POLYMEDICA INDUSTRIES, INC.
                    POLYMEDICA PHARMACEUTICALS (U.S.A.), INC.
                 POLYMEDICA PHARMACEUTICALS (PUERTO RICO), INC.
                                 11 State Street
                           Woburn, Massachusetts 01801


                                October 30, 1996           Exhibit 4.13

JOHN HANCOCK MUTUAL LIFE
   INSURANCE COMPANY
John Hancock Place
P. O. Box 111
Boston, Massachusetts 02117

Ladies and Gentlemen:

     POLYMEDICA  INDUSTRIES,  INC., a Massachusetts  corporation (the "Parent"),
and POLYMEDICA PHARMACEUTICALS (U.S.A.), INC., a Massachusetts corporation and a
Wholly-Owned   Subsidiary  of  the  Parent  (the   "Company"),   and  POLYMEDICA
PHARMACEUTICALS   (PUERTO  RICO),  INC.,  a  Massachusetts   corporation  and  a
Wholly-Owned  Subsidiary  of the  Company  ("PPR")  (the  Company  and  PPR  are
sometimes collectively referred to as the "Borrowers" and each as a "Borrower"),
agree with you as follows:

     1.  Definitions.  Reference is hereby made to that certain Note and Warrant
Agreement  dated January 26, 1993, as amended and  supplemented by eleven letter
agreements  dated April 27, 1993, June 15, 1993,  March 29, 1994, June 17, 1994,
June 30, 1994,  October 27, 1994,  June 26, 1995,  October 18, 1995,  January 1,
1996,  June 19,  1996,  and August 2, 1996 (the "Note and  Warrant  Agreement").
Capitalized  terms used herein without  definition have the meanings ascribed to
them in the Note and Warrant Agreement.

     2. Waiver of Default under Section 14.7 of the Note and Warrant  Agreement.
The Parent and the Borrowers  hereby request that you waive any Default or Event
of Default  arising  solely  from the  failure of the Company to comply with the
provisions of section 14.7 (b) of the Note and Warrant  Agreement for the period
of four (4) consecutive  quarterly  accounting periods ended September 30, 1996.
In consideration of the representations, warranties and agreements of the Parent
and the Borrowers set forth herein,  you, by your signature below,  hereby grant
such waiver,  solely with respect to such period four (4) consecutive  quarterly
accounting periods.

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     3. No Default, Representations and Warranties, etc.

     (a)  The  Parent  and  the   Borrowers   represent  and  warrant  that  the
representations  and warranties  contained in the Note and Warrant Agreement and
the other  Operative  Agreements  are correct on and as of the date hereof as if
made  on such  date  (except  to the  extent  affected  by the  consummation  of
transactions permitted by the Note and Warrant Agreement) and that no Default or
Event of Default exists.

     (b) The Parent and the  Borrowers  each  ratify  and  confirm  the Note and
Warrant Agreement and each of the other Operative  Agreements to which each is a
party and agree that each such  agreement,  document and  instrument  is in full
force  and  effect,  that its  obligations  thereunder  and  under  this  Letter
Agreement are its legal, valid and binding obligations enforceable against it in
accordance with the terms thereof and hereof and that it has no defense, whether
legal or equitable,  setoff or  counterclaim  to the payment and  performance of
such obligations.

     (c) The Parent and the  Borrowers  agree that (i) if any  default  shall be
made in the  performance  or observance of any covenant,  agreement of condition
contained in this Letter  Agreement or in any agreement,  document or instrument
executed in connection herewith or pursuant hereto or (ii) if any representation
or warranty made by the Parent or the Borrowers herein or therein shall prove to
have  been  false or  incorrect  on the date as of which  made,  the same  shall
constitute  an Event of Default  under the Note and  Warrant  Agreement  and the
other Operative  Agreements and, in such event, you and each other holder of any
of the Notes shall have all rights and remedies  provided by law and/or provided
or  referred  to in the Note  and  Warrant  Agreement  and the  other  Operative
Agreements.  The  Parent  and the  Borrowers  further  agree  that  this  Letter
Agreement is an Operative  Agreement and all  references in the Note and Warrant
Agreement and in any other of the other Operative Agreements referred to therein
shall include this Letter Agreement.

     4. Payment of Transaction  Costs.  Concurrently  with the execution of this
Letter Agreement, the Parent and the Borrowers shall pay all reasonable fees and
disbursements  incurred  by you at or prior  to such  time,  including,  without
limitation,  the reasonable  fees,  expenses and  disbursements  of your special
counsel.



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     5. Governing Law. This Letter Agreement,  including the validity hereof and
the rights and  obligations  of the parties  hereunder,  shall be  construed  in
accordance  with  and  governed  by  the  domestic   substantive   laws  of  The
Commonwealth  of  Massachusetts  without  giving  effect to any choice of law or
conflicts  of law  provision  or rule that would  cause the  application  of the
domestic substantive laws of any other jurisdiction.

     6. Miscellaneous. The headings in this Letter Agreement are for purposes of
reference only and shall not limit or otherwise affect the meaning hereof.  This
Letter  Agreement  embodies the entire  agreement  and  understanding  among the
parties hereto and supersedes all prior agreements and  understandings  relating
to the subject  matter  hereof.  In case any provision in this Letter  Agreement
shall  be  invalid,  illegal  or  unenforceable,   the  validity,  legality  and
enforceability  of the remaining  provisions shall not in any way be affected or
impaired  thereby.  This  Letter  Agreement  may be  executed  in any  number of
counterparts  and by the parties  hereto on separate  counterparts  but all such
counterparts shall together constitute but one and the same instrument.



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         If you are in  agreement  with the  foregoing,  please sign the form of
agreement  on  the  accompanying   counterpart  hereof,  whereupon  this  Letter
Agreement shall become a binding  agreement under seal among the parties hereto.
Please then return one of such counterparts to the Company.


                                  Very truly yours,
          
                                  POLYMEDICA INDUSTRIES, INC.

                                  By:  /s/ Steven James Lee
                                       Steven James Lee
                                       Chairman and Chief Executive Officer

                                  POLYMEDICA PHARMACEUTICALS
                                  (U.S.A.), INC.

                                  By:  /s/ Steven James Lee
                                       Steven James Lee
                                       Chief Executive Officer

                                  POLYMEDICA PHARMACEUTICALS
                                  (PUERTO RICO), INC.

                                  By:  /s/ Steven James Lee
                                       Steven James Lee
                                       Chief Executive Officer

         The terms and provisions of the foregoing  Letter  Agreement are hereby
acknowledged and agreed to.

POLYMEDICA SECURITIES, INC.                    POLYMEDICA PHARMACEUTICALS
                                               SECURITIES, INC.

By: /s/ Steven James Lee                       By: /s/ Steven James Lee
    Steven James Lee                               Steven James Lee
    President                                      President

The foregoing is hereby accepted and agreed to:
JOHN HANCOCK MUTUAL LIFE
  INSURANCE COMPANY


By: /s/ D. Dana Donovan
    D. Dana Donovan
    Senior Investment Officer



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