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                                                                  EXHIBIT 4.18







                                FIRST SUPPLEMENT

                                       to

                              MASTER UNIT AGREEMENT

                                     between

                         AMERICAN MUTUAL HOLDING COMPANY

                                       and

                    FIRST UNION NATIONAL BANK, as Unit Agent









                            Dated September 20, 2000




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                          FIRST SUPPLEMENTAL AGREEMENT

     This First Supplemental Agreement (this "First Supplemental Agreement"),
dated as of September 20, 2000, is among AMERICAN MUTUAL HOLDING COMPANY, an
Iowa mutual insurance holding company ("AMHC"), as successor to AMERUS LIFE
HOLDINGS, INC., an Iowa insurance holding company (the "Company"), and FIRST
UNION NATIONAL BANK, a national banking corporation, acting as unit agent for
the Holders of Units from time to time (the "Unit Agent").

     WHEREAS, the Company and the Unit Agent entered into a Master Unit
Agreement, dated as of July 27, 1998 (the "Master Unit Agreement"), in which the
obligations of the Company under the Units are provided;

     WHEREAS, AMHC has executed a Plan of Conversion, dated as of December 17,
1999, pursuant to which AMHC will convert from a mutual insurance holding
company into a stock holding company;

     WHEREAS, the Company and AMHC have entered into an Agreement and Plan of
Merger, dated December 17, 1999 (the "Merger Agreement"), pursuant to which the
Company will merge with and into AMHC, with AMHC continuing as the surviving
company (the "Merger") and AMHC will thereafter change its name to AmerUs Group
Co.;

     WHEREAS, AMHC wishes to assume the obligations of the Company under the
Master Unit Agreement, as authorized by Article Eight of the Master Unit
Agreement and without the consent of the Holders; and

     WHEREAS, AMHC wishes to provide the rights provided by Section 506 of the
Master Unit Agreement to the Holders of each Outstanding Unit, pursuant to the
requirements of Section 5.06(b) of the Master Unit Agreement, as authorized by
Article Eight of the Master Unit agreement and without the consent of the
Holders.

     NOW THEREFORE, in consideration of the foregoing, the parties agree as
follows:

Section 1.  Definitions.  Capitalized terms not otherwise defined herein shall
            have the meanings set forth in the Master Unit Agreement.

Section 2.  Assumption.  AMHC hereby agrees to assume the obligations of the
            Company, as its successor, under the Master Unit Agreement and to
            be bound by the provisions of such agreements.

Section 3.  Adjustment of Settlement Rate. The Holders of each Outstanding
            Unit shall have the rights provided by Section 506 of the Master
            Unit Agreement and adjustment to the Settlement Rate will be made
            accordingly.



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Section 4.  Subsequent Adjustment of Settlement Rate. Adjustments to the
            Settlement Rate for events that occur subsequent to the Effective
            Time (as defined in the Merger Agreement) of the Merger shall be
            as nearly equivalent as may be practicable to adjustments provided
            for in Section 506.

Section 5.  Notice.  Section 1.05 of the Master Unit Agreement will be amended
            to delete the Trustee's notice address and insert the following
            notice in lieu thereof:

                           401 South Tryon Street
                           12th Floor
                           Charlotte, NC 28288-1179

Section 6.  Effectiveness.  This Supplemental Agreement shall become effective
            as of the Effective Time (as defined in the Merger Agreement) of
            the Merger.

Section 7.  Counterparts.  This Supplemental Agreement may be executed in two
            or more counterparts, each of which will be deemed to be an
            original, but all of which together will constitute one and the
            same agreement.

Section 8.  Governing Law.  This Supplemental Agreement will be governed by and
            interpreted in accordance with the internal laws of the State of
            New York, without giving effect to principles of conflicts of laws.

            IN WITNESS WHEREOF, the parties hereto have executed and delivered
this Supplemental Agreement as of the date set forth above.


                                    AMERICAN MUTUAL HOLDING COMPANY


                                    By: /s/ Roger K. Brooks
                                        ---------------------------------------
                                          Name:  Roger K. Brooks
                                          Title: Chairman, President and
                                                 Chief Executive Officer


                                    FIRST UNION NATIONAL BANK, as Unit Agent


                                    By: /s/ Shawn K. Bednasek
                                        ---------------------------------------
                                          Name:  Shawn K. Bednasek
                                          Title: Vice President