Three cases of myastenia gravis treated with ACTH and Cortisone after failure of classic therapy, are reported. All cases were symptoms free for about one month after withdrawall of hormone therapy. According to the evolution treatment was resumed several times. A minimal maintenance dosis was tried in cases 1 and 2, controled during a period of at least 40 days. ACTH was used intravenously (2.5 to 25 mgm. in 250 to 1,000 ml. isotonic glucose solution daily) at the rate of 20 to 25 drops per minute. Prostigmine was administered simultaneously in very small dosis. Serious relapse of symptoms occurred in the first week in each series of ACTH in case 2, and after the first series in case 1. All patients had a follow-up of two years.