Aminoglutethimide (Elipten-Ciba) has been shown to be a potent inhibitor of adrenal steroidogenesis as well as thyroidal organification of iodine. Administration of the drug to animals and humans resulted in distinct histologic changes of the adrenals, including cellular hypertrophy, cytoplasmic vacuolation, and excessive accumulation of lipid. It is suggested that these findings may be similar to that described by Prader as lipoid adrenal hyperplasia. Assays for the adrenal cholesterol side chain cleaving enzyme system (desmolase complex) were performed. The presence of Elipten in the incubation mixture produced inhibition of the enzymatic conversion of cholesterol to Δ5-pregnenolone. This early pathway is required for the biosynthesis of all steroid hormones. The drug was administered to 2 patients in a therapeutic attempt to inhibit steroid synthesis, with apparent success. Elipten inhibits enzymatic cleavage of the cholesterol side chain and may be a valuable drug in the treatment of diseases associated with excessive steroid hormone production and in those conditions which might be ameliorated by diminished steroid production. The inhibition of the desmolase complex appears to be the primary adrenal effect of the drug, although other sites of enzymatic inhibition are not excluded.