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                                                                    Exhibit 10.2


                              AMENDED AND RESTATED

                               OPERATING AGREEMENT

                                       of

                                   RENAGEL LLC

                            dated as of April 1, 2000

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                                TABLE OF CONTENTS

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

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

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

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

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

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

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

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

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


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

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

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



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                              AMENDED AND RESTATED

                               OPERATING AGREEMENT

                                       OF

                                   RENAGEL LLC


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

                       ARTICLE 1. FORMATION AND MEMBERSHIP

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

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

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

                         ARTICLE 2. OFFICES, NAME, ETC.

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


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

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

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

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

                         ARTICLE 3. PURPOSES AND POWERS

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


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

              ARTICLE 4. MEMBERS AND THEIR CONTRIBUTIONS AND LOANS

     SECTION 4.1 CONTRIBUTIONS.


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

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


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

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

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

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

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


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

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

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

     SECTION 4.5 LIABILITY OF MEMBERS.

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

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

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


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

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

                             ARTICLE 5. ALLOCATIONS

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

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


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

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

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

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

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


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

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

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

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

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

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


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

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

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

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



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

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

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

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

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

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


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

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

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


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

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

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

                            ARTICLE 6. DISTRIBUTIONS

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


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

                           ARTICLE 7. INDEMNIFICATION

     SECTION 7.1 INDEMNIFICATION OF MEMBERS.

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


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

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

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

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

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


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

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

                ARTICLE 8. ASSIGNABILITY OF MEMBERSHIP INTERESTS

     SECTION 8.1 ASSIGNMENT.

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

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

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

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


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

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

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

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

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

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

             ARTICLE 9. FISCAL YEAR, ACCOUNTING, INSPECTION OF BOOKS

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


                                       17

<PAGE>   21


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

                             ARTICLE 10. DISSOLUTION

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

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

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

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

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

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

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


                                       18

<PAGE>   22

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

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

     SECTION 10.3 DISTRIBUTION UPON DISSOLUTION.

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

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


                                       19

<PAGE>   23


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

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

                         ARTICLE 11. GENERAL PROVISIONS

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

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


                                       20

<PAGE>   24



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

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

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

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

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


                                       21

<PAGE>   25


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


MEMBERS:
-------


GELTEX PHARMACEUTICALS, INC.


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

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

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


RENAGEL, INC.


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

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

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


GENZYME CORPORATION


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

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

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


                                       22

<PAGE>   26


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

<TABLE>
<CAPTION>

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

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

RenaGel, Inc.                          $500,000                     1.00%

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

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



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