Document:

<PAGE>   1
                                                                    Exhibit 10.1

Certain Confidential Information contained in this document has been omitted and
filed separately with the Securities and Exchange Commission.

                              AMENDED AND RESTATED

                             COLLABORATION AGREEMENT

                                      among

                          GELTEX PHARMACEUTICALS, INC.,

                               GENZYME CORPORATION

                                       and

                                   RENAGEL LLC

                            dated as of April 1, 2000

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                                TABLE OF CONTENTS

<TABLE>

<S>                                                                                                              <C>
ARTICLE 1.  DEFINITIONS...........................................................................................1
         1.1.     "Abbott Agreement"..............................................................................1
         1.2.     "Affiliate".....................................................................................1
         1.3.     "Chugai Agreement"..............................................................................2
         1.4.     "Chugai Territory"..............................................................................2
         1.5.     "Collaboration Product".........................................................................2
         1.6.     "Commercialization Costs".......................................................................2
         1.7.     "Commercialization Plan"........................................................................2
         1.8.     "Development Costs".............................................................................2
         1.9.     "Development Plan" .............................................................................3
         1.10.    "Development Program" ..........................................................................3
         1.11.    "Distribution Margin"...........................................................................3
         1.12.    "Distributor's Discount"........................................................................3
         1.13.    "Dow Agreement" ................................................................................4
         1.14.    "Dow Research Agreement" .......................................................................4
         1.15.    "Effective Date"................................................................................4
         1.16.    "Estimated Net Selling Price"...................................................................4
         1.17.    "Field".........................................................................................4
         1.18.    "FDA"...........................................................................................4
         1.19.    "Fully Absorbed Cost of Goods"..................................................................4
         1.20.    "GAAP"..........................................................................................5
         1.21.    "GelTex Companies"..............................................................................5
         1.22.    "GelTex Patent Rights"..........................................................................5
         1.23.    "GelTex Technology".............................................................................5
         1.24.    "Genzyme Patent Rights".........................................................................5
         1.25.    "Genzyme Technology"............................................................................6
         1.26.    "Major Market Countries"........................................................................6
         1.27.    "Manufacturing Know-how"........................................................................6
         1.28.    "Member"........................................................................................6
         1.29.    "NDA"...........................................................................................6
         1.30.    "Net Profit"....................................................................................6
         1.31.    "Net Sales".....................................................................................6
         1.32.    "Nittobo License"...............................................................................7
         1.33.    "Operating Agreement"...........................................................................7
         1.34.    "Patent Rights".................................................................................7
         1.35.    "Program".......................................................................................7
         1.36.    "Program Costs".................................................................................7
         1.37.    "Program Management Team".......................................................................7
         1.38.    "Purchase Agreement"............................................................................7
         1.39.    "Regulatory Approvals"..........................................................................7
         1.40.    "Regulatory Scheme".............................................................................8
         1.41.    "Specifications"................................................................................8
</TABLE>

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<TABLE>

<S>                                                                                                              <C>
         1.42.    "Steering Committee"............................................................................8
         1.43.    "Technology"....................................................................................8
         1.44.    "Territory".....................................................................................8
         1.45.    "Third Party"...................................................................................8
         1.46.    "Wholesale Acquisition Cost"....................................................................8

ARTICLE 2.  SCOPE AND STRUCTURE OF THE COLLABORATION..............................................................8
         2.1.     General.........................................................................................8
         2.2.     Exclusive Relationship..........................................................................9
         2.3.     Chugai Agreement................................................................................9
         2.4.     Nittobo License................................................................................10

ARTICLE 3.  GRANTS AND RESERVATIONS OF RIGHTS....................................................................10
         3.1.     Assignments and Licenses to RenaGel LLC........................................................10
                  3.1.1.   Grants from GelTex....................................................................10
                  3.1.2.   Grants from Genzyme...................................................................10
                  3.1.3.   Technology or Patent Rights Developed Outside the Program.............................11
                  3.1.4.   RenaGel LLC Undertakings; Sublicenses.................................................11
         3.2.     Licenses of Rights from RenaGel LLC to GelTex and Genzyme......................................11
         3.3.     Reservation of Rights..........................................................................12

ARTICLE 4.   EQUITY INVESTMENTS; PROGRAM FUNDING.................................................................12
         4.1.     Equity Investments. ...........................................................................12
         4.2.     Program Funding Commitment.....................................................................12
         4.3.     Program Funding Capital Contributions..........................................................13
                  4.3.1.   Initial Capital Contributions.........................................................13
                  4.3.2.   Monthly Capital Contributions.........................................................13
                  4.3.3.   Quarterly Statements; Quarterly Reconciliation........................................13
         4.4.     Distributions..................................................................................13
         4.5.     Books of Account; Audit. ......................................................................14

ARTICLE 5.   THE DEVELOPMENT PROGRAM.............................................................................14
         5.1.     Conduct of the Development Program.............................................................14
                  5.1.1.   General...............................................................................14
                  5.1.2.   Development Plan......................................................................14
                  5.1.3.   Initial and Updated Development Plan..................................................15
                  5.1.4.   Execution and Performance.............................................................15
                  5.1.5.   Attendance at Regulatory Meetings.....................................................15
         5.2.     Development Information........................................................................16
                  5.2.1.   Reports and Information Exchange......................................................16
                  5.2.2.   Adverse Reaction Reporting............................................................16
                  5.2.3.   Clinical and Regulatory Audits........................................................16
         5.3.     Regulatory Approval Filings....................................................................16
         5.4.     Facilities Visits..............................................................................17
</TABLE>

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<TABLE>

<S>                                                                                                              <C>
ARTICLE 6.   SALES, MARKETING AND ADMINISTRATIVE SERVICES........................................................17
         6.1.     Commercialization Plans........................................................................17
                  6.1.1.   General...............................................................................17
                  6.1.2.   Initial and Updated Commercialization Plans...........................................17
         6.2.     Exclusive Distributorship......................................................................17
         6.3.     Orders and Forecasting.........................................................................18
         6.4.     Prices and Payment Terms; Costs................................................................18
                  6.4.1.   Prices................................................................................18
                  6.4.2.   Terms of Payment......................................................................18
                  6.4.3.   Marketing and Distribution Expenses...................................................18
         6.5.     Marketing Service..............................................................................18
                  6.5.1.   Exclusive Engagement..................................................................18
                  6.5.2.   Responsibilities of Genzyme...........................................................18
         6.6.     Responsibilities of RenaGel LLC and GelTex.....................................................20
         6.7.     General and Administrative Services............................................................20

ARTICLE 7.  MANUFACTURE AND SUPPLY...............................................................................20
         7.1.     Process Development; Manufacturing Approvals...................................................20
         7.2.     Manufacture and Supply of Collaboration Products...............................................21
                  7.2.1.   General...............................................................................21
                  7.2.2.   Forecasts.............................................................................21
         7.3.     Certificates of Analysis.......................................................................21
         7.4.     Certificates of Manufacturing Compliance.......................................................22
         7.5.     Manufacture and Supply of Starting Material....................................................22
         7.6.     Access to Facilities...........................................................................22

ARTICLE 8.  MANAGEMENT...........................................................................................23
         8.1.     Program Management Team........................................................................23
                  8.1.1.   General...............................................................................23
                  8.1.2.   Development Program Functions.........................................................23
                  8.1.3.   Commercialization Functions...........................................................23
                  8.1.4.   Minutes...............................................................................23
         8.2.     Steering Committee.............................................................................24
                  8.2.1.   General...............................................................................24
                  8.2.2.   Functions.............................................................................24
                  8.2.3.   Minutes...............................................................................24
         8.3.     General Disagreements..........................................................................25

ARTICLE 9.  INTELLECTUAL PROPERTY RIGHTS.........................................................................25
         9.1.     Ownership......................................................................................25
                  9.1.1.   Ownership of Discoveries and Improvements.............................................25
                  9.1.2.   Ownership of Trademarks...............................................................26
                  9.1.3.  Cooperation of Employees...............................................................26
</TABLE>

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<TABLE>

<S>                                                                                                              <C>
         9.2.     Filing, Prosecution and Maintenance of Patent Rights...........................................26
                  9.2.1.  Filing, Prosecution and Maintenance....................................................26
                  9.2.2.   Patent Filing Costs...................................................................26
         9.3.     Cooperation....................................................................................26
         9.4.     Notification of Patent Term Restoration........................................................27
         9.5.     No Other Technology Rights.....................................................................27
         9.6.     Enforcement of Patent Rights; Defense of Infringement Actions..................................27
                  9.6.1.   First Right to Respond................................................................27
                  9.6.2.   Sharing of Litigation and Settlement Expenses.........................................27
                  9.6.3.   Second Right to Respond...............................................................28

ARTICLE 10.  CONFIDENTIALITY.....................................................................................28
         10.1.    Nondisclosure Obligations......................................................................28
         10.2.    Terms of this Agreement........................................................................29
         10.3.    Publications...................................................................................29

ARTICLE 11.  REPRESENTATIONS AND WARRANTIES......................................................................30
         11.1.    Authorization..................................................................................30
         11.2.    Intellectual Property Rights...................................................................30
         11.3.    Warranties.....................................................................................30
                  11.3.1. Genzyme Warranties.....................................................................30
                  11.3.2. RenaGel LLC Warranties.................................................................31
                  11.3.3. GelTex Warranties......................................................................31
         11.4.    Disclaimer of Representations and Warranties...................................................31
         11.5.    Limitation of Liability........................................................................31

ARTICLE 12.  INDEMNITY...........................................................................................32
         12.1.    RenaGel LLC Indemnity Obligations..............................................................32
         12.2.    Insurance......................................................................................32

ARTICLE 13.  TERM AND TERMINATION................................................................................32
         13.1.    Term...........................................................................................32
         13.2.    Termination....................................................................................32
                  13.2.1. For Certain Material Breaches..........................................................32
                  13.2.2. For Failure to Make a Milestone Payment................................................33
                  13.2.3. For Convenience........................................................................33
                  13.2.4. [Intentionally Omitted]................................................................33
                  13.2.5. Upon Bankruptcy........................................................................33
         13.3.    Effects of Termination.........................................................................34
                  13.3.1. For Certain Material Breaches..........................................................34
                  13.3.2. For Failure to Make a Milestone Payment................................................35
                  13.3.3. For Convenience........................................................................36
                  13.3.4. [Intentionally Omitted]................................................................37
                  13.3.5. Upon Bankruptcy........................................................................38
</TABLE>

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<TABLE>

<S>                                                                                                              <C>
                  13.3.6. Fair Value.............................................................................39
         13.4.    Inventory......................................................................................39
         13.5.    Survival of Rights and Duties..................................................................40

ARTICLE 14.  MISCELLANEOUS.......................................................................................40
         14.1.    Cooperation....................................................................................40
         14.2.    Exchange Controls..............................................................................40
         14.3.    Withholding Taxes..............................................................................40
         14.4.    Interest on Late Payments......................................................................40
         14.5.    Force Majeure..................................................................................41
         14.6.    Assignment.....................................................................................41
         14.7.    Severability...................................................................................41
         14.8.    Notices........................................................................................41
         14.9.    Applicable Law.................................................................................43
         14.10.   Arbitration....................................................................................43
                  14.10.1. General...............................................................................43
                  14.10.2. Procedure.............................................................................43
         14.11.   Entire Agreement...............................................................................44
         14.12.   Headings.......................................................................................44
         14.13.   Independent Contractors........................................................................44
         14.14.   Waivers........................................................................................44
         14.15.   Counterparts...................................................................................44

Appendix A - Form of Press Release...............................................................................47
</TABLE>

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<PAGE>   7

                              AMENDED AND RESTATED

                             COLLABORATION AGREEMENT

     THIS AMENDED AND RESTATED COLLABORATION AGREEMENT dated as of April 1, 2000
(the "AGREEMENT") is made by and among GelTex Pharmaceuticals, Inc., a Delaware
corporation having its principal place of business at 153 Second Avenue,
Waltham, Massachusetts 02451 ("GELTEX"), Genzyme Corporation, a Massachusetts
corporation having its principal place of business at One Kendall Square,
Cambridge, Massachusetts 02139 ("GENZYME"), and RenaGel LLC, a Delaware limited
liability company having its principal place of business at 153 Second Avenue,
Waltham, Massachusetts 02451 ("RENAGEL LLC"). GelTex, Genzyme and RenaGel LLC
are sometimes referred to herein individually as a "PARTY" and collectively as
the "PARTIES." This Agreement amends and restates the Collaboration Agreement
dated as of June 17, 1997 entered into by and among GelTex, Genzyme and RenaGel
LLC, as amended.

                                 R E C I T A L S

     WHEREAS, GelTex is currently developing RenaGel(R) non-absorbed phosphate
binder, an orally administered hydrogel intended to control hyperphosphatemia in
patients with chronic kidney failure; and

     WHEREAS, Genzyme has expertise in the areas of development and marketing of
bio-pharmaceutical products; and

     WHEREAS, RenaGel LLC has been organized by GelTex for use as the vehicle
for a joint venture between GelTex and Genzyme to develop and commercialize the
Collaboration Products (as defined herein) throughout the world (excluding the
Chugai Territory (as defined herein)).

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

                             ARTICLE 1. DEFINITIONS

     For purposes of this Agreement, the terms defined in this Article shall
have the meanings specified below. Certain other capitalized terms are defined
elsewhere in this Agreement.

     1.1. "ABBOTT AGREEMENT" shall mean the Development Agreement dated November
21, 1995 by and between GelTex and Abbott Laboratories ("ABBOTT").

     1.2. "AFFILIATE" shall mean any corporation or other entity which controls,
is controlled by, or is under common control with a Party. A corporation or
other entity shall be regarded as in

<PAGE>   8

control of another corporation or entity if it owns or directly or indirectly
controls more than fifty percent (50%) of the voting stock or other ownership
interest of the other corporation or entity, or if it possesses, directly or
indirectly, the power to direct or cause the direction of the management and
policies of the corporation or other entity or the power to elect or appoint
more than fifty percent (50%) of the members of the governing body of the
corporation or other entity.

     1.3. "CHUGAI AGREEMENT" shall mean the License Agreement dated as of
December 26, 1994 by and between GelTex and Chugai Pharmaceutical Co. Ltd.
("CHUGAI"), as in effect as of the Effective Date.

     1.4. "CHUGAI TERRITORY" shall mean Japan, Taiwan, South Korea, Peoples
Republic of China, Singapore, Malaysia, India, Thailand, Vietnam, Indonesia,
Philippines, New Zealand and Australia.

     1.5. "COLLABORATION PRODUCT" shall mean any product developed for use in
the Field by a Party utilizing, based upon or arising out of the GelTex Patent
Rights, the Genzyme Patent Rights, the GelTex Technology, the Genzyme Technology
or the Manufacturing Know-How owned or controlled by any Party, including
without limitation RenaGel(R) non-absorbed phosphate binder ("RENAGEL(R)") and
any and all improvements, combination products, delivery systems and dosage
forms related thereto.

     1.6. "COMMERCIALIZATION COSTS" with respect to a Collaboration Product
shall mean the direct variable costs and direct fixed costs incurred by RenaGel
LLC with respect to work performed by the Parties and their Affiliates and
subcontractors in connection with the conduct of the Commercialization Plan for
such Collaboration Product, including without limitation sales and marketing
costs related to performing market research, advertising, producing promotional
literature, sponsoring seminars and symposia, originating sales and providing
reimbursement and other patient support services, and distribution costs. For
purposes of this Section 1.6, "DIRECT VARIABLE COSTS" shall be deemed to be the
cost of labor, raw materials, supplies and other resources directly consumed in
the conduct of the Commercialization Plan. For purposes of this Section 1.6,
"DIRECT FIXED COSTS" shall be deemed to be the cost of facilities, utilities,
insurance, equipment depreciation and other fixed costs directly related to the
conduct of the Commercialization Plan, allocated based upon the proportion of
such costs directly attributable to support of the Commercialization Plan or by
such other method of cost allocation as may be approved by the Steering
Committee. All cost determinations made hereunder shall be made in accordance
with GAAP.

     1.7. "COMMERCIALIZATION PLAN" shall mean the comprehensive plan for the
commercialization of a Collaboration Product, as more specifically described in
Section 6.1.1 hereof.

     1.8. "DEVELOPMENT COSTS" with respect to a Collaboration Product shall mean
the direct variable costs and direct fixed costs incurred by RenaGel LLC on or
after the Effective

                                       2

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Date with respect to work performed by the Parties and their Affiliates and
subcontractors in connection with the conduct of the Development Plan for such
Collaboration Product, including without limitation (a) direct, out-of-pocket
external costs, including clinical grants, clinical laboratory fees, positive
controls and the cost of studies conducted and services provided by contract
research organizations and individuals, consultants, toxicology contractors and
manufacturers necessary or useful for the purpose of obtaining Regulatory
Approvals for such Collaboration Product, (b) amounts paid to GelTex and Genzyme
by RenaGel LLC in respect of research and development and pre-commercialization
sales and marketing efforts as set forth in the Development Plan for such
Collaboration Product, (c) amounts paid to contract manufacturers to develop a
process for the manufacture of such Collaboration Product (including amounts
payable to Dow Chemical after the Effective Date pursuant to the Dow Research
Agreement) and for FDA qualification efforts and amounts payable to Abbott
pursuant to the Abbott Agreement after the Effective Date, (d) amounts paid to
purchase capital equipment used to manufacture such Collaboration Product
(including amounts payable to Dow Chemical after the Effective Date pursuant to
the Dow Agreement) and the Fully Absorbed Cost of Goods for batches of such
Collaboration Product manufactured and supplied for use in pre-clinical and
clinical trials, (e) costs related to data management, statistical designs and
studies, document preparation and other expenses associated with the clinical
testing program for such Collaboration Product and (f) costs for preparing,
submitting, reviewing or developing data or information for the purpose of
submission of applications to obtain Regulatory Approvals for such Collaboration
Product. For purposes of this Section 1.8, "DIRECT VARIABLE COSTS" shall be
deemed to be the cost of labor, raw materials, supplies and other resources
directly consumed in the conduct of the Development Program. For purposes of
this Section 1.8, "DIRECT FIXED COSTS" shall be deemed to be the cost of
facilities, utilities, insurance, equipment depreciation and other fixed costs
directly related to the conduct of the Development Program, allocated based upon
the proportion of such costs directly attributable to support of the Development
Program or by such other method of cost allocation as may be approved by the
Steering Committee. All cost determinations made hereunder shall be made in
accordance with GAAP.

     1.9. "DEVELOPMENT PLAN" shall mean the comprehensive plan and budget for
the development of a Collaboration Product under the Development Program, as
more specifically described in Section 5.1.2 hereof.

     1.10. "DEVELOPMENT PROGRAM" shall mean the pre-clinical and clinical
development of Collaboration Products, including the preparation and filing of
all applications for Regulatory Approvals for each Collaboration Product.

     1.11. "DISTRIBUTION MARGIN" with respect to Net Sales of a Collaboration
Product shall mean the amount of the Distributor's Discount PLUS the amount by
which Genzyme's actual selling price exceeds the Estimated Net Selling Price OR,
if Genzyme's actual selling price is less than the Estimated Net Selling Price
for such Collaboration Product, MINUS the amount of such difference. "Genzyme's
actual selling price shall be Genzyme's gross invoiced sales price billed to
customers reduced to reflect any amounts incurred resulting from any rebates,
charge backs or

                                       3

<PAGE>   10

refunds subsequently allowed and taken.

     1.12. "DISTRIBUTOR'S DISCOUNT" shall mean the dollar amount per unit of
Collaboration Product fixed by the Steering Committee as a discount from the
Estimated Net Selling Price at which Genzyme purchases such Collaboration
Product from RenaGel LLC. In the event that RenaGel LLC does not have sufficient
items of gross income to allocate to the GelTex Companies in accordance with
Section 5.2(b) of the Operating Agreement with respect to any two consecutive
calendar quarters, the Steering Committee shall adjust the Distributor's
Discount to ensure, to the extent possible, that for future calendar quarters
the GelTex Companies will receive an allocation of items of gross income and a
subsequent distribution from RenaGel LLC in an amount equal to the Distribution
Margin taken by Genzyme during such calendar quarters, or such other amount as
may be owed to the GelTex Companies as a result of a change in the aggregate
Percentage Interest of the GelTex Companies from fifty percent (50%).

     1.13. "DOW AGREEMENT" shall mean the Contract Manufacturing Agreement dated
as of April 21, 1997 by and between GelTex and The Dow Chemical Company ("DOW
CHEMICAL") and the related Ground Lease and Equipment Lease of even date
therewith.

     1.14. "DOW RESEARCH AGREEMENT" shall mean the Research Services Agreement
dated as of September 1, 1996 by and between GelTex and Dow Chemical, as amended
by the Amendment to Research Service Agreement dated as of April 21, 1997.

     1.15. "EFFECTIVE DATE" shall mean the date appearing on the cover page of
this Agreement.

     1.16. "ESTIMATED NET SELLING PRICE" with respect to a Collaboration Product
shall mean the price estimated by the Steering Committee at which such
Collaboration Product will be sold by Genzyme to Third Party customers
purchasing such Collaboration Product for resale. The Estimated Net Selling
Price shall be set forth in the Commercialization Plan for such Collaboration
Product. The Steering Committee may adjust the Estimated Net Selling Price for a
Collaboration Product to the extent necessary or appropriate to reflect changes
in market conditions and actual sales experience.

     1.17. "FIELD" shall mean all indications for non-absorbed products which
achieve their primary therapeutic effect by binding phosphate.

     1.18. "FDA" shall mean the United States Food and Drug Administration, any
successor agency or the regulatory authority of any country other than the
United States with responsibilities comparable to those of the United States
Food and Drug Administration.

     1.19. "FULLY ABSORBED COST OF GOODS" with respect to a Collaboration
Product shall mean (a) the transfer price for batches of such Collaboration
Product purchased from Third Party contract manufacturers plus the amount of the
royalties ("NITTOBO ROYALTIES") paid by GelTex to

                                       4

<PAGE>   11

Nittobo with respect to the manufacture of the Starting Material (hereinafter
defined) and the cost of the Starting Material (to the extent such cost is not
incorporated into the transfer price for the batches of the Collaboration
Product) for the manufacture of RenaGel(R) pursuant to the Nittobo License or
(b) if such Collaboration Product is manufactured by RenaGel LLC, the direct
variable costs and direct fixed costs associated with the manufacture of batches
of such Collaboration Product plus the Nittobo Royalties and the cost of the
Starting Materials. For purposes of this Section 1.19, "DIRECT VARIABLE COSTS"
shall be deemed to be the cost of labor, raw materials, supplies and other
resources directly consumed in the manufacture of batches of such Collaboration
Product. For purposes of this Section 1.19, "DIRECT FIXED COSTS" shall be deemed
to be the cost of facilities, utilities, insurance, equipment depreciation and
other fixed costs directly related to the manufacture of batches of such
Collaboration Product. Direct fixed costs shall be allocated to such
Collaboration Product based upon the proportion of such costs directly
attributable to support of the manufacturing process for such Collaboration
Product. If a RenaGel LLC facility is used to manufacture Collaboration Products
and products for other programs of either GelTex or Genzyme (including without
limitation products for use in the Chugai Territory), Fully Absorbed Cost of
Goods shall be allocated in proportion to the use of such facility for the
manufacture of Collaboration Products and products for such other programs.
Fully Absorbed Cost of Goods shall exclude all costs otherwise reimbursed
pursuant to this Agreement. Except as otherwise provided in this Agreement, all
cost determinations made hereunder shall be made in accordance with GAAP.

     1.20. "GAAP" shall mean United States generally accepted accounting
principles, consistently applied, except when different accounting principles
are required under the terms of the Operating Agreement, in which case the
accounting principles mandated under the Operating Agreement shall control.

     1.21. "GELTEX COMPANIES" shall mean GelTex and RenaGel, Inc., a Delaware
corporation and a wholly-owned subsidiary of GelTex ("RENAGEL, INC.").

     1.22. "GELTEX PATENT RIGHTS" shall mean all present and, to the extent such
Patent Rights claim * that are discovered, made or conceived during and in
connection with the Program, future Patent Rights owned or controlled by, or
licensed (with the right to sublicense) to, GelTex, to the extent that such
Patent Rights cover a compound, composition, biological or other material,
product-by-process, method, apparatus, manufacturing or other process, relating
to or useful in the Field.

     1.23. "GELTEX TECHNOLOGY" shall mean all present and, to the extent such
Technology is discovered, made or conceived during and in connection with the
Program, future Technology owned or controlled by, or licensed (with the right
to sublicense) to, GelTex relating to or useful in the Field, including without
limitation Chugai Program Technology (as defined in the Chugai Agreement).

* Confidential Information omitted and filed separately.

                                       5
<PAGE>   12

     1.24. "GENZYME PATENT RIGHTS" shall mean Patent Rights claiming *
discovered, made or conceived during and in connection with the Program that are
owned or controlled by, or licensed (with the right to sublicense) to, Genzyme,
to the extent that such Patent Rights cover a compound, composition, biological
or other material, product-by-process, method, apparatus, manufacturing or other
process, relating to or useful in the Field.

     1.25. "GENZYME TECHNOLOGY" shall mean Technology discovered, made or
conceived during and in connection with the Program, that is owned or controlled
by, or licensed (with the right to sublicense) to, Genzyme relating to or useful
in the Field.

     1.26. "MAJOR MARKET COUNTRIES" shall mean the *.

     1.27. "MANUFACTURING KNOW-HOW" shall mean all information, techniques,
inventions, discoveries, improvements, practices, methods, knowledge, skill,
experience and other technology, whether or not patentable or copyrightable, and
any patent applications, patents or copyrights based thereon, relating to or
necessary or useful for the production, packaging, storage and transportation of
Collaboration Products, including without limitation manufacturing processes
developed by Abbott and Dow Chemical pursuant to the Abbott Agreement and the
Dow Research Agreement, respectively, specifications, acceptance criteria,
manufacturing batch records, standard operating procedures, engineering plans,
installation, operation and process qualification protocols for equipment,
validation records, master files submitted to the FDA, process validation
reports, environmental monitoring processes, test data including
pharmacological, toxicological and clinical test data, cost data and employee
training materials.

     1.28. "MEMBER" shall mean, upon execution and delivery of the Operating
Agreement, Genzyme, GelTex and RenaGel, Inc.

     1.29. "NDA" shall mean a new drug application filed with the FDA after
completion of human clinical trials to obtain marketing approval for a
Collaboration Product.

     1.30. "NET PROFIT" of RenaGel LLC for any period shall be equal to (a) the
sum during such period of (i) Net Sales of all Collaboration Products sold
directly by RenaGel LLC, (ii) all revenues received by RenaGel LLC or Genzyme
from Third Parties as consideration for sublicensing the manufacture, use,
distribution or sale of Collaboration Products and (iii) all other revenues of
RenaGel LLC from any source LESS (b) all expenses incurred by RenaGel LLC during
such period, including expenses incurred in respect of Development Costs and
Commercialization Costs. All cost determinations made hereunder shall be made in
accordance with GAAP.

     1.31. "NET SALES" with respect to Collaboration Products shall mean the
gross invoiced sales price of such Collaboration Product billed (a) to
independent Third Party customers,

* Confidential Information omitted and filed separately.

                                       6

<PAGE>   13

including without limitation distributors other than Genzyme and its Affiliates,
in bona fide arms-length transactions and (b) to Genzyme and its Affiliates,
LESS, in both cases for purposes only of calculating the payments set forth in
Article 13 hereof, to the extent such amounts are included in the gross invoiced
sales price, actual: (i) freight and insurance costs incurred in transporting
such Collaboration Product to such customers; (ii) quantity, cash and other
trade discounts actually allowed and taken; (iii) customs duties, surcharges and
taxes and other governmental charges incurred in connection with the exportation
or importation of such Collaboration Product in final form; (iv) bad debt
expense; (v) amounts repaid or credited by reason of rejections (due to
Collaboration Product spoilage, damage, expiration of useful life or otherwise)
or retroactive price reductions; (vi) amounts incurred resulting from
governmental mandated rebate or discount programs; and (vii) Third Party rebates
and chargebacks actually allowed and taken, including hospital buying group
chargebacks, hospital buying group/group purchasing organization administration
fees or managed care organization rebates. The Steering Committee shall
determine how any transfers of Collaboration Products by RenaGel LLC to Genzyme
and its Affiliates for use as samples shall be treated for purposes of this
Section 1.31, and RenaGel LLC shall make such transfers in accordance with such
determination. The amount of Net Sales for any period shall be determined on the
basis of sales recorded in such period in accordance with GAAP.

     1.32. "NITTOBO LICENSE" shall mean the Agreement dated June 9, 1997 by and
between GelTex and Nitto Boseki Co., Ltd. ("NITTOBO")

     1.33. "OPERATING AGREEMENT" shall mean the Operating Agreement of RenaGel
LLC dated of even date herewith by and among GelTex, Genzyme and RenaGel, Inc.

     1.34. "PATENT RIGHTS" shall mean patents, patent applications, certificates
of invention, or applications for certificates of invention, together with any
extensions, registrations, confirmations, reissues, divisions, continuations or
continuations-in-part, re-examinations or renewals thereof.

     1.35. "PROGRAM" shall mean the collaboration among RenaGel LLC, GelTex and
Genzyme described in this Agreement.

     1.36. "PROGRAM COSTS" shall mean all Program-related costs, including
without limitation Development Costs, Commercialization Costs, the Nittobo
Royalties and the costs of the Starting Material (to the extent such cost is not
included in the cost of the Collaboration Products purchased from contract
manufacturer(s)), in each case as such costs are incurred or accrued on or after
the Effective Date.

     1.37. "PROGRAM MANAGEMENT TEAM" shall mean the joint team composed of
representatives of GelTex and Genzyme described in Section 8.1.1 hereof.

     1.38. "PURCHASE AGREEMENT" shall mean the Purchase Agreement dated of even
date

                                       7

<PAGE>   14

herewith by and between GelTex and Genzyme.

     1.39. "REGULATORY APPROVALS" shall mean all approvals from regulatory
authorities in any country required lawfully to market Collaboration Products in
any such country, including without limitation any NDA approvals and any product
pricing approvals where applicable.

     1.40. "REGULATORY SCHEME" shall mean the United States Public Health
Service Act and the regulations, interpretations and guidelines promulgated
thereunder by the FDA or the regulatory scheme applicable to the Collaboration
Products in any country other than the United States, as such statutes,
regulations, interpretations and guidelines or regulatory schemes may be amended
from time to time.

     1.41. "SPECIFICATIONS" with respect to a Collaboration Product shall mean
the written specifications for such Collaboration Product determined by the
Program Management Team and approved by the Steering Committee; provided, that
such specifications shall at all times comply with the relevant Regulatory
Scheme in the country of sale and in the country of use. The Specifications may
be amended from time to time by the Program Management Team; provided, that such
amendments are approved by the Steering Committee or the written agreement of
GelTex and Genzyme, as the case may be. Copies of such Specifications shall be
maintained by both GelTex and Genzyme, and shall become a part of this Agreement
as if incorporated herein.

     1.42. "STEERING COMMITTEE" shall mean the governing body of RenaGel LLC
composed of representatives of GelTex and Genzyme described in Section 8.2.1
hereof.

     1.43. "TECHNOLOGY" shall mean inventions, trade secrets, copyrights,
know-how, data and other intellectual property of any kind (including without
limitation any proprietary materials, compounds or reagents, but not including
Patent Rights).

     1.44. "TERRITORY" shall mean all countries of the world, excluding the
Chugai Territory.

     1.45. "THIRD PARTY" shall mean any entity other than RenaGel LLC, GelTex,
RenaGel, Inc. or Genzyme and their respective Affiliates.

     1.46. "WHOLESALE ACQUISITION COST" with respect to a Collaboration Product
shall mean the price set by the Steering Committee as the catalogue price for
such Collaboration Product. The Steering Committee may adjust the Wholesale
Acquisition Cost for a Collaboration Product to the extent necessary or
appropriate to reflect changes in market conditions and actual sales experience.

                                       8
<PAGE>   15

               ARTICLE 2. SCOPE AND STRUCTURE OF THE COLLABORATION

     2.1. GENERAL. GelTex has previously formed RenaGel LLC as the vehicle for a
joint venture between GelTex and Genzyme to develop and commercialize
Collaboration Products in and throughout the Territory. GelTex is the sole
initial member of RenaGel LLC and, immediately following the execution and
delivery of this Agreement, will transfer and assign one percent (1%) of its
interest in RenaGel LLC to RenaGel, Inc., and RenaGel, Inc. will be admitted as
a Member of RenaGel LLC. Immediately thereafter, GelTex will sell and assign to
Genzyme a fifty percent (50%) interest in RenaGel LLC (subject to adjustment
pursuant to Section 4.2 hereof and pursuant to the Operating Agreement) pursuant
to the Purchase Agreement and Article 4 hereof and, upon execution and delivery
of the Operating Agreement, Genzyme will be admitted as a Member of RenaGel LLC.
RenaGel LLC will undertake the Development Program for each of the Collaboration
Products, with each of the Parties assuming responsibility for those portions of
the Development Program allocated to it under this Agreement or under the
Development Plan. Upon completion of the Development Program, RenaGel LLC or its
designated subcontractor will manufacture the Collaboration Products for
commercial sale and Genzyme will market and sell the Collaboration Products as
exclusive distributor for RenaGel LLC on the terms and conditions set forth in
this Agreement or such other terms and conditions as the Parties may agree upon.

     2.2. EXCLUSIVE RELATIONSHIP. During the term of this Agreement, neither
RenaGel LLC, GelTex nor Genzyme, nor any of their respective Affiliates shall
independently, or with a Third Party, conduct research regarding, or engage in
the manufacture, marketing, sale or distribution of, products in the Field and
in the Territory other than as part of the Program. In addition, during the
two-year period following termination of this Agreement, neither (a) the
breaching Party or its Affiliates in the case of termination pursuant to Section
13.2.1 hereof, (b) Genzyme or its Affiliates in the case of termination pursuant
to Section 13.2.2 hereof, (c) the terminating Party and its Affiliates in the
case of termination pursuant to Section 13.2.3 hereof or (d) the non-terminating
Party and its Affiliates in the case of termination pursuant to Sections 13.2.4
and 13.2.5 hereof shall independently, or with a Third Party, conduct research
regarding, or engage in the manufacture, marketing, sale or distribution of,
products in the Field in the Territory; provided, however, that in the event
that this Agreement is terminated pursuant to Section 13.2.3 and the
non-terminating Party does not exercise its option under Section 13.3.3(a), then
the restrictions set forth in this sentence shall not apply.

     2.3. CHUGAI AGREEMENT. Genzyme and RenaGel LLC each hereby acknowledges
that GelTex has granted a license to Chugai to make, use and sell RenaGel(R) in
the Chugai Territory and that, pursuant to the Chugai Agreement, GelTex is
obliged to provide Chugai with copies of all U.S. regulatory filings for
RenaGel(R) and all data from toxicology and pharmacology studies and clinical
trials of RenaGel(R) conducted by or under the supervision of GelTex. The
Parties also understand that the contract manufacturer to be engaged by RenaGel
LLC hereunder may also be engaged by Chugai to manufacture RenaGel(R) for
development, use and/or sale in the Chugai Territory. Each of the Parties hereby
acknowledges that none of the amounts payable by Chugai to GelTex under the
Chugai Agreement are subject to this Agreement. The Parties hereby agree that
neither Genzyme nor RenaGel LLC shall bear any portion of the costs attributable
to the

                                       9

<PAGE>   16

development or manufacture of RenaGel(R) or any other products that may be
subject to the Chugai Agreement for use in the Chugai Territory. The Parties
also hereby agree that if any equipment owned or leased to RenaGel LLC is used
for the manufacture of RenaGel(R) or any other products that may be subject to
the Chugai Agreement for use in the Chugai Territory, GelTex and/or Chugai shall
be solely responsible for the costs of the manufacturing such products for
Chugai and neither Genzyme nor RenaGel LLC shall be entitled to any compensation
for the use of such equipment; provided, however, that at all times the
manufacture of Collaboration Products in accordance with Article 7 hereof shall
be given priority with respect to the use of all equipment owned or leased by
RenaGel LLC, subject to any limitations set forth in the Dow Agreement while
such agreement is in full force and effect. GelTex shall keep the Steering
Committee informed as to any Chugai Program Technology and Chugai In-Licensed
Technology (as such terms are defined in the Chugai Agreement) that arises under
the Chugai Agreement and upon request by the Steering Committee agrees to
exercise its option under Section 2.2.2 of the Chugai Agreement to obtain a
license to any Chugai In-Licensed Technology deemed by the Steering Committee to
be necessary or desirable to include in the Program, which Technology shall be
sublicensed to RenaGel LLC pursuant to Section 3.1.1 hereof.

     2.4. NITTOBO LICENSE. Pursuant to the Nittobo License, GelTex has obtained
the non-exclusive license to use certain technology owned by Nittobo for the
manufacture of the starting material (the "STARTING MATERIAL") for use in the
manufacture of RenaGel(R) in the Territory. GelTex shall use commercially
reasonable and diligent efforts to obtain the irrevocable and unconditional
consent of Nittobo to the grant of a sublicense by GelTex to RenaGel LLC under
the Nittobo License for the non-exclusive right (including the right to grant
sublicenses) to use, manufacture and sell the Starting Material, and shall grant
such a sublicense to RenaGel LLC promptly upon obtaining said consent from
Nittobo. GelTex shall be solely responsible for paying all amounts payable to
Nittobo under the Nittobo License other than the Nittobo Royalties, and GelTex
will not charge RenaGel LLC for such amounts.

                  ARTICLE 3. GRANTS AND RESERVATIONS OF RIGHTS

     3.1. ASSIGNMENTS AND LICENSES TO RENAGEL LLC.

          3.1.1. GRANTS FROM GELTEX. Except as otherwise expressly provided
herein, GelTex hereby grants to RenaGel LLC (a) the exclusive (except with
respect to licenses previously granted to (i) Dow Chemical and its sublicensees,
if any, pursuant to the Dow Agreement and (ii) Abbott Laboratories, pursuant to
the Abbott Agreement), irrevocable (during the term of this Agreement),
royalty-free right and license, with the right to grant sublicenses, under the
GelTex Patent Rights, the GelTex Technology and the Manufacturing Know-How owned
or controlled by GelTex to develop, make, have made, use, offer for sale, sell,
have sold, import and export Collaboration Products for use in the Territory in
the Field (provided, however, that with respect to Manufacturing Know-How
licensed by GelTex from Dow Chemical and Abbott, the license granted by GelTex
to RenaGel LLC for such Manufacturing Know-How pursuant to this clause (a) shall
be for the same level of exclusivity as the rights held by GelTex with respect
thereto), (b) the exclusive, irrevocable (during the term of this Agreement)
royalty-free right and license, with the right to grant sublicenses, to use the
registered

                                       10

<PAGE>   17

trademark "RenaGel(R)" in the Territory and (c) the non-exclusive, irrevocable
(during the term of this Agreement) right and sublicense under any Chugai
In-Licensed Technology (as defined in the Chugai Agreement) as to which GelTex
may obtain a license in accordance with Section 2.3 hereof to develop, make,
have made, use, offer for sale, sell, have made, sold, import and export
Collaboration Products for use in the Territory in the Field.

          3.1.2. GRANTS FROM GENZYME. Except as otherwise expressly provided
herein, Genzyme hereby grants to RenaGel LLC the exclusive, irrevocable (during
the term of this Agreement), royalty-free right and license, with the right to
grant sublicenses, under the Genzyme Patent Rights, the Genzyme Technology and
the Manufacturing Know-How owned or controlled by Genzyme, to develop, make,
have made, use, offer for sale, sell, have sold, import and export Collaboration
Products for use in the Territory in the Field.

          3.1.3. TECHNOLOGY OR PATENT RIGHTS DEVELOPED OUTSIDE THE PROGRAM. In
the event that either GelTex or Genzyme develops, acquires rights to or
otherwise comes to own or control Technology or Patent Rights after the
Effective Date other than in connection with the Program and such Technology or
Patent Rights are useful in the Field, the Party owning or controlling such
Technology or Patent Rights hereby grants to RenaGel LLC an option exercisable
at the discretion of the Steering Committee to obtain an exclusive, irrevocable
(during the term of this Agreement) right and license, with the right to grant
sublicenses, to such Technology or Patent Rights limited to use in the Territory
and in the Field to the extent necessary to enable RenaGel LLC to develop, make,
have made, use, offer for sale, sell, have sold, import and export Collaboration
Products, in each case subject only to RenaGel LLC's undertaking to pay (a) a
commercially reasonable portion of all costs incurred by GelTex or Genzyme, as
the case may be, to acquire such Technology or Patent Rights, (b) a commercially
reasonable portion of any and all development or other costs incurred by GelTex
or Genzyme, as the case may be, since the date such Party acquired such
Technology or Patent Rights and (c) all royalties, sublicense fees and other
costs or expenses payable to Third Parties associated with the acquisition or
use of such license by RenaGel LLC; provided, however, that if GelTex or Genzyme
does not own or have exclusive rights to such Technology or Patent Rights, the
license subject to RenaGel LLC's option hereunder shall be for the same level of
exclusivity as the rights held by GelTex or Genzyme with respect to such
Technology or Patent Rights.

          3.1.4. RENAGEL LLC UNDERTAKINGS; SUBLICENSES In consideration of the
licenses granted under this Section 3.1, RenaGel LLC hereby undertakes to pay
all royalties, sublicense fees and other costs or expenses payable to Third
Parties associated with the acquisition or use of such license by RenaGel LLC.
Except as provided in Section 3.2 below, all sublicenses granted by RenaGel LLC
shall be subject to prior written approval by the Steering Committee.

     3.2. LICENSES OF RIGHTS FROM RENAGEL LLC TO GELTEX AND GENZYME. RenaGel LLC
hereby grants to each of GelTex and Genzyme a non-exclusive, irrevocable right
and sublicense under the Patent Rights, Technology and Manufacturing Know-How
licensed to it pursuant to Section 3.1 above solely to the extent required to
permit such Party to perform its duties under this Agreement. RenaGel LLC also
hereby agrees to grant to each of GelTex and Genzyme a non-exclusive,
irrevocable right and sublicense under any Chugai In-Licensed Technology or any
other Technology or Patent Rights as to which RenaGel LLC elects to obtain a
license pursuant

                                       11

<PAGE>   18

to Sections 2.3 and 3.1.3 above solely to the extent required to permit such
Party to perform its duties under this Agreement. RenaGel LLC hereby grants to
Genzyme a non-exclusive, irrevocable (during the term of this Agreement) right
and license to use any and all present and future trademarks owned by or
licensed (with the right to sublicense) to RenaGel LLC, including without
limitation the registered trademark "RenaGel(R)", in connection with the
commercialization of Collaboration Products in the Territory to the extent
required to permit Genzyme to perform its duties under this Agreement.

     3.3. RESERVATION OF RIGHTS. Notwithstanding the license grants set forth in
Section 3.1 above, GelTex at all times reserves the right under the GelTex
Patent Rights, the GelTex Technology and the Manufacturing Know-How owned or
controlled by GelTex to (i) make, have made and use Collaboration Products for
research and development purposes outside of the Field, (ii) develop, make, have
made, use, offer for sale, sell, have sold, import and export products outside
the Field or outside of the Territory and (iii) grant licenses to Third Parties
for the foregoing purposes. Notwithstanding the license grants set forth in
Section 3.1 above, Genzyme at all times reserves the right under the Genzyme
Patent Rights, the Genzyme Technology and the Manufacturing Know-How owned or
controlled by Genzyme (i) to make, have made and use Collaboration Products for
research and development purposes outside of the Field, (ii) to develop, make,
have made, use, offer for sale, sell, have sold, import and export products
outside the Field and (iii) to grant licenses to Third Parties for the foregoing
purposes.

                 ARTICLE 4. EQUITY INVESTMENTS; PROGRAM FUNDING

     4.1. EQUITY INVESTMENTS. Immediately after the execution and delivery of
this Agreement and the assignment by GelTex of one percent (1%) of its interest
in RenaGel LLC to RenaGel, Inc., GelTex shall (a) issue and sell to Genzyme, and
Genzyme shall purchase from GelTex, one hundred thousand (100,000) shares of the
common stock, $.01 par value per share, of GelTex (the "SHARES") for an
aggregate purchase price of Two Million Five Hundred Thousand Dollars
($2,500,000) payable by Genzyme to GelTex upon the execution and delivery of the
Purchase Agreement in accordance with the terms thereof and (b) assign, transfer
and sell to Genzyme a fifty percent (50%) interest in RenaGel LLC (subject to
adjustment pursuant to Section 4.2 below and pursuant to the Operating
Agreement) (the "LLC INTEREST") for an aggregate purchase price of Twenty-Five
Million Ten Dollars ($25,000,010) payable as follows: (i) Ten Dollars ($10)
payable by Genzyme to GelTex upon execution of the Purchase Agreement; (ii)
Fifteen Million Dollars ($15,000,000) payable by Genzyme to GelTex within thirty
(30) days following receipt by GelTex of FDA approval of the NDA for RenaGel(R);
and (iii) Ten Million Dollars ($10,000,000) payable by Genzyme to GelTex on the
first anniversary of the date of receipt by GelTex of FDA approval of the NDA
for RenaGel(R), all in accordance with the terms and conditions of the Purchase
Agreement. All of the aforementioned payments shall be made in United States
dollars by certified or bank check or wire transfer.

     4.2. PROGRAM FUNDING COMMITMENT. Genzyme hereby undertakes to make capital
contributions to RenaGel LLC in an amount equal to fifty percent (50%) of all
Program Costs and GelTex hereby undertakes to make capital contributions to
RenaGel LLC on behalf of the GelTex Companies in an aggregate amount equal to
fifty percent (50%) of all Program Costs. In

                                       12

<PAGE>   19

the event that either GelTex, on behalf of the GelTex Companies, or Genzyme
fails to make a capital contribution pursuant to Section 4.3 below, and the
other Party does not elect to terminate this Agreement pursuant to Section
13.2.1 hereof, then the Percentage Interest (as defined in the Operating
Agreement) in RenaGel LLC and the future funding responsibility of the
defaulting Party (and, in the case of a default by GelTex, RenaGel, Inc.) shall
be adjusted proportionately as provided in Section 4.1(b) of the Operating
Agreement.

     4.3. PROGRAM FUNDING CAPITAL CONTRIBUTIONS.

          4.3.1. INITIAL CAPITAL CONTRIBUTIONS. Within five (5) working days
after the Effective Date, GelTex, on behalf of the GelTex Companies, and Genzyme
shall each make a capital contribution to RenaGel LLC in an amount equal to
one-half of the Program Costs budgeted to be incurred by RenaGel LLC from the
Effective Date through and including July 31, 1997.

          4.3.2. MONTHLY CAPITAL CONTRIBUTIONS. With respect to each calendar
month after July 1997, during the Program Genzyme and GelTex, on behalf of the
GelTex Companies, shall each make capital contributions to RenaGel LLC, monthly
in advance, not later than the fifteenth (15th) day of the prior calendar month,
in an aggregate amount equal to one-third of the Program Costs budgeted to be
incurred by RenaGel LLC in any then-current Development Plan or
Commercialization Plan for the calendar quarter in which such calendar month
occurs, allocated between such Parties in accordance with the funding
responsibility assumed by Genzyme and GelTex, on behalf of the GelTex Companies,
pursuant to Section 4.2 above. Upon receipt of each such capital contribution
from Genzyme or GelTex, as the case may be, RenaGel LLC shall promptly pay each
of the Parties an amount equal to that portion of the budgeted Program Costs to
which they are respectively entitled.

          4.3.3. QUARTERLY STATEMENTS; QUARTERLY RECONCILIATION. Within thirty
(30) days after the end of each of the first three calendar quarters of each
year and within sixty (60) days after the end of each calendar year, each of
GelTex and Genzyme shall provide RenaGel LLC with a detailed itemization of its
Program Costs actually incurred during the previous quarter. Within thirty (30)
days following receipt of the quarterly statement of actual Program Costs
provided by each of GelTex and Genzyme, GelTex, on behalf of the GelTex
Companies, and Genzyme shall each make an additional capital contribution to
RenaGel LLC in accordance with the funding responsibility assumed by the Parties
pursuant to Section 4.2 above in the aggregate amount of any actual Program
Costs shown on such statement and not yet paid for, but only to the extent that
such amount, together with all prior capital contributions to date during such
year, does not exceed * of the Program Costs budgeted year-to-date through the
end of the quarter to which such statement relates (except to the extent such
excess is approved by the Steering Committee pursuant to Sections 5.1.3 or 6.1.2
hereof). If the aggregate amount stated to be due from RenaGel LLC in such
quarterly statements for actual Program Costs is less than the amount already
contributed by the Parties to the capital of RenaGel LLC with respect to
budgeted Program Costs for such calendar quarter, such excess shall be credited
pro rata against the next successive monthly capital contribution due from
Genzyme, GelTex or RenaGel, Inc. hereunder.

* Confidential Information omitted and filed separately.

                                       13
<PAGE>   20

     4.4. DISTRIBUTIONS. Distributions shall be made semi-annually to each
Member in amounts determined in accordance with the Operating Agreement. Amounts
available for distribution shall be calculated for each calendar quarter after
the date of the first sale of a Collaboration Product by RenaGel LLC following
Regulatory Approval of such Collaboration Product and shall be reported to each
Member within ninety (90) days following the end of each such quarter. All
distributions to Members will be accompanied by a report setting forth the basis
for such distribution. Such reports shall be subject to audit rights as set
forth in Section 4.5 below, mutatis mutandis.

     4.5. BOOKS OF ACCOUNT; AUDIT. Genzyme shall keep and maintain proper and
complete books of account on behalf of RenaGel LLC. Each of GelTex and Genzyme
shall keep and maintain proper and complete records and books of account
documenting all Program Costs incurred by it. GelTex and Genzyme shall each
permit independent accountants retained by the other Parties to have access to
its records and books for the sole purpose of determining the appropriateness of
Program Costs charged by the non-auditing Party hereunder. Such examination
shall be conducted during regular business hours and upon reasonable advance
notice, at the auditing Party's own expense and no more than once in each
calendar year during the term of this Agreement and once during the three (3)
calendar years following the termination hereof. If such examination reveals
that such Program Costs have been overstated, any overpayment shall be promptly
refunded. The auditing Party shall pay the fees and expenses of the accountant
engaged to perform the audit, unless such audit reveals an overcharge of * or
more for the period examined, in which case the Party who received such
overpayment shall pay all reasonable costs and expenses incurred by the auditing
Party in the course of making such determination, including the fees and
expenses of the accountant.

                       ARTICLE 5. THE DEVELOPMENT PROGRAM

     5.1. CONDUCT OF THE DEVELOPMENT PROGRAM.

          5.1.1. GENERAL. Each of the Parties hereby agrees to collaborate
diligently in the development of Collaboration Products in the Field and to use
commercially reasonable and diligent efforts to develop, obtain Regulatory
Approvals for and bring to market Collaboration Products in the Field and in the
Territory as soon as practicable, all in accordance with the Development Plan
and the Commercialization Plan for each Collaboration Product. The Parties agree
to execute and substantially perform and to cooperate with each other in
carrying out the Development Plan for each Collaboration Product. No Party shall
be required to undertake activities in furtherance of the Development Plan or
Commercialization Plan in the absence of funding from RenaGel LLC pursuant to
the provisions of this Agreement. As used in this Agreement, the term
"COMMERCIALLY REASONABLE AND DILIGENT EFFORTS" shall mean that level of effort
which, consistent with the exercise of prudent scientific and business judgment,
is applied by the Party in question to its other therapeutic products at a
similar stage of development and with similar commercial potential.

          5.1.2. DEVELOPMENT PLAN. The Development Program shall be conducted by
RenaGel LLC under a Development Plan which shall describe the proposed overall
program of

* Confidential Information omitted and filed separately.

                                       14

<PAGE>   21

development for each of the Collaboration Products, including pre-clinical
studies, toxicology, formulation, clinical trials and regulatory plans and other
key elements necessary to obtain Regulatory Approvals for each Collaboration
Product. The Development Plan shall include a summary of estimated Development
Costs expected during the development process through obtaining such Regulatory
Approvals and a detailed description of and budget for all development
activities proposed for each calendar year for each Collaboration Product.

          5.1.3. INITIAL AND UPDATED DEVELOPMENT PLAN. A preliminary initial
Development Plan has been agreed to by the Parties for the period beginning on
the Effective Date and ending on December 31, 1997. Within thirty (30) days
after the Effective Date, GelTex, in consultation with the Program Management
Team, shall submit to the Steering Committee for review and approval the
definitive initial Development Plan for the period beginning on the Effective
Date and ending on December 31, 1997. Upon such approval, the definitive initial
Development Plan shall be signed by an authorized representative of each of
GelTex and Genzyme. The Development Plan shall be updated annually by the
Program Management Team and submitted to the Steering Committee for review and
approval not later than sixty (60) days prior to January 1 of each year during
the Development Program. Each such updated Development Plan shall include (a) an
overall development plan for each Collaboration Product which sets forth all
major development tasks remaining to be accomplished prior to submission of
filings for Regulatory Approvals and (b) a detailed description and budget for
the development activities proposed for the forthcoming calendar year, in each
case including estimated time lines to accomplish such major tasks or detailed
activities, respectively. The Program Management Team shall be primarily
responsible for preparing the annual updates to the Development Plan and, in
connection with the preparation of such updates, shall consult with GelTex and
Genzyme regarding the identification, timing and execution of and budget for the
major tasks and detailed activities required to perform the updated Development
Plan. Each such updated Development Plan approved by the Steering Committee
shall be signed by an authorized representative of each of GelTex and Genzyme.
The members of the Program Management Team shall actively consult with one
another throughout the term of the Development Program so as to adjust the
specific work performed under the Development Plan to conform to evolving
developments in technology and the results of the development work performed.
While minor adjustments to the Development Plan may be made from time to time
upon approval of the Program Management Team, significant changes in the scope
or direction of the work and any changes in funding exceeding * of the total
amount budgeted in any calendar year must be approved by the Steering Committee,
in the absence of which approval the most recently approved Development Plan
shall remain in effect.

          5.1.4. EXECUTION AND PERFORMANCE. The Development Plan shall allocate
among the Parties responsibility for each of the activities described therein.
The Parties shall use commercially reasonable and diligent efforts to conduct
the activities described in the Development Plan. The Development Program shall
be supervised by the Program Management Team. The Program Management Team will
coordinate pre-clinical and clinical testing of the Collaboration Products and
work with designated individuals at GelTex and Genzyme in the preparation of
Regulatory Approval filings for the Collaboration Products.

          5.1.5. ATTENDANCE AT REGULATORY MEETINGS. Each Party shall provide the
others

* Confidential Information omitted and filed separately.

                                       15

<PAGE>   22

with prior notice of all meetings between representatives of the notifying Party
and regulatory authorities regarding any Collaboration Product. Except as
otherwise provided herein, the Party receiving such notice shall have the right
to have representatives present at all such meetings.

     5.2. DEVELOPMENT INFORMATION.

          5.2.1. REPORTS AND INFORMATION EXCHANGE. RenaGel LLC shall own all
data accumulated from all pre-clinical studies and clinical trials of
Collaboration Products in the Territory. Each of GelTex and Genzyme shall use
commercially reasonable and diligent efforts to disclose to RenaGel LLC and to
the other Party all material information relating to any Collaboration Product
promptly after it is learned or its materiality is appreciated. The Party
performing or supervising clinical trials of Collaboration Products in
accordance with the Development Plan shall, on behalf and in the name of RenaGel
LLC, maintain the database of clinical trial data accumulated from all clinical
trials of Collaboration Products and of adverse reaction information for all
such Collaboration Products. Each Party shall keep the Program Management Team
informed as to its progress in the Development Plan. Within sixty (60) days
following the end of each calendar quarter during the Development Program, each
of GelTex and Genzyme shall provide to RenaGel LLC and to the other Party a
reasonably detailed written report, which shall describe the progress to date of
all activities for which such Party was allocated responsibility during such
quarter under the Development Plan.

          5.2.2. ADVERSE REACTION REPORTING. Each of GelTex and Genzyme shall
notify RenaGel LLC and the other Party of any adverse reaction information
relating to any Collaboration Product within twenty-four (24) hours of the
receipt of such information and as necessary for compliance with regulatory
requirements. "ADVERSE REACTION INFORMATION" includes without limitation
information relating to any experience that (a) suggests a significant hazard,
contraindication, side effect or precaution, (b) is fatal or life threatening,
(c) is permanently disabling, (d) requires or prolongs inpatient
hospitalization, (e) involves a congenital anomaly, cancer or overdose or (f) is
one not identified in nature, specificity, severity or frequency in the current
investigator brochure or the United States labeling for the Collaboration
Product.

          5.2.3. CLINICAL AND REGULATORY AUDITS. Each of GelTex and Genzyme
shall permit RenaGel LLC and the other Party or the representatives of RenaGel
LLC or the other Party to have access during regular business hours and upon
reasonable advance notice, at the auditing Party's own expense and no more than
once in each calendar year during the term of this Agreement, to the
non-auditing Party's records and facilities relating to the Development Program
for the purpose of monitoring compliance with Good Clinical Practice and other
applicable requirements of the Regulatory Scheme.

     5.3. REGULATORY APPROVAL FILINGS. GelTex shall file the NDA for RenaGel(R)
with the U.S. FDA in GelTex's name and shall promptly assign such NDA to RenaGel
LLC upon receipt of U.S. FDA approval thereof. Regulatory Approval filings for
Collaboration Products other than the NDA to be filed with the U.S. FDA for
RenaGel(R) shall be filed in the name of RenaGel LLC. In the event that the
Steering Committee determines that, due to the applicable provisions of the
Regulatory Scheme, (i) any Regulatory Approval filings for Collaboration
Products cannot be made by or in the name of RenaGel LLC (such as filings for
European Regulatory Approvals)

                                       16

<PAGE>   23

or (ii) it is not in the best interests of the Parties to make specific
Regulatory Approval filings in the name of RenaGel LLC, then such filings shall
be made by Genzyme, either by itself or through one or more of its Affiliates,
as the Steering Committee shall determine. Prior to submission to the FDA and
other governmental regulatory authorities, the Parties, through the Program
Management Team, shall consult, cooperate in preparing and mutually agree on the
content and scope of the Regulatory Approval filings. With respect to each such
filing made by Genzyme and/or its Affiliates, Genzyme hereby agrees, and if such
filing is made by one of its Affiliates, Genzyme shall cause such Affiliate to
agree, to (a) hold the licenses issued in respect of such Regulatory Approval
filings to the extent required by the Regulatory Scheme, (b) grant the Parties
an irrevocable (during the term of this Agreement) right of access and reference
to such Regulatory Approval filings, licenses and facilities, (c) reasonably
cooperate with the Parties in keeping contract manufacturers engaged by RenaGel
LLC or GelTex in accordance with Section 7.2 hereof informed as to any changes
with respect to such Regulatory Approval filings and licenses to the extent
necessary or advisable in connection with the manufacture and supply of
Collaboration Products and (d) comply with the provisions of Article 13 hereof
with respect to the ownership and/or disposition of such Regulatory Approvals in
the event this Agreement is terminated and provide the level of cooperation
described in Section 14.1 hereof in connection therewith.

     5.4. FACILITIES VISITS. Representatives of GelTex and Genzyme may visit all
manufacturing sites and the sites of any clinical trials or other experiments
being conducted by the other Parties in connection with the Development Program.
If requested by the other Party, GelTex and Genzyme shall cause appropriate
individuals working on the Development Program to be available for meetings at
the location of the facilities where such individuals are employed at times
reasonably convenient to the Party responding to such request.

             ARTICLE 6. SALES, MARKETING AND ADMINISTRATIVE SERVICES

     6.1. COMMERCIALIZATION PLANS.

          6.1.1. GENERAL. The commercialization of each Collaboration Product
shall be governed by a Commercialization Plan, which shall describe the overall
plan for commercializing such Collaboration Product, including (a) a
comprehensive marketing, sales, pricing, manufacturing, distribution and
licensing strategy for such Collaboration Product in all applicable countries,
including the Third Parties to be utilized and the arrangements with them that
have been or are proposed to be agreed upon (including without limitation
policies and procedures for adjustments, rebates, bundling and the like), (b)
the estimated launch date, market and sales forecasts (in numbers of patients
and local currency) and competitive analysis for such Collaboration Product and
(c) a detailed budget for the Commercialization Costs to be incurred in
connection with performing such Commercialization Plan.

          6.1.2. INITIAL AND UPDATED COMMERCIALIZATION PLANS. Upon the
submission of all Regulatory Approval filings for a Collaboration Product in any
given country, Genzyme shall develop and submit to the Steering Committee for
review and approval an initial Commercialization Plan in accordance with its
customary standard for a product of comparable

                                       17

<PAGE>   24

market potential, taking into consideration factors such as market conditions,
regulatory factors, competition and the costs and profits of such Collaboration
Product. Genzyme shall be primarily responsible for developing each
Commercialization Plan and, in connection therewith, shall consult with GelTex
regarding the identification, timing and execution of and budget for the major
commercialization tasks required to perform the Commercialization Plan. Each
Commercialization Plan shall be updated annually by Genzyme, in consultation
with GelTex as herein provided, and shall be submitted to the Steering Committee
for approval not later than sixty (60) days prior to January 1 of each year.
Each Commercialization Plan approved by the Steering Committee shall be signed
by an authorized representative of each of GelTex and Genzyme. While minor
adjustments to the Commercialization Plan may be made from time to time without
Steering Committee approval, significant changes in the scope or direction of
the work and any changes in funding exceeding * of the total amount budgeted in
any calendar year must be approved by the Steering Committee, and in the absence
of such approval, the provisions of the most recently approved Commercialization
Plan shall remain in effect.

     6.2. EXCLUSIVE DISTRIBUTORSHIP. RenaGel LLC hereby grants to Genzyme the
exclusive right to distribute and sell the Collaboration Products within the
Territory and for use within the Field. All revenues from the sales of
Collaboration Products in the Territory (other than sales by RenaGel LLC to
Genzyme) shall be booked by Genzyme.

     6.3. ORDERS AND FORECASTING. Genzyme shall purchase the Collaboration
Products exclusively from RenaGel LLC. At all times, Genzyme shall provide
RenaGel LLC with non-binding forecasts and binding purchase orders consistent
with RenaGel LLC's obligations to its suppliers, including without limitation
RenaGel LLC's obligations under Section 5.3 of the Dow Agreement. The Program
Management Team shall meet on a monthly basis to review the standard operating
procedures document agreed upon by the Parties and the forecasts. Genzyme shall
place orders for the Collaboration Products with RenaGel LLC on a purchase order
setting forth the quantity of Collaboration Products ordered, any specifications
therefor and the date required. RenaGel LLC, on the date set forth in the
applicable purchase order, shall sell the Collaboration Products to Genzyme for
resale within the Territory. All freight, insurance, duties and all other
charges associated with shipment of the Collaboration Products shall be
considered Commercialization Costs for such Collaboration Products only to the
extent such costs are not charged to Genzyme's customers.

     6.4. PRICES AND PAYMENT TERMS; COSTS.

          6.4.1. PRICES. Genzyme shall purchase Collaboration Products from
RenaGel LLC at the Estimated Net Selling Price for such Collaboration Products
LESS the Distributor's Discount. The Distributor's Discount is intended by the
Parties to compensate Genzyme for acting as distributor for the Collaboration
Products.

          6.4.2. TERMS OF PAYMENT. Unless otherwise agreed by the Parties in
writing, payment by Genzyme to RenaGel LLC for Collaboration Products shall be
due within sixty (60) days of the date of invoice therefor.

* Confidential Information omitted and filed separately.

                                       18

<PAGE>   25

          6.4.3. TITLE. Title to each batch of Collaboration Products shall pass
from RenaGel LLC to Genzyme at such time as such batch is bottled (prior to
labeling). The Parties hereto agree that prior to the transfer of title, RenaGel
LLC shall accrue on its books any bottling and labeling charges that will be
paid by RenaGel LLC following the transfer of title, and that notwithstanding
the transfer of title to Genzyme, RenaGel LLC shall be obligated to pay for the
labeling costs to be incurred following the transfer of title to Genzyme.
RenaGel LLC hereby agrees that the Collaboration Products will be labeled in
accordance with Genzyme's instructions.

          6.4.4. MARKETING AND DISTRIBUTION EXPENSES. Genzyme's ordinary
expenses incurred in the course of performing its marketing and distribution
obligations hereunder shall constitute Commercialization Costs and, as such,
shall be reimbursed by RenaGel LLC, but only to the extent that such amounts,
together with all other Commercialization Costs to date during such calendar
year, do not exceed * of the Commercialization Costs budgeted in the
Commercialization Plan then in effect for such calendar year (except to the
extent such excess is approved by the Steering Committee pursuant to Section
6.1.2 above). Ordinary marketing and distribution expenses include, but are not
limited to, salaries and associated expenses for sales and marketing personnel
and support staff, advertising and promotion costs, transportation expenses
including insurance (but only to the extent not charged to customers and only
such proportion of all such costs directly attributable to support of the
Commercialization Plan), duties and taxes, and costs associated with cash
discounts and allowances and other marketing concessions to customers.

     6.5. MARKETING SERVICE.

          6.5.1. EXCLUSIVE ENGAGEMENT. RenaGel LLC hereby engages Genzyme on a
exclusive basis to market Collaboration Products within the Territory and for
use within the Field. Genzyme hereby accepts such engagement and agrees (by
itself or through its Affiliates or Third Party distributors) to use
commercially reasonable and diligent efforts to establish each Collaboration
Product in the markets, fulfill market demand and meet the marketing and
distribution goals set forth in the Commercialization Plan for such
Collaboration Product.

          6.5.2. RESPONSIBILITIES OF GENZYME. Genzyme shall be solely
responsible for all aspects of the marketing of the Collaboration Products in
accordance with the strategy, policies and procedures established in the
Commercialization Plan, including without limitation the responsibilities listed
below.

          (a)  Genzyme shall be primarily responsible for the implementation of
each Commercialization Plan, including without limitation setting all terms of
sale, including establishing pricing policies, credit terms and cash discounts
and allowances, formulating marketing plans, providing patient information,
providing customer support services, providing reimbursement counselling
services and sales force training.

          (b)  Genzyme shall employ sufficiently trained and experienced
individuals in numbers adequate to carry out its responsibilities under this
Article 6. Sales and support personnel shall be familiar with the Collaboration
Products and with competitive products and

* Confidential Information omitted and filed separately.

                                       19

<PAGE>   26

shall respond promptly to customer requests for support.

          (c)  Genzyme shall provide instructions and appropriate training to
customers in the proper use and handling of the Collaboration Products and shall
monitor performance of the Collaboration Products.

          (d)  Prior to sale, Genzyme shall store, maintain and handle
Collaboration Products in accordance with the requirements of the Regulatory
Schemes and the normal and customary commercial practice with respect to
regulated medical products.

          (e)  Genzyme shall comply with all laws and government regulations
applicable to the sale of Collaboration Products within the Territory.

          (f)  The Collaboration Products shall be sold under trademarks
selected by the Steering Committee and owned by or licensed to RenaGel LLC in
accordance with Sections 3.1.1 and 9.1.2 hereof.

          (g)  Genzyme shall not (i) establish any branch, sales offices,
warehouses or other facilities outside the Territory with respect to the
Collaboration Products, (ii) adopt a policy of actively selling Collaboration
Products outside the Territory nor undertake the active sale or promotion of
sales of Collaboration Products outside the Territory or (iii) seek customers or
solicit orders from a prospective customer with its principal address or place
of business located outside the Territory. Without RenaGel LLC's prior consent,
Genzyme may not deliver or tender, or cause to be delivered or tendered,
Collaboration Products outside of the Territory. Genzyme shall not sell
Collaboration Products to a customer if Genzyme knows that such customer intends
to remove those Collaboration Products from the Territory. If Genzyme receives
an order from a prospective customer located outside of the Territory or who
Genzyme knows intends to remove the Collaboration Products from the Territory,
Genzyme shall immediately refer that customer to GelTex.

          (h)  Genzyme shall maintain complete and accurate records of all
movements and transactions involving Collaboration Products by unit, by batch
number and by customer so that all such movements and transactions can be traced
quickly and effectively. Upon written request, Genzyme will provide copies of
such records to the other Parties, with access to facilities used by Genzyme in
performing its duties under this Article 6 during normal business hours and upon
reasonable advance notice for the purpose of inspecting such facilities for
compliance with the terms of this Agreement. The records maintained by Genzyme
pursuant to this clause (h) shall be subject to the other Parties' audit rights
under Section 4.5 hereof.

          (i)  Within forty-five (45) days after the end of each calendar
quarter, Genzyme will report to RenaGel LLC the actual prices at which all sales
of Collaboration Products were made to its customers during the preceding
calendar quarter, future prospects for the Collaboration Products and related
issues. Genzyme shall report promptly to the Steering Committee in writing the
occurrence of each material incident of Collaboration Product performance
required to be reported to regulatory authorities, including without limitation
adverse reaction information in accordance with Section 5.2.2 hereof.

                                       20

<PAGE>   27

     6.6. RESPONSIBILITIES OF RENAGEL LLC AND GELTEX. RenaGel LLC shall supply
Collaboration Products to Genzyme in accordance with purchase orders placed
pursuant to Section 6.3 above. Neither RenaGel LLC nor GelTex shall actively
solicit for its own account sales of Collaboration Products in the Territory.
Any solicitations or requests to purchase Collaboration Products received by
RenaGel LLC or GelTex from any customer or prospective customer with its
principal address or place of business located in the Territory or who GelTex or
RenaGel LLC knows intends to use the Collaboration Products in the Territory or
ship such Collaboration Products into the Territory shall be immediately
referred to Genzyme.

     6.7. GENERAL AND ADMINISTRATIVE SERVICES. General and administrative
services required by RenaGel LLC shall be provided at cost by either or both of
GelTex and Genzyme as determined by the Steering Committee. All such costs, in
addition to general and administrative costs payable to Third Parties (such as
accountants), shall be considered to be Program Costs.

                        ARTICLE 7. MANUFACTURE AND SUPPLY

     Subject to the terms and conditions of this Agreement, Collaboration
Products shall be manufactured and supplied for pre-clinical and clinical
testing and for commercial sale upon the following terms and conditions:

     7.1. PROCESS DEVELOPMENT; MANUFACTURING APPROVALS. The Parties will use
commercially reasonable and diligent efforts to develop a process for the
manufacture of each Collaboration Product and to scale-up that process to a
scale sufficient to manufacture and supply (a) the anticipated demand for
pre-clinical studies and clinical trials of such Collaboration Product in
accordance with the projections set forth in the Development Plan and (b) the
anticipated market demand for such Collaboration Product at the time Regulatory
Approval is obtained for such Collaboration Product in accordance with the
projections set forth in the Commercialization Plan for such Collaboration
Product. The development of the process for the manufacture of Collaboration
Products as well as the scale up of such process and all material issues
incident to the development of the ability to produce Collaboration Products for
commercial purposes in sufficient quantity and in a timely manner will be within
the purview of the Program Management Team.

     7.2. MANUFACTURE AND SUPPLY OF COLLABORATION PRODUCTS. RenaGel LLC shall
manufacture and supply, or cause to be manufactured and supplied, Collaboration
Products for clinical trials and commercial sale on the following terms and
conditions:

          7.2.1. GENERAL. The Parties agree that they will initially use Dow
Chemical as a Third Party manufacturer and supplier of Collaboration Products.
GelTex will use its best efforts to, as soon as practicable after the Effective
Date, obtain Dow Chemical's irrevocable and unconditional written consent to the
assignment of the Dow Agreement and the Dow Research Agreement by GelTex to
RenaGel LLC with the same terms and conditions as in effect on the Effective
Date, and shall assign the Dow Agreement and the Dow Research Agreement to
RenaGel LLC as soon as such consent is obtained. Until such time as GelTex
receives the

                                       21

<PAGE>   28

aforementioned consent from Dow Chemical, GelTex shall use commercially
reasonable and diligent efforts to cause Dow Chemical to manufacture and supply
Collaboration Products for pre-clinical studies and clinical trials in
quantities and within a time period sufficient to conduct the activities set
forth in the Development Plan and to meet market demand for Collaboration
Products ordered in accordance with the terms hereof. Thereafter, RenaGel LLC
shall use commercially reasonable and diligent efforts to manufacture and
supply, or cause Dow Chemical and/or such other contract manufacturers engaged
by RenaGel LLC to manufacture and supply, Collaboration Products for
pre-clinical studies and clinical trials in quantities and within a time period
sufficient to conduct the activities set forth in the Development Plan and to
meet market demand for Collaboration Products ordered in accordance with the
terms hereof. RenaGel LLC may subcontract with contract manufacturers other than
and in addition to Dow Chemical, including Genzyme and its Affiliates, for the
manufacture, supply or packaging of Collaboration Products; provided that during
the term of the Dow Agreement, RenaGel LLC's ability to subcontract with
contract manufacturers for the manufacture of RenaGel(R) shall be subject to the
terms of the Dow Agreement.

          7.2.2. FORECASTS. The Program Management Team shall establish a
procedure for providing forecasts of requirements for Collaboration Products,
updating such forecasts and ordering Collaboration Product for such
requirements, in each case within time periods sufficient to enable RenaGel LLC
to manufacture such Collaboration Products, or cause such Collaboration Products
to be manufactured, as the case may be, to meet such forecasts in a commercially
reasonable and diligent manner; provided that during the term of the Dow
Agreement, such forecasts shall be consistent with the obligations set forth
under the Dow Agreement.

     7.3. CERTIFICATES OF ANALYSIS. RenaGel LLC shall perform, or cause its
contract manufacturer(s) to perform, quality assurance and control tests on each
lot of Collaboration Products manufactured pursuant to this Agreement before
delivery and shall prepare, or cause its contract manufacturer(s) to prepare and
deliver to RenaGel LLC, a written report of the results of such tests. Each test
report shall set forth for each lot delivered the items tested, specifications
and results in a certificate of analysis containing the types of information
which shall have been approved by the Program Management Team or required by the
FDA or other applicable regulatory agency. RenaGel LLC shall maintain such
certificates for a period of not less than five (5) years from the date of
manufacture and for so long as required under applicable requirements of the FDA
or other applicable regulatory agency.

     7.4. CERTIFICATES OF MANUFACTURING COMPLIANCE. RenaGel LLC shall prepare,
or cause its contract manufacturer(s) to prepare and deliver to RenaGel LLC, and
maintain for a period of not less than five (5) years and for so long as
required under applicable requirements of the FDA or other applicable regulatory
agency for each lot of Collaboration Products manufactured a certificate of
manufacturing compliance containing the types of information that shall have
been approved by the Program Management Team or required by the FDA or other
applicable regulatory agency, which certificate will certify that the lot of
Collaboration Products was manufactured in accordance with the Specifications
and the Good Manufacturing Practices of the FDA or other applicable governmental
regulatory agency as the same may be amended from time to time. RenaGel LLC
shall advise the other Parties immediately if an authorized agent of the FDA or
other governmental regulatory agency visits any facilities where the
Collaboration

                                       22

<PAGE>   29

Products are being manufactured for an inspection with respect to the
Collaboration Products. RenaGel LLC shall furnish to the other Parties the
report by such agency of such visit, to the extent that such report relates to
Collaboration Products, within ten (10) business days of RenaGel LLC's receipt
of such report.

     7.5. MANUFACTURE AND SUPPLY OF STARTING MATERIAL. Until such time as
RenaGel LLC obtains a sublicense under the Nittobo License pursuant to Section
2.4 hereof, GelTex shall manufacture and supply, or cause its contract
manufacturer(s) to manufacture and supply, the Starting Material for use by
RenaGel LLC or its contract manufacturer(s), as the case may be, in quantities
and within a period of time sufficient to enable RenaGel LLC or its contract
manufacturer(s), as the case may be, to meet its obligations under Section 7.2.
GelTex and its contract manufacturer(s) shall perform tests, prepare, deliver
and maintain test reports, certificates and notices of the type described in
Sections 7.3 and 7.4 above with respect to the manufacture and supply of the
Starting Material. Upon the grant of the sublicense under the Nittobo License by
GelTex to RenaGel LLC, RenaGel LLC shall manufacture and supply, or cause its
contract manufacturer(s) to manufacture and supply, the Starting Material, and
RenaGel LLC and its contract manufacturer(s) shall perform tests, prepare,
deliver and maintain test reports, certificates and notices of the type
described in Sections 7.3 and 7.4 above with respect to the manufacture and
supply of the Starting Material.

     7.6. ACCESS TO FACILITIES. Each Party shall have the right to inspect those
portions of the manufacturing or storage facilities of (i) RenaGel LLC where
Collaboration Products are being manufactured or stored, (ii) any subcontractor
who is manufacturing or storing Collaboration Products for RenaGel LLC, (iii)
GelTex where Starting Material is being manufactured and stored or (iv) any
subcontractor who is manufacturing or storing Starting Material for GelTex at
any time during regular business hours and upon reasonable notice to ascertain
compliance with the Good Manufacturing Practices of the FDA or other applicable
governmental regulatory agency as the same may be amended from time to time. Any
confidential information disclosed to or otherwise gathered by the Party
conducting such inspection during any such inspection shall be deemed
"Information" as defined in Section 10.1 below.

                              ARTICLE 8. MANAGEMENT

     8.1. PROGRAM MANAGEMENT TEAM.

          8.1.1. GENERAL. Within five (5) working days of the Effective Date,
the Parties shall establish a Program Management Team to oversee and control
development of Collaboration Products and to prepare for and oversee the launch
of Collaboration Products. The Program Management Team will be composed of four
(4) representatives appointed by GelTex and four (4) representatives appointed
by Genzyme. Such representatives will include individuals with expertise and
responsibilities in such areas as pre-clinical development, clinical
development, manufacturing, regulatory affairs, marketing, sales management and
reimbursement. The Program Management Team shall meet as needed but not less
than bi-weekly. The Team shall appoint one of its members to act as Secretary.
Such meetings shall be at times and places or in such form (e.g., telephone or
video conference) as the members of the

                                       23

<PAGE>   30

Program Management Team shall agree. A Party may change one or more of its
representatives to the Program Management Team at any time. Members of the
Program Management Team may be represented at any meeting by another member of
the Program Management Team, or by a deputy. Any approval, determination or
other action agreed to by a majority of the members of the Program Management
Team appointed by each of GelTex and Genzyme or their deputies present at the
relevant Team meeting shall be the approval, determination or other action of
the Program Management Team, provided at least two (2) representatives of each
of GelTex and Genzyme are present at such meeting. Representatives of either
GelTex and Genzyme who are not members of the Program Management Team may attend
meetings of the Team as agreed to by the representative members of the other
Party. The Project Management Team may designate Project Leaders to the extent
they deem it necessary or advisable.

          8.1.2. DEVELOPMENT PROGRAM FUNCTIONS. During the term of the
Development Program, the Program Management Team shall coordinate, expedite and
control the development of Collaboration Products to obtain Regulatory
Approvals. The Program Management Team will develop and recommend to the
Steering Committee Development Plans (including annual development budgets),
facilitate the flow of information with respect to development work being
conducted for each Collaboration Product on a worldwide basis, and discuss and
cooperate regarding such worldwide development.

          8.1.3. COMMERCIALIZATION FUNCTIONS. Following submission of filings
for Regulatory Approvals for the first Collaboration Product, the Program
Management Team shall function as the operational staff of RenaGel LLC and the
functions of the Program Management Team shall be expanded to include: (a)
monitoring the commercialization of Collaboration Products pursuant to the
Commercialization Plan, including oversight of planning, annual budgeting,
manufacturing, marketing, sales and distribution, and licensing of Collaboration
Products; (b) monitoring actual expenses incurred in the manufacture, marketing,
sale and distribution of Collaboration Products; and (c) facilitating
cooperation regarding the worldwide commercialization and marketing activities
of the Parties.

          8.1.4. MINUTES. The Program Management Team shall keep accurate
minutes of its deliberations which shall record all proposed decisions and all
actions recommended or taken. Draft minutes shall be sent to all members of the
Program Management Team and to all members of the Steering Committee within five
(5) working days after each meeting. All records of the Program Management Team
shall at all times be available to both GelTex and Genzyme.

     8.2. STEERING COMMITTEE.

          8.2.1. GENERAL. Within five (5) working days after the Effective Date,
the Parties shall establish a Steering Committee to oversee and manage the
collaboration contemplated by this Agreement. The Steering Committee will be
composed of three (3) representatives appointed by GelTex and three (3)
representatives appointed by Genzyme. Such representatives will be senior
officers and/or managers of their respective companies. The Steering Committee
will meet as needed but not less than once each calendar quarter. The Committee
shall appoint one of its members to act as Chairman or the Committee may elect
to appoint two of its members to act as Co-Chairmen. Such meetings shall be at
times and places or in such form (e.g.,

                                       24

<PAGE>   31

telephone or video conference) as the members of the Steering Committee shall
agree. A Party may change one or more of its representatives to the Steering
Committee at any time. Members of the Steering Committee may be represented at
any meeting by another member of the Steering Committee, or by a deputy. Any
approval, determination or other action agreed to by unanimous consent of the
members of the Steering Committee or their deputies present at the relevant
Committee meeting shall be the approval, determination or other action of the
Steering Committee, provided at least two (2) representatives of each of GelTex
and Genzyme is present at such meeting. Representatives of either GelTex and
Genzyme who are not members of the Steering Committee may attend meetings of the
Committee as agreed to by the representative members of the other Party.

          8.2.2. FUNCTIONS. The Steering Committee shall perform the following
functions: (a) determine the overall strategy for the Program in the manner
contemplated by this Agreement; (b) coordinate the activities of the Parties
hereunder; (c) settle disputes or disagreements that are unresolved by the
Program Management Team; (d) approve any agreements with Third Parties regarding
a Collaboration Product or which involve the grant of any rights related to the
development, manufacture or marketing of a Collaboration Product and any
material amendments or modifications thereto; (e) review and approve each
Development Plan, including each annual update, submitted to it pursuant to
Section 5.1.3 hereof; (f) review and approve each Commercialization Plan,
including each annual update, submitted to it for approval pursuant to Section
6.1.2 hereof; (g) serve as the governing body of RenaGel LLC; (h) set the
Estimated Net Selling Price, Wholesale Acquisition Cost and Distributor's
Discount for Collaboration Products; and (i) perform such other functions as
appropriate to further the purposes of this Agreement as determined by the
Parties.

          8.2.3. MINUTES. The Steering Committee shall keep accurate minutes of
its deliberations which shall record all proposed decisions and all actions
recommended or taken. The Chairman shall be responsible for the preparation of
draft minutes. Draft minutes shall be sent to all members of the Steering
Committee within ten (10) working days after each meeting. All records of the
Steering Committee shall at all times be available to both GelTex and Genzyme.

     8.3. GENERAL DISAGREEMENTS. All disagreements within the Program Management
Team and the Steering Committee shall be subject to the following:

          (a) The representatives to the Team or Committee will negotiate in
     good faith for a period of not less than thirty (30) days to attempt to
     resolve the dispute. In the case of the Program Management Team, any
     unresolved dispute shall be referred to the Steering Committee for good
     faith negotiations for an additional period of not less than thirty (30)
     days to attempt to resolve the dispute.

          (b) In the event that the dispute is not resolved after the period
     specified in clause (a) above, the representatives shall promptly present
     the disagreement to the Chief Executive Officer of each of GelTex and
     Genzyme or a designee of such Chief Executive Officer reasonably acceptable
     to the other Party.

                                       25

<PAGE>   32

          (c) Such executives shall meet or discuss in a telephone or video
     conference each of GelTex and Genzyme's views and explain the basis for
     such dispute.

          (d) If such executives cannot resolve such disagreement within sixty
     (60) days after such issue has been referred to them, then such dispute
     shall be referred to arbitration as described in Section 14.10 hereof.

                     ARTICLE 9. INTELLECTUAL PROPERTY RIGHTS

     9.1. OWNERSHIP. The Parties acknowledge that the ownership rights set forth
herein (i) shall not be affected by the participation in the discovery or
development of an Invention by the Program Management Team or the Steering
Committee in the course of discharging their duties hereunder and (ii) are
subject to the license grants set forth in Article 3 above.

          9.1.1. OWNERSHIP OF DISCOVERIES AND IMPROVEMENTS. All right, title and
interest in all writings, inventions, discoveries, improvements and other
technology, whether or not patentable or copyrightable, and any patent
applications, patents or copyrights based thereon (collectively, the
"INVENTIONS") that are discovered, made or conceived during and in connection
with the *. Each of GelTex and Genzyme shall promptly disclose to RenaGel LLC
and the other Party the making, conception or reduction to practice of
Inventions by employees or others acting on behalf of such Party. Patent Rights
and Technology covering * shall be automatically licensed to RenaGel LLC in
accordance with Section 3.1.1 hereof.

          9.1.2. OWNERSHIP OF TRADEMARKS. The Steering Committee shall select
all trademarks for the sale and use of Collaboration Products and RenaGel LLC
shall bear all expenses thereof. RenaGel LLC shall own all such trademarks,
except for the registered trademark "RenaGel(R)" as to which it has been granted
a license pursuant to Section 3.1.1 hereof.

          9.1.3. COOPERATION OF EMPLOYEES. Each of GelTex and Genzyme represents
and agrees that all employees or others acting on its behalf in performing its
obligations under this Agreement shall be obligated under a binding written
agreement to assign to such Party, or as such Party shall direct, all Inventions
made or conceived by such employee or other person. In the case of non-employees
working for other companies or institutions on behalf of GelTex or Genzyme,
GelTex or Genzyme, as applicable, shall have the right to obtain licenses for
all Inventions made by such non-employees on behalf of GelTex or Genzyme, as
applicable, in accordance with the policies of said company or institution.
GelTex and Genzyme agree to undertake to enforce such agreements (including,
where appropriate, by legal action) considering, among other things, the
commercial value of such Inventions.

* Confidential Information omitted and filed separately.

                                       26

<PAGE>   33

     9.2. FILING, PROSECUTION AND MAINTENANCE OF PATENT RIGHTS.

          9.2.1. FILING, PROSECUTION AND MAINTENANCE. The Steering Committee
shall determine which Party shall be responsible for the filing, prosecution and
maintenance of all patent applications and patents included in Patent Rights
*. Otherwise, each of GelTex and Genzyme shall be responsible for the filing,
prosecution and maintenance of all patent applications and patents which make up
its Patent Rights. For so long as any of the license grants set forth in Article
3 hereof remain in effect and upon request of the other Party, each of GelTex
and Genzyme agrees to file and prosecute patent applications and maintain the
patents covering its Patent Rights in all countries in the Territory selected by
the Steering Committee in accordance with the Commercialization Plan. Each of
GelTex and Genzyme shall consult with and keep the other fully informed of
important issues relating to the preparation and filing (if time permits),
prosecution and maintenance of such patent applications and patents, and shall
furnish to the other Party copies of documents relevant to such preparation,
filing, prosecution or maintenance in sufficient time prior to filing such
document or making any payment due thereunder to allow for review and comment by
the other Party and, to the extent possible in the reasonable exercise of its
discretion, the filing Party shall incorporate all such comments.

          9.2.2. PATENT FILING COSTS. All costs associated with filing,
prosecuting and maintaining patent applications and patents covering each of
GelTex and Genzyme's Patent Rights specific to the Field shall be deemed
Development Costs; provided, however, that if the claims of any such Patent
Rights include claims outside the Field, each of RenaGel LLC and the Party
filing, prosecuting and maintaining such patents and patent applications shall
bear one-half (1/2) of such costs.

     9.3. COOPERATION. Each of GelTex and Genzyme shall make available to the
other Party (or to the other Party's authorized attorneys, agents or
representatives) its employees, agents or consultants to the extent necessary or
appropriate to enable the appropriate Party to file, prosecute and maintain
patent applications and resulting patents with respect to inventions owned by a
Party and for periods of time sufficient for such Party to obtain the assistance
it needs from such personnel. Where appropriate, each of GelTex and Genzyme
shall sign or cause to have signed all documents relating to said patent
applications or patents at no charge to the other Party.

     9.4. NOTIFICATION OF PATENT TERM RESTORATION. Each of GelTex and Genzyme
shall notify the other Party of (a) the issuance of each United States patent
included within the notifying Party's Patent Rights, giving the date of issue
and patent number for each such patent, and (b) each notice pertaining to any
patent included within the notifying Party's Patent Rights which it receives as
patent owner pursuant to the Drug Price Competition and Patent Term Restoration
Act of 1984, including notices pursuant to ss.ss.101 and 103 of such Act from
persons who have filed an abbreviated NDA. Such notices shall be given promptly,
but in any event within ten (10) business days after receipt of each such notice
pursuant to such Act. Each of GelTex and Genzyme shall notify the other Party of
each filing for patent term restoration under such Act, any allegations of
failure to show due diligence and all awards of patent term

* Confidential Information omitted and filed separately.

                                       27

<PAGE>   34

restoration (extensions) with respect to the notifying Party's Patent Rights.

     9.5. NO OTHER TECHNOLOGY 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 the Patent Rights,
Technology or Manufacturing Know-How 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. It is understood and agreed
that this Agreement does not grant either Party any license or other right in
the Patent Rights of the other Party other than as specified in Article 3 hereof
and this Article 9.

     9.6. ENFORCEMENT OF PATENT RIGHTS; DEFENSE OF INFRINGEMENT ACTIONS. GelTex
and Genzyme shall each promptly notify the other in writing of any alleged or
threatened infringement of any patents or patent applications for which they are
responsible pursuant to Section 9.2 above or if either Party, or any of their
respective Affiliates, shall be individually named as a defendant in a legal
proceeding by a Third Party for infringement of a patent because of the
manufacture, use or sale of a Collaboration Product or because of attempts to
invalidate Genzyme or GelTex Patent Rights.

          9.6.1. FIRST RIGHT TO RESPOND. Each of GelTex and Genzyme shall have
the first right to respond to or defend (in consultation with the Steering
Committee) against such challenge or infringement of the Patent Rights for which
it is responsible for pursuant to Section 9.2 above or charge of infringement.
In the event such Party elects to so respond or defend, the other Party will
cooperate with the responding Party's legal counsel, join in such suits as may
be brought by the responding Party to enforce its Patent Rights, and be
available at the responding Party's reasonable request to be an expert witness
or otherwise to assist in such proceedings.

          9.6.2. SHARING OF LITIGATION AND SETTLEMENT EXPENSES. The costs
incurred (i) in responding to or defending against a challenge to or
infringement of a Party's Patent Rights specific to the Field or a charge that
the manufacture, use or sale of Collaboration Products infringe upon the Patent
Rights of Third Parties, (ii) in settling any such actions, which may not be
done without the prior written consent of the Steering Committee, which consent
shall not be unreasonably withheld or delayed, and (iii) as damages paid as a
result of such actions shall be deemed Program Costs.

          9.6.3. SECOND RIGHT TO RESPOND. If a Party does not exercise its right
to respond to or defend against challenges or infringements of its Patent Rights
as provided in Section 9.6.1 above within sixty (60) days of becoming aware of
or being notified of such challenges or infringements, then the other Party
shall have the option to do so at its sole cost; provided that in such case all
amounts so recovered from such Third Party shall be retained by the Party
undertaking such response or defense and the Party so responding shall have no
further obligations to the other Party with respect to the response or defense
thereof.

                                       28

<PAGE>   35

                           ARTICLE 10. CONFIDENTIALITY

     10.1. NONDISCLOSURE OBLIGATIONS. Except as otherwise provided in this
Article 10, during the term of this Agreement and for a period of * years
thereafter, the Parties shall, and GelTex shall cause RenaGel, Inc. to, maintain
in confidence and use only for purposes specifically authorized under this
Agreement (a) confidential information and data resulting from or related to the
development of Collaboration Products and (b) all information and data not
described in clause (a) but supplied by another Party under this Agreement and
marked "Confidential."

     For purposes of this Article 10, information and data described in clause
(a) or (b) of the preceding paragraph shall be referred to as "INFORMATION." To
the extent it is reasonably necessary or appropriate to fulfil its obligations
or exercise its rights under this Agreement, a Party may disclose Information it
is otherwise obligated under this Section not to disclose to its Affiliates,
sublicensees, consultants, outside contractors and clinical investigators, on a
need-to-know basis and on the condition that such entities or persons agree 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 a
Party or its sublicensees 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 with
and to market commercially Collaboration Products. The obligation not to
disclose Information shall not apply to any part of such Information that: (i)
is or becomes patented, published or otherwise becomes publicly known other than
by acts of the Party obligated not to disclose such Information or its
Affiliates or sublicensees in contravention of this Agreement; (ii) can be shown
by written documents to have been disclosed to the receiving Party or its
Affiliates or sublicensees by a Third Party, provided that such Information was
not obtained by such Third Party directly or indirectly from the other Party
under this Agreement; (iii) prior to disclosure under this Agreement, was
already in the possession of the receiving Party or its Affiliates or
sublicensees, provided that such Information was not obtained directly or
indirectly from the other Party under this Agreement; (iv) can be shown by
written documents to have been independently developed by the receiving Party or
its Affiliates without breach of any of the provisions of this Agreement; or (v)
is disclosed by the receiving Party or its Affiliates pursuant to a subpoena
lawfully issued by a court or governmental agency, provided that the receiving
Party or its Affiliates, as the case may be, notifies the other Parties
immediately upon receipt of any such subpoena.

     10.2. TERMS OF THIS AGREEMENT. The Parties agree that the public
announcement of the execution of this Agreement shall be substantially in the
form of the press release attached to this Agreement as APPENDIX A and, from and
after the Effective Date, each Party shall be entitled to make or publish any
statement limited to the contents of such press release. The Parties further
agree to seek confidential treatment for the filing of this Agreement with the
Securities and Exchange Commission and shall agree upon the content of the
request for confidential treatment made by each Party in respect of such filing.
Except as permitted by the foregoing provisions or as otherwise required by law,
each of the Parties hereby agrees not to disclose any terms or conditions of
this Agreement to any Third Party without the prior consent of the other Party;
provided, that each Party shall be entitled to disclose the terms of this
Agreement without such consent to potential investors or other financing sources
on the condition that such entities or

* Confidential Information omitted and filed separately.

                                       29

<PAGE>   36

persons agree to keep such terms confidential for the same time periods and to
the same extent as such Party is required to keep such terms confidential.

     10.3. PUBLICATIONS. Each Party recognizes the mutual interest in obtaining
valid patent protection. Consequently, any Party, its employees or consultants
wishing to make a publication (including any oral disclosure made without
obligation of confidentiality) relating to work performed by such Party as part
of the Program (the "PUBLISHING PARTY") shall transmit to the other Party (the
"REVIEWING PARTY") a copy of the proposed written publication at least
forty-five (45) days prior to submission for publication, or an abstract of such
oral disclosure at least fifteen (15) days prior to submission of the abstract
or the oral disclosure, whichever is earlier. The Reviewing Party shall have the
right to (a) request a delay in publication or presentation in order to protect
patentable information, (b) propose modifications to the publication for patent
reasons or (c) request that the information be maintained as a trade secret.

     If the Reviewing Party requests a delay as described in clause (a) above,
the Publishing Party shall delay submission or presentation of the publication
for a period of ninety (90) days to enable patent applications protecting each
Party's rights in such information to be filed. Upon the expiration of
forty-five (45) days, in the case of proposed written disclosures, or fifteen
(15) days, in the case of an abstract of proposed oral disclosures, from
transmission of such proposed disclosures to the Reviewing Party, the Publishing
Party shall be free to proceed with the written publication or the oral
presentation, respectively, unless the Reviewing Party has requested the delay
described above.

     To the extent possible in the reasonable exercise of its discretion, the
Publishing Party shall incorporate all modifications proposed under clause (b)
above. If a trade secret that is the subject of a request made under clause (c)
above cannot be otherwise protected without unreasonable expense to the
Reviewing Party, such information shall be omitted from the publication.

                   ARTICLE 11. REPRESENTATIONS AND WARRANTIES

     11.1. AUTHORIZATION. Each Party warrants and represents to the other
Parties that (a) it has the legal right and power to enter into this Agreement,
to extend the rights and licenses granted to the other in this Agreement, and to
perform fully its obligations hereunder, (b) this Agreement has been duly
executed and delivered and is a valid and binding agreement of such Party,
enforceable in accordance with its terms, (c) such Party has obtained all
necessary approvals to the transactions contemplated hereby and (d) such Party
has not made nor will it make any commitments to others in conflict with or in
derogation of such rights or this Agreement.

     11.2. INTELLECTUAL PROPERTY RIGHTS.

           11.2.1. GelTex hereby represents and warrants that immediately prior
to the execution and delivery of this Agreement, (a) it possesses an exclusive
right, title and interest to the GelTex Patent Rights and the GelTex Technology
in the Territory (except for licenses granted to Dow Chemical and Abbott
Laboratories and certain manufacturing technology owned

                                       30

<PAGE>   37

by Nittobo or covered by the Abbott and the Dow Agreements as to which GelTex
has non-exclusive licenses), (b) that the GelTex Patent Rights and the GelTex
Technology are free and clear of any lien or other encumbrance and (c) that it
has the right to (i) enter into the obligations set forth in this Agreement and
(ii) grant the rights and licenses set forth in Article 3 hereof.

           11.2.2. GelTex warrants that it is not aware of any issued patent
that would be infringed by the manufacture and sale of Collaboration Products as
contemplated by this Agreement.

           11.2.3. GelTex hereby represents and warrants that it shall use
commercially reasonable and diligent efforts (a) during such time as GelTex is
obliged to supply the Starting Material pursuant to Section 7.5 to either (i)
maintain the Nittobo License in full force and effect during the term of this
Agreement or (ii) supply RenaGel LLC or its contract manufacturer(s), as the
case may be, Starting Material in accordance with Section 7.5 hereof in a manner
such that the manufacture, use and sale of such Starting Material will not
infringe any Third Party patents, including but not limited to those covered by
the Nittobo License and (b) if RenaGel LLC is obliged to supply the Starting
Material pursuant to Section 7.5 hereof, to maintain the Nittobo License in full
force and effect during the term of this Agreement or until such time as GelTex
receives prior written authorization from the Steering Committee to terminate
the Nittobo License. GelTex further represents that, *

     11.3. WARRANTIES.

           11.3.1. GENZYME WARRANTIES. Genzyme warrants that the Collaboration
Products sold pursuant to Article 6 hereof will be marketed and sold in all
material respects in accordance with the conditions of any applicable Regulatory
Approvals and any applicable labelling claims.

           11.3.2. RENAGEL LLC WARRANTIES. RenaGel LLC warrants that the
Collaboration Products delivered pursuant to Section 7.2 hereof will conform in
all material respects to the Specifications, the conditions of any applicable
Regulatory Approvals regarding the manufacturing process and any applicable
requirements of the Regulatory Scheme regarding the manufacturing process.
RenaGel LLC further warrants that the Starting Material delivered by RenaGel LLC
or its contract manufacturer(s) pursuant to Section 7.5 hereof will conform in
all material respects to the conditions of any applicable Regulatory Approvals
regarding the manufacturing process and any applicable requirements of the
Regulatory Scheme regarding the manufacturing process.

           11.3.3. GELTEX WARRANTIES. GelTex warrants that during such time as
GelTex is obligated to cause Dow Chemical to supply the Collaboration Products
to RenaGel LLC pursuant to Section 7.2 hereof, the Collaboration Products
manufactured by Dow Chemical will conform in all material respects to the
Specifications, the conditions of any applicable Regulatory Approvals regarding
the manufacturing process and any applicable requirements of the Regulatory
Scheme regarding the manufacturing process. GelTex further warrants that the

* Confidential information omitted and filed separately.

                                       31

<PAGE>   38

Starting Material utilized by Dow Chemical in the manufacture of the
Collaboration Products or supplied by GelTex for use by RenaGel LLC or its other
contract manufacturer(s) pursuant to Section 7.5 hereof will conform in all
material respects to the conditions of any applicable Regulatory Approvals
regarding the manufacturing process and any applicable requirements of the
Regulatory Scheme regarding the manufacturing process.

     11.4. DISCLAIMER OF REPRESENTATIONS AND WARRANTIES. EXCEPT AS OTHERWISE
EXPRESSLY SET FORTH IN THIS AGREEMENT, NONE OF GELTEX, GENZYME OR RENAGEL LLC
MAKES ANY REPRESENTATIONS OR EXTENDS ANY WARRANTIES OF ANY KIND, EITHER EXPRESS
OR IMPLIED, INCLUDING WITHOUT LIMITATION WARRANTIES OF MERCHANTABILITY, FITNESS
FOR A PARTICULAR PURPOSE, AND THE NON-INFRINGEMENT OF ANY THIRD-PARTY PATENTS OR
PROPRIETARY RIGHTS. ALL UNIFORM COMMERCIAL CODE WARRANTIES ARE EXPRESSLY
DISCLAIMED BY THE PARTIES.

     11.5. LIMITATION OF LIABILITY. It is agreed by the Parties that no Party
shall have a right to or shall claim special, indirect or consequential damages,
including lost profits, for breach of this Agreement. Remedies shall be limited
to claims for amounts due hereunder or as otherwise provided in this Agreement,
including claims for indemnification as provided in Section 12.1 hereof.

                              ARTICLE 12. INDEMNITY

     12.1. RENAGEL LLC INDEMNITY OBLIGATIONS. The Operating Agreement shall
provide that RenaGel LLC shall indemnify each of the Members and their
respective Affiliates, employees and agents for any act performed by such Member
within the scope of the authority conferred upon such Member under this
Agreement; provided, that it shall be a condition to such indemnity that (i) the
Member seeking indemnification acted in good faith and in a manner reasonably
believed to be in, or not opposed to, the best interests of RenaGel LLC, (ii)
the act for which indemnification is sought did not constitute gross negligence
or wilful misconduct by such Member and (iii) payment and indemnification of any
matter disposed of by a compromise payment by such Member, pursuant to consent
decree or otherwise, shall have been approved by the Members, which approval
shall not be unreasonably withheld, or by a court of competent jurisdiction.

     12.2. INSURANCE. RenaGel LLC shall maintain product liability insurance
with respect to development, manufacture and sales of Collaboration Products in
an amount reasonably believed by Genzyme and GelTex to be adequate and customary
for the development, manufacture and sale of novel therapeutic products.
Genzyme, GelTex and Dow Chemical shall be named as additional insureds on any
such policy.

                        ARTICLE 13. TERM AND TERMINATION

     13.1. TERM. The term of this Agreement shall be perpetual unless terminated
pursuant to Section 13.2 below.

                                       32

<PAGE>   39

     13.2. TERMINATION. This Agreement may be terminated in the following
circumstances:

           13.2.1. FOR CERTAIN MATERIAL BREACHES. If (a) either GelTex or
Genzyme fails to use commercially reasonable and diligent efforts to perform any
material duty imposed upon such Party under this Agreement or a Development
Plan, (b) either GelTex or Genzyme fails to make the program funding capital
contributions in accordance with Article 4 hereof, (c) Genzyme fails to use
commercially reasonable and diligent efforts to commercialize any Collaboration
Product in any Major Market Country in accordance with the Commercialization
Plan for such Collaboration Product or (d) (1) if GelTex is obliged to supply
the Starting Material pursuant to Section 7.5 hereof, GelTex fails to either
maintain the Nittobo License in full force and effect or supply RenaGel LLC or
its contract manufacturer(s), as the case may be, Starting Material in
accordance with Section 7.5 hereof in a manner such that the manufacture, use
and sale of such Starting Material will not infringe any Third Party patents,
including but not limited to those covered by the Nittobo License or (2) if
RenaGel LLC is obliged to supply the Starting Material pursuant to Section 7.5
hereof, GelTex fails to maintain the Nittobo License in full force and effect
and the Steering Committee has not provided GelTex with prior written
authorization to terminate the Nittobo License, and, in any case described in
clauses (a) - (d), such failure to perform is not cured within ninety (90) days
of written notice thereof from the non-breaching Party, the non-breaching Party
may elect, in its sole discretion, to (i) except with respect to clause (b)
above, enforce the terms of this Agreement and seek any and all remedies
available to it at law and in equity, (ii) in the case of clause (b) above,
waive the terms of Article 4 with respect to any one or more required capital
contributions and cause the Percentage Interests (as defined in the Operating
Agreement) and future funding responsibilities of the Parties to be adjusted in
accordance with Section 4.2 hereof or (iii) terminate this Agreement with the
consequences set forth in Section 13.3.1 below. Such 90-day period shall be
extended to one hundred eighty (180) days if the breaching Party has engaged in
good faith efforts to remedy such default within such 90-day period and
indicated in writing to the non-breaching Party prior to the expiration of such
90-day period that it believes that it will be able to remedy the default within
such 180-day period, but such extension shall apply only so long as the
breaching Party is engaging in good faith efforts to remedy such default.

           13.2.2. FOR FAILURE TO MAKE A MILESTONE PAYMENT. In the event that
Genzyme fails to make a milestone payment pursuant to Article 4 hereof and such
failure is not cured within sixty (60) days of written notice thereof from
GelTex, GelTex may elect, in its sole discretion, to either (a) enforce the
terms of this Agreement and seek any and all remedies available to it at law and
in equity or (b) terminate this Agreement with the consequences set forth in
Section 13.3.2 below.

           13.2.3. FOR CONVENIENCE. Either GelTex or Genzyme may elect to
terminate this Agreement for any reason at any time after the earlier of (i)
such time as GelTex has received FDA approval for the NDA for RenaGel(R) or (ii)
*if GelTex has not received FDA approval of the NDA for RenaGel(R) on or before
such date upon one (1) year prior written notice to the other Party (during
which one-year period the obligations of the Parties, including without
limitation obligations with respect to capital contributions, shall continue in
full force and effect).

* Confidential information omitted and filed separately.

                                       33

<PAGE>   40

           13.2.4. [Intentionally Omitted]. -

           13.2.5. UPON BANKRUPTCY. Either GelTex or Genzyme may terminate this
Agreement upon the bankruptcy, insolvency, dissolution or winding-up of the
other Party, except in the case of a petition in bankruptcy filed involuntarily
against a Party, if such petition is dismissed within sixty (60) days of the
date of its filing.

     13.3. EFFECTS OF TERMINATION.

           13.3.1. FOR CERTAIN MATERIAL BREACHES. In addition to the rights and
duties set forth in Sections 13.4 and 13.5 below, RenaGel, Inc. shall have the
following rights and GelTex and Genzyme shall have the following rights and
duties upon termination of this Agreement pursuant to Section 13.2.1(iii) above:

           (a)  the non-breaching Party shall obtain from the breaching Party
the exclusive and irrevocable right and license, with the right to grant
sublicenses, under the breaching Party's Patent Rights, Technology and
Manufacturing Know-How to develop, make, have made, use, offer for sale, sell,
have sold, import and export Collaboration Products in the Territory and in the
Field, and the breaching Party shall execute such documents and take all action
as may be necessary or desirable to affect the foregoing; provided, that any
license granted hereunder shall be subject to the obligation of the
non-breaching Party to use commercially reasonable and diligent efforts to
develop and market Collaboration Products pursuant to such license;

           (b)  the breaching Party shall assign and transfer all of its
interest in RenaGel LLC to the non-breaching Party, and the non-breaching Party
may dissolve RenaGel LLC in its sole discretion, provided that in the event that
GelTex is the breaching Party, it shall also cause RenaGel, Inc. to assign and
transfer all of its interest in RenaGel LLC to Genzyme;

           (c)  (i) all licenses granted pursuant to Article 3 shall be revoked,
(ii) if RenaGel LLC is dissolved, the sublicense under the Nittobo License (if
obtained) and any applicable Regulatory Approval (other than any Regulatory
Approval filed or obtained by Genzyme and/or its Affiliates pursuant to Section
5.3 hereof) and clinical data owned or licensed by RenaGel LLC and any
trademarks owned or licensed by RenaGel LLC shall be assigned or licensed to the
non-breaching Party and (iii) in the case of Regulatory Approvals obtained by
Genzyme and/or its Affiliates pursuant to Section 5.3 hereof, such Regulatory
Approvals shall be (A) exclusively licensed (as against all parties, including
the breaching Party) to RenaGel LLC, the non-breaching Party or its designee
until such time as RenaGel LLC, the non-breaching Party or its designee, as
determined by the non-breaching Party, is qualified to hold such Regulatory
Approvals under the applicable provisions of the Regulatory Scheme and (B)
transferred or assigned to RenaGel LLC, the non-breaching Party or its designee,
as appropriate, as soon as practicable thereafter;

           (d)  the non-breaching Party shall become obligated to pay the
breaching Party an amount equal to *

* Confidential information omitted and filed separately.

                                       34

<PAGE>   41

*, plus interest thereon at the Base Rate of interest declared from time to time
by The First National Bank of Boston in Boston, Massachusetts from the date of
termination to the date payment is made (the "BREACH BUYOUT AMOUNT"), payable as
follows:

                    (1)  if the non-breaching Party elects to sell or otherwise
dispose of all or any portion of its or its Affiliates' right, title and
interest in the Collaboration Products, then the non-breaching Party shall, upon
any such sale or other disposition, pay the breaching Party an amount equal to *

                    (2)  for as long as the non-breaching Party (together, in
the case of GelTex, with RenaGel, Inc.) has not sold or otherwise disposed of
all or a portion of its (together, in the case of GelTex, with RenaGel, Inc.'s)
right, title and interest in the Collaboration Products which is equal to or
greater than the breaching Party's (together, in the case of GelTex, with
RenaGel, Inc.'s) Percentage Interest (as defined in the Operating Agreement) as
of the date of termination, the non-breaching Party shall pay the breaching
Party (and, in the event that GelTex is the breaching Party, RenaGel, Inc.) *
shall equal (i) the breaching Party's (and, in the event that GelTex is the
breaching Party, RenaGel, Inc.'s) *; and

                    (3)  on the * of the date of termination, the non-breaching
Party shall pay the breaching Party (and, in the event that GelTex is the
breaching Party, RenaGel, Inc.) the difference between the aggregate amounts
paid pursuant to clauses (1) and (2) above and the Breach Buyout Amount;

provided, that the aggregate amount of all payments made under clauses (1), (2)
and (3) shall not exceed the Breach Buyout Amount; and

               (e)  if Genzyme has not paid all of the payments described in
Section 4.1 on or before the date of termination, termination of this Agreement
shall not relieve Genzyme of its obligation to pay any such unpaid amount at
such time as it becomes due and payable in accordance with the schedule set
forth in Section 4.1, and if GelTex is the non-breaching Party and such payments
remain unpaid after they have become due and payable, GelTex shall have the
right to offset the payments otherwise due to Genzyme pursuant to clause (d)
above in an amount equal to the outstanding payments due and payable to GelTex
pursuant to Section 4.1 hereof.

               13.3.2. FOR FAILURE TO MAKE A MILESTONE PAYMENT. In addition to
the rights and duties set forth in Sections 13.4 and 13.5 below, GelTex shall
have the following rights and duties upon termination of this Agreement pursuant
to Section 13.2.2(b) above:

* Confidential Information omitted and filed separately.

                                       35

<PAGE>   42

               (a)  GelTex shall obtain from Genzyme the exclusive and
irrevocable right and license, with the right to grant sublicenses, under the
Genzyme's Patent Rights, Technology and Manufacturing Know-How to develop, make,
have made, use, offer for sale, sell, have sold, import and export Collaboration
Products in the Territory and in the Field, and Genzyme shall execute such
documents and take all action as may be necessary or desirable to affect the
foregoing; provided, that any license granted hereunder shall be subject to the
obligation of GelTex to use commercially reasonable and diligent efforts to
develop and market Collaboration Products pursuant to such license;

               (b)  Genzyme shall assign and transfer all of its interest in
RenaGel LLC to GelTex, and GelTex may dissolve RenaGel LLC in its sole
discretion;

               (c)  (i) all licenses granted pursuant to Article 3 shall be
revoked, (ii) if RenaGel LLC is dissolved, the sublicense under the Nittobo
License (if obtained) and any Regulatory Approval (other than any Regulatory
Approval filed or obtained by Genzyme and/or its Affiliates pursuant to Section
5.3 hereof) and clinical data owned or licensed by RenaGel LLC and any
trademarks owned or licensed by RenaGel LLC shall be assigned or licensed to
GelTex and (iii) in the case of Regulatory Approvals obtained by Genzyme and/or
its Affiliates pursuant to Section 5.3 hereof, such Regulatory Approvals shall
be (A) exclusively licensed (as against all parties, including Genzyme and its
Affiliates) to RenaGel LLC, GelTex or its designee until such time as RenaGel
LLC, GelTex or its designee, as determined by GelTex, is qualified to hold such
Regulatory Approvals under the applicable provisions of the Regulatory Scheme
and (B) transferred or assigned to RenaGel LLC, GelTex or its designee, as
appropriate, as soon as practicable thereafter; and

               (d)  GelTex shall become obligated to pay Genzyme an amount equal
to *, plus interest thereon at the Base Rate of interest declared from time to
time by The First National Bank of Boston in Boston, Massachusetts from the date
of termination to the date payment is made less the aggregate amount of the
milestone payments described in Section 4.1 that have not been paid by Genzyme
as of such termination, whether or not all such payments have become due (the
"MILESTONE BREACH BUYOUT AMOUNT"), payable on the terms and conditions and in
accordance with the scheduled of payments set forth in Section 13.3.1.(d),
mutatis mutandis.

               13.3.3. FOR CONVENIENCE.  In addition to the rights and duties
set forth in Sections 13.4 and 13.5 below, RenaGel, Inc. shall have the
following rights and GelTex and Genzyme shall have the following rights and
duties upon termination of this Agreement pursuant to Section 13.2.3 above:

               (a)  the non-terminating Party shall have an option exercisable
upon written notice to the terminating Party within the one-year period provided
in Section 13.2.3 hereof to obtain from the terminating Party the exclusive and
irrevocable right and license, with the right to grant sublicenses, under the
terminating Party's Patent Rights, Technology and Manufacturing Know-How to
develop, make, have made, use, offer for sale, sell, have sold, import and
export Collaboration Products in the Territory and in the Field, and the
terminating Party shall execute

* Confidential Information omitted and filed separately.

                                       36

<PAGE>   43

such documents and take all action as may be necessary or desirable to affect
the foregoing; provided, that any license granted hereunder shall be subject to
the obligation of the non-terminating Party to use commercially reasonable and
diligent efforts to develop and market Collaboration Products pursuant to such
license;

               (b)  upon exercise of its license option provided in paragraph
(a) of this Section 13.3.3, the terminating Party shall assign and transfer all
of its interest in RenaGel LLC to the non-terminating Party, and the
non-terminating Party may dissolve RenaGel LLC in its sole discretion, provided
that in the event that GelTex is the terminating Party, it shall also cause
RenaGel, Inc. to assign and transfer all of its interest in RenaGel LLC to
Genzyme;

               (c)  upon exercise of its license option provided in paragraph
(a) of this Section 13.3.3, (i) all licenses granted pursuant to Article 3 shall
be revoked, (ii) if RenaGel LLC is dissolved, the sublicense under the Nittobo
License (if obtained) and any applicable Regulatory Approval (other than any
Regulatory Approval filed or obtained by Genzyme and/or its Affiliates pursuant
to Section 5.3 hereof) and clinical data owned or licensed by RenaGel LLC and
any trademarks owned or licensed by RenaGel LLC shall be assigned or licensed to
the non-terminating Party and (iii) in the case of Regulatory Approvals filed or
obtained by Genzyme and/or its Affiliates pursuant to Section 5.3 hereof, such
Regulatory Approvals shall be (A) exclusively licensed (as against all parties,
including the terminating Party) to RenaGel LLC, the non-terminating Party or
its designee until such time as RenaGel LLC, the non-terminating Party or its
designee, as determined by the non-terminating Party, is qualified to hold such
Regulatory Approvals under the applicable provisions of the Regulatory Scheme
and (B) transferred or assigned to RenaGel LLC, the non-terminating Party or its
designee, as appropriate, as soon as practicable thereafter; and

               (d)  upon the exercise of its license option provided in
paragraph (a) of this Section 13.3.3, the non-terminating Party shall become
obligated to pay to the terminating Party an amount equal to * plus interest
thereon at the Base Rate of interest declared from time to time by The First
National Bank of Boston in Boston, Massachusetts from the date of termination to
the date payment is made (the "CONVENIENCE BUYOUT AMOUNT"), payable on the terms
and conditions and in accordance with the scheduled of payments set forth in
Section 13.3.1.(d), mutatis mutandis;

               (e)  if the license option provided in paragraph (a) of this
Section 13.3.3 is not exercised, then all right, title and interest in the
Collaboration Products shall be sold to the highest bidder within * from the
date of termination and the proceeds shall be allocated between the Members in
proportion to their Percentage Interests (as defined in the Operating Agreement)
in RenaGel LLC as of the date of termination and RenaGel LLC shall be dissolved;
and

               (f)  if Genzyme has not paid all of the payments described in
Section 4.1 on or before the date of termination, termination of this Agreement
shall not relieve Genzyme of its

* Confidential Information omitted and filed separately.

                                       37

<PAGE>   44

obligation to pay any such unpaid amount at such time as it becomes due and
payable in accordance with the schedule set forth in Section 4.1, and if GelTex
is the non-terminating Party and such payments remain unpaid after they have
become due and payable, GelTex shall have the right to offset the payments
otherwise due to Genzyme pursuant to clause (d) above in an amount equal to the
outstanding payments due and payable to GelTex pursuant to Section 4.1 hereof.

          13.3.4. [Intentionally Omitted].

          13.3.5. UPON BANKRUPTCY. In addition to the rights and duties set
forth in Sections 13.4 and 13.5 below, RenaGel, Inc. shall have the following
rights and GelTex and Genzyme shall have the following rights and duties upon
termination of this Agreement pursuant to Section 13.2.5 above:

          (a)  the terminating Party shall obtain from the non-terminating Party
the exclusive, irrevocable, royalty-bearing right and license, with the right to
grant sublicenses, under the non-terminating Party's Patent Rights, Technology
and Manufacturing Know-How to develop, make, have made, use, offer for sale,
sell, have sold, import and export Collaboration Products in the Territory and
in the Field, and the non-terminating Party shall execute such documents and
take all action as may be necessary or desirable to affect the foregoing;
provided, that any license granted hereunder shall be subject to the obligation
of the terminating Party to use commercially reasonable and diligent efforts to
develop and market Collaboration Products pursuant to such license;

          (b)  the non-terminating Party shall assign and transfer all of its
interest in RenaGel LLC to the terminating Party, and the terminating Party may
dissolve RenaGel LLC in its sole discretion, provided that in the event that
GelTex is the non-terminating Party, it shall also cause RenaGel, Inc. to assign
and transfer all of its interest in RenaGel LLC to Genzyme;

          (c)  (i) all licenses granted to Article 3 shall be revoked, (ii) if
RenaGel LLC is dissolved, the sublicense under the Nittobo License (if obtained)
and any applicable Regulatory Approval (other than any Regulatory Approval filed
or obtained by Genzyme and/or its Affiliates pursuant to Section 5.3 above) and
clinical data owned or licensed by RenaGel LLC and any trademarks owned or
licensed by RenaGel LLC shall be assigned or licensed to the terminating Party
and (iii) in the case of Regulatory Approvals filed or obtained by Genzyme
and/or its Affiliates pursuant to Section 5.3 hereof, such Regulatory Approvals
shall be (A) exclusively licensed (as against all parties, including the
non-terminating Party) to RenaGel LLC, the terminating Party or its designee,
until such time as RenaGel LLC, the terminating Party or its designee, as
determined by the terminating Party, is qualified to hold such Regulatory
Approvals under the applicable provisions of the Regulatory Scheme and (B)
transferred or assigned to RenaGel LLC, the terminating Party or its designee,
as appropriate, as soon as practicable thereafter;

          (d)  the terminating Party shall become obligated to pay to the
non-terminating Party an amount equal to *

* Confidential Information omitted and filed separately.

                                       38

<PAGE>   45

*, plus interest thereon at the Base Rate of interest declared from time to time
by The First National Bank of Boston in Boston, Massachusetts from the date of
termination to the date payment is made (the "BANKRUPTCY BUYOUT AMOUNT"),
payable on the terms and conditions and in accordance with the scheduled of
payments set forth in Section 13.3.1.(d), mutatis mutandis.

           (e)  if Genzyme has not paid all of the payments described in Section
4.1 on or before the date of termination, termination of this Agreement shall
not relieve Genzyme of its obligation to pay any such unpaid amount at such time
as it becomes due and payable in accordance with the schedule set forth in
Section 4.1, and if GelTex is the terminating Party and such payments remain
unpaid after they have become due and payable, GelTex shall have the right to
offset the payments otherwise due to Genzyme pursuant to clause (d) above in an
amount equal to the outstanding payments due and payable to GelTex pursuant to
Section 4.1 hereof.

           13.3.6. FAIR VALUE. For purposes of this Section 13.3, the *. In the
event that GelTex and Genzyme are unable to agree upon the Fair Value within *
of the date of termination, the Fair Value shall be determined by an investment
banking firm selected by mutual agreement of GelTex and Genzyme, and the costs
and expenses incurred in connection with the engagement of such investment
banking firm shall be shared equally by GelTex and Genzyme.

     13.4. INVENTORY. Upon the termination of this Agreement, if Genzyme does
not obtain a license pursuant to Sections 13.3.1(a), 13.3.3(a), 13.3.4(a) or
13.3.5(a), GelTex shall have the option to repurchase Genzyme's inventory of
Collaboration Products acquired by Genzyme pursuant to Article 6 hereof. Within
ten (10) days after such termination, GelTex shall elect in writing to either
(a) permit Genzyme to sell off its remaining inventory or Collaboration
Products, provided that Genzyme shall comply with all of the terms and
conditions of this Agreement restricting such selling activities as in effect
immediately prior to such termination, or (b) repurchase Genzyme's inventory of
Collaboration Products. If GelTex fails to make such an election, Genzyme shall
be permitted to sell-off its remaining inventory of Collaboration Products in
accordance with clause (a) of this Section 13.4. Any repurchase of Genzyme's
inventory of Collaboration Products shall be at the price * to be reasonably
determined by the Parties.

     13.5. SURVIVAL OF RIGHTS AND DUTIES. No termination of this Agreement shall
eliminate any rights or duties accrued prior to such termination. The provisions
of Articles 1, 10 and 12 and Sections 2.2, 3.3, 4.1 (to the extent certain
payments by Genzyme have not been made prior to termination), 4.3, 4.5, 9.1.1,
9.1.3, 9.3, 9.5, 13.3, 13.4, 13.5, 14.1, 14.3, 14.4, 14.9 and 14.10 hereof shall
survive any termination of this Agreement.

* Confidential Information omitted and filed separately.

                                       39

<PAGE>   46

                            ARTICLE 14. MISCELLANEOUS

     14.1. COOPERATION. If either GelTex or Genzyme (the "ASSUMING PARTY") shall
assume the Program rights from the other Party (the "RESPONSIBLE PARTY") in
accordance with the provisions of Article 13 hereof, the Responsible Party shall
promptly provide to the Assuming Party (or any Third Party or Affiliate
designated by the Assuming Party) all Technology, Manufacturing Know-How and
access to regulatory filings sufficient to allow the Assuming Party to perform
the duties assumed. The Responsible Party shall further use its best efforts to
provide all assistance required by the Assuming Party with respect to such
transfer so as to permit the Assuming Party to begin to perform such duties as
soon as possible to minimize any disruption in the continuity of supply or
marketing of Collaboration Products. In addition, if upon the date this
Agreement is terminated Collaboration Products are being manufactured in
facilities owned or leased by the Responsible Party (including facilities
subleased by RenaGel LLC from the Responsible Party), the Responsible Party
agrees to lease such facilities to the Assuming Party on commercially reasonable
terms for a period of up to *.

     14.2. EXCHANGE CONTROLS. All payments due hereunder shall be paid in United
States dollars. If at any time legal restrictions prevent the prompt remittance
of part or all payments with respect to any country where a Collaboration
Product is sold, payment shall be made through such lawful means or methods as
the Parties may determine.

     14.3. WITHHOLDING TAXES. If applicable laws or regulations require that
taxes be withheld from payments made hereunder, the Party paying such taxes will
(a) deduct such taxes, (b) timely pay such taxes to the proper authority and (c)
send written evidence of payment to the Party from whom such taxes were withheld
within sixty (60) days after payment. Each Party will assist the other Parties
in claiming tax refunds, deductions or credits at such other Party's request and
will cooperate to minimize the withholding tax, if available, under various
treaties applicable to any payment made hereunder.

     14.4. INTEREST ON LATE PAYMENTS. Any payments to be made hereunder that are
not paid on or before the date such payments are due under this Agreement shall
bear interest, to the extent permitted by applicable law, at the Base Rate of
interest declared from time to time by The First National Bank of Boston in
Boston, Massachusetts, calculated on the number of days payment is delinquent.

     14.5. FORCE MAJEURE. No Party shall be held liable or responsible to the
other Parties 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 without limitation 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 one
or both of the other Parties; provided, however, that the Party so affected
shall use commercially reasonable and diligent efforts to avoid or remove such
causes of non-performance, and shall continue performance hereunder with
reasonable dispatch whenever such causes are removed. Each Party shall provide
the other Parties with prompt written notice of any delay or failure to perform
that

* Confidential Information omitted and filed separately.

                                       40

<PAGE>   47

occurs by reason of force majeure. The Parties shall mutually seek a resolution
of the delay or the failure to perform as noted above.

     14.6. ASSIGNMENT. This Agreement may not be assigned or otherwise
transferred by any Party without the consent of the other Parties; provided,
however, that either GelTex or Genzyme may, without such consent, assign its
rights and obligations under this Agreement (a) in connection with a corporate
reorganization, to any member of an affiliated group, 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 (b) 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 in writing.

     Without limiting the foregoing, it is understood and agreed by the Parties
that in the event that GelTex assigns its rights and obligations under this
Agreement pursuant to clause (a) or (b) above,

          (i) Genzyme shall become the Party primarily responsible in its
reasonable sole discretion for managing the manufacture and supply requirements
for the Collaboration Products and selecting and engaging manufacturers and
suppliers for the Collaboration Products (either through agreements with Genzyme
or its Affiliates or RenaGel LLC),

          (ii) GelTex shall use its best efforts to cause all agreements related
to the manufacture and supply of Collaboration Products (other than the Nittobo
License and the Manufacture and Supply Agreement with Salsbury Chemicals) that
are in GelTex's name at the time to be assigned to Genzyme or its designee if
requested by Genzyme,

          (iii) in the event that RenaGel LLC has not received a sublicense
under the Nittobo License from GelTex as contemplated by Section 2.4 of the
Collaboration Agreement or, if granted, such sublicense is no longer in full
force and effect or is subject to termination due to the transaction
contemplated by clause (a) or (b) above, as applicable, GelTex and its assignee
shall ensure the continued and uninterrupted supply of polyallylamine
hydrochloride at cost for use by Genzyme and any other manufacturer of
Collaboration Products pursuant to Section 7.5 of this Agreement in quantities
and within a period of time sufficient to conduct the activities set forth in
the Development Plan and to meet market demand for Collaboration Products
ordered in accordance with the terms of the Collaboration Agreement, and

          (iv) GelTex and its assignee shall ensure the continued and
uninterrupted supply of polyallylamine hydrochloride at cost for use by Genzyme
and any other manufacturer of Collaboration Products in quantities and within a
period of time sufficient to conduct the activities set forth in the Development
Plan and to meet market demand for Collaboration Products ordered in accordance
with the terms of the Collaboration Agreement if at the time of a transaction
contemplated by clause (a) or (b) above the effective supply agreement for

                                       41

<PAGE>   48

polyallylamine hydrochloride is between GelTex and such supplier (such as the
Manufacture and Supply Agreement with Salsbury Chemicals).

     14.7. 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. 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.

     14.8. 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 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 in accordance with this Section 14.8, and shall be effective upon
receipt by the addressee.

     If to             GelTex Pharmaceuticals, Inc.
     GelTex or         153 Second Avenue
     RenaGel, Inc.:    Waltham, Massachusetts 02451
                       Attention: President
                       Facsimile: (781) 672-5822

     with a copy to:   GelTex Pharmaceuticals, Inc.
                       153 Second Avenue
                       Waltham, Massachusetts 02451
                       Attention: Corporate Counsel
                       Facsimile: (781) 895-4982

     If to             Genzyme Corporation
     Genzyme:          One Kendall Square
                       Cambridge, Massachusetts 02139
                       Attention: President
                       Facsimile: (617) 374-7423

     with a copy to:   Genzyme Corporation
                       One Kendall Square
                       Cambridge, Massachusetts 02139
                       Attention: Chief Legal Counsel
                       Facsimile: (617) 252-7553

                                       42

<PAGE>   49

     If to RenaGel     RenaGel LLC
     LLC (if such      c/o Genzyme Corporation
     notice is sent    One Kendall Square
     by GelTex):       Cambridge, Massachusetts 02139
                       Attention: President
                       Facsimile: (617) 374-7423

     with a copy to:   Genzyme Corporation
                       One Kendall Square
                       Cambridge, Massachusetts 02139
                       Attention: Chief Legal Counsel
                       Facsimile: (617) 252-7553

     If to RenaGel     RenaGel LLC
     LLC (if such      c/o GelTex Pharmaceuticals, Inc.
     notice is sent    153 Second Avenue
     by Genzyme):      Waltham, Massachusetts 02451
                       Attention: President
                       Facsimile: (781) 672-5822

     with a copy to:   GelTex Pharmaceuticals, Inc.
                       153 Second Avenue
                       Waltham, Massachusetts 02451
                       Attention: Corporate Counsel
                       Facsimile: (781) 895-4982

     14.9.  APPLICABLE LAW. This Agreement shall be governed by and construed in
accordance with the laws of the Commonwealth of Massachusetts.

     14.10. ARBITRATION. Any disputes arising between the Parties relating to,
arising out of or in any way connected with this Agreement or any term or
condition hereof, or the performance by either Party of its obligations
hereunder, whether before or after termination of this Agreement (a "DISPUTE"),
which has not resolved in accordance with the provisions of Section 8.3 hereof,
shall be finally resolved by binding arbitration as herein provided.

            14.10.1. GENERAL. Except as otherwise provided in this
Section 14.10, any arbitration hereunder shall be conducted under the commercial
rules of the American Arbitration Association. Each such arbitration shall be
conducted in the English language by a panel of three arbitrators (the
"ARBITRATION PANEL"). Each of GelTex and Genzyme shall appoint one arbitrator to
the Arbitration Panel and the third arbitrator shall be appointed by the two
arbitrators appointed by GelTex and Genzyme. The Arbitration Panel shall be
convened upon delivery of the Notice of Arbitration (as defined below). Any such
arbitration shall be held in Boston, Massachusetts. The Arbitration Panel shall
have the authority to grant specific performance, and to allocate between the
Parties the costs of arbitration in such equitable manner as it shall determine.
Judgment upon the award so rendered may be entered in any court having
jurisdiction or application may be made to such court for judicial acceptance of
any award and an order of enforcement, as the case may be.

                                       43

<PAGE>   50

            14.10.2. PROCEDURE.

                     (a)  Whenever a Party (the "CLAIMANT") shall decide to
institute arbitration proceedings, it shall give written notice to that effect
(the "NOTICE OF ARBITRATION") to the other Party (the "RESPONDENT"). The Notice
of Arbitration shall set forth in detail the nature of the Dispute, the facts
upon which the Claimant relies and the issues to be arbitrated (collectively,
the "ARBITRATION ISSUES"). Within thirty (30) days of its receipt of the Notice
of Arbitration, the Respondent shall send the Claimant and the Arbitration Panel
a written Response (the "RESPONSE"). The Response shall set forth in detail the
facts upon which the Respondent relies. In addition, the Response shall contain
all counterclaims which the Respondent may have against the Claimant which are
within the Arbitration Issues, whether or not such claims have previously been
identified. If the Response sets forth a counterclaim, the Claimant may, within
thirty (30) days of the receipt of the Response, deliver to the Respondent and
the Arbitration Panel a rejoinder answering such counterclaim.

                     (b)  Within fifteen (15) days after the later of (i) the
expiration of the period provided in clause (a) above for the Claimant to
deliver a rejoinder or (ii) the completion of any discovery proceedings
authorized by the Arbitration Panel: (A) the Claimant shall send to the
Arbitration Panel a proposed resolution of the Arbitration Issues and a proposed
resolution of any counterclaims set forth in the Response (the "CLAIMANT'S
PROPOSAL"), including the amount of monetary damages, if any, or other relief
sought; and (B) the Respondent shall send to the Arbitration Panel a proposed
resolution of the Arbitration Issues, a proposed resolution of any counterclaims
set forth in the Response and a proposed resolution of any rejoinder submitted
by the Claimant (the "RESPONDENT'S PROPOSAL"), including the amount of monetary
damages, if any, or other relief sought. Once both the Claimant's Proposal and
the Respondent's Proposal have been submitted, the Arbitration Panel shall
deliver to each Party a copy of the other Party's proposal.

                     (c)  The Arbitration Panel shall issue an opinion with
respect to any Dispute, which opinion shall explicitly accept either the
Claimant's Proposal or the Respondent's Proposal in its entirety (the "FINAL
DECISION"). The Arbitration Panel shall not have the authority to reach a Final
Decision that provides remedies or requires payments other than those set forth
in the Claimant's Proposal or the Respondent's Proposal. The concurrence of two
(2) arbitrators shall be sufficient for the entry of a Final Decision. The
arbitrators shall issue a Final Decision within one (1) month from the later of
(i) the last day for submission of proposals under clause (b) above or (ii) the
date of the final hearing on any Dispute held by the Arbitration Panel. A Final
Decision shall be binding on all of the Parties.

     14.11. ENTIRE AGREEMENT. This Agreement, together with the Operating
Agreement and the Purchase Agreement contain 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 the Parties. Each of the Parties hereby acknowledges that this Agreement, the
Operating Agreement and the Purchase Agreement are each the result of mutual
negotiation and

                                       44

<PAGE>   51

therefore any ambiguity in their respective terms shall not be construed against
the drafting Party.

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

     14.13. INDEPENDENT CONTRACTORS. It is expressly agreed that GelTex and
Genzyme shall be independent contractors and that, except as members of RenaGel
LLC, the relationship between the two Parties shall not constitute a
partnership, joint venture or agency. Neither GelTex nor Genzyme 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.

     14.14. WAIVERS. No delay on the part of any party in exercising any right,
power or privilege hereunder shall operate as a waiver thereof nor shall any
waiver on the part of any party of any such right, power or privilege, nor any
single or partial exercise of any such right, power or privilege, preclude any
further exercise thereof or the exercise of any other such right, power or
privilege.

     14.15. 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.

                [REMAINDER OF THIS PAGE INTENTIONALLY LEFT BLANK]

                                       45

<PAGE>   52

     IN WITNESS WHEREOF, the parties have executed this Agreement as of the date
first set forth above.

                                     GELTEX PHARMACEUTICALS, INC.

                                     By: /s/ Mark Skaletsky
                                        ---------------------------------------

                                     Title: President and CEO
                                           ------------------------------------

                                     GENZYME CORPORATION

                                     By: /s/ Peter Wirth
                                        ---------------------------------------

                                     Title: Executive Vice President
                                           ------------------------------------

                                     RENAGEL LLC

                                     By:      GelTex Pharmaceuticals, Inc.

                                     By: /s/ Mark Skaletsky
                                        ---------------------------------------

                                     Title: President and CEO
                                           ------------------------------------

                                       46<PAGE>   1
                                                                    Exhibit 10.2

                              AMENDED AND RESTATED

                               OPERATING AGREEMENT

                                       of

                                   RENAGEL LLC

                            dated as of April 1, 2000

<PAGE>   2

                                TABLE OF CONTENTS

ARTICLE 1.  FORMATION AND MEMBERSHIP..........................................1
         SECTION 1.1  Formation...............................................1
         SECTION 1.2  Member..................................................2
         SECTION 1.3  Management..............................................2

ARTICLE 2.  OFFICES, NAME, ETC................................................2
         SECTION 2.1  Principal Office........................................2
         SECTION 2.2  Registered Office; Resident Agent.......................2
         SECTION 2.3  Name....................................................3
         SECTION 2.4  Term....................................................3
         SECTION 2.5  Business Ventures.......................................3

ARTICLE 3.  PURPOSES AND POWERS...............................................3
         SECTION 3.1  Purpose.................................................3
         SECTION 3.2  Powers..................................................4

ARTICLE 4.  MEMBERS AND THEIR CONTRIBUTIONS AND LOANS.........................4
         SECTION 4.1  Contributions...........................................4
         SECTION 4.2  Capital Accounts........................................5
         SECTION 4.3  Loans...................................................6
         SECTION 4.4  Additional Members......................................6
         SECTION 4.5  Liability of Members....................................6
         SECTION 4.6  Withdrawal of Members...................................7

ARTICLE 5.  ALLOCATIONS.......................................................7
         SECTION 5.1  Certain Definitions.....................................7
         SECTION 5.2  Allocations of Profit and Loss.........................10
         SECTION 5.3  Special Allocations....................................11

ARTICLE 6.  DISTRIBUTIONS....................................................14
         SECTION 6.1  Distribution of Company Funds..........................14

ARTICLE 7.  INDEMNIFICATION..................................................14
         SECTION 7.1  Indemnification of Members.............................14

ARTICLE 8.  ASSIGNABILITY OF MEMBERSHIP INTERESTS............................16
         SECTION 8.1  Assignment.............................................16
         SECTION 8.2  Substitute Members.....................................17
         SECTION 8.3  Rights of Assignees....................................17
         SECTION 8.4  Other Restrictions.....................................18

ARTICLE 9.  FISCAL YEAR, ACCOUNTING, INSPECTION OF BOOKS.....................18
         SECTION 9.1  Fiscal Year and Accounting.............................18

<PAGE>   3

         SECTION 9.2  Inspection of Books....................................18

ARTICLE 10.  DISSOLUTION.....................................................18
         SECTION 10.1  Events of Dissolution.................................18
         SECTION 10.2  Consent to Continue Company...........................19
         SECTION 10.3  Distribution Upon Dissolution.........................19

ARTICLE 11.  GENERAL PROVISIONS..............................................20
         SECTION 11.1  Complete Agreement; Modification......................20
         SECTION 11.2  Governing Law; Severability...........................21
         SECTION 11.3  Notice................................................21
         SECTION 11.4  Pronouns..............................................21
         SECTION 11.5  Titles................................................22
         SECTION 11.6  Successors and Assigns................................22
         SECTION 11.7  Counterparts..........................................22

<PAGE>   4

                              AMENDED AND RESTATED

                               OPERATING AGREEMENT

                                       OF

                                   RENAGEL LLC

     THIS AMENDED AND RESTATED OPERATING AGREEMENT (this "AGREEMENT") is made
and adopted as of April 1, 2000 by and among GelTex Pharmaceuticals, Inc., a
Delaware corporation having its principal place of business at 153 Second
Avenue, Waltham, Massachusetts 02451 ("GELTEX"), RenaGel, Inc., a Delaware
corporation and a wholly-owned subsidiary of GelTex having its principal place
of business at 153 Second Avenue, Waltham, Massachusetts 02451 ("RENAGEL,
INC."), Genzyme Corporation, a Massachusetts corporation having its principal
place of business at One Kendall Square, Cambridge, Massachusetts 02139
("GENZYME") and such other persons who may become members of RenaGel LLC (the
"COMPANY") in accordance with law or the terms hereof (hereinafter collectively
referred to as the "MEMBERS" and individually as a "MEMBER"). GelTex and
RenaGel, Inc. are hereinafter collectively referred to as the "GELTEX
COMPANIES." Capitalized terms used but not defined herein shall be given the
same meaning as provided in the Amended and Restated Collaboration Agreement of
even date herewith among the Company, GelTex and Genzyme ("COLLABORATION
AGREEMENT"). This Agreement amends and restates the Operating Agreement dated as
of June 17, 1997 entered into by and among GelTex, RenaGel, Inc., Genzyme and
the Members, as amended.

                       ARTICLE 1. FORMATION AND MEMBERSHIP

<PAGE>   5

     SECTION 1.1 FORMATION. The Company has been organized as a limited
liability company pursuant to the Delaware Limited Liability Company Act (the
"ACT"). The Act shall govern the rights and liabilities of the parties hereto
except as otherwise expressly stated herein.

     SECTION 1.2 MEMBER. The sole initial Member of the Company was GelTex.
Following the execution and delivery of the Collaboration Agreement, GelTex
assigned one percent (1%) of its interest in the Company to RenaGel, Inc., and
RenaGel, Inc. was admitted as a Member of the Company. The Company elected under
Section 754 of the Internal Revenue Code of 1986, as amended ("IRC"), to apply
the provisions of Sections 734(b) and 743(b) of the IRC. Thereafter, effective
upon execution and delivery of the Purchase Agreement of even date herewith by
and between GelTex and Genzyme (the "PURCHASE AGREEMENT"), GelTex has sold and
assigned to Genzyme a fifty percent (50%) interest in the Company (subject to
adjustment as provided herein and in Section 4.2 of the Collaboration
Agreement). Upon execution and delivery of this Agreement, GelTex and RenaGel,
Inc. each hereby consent to the admission of Genzyme as a Member of the Company
and Genzyme is hereby admitted as a Member of the Company. Hence, the Members of
the Company are those persons listed on SCHEDULE A attached hereto, as amended
from time to time.

     SECTION 1.3 MANAGEMENT. The Company shall be managed by the Steering
Committee provided for in Section 8.2 of the Collaboration Agreement

                         ARTICLE 2. OFFICES, NAME, ETC.

     SECTION 2.1 PRINCIPAL OFFICE. The principal office of the Company shall be
located at 153 Second Avenue, Waltham, Massachusetts 02451 or such place within
the Commonwealth of Massachusetts as may be determined by the Members from time
to time. The Company shall maintain its records at such address.

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     SECTION 2.2 REGISTERED OFFICE; RESIDENT AGENT. The name and address of the
Company's registered agent for service of process in the State of Delaware shall
be Corporation Service Company, 1013 Centre Road, Wilmington, Delaware
19805-1297. The name and address of the Company's registered agent for service
of process in the Commonwealth of Massachusetts shall be GelTex Pharmaceuticals,
Inc., 153 Second Avenue, Waltham, Massachusetts 02451.

     SECTION 2.3 NAME. The business of the Company shall be conducted under the
name of "RenaGel LLC".

     SECTION 2.4 TERM. The term of the Company shall commence upon the filing of
the Certificate of Formation(the "EFFECTIVE DATE") and shall be perpetual until
it is terminated as hereinafter provided.

     SECTION 2.5 BUSINESS VENTURES. Any Member may engage independently or with
others in other business ventures of every nature and description, and neither
the Company nor any Member shall have any rights in and to such independent
ventures or the income or profits derived therefrom; provided, however, that a
Member's participation in such venture is subject to and consistent with the
provisions of Section 2.2 of the Collaboration Agreement.

                         ARTICLE 3. PURPOSES AND POWERS

     SECTION 3.1 PURPOSE. The purpose of the Company is to: (i) develop and
commercialize the Collaboration Products; (ii) act as a partner in limited
partnerships, general partnerships and limited liability partnerships, and as a
member of limited liability companies; and (iii) engage in any other business
permitted under the Act that the Members shall deem desirable or expedient.

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     SECTION 3.2 POWERS. The Company shall have all the powers necessary or
convenient to the conduct, promotion or attainment of the business, trade,
purposes or activities of the Company, including, without limitation, all the
powers of an individual, partnership, corporation or other entity.

              ARTICLE 4. MEMBERS AND THEIR CONTRIBUTIONS AND LOANS

     SECTION 4.1 CONTRIBUTIONS.

     (a)  Each Member has agreed to contribute the amounts and/or property set
forth in Sections 3.1, 3.3, 4.2 and 4.3 of the Collaboration Agreement. The
amount so contributed is hereinafter referred to as each Member's "CAPITAL
CONTRIBUTION". The cash and agreed value of any property contributed by each
Member as of the date hereof is set forth in SCHEDULE A attached hereto.

     (b)  Pursuant to the terms of the Collaboration Agreement, GelTex, on
behalf of the GelTex Companies, and Genzyme each has undertaken to make monthly
Capital Contributions to the Company in the amount equal to fifty percent (50%)
of all Program Costs (as defined in the Collaboration Agreement). If either
Genzyme or GelTex (on behalf of the GelTex Companies) fails to make all or any
portion of a monthly Capital Contribution, the other Member may elect to make
such Contribution (or a portion thereof). If either Genzyme or GelTex (on behalf
of the GelTex Companies) fails to make all or any portion of a monthly Capital
Contribution, the Percentage Interests (as defined below) shall be adjusted to
correspond to the percentage of cumulative Capital Contributions made by or on
behalf of each Member and subsequent monthly Capital Contributions shall be made
by the Members in proportion to their adjusted Percentage Interests.

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     (c)  No interest shall accrue on any Capital Contributions, and no Member
shall have the right to withdraw or to be repaid any capital it has contributed,
except as otherwise specifically provided in this Agreement.

     (d)  Each Member's percentage interest ("PERCENTAGE INTEREST") is as set
forth in SCHEDULE A hereto, subject to adjustment as provided in Section 4.1(b)
of this Agreement.

     SECTION 4.2 CAPITAL ACCOUNTS. A separate account (a "CAPITAL ACCOUNT")
shall be maintained for each Member and adjusted in accordance with Treasury
Regulation Section 1.704-1(b) as follows:

     (a)  There shall be credited to each Member's Capital Account the amount of
such Member's Capital Contribution as of the date, and to the extent, that such
Capital Contribution has been paid, and such Member's allocable share of Net
Profits (and any items in the nature of income or gain separately allocated to
such Member); and there shall be charged against each Member's Capital Account
the amount of all distributions to such Member and such Member's allocable share
of Net Losses (and any items in the nature of losses or deductions separately
allocated to such Member). Capital Contributions made by or on behalf of the
GelTex Companies shall be credited to their Capital Accounts in proportion to
their relative Percentage Interests.

     (b)  If the Company at any time distributes any of its assets in kind to
any Member, the Capital Account of each Member shall be adjusted to account for
that Member's allocable share (as determined under Section 5.1 below) of the Net
Profits or Net Losses that would have been realized by the Company had it sold
the assets that were distributed at their respective fair market values
immediately prior to their distribution.

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     (c)  In the event any Member's interest is transferred in accordance with
the terms of this Agreement, the transferee shall succeed to the Capital Account
of the transferor to the extent it relates to the transferred interest.

     SECTION 4.3 LOANS. The Members shall not make loans to the Company unless
the Members unanimously agree in writing to make such loans.

     SECTION 4.4 ADDITIONAL MEMBERS. Except as otherwise provided in Section 8.2
below with respect to Substitute Members, additional Members may only be
admitted with the prior written unanimous approval of the Members. Such
additional Members shall execute and acknowledge a counterpart to this Agreement
or shall otherwise evidence in writing their agreement to be bound by the terms
hereof in such manner as the Members shall determine.

     SECTION 4.5 LIABILITY OF MEMBERS.

     (a)  No Member shall be liable for the obligations of the Company solely by
reason of being a Member.

     (b)  No Member shall be required to make any contributions to the capital
of the Company other than as provided in this Article 4.

     (c)  No Member shall be personally liable to the Company or its other
Members for monetary damages for breach of fiduciary duty as a Member to the
extent permitted by applicable law; provided, however, that this provision shall
not eliminate the liability of a Member (i) for any breach of the Member's duty
of loyalty to the Company or its other Members, (ii) for acts or omissions not
in good faith or which involve intentional misconduct or a knowing violation of
law or (iii) for any transaction from which the Member derived an improper
personal benefit. No amendment to or repeal of this Section 4.5(c) shall apply
to or have any effect on the liability or

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alleged liability of any Member for or with respect to any acts or omissions of
such Member occurring prior to such amendment or repeal.

     SECTION 4.6 WITHDRAWAL OF MEMBERS. No Member shall have the right to
withdraw from the Company or to demand a return of its capital interest at any
time except upon termination and dissolution of the Company, unless agreed to by
the unanimous written consent of the other Members.

                             ARTICLE 5. ALLOCATIONS

     SECTION 5.1 CERTAIN DEFINITIONS. For purposes of this Agreement, the
following terms shall have the meanings given them in this Article 5:

          (a)  "ADJUSTED CAPITAL ACCOUNT" for a Member means such Member's
               Capital Account (i) reduced by the net adjustments, allocations
               and distributions described in Treasury Regulation Sections
               1.704-1(b)(2)(ii)(d)(4), (5) and (6) which, as of the end of the
               Company's taxable year are reasonably expected to be made to such
               Member, and (ii) increased by the sum of (A) the amounts a Member
               is deemed obligated to restore pursuant to the penultimate
               sentences of Treasury Regulation Sections 1.704-2(g)(1) and
               2(i)(5), (B) the excess, if any, of such Member's Capital
               Contribution over such Member's actual paid-in capital
               contribution and (C) that portion of any indebtedness of the
               Company (other than "partner nonrecourse debt" as defined in
               Treasury Regulation Section 1.704-2(b)(4)) with respect to which
               the Member bears the economic risk of loss that such indebtedness
               would not be repaid out of the assets of the Company if all of
               the assets of the Company were sold at

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               their respective book values as of the end of the fiscal period
               and the proceeds from the sales together with any amounts
               described in clause (B) above, were used to pay the liabilities
               of the Company.

          (b)  "NET PROFITS" and "NET LOSSES" mean the taxable income or loss,
               as the case may be, for a period (or from a transaction) as
               determined in accordance with Section 703(a) of the IRC (for this
               purpose, all items of income, gain, loss or deduction required to
               be separately stated pursuant to IRC Section 703(a)(1) shall be
               included in taxable income or loss) computed with the following
               adjustments:

               (i)  To the extent required by (and in the manner described in)
                    Treasury Regulation 1.704-1(b)(2), items of gain, loss and
                    deduction shall be computed based upon the book values of
                    the Company's assets rather than upon such assets' adjusted
                    bases for federal income tax purposes (if different);

               (ii) Any tax-exempt income received by the Company shall be
                    included as an item of gross income;

              (iii) The amount of any adjustments to the adjusted bases (or
                    book values if clause (i) above applies) of any assets of
                    the Company pursuant to IRC Section 743 shall not be taken
                    into account; and

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               (iv) Any expenditure of the Company described or treated as being
                    described in IRC Section 705(a)(2)(B) shall be treated as a
                    deductible expense.

          (c)  "MEMBER LOAN NONRECOURSE DEDUCTIONS" means any Company deductions
               that would be Nonrecourse Deductions if they were not
               attributable to a liability owed to or guaranteed by a Member
               within the meaning and intent of Treasury Regulation Section
               1.704-2(i).

          (d)  "MEMBER LOAN MINIMUM GAIN" has the meaning set forth in Treasury
               Regulation Section 1.704-2(i)(3).

          (e)  "MINIMUM GAIN" has the meaning set forth in Treasury Regulation
               Section 1.704-2(d). Minimum Gain shall be computed separately for
               each Member in a manner consistent with the Treasury Regulations
               under IRC Section 704(b).

          (f)  "NONRECOURSE DEDUCTIONS" has the meaning set forth in Treasury
               Regulation Section 1.704-2(b)(1). The amount of Nonrecourse
               Deductions for a taxable year of the Company shall be determined
               according to the provisions of Treasury Regulation Section
               1.704-2(c).

          (g)  "NONRECOURSE LIABILITY" means any liability of the Company with
               respect to which no Member has personal liability, as determined
               in accordance with IRC Section 752 and the Treasury Regulations
               promulgated thereunder.

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     SECTION 5.2 ALLOCATIONS OF PROFIT AND LOSS. As of the end of each fiscal
year of the Company, or at the time any allocation is determined to be necessary
by the Members, Net Profits or Net Losses shall be allocated as follows:

     (a) Except as provided in Sections 5.2(b) and 5.3, any allocation required
by this Section 5.2 to be made to the Members shall be allocated among the
Members in proportion to their respective Percentage Interests.

     (b) After making the special allocations provided for in Section 5.3, there
shall be allocated to the GelTex Companies items of gross income of the Company
in an amount equal to (i) the excess, if any, of the cumulative Distribution
Margin for sales of Collaboration Products (as such terms are defined in the
Collaboration Agreement) over the cumulative amount of items of gross income
previously allocated to the GelTex Companies pursuant to this section 5.2(b)
multiplied by (ii) a fraction, the numerator of which shall be the GelTex
Companies' aggregate Percentage Interest during the applicable period, and the
denominator of which shall be Genzyme's Percentage Interest during the
applicable period. All amounts allocated to the GelTex Companies shall be shared
by them in proportion to their relative Percentage Interests.

     (c) With respect to the allocation of Net Losses or Net Profits pursuant to
this Section 5.2 among the Members for any fiscal year in which an additional or
substitute Member is admitted to the Company or there is an adjustment to the
Percentage Interests during such fiscal year, all Net Losses or Net Profits so
allocable shall be allocated in a manner which takes into account the varying
Percentage Interests during such fiscal year based on an accounting convention
chosen by the Members. In no event shall a retroactive allocation of Net Losses
be made pursuant to this Section 5.2.

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     SECTION 5.3 SPECIAL ALLOCATIONS. Notwithstanding the provisions of Section
5.2 above, the following allocations of Net Profits and Net Losses and items
thereof shall be made:

     (a) If, during any year a Member unexpectedly receives any adjustment,
allocation or distribution described in Treasury Regulation Section
1.704-1(b)(2)(ii)(d)(4), (5) or (6) and, as a result of such adjustment,
allocation or distribution, such Member's Adjusted Capital Account has a
negative balance (computed with the adjustments set forth in clauses (i) and
(ii) of Section 5.1(a)), then items of gross income for such year (and, if
necessary, subsequent years) shall first be allocated to such Member in the
amount necessary to eliminate such negative balance as quickly as possible. This
Section 5.3(a) is intended to constitute a "qualified income offset" provision
within the meaning of the above Treasury Regulations, and shall be so
interpreted.

     (b) Nonrecourse Deductions for a taxable year or other period shall be
specially allocated among the Members in proportion to their Percentage
Interests.

     (c) Any Member Loan Nonrecourse Deduction for any taxable year or other
period shall be specially allocated to the Member or Members who bear the risk
with respect to the loan to which the Member Loan Nonrecourse Deduction is
attributable in accordance with Treasury Regulation Section 1.704-2(b).

     (d) In no event shall Net Losses of the Company be allocated to a Member if
such allocation would cause or increase a negative balance in such Member's
Adjusted Capital Account.

     (e) Except as set forth in Treasury Regulation Section 1.704-2(f)(2), (3)
and (4), if, during any taxable year, there is a net decrease in Minimum Gain,
each Member, prior to any other allocation pursuant to this Article 5, shall be
specially allocated items of gross income and gain for such taxable year (and,
if necessary, subsequent taxable years) in an amount equal to that Member's

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share of the net decrease in Minimum Gain, computed in accordance with Treasury
Regulation Section 1.704-2(g). Allocation of gross income and gain pursuant to
this Section 5.3(e) shall be made first from gain recognized from the
disposition of Company assets subject to non-recourse liabilities (within the
meaning of the Treasury Regulations promulgated under IRC Section 752), to the
extent of the Minimum Gain attributable to those assets, and thereafter, from a
pro rata portion of the Company's other items of income and gain for the taxable
year. It is the intent of the parties hereto that any allocation pursuant to
this Section 5.3(e) shall constitute a "minimum gain chargeback" under Treasury
Regulation Section 1.704-2(f). With respect to a net decrease in Member Loan
Minimum Gain, items of gross income shall be specially allocated consistent with
the preceding sentence, and Treasury Regulation Section 1.704-2(i)(4).

     (f) In the event that Net Profits, Net Losses or items thereof are
allocated to one or more Members pursuant to paragraphs (a) or (d) above,
subsequent Net Profits and Net Losses will first be allocated (subject to the
provisions of paragraphs (a) through (d)) to the Members in a manner designed to
result in each Member having a Capital Account balance equal to what it would
have been had the original allocation of Net Profits, Net Losses or items
thereof pursuant to paragraphs (a) or (d) not occurred.

     (g) The respective Percentage Interests in the Net Profits and Net Losses
or items thereof shall remain as set forth above (subject to adjustment as
provided in Section 4.1(b) and Article 5) unless changed by amendment to this
Agreement or by an assignment of an interest in the Company authorized by the
terms of this Agreement. Except as otherwise provided herein, for tax purposes,
all items of income, gain, loss, deduction or credit shall be allocated to the
Members in the same manner as are Net Profits and Net Losses; provided, however,
that if, as a result of clause (i) of

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Section 5.1(b), the book value of any property of the Company was used in
computing Net Profits or Net Losses, then items of income, gain, deduction or
credit related to such property for tax purposes shall be allocated among the
Members so as to take account of the variation between the adjusted basis of the
property for tax purposes and its book value in the manner provided for under
IRC Section 704(c).

     (h) If a Member's Percentage Interest is reduced (provided the reduction
does not result in a complete termination of the Member's interest in the
Company), the Member's share of the Company's "unrealized receivables" and
"substantially appreciated inventory" (within the meaning of IRC Section 751)
shall not be reduced, so that, notwithstanding any other provisions of this
Agreement to the contrary, that portion of the Net Profit otherwise allocable
upon a liquidation or dissolution of the Company pursuant to Article 5 hereof
which is taxable as ordinary income (recaptured) for federal income tax purposes
shall, to the extent possible without increasing the total gain to the Company
or to any Member, be specially allocated among the Members in proportion to the
deductions (or basis reductions treated as deductions) giving rise to such
recapture.

     (i) In each taxable year of the Company, items of deduction and credit
attributable to Program Costs shall be allocated to the Members in proportion to
the Capital Contributions which funded the applicable expenditure.

                            ARTICLE 6. DISTRIBUTIONS

     SECTION 6.1 DISTRIBUTION OF COMPANY FUNDS. The timing of distributions by
the Company (other than distributions in dissolution to which Section 10.3
applies) shall be determined in accordance with the provisions of Section 4.4 of
the Collaboration Agreement. Such distributions shall be made first one hundred
percent (100%) to the GelTex Companies until the GelTex

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Companies have received distributions equal to the amount of items of gross
income allocated to them pursuant to Section 5.2(b) hereof and, thereafter, to
the Members in proportion to their positive Capital Accounts reduced by the
amounts of their initial Capital Contributions listed in SCHEDULE A hereto;
provided, however, that the amount of Net Profit distributable to the Members
shall be reduced by the amount required to fund the budgeted capital, working
capital and reserve requirements of the Company during the one hundred and
eighty (180) day period following the proposed distribution date and by such
other amounts as the Steering Committee reasonably determines to be necessary or
appropriate for the operation of the Company.

                           ARTICLE 7. INDEMNIFICATION

     SECTION 7.1 INDEMNIFICATION OF MEMBERS.

     (a) The Company shall, to the fullest extent permitted by the Act, as
amended from time to time, indemnify each Member, each Member's Affiliates, and
the respective directors, officers, employees and agents of each Member and its
Affiliates (collectively, "INDEMNIFIED PERSONS") from and against all expenses
and liabilities (including counsel fees, judgments, fines, excise taxes,
penalties and amounts paid in settlements) reasonably incurred by or imposed
upon an Indemnified Person in connection with any threatened, pending or
completed action, suit or other proceeding, whether civil, criminal,
administrative or investigative, in which such Indemnified Person may become
involved by reason of (i) any act performed by such Indemnified Person in
connection with the performance of and within the scope of the authority
conferred by the Collaboration Agreement or (ii) such Indemnified Person's
service as a director, officer, manager or member of the Company or any of its
subsidiaries or, if such service was undertaken at the request of the Company,
such

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Indemnified Person's service as a director, officer or trustee of, or in a
similar capacity with, another organization.

     (b) Indemnification may include payment by the Company of expenses in
defending an action or proceeding in advance of the final disposition of such
action or proceeding upon receipt of an undertaking by the Indemnified Person to
repay such payment if it is ultimately determined that such Indemnified Person
is not entitled to indemnification under this Article 7, which undertaking may
be accepted without reference to the financial ability of the Indemnified Person
to make such repayments.

     (c) The Company shall not indemnify any Indemnified Person in connection
with a proceeding (or part thereof) initiated by such person unless such
Indemnified Person is successful on the merits, the proceeding was authorized by
the Members or the proceeding seeks a declaratory judgment regarding such
Indemnified Person's own conduct.

     (d) The indemnification rights provided in this Article 7 (i) shall not be
deemed exclusive of any other rights to which Indemnified Persons may be
entitled under any law, agreement or vote of disinterested Members or otherwise
and (ii) shall inure to the benefit of the heirs, executors and administrators
of Indemnified Persons. The Company may, to the extent authorized from time to
time by its Members, grant indemnification rights to employees or agents of the
Company or persons other than Indemnified Persons serving the Company and such
rights may be equivalent to, or greater or less than, those set forth in this
Article 7.

     (e) No indemnification shall be provided for any Indemnified Person with
respect to (i) any matter as to which such Indemnified Person shall have been
finally adjudicated in any proceeding not to have acted in good faith in the
reasonable belief that such Indemnified Person's

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action was in the best interests of the Company, (ii) any act which constitutes
gross negligence or wilful misconduct or (iii) any matter disposed of by a
compromise payment by such Indemnified Person, pursuant to a consent decree or
otherwise, unless the payment and indemnification thereof have been approved by
the Members, which approval shall not unreasonably be withheld, or by a court of
competent jurisdiction.

     (f) Any amendment or repeal of the provisions of this Article 7 shall not
adversely affect any right or protection of an Indemnified Person with respect
to any act or omission of such Indemnified Person occurring prior to such
amendment or repeal.

                ARTICLE 8. ASSIGNABILITY OF MEMBERSHIP INTERESTS

     SECTION 8.1 ASSIGNMENT.

     (a) Except in accordance with Article 13 of the Collaboration Agreement, a
Member may not assign his or her interest in whole or in part to any assignee
which is not already a Member without the prior written consent of all of the
other Members who may or may not consent in their absolute discretion.

     (b) An assignment of a Member's interest does not of itself dissolve the
Company or permit the assignee to participate in the business and affairs of the
Company or to become a Member or exercise any rights or powers of a Member.

     SECTION 8.2 SUBSTITUTE MEMBERS. No assignee of a Member's interest (other
than an assignee which is already a Member) shall have the right to be admitted
as a substitute member in place of the assignor (a "SUBSTITUTE MEMBER") unless:

          (a) the assignor shall designate in writing satisfactory to the other
     Members the intention that the assignee is to become a Substitute Member;

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          (b) the assignee shall agree in writing to be bound by all of the
     terms of this Agreement;

          (c) all of the other Members consent in writing to the admission of
     the assignee as a Substitute Member, which consent may be withheld in their
     absolute discretion;

          (d) the assignee shall execute and/or deliver such instruments,
     including without limitation, an opinion of counsel satisfactory to the
     Members, to the effect that such proposed assignment and substitution does
     not violate the registration requirements of state or federal securities
     laws, and such instrument as the Members deem necessary or desirable to
     effect such assignee's admission as a Substitute Member and to evidence the
     assignee's acceptance of the terms of this Agreement; and

          (e) the assignee shall pay all reasonable expenses in connection with
     the assignee's admission as a Substitute Member.

     SECTION 8.3 RIGHTS OF ASSIGNEES. An assignee who does not become a
Substitute Member shall succeed only to the rights of the assignor to receive
allocations and distributions from the Company as provided in Articles 5, 6 and
10 hereof, and shall not have the right to become a Member or exercise any
rights or powers of a Member.

     SECTION 8.4 OTHER RESTRICTIONS. A Member may not pledge, encumber or
hypothecate any of its interest without the consent of the other Members.

             ARTICLE 9. FISCAL YEAR, ACCOUNTING, INSPECTION OF BOOKS

     SECTION 9.1 FISCAL YEAR AND ACCOUNTING. Except as otherwise approved by the
Members, or required by law, the fiscal year of the Company shall be the
calendar year and the books of the Company shall be kept on the accrual method.

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     SECTION 9.2 INSPECTION OF BOOKS. The books of the Company shall at all
times be available for inspection and audit by any Member at the Company's
principal place of business during business hours. The Company shall furnish
each Member with all necessary tax reporting information as to its interest in
the Company, with an annual balance sheet and profit and loss statement and with
a cash flow statement showing any distributions made to the Members, within
sixty (60) days after the close of each fiscal year.

                             ARTICLE 10. DISSOLUTION

     SECTION 10.1 EVENTS OF DISSOLUTION. The term of the Company shall commence
on the Effective Date and shall be in full force and effect until the earliest
of the following:

          (a) the sale or disposition of all or substantially all of the Company
property;

          (b) the dissolution of the Company by the unanimous written consent of
the Members;

          (c) the bankruptcy or dissolution of a Member other than RenaGel,
Inc.; provided, however, that if there are at least two remaining Members, the
Members may consent to the continuation of the business of the Company after the
occurrence of such an event, pursuant to Section 18-802 of the Act and Section
10.2 of this Agreement;

          (d) the entry of a decree of judicial dissolution under Section 18-802
of the Act;

          (e) the occurrence of any event, other than those referred to in
paragraph (d), which causes dissolution of a limited liability company under the
Act; or

          (f)  upon the occurrence of an event and at the time specified in
Article 13 of the Collaboration Agreement.

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     Notwithstanding the dissolution of the Company, the business of the Company
shall continue to be governed by this Agreement until the winding up of the
Company occurs.

     SECTION 10.2 CONSENT TO CONTINUE COMPANY. The Members may vote to continue
the business of the Company within 90 days after the occurrence of an event of
dissolution set forth in Section 10.1(d) of this Agreement, pursuant to and in
accordance with Section 18-801(4) of the Act. The agreement of the remaining
Members holding a majority of the remaining Percentage Interests shall
constitute the consent of the Members to the continuation of the Company.

     SECTION 10.3 DISTRIBUTION UPON DISSOLUTION.

     (a) After payment of liabilities owing to creditors, the Members or
liquidator shall set up such reserves as they deem reasonably necessary for any
contingent or unforeseen liabilities or obligations of the Company, including
the expenses of liquidation. Such reserves may be paid over by the Members or
liquidator to a bank, to be held in escrow for the purpose of paying any such
contingent or unforeseen liabilities or obligations and, at the expiration of
such period as the Members or liquidator may deem advisable, such reserves shall
be distributed to all of the Members or their assigns in the manner set forth in
Section 10.3(b) below. In the event that any part of such net assets consists of
securities or other non-cash assets, the Members or liquidator may (but shall
not be required to) take whatever steps they deem appropriate to convert such
assets into cash or into any other form that would facilitate the distribution
thereof.

     (b) After payment has been made pursuant to Section 10.3(a) above, the
Members or the liquidator shall cause the remaining net assets of the Company to
be distributed to and among the Members in proportion to and to the extent of
their positive Capital Account balances (after such balances have been adjusted
to reflect all allocations of Net Profits and Net Losses and the payments

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made in Section 10.3(a) above). Cash and non-cash assets shall be distributed to
each Member on a pro rata basis, or in such other manner as the Members may
agree, with all noncash assets being distributed on the basis of their fair
market value.

     (c) The Company shall terminate when all property has been distributed
among the Members. Upon such termination, the Members shall execute and cause to
be filed a certificate of cancellation of the Company, as provided for in
Section 18-203 of the Act, and any and all other documents necessary in
connection with the termination of the Company.

                         ARTICLE 11. GENERAL PROVISIONS

     SECTION 11.1 COMPLETE AGREEMENT; MODIFICATION. This Agreement, the
Collaboration Agreement and the Purchase Agreement together contain a complete
statement of all the agreements among the parties with respect to the Company.
There are no representations, agreements, arrangements or undertakings, oral or
written, between or among the parties to this Agreement relating to the subject
matter of this Agreement which are not fully expressed in this Agreement. This
Agreement may be amended or modified only with the unanimous consent of the
Members.

     SECTION 11.2 GOVERNING LAW; SEVERABILITY. All questions with respect to the
construction of this Agreement and the rights and liabilities of the parties
shall be determined in accordance with the applicable provisions of the laws of
the State of Delaware, and this Agreement is intended to be performed in
accordance with, and only to the extent permitted by, all applicable laws,
ordinances, rules and regulations of such state. If any provision of this
Agreement, or the application thereof to any person or circumstances, shall, for
any reason and to any extent, be invalid or unenforceable, the remainder of this
Agreement and the application of that provision to other persons or
circumstances shall not be affected but rather be enforced to the extent
permitted by law.

                                       20

<PAGE>   24

     SECTION 11.3 NOTICE. All notices, requests, consents and statements
hereunder shall be deemed to have been properly given if mailed from within the
United States by prepaid certified mail, return receipt requested, or if sent by
prepaid telegram, or overnight delivery service, or if hand delivered, addressed
in each case if to the Company at its principal place of business and, if to any
Member, to the address set forth herein, or to such other address or addresses
as any such Member shall have theretofore designated in writing to the Company
in accordance with this Section 11.3.

     SECTION 11.4 PRONOUNS. Feminine or masculine pronouns shall be substituted
for the neuter pronouns, neuter pronouns for masculine or feminine pronouns,
plural for the singular and the singular for the plural, in any place in this
Agreement where the context may require such substitution.

     SECTION 11.5 TITLES. The titles of Articles and Sections are included only
for convenience and shall not be construed as a part of this Agreement or in any
respect affecting or modifying its provisions.

     SECTION 11.6 SUCCESSORS AND ASSIGNS. This Agreement shall be binding upon
and inure to the benefit of all parties hereto and their heirs, successors,
assigns and legal representatives.

     SECTION 11.7 COUNTERPARTS. This Agreement may be signed in one or more
counterparts and all counterparts so executed shall constitute one agreement
binding on all parties hereto, notwithstanding that all parties have not signed
the original or the same counterpart.

                                       21

<PAGE>   25

     IN WITNESS WHEREOF, we have affixed our signatures as of the day first
above written.

MEMBERS:
-------

GELTEX PHARMACEUTICALS, INC.

By: /s/ Mark Skaletsky
   --------------------------------------

Print Name: Mark Skaletsky
           ------------------------------

Title: President and CEO
      -----------------------------------

RENAGEL, INC.

By: /s/ Mark Skaletsky
   --------------------------------------

Print Name: Mark Skaletsky
           ------------------------------

Title: President
      -----------------------------------

GENZYME CORPORATION

By: /s/ Peter Wirth
   --------------------------------------

Print Name: Peter Wirth
           ------------------------------

Title: Executive Vice President
      -----------------------------------

                                       22

<PAGE>   26

                                   Schedule A
                                   ----------

<TABLE>
<CAPTION>

Members                         Capital Contribution        Percentage Interest
-------                         --------------------        -------------------

<S>                                 <C>                           <C>
GelTex Pharmaceuticals, Inc.        $24,500,000                    49.00%

RenaGel, Inc.                          $500,000                     1.00%

Genzyme Corporation                 $25,000,000                    50.00%
                                    -----------                   ------

        TOTAL:                      $50,000,000                   100.00%
</TABLE>

                                       23

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