ACTH has been shown to have a simulatory effect upon the accumulation of cholesterol by the rat adrenal. The demonstration of this effect was facilitated by the use of amino-glutethimide, an agent that inhibits the conversion of cholesterol to corticosteroids. When amino-glutethimide was given in the absence of ACTH, cholesterol accumulation in the adrenal was minimal. When the drug was given in the presence of ACTH, the adrenal cholesterol concentration was greatly increased. This effect of ACTH might be biologically important in assuring the continuing availability of cholesterol as a corticosteroid precursor during prolonged rapid steroidogenesis.