Adenylate cyclase activity was measured in particulate fractions prepared from bovine and human corenal endothelium. Bovine enzyme activity was stimulated by Fl, 5''-guanylylimidodiphosphate (GppNp) and .beta.-adrenergic agonists. Drug stimulation patterns of the human enzyme appeared qualitatively similar, but activities were generally higher than those of the bovine enzyme. The existence of a receptor-mediated adenylate cyclase system in bovine and human corneal endothelium was demonstrated; a possible role for cAMP in corneal endothelial physiology was suggested.