment or
intellectual property rights; promptly informing the other party of any matters
coming to such party's attention that may affect the preparation, filing, or
prosecution of any such patent applications; and undertaking no actions that are
potentially deleterious to the preparation, filing, or prosecution of such
patent applications.

         7.6 TRADEMARKS. AHP shall be free to use and to register in any
trademark office in the world any trademark for use with Products it desires in
its sole discretion. AHP shall own all right, title and interest in and to any
such trademark in its own name or that of its designated Affiliate during and
after the term of this Agreement except as otherwise provided expressly herein.

                                    Article 8
                                 CONFIDENTIALITY

         8.1 NONDISCLOSURE OBLIGATIONS.

                                       21
<PAGE>

                  8.1.1 GENERAL. Except as otherwise provided in Article 8,
during the term of this Agreement and for a period of five (5) years
thereafter, the parties shall maintain in confidence and use only for
purposes specifically authorized under this Agreement (i) GTC Program
Technology and AHP Program Technology, (ii) any other written, oral,
electronic or other form of information and data received from the other
party or an Academic Collaborator resulting from or related to the Research
Collaboration, Research Agreements, or the Products (including without
limitation visual and other information acquired by a party's employees or an
Academic Collaborator on the premises of the other party), and (iii) all
information and data not described in clauses (i) or (ii) but supplied by the
other party under this Agreement marked "Confidential." For purposes of
Article 8, information and data described in clauses (i), (ii) or (iii) shall
be referred to as "Information."

                  8.1.2 LIMITATIONS. To the extent it is reasonably necessary or
appropriate to fulfill its obligations or exercise its rights under this
Agreement: (i) a party may disclose Information it is otherwise obligated under
Section 8.1 not to disclose to its employees, Affiliates, sublicensees,
consultants, contractors, Academic Collaborators involved in the Research
Collaboration and clinical investigators (collectively, "Agents") on a
need-to-know basis and on condition that such Agents agree to non-use and
non-disclosure obligations essentially the same as those set forth herein and to
keep the Information confidential for the same time periods and to the same
extent as such party is required to keep the Information confidential; and (ii)
a party or its Agents may disclose such Information to government or other
regulatory authorities to the extent that such disclosure is reasonably
necessary to obtain patents or authorizations to conduct clinical trials of, and
to commercially market, Products pursuant to this Agreement. The obligation not
to disclose Information shall not apply to any part of such Information that:
(i) is or becomes part of the public domain other than by unauthorized acts or
omissions of the party obligated not to disclose such Information or its Agents
(collectively, the "Receiving Party"); (ii) can be shown by written documents to
have been disclosed to the Receiving Party by a Third Party, provided such Third
Party had no obligation of confidentiality or non-use with respect to such
Information; (iii) can be shown by written documents to have been in the
possession of the Receiving Party prior to disclosure by the disclosing party,
provided such Information was not obtained directly or indirectly from the other
party to this Agreement pursuant to a confidentiality agreement; (iv) can be
shown by written documents to have been independently developed by or for the
Receiving Party without breach of any of the provisions of this Agreement; or
(v) is required to be disclosed by the Receiving Party pursuant to
interrogatories, requests for information or documents, subpoena, civil
investigative demand issued by a court or governmental agency or as otherwise
required by law, PROVIDED, HOWEVER, that the Receiving Party notifies the other
party immediately upon receipt thereof, giving such other party sufficient
advance notice to permit it to seek a protective order or other similar order
with respect to such Information AND PROVIDED, FURTHER, that the disclosing
party furnishes only that portion of the Information which it is advised by
counsel is legally required whether or not a protective order or other similar
order is obtained by the other party.

         8.2 SAMPLES. Materials and samples, including without limitation genes
or other biological targets identified, sequenced, synthesized, purified or
developed in the course of the Research Collaboration (collectively, the
"Materials"), shall not be supplied or sent by either party to any Third Party,
other than to regulatory agencies or for use in clinical trials, unless such
release is approved by one (1) member of the Joint Research Committee
representing the other

                                       22
<PAGE>

party; PROVIDED, HOWEVER, that the transfer of such Materials is protected by
an appropriate materials transfer agreement substantially similar to the form
of Material Transfer Agreement attached hereto as EXHIBIT C. Samples of
materials other than those described above provided by one party to the other
party in the course of the Research Collaboration shall not be supplied or
sent by the party receiving such materials to any Third Party, other than to
regulatory agencies or for use in clinical trials, without the written
consent of the party providing such materials.

         8.3 PUBLICATION OF RESULTS. Neither party shall publicly disclose,
or permit its Agents to publicly disclose, through submission to a journal or
review committee, press releases, lectures or otherwise any competitively
important information in the Field resulting from the Research Collaboration
("Results") except as provided in this Section 8.3. Publication, or public
announcement in any format, of the Results shall be allowed only after the
earlier to occur of *** from the date of discovery of such Result *** or the
publication of such Results in a PCT patent application. Each party (the
"Disclosing Party") shall provide a copy of a proposed public disclosure to
the other party (the "Reviewing Party") at least sixty (60) days prior to the
date of any submission of any proposed written publication and forty-five
(45) days prior to any proposed oral public disclosure (the "Review Period").
If the Reviewing Party determines in good faith that the proposed public
disclosure would reveal a patentable invention or constitutes Information
that it desires to maintain in confidence, the Reviewing Party will so notify
the Disclosing Party of such determination and its basis prior to the
expiration of the Review Period. In the case of an objection to public
disclosure based on a potentially patentable invention, where the Reviewing
Party does not wish to maintain the invention in confidence after filing a
patent application, the Disclosing Party will cause the public disclosure of
the invention to be delayed a reasonable length of time not less than sixty
(60) days as necessary for the Reviewing Party to file a patent application
covering the invention. In the case of an objection to public disclosure
based on disclosure of Information (including Information consisting of a
patentable invention the Reviewing Party desires to maintain in confidence),
the Disclosing Party will cause either the deletion of any such Information
from the proposed public disclosure or the deferral of the public disclosure
until such time as all Information is no longer treated as such under Section
8.1.2 (such as, for example, through publication of a patent application
covering a patentable invention).

                                  Article 9
                         REPRESENTATIONS AND WARRANTIES

         9.1 REPRESENTATIONS, WARRANTIES AND COVENANTS OF GTC. GTC represents
and warrants to and covenants with AHP that:

                  9.1.1 GTC is a corporation duly organized, validly existing
and in corporate good standing under the laws of Massachusetts;

                  9.1.2 GTC has the legal right, authority and power to enter
into this Agreement, and to extend the rights and licenses granted to AHP in
this Agreement;

                  9.1.3 GTC has taken all necessary action to authorize the
execution, delivery and performance of this Agreement;

                  9.1.4 upon the execution and delivery of this Agreement, this
Agreement shall constitute a valid and binding obligation of GTC enforceable in
accordance with its terms, except

                                       23
<PAGE>

as enforceability may be limited by applicable bankruptcy, insolvency,
reorganization, moratorium or similar laws affecting creditors' and contracting
parties' rights generally and except as enforceability may be subject to general
principles of equity (regardless of whether such enforceability is considered in
a proceeding in equity or at law);

                  9.1.5 the performance of its obligations under this Agreement
will not conflict with its charter documents or result in a breach of any
agreements, contracts or other arrangements to which it is a party;

                  9.1.6 GTC will not during the term of this Agreement   ***

                  9.1.7 GTC will not during the term of this Agreement   ***
including without limitation   ***  .  GTC is currently   ***  .

                  9.1.8 As of the Effective Date, *** .

         9.2 REPRESENTATIONS, WARRANTIES AND COVENANTS OF AHP. AHP represents
and warrants to and covenants with GTC that:

                  9.2.1 AHP is a corporation duly organized, validly existing
and in corporate good standing under the laws of Delaware.

                  9.2.2 AHP has the legal right, authority and power to enter
into this Agreement, and to extend the rights and licenses granted to GTC in
this Agreement;

                  9.2.3 AHP has taken all necessary action to authorize the
execution, delivery and performance of this Agreement;

                  9.2.4 upon the execution and delivery of this Agreement, this
Agreement shall constitute a valid and binding obligation of AHP enforceable in
accordance with its terms, except as enforceability may be limited by applicable
bankruptcy, insolvency, reorganization, moratorium or similar laws affecting
creditors' and contracting parties' rights generally and except as
enforceability may be subject to general principles of equity (regardless of
whether such enforceability is considered in a proceeding in equity or at law);

                  9.2.5 the performance of its obligations under this Agreement
will not conflict with AHP's charter documents or result in a breach of any
agreements, contracts or other arrangements to which it is a party; and

                  9.2.6 AHP will not after the Effective Date enter into any
agreements, contracts or other arrangements that would be inconsistent with its
obligations under this Agreement.

         9.3 VALIDITY AND SCOPE. Nothing in this Agreement shall be construed as
a warranty or representation by either party as to the accuracy or completeness
of the GTC Program Technology or the validity or scope of the Product Patent
Rights.

         9.4 WARRANTY DISCLAIMER. EXCEPT AS OTHERWISE EXPRESSLY PROVIDED IN THIS
AGREEMENT, NEITHER PARTY MAKES ANY WARRANTY WITH RESPECT

                                       24
<PAGE>

TO ANY GTC PROGRAM TECHNOLOGY, AHP PROGRAM TECHNOLOGY, PRODUCT PATENT RIGHTS,
GOODS, SERVICES OR OTHER SUBJECT MATTER OF THIS AGREEMENT AND HEREBY DISCLAIMS
WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NON-INFRINGEMENT WITH RESPECT TO ANY AND ALL OF THE FOREGOING.

         9.5 LIMITED LIABILITY. NOTWITHSTANDING ANYTHING ELSE IN THIS AGREEMENT
OR OTHERWISE TO THE CONTRARY, NEITHER GTC NOR AHP WILL BE LIABLE WITH RESPECT TO
ANY SUBJECT MATTER OF THIS AGREEMENT UNDER ANY CONTRACT, NEGLIGENCE, STRICT
LIABILITY OR OTHER LEGAL OR EQUITABLE THEORY FOR (I) ANY PUNITIVE, EXEMPLARY,
INCIDENTAL OR CONSEQUENTIAL DAMAGES OR LOST PROFITS OR (II) COST OF PROCUREMENT
OF SUBSTITUTE GOODS, TECHNOLOGY OR SERVICES.

                                   Article 10
                                    INDEMNITY

         10.1 CROSS INDEMNITY. Each party agrees to defend, indemnify and hold
the other party, its Affiliates and their respective employees and agents
harmless from all Third Party claims, losses, damages or expenses arising as a
result of breach by such party of a representation, warranty or covenant under
Article 9.

         10.2 AHP INDEMNITY OBLIGATIONS. AHP agrees to defend, indemnify and
hold GTC, its Affiliates and their respective employees and agents harmless from
all Third Party claims, losses, damages or expenses arising as a result of: (a)
actual or asserted violations of any applicable law or regulation by AHP, its
Affiliates or sublicensees by virtue of which the Products manufactured,
distributed or sold hereunder shall be alleged or determined to be adulterated,
misbranded, mislabeled or otherwise not in compliance with any applicable law or
regulation; (b) claims for bodily injury, death or property damage attributable
to the manufacture, distribution, sale or use of the Products by AHP, its
Affiliates or sublicensees; or (c) a Product recall ordered by a governmental
agency or required by a confirmed Product failure as reasonably determined by
the parties hereto.

         10.3 LIMITATION ON AHP INDEMNITY OBLIGATIONS. GTC, its Affiliates and
their respective employees and agents shall not be entitled to the indemnities
set forth in Section 10.1 where the claim, loss, damage or expense for which
indemnification is sought was caused by negligence or intentional act of
misconduct or omission by GTC, its directors, officers, employees or authorized
agents.

         10.4 PROCEDURE. If a party or any of its Affiliates or their respective
employees or agents (the "Indemnitee") intends to claim indemnification under
Article 10, the Indemnitee shall promptly notify the other party (the
"Indemnitor") of any loss, claim, damage, liability or action in respect of
which the Indemnitee intends to claim such indemnification, and the Indemnitor
shall assume the defense thereof with counsel mutually satisfactory to the
parties; PROVIDED, HOWEVER, that an Indemnitee shall have the right to retain
its own counsel, with the fees and expenses to be paid by the Indemnitor, if
representation of such Indemnitee by the counsel retained by the Indemnitor
would be inappropriate due to actual or potential differing interests

                                       25
<PAGE>

between such Indemnitee and any other party represented by such counsel in such
proceedings. The indemnity agreement in Article 10 shall not apply to amounts
paid in settlement of any loss, claim, damage, liability or action if such
settlement is effected without the consent of the Indemnitor, which consent
shall not be withheld unreasonably. The failure to deliver notice to the
Indemnitor within a reasonable time after the commencement of any such action,
if prejudicial to its ability to defend such action, shall relieve such
Indemnitor of any liability to the Indemnitee under Article 10, but the omission
so to deliver notice to the Indemnitor will not relieve it of any liability that
it may have to any Indemnitee otherwise than under Article 10. The Indemnitee
under Article 10 shall cooperate fully with the Indemnitor and its legal
representatives in the investigation of any action, claim or liability covered
by this indemnification. The Indemnitor shall additionally be liable to pay the
reasonable legal costs and attorneys' fees incurred by the Indemnitee in
establishing its claim for indemnity.

         10.5 INSURANCE. AHP shall maintain appropriate product liability
insurance or self-insurance with respect to development, manufacture and sales
of the Products by AHP in such amount as AHP customarily maintains with respect
to sales of its other products. AHP shall maintain such insurance for so long as
it continues to manufacture or sell the Products, and thereafter for so long as
AHP maintains insurance for itself covering such manufacture or sales.

                                   Article 11
                           EXPIRATION AND TERMINATION

         11.1 TERM OF RESEARCH COLLABORATION; EXTENSION. Unless this
Agreement is sooner terminated in accordance with the provisions of Article
11, the Research Collaboration shall continue for a minimum term of two (2)
Contract Years, and may be extended, at the option of AHP upon written notice
given no later than six (6) months prior to the end of the second Contract
Year, for a period of one (1) Contract Year. Any extension beyond three (3)
Contract Years in total shall be by mutual agreement. Upon the expiration of
the Research Collaboration all licenses to AHP to continue to use the GTC
Program Technology and Diagnostic Information as such rights exist on the
expiration of the Research Collaboration shall continue in full force and
effect for the remaining term of the Agreement.

         11.2 TERMINATION OF THE RESEARCH COLLABORATION.  AHP shall have the
following rights to terminate the Research Collaboration:

                  11.2.1 TERMINATION UPON CERTAIN TRANSACTIONS INVOLVING GTC.
If GTC is acquired, GTC will make all reasonable efforts to prevent the
disruption of the Research Collaboration and to ensure its continuance in a
timely fashion. AHP shall have the right to terminate the Research
Collaboration in the event that GTC is acquired by, or otherwise becomes an
Affiliate of, a fully-integrated pharmaceutical company with a market
capitalization in excess of $1 billion (at the time of any such acquisition)
that has a substantial research or drug development project in the Bone
Disorder Field ("Competitor Affiliation") by providing written notice of
termination to GTC's acquiror within ninety (90) days following receipt of
written notice of the occurrence of the Competitor Affiliation (which notice
shall be promptly given by GTC). In the event of termination of the Research
Collaboration under this Section 11.2.1, AHP shall *** .

                  11.2.2 TERMINATION UPON A TECHNOLOGY PATENT BLOCKING EVENT.
If *** a Technology Patent Block Event has occurred, then AHP shall have the
right to terminate the Research Collaboration upon six (6) month written
notice to GTC with respect to a Technology Patent Block Event under (i)
above, or with immediate effect with respect to a Technology Patent Blocking
Event under (ii) above. In the event of termination of the Research
Collaboration under this Section 11.2.2, the rights and licenses granted to
AHP pursuant to Article 3 shall terminate and any and all Information and
materials provided by GTC pursuant to this Agreement shall be promptly
returned by AHP to GTC.

                                       26
<PAGE>

                  11.2.3 MINIMAL DRUG DISCOVERY PROSPECTS. AHP shall have the
right to terminate the Research Collaboration upon three (3) months prior
written notice. In the event of termination of the Research Collaboration
under this Section 11.2.3, the rights and licenses granted to AHP pursuant to
Article 3 shall terminate and any and all Information and materials provided
by GTC pursuant to this Agreement shall be promptly returned by AHP to GTC.

                  11.2.4 GTC INADEQUATE RESEARCH PERFORMANCE. If AHP
reasonably determines that GTC is failing to meet its obligations for
performance of the Research Collaboration during any Contract Year of the
Research Collaboration, AHP will submit the matter to the Joint Research
Committee. The Joint Research Committee shall develop a new work plan to
achieve improved performance by GTC and set a time period for GTC to
demonstrate that it is adequately performing its obligations under the new
work plan. If the Joint Research Committee determines that GTC is not
adequately performing within the specified time period, AHP shall have the
right to terminate the Research Collaboration upon three (3) months prior
written notice to GTC. In the event of termination of the Research
Collaboration under this Section 11.2.4, AHP shall have the right to *** ,
subject to the terms and conditions of this Agreement (including, without
limitation, the terms of Article 6 of this Agreement).

         11.3 TERM OF AGREEMENT. Unless this Agreement is sooner terminated
in accordance with the provisions of Article 11, the licenses granted by GTC
to AHP hereunder shall become fully paid and irrevocable, on a Product-by-
Product and country-by-country basis, ten (10) years after the First
Commercial Sale of the relevant Product in the relevant country or, if later,
upon the last to expire of any Claim included in the Product Patent Rights
with respect to such Product in such country. This Agreement shall expire
upon the expiration of the last to expire of any license granted by GTC to
AHP hereunder. *** .

         11.4 EVENTS OF DEFAULT.

                  11.4.1 DEFAULT BY EITHER PARTY. An Event of Default shall have
occurred upon (i) the occurrence of a breach of a material term of this
Agreement (other than a material breach described in clause (ii) below or in
Section 11.4.2) if the breaching party fails to remedy such breach within ***
days after written notice thereof by the nonbreaching party, or (ii) the
bankruptcy, insolvency, dissolution or sale of all or substantially all of the
assets of a party that are necessary for the performance of this Agreement.

                  11.4.2 DEFAULT BY AHP. An Event of Default shall have occurred
if:

                           (i) AHP fails to make payments due hereunder, ***
         days after GTC delivers written notice thereof to AHP specifying such
         failure and its claim of right to terminate, unless AHP makes such
         payments plus interest calculated under Section 6.6 *** ,

                           (ii) AHP fails to undertake any discovery or
         development efforts for a Validated Target to the extent required by
         Sections 5.1 or 5.2 and does not cure such breach within *** days after
         GTC delivers written notice thereof to AHP specifying such failure
         ***; or

                                       27
<PAGE>

                           (iii) AHP fails to market an approved Product in any
         Product Category in *** Major Market Countries to the extent required
         by Section 5.3 and does not cure such breach *** after GTC delivers
         written notice thereof to AHP specifying such failure.

         11.5 EFFECT OF AN EVENT OF DEFAULT.

                  11.5.1 REMEDIES AVAILABLE TO GTC. In the event that an Event
of Default described in Section 11.4 occurs relating to AHP and AHP fails to
cure such default during any applicable cure period, GTC shall have the right,
at its option exercisable in its sole discretion, in addition to any other
rights or remedies available to it at law or in equity, subject to the
limitations of Section 9.5 and Section 12.6, to either

                  (i) terminate this Agreement upon notice thereof to AHP, in
which case: (A) the rights and licenses granted to AHP pursuant to Article 3
shall terminate, (B) any and all Information and materials provided by GTC
pursuant to this Agreement shall be promptly returned by AHP to GTC, (C) AHP
shall promptly deliver to GTC all preclinical and clinical data relating to
Products owned or controlled by AHP and necessary or useful to the development
or commercialization of such Products, (D) if AHP has obtained any regulatory
Approvals in any country for the Products, then AHP shall, to the extent legally
permissible, take all additional action reasonably necessary to assign all of
its right, title and interest in and transfer possession and control to GTC of
such regulatory Approvals, (E) if AHP has filed Product Patent Rights relating
to any Product, then AHP shall take all action reasonably necessary to grant GTC
an exclusive fully paid-up, non-royalty bearing license to all of its right,
title and interest in such Product Patent Rights solely with respect to such
Products, (F) AHP will grant GTC licenses on reasonable and customary terms to
be negotiated in good faith by the parties for any technology or know-how
developed by AHP or its Third Party manufacturer, if any, relating to the
manufacture of the Products, (G) AHP will assign to GTC all of its right, title
and interest in any trademark under which AHP shall solely have marketed the
Products or registered for use with such Products together with the goodwill
associated therewith, (H) AHP shall assign to GTC all sublicenses of the GTC
Technology granted by AHP pursuant to Section 3.1.3, and (I) the rights and
licenses granted to GTC pursuant to Section 3.3.1 shall survive; or

                  (ii) (Y) terminate only Articles 2, 4 and 5, including the
Research Collaboration (if not earlier expired pursuant to Section 11.1), and
Sections 6.1 and 6.3 and (Z) convert the licenses granted by GTC to AHP pursuant
to Section 3.1.1 into non-exclusive licenses.

In addition, and regardless of GTC's election of remedies, *** .

                  11.5.2 REMEDIES AVAILABLE TO AHP. In the event that an Event
of Default described in Section 11.4 relating to GTC and GTC fails to cure such
default during any applicable cure period, then AHP shall have the right, at its
option exercisable in its sole discretion, to seek any rights or remedies
available to it at law or in equity, subject to the limitations set forth in
Section 9.5 and Section 12.6.

                                       28
<PAGE>

         11.6 ELECTIVE TERMINATION BY AHP. AHP shall have the right to
terminate this Agreement *** . Such termination shall be effective sixty (60)
days following the date of such notice. In the event of termination pursuant
to this Section 11.6, the provisions of Section 11.5.1(i)(A)-(H) shall govern
the effect of such termination.

         11.7 EFFECT OF EXPIRATION OR TERMINATION OF THE AGREEMENT. The
expiration or termination of this Agreement shall not relieve the parties of any
obligation accruing prior to such expiration or termination.

                  11.7.1 SURVIVAL OF PROVISIONS UPON EXPIRATION OR TERMINATION.
The provisions of Sections 3.4, 6.4.5, 9.4, 9.5, 12.6 and 12.9 and Articles 7,
8, 10 and 11 shall survive the expiration or termination of this Agreement;
PROVIDED, HOWEVER, that GTC shall have no obligation to maintain the
confidentiality of the GTC Program Technology in the event that this Agreement
is terminated due to breach by AHP.

                                   Article 12
                                  MISCELLANEOUS

         12.1 FORCE MAJEURE. Neither party shall be held liable or responsible
to the other party nor be deemed to have defaulted under or breached this
Agreement for failure or delay in fulfilling or performing any term of this
Agreement when such failure or delay is caused by or results from causes beyond
the reasonable control of the affected party, including but not limited to fire,
floods, embargoes, war, acts of war (whether war is declared or not),
insurrections, riots, civil commotions, strikes, lockouts or other labor
disturbances, acts of God or acts, omissions or delays in acting by any
governmental authority or the other party; PROVIDED, HOWEVER, that the party so
affected shall use reasonable commercial efforts to avoid or remove such causes
of nonperformance, and shall continue performance hereunder with reasonable
dispatch whenever such causes are removed. Either party shall provide the other
party with prompt written notice of any delay or failure to perform that occurs
by reason of FORCE MAJEURE. The parties shall mutually seek a resolution of the
delay or the failure to perform as noted above.

         12.2 ASSIGNMENT. This Agreement may not be assigned or otherwise
transferred by either party without the consent of the other party; PROVIDED,
HOWEVER, that either GTC, *** , or AHP may, without such consent, assign its
rights and obligations under this Agreement (i) to any Affiliate, all or
substantially all of the equity interest of which is owned and controlled by
such party or its direct or indirect parent corporation, or (ii) in connection
with a merger, consolidation or sale of substantially all of such party's assets
to an unrelated Third Party; PROVIDED, HOWEVER, that such party's rights and
obligations under this Agreement shall be assumed by its successor in interest
in any such transaction and shall not be transferred separate from all or
substantially all of its other business assets, including those business assets
that are the subject of this Agreement. Any purported assignment in violation of
the preceding sentence shall be void. Any permitted assignee shall assume all
obligations of its assignor under this Agreement.

         12.3 SEVERABILITY. Each party hereby agrees that it does not intend to
violate any public policy, statutory or common laws, rules, regulations, treaty
or decision of any government agency or executive body thereof of any country or
community or association of countries.

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<PAGE>

Should one or more provisions of this Agreement be or become invalid, the
parties hereto shall substitute, by mutual consent, valid provisions for such
invalid provisions which valid provisions in their economic effect are
sufficiently similar to the invalid provisions that it can be reasonably assumed
that the parties would have entered into this Agreement with such valid
provisions. In case such valid provisions cannot be agreed upon, the invalidity
of one or several provisions of this Agreement shall not affect the validity of
this Agreement as a whole, unless the invalid provisions are of such essential
importance to this Agreement that it is to be reasonably assumed that the
parties would not have entered into this Agreement without the invalid
provisions.

         12.4 NOTICES. Any consent, notice or report required or permitted to be
given or made under this Agreement by one of the parties hereto to the other
shall be in writing, delivered personally or by facsimile (and promptly
confirmed by telephone, personal delivery or courier) or courier, postage
prepaid (where applicable), addressed to such other party at its address
indicated below, or to such other address as the addressee shall have last
furnished in writing to the addressor and shall be effective upon receipt by the
addressee.

         If to GTC:              Genome Therapeutics Corporation
                                 100 Beaver Street
                                 Waltham, Massachusetts  02154
                                 Attention: President
                                 Telephone: 781-398-2300
                                 FAX:     781-893-8277

         with a copy to:         Palmer & Dodge, LLP
                                 One Beacon Street
                                 Boston, Massachusetts  02108
                                 Attention: Marc Rubenstein, Esq.
                                 Telephone: 617-573-0100
                                 FAX:     617-227-4420

         If to AHP:              Wyeth-Ayerst Laboratories
                                 555 E. Lancaster Avenue
                                 St. Davids, PA  19087
                                 Attention: Sr. Vice Pres., Business Devp.
                                 Telephone: 610-971-5809
                                 FAX:       610-688-9498

         with a copy to:         American Home Products Corporation
                                 5 Giralda Farms
                                 Madison, NJ  07940
                                 Attention: Sr. Vice Pres., and General Counsel
                                 Telephone: 973-660-6040
                                 FAX:       973-660-7156

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<PAGE>

         12.5 APPLICABLE LAW. This Agreement shall be governed by and construed
in accordance with the laws of the Commonwealth of Massachusetts, without giving
effect to the choice of laws provisions thereof.

         12.6 DISPUTE RESOLUTION. The parties hereby agree that they will
attempt in good faith to resolve any controversy including, without
limitation, *** , or claim arising out of or relating to this Agreement
promptly by negotiations. If a controversy or claim should arise hereunder,
the members of the Joint Research Committee or the Joint Patent Committee, as
applicable, will confer at least once and will attempt to resolve the matter.
If any such matter arises under Sections 4.5.6 or 4.6 and has not been
resolved within thirty (30) days, or earlier at the election of either party,
the matter shall be referred to (i) the Chief Scientific Officer (or the
equivalent position or designee) of GTC and (ii) the President of
Wyeth-Ayerst Research (or the equivalent position or designee) if the matter
pertains to research and development or the President of Wyeth-Ayerst Global
Pharmaceuticals (or the equivalent position or designee) if the matter
pertains to the commercialization of a Product (the "Representatives"). If
the matter has not been resolved within thirty (30) days, or earlier at the
election of either party, by the Representatives, or if the matter arises
under other provisions of this Agreement, then the matter shall be referred
to the Chief Executive Officer of GTC and the Executive Vice President of AHP
or their respective designees, to resolve through good faith discussions, or
if still unresolved, to promptly agree upon a binding independent third-party
dispute resolution mechanism intended to promptly and fairly resolve the
matter in dispute or to remedies at law.

         12.7 ENTIRE AGREEMENT. This Agreement, together with the exhibits
hereto, contains the entire understanding of the parties with respect to the
subject matter hereof. All express or implied agreements and understandings,
either oral or written, heretofore made are expressly merged in and made a part
of this Agreement. This Agreement may be amended, or any term hereof modified,
only by a written instrument duly executed by both parties hereto.

         12.8 PUBLICITY. GTC and AHP each agree not to disclose any terms or
conditions of, this Agreement, or any results arising from the Research
Collaboration, to any Third Party without consulting the other party prior to
such disclosure. Notwithstanding the foregoing, prior to execution of this
Agreement, GTC and AHP shall agree upon (i) the exact text of a press release
announcing the Research Collaboration and (ii) the substance of information that
can be used as a routine reference in the usual course of business to describe
the terms of this transaction, and GTC and AHP may disclose such information, as
modified by mutual agreement from time to time, without consulting the other
party. Thereafter, any public announcement apart from that agreed in Section
12.8 (ii) shall be subject to each Party's prior written approval.
Notwithstanding the foregoing, either party may disclose the terms of this
Agreement to the extent required to comply with applicable laws, including
without limitation the rules and regulations promulgated by the Securities and
Exchange Commission and the party intending to disclose the terms of this
Agreement shall provide the nondisclosing party an opportunity to review and
comment on the intended disclosure which is reasonable under the circumstances.

         12.9 AGREEMENT NOT TO SOLICIT EMPLOYEES. During the term of the
Research Collaboration and for a period of six (6) months following the
expiration or termination of the Research Collaboration pursuant to Article
11, GTC and AHP agree not to seek to persuade or induce any scientific
employee of the other company to discontinue his or her employment with that

                                       31
<PAGE>

company in order to become employed by or associated with any business,
enterprise or effort that is associated with its own business; PROVIDED,
HOWEVER, these provisions shall not apply to (i) employees of either party
actively being considered for employment by the other party as of the Effective
Date (ii) any other employee designated in writing by his or her employer after
the Effective Date and (iii) any employee who has responded to a general
solicitation by the other party for an available position.

         12.10 HEADINGS. The captions to the several Sections and Subsections
hereof are not a part of this Agreement, but are merely guides or labels to
assist in locating and reading the several Sections and Subsections hereof.

         12.11 INDEPENDENT CONTRACTORS. It is expressly agreed that GTC and AHP
shall be independent contractors and that the relationship between the two
parties shall not constitute a partnership, joint venture or agency. Neither GTC
nor AHP shall have the authority to make any statements, representations or
commitments of any kind, or to take any action, which shall be binding on the
other, without the prior consent of the other party to do so.

         12.12 RIGHTS UNDER SECTION 365(n). All rights and licenses granted
under or pursuant to this Agreement by GTC to AHP are, for all purposes of
Section 365(n) of Title 11 of the U.S. Code ("Title 11"), licenses of rights to
intellectual property as defined in Title 11. GTC agrees during the term of this
Agreement to maintain and preserve any current copies of all such intellectual
property which are in existence and in its possession as of the commencement of
a case under Title 11 by or against GTC. If a case is commenced by or against
GTC under Title 11, then, unless and until this Agreement is rejected as
provided in Title 11, GTC (in any capacity, including debtor-in-possession) and
its successors and assigns (including, without limitation, a Title 11 Trustee)
shall, as AHP may elect in a written request, immediately upon such request (A)
(i) perform all of the obligations provided in this Agreement to be performed by
GTC, or (ii) provide to AHP copies of all such intellectual property (including
all embodiments thereof) held by GTC and such successors and assigns as of the
commencement of a case under Title 11 by or against GTC and from time to time
thereafter, and (B) not interfere with the rights of AHP as provided in this
Agreement, or any agreement supplementary hereto, to such intellectual property
(including all such embodiments thereof), including any right of AHP to obtain
such intellectual property (or such embodiment) from any other entity.

         12.13 EXPORTS. The parties acknowledge that the export of technical
data, materials or products is subject to the exporting party receiving any
necessary export licenses and that the parties cannot be responsible for any
delays attributable to export controls which are beyond the reasonable control
of either party. GTC and AHP agree not to export or re-export, directly or
indirectly, any information, technical data, the direct product of such data,
samples or equipment received or generated under this Agreement in violation of
any applicable export control laws or governmental regulations. GTC and AHP
agree to obtain similar covenants from their licensees, sublicensees with
respect to the subject matter of this Section 12.13.

         12.14 WAIVER. The waiver by either party hereto of any right hereunder
or the failure to perform or a breach by the other party shall not be deemed a
waiver of any other right hereunder or of any other breach or failure by said
other party whether of a similar nature or otherwise.

                                       32
<PAGE>

         12.15 COUNTERPARTS. This Agreement may be executed in two or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

                                       33
<PAGE>

         IN WITNESS WHEREOF, the parties have caused their duly authorized
officer to execute and deliver this Agreement as of the date first set forth
above.

GENOME THERAPEUTICS CORPORATION

By:               S/S
    ----------------------------------------
           Christopher T. Kelly

Title:   Senior Vice President Strategic Planning/Business Development

AMERICAN HOME PRODUCTS CORPORATION

By:               S/S
    ----------------------------------------
            Egon E. Berg

Title:   Vice President

                                       34
<PAGE>

                                    EXHIBIT A

                           DRAFT OVERALL RESEARCH PLAN

                                       ***

<PAGE>

                                    EXHIBIT B
                             MILESTONES AND PAYMENTS

Section 6.2.1.  Research Milestones

         ***

Section 6.2.2.  Development Milestones.

         ***

<PAGE>

Section 6.2.3.  Approval Milestones

         ***

<PAGE>

                                    EXHIBIT C

                           MATERIAL TRANSFER AGREEMENT

         This MATERIAL TRANSFER AGREEMENT, including the attached Schedules,
(collectively the "Agreement") is entered into as of the last date on the
signature page hereof (the "Effective Date") by and between
____________________________, a ____________corporation with its office and
place of business at __________________, (the "SUPPLIER"), and the organization
identified on the signature page (the "RECIPIENT").

1. BACKGROUND. SUPPLIER has developed and produced certain Material (as defined
below). RECIPIENT is conducting certain non-commercial Research (as defined
below). RECIPIENT desires to obtain samples of the Material for use in
conjunction with said Research. SUPPLIER is willing to provide the Material to
RECIPIENT on the terms and conditions set forth in this Agreement.

2. DEFINITIONS.

         2.1 "CONFIDENTIAL INFORMATION" includes, without limitation any
scientific, technical, trade or business information given to one party (the
"Receiving Party") by the other party (the "Disclosing Party") which is treated
by the Disclosing Party as confidential or proprietary, whether or not such
information is labeled or identified as "confidential". Confidential Information
does not include information:

         (a) in or entering the public domain (through no fault of Receiving
Party), or

         (b) which is lawfully made available to Receiving Party by an
independent third party owing no obligation of confidentiality to Disclosing
Party with regard thereto (and such lawful right can be properly demonstrated by
Receiving Party), or

         (c) already in Receiving Party's possession at the time of receipt from
Disclosing Party (and such prior possession can be properly demonstrated by
Receiving Party), or

         (d) which is independently developed by employees of Receiving Party
and or affiliates of its parent corporation (and such independent development
can be properly demonstrated by Receiving Party), or

         (e) which is required by law, regulation, statute, rule, act or order
of any governmental authority or agency to be disclosed by Receiving Party.

         To permit Disclosing Party an opportunity to intervene, in order to
obtain a protective order or other similar order to limit or prevent disclosures
of Confidential Information, Receiving Party shall immediately notify Disclosing
Party, in writing, if it is requested by a court order, a governmental agency,
or any other entity to disclose Confidential Information in Receiving Party's
possession and thereafter Receiving Party shall disclose only the minimum
Confidential Information required to be disclosed in order to comply, whether or
not a protective order or other similar order is obtained by Disclosing Party.

                                       1
<PAGE>

         2.2 "DEVELOPMENTS" include, without limitation, ideas, concepts,
discoveries, inventions, developments, know-how, trade secrets, techniques,
methodologies, modifications, innovations, improvements, writings,
documentation, data and rights (whether or not protectable under state, federal,
or foreign patent, trademark, copyright or similar laws) that incorporate the
Material, or that could not have been developed without the use of the Material,
or that require the use of the Material, that are discovered, developed,
created, conceived or reduced to practice by the RECIPIENT, alone or jointly
with others, during the term of this Agreement. Developments include, without
limitation, New Substances and New Uses.

         2.3 "MATERIAL" means the material to be transferred from SUPPLIER to
RECIPIENT, as described in SCHEDULE A attached to this Agreement, together with
any refills of the Material and any Progeny and Unmodified Derivatives of the
Material (including, without limitation, expression products, subclones,
sub-units or fractionations).

         2.4 "NEW SUBSTANCE" means any material first produced or isolated with
or by use of the Material.

         2.5 "NEW USE" means any new use of the Material, including, without
limitation, new therapeutic uses or methods of treatment.

         2.6 "RESEARCH" means RECIPIENT's noncommercial research, as described
in SCHEDULE B attached to this Agreement.

         2.7 "PROGENY" means an unmodified descendent generated from the
Material, such as virus from virus, cell from cell, or organism from organism.

         2.8 "UNMODIFIED DERIVATIVE" means substances created by the RECIPIENT
which constitute an unmodified functional subunit or product expressed by or
generated from the original Material, including, but not limited to, subclones
of unmodified cell lines, purified or fractionated subsets of the original
Material, proteins expressed by DNA/RNA supplied by SUPPLIER, or monoclonal
antibodies secreted by a hybridoma cell line.

         2.9 "MODIFICATIONS" means substances created by the RECIPIENT which
contain or incorporate the Material or are derived by chemical modification of
the Material.

         2.10 "COMMERCIAL PURPOSE" means the sale, lease, license, or other
transfer of the Material or Modifications to a for-profit organization.
Commercial Purposes shall also include uses of the Material or Modifications by
any organization, including RECIPIENT, to perform contract research, to screen
compound libraries, to produce or manufacture products for general sale, or to
conduct research activities that result in any sale, lease, license, or transfer
of the Material or Modifications to a for-profit organization. However,
industrially sponsored academic research shall not be considered a use of the
Material or Modifications for Commercial Purposes per se, unless any of the
above conditions of this definition are met.

3. USE OF MATERIAL. RECIPIENT certifies and attests that it will use the
Material only in connection with its Research as described in SCHEDULE B, and
that the Material will not be used for any other purpose or for any Commercial
Purpose. RECIPIENT further attests that no

                                       2
<PAGE>

quantity of the Materials will be distributed to any third party without the
prior written permission of SUPPLIER.

4. ACKNOWLEDGMENT.

         4.1 RECIPIENT acknowledges that the Material is experimental in nature
and may have hazardous properties. RECIPIENT agrees to comply with all laws and
regulations applicable to its handling.

         4.2 RECIPIENT acknowledges and agrees that the Material is or may be
the subject of a patent or patent application. Except as expressly provided in
this Agreement, no licenses or other rights, either expressed or implied, are
provided to the RECIPIENT under any patents, patent applications, trade secrets
or other proprietary rights of the SUPPLIER. In particular, no express or
implied licenses or other rights are provided to use the Material,
Modifications, Developments, or any related patents or patent applications of
SUPPLIER for any Commercial Purposes.

5. NO WARRANTY. THE MATERIAL IS PROVIDED BY SUPPLIER TO RECIPIENT WITHOUT ANY
WARRANTEE EXPRESS OR IMPLIED, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR
FITNESS FOR OR A PARTICULAR PURPOSE, AND SUPPLIER MAKES NO REPRESENTATION THAT
RECIPIENT'S USE OF THE MATERIAL WILL NOT INFRINGE ANY PATENT OR OTHER
PROPRIETARY RIGHTS OF ANY THIRD PARTY. THE MATERIAL IS PROVIDED TO RECIPIENT
WITH THE UNDERSTANDING THAT SUPPLIER AND ITS AGENTS, EMPLOYEES AND AFFILIATES,
HAVE NO LIABILITY WHATSOEVER IN CONNECTION WITH SUCH MATERIAL OR ITS USE.

6. INDEMNIFICATION. Except to the extent prohibited by law, RECIPIENT assumes
all liability for damages which may arise from its use, storage or disposal of
the Material. To the extent allowable under applicable law, RECIPIENT agrees to
indemnify and hold SUPPLER harmless from any claims and liabilities which might
arise from RECIPIENT's use of the Material, except for those arising from the
gross negligence or willful misconduct of SUPPLIER.

7. OWNERSHIP AND GRANT OF RIGHTS.

         7.1 MATERIAL. SUPPLIER has developed the Material over a substantial
period of time at considerable expense, and the Material is of great importance
to SUPPLIER's business. RECIPIENT acknowledges that SUPPLIER is and will at all
times remain the owner of the Material.

         7.2 OWNERSHIP OF DEVELOPMENTS. RECIPIENT acknowledges and agrees that
all rights, title and interest in and to any and all Developments resulting from
RECIPIENT's use of the Materials provided hereunder will belong solely to
SUPPLIER, and RECIPIENT will take all steps reasonably necessary to enable
SUPPLIER to perfect its rights to all such Developments.

         7.3 DISCLOSURE OF DEVELOPMENTS. RECIPIENT will promptly and fully
disclose in writing to SUPPLIER any and all Developments. RECIPIENT will keep
complete and accurate written records of its Research. At SUPPLIER's request,
RECIPIENT will meet with

                                       3
<PAGE>

SUPPLIER to discuss the Research. In addition, RECIPIENT will provide SUPPLIER
with periodic written summaries of its Research.

         7.4 PATENT APPLICATIONS. Any patent applications considered necessary
in the reasonable legal and business Judgment of SUPPLIER to protect SUPPLIER's
proprietary position in any Developments will be prepared and filed by SUPPLIER
(jointly in SUPPLIER's and RECIPIENT's names, if jointly invented; solely in
SUPPLIER's or RECIPIENT's name, if solely invented) with the expenses of these
patent applications being born by SUPPLIER. At SUPPLIER's request and expense,
RECIPIENT will cause its interest in any Developments, including, without
limitation, any patents or patent applications relating to such Developments, to
be assigned to SUPPLIER, and will provide SUPPLIER with reasonable assistance in
preparing and maintaining such applications, including causing the execution of
any assignments or other documents.

8. CONFIDENTIALITY.

         8.1 NONDISCLOSURE OF CONFIDENTIAL INFORMATION. Except as provided in
Section 10 below, neither party will directly or indirectly publish, disseminate
or otherwise disclose, deliver or make available to any third party any of the
other party's Confidential Information other than in furtherance of this
Agreement. RECIPIENT acknowledges that the Federal Food and Drug Administration
(FDA) requires SUPPLIER to be knowledgeable concerning all available data on its
compounds and drugs and that such data must be maintained and made available to
FDA. RECIPIENT therefore acknowledges and agrees that data transmitted to
SUPPLIER cannot be considered as confidential.

         8.2 PROTECTION. RECIPIENT will exercise all commercially reasonable
precautions to protect the integrity and confidentiality of the Material.
RECIPIENT will not remove the Material from RECIPIENT's premises except to the
extent necessary to fulfill its obligations under this Agreement, and then only
with the prior written consent of SUPPLIER.

9. PUBLICATION.

         9.1 RIGHT TO PUBLISH; REVIEW BY SUPPLIER. Notwithstanding
RECIPIENT's confidentiality obligations under Section 8 above, RECIPIENT will
have the right to publish and disclose the final results of the Research. In
order to balance this right with SUPPLIER's proprietary interests, RECIPIENT
will submit for SUPPLIER's review all manuscripts, abstracts or presentations
intended for publication or other public disclosure ("Publications") at least
sixty (60) days prior to the date of submission for publication or public
disclosure. SUPPLIER will use reasonable efforts to complete its review
promptly and will complete its review within sixty (60) days of receipt of
the Publications. No Publication shall contain any Confidential Information
of SUPPLIER. At SUPPLIER's request RECIPIENT agrees to delete from its
Publications any references deemed by SUPPLIER to be Confidential
Information. At the end of this sixty (60) day period, RECIPIENT will have
the right to publish the Publications, as amended by SUPPLIER and subject to
SUPPLIER's rights under Section 9.2 below.

         9.2 OPPORTUNITY TO FILE PATENT APPLICATIONS. If during its sixty
(60) day Publication review period SUPPLIER notifies RECIPIENT that it
desires patent applications to be filed on

                                       4
<PAGE>

any Developments disclosed or contained in the Publications, RECIPIENT will
defer publication or other disclosure for a period sufficient to permit SUPPLIER
to file any such patent applications, such period not to exceed *** days from
the date of submission of the Publication to SUPPLIER.

10. TERMINATION.

         10.1 This Agreement will terminate upon completion of the RECIPIENT's
current Research as defined in Section 2.6.

         10.2 TERMINATION FOR CAUSE. Either party may terminate this
Agreement for cause at any time upon thirty (30) days prior written notice to
the other party. "Cause" means a material breach of this Agreement by the
other party where such breach, if curable, is not remedied to the
nonbreaching party's satisfaction within such thirty (30) day period.

         10.3 TERMINATION BY EITHER PARTY WITHOUT CAUSE. Either party may
terminate this Agreement at any time without cause upon not less than sixty
(60) days prior written notice to the other party.

         10.4 EFFECT OF TERMINATION OR EXPIRATION. Upon termination or
expiration of this Agreement for any reason RECIPIENT shall immediately return
to SUPPLIER all its Confidential Information and copies thereof, and shall
return or, at SUPPLIER's direction, to destroy any and all unused Material, and
if instructed to destroy such Material will provide evidence documenting the
manner of destruction to SUPPLIER. All of RECIPIENT's rights to use the Material
shall cease. Following termination or expiration, neither party shall have any
further obligations under this Agreement, except that Sections 5, 6, 7, 8, 9,
10, 11, 12, 13, 14, 15 and 16 shall survive and remain in force.

11. NOTICE. All communications and notices from one party to the other will be
in writing and will be given by addressing the same to the other party at the
address or facsimile number set forth in this Agreement, or at such other
address or facsimile number as either party may specify in writing to the other.
All notices will become effective when deposited in the United States Mail with
proper postage for first class registered or certified mail prepaid, return
receipt requested, or when delivered personally, or, if promptly confirmed by
mail as above, when dispatched by facsimile.

12. ASSIGNMENT. This Agreement, and the rights and obligations hereunder, may
not be assigned or transferred by either party without the prior written consent
of the other party, except that SUPPLIER may assign this Agreement to an
affiliated company or in connection with the merger, consolidation or sale of
all or substantially all of its assets.

13. ENTIRE AGREEMENT. This Agreement constitutes the entire agreement of the
parties with regard to its subject matter, and supersedes all previous written
or oral representations, agreements and understandings between SUPPLIER and
RECIPIENT.

14. NO MODIFICATION. This Agreement may be changed only by a writing signed by
both parties.

                                       5
<PAGE>

15. SEVERABILITY. In the event that any one or more of the provisions in this
Agreement shall, for any reason, be held to be invalid, illegal or unenforceable
in any respect, such invalidity, illegality or unenforceability shall not affect
any other provisions of this Agreement, and all other provisions shall remain in
full force and effect. If any of the provisions of this Agreement is held to be
excessively broad it shall be reformed and construed by limiting and reducing it
so as to be enforceable to the maximum extent permitted by law.

16. APPLICABLE LAW. This Agreement will in all events and for all purposes be
governed by, and construed in accordance with the law of the Commonwealth of
Massachusetts without regard to any choice of law principles that would dictate
the application of the law of another jurisdiction.

17. MISCELLANEOUS PROVISIONS.

         17.1 RECIPIENT acknowledges and agrees that receipt of the Materials
from SUPPLIER does not create or imply a particular relationship between
SUPPLIER and RECIPIENT, and further agrees that RECIPIENT is acting
independently of SUPPLIER and not as an affiliate, employee, agent, or joint
venturer of or with SUPPLIER. RECIPIENT shall have no authority to represent,
bind or act on behalf of SUPPLIER.

         17.2 In accordance with the requirements of the Federal Food, Drug and
Cosmetic Act and with DEA regulations, where applicable, RECIPIENT certifies
that it is regularly engaged in conducting laboratory studies or animal tests
and that all shipments of Materials received pursuant hereto will be actually
used by RECIPIENT or under RECIPIENT's direction for tests in vitro and in
animals used only for laboratory research and will not be used in tests
involving administration of the Materials in humans. RECIPIENT understands that
the Materials are not to be used for in vitro use in the regular course of
treating or diagnosing disease in humans. RECIPIENT also certifies that no
animals used in such tests, or their products, shall be used for food purposes
without the prior approval of the Food and Drug Administration. RECIPIENT
further certifies and attests that RECIPIENT's handling and use of the Materials
will be done in accordance with all provisions and requirements of the Federal
Food, Drug and Cosmetic Act and with DEA regulations, where applicable.

         17.3 RECIPIENT certifies that it will not use the services of any
individual who has been debarred under the Federal Food, Drug and Cosmetic Act
in the course of the Research with the Materials.

         17.4 RECIPIENT certifies and attests that the individual executing this
Agreement is a duly authorized representative of RECIPIENT with full power and
authority to sign, bind and otherwise commit RECIPIENT to the terms and
obligations of this Agreement. Recipient further certifies and attests that it
has the power and authority to execute and deliver this Agreement and to perform
its obligations hereunder.

                                       6
<PAGE>

     IN WITNESS WHEREOF, the parties have caused this Agreement to be executed,
by duly authorized representatives, as of the last date written below.

SUPPLIER:                                                 RECIPIENT:

By:________________________                      By:__________________________

Name:______________________                      Name:________________________

Title:_____________________                      Title:_______________________

Date:______________________                      Date:________________________

                                                 Address:_____________________

                                                 _____________________________

                                                 _____________________________

                                                 Agreed and Acknowledged:

                                                 By:__________________________

                                                 Name:________________________
                                                 Principal Investigator

                                                 Date:________________________

                                       7<PAGE>

                                                                    Exhibit 4.01

                               essential.com. inc.

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                          Dated as of February 8, 2000

<PAGE>

                                TABLE OF CONTENTS
                                                                           Page
                                                                           ----

1.     Definitions .......................................................... 1

2.     Demand Registration .................................................. 3

       A.    Demand Rights .................................................. 3
       B.    S-3 Registration Rights ........................................ 4

3.     Company Registration ................................................. 4

4.     Obligations of the Company ........................................... 5

5.     Furnish Information .................................................. 7

6.     Expenses of Registration ............................................. 7

7.     Underwriting Requirements ............................................ 8

8.     Indemnification ...................................................... 8

9.     Reports Under the Exchange Act .......................................10

10.    Assignment of Registration Rights ....................................11

11.    Limitations on Registration Rights ...................................11

12.    "Market Stand-Off' Agreement .........................................11

13.    Amendment; Waiver ....................................................12

14.    Changes in Registrable Securities ....................................12

15.    Information ..........................................................12

       (a)    Financial and Related Data ....................................13
       (b)    Access to Properties ..........................................14

16.    Termination of Registration Rights ...................................14

17.    Legends and Opinions .................................................15

18.    Entire Agreement .....................................................15

19.    Governing Law ........................................................15

20.    Successors and Assigns ...............................................15

                                      - i -
<PAGE>

21.    Notices ..............................................................15

22.    Severability .........................................................16

23.    Titles and Subtitles .................................................16

24.    Delays or Omissions; Remedies Cumulative .............................16

25.    Arbitration ..........................................................16

26.    Counterparts .........................................................16

27.    Accession to Agreement ...............................................16

                                     - ii -
<PAGE>

                  SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

      This Second Amended and Restated Investor Rights Agreement (this
"Agreement") is made as of the 8th day of February, 2000 by and among (i)
essential.com, inc., a Delaware corporation (the "Company"), (ii) those holders
of the Company's Series A Preferred Stock, $.01 par value per share (the "Series
A Stock"), set forth on Schedule I hereto under the heading "Angel Investor"
(the "Angel Investors"), (iii) those holders of Series A Stock and the Company's
Series B Preferred Stock, $.0l par value per share (the "Series B Stock"), set
forth on Schedule I hereto under the heading "Existing Outside Investors" (the
"Existing Outside Investors"), and (iv) those holders of the Company's Series C
Preferred Stock, $.0 1 par value per share (the "Series C Stock"), set forth on
Schedule I hereto under the heading "Series C Investors" (the "Series C
Investors"), as such Schedule shall be amended from time to time to reflect each
person who shall, after the date hereof, acquire shares of capital stock and
join in and become party to this Agreement as a Series C Investor by executing
and delivering to the Company an Instrument of Accession in the form of Schedule
II hereto. The Existing Outside Investors and the Series C Investors are
referred to collectively herein as the "Outside Investors." The Angel Investors
and the Outside Investors are referred to collectively herein as the "Investors"
and each collectively as an "Investor." For purposes of this Agreement, Zafa
shall be entitled to the rights of an Outside Investor set forth herein only to
the extent of his ownership of shares of Series B Stock.

                                    RECITALS:

      A. Concurrently with the execution of this Agreement, the Series C
Investors are acquiring from the Company shares of the Company's Series C Stock,
pursuant to the Series C Convertible Preferred Stock Purchase Agreement of even
date herewith (the "Purchase Agreement").

      B. By entering into this Agreement, the Company wishes to provide a
further inducement to the Series C Investors to purchase the Company's Series C
Stock pursuant to the Purchase Agreement.

            NOW, THEREFORE, in consideration of the foregoing, the parties agree
as follows:

            1.    Definitions. For purposes of this Agreement:

      (a) "Common Shares" means shares of Common Stock, par value $0.01 per
share, of the Company.

      (b) "Exchange Act" means the Securities Exchange Act of 1934, as amended.

      (c) "Form S-3" means such form of registration statement under the
Securities Act as in effect on the date hereof or any registration form under
the Securities Act subsequently adopted by the SEC which permits inclusion or
incorporation of substantial information by reference to other documents filed
by the Company with the SEC.

<PAGE>

      (d) "Holder" means any Person owning or having the right to acquire
Registrable Securities, or any assignee thereof in accordance with Section 11.

      (e) "Initiating Holders" means the Holder(s) initiating a registration
request under Section 2.

      (f) "Majority in Interest of the Initiating Holders" means Initiating
Holders holding a majority of the Registrable Securities held by all Initiating
Holders.

      (g) "Person" means any individual, partnership, limited liability company,
joint venture, corporation, association, trust or any other entity or
organization.

      (h) "Preferred Stock" means collectively, the Series A Stock, the Series B
Stock and the Series C Stock.

      (i) "Qualifying Request" means a written request to register Registrable
Securities with a reasonably anticipated aggregate offering price in excess of
$5,000,000 from any of the Investors that in the aggregate possess either (i) at
least fifty percent (50%) of the Registrable Securities outstanding as of the
date of such request or (ii) at least fifty percent (50%) of the Registrable
Securities issued or issuable upon conversion of the Series C Stock and held by
the Series C Investors or their successors, assigns or donees on the date of
such request.

      (j) "Register," "registered," and "registration" refer to a registration
effected by preparing and filing a registration statement or similar document in
compliance with the Securities Act, and the declaration or ordering of
effectiveness of such registration statement or document.

      (k) "Registrable Securities" means (1) any Common Shares issuable (without
regard to any restriction on conversion that may be applicable to any particular
holder of Preferred Stock) or issued upon conversion of the Preferred Stock; (2)
any Common Shares issued as (or issuable upon the conversion or exercise of any
warrant, right or other security which is issued as) a dividend or other
distribution with respect to, or in exchange for or in replacement of, or upon
conversion of, such Preferred Stock; and (3) any other capital stock of the
Company whether now owned or hereafter acquired upon the conversion of, exchange
for, or in replacement of, Preferred Stock; provided, however, that any
Registrable Securities sold by a Person in a transaction in which such Person's
rights under this Agreement are not assigned pursuant to Section 11 below shall
cease to be Registrable Securities from and after the time of such sale.

      (l) The number of shares of "Registrable Securities then outstanding"
shall be determined by the number of Common Shares outstanding, and the number
of Common Shares issuable, which are Registrable Securities.

      (m) "SEC" means the Securities and Exchange Commission.

      (n) "Securities Act" means the Securities Act of 1933, as amended.

                                     - 2 -
<PAGE>

      (o) "Series C Qualifying Request" means a Qualifying Request from the
Series C Investors pursuant to (ii) in the definition of Qualifying Request
contained in this Section 1.

      (p) "Violation" means any of the following statements, omissions or
violations: (i) any untrue statement or alleged untrue statement of a material
fact contained in a registration statement under this Agreement, including any
preliminary prospectus or final prospectus contained therein or any amendments
or supplements thereto or any documents filed under state securities or "blue
sky" laws in connection therewith, (ii) the omission or alleged omission to
state therein a material fact required to be stated therein, or necessary to
make the statements therein not misleading; or (iii) any violation or alleged
violation by the Company of the Securities Act, the Exchange Act, any state
securities law or any rule or regulation promulgated under the Securities Act,
the Exchange Act or any state securities law.

            2. Demand Registration.

            A. Demand Rights.

            (a) If, after the earlier of (i) one hundred eighty (180) days after
the consummation of the initial public offering of the Company's Common Stock,
or (ii) March 29, 2002, the Company shall receive a Qualifying Request that the
Company file a registration statement under the Securities Act with respect to
Registrable Securities then outstanding, then the Company shall, subject to the
limitations of Section 2A(b) below, use its best efforts to effect as soon as
practicable, and in any event within ninety (90) days of the receipt of such
Qualifying Request, such registration. Notwithstanding the foregoing, the
Company shall not be obligated to effect any such registration within 6 months
after the effective date of an immediately preceding registration pursuant to
this Section 2A. The Company shall be obligated to effect only two (2)
registrations pursuant to this Section 2A (an offering which is not consummated
shall not be counted for this purpose).

            (b) If Initiating Holders intend to distribute the Registrable
Securities covered by their request by means of an underwriting, they shall so
advise the Company as a part of their request made pursuant to this Section 2A.
In such event, the right of any Holder to include such Holder's Registrable
Securities in such registration shall be conditioned upon such Holder's
participation in such underwriting and the inclusion of such Holder's
Registrable Securities in the underwriting (unless otherwise mutually agreed by
a Majority in Interest of the Initiating Holders and such Holder) to the extent
provided herein. The Company shall select the managing underwriter or
underwriters in such underwriting, such underwriter(s) to be reasonably
satisfactory to a Majority in Interest of the Initiating Holders. All Holders
proposing to distribute their securities through such underwriting shall
(together with the Company as provided in Section 4(f)) enter into an
underwriting agreement in customary form with the underwriter or underwriters so
selected for such underwriting by a Majority in Interest of the Initiating
Holders; provided, however, that the Company shall use commercially reasonable
efforts to negotiate with the underwriters to assure that none of the Holders
shall be required to make any representations or warranties or provide
indemnification except as relates to such Holder's ownership of shares and
authority to enter into the underwriting agreement and to such Holder's intended
method of distribution, and the liability of such Holder shall be limited to an
amount equal to the net proceeds from the offering received by such Holder. In
the event that the underwriters advise the

                                     - 3 -
<PAGE>

Company that marketing factors require a limitation of the number of shares to
be underwritten, the Company and its underwriters shall allocate the number of
Registrable Securities requested to be registered by each of the Holders as
follows: (i) first, to the Outside Investors holding Registrable Securities that
have elected to participate in such offering, pro rata according to the number
of Registrable Securities held by each such Outside Investor; and (ii)
thereafter, to the extent additional securities may be included in such
offering, to the Angel Investors holding Registrable Securities that have
elected to participate in such underwritten offering, pro rata according to the
number of Registrable Securities held by each such Angel Investor; provided,
however, that if the Qualifying Request is a Series C Qualifying Request, and in
the event that the underwriters advise the Company that marketing factors
require a limitation of the number of shares to be underwritten, the Company and
its underwriters shall allocate the number of Registrable Securities requested
to be registered by each of the Holders as follows: (i) first, to the Series C
Investors holding Registrable Securities that have elected to participate in
such offering, pro rata according to the number of Registrable Securities held
by each such Series C Investor; (ii) second, to the Outside Investors (other
than the Series C Investors) holding Registrable Securities that have elected to
participate in such offering, pro rata according to the number of Registrable
Securities held by each such Outside Investor (other than the Series C
Investors); and (iii) thereafter, to the extent additional securities may be
included in such offering, to the Angel Investors holding Registrable Securities
that have elected to participate in such underwritten offering, pro rata
according to the number of Registrable Securities held by each such Angel
Investor.

            B. S-3 Registration Rights.

            The Company shall be obligated to effect up to two (2) registrations
pursuant to this Section 2B as may be requested by the Investors in the event
and so long as a registration statement pursuant to Form S-3 or any similar
"short-form" registration (a "Short-Form Registration") is available for such
Registration, provided further, that the reasonably anticipated aggregate
offering price will be in excess of $1,000,000. The Company shall not be
obligated to effect a Short Form Registration more than once in any six-month
period.

            C. Notwithstanding the foregoing provisions of Sections 2A and 2B,
if the Company shall furnish to Holders requesting a registration statement
pursuant to this Section 2, a certificate signed by the President of the Company
stating that, in the good faith judgment of the Board of Directors of the
Company, it would be detrimental to the Company and its shareholders for such
registration statement to be filed by reason of a material pending announcement
or transaction or series of pending transactions and it is therefore necessary
to defer the filing of such registration statement, the Company shall have the
right to defer such filing for a period of not more than one hundred eighty
(180) days after receipt of the request of the Holders; provided, however, that
the Company may not utilize this right more than once in any twelve (12) month
period.

            3. Company Registration. If (but without any obligation to do so)
the Company proposes to register (including for this purpose a registration
effected by the Company for shareholders) any of its stock or other securities
under the Securities Act in connection with a public offering of such securities
solely for cash other than (i) a registration on Form S-8 (or other similar
successor form) relating solely to the sale of securities to participants in a
Company

                                     - 4 -
<PAGE>

stock plan or to other compensatory arrangements to the extent includable on
Form S-8 (or other similar successor form), or (ii) a registration on Form S-4
(or other similar successor form), the Company shall, at such time, promptly
give each Holder written notice of such registration. Upon the written request
of each Holder given within twenty (20) days after mailing of such notice by the
Company in accordance with Section 22, the Company shall, subject to the
provisions of Section 7, use its best efforts to cause to be registered under
the Securities Act all of the Registrable Securities that each such Holder has
requested to be registered. In the event that the underwriters advise the
Company that marketing factors require a limitation of the number of shares to
be underwritten, the Company and its underwriters shall allocate the number of
Registrable Securities requested to be registered by each of the Holders as
follows: (i) first, to the Company; (ii) second, to the Outside Investors
holding Registrable Securities that have elected to participate in such
offering, pro rata according to the number of Registrable Securities held by
each such Outside Investor; and (iii) thereafter, to the extent additional
securities may be included in such offering, to the Angel Investors holding
Registrable Securities that have elected to participate in such underwritten
offering, pro rata according to the number of Registrable Securities held by
each such Angel Investor; provided, however, that in no event shall the number
of Registrable Securities to be registered by the Outside Investors be less than
twenty percent (20%) of the total number of shares to be sold in such offering.
The Company shall have no obligation under this Section 3 to make any offering
of its securities, or to complete an offering of its securities that it proposes
to make, and shall incur no liability to any Holder for its failure to do so.

            4. Obligations of the Company. Whenever required under this
Agreement to effect the registration of any Registrable Securities, the Company
shall, as expeditiously as reasonably possible:

            (a) Prepare and file with the SEC a registration statement with
respect to such Registrable Securities and use its best efforts to cause such
registration statement to become effective, and, upon the request of the Holders
of a majority of the Registrable Securities being registered thereunder, keep
such registration statement effective for up to one hundred twenty (120) days or
until the Holders have completed the distribution referred to in such
registration statement, whichever occurs first (but in any event for at least
any period required under the Securities Act); provided that before filing such
registration statement or any amendments thereto, the Company will furnish to
the directors elected by the holders of the Preferred Stock copies of all such
documents proposed to be filed; provided, further, however, that each such
director may elect to waive such requirement by written notice to the Company.

            (b) Prepare and file with the SEC such amendments and supplements to
such registration statement and the prospectus used in connection with such
registration statement as may be necessary to comply with the provisions of the
Securities Act with respect to the disposition of all securities covered by such
registration statement.

            (c) Furnish to the Holders such number of copies of such
registration statement and of each amendment and supplement thereto (in each
case including all exhibits), such number of copies of the prospectus contained
in such registration statement (including each preliminary prospectus and any
summary prospectus) and any other prospectus filed under Rule 424 under the
Securities Act, in conformity with the requirements of the Securities Act, and
such

                                     - 5 -
<PAGE>

other documents as Holders may reasonably request in order to facilitate the
disposition of Registrable Securities owned by them.

            (d) Use commercially reasonable efforts to register and qualify the
securities covered by such registration statement under such other securities or
"blue sky" laws of such states or jurisdictions as shall be reasonably requested
by the Holders, provided that the Company shall not be required in connection
therewith or as a condition thereto (i) to qualify to do business in any state
or jurisdiction where it would not otherwise be required to qualify but for the
requirements of this clause (d), or (ii) to file a general consent to service of
process in any such state or jurisdiction.

            (e) Use commercially reasonable efforts to cause all Registrable
Securities covered by such registration statement to be registered with or
approved by such other governmental agencies or authorities as may be necessary
by virtue of the Company's business or operations to enable the seller or
sellers thereof to consummate the disposition of such Registrable Securities.

            (f) In the event of any underwritten public offering, enter into and
perform its obligations under an underwriting agreement, in usual and customary
form, with the managing underwriter of such offering.

            (g) Notify each Holder of Registrable Securities covered by such
registration statement at any time when a prospectus relating thereto is
required to be delivered under the Securities Act of the happening of any event
as a result of which the prospectus included in such registration statement, as
then in effect, includes an untrue statement of a material fact or omits to
state a material fact required to be stated therein or necessary to make the
statements therein not misleading in the light of the circumstances then
existing.

            (h) Notify each Holder of Registrable Securities covered by such
registration statement and such Holder's underwriters, if any, and confirm such
advice in writing: (i) when the registration statement has become effective;
(ii) when any post-effective amendment to the registration statement becomes
effective; and (iii) of any request by the SEC for any amendment or supplement
to the registration statement or prospectus or for additional information.

            (i) Notify each Holder of Registrable Securities if at any time the
SEC should institute or threaten to institute any proceedings for the purpose of
issuing, or should issue, a stop order suspending the effectiveness of the
Registration Statement. Upon the occurrence of any of the events mentioned in
the preceding sentence, the Company will use commercially reasonable efforts to
prevent the issuance of any stop order or to obtain the withdrawal thereof as
soon as possible. The Company will advise each Holder of Registrable Securities
promptly of any order or communication of any public board or body addressed to
the Company suspending or threatening to suspend the qualification of any
Registrable Securities for sale in any jurisdiction.

            (j) Furnish, at the request of any Holder requesting registration of
Registrable Securities pursuant to this Agreement, (i) on the date that such
Registrable Securities are delivered to the underwriters for sale in connection
with any registration pursuant to this Agreement in which securities are being
sold through underwriters, an opinion, dated such date,

                                     - 6 -
<PAGE>

of the counsel representing the Company for the purposes of such registration,
in form and substance as is customarily given to underwriters in an underwritten
public offering, addressed to the underwriters, if any, and to the Holders
requesting registration of Registrable Securities and (ii) on the date that the
registration statement with respect to such securities becomes effective, a
"comfort" letter dated such date, from the independent certified public
accountants of the Company, in form and substance as is customarily given by
independent certified public accountants to underwriters in an underwritten
public offering, addressed to the underwriters, if any, and to the Holders
requesting registration of Registrable Securities, and a reaffirmation of such
letter on the date that such Registrable Securities are delivered to the
underwriters for sale.

            (k) As soon as practicable after the effective date of the
registration statement, and in any event within sixteen (16) months thereafter,
have "made generally available to its security holders" (within the meaning of
Rule 158 under the Securities Act) an earning statement (which need not be
audited) covering a period of at least twelve (12) months beginning after the
effective date of the registration statement and otherwise complying with
Section 11(a) of the Securities Act.

            5. Furnish Information. It shall be a condition precedent to the
obligations of the Company to take any action pursuant to this Agreement with
respect to the Registrable Securities of any selling Holder that such Holder
shall furnish to the Company such information regarding itself, the Registrable
Securities held by it, and the intended method of distribution of such
securities as shall be required to effect the registration of such Holder's
Registrable Securities. If any registration statement or comparable statement
under the Securities Act refers to an Investor or any of its affiliates, by name
or otherwise, as the holder of any securities of the Company then, unless
counsel to the Company advises the Company that the Securities Act or the SEC
requires that such reference be included in any such statement, each such
Investor shall have the right to require the deletion of such reference to
itself and its affiliates.

            6. Expenses of Registration. All expenses, other than underwriting
discounts and commissions relating to Registrable Securities, incurred in
connection with registrations, filings or qualifications pursuant to this
Agreement, including without limitation all registration, filing and
qualification fees, printers' and accounting fees, fees and disbursements (up to
$25,000) of one counsel (selected by a majority of Holders participating in such
a registration) for the selling Holders shall be borne by the Company; provided,
however, that the Company shall not be required to bear such expenses in
connection with any registration begun pursuant to Section 2 if the offering is
not consummated primarily as a result of any act or omission of any
participating Holder (in which case all participating Holders shall bear such
expenses pro rata), unless with respect to a demand made pursuant to Section 2,
a Majority in Interest of the Initiating Holders agree to forfeit one (1) of the
demand registration(s) to which they are then entitled pursuant to Section 2;
provided, further, however, that if (i) at the time of such withdrawal, the
Holders have learned of a material adverse change in the financial condition or
business of the Company from that known to the Holders at the time of their
request, or (ii) if such withdrawal is at the request of, caused by, or the
result of an unreasonable delay by the Company, then the Holders shall not be
required to pay any such expenses and shall retain their rights pursuant to
Section 2 of this Agreement.

                                     - 7 -
<PAGE>

            7. Underwriting Requirements. In connection with any offering
involving an underwriting of shares being issued by the Company, the Company
shall not be required under Section 3 to include any Holder's securities in such
underwriting unless such Holder accepts the terms of the underwriting as agreed
upon between the Company and the underwriters selected by the Company (with the
approval of Holders holding a majority of the Registrable Securities held by all
Holders, such approval not to be unreasonably withheld); provided, however, that
no Holder participating in such underwriting shall be required to make any
representations or warranties or provide indemnification except as relates to
such Holder's ownership of shares and authority to enter into the underwriting
agreement and to such Holder's intended method of distribution, and the
liability of such Holder shall be limited to an amount equal to the net proceeds
from the offering received by such Holder.

            8. Indemnification. In the event any Registrable Securities are
included in a registration statement under this Agreement:

            (a) The Company will indemnify and hold harmless each Holder, his or
her heirs, personal representatives and assigns, each of such Holder's partners,
officers, directors, employees and affiliates, any underwriter (as defined in
the Securities Act) for such Holder and each Person, if any, who controls such
Holder or underwriter within the meaning of the Securities Act or the Exchange
Act against any losses, claims, damages or liabilities (joint or several) to
which they may become subject under the Securities Act, the Exchange Act or
other federal or state law, insofar as such losses, claims, damages or
liabilities (or actions in respect thereof) arise out of or are based upon a
Violation (provided, however, that the Company will not be required to indemnify
any of the foregoing Persons on account of any losses, claims, damages or
liabilities arising from a Violation if and to the extent that such Violation
was made in a preliminary prospectus and was corrected in a subsequent
prospectus that was required by law to be delivered to the Person making the
claim with respect to which indemnification is sought hereunder, and such
subsequent prospectus was made available by the Company to permit delivery of
such prospectus in a timely manner, and such subsequent prospectus was not so
delivered to such Person by a selling stockholder making use of a prospectus
from a Registration Statement on Form S-3); and the Company will pay to each
such indemnified party, as incurred, any legal or other expenses reasonably
incurred by them in connection with investigating or defending any such loss,
claim, damage, liability, or action; provided, however, that the indemnity
agreement contained in this Section 8(a) shall not apply to amounts paid in
settlement of any such loss, claim, damage, liability or action if such
settlement is effected without the consent of the Company (which consent shall
not be unreasonably withheld), nor shall the Company be liable in any such case
to a particular indemnified party for any such loss, claim, damage, liability or
action to the extent that it arises out of or is based upon a Violation which
occurs in reliance upon, and in conformity with, written information furnished
expressly for use in connection with such registration by or on behalf of such
indemnified party.

            (b) Each selling Holder will indemnify and hold harmless the
Company, each of its directors, each of its officers who has signed the
registration statement, each Person, if any, who controls the Company within the
meaning of the Securities Act, any underwriter, any other Holder selling
securities in such registration statement and any controlling Person of any such
underwriter or other Holder, against any losses, claims, damages or liabilities
(joint or several) to which any of the foregoing Persons may become subject,
under the Securities Act, the Exchange

                                     - 8 -
<PAGE>

Act or other federal or state law, insofar as such losses, claims, damages or
liabilities (or actions in respect thereto) arise out of or are based upon any
Violation, in each case to the extent (and only to the extent) that such
Violation occurs in reliance upon and in conformity with written information
furnished by or on behalf of such Holder expressly for use in connection with
such registration; and each such Holder will pay, as incurred, any legal or
other expenses reasonably incurred by any Person intended to be indemnified
pursuant to this Section 8(b), in connection with investigating or defending any
such loss, claim, damage, liability, or action; provided, however, that the
indemnity agreement contained in this Section 8(b) shall not apply to amounts
paid in settlement of any such loss, claim, damage, liability or action if such
settlement is effected without the consent of the Holder, which consent shall
not be unreasonably withheld; and provided further, that, in no event shall the
liability of any Holder under this Section 8(b) exceed the net proceeds from the
offering received by such Holder.

            (c) Promptly after receipt by an indemnified party under this
Section 8 of notice of the commencement of any action (including any
governmental action), such indemnified party will, if a claim in respect thereof
is to be made against any indemnifying party under this Section 8, deliver to
the indemnifying party a written notice of the commencement thereof and the
indemnifying party shall have the right to participate in, and, to the extent
the indemnifying party so desires, jointly with any other indemnifying party
similarly noticed, to assume the defense thereof with counsel mutually
satisfactory to the parties; provided, however, that the indemnified parties
shall have the right to retain one counsel of their own, with the fees and
expenses of one such counsel to be paid by the indemnifying party, if
representation of such indemnified parties by the counsel retained by the
indemnifying party would be inappropriate due to actual or potential differing
interests between such indemnified parties and any other party represented by
such counsel in such proceeding. The failure to deliver written notice to the
indemnifying party within a reasonable time of the commencement of any such
action shall not relieve such indemnifying party of any liability to the
indemnified party under this Section 8 except if, and only to the extent that,
the indemnifying party is actually prejudiced thereby; and such failure to
deliver written notice to the indemnifying party will not relieve it of any
liability that it may have to any indemnified party otherwise than under this
Section 8.

            (d) The obligations of the Company and Holders under this Section 8
shall survive the completion of any offering of Registrable Securities in a
registration statement under this Agreement, and otherwise.

            (e) Any indemnity agreements contained herein shall be in addition
to any other rights to indemnification or contribution which any indemnified
party may have pursuant to law or contract and shall remain operative and in
full force and effect regardless of any investigation made or omitted by or on
behalf of any indemnified party.

            (f) If for any reason the foregoing indemnity is unavailable, then
the indemnifying party shall contribute to the amount paid or payable by the
indemnified party as a result of such losses, claims, damages, liabilities or
expenses (i) in such proportion as is appropriate to reflect the relative
benefits received by the indemnifying party on the one hand and the indemnified
party on the other (taking into consideration, among other things, the fact that
the provision of the registration rights and indemnification hereunder is a
material inducement to the Investors to purchase Registrable Securities pursuant
to the Purchase Agreement) or (ii) if the

                                     - 9 -
<PAGE>

allocation provided by clause (i) above is not permitted by applicable law or
provides a lesser sum to the indemnified party than the amount hereinafter
calculated, in such proportion as is appropriate to reflect not only the
relative benefits received by the indemnifying party on the one hand and the
indemnified party on the other (taking into consideration, among other things,
the fact that the provision of the registration rights and indemnification
hereunder is a material inducement to the Investors to purchase Registrable
Securities pursuant to the Purchase Agreement) but also the relative fault of
the indemnifying party and the indemnified party as well as any other relevant
equitable considerations. The relative fault shall be determined by reference
to, among other things, whether the untrue or alleged untrue statement of a
material fact or the omission or alleged omission to state a material fact
relates to information supplied by or on behalf of the indemnifying party or the
indemnified party and the parties' relative intent, knowledge, access to
information and opportunity to correct or prevent such untrue statement or
omission. No Person guilty of fraudulent misrepresentation (within the meaning
of Section 11(f) of the Securities Act) shall be entitled to contribution from
any Person who was not guilty of such fraudulent misrepresentation.
Notwithstanding anything to the contrary in this Section 8, no Holder shall be
required, pursuant to this Section 8, to contribute any amount in excess of the
net proceeds received by such indemnifying party from the sale of Common Stock
in the offering to which the losses, claims, damages, liabilities or expenses of
the indemnified party relate.

            9. Reports Under the Exchange Act. With a view to making available
to the Holders the benefits of Rule 144 under the Securities Act and any other
rule or regulation of the SEC that may at any time permit a Holder to sell
securities of the Company to the public without registration or pursuant to a
registration on Form S-3, the Company agrees to use commercially reasonable
efforts to:

            (a) make and keep public information available, as those terms are
understood and defined in Rule 144 under the Securities Act, at all times after
the effective date of the first registration statement filed by the Company for
the offering of its securities to the general public;

            (b) take such action as is necessary to enable the Holders to
utilize Form S-3 for the sale of their Registrable Securities;

            (c) file with the SEC in a timely manner all reports and other
documents required of the Company under the Securities Act and the Exchange Act;
and

            (d) furnish to any Holder, so long as the Holder owns any
Registrable Securities, forthwith upon request (i) a written statement by the
Company that it has complied with the reporting requirements of Rule 144 under
the Securities Act (at any time after the effective date of the first
registration statement filed by the Company) and the Securities Act and Exchange
Act (at any time after it has become subject to such reporting requirements) or
that it qualifies as a registrant whose securities may be resold pursuant to
Form S-3 (at any time it so qualifies), (ii) a copy of the most recent annual or
quarterly report of the Company and such other reports and documents so filed by
the Company, and (iii) such other information as may be reasonably requested in
availing any Holder of any rule or regulation of the SEC which permits the
selling of any such securities without registration or pursuant to such form.

                                     - 10 -
<PAGE>

            10. Rule 144A Information. During any period in which the Company is
not subject to Section 13 or 15(d) of the Exchange Act, the Company shall make
available information required to be provided by Rule 144A(d)(4), upon request.

            11. Assignment of Registration Rights. The rights to cause the
Company to register Registrable Securities pursuant to this Agreement may be
assigned in whole or in part by a Holder to one or more transferees or assignees
of not less than 1,000,000 shares of Registrable Securities; provided, however,
that (i) such transferee or assignee delivers to the Company a written
instrument by which such transferee or assignee agrees to be bound by the
obligations imposed on Holders under this Agreement to the same extent as if
such transferee or assignee was a party hereto; and (ii) such volume limitation
shall not apply to transferees or assignees who are Affiliates or the transferor
or assignor.

            12. Limitations on Registration Rights. Except as set forth in the
Amended Investor Rights Agreement dated as of July 30, 1999, as amended, the
Company represents and warrants to the Holders that no other "registration
rights" relating to securities of the Company exist on the date hereof. Except
as set forth in the Amended Investor Rights Agreement dated as of July 30, 1999,
as amended, each of the Holders represents to each other Holder that it has no
other "registration rights" relating to securities of the Company as of the date
hereof. From and after the date of this Agreement, the Company shall not,
without the prior written consent of the Holders of a majority of the
outstanding Registrable Securities, enter into any agreement with any holder or
prospective holder of any securities of the Company which would allow such
holder or prospective holder (a) to include such securities in any registration
filed under this Agreement, unless under the terms of such agreement, such
holder or prospective holder may include such securities in any such
registration only to the extent that the inclusion of such holder's securities
will not reduce the amount of the Registrable Securities of the Holders which is
included therein or (b) to request a registration. From and after the date of
this Agreement, the Company shall not, without the prior written consent of the
Holders of a majority of the Series C Stock, enter into any agreement with any
holder or prospective holder of any securities of the Company which would grant
such holder or prospective holder rights superior to those granted hereunder to
the Holders of the Series C Stock. It is understood and agreed that the
registration rights set forth herein apply only to the Common Shares and that
nothing contained herein shall obligate the Company to register any shares of
the Preferred Stock.

            13. "Market Stand-Off" Agreement. Each Holder hereby agrees that, if
requested by an underwriter in connection with an initial underwritten public
offering of the Company's Common Stock, during the period of 180 days following
the effective date of a registration statement of the Company filed under the
Securities Act in connection with such underwritten offering, it shall not, to
the extent requested by the Company and such underwriter, sell or otherwise
transfer or dispose of (other than to donees or partners who agree to be
similarly bound) any Common Stock or any securities of the Company convertible
into Common Stock held by it, except Common Stock included in such registration.
In addition, for a period of 180 days following the consummation of an initial
public offering and for such reasonable amount of time prior to such
consummation as the underwriters may request (collectively, the "Lock-up
Period"), the Company shall use commercially reasonable efforts to require that
during the Lock-Up Period its directors, officers and beneficial owners of five
percent (5%) or more of the Company's securities do not, sell or otherwise
transfer or dispose of (other than to donees or

                                     - 11 -
<PAGE>

partners who agree to be similarly bound) any Common Stock or any securities of
the Company convertible into Common Stock held by it, except Common Stock
included in such registration, without the express written consent of the
underwriters. Notwithstanding the foregoing, the provisions of this Section 13
shall not apply (i) to shares of Common Stock acquired by a Holder in the
Company's initial public offering of Common Stock pursuant to an effective
registration statement filed with the SEC or (ii) to shares of Common Stock
acquired by a Holder in the public market subsequent to the Company's initial
public offering of Common Stock pursuant to an effective registration statement
filed with the SEC.

            14. Amendment Waiver. Any provision of this Agreement may be amended
only with the written consent of the Company and the Holders of a majority of
the Registrable Securities then outstanding (including at least a majority in
interest of the Outside Investors and at least a majority in interest of the
Series C Stock and Common Stock obtained upon conversion thereof and that is
held by the Series C Investors); provided, however, that should an amendment
hereto be detrimental to the interests of the Series C Investors with respect to
their holdings of Series C Stock, such amendment shall required the written
consent of each Series C Investor. The observance of any provision of this
Agreement may be waived (either generally or in a particular instance and either
retroactively or prospectively) only with the written consent of the party to be
charged, provided that the Holders of a majority of the Registrable Securities
then outstanding (including at least a majority in interest of the Outside
Investors) may act on behalf of all such Holders of Registrable Securities. Any
amendment or waiver effected in accordance with this Section 14 shall be binding
upon each Holder of Registrable Securities at the time outstanding, each future
Holder of all such securities, and the Company.

            15. Changes in Registrable Securities. If, and as often as, there
are any changes in the Registrable Securities by way of stock split, stock
dividend, combination or reclassification, or through merger, consolidation,
reorganization or recapitalization, or by any other means, appropriate
adjustment shall be made in the provisions of this Agreement, as may be
required, so that the rights and privileges granted hereby shall continue with
respect to the Registrable Securities as so changed. Without limiting the
generality of the foregoing, the Company will require any successor by merger or
consolidation to assume and agree to be bound by the terms of this Agreement, as
a condition to any such merger or consolidation.

            16. Information. Each of the Outside Investors (and, in the case of
clauses (ii) and (iii) below, each of the Angel Investors) and each of their
respective assignees shall be entitled to receive, and the Company agrees to
provide to each of the Outside Investors (and, in the case of clauses (ii) and
(iii) below, each of the Angel Investors) and each of their respective
assignees, the following:

            (a) Financial and Related Data.

                  (i) As soon as available, but in any event not later than
thirty (30) days after the end of each month, the unaudited balance sheet as at
the end of such month of the Company and the related unaudited statements of
operations, stockholders' equity and cash flows for such month and for the
elapsed period in such fiscal year, all in reasonable detail and stating in
comparative form the figures as of the end of and for the comparable period of
the preceding fiscal year and budgeted figures for the period. All such
financial statements shall be complete

                                     - 12 -
<PAGE>

and correct in all material respects, and shall be accompanied by a certificate
of the President or chief financial officer of the Company to such effect.

                  (ii) As soon as available, but in any event not later than
forty-five (45) days after the end of each fiscal quarter, the unaudited balance
sheet as at the end of such quarter of the Company and the related unaudited
statements of operations, stockholders' equity and cash flows of such quarter
and for the elapsed period of such fiscal year, all in reasonable detail and
stating in comparative form the figures as of the end of and for the comparable
period of the preceding fiscal year and budgeted figures for the period. All
such financial statements shall be complete and correct in all material
respects, and shall be accompanied by a certificate of the President or chief
financial officer of the Company to such effect.

                  (iii) As soon as available, but in any event within ninety
(90) days after the end of each fiscal year of the Company, the audited balance
sheet of the Company as at the end of such fiscal year and the related audited
statements of operations, stockholders' equity and cash flows of the Company for
such fiscal year, all in reasonable detail and stating in comparative form the
figures as at the end of and for the previous fiscal year and budgeted figures
for the fiscal year, accompanied by an opinion of an accounting firm of
nationally recognized standing selected by the Company with respect to such
financial statements, which opinion shall state that such accounting firm's
audit was conducted in accordance with generally accepted auditing standards
and, accordingly, included such tests of accounting records and such other
auditing procedures as were considered necessary under the circumstances. All
such financial statements shall be complete and correct in all material respects
and prepared in reasonable detail and in accordance with GAAP applied, except as
stated therein, on a consistent basis throughout the periods reflected therein.

                  (iv) As soon as available, but in any event not later than
thirty (30) days prior to the end of each fiscal year of the Company, the
financial plan and business plan of the Company for the next succeeding fiscal
year, including but not limited to cash flow and balance sheet projections,
capital budget and operating budget, calculated monthly, and any updates or
revisions as soon as available.

                  (v) Promptly after receipt, copies of all management letters
from accountants and all certificates prepared by or for the Company as to
compliance, defaults, material adverse changes, material litigation or similar
matters, but only to the extent that the delivery thereof would not result in
the loss of any generally recognizable privilege otherwise applicable thereto.

                  (vi) Within fifteen (15) days after the Company obtains
knowledge of the commencement or written threat of commencement of any material
litigation or proceeding against the Company or its assets, written notice by
the Company of the nature and extent of such litigation or proceeding.

                  (vii) Promptly, but in any event within five (5) days, after
any distribution to its stockholders generally or to specific stockholders by
agreement, to its directors, to prospective investors or to the financial
community of an annual report, proxy statement, registration statement or other
similar report or communication, a copy of each such report, proxy

                                     - 13 -
<PAGE>

statement, registration statement or other similar report or communication; and
promptly, but in any event within ten (10) days after any filing with the SEC or
with any national securities exchange or with the National Association of
Securities Dealers, Inc., of any publicly available annual or periodic or
special report or proxy statement or registration statement, a copy of such
report or statement; and promptly, but in any event within two (2) business
days, after released, copies of all press releases and other statements made
available generally by the Company to the public concerning material
developments.

                  (viii) Within sixty (60) days after the end of each fiscal
year, a list of stockholders and other security holders, showing the authorized
and outstanding shares by class (including the common stock equivalents of any
convertible security), the holdings of each stockholder (both before giving
effect to dilution and on a fully-diluted basis) and the holdings of each Person
that holds options, warrants or convertible securities (both before giving
effect to dilution and on a fully diluted basis).

                  (ix) From time to time, and promptly, such additional
information and financial data regarding results of operations, financial
condition, business, affairs or prospects of the Company, which any Investor may
reasonably request.

The obligation of the Company to provide the items required by clauses (v), (vi)
and (viii) shall terminate upon the consummation of an underwritten public
offering by the Company under the Securities Act. Provided that the Company is a
reporting company under the Exchange Act, the obligation of the Company to
provide the items required by the remaining clauses of this Section 14(a) shall
terminate as to any Investor in the event such Investor (1) holds less than 3%
of the outstanding capital stock of the Company (calculated on an as-converted
to common stock basis) or (2) elects by written notice to the Company to
terminate such obligation.

            (b) Access to Properties. The Company shall permit representatives
designated by each Outside Investor, upon reasonable prior notice to the
Company, to visit and inspect each of the Company's properties, to examine its
respective corporate and financial records (and make copies thereof or extracts
therefrom), to discuss its respective affairs, finances and accounts with the
Company's directors and officers, and, through the President or chief financial
officer of the Company, as the case may be, its key employees and accountants,
all at such reasonable times as may be requested by any such Investor.

            17. Termination of Registration Rights. The registration rights of
any Holder provided herein shall terminate if in the written opinion of counsel
for the Company, which counsel and the opinion so rendered shall be reasonably
acceptable to such Holder of Registrable Securities, such Holder may sell
without registration under the Securities Act all Registrable Securities then
held by such Holder under Rule 144 of the Securities Act without regard to
volume limitations.

            18. Legends and Opinions. The Company shall not require an opinion
of counsel for the Holders before (i) authorizing the transfer of shares of
Registrable Securities (A) pursuant to an effective registration statement or
Rule 144 of the Securities Act or (B) in connection with any distributions to
any partner of a Holder or (ii) the removal of securities legends for the
certificates representing such Registrable Securities; provided, however, that
in

                                     - 14 -
<PAGE>

the case of clause (ii), such Holder shall certify to the Company that such
Holder is permitted to sell such Registrable Securities pursuant to Rule 144(k)
of the Securities Act. The foregoing shall not imply that an opinion of counsel
to the Company shall not be required in such circumstances.

            19. Entire Agreement. Each of the Investor Rights Agreement, dated
March 29, 1999, by and among the Company and the parties set forth on the
signature pages thereto, and the Amended and Restated Investor Rights Agreement,
dated as of July 29, 1999, by and among the Company and the parties set forth on
the signature pages thereto, are hereby terminated and each shall be of no
further force or effect. This Agreement constitutes the full and entire
understanding and agreement among the parties with regard to the subject matter
hereof. Nothing in this Agreement, express or implied, is intended to confer
upon any Person, other than the parties hereto and their respective successors
and assigns, any rights, remedies, obligations, or liabilities under or by
reason of this Agreement, except as expressly provided herein.

            20. Governing Law. This Agreement shall be governed in all respects
by the laws of the State of Delaware, exclusive of reference to rules and
principles of conflicts of law.

            21. Successors and Assigns. The provisions hereof shall inure to the
benefit of, and be binding upon, the successors, permitted assigns (as provided
in Section 11), heirs, executors and administrators of the parties hereto;
provided, however, that except as provided in Section 11, this Agreement may
only be assigned in connection with an estate transfer or as otherwise approved
in writing by the directors elected solely by the holders of the Preferred
Stock.

            22. Notices. Unless otherwise provided, any notice required or
permitted under this Agreement shall be given in writing and shall be deemed
effectively given upon receipt by the party to be notified or three (3) days
after deposit with the United States Post Office, by registered or certified
mail, postage prepaid and addressed to the party to be notified (a) if to a
party other than the Company, at such party's address set forth at the end of
this Agreement or at such other address as such party shall have furnished the
Company in writing, or, until any such party so furnishes an address to the
Company, then to and at the address of the last holder of the shares covered by
this Agreement who has so furnished an address to the Company, or (b) if to the
Company, at its address set forth at the end of this Agreement, or at such other
address as the Company shall have furnished to the parties in writing.

            23. Severability. Any invalidity, illegality or limitation on the
enforceability of this Agreement or any part thereof, by any party whether
arising by reason of the law of the respective party's domicile or otherwise,
shall in no way affect or impair the validity, legality or enforceability of
this Agreement with respect to other parties. If any provision of this Agreement
shall be judicially determined to be invalid, illegal or unenforceable, the
validity, legality and enforceability of the remaining provisions shall not in
any way be affected or impaired thereby.

            24. Titles and Subtitles. The titles of the Sections of this
Agreement are for convenience of reference only and are not to be considered in
construing this Agreement.

            25. Delays or Omissions: Remedies Cumulative. It is agreed that no
delay or omission to exercise any right, power or remedy accruing to the
parties, upon any breach or

                                     - 15 -
<PAGE>

default of the Company under this Agreement, shall impair any such right, power
or remedy, nor shall it be construed to be a waiver of any such breach or
default, or any acquiescence therein, or of any similar breach or default
thereafter occurring; nor shall any waiver of any single breach or default be
deemed a waiver of any other breach or default theretofore or thereafter
occurring. It is further agreed that any waiver, permit, consent or approval of
any kind or character by a party of any breach or default under this Agreement,
or any waiver by a party of any provisions or conditions of this Agreement must
be in writing and shall be effective only to the extent specifically set forth
in writing and that all remedies, either under this Agreement, or by law or
otherwise afforded to a party, shall be cumulative and not alternative.

            26. Arbitration. Any controversy or claim arising out of or in
conjunction with this Agreement (other than an action for injunctive relief)
shall be settled by arbitration in accordance with the rules of the American
Arbitration Association then in effect in the State of Delaware and judgment
upon such award rendered by the arbitrator shall be final and binding upon the
parties and may be entered and enforced in any court having jurisdiction
thereof. The arbitration shall be held in the State of Delaware. The arbitration
award shall include attorneys' fees and costs to the prevailing party.

            27. Counterparts. This Agreement may be executed in any number of
counterparts, each of which shall be an original, but all of which together
shall constitute one instrument.

            28. Accession to Agreement. Any person or entity who becomes a party
to the Purchase Agreement as an Additional Investor (as defined therein) shall
become a party to this Agreement by executing a counterpart signature page
hereto, whereupon such person shall become a party to this Agreement for all
purposes hereunder as if such person had been an original signatory.

            29. Aggregation. For purposes of determining the rights exercisable
by a Holder hereunder, all shares of Registrable Securities held by a Series C
Investor and that constitute either Series C Stock or Common Stock obtained upon
the conversion of Series C Stock may be aggregated by the Holder with those
shares of Registrable Securities constituting Series C Stock or Common Stock
obtained upon conversion of Series C Stock beneficially held by Affiliates of
such Holder. For purposes hereof, "Affiliate" shall mean with respect to any
Holder that is a corporation, partnership or other business entity, any of the
stockholders, subsidiaries, officers, directors, members or partners of such
Holder, and any other corporation, partnership or other business entity which
directly or indirectly controls, is controlled by or is under common control
with such Holder. For purposes hereof, the following entities shall be deemed to
be Affiliates of each other: Amerindo Technology Growth Fund II; Matthew
Fitzmaurice; Litton Master Trust; Emeric McDonald; William S. Slattery; James
Stableford; Vertex Capital II, LLC; Sand Brothers Venture Capital LLC; and SB
Necessary Associates LLC. For purposes hereof, the following entities shall be
deemed to be Affiliates of each other: BayStar Capital L.P., BayStar
International Ltd., Wolstar BV and Stichting Wolstar Administratiekantoor.

                                    * * * * *

                                     - 16 -
<PAGE>

            IN WITNESS WHEREOF, the parties hereto have executed this Agreement
as of the day and year first above written.

                                                      Address

ESSENTIAL.COM, INC.                        Three Burlington Woods Drive
                                           Burlington, Massachusetts 01803-4543
By: /s/ Akhil Garland                      Attention:  Akhil Garland, President
    -----------------------                Telephone:  (781) 932-0088
    Name:  Akhil Garland                   Telecopier: (781) 932-6611
    Title: President

                                     - 17 -
<PAGE>

             SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ [ILLEGIBLE]
                                    -----------------------------------------
                                    Signature of Investor

                                    Amerindo Technology Growth Fund II
                                    -----------------------------------------
                                    Printed Name of Investor

                                    Address:
                                             --------------------------------

                                     - 18 -
<PAGE>

             SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Rachel E. Hyman, Manager
                                    -----------------------------------------
                                    Signature of Investor

                                    Aurora Technology Fund LLC
                                    by Aurora Technology Fund Management LLC
                                    by Rachel E. Hyman
                                    -----------------------------------------
                                    Printed Name of Investor

                                             152 W. 57th St., 57th Floor
                                    Address: New York, NY 10019
                                             --------------------------------

                                     - 18 -
<PAGE>

             SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Gregory Bellow
                                    -----------------------------------------
                                    Signature of Investor

                                    Bellow 1984 Trust u/a 11/20/84
                                    By: Gregory Bellow
                                    -----------------------------------------
                                    Printed Name of Investor

                                             775 Hillcrest Way
                                    Address: Redwood City, CA 94062
                                             --------------------------------

                                     - 18 -
<PAGE>

             SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Michael A. Roth
                                    -----------------------------------------
                                    Signature of Investor

                                    BayStar Capital. L.P.
                                    -----------------------------------------
                                    Printed Name of Investor

                                             1500 W. Market St.
                                             Suite 200
                                    Address: Mequon, WI 53092
                                             --------------------------------

                                     - 18 -
<PAGE>

             SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Michael A. Roth
                                    -----------------------------------------
                                    Signature of Investor

                                    BayStar International Ltd.
                                    -----------------------------------------
                                    Printed Name of Investor

                                             1500 W. Market St.
                                             Suite 200
                                    Address: Mequon, WI 53092
                                             --------------------------------

                                     - 18 -
<PAGE>

             SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Robert H. Buescher
                                    -----------------------------------------
                                    Signature of Investor

                                    Bessec Ventures IV LP
                                    By: Deer IV & Co. LLC, General Partner
                                    By: Robert H. Buescher. Manager
                                    -----------------------------------------
                                    Printed Name of Investor

                                    Address:
                                             --------------------------------

                                     - 18 -
<PAGE>

             SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Robert H. Buescher
                                    -----------------------------------------
                                    Signature of Investor

                                    BESSEMER VENTURE PARTNERS IV. L.P.
                                    By: Deer IV & Co. LLC, General Partner
                                    By: Robert H. Buescher, Manager
                                    -----------------------------------------
                                    Printed Name of Investor

                                    Address:
                                             --------------------------------

                                     - 18 -
<PAGE>

             SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                  INVESTOR:

                                  BRAND EQUITY VENTURES I, L.P.
                                  /s/ William Meurer
                                  ----------------------------------------------
                                  Signature of Investor

                                  By: William Meurer, Vice President, Brand
                                  Equity Partners I, L.L.C., its General Partner
                                  ----------------------------------------------
                                  Printed Name of Investor

                                  Address:
                                           -------------------------------------

                                     - 18 -
<PAGE>

             SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Manuel Harrington
                                    -----------------------------------------
                                    Signature of Investor

                                    COMDISCO, INC.
                                    Manuel A. Harrington
                                    -----------------------------------------
                                    Printed Name of Investor

                                             611 North River Road
                                             Rosemont, IL 60018
                                    Address: Attn: Venture Group
                                             --------------------------------

                                     - 18 -
<PAGE>

             SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Hussain Sajwani
                                    -----------------------------------------
                                    Signature of Investor

                                    DAMAC INVESTORS XII INC.
                                    Hussain Sajwani -- Director
                                    -----------------------------------------
                                    Printed Name of Investor

                                             Post Box: 2195
                                    Address: Dubai, UAE
                                             --------------------------------

                                     - 18 -
<PAGE>

             SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                 INVESTOR:

                                 /s/ Hussain Sajwani
                                 -----------------------------------------------
                                 Signature of Investor

                                 DAMAC TECHNOLOGY PARTNERS, LP
                                 Hussain Sajwani -- Director of General Partner
                                 -----------------------------------------------
                                 Printed Name of Investor

                                          Post Box: 2195
                                 Address: Dubai, UAE
                                          -----------------------------------

                                     - 18 -
<PAGE>

             SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Linda DeRenzo
                                    -----------------------------------------
                                    Signature of Investor

                                    Linda DeRenzo
                                    -----------------------------------------
                                    Printed Name of Investor

                                             238 Kenrick Street
                                    Address: Newton, MA 02458
                                             --------------------------------

                                     - 18 -
<PAGE>

             SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Ivy Dodes
                                    -----------------------------------------
                                    Signature of Investor

                                    DLJ ESC II, L.P.
                                    By: DLJ LBO Plans Management Corporation
                                    By: Ivy Dodes, Vice President
                                    -----------------------------------------
                                    Printed Name of Investor

                                             277 Park Avenue, 23rd Floor
                                    Address: New York, NY 10172
                                             --------------------------------

                                     - 18 -
<PAGE>

             SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Ivy Dodes
                                    -----------------------------------------
                                    Signature of Investor

                                    DLJ FUND INVESTMENT PARTNERS II, L.P.
                                    By: DLJ LBO Plans Management Corporation
                                    By: Ivy Dodes, Vice President
                                    -----------------------------------------
                                    Printed Name of Investor

                                             277 Park Avenue, 23rd Floor
                                    Address: New York, NY 10172
                                             --------------------------------

                                     - 18 -
<PAGE>

             SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Ivy Dodes
                                    -----------------------------------------
                                    Signature of Investor

                                    DLJ Private Equity Employees Fund, L.P.
                                    By: DLJ LBO Plans Management Corporation
                                    By: Ivy Dodes, Vice President
                                    -----------------------------------------
                                    Printed Name of Investor

                                             277 Park Avenue, 23rd Floor
                                    Address: New York, NY 10172
                                             --------------------------------

                                     - 18 -
<PAGE>

             SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

       The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Ivy Dodes
                                    -----------------------------------------
                                    Signature of Investor

                                    DLJ Private Equity Partners Fund, L.P.
                                    By: WSW Capital, Inc.
                                    By: Ivy Dodes, Vice President
                                    -----------------------------------------
                                    Printed Name of Investor

                                             277 Park Avenue, 23rd Floor
                                    Address: New York, NY 10172
                                             --------------------------------

                                     - 18 -
<PAGE>

             SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                              INVESTOR:

                              /s/ Scott B. Ungerer
                              --------------------------------------------------
                              Signature of Investor

                              EnerTech Capital Partners, L.P.
                              By: EnerTech Management, L.P., its General Partner
                              By: EnerTech Management Company, L.L.C.,
                                   its General Partner
                              --------------------------------------------------
                              Printed Name of Investor

                              Address:
                                       -------------------------------------

                                     - 18 -
<PAGE>

             SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                              INVESTOR:

                              /s/ Scott B. Ungerer
                              --------------------------------------------------
                              Signature of Investor

                              EnerTech Capital Partners II, L.P.
                              By: ECP II Management, L.P., its General Partner
                              By: ECP II Management, L.L.C., its General Partner
                              --------------------------------------------------
                              Printed Name of Investor

                              Address:
                                       -------------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Matthew O. Fitzmaurice
                                    ----------------------------------------
                                    Signature of Investor

                                    Matthew O. Fitzmaurice
                                    ----------------------------------------
                                    Printed Name of Investor

                                             130 West Lake Street
                                    Address: Wayzata, MN 55391
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Marie Paulette Galliker
                                    ----------------------------------------
                                    Signature of Investor

                                    Marie Paulette Galliker
                                    ----------------------------------------
                                    Printed Name of Investor

                                             14 Ship Pasture Way
                                    Address: E. Sandwich, MA 02537
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Thomas C. O'Laughlin
                                    ----------------------------------------
                                    Signature of Investor

                                    Gas Research Institute
                                    ----------------------------------------
                                    Printed Name of Investor

                                             8600 West Bryn Mawr Avenue
                                    Address: Chicago, IL 60631
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                   INVESTOR:

                                   /s/ Eric J. Hall
                                   ---------------------------------------------
                                   Signature of Investor

                                   Robert Hall, Eric Hall & William Hall, JTWROS
                                   ---------------------------------------------
                                   Printed Name of Investor

                                            183 State Street
                                   Address: Boston, MA 02109
                                            ------------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                   INVESTOR:

                                   /s/ Robert A. Hall
                                   ---------------------------------------------
                                   Signature of Investor

                                   Robert Hall, Eric Hall & William Hall, JTWROS
                                   ---------------------------------------------
                                   Printed Name of Investor

                                            183 State Street
                                   Address: Boston, MA 02109
                                            ------------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                   INVESTOR:

                                   /s/ William J. Hall
                                   ---------------------------------------------
                                   Signature of Investor

                                   Robert Hall, Eric Hall & William Hall, JTWROS
                                   ---------------------------------------------
                                   Printed Name of Investor

                                            183 State Street
                                   Address: Boston, MA 02109
                                            ------------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ George W. Thibeault
                                    ----------------------------------------
                                    Signature of Investor

                                    HIGH STREET INVESTORS 2000
                                    By: Testa, Hurwitz & Thibeault, LLP
                                    By: George W. Thibeault, Partner
                                    ----------------------------------------
                                    Printed Name of Investor

                                             125 High Street
                                    Address: Boston, MA 02110
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Michael B. Kolowich
                                    ----------------------------------------
                                    Signature of Investor

                                    Michael E. Kolowich
                                    ----------------------------------------
                                    Printed Name of Investor

                                             116 Monument Street
                                    Address: Concord, MA 01742
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Edmund W. Lang
                                    ----------------------------------------
                                    Signature of Investor

                                    Edmund W. Lang
                                    ----------------------------------------
                                    Printed Name of Investor

                                             5 Tabor Hill Road
                                    Address: Lincoln, MA 01773
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Ilene H. Lang
                                    ----------------------------------------
                                    Signature of Investor

                                    Ilene H. Lang
                                    ----------------------------------------
                                    Printed Name of Investor

                                             78 Jason Street
                                    Address: Arlington, MA 02476
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    [ILLEGIBLE]
                                    ----------------------------------------
                                    Signature of Investor

                                    Litton Master Trust
                                    ----------------------------------------
                                    Printed Name of Investor

                                    Address:
                                            --------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Emeric J. McDonald
                                    ----------------------------------------
                                    Signature of Investor

                                    Emeric J. McDonald
                                    ----------------------------------------
                                    Printed Name of Investor

                                             707 Continental Circle, #431
                                    Address: Mt. View, CA 94040
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Robert W. Driscoll, Jr.
                                    ----------------------------------------
                                    Signature of Investor

                                    Mellon Ventures II, L.P.
                                    By MVMA II, L.P., its General Partner
                                    By MVMA, Inc. its General Partner
                                    ----------------------------------------
                                    Printed Name of Investor

                                             Mellon Ventures, Inc.
                                             Five Radnor Corporate Center
                                             100 Matsonford Road, Suite 170
                                    Address: Radner, PA 19087
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Norman C. Nicholson
                                    ----------------------------------------
                                    Signature of Investor

                                    Norman C. Nicholson
                                    ----------------------------------------
                                    Printed Name of Investor

                                    Address:
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/[ILLEGIBLE], EVP & CFO
                                    ----------------------------------------
                                    Signature of Investor

                                    Rare Medium Group, Inc.
                                    ----------------------------------------
                                    Printed Name of Investor

                                    Address:
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Pamela Stone Ryan
                                    ----------------------------------------
                                    Signature of Investor

                                    Pamela Stone Ryan
                                    ----------------------------------------
                                    Printed Name of Investor

                                    Address:
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Martin Sands
                                    ----------------------------------------
                                    Signature of Investor

                                    Sands Brothers Venture Capital LLC
                                    By: SB Venture Capital Management LLC
                                    By: Martin Sands, Manager
                                    ----------------------------------------
                                    Printed Name of Investor

                                             c/o Sands Brothers
                                             90 Park Avenue, 39th Floor
                                    Address: New York, New York 10016
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Martin Sands
                                    ----------------------------------------
                                    Signature of Investor

                                    SB Necessary Associates LLC
                                    By: SB Necessary Management Associates LLC
                                    By: Martin Sands, Manager
                                    ----------------------------------------
                                    Printed Name of Investor

                                             c/o Sands Brothers
                                             90 Park Avenue, 39th Floor
                                    Address: New York, New York 10016
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Abdullah Mosa'ad Abdulaziz
                                    ----------------------------------------
                                    Signature of Investor

                                    Saudi Paper Manufacturing Company, Ltd.
                                    Abdullah Mosa'ad Abdulaziz, Chairman
                                    ----------------------------------------
                                    Printed Name of Investor

                                             P.O. Box 55375
                                    Address: Riyadh 11534, K.S.A
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ William S. Slattery
                                    ----------------------------------------
                                    Signature of Investor

                                    William S. Slattery
                                    ----------------------------------------
                                    Printed Name of Investor

                                    Address:
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ James Stableford
                                    ----------------------------------------
                                    Signature of Investor

                                    James Stableford
                                    ----------------------------------------
                                    Printed Name of Investor

                                    Address:
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ William A. Stone
                                    ----------------------------------------
                                    Signature of Investor

                                    William A. Stone
                                    ----------------------------------------
                                    Printed Name of Investor

                                             5208 Indian Woods Ct.
                                    Address: Louisville, KY 40207
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ James W. Storey
                                    ----------------------------------------
                                    Signature of Investor

                                    James W. Storey
                                    ----------------------------------------
                                    Printed Name of Investor

                                    Address:
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Scott D. Sullivan
                                    ----------------------------------------
                                    Signature of Investor

                                    Scott D. Sullivan
                                    ----------------------------------------
                                    Printed Name of Investor

                                             6318 Woodbury Road
                                    Address: Boca Raton, FL 33433
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Brad Rudderman
                                    ----------------------------------------
                                    Signature of Investor

                                    Talon Ventures Two, LLC
                                    ----------------------------------------
                                    Printed Name of Investor

                                             9440 Santa Monica Blvd, #600
                                    Address: Beverly Hills, CA 90210
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Matthew O. Fitzmaurice
                                    ----------------------------------------
                                    Signature of Investor

                                    Vertex Capital II, L.L.C.
                                    By: Matthew O. Fitzmaurice, Manager
                                    ----------------------------------------
                                    Printed Name of Investor

                                             Attn: Matthew O. Fitzmaurice
                                             130 West Lake Street
                                    Address: Wayzata, MN 55391
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Brooks Whitehouse, Jr.
                                    ----------------------------------------
                                    Signature of Investor

                                    Brooks Whitehouse, Jr.
                                    ----------------------------------------
                                    Printed Name of Investor

                                             74 Gates Street
                                    Address: Portsmouth, NH 03801
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Maurice Wyatt
                                    ----------------------------------------
                                    Signature of Investor

                                    Maurice Wyatt
                                    ----------------------------------------
                                    Printed Name of Investor

                                             7 Bertwell Ct.
                                    Address: Timonium, MD 21093
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Henry M. Zachs
                                    ----------------------------------------
                                    Signature of Investor

                                    Henry M. Zachs
                                    ----------------------------------------
                                    Printed Name of Investor

                                             40 Woodland Street
                                    Address: Hartford, CT 06105
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Henry M. Zachs
                                    ----------------------------------------
                                    Signature of Investor

                                    Zafa II LLC
                                    Henry M. Zachs
                                    ----------------------------------------
                                    Printed Name of Investor

                                             40 Woodland Street
                                    Address: Hartford, CT 06105
                                             -------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                    INVESTOR:

                                    /s/ Kevin Cannon
                                    ------------------------------------------
                                    Signature of Investor

                                    Kevin Cannon, CEO Zweig-Dimenna
                                    International, Managers, Inc., Investment
                                    Manager of Zweia-Dimenna International Ltd
                                    ------------------------------------------
                                    Printed Name of Investor

                                             Zweig-Dimenna International Ltd
                                             c/o Zwieg-Dimenna International
                                                 Managers, Inc.
                                             900 Third Avenue
                                    Address: New York, New York 10022
                                             ---------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                 INVESTOR:

                                 /s/ Kevin Cannon
                                 -----------------------------------------------
                                 Signature of Investor

                                 Kevin Cannon, CEO, Zweig-Dimenna Assoc. LLC
                                 General Partner of Zweig-Dimenna Investors, L.P
                                 -----------------------------------------------
                                 Printed Name of Investor

                                          Zweig-Dimenna Investors, L.P.
                                          900 Third Avenue
                                 Address: New York, New York 10022
                                          --------------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                 INVESTOR:

                                 /s/ Kevin Cannon
                                 -----------------------------------------------
                                 Signature of Investor

                                 Kevin Cannon, CEO, Zweig-Dimenna Assoc. LLC
                                 General Partner of Zweig-Dimenna Partners, L.P.
                                 -----------------------------------------------
                                 Printed Name of Investor

                                          Zweig-Dimenna Partners, L.P.
                                          900 Third Avenue
                                 Address: New York, NY 10022
                                          --------------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                                   INVESTOR:

                                   /s/ Kevin Cannon
                                   ---------------------------------------------
                                   Signature of Investor

                                   Kevin Cannon, CEO, Zweig-Dimenna Assoc. LLC
                                   General Partner of Zweig-Dimenna Select, L.P.
                                   ---------------------------------------------
                                   Printed Name of Investor

                                            Zweig-Dimenna Select, L.P.
                                            900 Third Avenue
                                   Address: New York, NY 10022
                                            ------------------------------------

                                     - 18 -
<PAGE>

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                                 SIGNATURE PAGE

      The undersigned hereby (a) executes that certain Second Amended and
Restated Investor Rights Agreement dated as of the date first above written (the
"Investor Rights Agreement") by and among essential.com, inc. and the Investors
named in Schedule I thereto, (b) agrees to become a party to and be bound as an
"Investor" under such Investor Rights Agreement, and (c) authorizes this
signature page to be attached as a counterpart signature page to such Investor
Rights Agreement.

                               INVESTOR:

                               /s/ Kevin Cannon
                               -------------------------------------------------
                               Signature of Investor

                               Kevin Cannon, CEO, Zweig-Dimenna Assoc. LLC
                               General Partner of
                               Zweig-Dimenna Special Opportunities, L.P.
                               -------------------------------------------------
                               Printed Name of Investor

                                        Zweig-Dimenna Special Opportunities, L.P
                                        900 Third Avenue
                               Address: New York, NY 10022
                                        ----------------------------------------

                                     - 18 -
<PAGE>

                                   SCHEDULE I

Angel Investors

Bellow 1984 Trust u/a 11/20/84
Linda DeRenzo
Marie Paulette Galliker
Robert A. Hall, Eric J. Hall & William J. Hall, JTWROS
Michael E. Kolowich
Edmund W. Lang
Ilene H. Lang
David J. Mushlitz
Mark C. Nicholson
Norman C. Nicholson, Jr.
Pamela Stone Ryan
William A. Stone
James W. Storey
Brooks Whitehouse, Jr.
Maurice R. Wyatt, Sr.
Henry Zachs

Existing Outside Investors

EnerTech Capital Partners, L.P.
Bessemer Venture Partners IV L.P.
Bessec Venture Partners IV L.P.
Brand Equity Ventures I, L.P.
Comdisco, Inc.
Gas Research Institute
Zafa II, LLC

Series C Investors

Amerindo Technology Growth Fund II
Aurora Technology Fund II LLC
BayStar Capital L.P.
Bessec Ventures IV L.P.
Bessemer Venture Partners IV L.P.
Brand Equity Ventures I, L.P.
Comdisco, Inc.
Damac Investors XII Inc.
Damac Technology Partners, L.P.
DLJ ESC II, L.P.

                                     - 19 -
<PAGE>

DLJ Investment Partners II, L.P.
DLJ Private Equity Employees Fund, L.P.
DLJ Private Equity Partners Fund, L.P.
EnerTech Capital Partners II, L.P.
Matthew Fitzmaurice
High Street Investors
Litton Master Trust
Emeric McDonald
Mellon Ventures II, L.P.
Rare Medium Group Inc.
Sands Brothers Venture Capital LLC
Saudi Paper Manufacturing Company Ltd.
SB Necessary Associates LLC
William Slattery
James Stableford
Scott Sullivan
Talon Ventures Two, LLC
Vertex Capital II, LLC
Zweig-Dimenna International Ltd.
Zweig-Dimenna Investors, L.P.
Zweig-Dimenna Partners, L.P.
Zweig-Dimenna Select, L.P.
Zweig-Dimenna Special Opportunities, L.P.

                                     - 20 -
<PAGE>

                                   SCHEDULE II

                               essential.com, inc.

              SECOND AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                             INSTRUMENT OF ACCESSION

      The undersigned, __________________, as a condition precedent to becoming
the owner or holder of record of _____________________ (_______) shares of the
Series C Convertible Preferred Stock, par value $.01 per share, of
essential.com, inc., a Delaware corporation (the "Company"), hereby agrees to
become party to and bound by that certain Second Amended and Restated Investor
Rights Agreement, dated as of February 8, 2000, by and among the Company and
other stockholders of the Company as a Series C Investor. This Instrument of
Accession shall take effect and shall become an integral part of the said
Investor Rights Agreement immediately upon execution and delivery to the Company
of this Instrument.

      IN WITNESS WHEREOF, this INSTRUMENT OF ACCESSION has been duly executed by
or on behalf of the undersigned, as a sealed instrument under the laws of the
State of Delaware, as of the date below written.

                              Name:___________________________________

                              By:____________________________
                                 Name of Signator:
                                 Title (If Applicable):

                              Address:
                              ________________________________________
                              ________________________________________
                              ________________________________________

                              Date: __________________________________

                              Accepted:

                              essential.com, inc.

                              By:_____________________________________
                                Name:_________________________________
                                Title:________________________________

                              Date:___________________________________

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