The objectives of this proposal include the design, synthesis an devaluation of specific inhibitors of human placental aromatase (estrogen synthetase). These inhibitors include enzyme-generated irreversible inhibitors and also competitive reversible inhibitors. Specific inhibitors of human biosynthesis in placental tissue and in other tissues. They may also be of value in the study and treatment of estrogen-dependent tumors, and in studying the role played by peripheral aromatization of androgen in male endocrinology. Mechanistic studies with these inhibitors should be of interest in further examination of the mechanism of action of aromatase. Covalent labeling of purified enzyme by radiolabeled inhibitors may provide valuable information about the enzyme's active site. A chemical model for aromatase has been developed, and this model will be evaluated in terms of the enzymatic process's stereochemical and kinetic behavior.