1. Six normal volunteers were studied on four diets (10 mEq Na/40 mEq K, 10 mEq Na/200 mEq K, 200 mEq Na/40 mEq K, and 200 mEq Na/200 mEq K) and stimulated with a continuous 48-h infusion of ACTH. 2. Aldosterone secretions were measured basically and on the days of ACTH infusion. Basal aldosterone secretion was increased by restricting sodium or by increasing potassium. 3. The mean peak response of aldosterone secretion to ACTH on the 200 mEq Na/40 mEq K diet was 241 μg/day, and 1044 μg/day on the 200 mEq Na/200 mEq K diet. The mean peak response on the 10 mEq Na/40 mEq K diet was 1803 μg/day, and on the 10 mEq Na/200 mEq K diet was 2062 μg/day. 4. These results indicate that potassium, independent of sodium and angiotensin, can regulate basal aldosterone secretion and sensitize the adrenal response to the aldosterone stimulatory properties of ACTH.