<PAGE>   1

                                                                  EXHIBIT 10(n)



                    FIRST AMENDMENT TO REVOLVING CREDIT NOTE

          This First Amendment to Revolving Credit Note ("Amendment") is made 
and entered into effective as of the 31st day of March, 1999, by and between
RESPONSE ONCOLOGY, INC. ("Maker"), a Tennessee corporation, and NATIONSBANK,
N.A. ("Holder"), a national banking association formerly known as NationsBank of
Tennessee, N.A.

                                    RECITALS:

          WHEREAS, Maker has previously executed that Revolving Credit Note
dated as of April 21, 1997, payable to order of Lender in the original maximum
principal amount of $25,000,000 (the "Note"); and

          WHEREAS, Maker and Lender have agreed to extend the maturity of the
Note;

          NOW, THEREFORE, for valuable consideration, the receipt and 
sufficiency of which are acknowledged, it is agreed as follows:

          1. Amendment of Note. The Note is hereby amended by deleting the last
sentence of the second paragraph on page one thereof and substituting the
following therefor:

             As provided in the Loan Agreement, all remaining principal, 
             interest and expenses outstanding hereunder or under the Loan 
             Agreement shall become finally due on June 30, 1999.

          2. Full Force and Effect. The Note remains in full effect, as amended
hereby.

          3. Governing Law. This Amendment shall be governed by, and construed
and interpreted in accordance with, the internal laws of the State of Tennessee.

             Executed as of the date stated above.

                                         NATIONSBANK, N.A.

                                         By:
                                            -----------------------------------
                                         Title: Senior Vice President
                                               --------------------------------

                                         RESPONSE ONCOLOGY, INC.

                                         By:
                                            -----------------------------------
                                         Title: 
                                               --------------------------------







<PAGE>   2


                    FIRST AMENDMENT TO REVOLVING CREDIT NOTE

          This First Amendment to Revolving Credit Note ("Amendment") is made 
and entered into effective as of the 31st day of March, 1999, by and between
RESPONSE ONCOLOGY, INC. ("Maker"), a Tennessee corporation, and AMSOUTH BANK
("Holder"), a Tennessee banking corporation formerly known as AmSouth Bank of
Tennessee.

                                    RECITALS:

          WHEREAS, Maker has previously executed that Revolving Credit Note
dated as of April 21, 1997, payable to order of Holder in the original maximum
principal amount of $10,000,000 (the "Note"); and

          WHEREAS, Maker and Holder have agreed to extend the maturity of the
Note;

          NOW, THEREFORE, for valuable consideration, the receipt and
sufficiency of which are acknowledged, it is agreed as follows:

          1. Amendment of Note. The Note is hereby amended by deleting the last
sentence of the second paragraph on page one thereof and substituting the
following therefor:

             As provided in the Loan Agreement, all remaining principal,
             interest and expenses outstanding hereunder or under the Loan
             Agreement shall become finally due on June 30, 1999.

          2. Full Force and Effect. The Note remains in full effect, as amended
hereby.

          3. Governing Law. This Amendment shall be governed by, and construed
and interpreted in accordance with, the internal laws of the State of Tennessee.

             Executed as of the date stated above.

                                            AMSOUTH BANK

                                            By: 
                                               --------------------------------

                                            Title: 
                                                  -----------------------------

                                            RESPONSE ONCOLOGY, INC.

                                            By:
                                               --------------------------------

                                            Title:
                                                  -----------------------------


<PAGE>   3



                    FIRST AMENDMENT TO REVOLVING CREDIT NOTE

          This First Amendment to Revolving Credit Note ("Amendment") is made
and entered into effective as of the 31st day of March, 1999, by and between
RESPONSE ONCOLOGY, INC. ("Maker"), a Tennessee corporation, and UNION PLANTERS
BANK, N.A. ("Holder"), a national banking association formerly known as Union
Planters National Bank.

                                    RECITALS:

          WHEREAS, Maker has previously executed that Revolving Credit Note
dated as of April 21, 1997, payable to order of Holder in the original maximum
principal amount of $10,000,000 (the "Note"); and

          WHEREAS, Maker and Holder have agreed to extend the maturity of the
Note;

          NOW, THEREFORE, for valuable consideration, the receipt and 
sufficiency of which are acknowledged, it is agreed as follows:

          1. Amendment of Note. The Note is hereby amended by deleting the last
sentence of the second paragraph on page one thereof and substituting the
following therefor:

             As provided in the Loan Agreement, all remaining principal, 
             interest and expenses outstanding hereunder or under the Loan 
             Agreement shall become finally due on June 30, 1999.

          2. Full Force and Effect. The Note remains in full effect, as amended
hereby.

          3. Governing Law. This Amendment shall be governed by, and construed
and interpreted in accordance with, the internal laws of the State of Tennessee.

             Executed as of the date stated above.


                                           UNION PLANTERS BANK, N.A.

                                           By:
                                              ---------------------------------
                                           Title:
                                                 ------------------------------

                              
                                           RESPONSE ONCOLOGY, INC.

                                           By:
                                              --------------------------------- 

                                           Title: 
                                                 ------------------------------