<PAGE>   1
                                                               EXHIBIT 10.10(b)



                            SECOND AMENDMENT TO THE
                    USML TAX DEFERRED SAVINGS PLAN AND TRUST


            Pursuant to Section 8.1 of the USML Tax Deferred Savings Plan and
Trust ("Plan") and resolutions adopted by the Board of Directors on May 25,
1994, this Second Amendment to the Plan is hereby adopted as follows:

            1.      Effective January 1, 1994, paragraph (f) shall be added to
the end of Section 7.14 (direct rollover provision adopted in the First
Amendment to the Plan) to read as follows:

            (f)     If a distribution is one to which Code Sections 401(a)(11)
            and 417 do not apply, such distribution may commence less than 30
            days after the notice required under Section 1.41(a)-11(c) of the
            Income Tax regulations is given, provided that;

                             (1)  the Plan Administrator clearly informs the
                    Participant that the Participant has a right to a period of
                    at least 30 days after receiving the notice to consider the
                    decision of whether or not to elect a distribution (and, if
                    applicable, a particular distribution option), and

                             (2)  the Participant, after receiving the notice,
                    affirmatively elects a distribution.


            2.      Effective January 1, 1994, the following three paragraphs
shall be added to the end of Section 1.10 "Compensation" to read as follows:

            In addition to other applicable limitations set forth in the Plan,
            and notwithstanding any other provision of the Plan to the
            contrary, for Plan Years beginning on or after January 1, 1994, the
            annual compensation of each Employee taken into account under the
            Plan shall not exceed the OBRA '93 annual compensation limit.  The
            OBRA '93 annual compensation limit is $150,000, as adjusted by the
            Commissioner for increases in the cost of living in accordance with
            Code Section 401(a)(17)(B).  The cost-of-living adjustment in
            effect for a calendar year applies to any period, not exceeding 12
            months, over which compensation is determined (determination
            period) beginning in such calendar year.  If a determination period
            consists of fewer than 12 months, the OBRA '93 annual compensation
            limit shall be multiplied by a fraction, the numerator of which is
            the number of months in the determination period, and the
            denominator of which is 12.






<PAGE>   2




                    For Plan Years beginning on or after January 1, 1994, any
            reference in this Plan to the limitation under Code Section
            401(a)(17) shall mean the OBRA '93 annual compensation limit set
            forth in this provision.

                    If compensation for any prior determination period is taken
            into account in determining an Employee's benefits accruing in the
            current Plan Year, the compensation for that prior determination
            period is subject to the OBRA '93 annual compensation limit in
            effect for that prior determination period.  For this purpose, for
            determination periods beginning before the first day of the first
            Plan Year beginning on or after January 1, 1994, the OBRA '93
            annual compensation limit is $150,000.

            3.      Effective May 25, 1994, paragraph (e) shall be added to
Section 4.8 of the Plan, entitled "Directed Investments," to read as follows:

             (e)    The Plan and its operation are intended to comply with the
            provisions of ERISA Section 404(c) and the regulations thereunder
            applicable to participant directed investments.  The Employer may
            appoint one or more fiduciaries to assist in compliance with these
            provisions, which fiduciary or fiduciaries shall generate and
            disseminate to Participants the information required by the
            regulations.  Except as provided by ERISA Section 404(c) and the
            regulations thereunder, the Trustee shall have no fiduciary
            responsibility with respect to the selection of the Plan's
            investment funds, and neither the Employer, the Trustee, nor any
            other fiduciary with respect to the Plan shall have any liability
            in connection with any losses that are the direct and necessary
            result of the investment choices made by Participants.  The
            Trustee's only responsibility shall be with respect to the
            individual investments of any investment funds that are operated by
            the Trustee and made available for Participant investments under
            the Plan, and which are not controlled by an independent investment
            manager.  The only responsibility of the Employer shall be to
            review periodically, in its capacity as Plan Administrator, the
            performance of the investment funds made available under the Plan
            and to change the available funds offered when appropriate.


            3.      Effective May 25, 1994, a third paragraph shall be added to
Section 7.4(s) to read as follows:

            Participants and beneficiaries of the Plan shall have the right to
            direct the investment of their individual accounts under the Plan
            in accordance with uniform procedures adopted by the Plan
            Administrator.  It is the intention of the Employer that the Plan
            and the administration of these directed investments conform to
            ERISA Section 404(c) and the regulations thereunder, and that no
            Participant or beneficiary shall be deemed to be a fiduciary by
            reason of his or her control over assets in his or her account, and
            neither the Trustee nor any other person who is a fiduciary with
            respect to the Plan shall be liable for any loss, or by reason of
            any breach, which results from






<PAGE>   3




            such exercise of control.  However, the Trustee shall be obligated
            to comply with investment directions by participants and
            beneficiaries, except as limited by ERISA Section 404(c) and
            regulations thereunder.

            4.      Effective July 1, 1994, Section 7.13 shall be amended by
the addition of the following two paragraphs:

            A Participant may direct no more than one-third of his or her
            account into employer stock.  Stock rights (including warrants and
            options) issued with respect to employer stock held in the Plan
            shall be exercised by the Trustee on behalf of Participants to the
            extent that cash is available.  Rights which cannot be exercised
            due to the lack of cash shall be sold and the proceeds invested in
            employer stock.  Cash dividends paid on employer stock shall be
            allocated to participants' accounts as of the record date for the
            dividend and shall be invested by the Trustee in shares of employer
            stock for the participants' accounts.

            Each Participant shall have the right to direct the Trustee as to
            the manner in which employer stock held in his or her account shall
            be voted, and shall have a similar right with regard to tender
            offers.


            IN WITNESS WHEREOF, United Standard Medical Laboratories, Inc. Inc.
has caused this Amendment to be executed on June ____, 1994.


                                        UNITED STANDARD MEDICAL
                                        LABORATORIES, INC., Employer


____________________________            By:______________________________
Witness:
                                           Its:__________________________






<PAGE>   4





            The Plan Trustee hereby acknowledges receipt of a copy of this
Amendment and agrees to be bound by the terms of the Amendment as it relates to
the Trust created under the Plan.


                                        FRONTIER TRUST COMPANY, TRUSTEE UNDER
                                        THE USML, INC. TAX DEFERRED SAVINGS
                                        PLAN AND TRUST



__________________________              By:___________________________________
Witness:                                   Its:_______________________________





Dated:  June ___, 1994