Exhibit 10(a)

                                 FIRST AMENDMENT
                          TO THE AON STOCK OPTION PLAN
                      AS AMENDED AND RESTATED THROUGH 1997


      THIS FIRST AMENDMENT  ("First  Amendment") TO THE AON STOCK OPTION PLAN AS
AMENDED AND RESTATED  THROUGH  1997 (the "Plan") is hereby made  effective as of
the 19th day of March, 1999.

                                 R E C I T A L S


      WHEREAS,  the  Company  deems it in the best  interests  of the Company to
amend certain provisions of the Plan to clarify existing policies, practices and
procedures; and

      WHEREAS, the Company desires to make available to participants in the Plan
certain deferral features.

      NOW, THEREFORE, the Plan is hereby amended as follows:

1.    All references in the Plan to "paragraph"  when used in conjunction with a
      specific  paragraph  number,  e.g.,  "paragraph"  7,  shall be  changed to
      "Section."

2.    Section 2 of the Plan is hereby  amended by deleting  the second and third
      sentences and inserting the following:

            "Since the  adoption  of the Plan in 1982,  after  giving  effect to
            subsequent  additions approved by shareholders and stock splits, the
            aggregate  number  of shares  of  Common  Stock  which may be issued
            pursuant to options granted under the Plan shall be 23,250,000.  The
            administration of the Plan, agreements relating to Grants, including
            but not limited to agreements  governing unfair competition,  forms,
            practices,  procedures,  all questions involving the eligibility for
            Grants,  interpretations  of  the  provisions  of the  Plan,  or the
            operation of the Plan shall be decided by the Committee."

3.    Section 4 of the Plan is hereby amended by adding the following as a final
      sentence:

            "The  Committee  in its sole  discretion  may satisfy its  liability
            under  this  Section  4 by making a cash  payment  equal to the Fair
            Market Value of the shares of Common Stock to be delivered."







4.    Section 6 is hereby amended by adding the following as a final sentence:

            "Any Participant who terminates  employment,  other than by death or
            disability,  will be permitted  to exercise any vested  shares for a
            period  of  30  days   immediately   following   the   Participant's
            termination  of  employment,  after which any vested  shares will be
            forfeited."

5.    Section 7 is hereby amended by deleting the following sentence:

            "Shares  subject  to  a  Grant  shall  not  be  delivered  to  the
            Participant until such time as such payment has been made."

6.    Section 15 is hereby  amended by adding  the  following  as new second and
      third paragraphs, and moving the current second paragraph to be the fourth
      paragraph:

            "To the extent any shares of Common Stock covered by a Grant are not
            delivered  to a  Participant  or  beneficiary  because the Grant was
            forfeited  or  canceled,  or the  shares  of  Common  Stock  are not
            delivered  because the Grant or exercise of the option is settled in
            cash or used to satisfy the applicable tax  withholding  obligation,
            such shares shall not be deemed to have been  delivered for purposes
            of  determining  the  maximum  number  of  shares  of  Common  Stock
            available for delivery under the Plan.

            If the  exercise  price of any Grant under this Plan is satisfied by
            tendering  shares  of Common  Stock to the  Corporation  (by  either
            actual  delivery  of by  attestation),  only the number of shares of
            Common Stock issued net of shares of Common Stock  tendered shall be
            deemed  delivered for purposes of determining  the maximum number of
            shares of Common Stock available for delivery under the Plan."

7.    There is added a new Section 16 as follows:

            "The  Committee  may, in its discretion and subject to such rules as
            it may adopt, permit a Participant to defer all or a portion of such
            shares otherwise deliverable pursuant to an exercise of a Grant."