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                                                                  EXHIBIT 10.21


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

                               LICENSE AGREEMENT

THIS AGREEMENT is made on the 9th day of June, 1997, between Nitto Boseki Co.,
Ltd., a corporation organized under the laws of Japan, having its principal
place of business at 5-5, Nihombashi Tomizawacho, Chuo-ku, Tokyo 103, Japan
(hereinafter called "Nittobo"), and GelTex Pharmaceuticals, Inc., a corporation
organized under the laws of the State of Delaware, U.S.A., having its principal
place of business at 303 Bear Hill Road, Waltham, Massachusetts 02154, U.S.A.
(hereinafter called "GelTex").
        
        WHEREAS:

A.      Nittobo developed and possesses process Patents for *******



B.      GelTex has developed certain medicines named RenaGel and CholestaGel
        which are produced from ***** as starting material, and wishes to have
        manufacturing license right from Nittobo for producing ***** for
        pharmaceutical purposes.

C.      Nittobo is willing to grant a license to GelTex in accordance with the
        terms and conditions provided hereunder.

NOW, THEREFORE, in consideration for the mutual promises and obligations
expressed herein, the parties agree as follows.

Article 1  DEFINITIONS

1.1     ******** shall mean ********



1.2     ******** shall mean ********


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



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        and known as Nittobo's ********* manufactured in accordance with the
        Licensed Patents.

1.3     "RenaGel" shall mean ********** used for the treatment of
        hyperphosphatemia.

1.4     "CholestaGel" shall mean ********* used for the treatment of
        hypercholesterolemia.

1.5     "*****" shall mean ******** material to be
        manufactured as an intermediate to the GelTex Product hereunder.

1.6     "GelTex Product" shall mean RenaGel and CholestaGel.

1.7     "Licensed Patents" shall mean ********* and their corresponding
        patents registered in all countries as described in Annex I (List of
        the Licensed Patents) attached hereto, together with any divisions,
        continuations or continuations-in-part thereof.

1.8     "Know-How" shall mean trade secret and confidential information held by
        Nittobo which are useful for manufacture of **** and are actually
        employed by Nittobo for its commercial production. For the purpose of
        this Agreement, GelTex shall have no objection to include those
        confidential informations Nittobo has provided to GelTex during the
        course of negotiation of the sale of **** to GelTex.

1.9     "Territory" shall mean all the countries other than Japan, South Korea,
        Republic of China (Taiwan), People's Republic of China, Singapore,
        Malaysia, India, Thailand, Vietnam, Indonesia, Philippines, New Zealand
        and Australia. (such countries to be referred to as the "Chugai
        Territory")

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



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Article 2  GRANT OF LICENSE

2.1     Nittobo hereby grants to GelTex a non-exclusive license under the
        Licensed Patents and the Know-How to manufacture and sell ******
        in the Territory for the sole purpose of (i) using ******  as
        the starting material of GelTex Products to be sold in the Territory,
        and (ii) using ********** as the starting material for RenaGel to be
        manufactured by Dow or Abbott and sold by Chugai in the Chugai
        Territory, if Chugai requires ****** and if only Nittobo does not sell
        such ****** to Chugai. Provided however that GelTex will use best
        efforts to arrange for its contract manufacturers of RenaGel to
        purchase ***** from Nittobo for the exclusive use of Chugai, if and   
        when Nittobo becomes ready and wants to provide ***** to said GelTex
        contract manufacturers and if Chungai so desires.

        
2.2     The license hereunder shall be non transferable, and GelTex shall have
        no right to sublicense any other party without having Nittobo's prior
        written approval, provided, however, that such approval shall not be
        unreasonably withheld, and that GelTex shall be allowed to sublicense to
        The Dow Chemical Company, Chemie Linz and/or Salsbury Chemical for
        manufacture of ***** to be used in the manufacture of GelTex Products.

2.3     GelTex shall guarantee that the sublicensees of GelTex hereunder shall
        have the same obligations to Nittobo as GelTex shall owe to Nittobo
        hereunder, and shall submit to Nittobo a written consent of said
        sublicensee(s) that they shall agree to the terms and conditions of this
        Agreement and shall have obligation to be bound by this Agreement.

2.4     GelTex shall expressly agree that GelTex and its approved sublicensees
        shall have no right to make use of ***** for any other purposes than
        manufacturing RenaGel and CholestaGel.

Article 3  TRANSFER OF TECHNOLOGY

3.1     Within three (3) months of receipt of the first Initial Payment under

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        Article 4.1.1, Nittobo will provide the Know-How to GelTex in the form
        of documents, drawings and explanations. Within one month from receipt
        of the Know-How, GelTex shall specify those information to Nittobo,
        which fall in Article 5.3 together with written evidence to support the
        same.

3.2     GelTex employees or employees of GelTex's sublicensees who are
        designated by GelTex and accepted by Nittobo, but not exceeding six
        people, will be sent to Nittobo's plant in Japan up to seven (7) working
        days to learn the process of making **** including the Know-How. The
        specification of **** shall be as described in Annex II attached hereto.

        If reasonably requested by GelTex, Nittobo will dispatch its personnel
        to GelTex or to its sublicensee for up to thirty (30) man-days to assist
        GelTex or such sublicensee in setting up and implementing the Know-How.

3.4     All reasonable costs and expenses associated with transfer of the
        Know-How shall be paid by GelTex to Nittobo upon presentation by Nittobo
        of invoices properly documenting any such costs and expenses, and GelTex
        shall reimburse Nittobo for all Nittobo's assistance requested by GelTex
        at a rate of US$ 800 per person per working day, plus round trip
        business class air fare, traveling, accommodation, subsistence and
        communication expenses while Nittobo's employee is assisting GelTex or
        its sublicensee with respect to the Know-How. In addition, it is
        GelTex's obligation to prepare a translator while GelTex's or its
        sublicensee's employees are in Japan or Nittobo's employee is in USA, or
        sublicensee's country.

Article 4  ROYALTIES

4.1     In consideration of the license granted hereunder, GelTex shall make the
        following payments to Nittobo:

        4.1.1   Upon execution of this Agreement, the first Initial Payment of
                ****

        4.1.2   On the first and second anniversaries of the execution of this







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                Agreement, a payment of *****, respectively.
               

        4.1.3   During the period any of the Licensed Patents is in effect in
                any area in the Territory;

                (i)     *****
                        
                                                                               
                        
                        
                                                                               

                (ii)    *****
                                                                               
                                                                               
                                                                               
                                                                               
                                                                               
                (iii)   *****
                                                                               
                                                                               
                             
                                                                               
                                                                               
                                                                               
                                                                               
                                                                               
                                                                               
                                                                               
        4.1.4   After all the Licensed Patents expire in all areas in the
                Territory in consideration of the Know-How license hereunder;

                (i)    *****
                                                                              
                                                                              
                                                                              
                (ii)   *****
                                                                               
                                                                               
                                                                               
                                                                               
                                                                     
4.2     GelTex and its approved sublicensees shall keep true records relating to
        manufacture and sales of **** in sufficient detail to enable the
        royalties payable to be determined, and shall twice per calendar year
        during





* Confidential Treatment Requested for information omitted and filed separately
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        normal business hours permit accountants and personnel appointed by
        Nittobo to inspect such records and make copies thereof.

4.3     The royalty report shall be sent to Nittobo within sixty (60) days for
        the end of such semi-annual period. The running royalty shall be
        calculated and paid semi-annually (January - June, July - December)
        within sixty (60) days of the end of each semi-annual period. The
        formality and items to be contained in the royalty reports shall be
        agreed between Nittobo and GelTex.

4.4     Any withholding taxes imposed on Nittobo regarding payments from GelTex
        or its approved sublicensees to Nittobo shall be born by Nittobo, and
        GelTex or its approved sublicensees shall deduct such withholding tax
        from royalty payments otherwise due Nittobo and pay such withholding
        tax to the appropriate tax authorities and shall furnish Nittobo with
        appropriate evidence in order to enable Nittobo to claim exemption
        from or income credit for any tax so payable.

4.5     GelTex shall agree that any payments made hereunder shall be
        non-refundable, and termination of this Agreement shall not terminate
        GelTex's obligation to pay royalties on sales that may have accrued but
        have not yet been paid to Nittobo.

Article 5  CONFIDENTIALITY

5.1     The Know-How is and shall remain the property of Nittobo and GelTex
        shall maintain and shall have its approved sublicensees maintain in
        confidence the Know-How and shall not disclose it to any third party
        except to the party expressly permitted by Nittobo hereunder.

5.2     Notwithstanding the foregoing, GelTex may disclose the Know-How to
        officers and employees of GelTex and the approved sublicensees, who
        specifically need to know such Know-How in order to accomplish the
        manufacture of ****, and GelTex shall bear all responsibility and
        liability to have such officers and employees comply with the
        confidentiality obligations hereunder, whether or not such officers and



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









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        employees continue to be officers or employees of GelTex or the approved
        sublicensees.

5.3     The obligation of confidence hereunder shall not extend to information
        which:

        (a)     is already in GelTex's possession prior to receiving it from
                Nittobo;
 
        (b)     is or subsequently becomes public domain through no fault of
                GelTex;

        (c)     is acquired by GelTex from a third party owing no obligation of
                confidence to the disclosing party; or

        (d)     is independently developed by GelTex without reliance upon the
                confidential information disclosed by Nittobo.

5.4     The obligation of confidence hereunder shall not prohibit the disclosure
        of any information that GelTex or its sublicensees are required to
        disclose by law or regulation, or the disclosure of any information that
        may be necessary in order for GelTex to satisfy its regulatory
        obligations.

5.5     The obligation of GelTex and its approved sublicensees hereunder shall
        survive termination of this Agreement.

Article 6  REPRESENTATIONS, ETC.

6.1     Nittobo does not warrant that the License Patents is valid and that ****
        manufactured by the License Patents and/or the Know-How does not
        infringe on the intellectual property rights owned by third parties.

6.2     Nittobo specifically invites GelTex's attention to the fact that since
        Nittobo is selling *** only as industrial chemicals for use as a reagent
        and flocculating agent, Nittobo cannot give any warranty as to ****
        suitability for medical or pharmaceutical use.

6.3     GelTex shall ******
                                                                              
                                                                              
                                                                              



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        ************




        Nittobo shall give GelTex prompt written notice of ********




6.4     In no event shall Nittobo be liable for any indirect, incidental, or
        consequential damage arising out of or pertaining to **** or any use
        thereof, including any alleged defect of ****, whether such claim for
        damages is allegedly based on a breach of warranty, negligence, product
        liability or otherwise.

6.5     GelTex shall, at its own expense, be responsible for (i) complying with
        all applicable laws and regulations that affect when and where **** may
        be used or imported, and (ii) obtaining all approvals, licenses, etc.
        that may be required under such laws or regulations.

Article 7  TERM AND TERMINATION

7.1     This Agreement shall become effective upon signing the Agreement by the
        duly authorized representatives of the parties and shall terminate

        (i)     when the Licensed Patents expire in all countries in the
                Territory and all the Know-How loses its confidential status as
                identified in Article 5.3, or


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        (ii)    when GelTex and all its approved sublicensees cease production
                of **** for a period of twelve (12) consecutive months.

7.2     If either party fails to perform any material obligation and does not
        remedy any such failure within one (1) month of written notification
        of the default by the other party, the other party may forthwith
        terminate this Agreement.

7.3     Either party may terminate this Agreement immediately by giving written
        notice of termination in the event that the other party (a) becomes
        insolvent, files for bankruptcy or company reorganization, composition
        or any similar act; or (b) dissolves, ceases doing business, or
        changes its business substantially.

7.4     In the event of termination of this Agreement, other than in accordance
        with the provisions of Article 7.1(i), GelTex shall immediately cease
        use of the Know-How, nor thereafter utilize the Licensed Patents.

7.5     The provisions of this Article shall not limit any other additional
        remedies available to Nittobo or GelTex on termination of the Agreement.

Article 8  GENERAL PROVISIONS

8.1     A waiver by either party of any term or condition of this Agreement in
        any instance shall not be deemed or construed to be a waiver of such
        term or condition of the future, or of any subsequent breach thereof.
        All rights, remedies, undertakings or obligations contained in this
        Agreement shall be cumulative and none of them shall be in limitation of
        any other right, remedy, undertaking or obligation of either party.

8.2     Neither this Agreement nor any of the rights or obligations provided
        herein may be assigned by either party without the express written
        consent of the other party. This Agreement and the rights and
        obligations hereunder shall, however, be binding upon and inure to the
        benefit of each party's successors and permitted assigns.




* Confidential Treatment requested for information omitted and filed 
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8.3     If any part of this Agreement is found to be invalid or unenforceable,
        the remainder of the Agreement shall continue in full force and effect
        consistent with the intent of the parties.

8.4     This Agreement incorporates the parties' entire agreement and supersedes
        all prior understandings or agreements between the parties as to the
        subject matter hereof. This Agreement may only be modified, altered or
        amended by a writing of subsequent date signed by all parties.

8.5     This Agreement is to be governed by and construed according to the laws
        of Japan.

8.6     Any dispute between the parties concerning this Agreement or the
        performance of any obligation arising hereunder shall be resolved by
        binding arbitration in Tokyo, Japan, according to the rules of the Japan
        Commercial Arbitration Association. The decision of the arbitrator(s)
        shall be final, and the parties hereby waive any right to appeal or
        review of such decision.

        IN WITNESS WHEREOF, the Parties hereto have executed this Agreement, or
caused their duly authorized representatives to


                                     Nitto Boseki Co., Ltd.

                                     By: /s/ Atsuhiko Sagara
                                         ------------------------------------
                                         Atsuhiko Sagara
                                         Title: President



                                     GelTex Pharmaceuticals, Inc.

                                     By: /s/ Joseph E. Tyler
                                         ------------------------------------ 
                                         Joseph E. Tyler
                                         Title: Vice President, Manufacturing





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                                                                         Annex I

                            LIST OF LICENSED PATENTS

     -----------------------------------------------------------------------
          Country             Appln No.                     Reg. No.
                              Appln Date                    Reg. Date

     -----------------------------------------------------------------------


      *********************











* Confidential Treatment requested for information omitted and filed 
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                                                                        Annex II

                              SPECIFICATION OF *****


************





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