SIXTH AMENDMENT TO
                       AGREEMENT OF LIMITED PARTNERSHIP OF
                 TEXAS LITHOTRIPSY LIMITED PARTNERSHIP III L.P.


                  THIS AMENDMENT, effective as of the 1st day of November, 1999,
is entered  into by and among  Pacific  Lithotripsy,  a North  Carolina  general
partnership and the General Partner of Texas Lithotripsy Limited Partnership III
L.P., a Texas limited partnership (the "Partnership"),  and the Limited Partners
of the Partnership.

                                R E C I T A L S:
                                 ---------------

     1. The General Partner and the Limited Partners,  hereinafter  collectively
referred to as the "Partners," are parties to that certain  Agreement of Limited
Partnership of Texas Lithotripsy  Limited  Partnership III L.P., as amended (the
"Agreement").

                  2. Effective as of November 1, 1999,  the General  Partner and
the  requisite  percentage of the Limited  Partners  consented in writing to the
following  amendment  to the  Agreement,  such  amendment  intended to allow the
General Partner the authority to periodically  offer and sell additional limited
partner interests (a "Dilution Offering ") to local investors.

                  NOW,   THEREFORE,   in  accordance  with  Article  29  of  the
Partnership Agreement and pursuant to the written consent of the General Partner
and the requisite  percentage of the Limited Partners,  the parties hereto agree
as follows:

                           The  Agreement  is  hereby  amended  as set  forth in
                           Exhibit A hereto.

                                             [Signature Page Follows]



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                  IN WITNESS WHEREOF, the Partners have hereunto set their hands
and seals effective as of the date first above written.

                                   GENERAL PARTNER:

                                  PACIFIC LITHOTRIPSY, a North Carolina general
                                     partnership

                         By:  Lithotripters, Inc., a North Carolina  corporation
                                and a general partner of the Partnership

                                   By:_________________________________________
                                Title:________________________________________


                         By: LithoWest, Inc., a California corporation and a
                               general partner of the Partnership

                                   By: _______________________________________
                                Title: _____________________________________


                                      ALL THE LIMITED PARTNERS OF
                                      THE PARTNERSHIP WHOSE NAMES
                                      APPEARED ON SCHEDULE A-5

                                         By:/s/ Joseph Jenkins, M.D.
                                         ---------------------------
                                       Joseph Jenkins, M.D.
                                       Attorney-in-Fact*
--------
     *Pursuant  to a Power of  Attorney  given by the  Limited  Partners  in the
Agreement.



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                                    EXHIBIT A

                           DILUTION OFFERING AMENDMENT

1.       Capitalized  terms used in this Exhibit and not otherwise defined shall
         have the same meaning as provided in the Limited Partnership  Agreement
         (the "Partnership  Agreement") of Texas Lithotripsy Limited Partnership
         III L.P. (the "Partnership"), and any amendments thereto.

2.       The purpose of this Exhibit is to set forth a proposed amendment to the
         Partnership Agreement that would give the General Partner the authority
         periodically  to offer and sell additional  limited  partner  interests
         ("Dilution  Offering") to local urologists who are not investors in the
         Partnership ("Qualified  Investors").  As required by Article 29 of the
         Partnership Agreement,  to be effective this amendment must be approved
         by the Partners  representing  two-thirds of the aggregate interests in
         the Partnership.

3.       The purposes of a Dilution Offering are (i) to raise additional capital
         for any  valid  Partnership  purpose,  and (ii) to assure  the  highest
         quality  of  patient  care  by  admitting  Qualified  Investors  to the
         Partnership who will be dedicated and motivated as owners to follow the
         Partnership's treatment protocol, and comply with its quality assurance
         and outcome  analysis  programs.  Any additional  capital raised by the
         Partnership  in a  Dilution  Offering  can be used  for any  legitimate
         Partnership purpose including upgrading the Partnership's Lithostar(TM)
         Mobile System.

4.       Any sale of limited  partner  interests  to  Qualified  Investors  will
         result in the  proportionate  dilution  of the  Partnership  Percentage
         Interests of the existing Partners;  i.e., the interests of the General
         Partner  and the  Limited  Partners in  Partnership  allocations,  cash
         distributions  and voting rights will be  proportionately  reduced by a
         successful Dilution Offering.

5.       The  Percentage  Interests of the existing  Partners  cannot be diluted
         through  Dilution  Offerings by more than 20% in the aggregate  without
         the  prior  written  consent  of a  Majority  in  Interest  of all  the
         Partners.  Without  obtaining  this  additional  consent,  the existing
         Partners  cannot  be  diluted  to less  than  80% of  their  Percentage
         Interest ownership at the time of this Amendment.

6.       The  General  Partner has  determined  that the  purchase  price per 1%
         Partnership  Interest offered in the initial planned Dilution  Offering
         will be at its fair market value as determined by an independent  third
         party appraiser.  The price for Units sold in future dilution offerings
         also must be at a price no less than fair market value as determined by
         the General Partner.

7.       Upon  the  successful  sale  of  Partnership  Interests  in a  Dilution
         Offering,  the General Partner will prepare and attach a new Schedule A
         to the  Partnership  Agreement  to reflect (i) the  Partners'  adjusted
         Percentage Interests in the Partnership,  and (ii) the admission of the
         new Limited Partners to the Partnership.



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