1 EXHIBIT 16 [LETTERHEAD OF ARTHUR ANDERSEN] June 12, 1998 Office of the Chief Accountant Securities and Exchange Commission 450 Fifth Street, N.W. Washington, D.C. 20549 Dear Sir/Madam: We have read Item 4 included in the Form 8-K dated June 12, 1998, of Central Illinois Public Service Company filed with the Securities and Exchange Commission and are in agreement with the statements contained therein. Very truly yours, /s/ Arthur Andersen LLP Arthur Andersen LLP RAM Copy to: Mr. Warner L. Baxter Vice President and Controller Ameren Corporation