Exhibit 5.0

                       [LOGO OF ARTHUR J. GALLAGHER & CO.]


June 26, 2003


SECURITIES AND EXCHANGE COMMISSION
450 Fifth Street N.W.
Washington, D.C. 20549

                  Re:   Arthur J. Gallagher & Co.
                        Registration Statement on Form S-8

Ladies and Gentlemen:

         I am counsel for Arthur J. Gallagher & Co. (the "Company") in
connection with the above referenced Registration Statement on Form S-8 (the
"Registration Statement") being filed by the Company with the Securities and
Exchange Commission under the Securities Act of 1933, as amended (the
"Securities Act"), relating to the registration of 6,600,000 shares of the
Company's Common Stock, par value $1.00 per share (the "Shares"), together with
6,600,000 Common Share Purchase Rights of the Company (the "Rights") associated
therewith, to be issued pursuant to the terms of the Company's 1988 Nonqualified
Stock Option Plan and the Company's 1989 Non-Employee Directors' Stock Option
Plan (collectively, the "Plans"). The terms of the Rights are set forth in the
Rights Agreement dated as of May 12, 1987 between the Company and Harris Trust &
Savings Bank, as Rights Agent, and as amended on July 19, 1996 (the "Rights
Agreement").

         In this connection, I have examined the originals or copies identified
to my satisfaction of such documents, corporate and other records, certificates,
and other papers as I deemed necessary to examine for purposes of this opinion.

         Based upon such examination, I am of the opinion that:

         1. The Shares of Common Stock will be legally issued, fully paid and
nonassessable (i) when the Registration Statement shall have become effective
under the Securities Act; (ii) the Shares shall have been duly issued and
delivered in the manner contemplated by each Plan; and (iii) certificates
representing the Shares shall have been duly executed, countersigned and
registered and duly delivered to the persons entitled thereto against receipt of
the agreed consideration, if any, provided in accordance with each Plan.

         2. The Rights associated with the Shares will be legally issued when
such Rights have been duly issued in accordance with the terms of the Rights
Agreement and the Shares have been duly issued and delivered as set forth in
paragraph 1.

         I hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the reference to me in the Registration Statement
and the related Prospectuses.



SECURITIES AND EXCHANGE COMMISSION
June 26, 2003
Page 2

                                        Very truly yours,

                                        /s/ JOHN C. ROSENGREN
                                        ----------------------------------------
                                        JOHN C. ROSENGREN
                                        Vice President and General Counsel