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                                                              EXHIBIT 4.3(b)(2)



Michigan                                       Corporate Special Assets (10-60)
National                                       27777 Inkster Road
Bank                                           Farmington Hills, MI 48333-9065

March 21, 1997

Mr. Alan S. Ker
Chief Financial Officer
Universal Standard Medical Laboratories, Inc.
26500 Northwestern Highway
Southfield, Michigan  48076

RE:      MODIFICATION TO SECOND AMENDED AND RESTATED BUSINESS LOAN
         AGREEMENT AND RELATED DOCUMENTS DATED FEBRUARY 6, 1997

Dear Mr. Ker:

         On February 6, 1997, Michigan National Bank, a national banking
association (the "Bank") and Universal Standard Medical Laboratories, Inc., a
Michigan corporation (the "Borrower") entered into a Second Amended and
Restated Business Loan Agreement.  Pursuant to the Loan Agreement, Bank has
extended to Borrower the following loans:

         1.      Line of Credit in the amount of Five Million, Five Hundred
                 Thousand and 00/100 Dollars ($5,500,000.00);

         2.      Term Loan in the amount of Six Million and 00/100 Dollars
                 ($6,000,000.00);

         3.      Letter/Line of Credit-B in the amount Fifty Thousand and
                 00/100 Dollars ($50,000.00).

The loans described in the Loan Agreement shall be referred to in this letter
as the "Loans."  The Loans are secured by certain collateral described in
Section V of the Loan Agreement.

The Borrower has requested that the Bank agree to certain modifications in the
Second Amended and Restated Business Loan Agreement and Related Documents.
Bank is willing to make the modifications, subject to the terms and conditions
contained in this letter.  Therefore, for good and valuable consideration, the
receipt and sufficiency of which is expressly acknowledged, the parties agree
as follows:

         1.      Capitalized terms not defined in this Letter shall have the
                 same meaning given to them in the Second Amended and Restated
                 Business Loan Agreement.

         2.      Section III.A. of the Second Amended and Restated Business
                 Loan Agreement is amended to reach in its entirety as follows:
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March 21, 1997
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                 "A.      FINANCIAL REQUIREMENTS.

                          1.      Maintain a Cash Flow Coverage Ratio at the
                                  end of each of the following calendar
                                  quarters, of:

                                  (a)    10/1/96 through 12/31/96 - (2.50) to 1
                                  (b)    1/1/97 through 3/31/97 - .70 to 1
                                  (a)    4/1/97 through 6/30/97 - 1.50 to 1
                                  (a)    7/1/97 through 9/30/97 - 1.75 to 1
                                  (a)    10/1/97 through 12/31/97 - 2.00 to 1

                          2.      At the end of each of the above calendar
                                  quarters, Borrower's total funded debt
                                  excluding debt subordinated to the Bank and
                                  approximately $20,000.00 if quarterly Seller
                                  note interest payments to cash flow shall at
                                  no time be greater than:

                                  (a)    10/1/96 through 12/31/96 - (0.75) to 1
                                  (b)    1/1/97 through 3/31/97 - 3.0 to 1
                                  (a)    4/1/97 through 6/30/97 - 3.0 to 1
                                  (a)    7/1/97 through 9/30/97 - 3.0 to 1
                                  (a)    10/1/97 through 12/31/97 - 3.0 to 1

                                  This ratio shall be calculated with a
                                  numerator equal to total funded debt and a
                                  denominator equal to EBITDA for the quarter
                                  multiplied by 4.

                          3.      Maintain a Current Ratio of not less than 1.0
                                  to 1.0.

                                  All financial requirements described in this
                                  Section III.A. shall be calculated in
                                  accordance with GAAP.

         3.      Except as described in this letter, the Loan Agreement and
                 Related Documents will remain in full force and effect.  All
                 collateral securing the Loans will continue to secure the
                 Loans.

         4.      The modifications described in this letter shall not
                 constitute the establishment of a course of dealing between
                 the parties.  Bank reserves, and Borrower expressly
                 acknowledges that Bank has the right to deny any future
                 request for modification or waiver of any of the provisions of
                 the Loan Agreement or the Related Documents.
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March 21, 1997
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         5.      The effectiveness of the modifications contained in this
                 letter are expressly conditioned on the receipt of a
                 modification fee in the amount of $5,000.00.  However, Bank
                 agrees to refund the modification fee if Borrower is not in
                 default and makes payment in full of all outstanding
                 Indebtedness of Borrower by April 22, 1997.

         6.      Section IX.B. of the Second Amended and Restated Business Loan
                 Agreement provides for the payment by the Borrower of
                 reasonable expenses in connection with the preparation of any
                 amendments, modifications, waivers or consents with respect to
                 the Agreement.  Michigan National Bank has expended $4,490.00
                 for internal legal costs for the preparation, review, waiver
                 and modification of the Second Amended and Restated Business
                 Loan Agreement.  Bank requests payment of $4,490.00 as
                 reimbursement of internal legal costs.

         7.      This letter agreement shall be governed by and construed in
                 accordance with the laws of the State of Michigan.  This
                 letter may be modified only by written instrument signed by
                 both parties to this letter.

         If this letter accurately reflects the understanding of the parties,
please execute the letter in the indicated place and return it to me.

                                        Very truly yours,

                                        /s/ Eric L. Johnson

                                        Eric L. Johnson
                                        Corporate Asset Manager

This letter  accurately reflects the understanding of the parties.


Universal Standard Medical Laboratories, Inc.


By:   /s/ Alan S. Ker                          Date:  3/21/
    -----------------------------------------       ---------------------
      Alan S. Ker
Its:  Vice President - Finance and Treasurer