<PAGE>   1
                                                                  EXHIBIT 10.18

                                      Confidential Treatment has been requested
                                      for certain information omitted and filed
                                                       separately with the SEC.







                             COLLABORATION AGREEMENT

                                      among

                          GELTEX PHARMACEUTICALS, INC.,

                               GENZYME CORPORATION

                                       and

                                   RENAGEL LLC

                            dated as of June 17, 1997






<PAGE>   2


                                TABLE OF CONTENTS

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 *****"............................................. 3
     1.12.   "Distributor ********"........................................... 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



* Confidential Treatment requested for information omitted and filed 
  separately with the SEC.

                                        i


<PAGE>   3


     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



                                       ii


<PAGE>   4


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
     9.2.    Filing, Prosecution and Maintenance of Patent Rights............ 26

     

                                       iii


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             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. Upon Change of Control.................................. 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. Upon a Change of Control................................ 37
             13.3.5. Upon Bankruptcy......................................... 38
             13.3.6. Fair Value.............................................. 39




                                       iv


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     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




                                        v



<PAGE>   7


                             COLLABORATION AGREEMENT


        THIS COLLABORATION AGREEMENT dated as of June 17, 1997 (the "AGREEMENT")
is made by and among GelTex Pharmaceuticals, Inc., a Delaware corporation having
its principal place of business at 303 Bear Hill Road, Waltham, Massachusetts
02154 ("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 303 Bear Hill Road, Waltham, Massachusetts
02154 ("RENAGEL LLC"). GelTex, Genzyme and RenaGel LLC are sometimes referred to
herein individually as a "PARTY" and collectively as the "PARTIES."

                                 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 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






<PAGE>   8


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 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



                                        2


<PAGE>   9


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 ******" with respect to Net Sales of a
Collaboration Product shall mean ********

        1.12.   "DISTRIBUTOR** *******" shall mean ******

* Confidential Treatment requested for information omitted and filed 
  separately with the SEC.


                                        3


<PAGE>   10


*********. 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** ******** 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 ******* 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 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


* Confidential Treatment requested for information omitted and filed 
  separately with the SEC.
                                        4


<PAGE>   11


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).

        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

* Confidential Treatment requested for information omitted and filed 
  separately with the SEC.

                                        5


<PAGE>   12


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 *************.

        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 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, 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


* Confidential Treatment requested for information omitted and filed 
  separately with the SEC.
                                        6


<PAGE>   13


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 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.



                                        7


<PAGE>   14


        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.


               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



                                        8


<PAGE>   15


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 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



                                        9


<PAGE>   16


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 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



                                       10


<PAGE>   17


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 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.




                                       11


<PAGE>   18


        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 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.




                                       12


<PAGE>   19


        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.

        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

* Confidential Treatment requested for information omitted and filed 
  separately with the SEC.

                                       13


<PAGE>   20


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. GelTex 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 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.

* Confidential Treatment requested for information omitted and filed 
  separately with the the SEC.

                                       14


<PAGE>   21


                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 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.

* Confidential Treatment requested for information omitted and filed 
  separately with SEC.

                                       15


<PAGE>   22


        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 FDA in GelTex's name and shall promptly assign such NDA to
RenaGel LLC upon receipt of FDA approval thereof. Regulatory Approval filings
for Collaboration Products other than the NDA to be filed with the FDA for
RenaGel(R) shall be filed in the name of RenaGel LLC or, if required with
respect to filings to be made with governmental regulatory authorities other
than the FDA, in such other name as may be agreed upon by the Steering Committee
(such as filings for European Regulatory Approvals). 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.



                                       16


<PAGE>   23


        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 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 sell the Collaboration Products within the Territory and
for use within the Field.


* Confidential Treatment requested for information omitted and filed 
  separately with the SEC.
                                       17


<PAGE>   24


        6.3.    ORDERS AND FORECASTING. Genzyme shall purchase the Collaboration
Products exclusively from RenaGel LLC. As long as the Dow Agreement remains in
full force and effect, Genzyme shall provide RenaGel LLC with non-binding
forecasts and binding purchase orders in a manner consistent with RenaGel LLC's
obligations under Section 5.3 of the Dow Agreement. 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 *******.

                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.

                6.4.3.  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) 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


* Confidential Treatment requested for information omitted and filed 
  separately with the SEC.

                                       18


<PAGE>   25


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 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



                                       19


<PAGE>   26


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.

        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 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



                                       20


<PAGE>   27


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 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



                                       21


<PAGE>   28


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 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.




                                       22


<PAGE>   29


                              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 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



                                       23


<PAGE>   30


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., 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.




                                       24


<PAGE>   31


        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.

                (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 applications, patents or copyrights based thereon (collectively, the  
"INVENTIONS") that are discovered, made or conceived during and in connection
with ********** . 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.

* Confidential Treatment requested for information omitted and filed 
  separately with the SEC.


                                       25


<PAGE>   32


                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.

        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


* Confidential Treatment requested for information omitted and filed 
  separately with the SEC.
                                       26


<PAGE>   33


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
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 9.3 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



                                       27


<PAGE>   34


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.


                           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


* Confidential Treatment requested for information omitted and filed 
  separately with the SEC.
                                       28


<PAGE>   35


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 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.





                                       29


<PAGE>   36


                   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 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 Section 6.1.3 hereof will be marketed
and sold in all material


* Confidential Treatment requested for information omitted and filed 
  separately with the SEC.
                                       30


<PAGE>   37


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 the Starting
Material delivered by GelTex 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.

        11.4.   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.





                                       31


<PAGE>   38


                              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.

        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) enforce the terms of this Agreement



                                       32


<PAGE>   39


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).

                13.2.4. UPON CHANGE OF CONTROL. Either GelTex or Genzyme may
elect to terminate this Agreement (effective as of the effective date of such
transaction) in the event that:

                (a)     any Third Party or group of related Third Parties shall
directly or indirectly become the beneficial owner of capital stock representing
fifty percent (50%) or more of the total voting rights of all of the capital
stock of the other Party then outstanding or otherwise acquires the power to
direct or cause the direction of the management and policies of such Party or
the power to elect or appoint more than fifty percent (50%) of the members of
the Board of Directors of such Party; and

                (b)     the other Party shall consolidate or merge with any
other person and the stockholders of such Party of record immediately prior to
the consummation of such transaction do not beneficially own capital stock
representing fifty percent (50%) or more of the total voting rights of the
surviving corporation after the consummation of such transaction.

                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.


* Confidential Treatment requested for information omitted and filed 
  separately with the SEC.
                                       33


<PAGE>   40


        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)     all licenses granted pursuant to Article 3 shall be
revoked and, if RenaGel LLC is dissolved, the sublicense under the Nittobo
License (if obtained) and any applicable Regulatory Approval 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;

                (d)     the non-breaching Party shall become obligated to pay
the breaching 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 "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

* Confidential Treatment requested for information omitted and filed 
  separately with the SEC.

                                       34




<PAGE>   41


(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:

                (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)     all licenses granted pursuant to Article 3 shall be
revoked and, if RenaGel LLC is dissolved, any applicable Regulatory Approval and
clinical data owned or


* Confidential Treatment requested for information omitted and filed 
  separately with the SEC.
                                       35


<PAGE>   42


licensed by RenaGel LLC and any trademarks owned or licensed by RenaGel LLC
shall be assigned to GelTex; 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 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, all licenses granted pursuant to Article 3
shall be revoked and, if RenaGel LLC is dissolved, the sublicense under the
Nittobo License (if obtained) and any applicable Regulatory Approval and
clinical data owned or licensed by RenaGel LLC and any trademarks owned or
licensed by RenaGel LLC shall be assigned to the non-terminating Party;

                (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 ********

* Confidential Treatment requested for information omitted and filed 
  separately with the SEC.



                                       36


<PAGE>   43
*********** 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 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. UPON A CHANGE OF CONTROL. 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 13.2.4 above:

                (a)     the terminating Party shall obtain from the
non-terminating Party the exclusive and irrevocable 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)     all licenses granted pursuant to Article 3 shall be
revoked and, if


* Confidential Treatment requested for information omitted and filed 
  separately with the SEC.
                                       37


<PAGE>   44


RenaGel LLC is dissolved, the sublicense under the Nittobo License (if obtained)
and any applicable Regulatory Approval 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;

                (d)     the terminating Party shall become obligated to pay to
the non-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 "CHANGE OF CONTROL 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; and

                (e)     in any event, 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 royalty 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.

                13.3.5. 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;


* Confidential Treatment requested for information omitted and filed 
  separately with the SEC.

                                       38


<PAGE>   45


                (c)     all licenses granted to Article 3 shall be revoked and,
if RenaGel LLC is dissolved, the sublicense under the Nittobo License (if
obtained) any applicable Regulatory Approval 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;

                (d)     the terminating Party shall become obligated to pay to
the non-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 "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

* Confidential Treatment requested for information omitted and filed 
  separately with the SEC.

                                       39


<PAGE>   46


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.


                            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.

* Confidential Treatment Requested for information omitted and filed separately
  with the SEC.

                                       40


<PAGE>   47


        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 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.

        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



                                       41


<PAGE>   48


the addressee.

         If to                      GelTex Pharmaceuticals, Inc.
         GelTex or                  303 Bear Hill Road
         RenaGel, Inc.:             Waltham, Massachusetts 02154
                                    Attention: President
                                    Facsimile: (617) 672-5822

         with a copy to:            GelTex Pharmaceuticals, Inc.
                                    303 Bear Hill Road
                                    Waltham, Massachusetts 02154
                                    Attention: Corporate Counsel
                                    Facsimile: (617) 672-5822

         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

         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             303 Bear Hill Road
         by Genzyme):               Waltham, Massachusetts 02154
                                    Attention: President
                                    Facsimile: (617) 672-5822



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<PAGE>   49


         with a copy to:            GelTex Pharmaceuticals, Inc.
                                    303 Bear Hill Road
                                    Waltham, Massachusetts 02154
                                    Attention: Corporate Counsel
                                    Facsimile: (617) 672-5822

        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.

                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



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<PAGE>   50


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 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,



                                       44


<PAGE>   51


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