beta-Lipotropin has a potent aldosterone stimulating effect in vitro and in vivo in rats. 2. The maximum aldosterone response to beta-lipotropin was the same as to ACTH and greater than to angiotensin II. 3. Although doses of ACTH which maximally stimulated aldosterone significantly increased cyclic AMP production, maximally stimulating doses of sheep beta-lipotropin did not increase cyclic AMP production significantly. 4. These data suggest that beta-lipotropin may play a role in aldosterone regulation through a mechanism different from that of ACTH.