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                                                                       Exhibit 3


                                                               December 21, 1999


National Nephrology Associates, Inc.
511 Union Street, Suite 1800
Nashville, TN  37219

Gentlemen:

         In connection with our consideration of a possible transaction with
National Nephrology Associates, Inc. (the "Company"), we have requested
information concerning the Company. As a condition to your furnishing of that
information to us, we agree, as set forth below, to treat confidentially that
information and any other information (collectively, "Evaluation Data")
furnished to us (at any time on, before or after the date of this agreement) by
the Company or its affiliates or representatives concerning the Company.

         We will not use the Evaluation Data for any purpose other than the
evaluation of the possible transaction with the Company and the Evaluation Data
shall be kept confidential by us and our agents; however, Evaluation Data may be
disclosed to those of our directors, officers and representatives who need to
have access to such Evaluation Data for our evaluation of a possible transaction
with the Company (we shall (x) inform such directors, officers and
representatives of the confidential nature of such information and (y) direct
and cause them (i) to keep such information confidential, and (ii) not to use
such information for any purpose other than the evaluation of the possible
transaction between us and the Company).

         In addition, without the prior written consent of the Company, we shall
not, and shall direct and cause our directors, officers and representatives not
to, disclose to any person the fact that discussions or negotiations are taking
place concerning a possible transaction between us and the Company or any of the
terms, conditions or other facts with respect to any such possible transaction,
including, but not limited to, the status thereof. The term "person" as used in
this agreement shall be interpreted very broadly and shall include, but not be
limited to, any individual, corporation, company, partnership, limited liability
company, governmental body or agency, or other legal entity.

         At any time at the request of the Company, we shall promptly deliver to
the Company all documents and other material in our possession (or in the
possession of any of our directors, officers and representatives) containing or
based upon any of the Evaluation Data, whether prepared by the Company, us or
any other person at any time before or after the date of this agreement, without
retaining any copies thereof.

         This agreement shall not apply to particular portions of the Evaluation
Data that (x) are or become matters of general public knowledge other than as a
result of a disclosure by us or our directors, officers, employees or
representatives or (y) are disclosed to us on a non-confidential basis by a
source (other than the Company or its agents) not thereby violating any
agreement with or other duty to the Company.
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         We acknowledge that, although the Company has endeavored to provide the
Evaluation Data requested by us, the Company and its agents make no
representation or warranty as to the accuracy or completeness of the Evaluation
Data. We agree that none of the Company, its affiliates, and their respective
directors, officers, employees and representatives shall have any liability to
us or any of our representatives resulting from or in connection with the use of
any of the Evaluation Data by us or our representatives.

         No failure or delay by the Company to exercise any right or remedy
under or with respect to this agreement shall operate as a waiver nor shall any
single or partial exercise thereof preclude any other or further exercise
thereof or the exercise of any other right or remedy. This agreement may not be
changed or terminated orally; all waivers hereunder must be in writing and
executed by the Company. This agreement shall be governed and construed in
accordance with the internal laws of the State of New York and we hereby consent
to the jurisdiction of the courts of the State of New York (and the federal
courts located therein) for purposes of any action or proceeding to enforce, or
otherwise relating to, this agreement and agree that process in any such action
or proceeding may be served on us anywhere in the world.

                                Very truly yours,

                                Renex Corp.

                                By: /s/ James P. Shea
                                    ---------------------------------
                                    Name: James P. Shea
                                    Title: President and Chief Executive Officer


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