The transformation of androgens to estrogens involves three hydroxylations, the first two of which take place at the C-19 position and third at 2Beta. The product of these reactions the 2Beta-hydroxy-19-aldehyde, is transformed nonenzymatically to estrogen. An antibody to the 2Beta-hydroxy aldehyde has been prepared and it inhibits estrogen formation by delaying the collapse of the labile enzymatic product of placental aromatase. The purpose of this project is to utilize this immunological probe and the high specific activity androgen substrates which have been synthesized, to examine the individual hydroxylations participating in estrogen biosynthesis in tissues other than the placenta such as the gonads, brain and adipose tissue. The step(s) in the aromatization sequence which are influenced by pituitary hormones will be analyzed by means of the above probes. The new radiolabeled substrates will be employed to examine changes in peripheral aromatization in in vivo studies contrasting normals and subjects with body weight distortions, as well as patients with liver disease. The mechanism of estrogen biosynthesis will provide the basis for the synthesis of structures which bid well to be effective and specific aromatization inhibitors and can prove to be useful therapeutic agents in diseases in which cessation of estrogen biosynthesis is desirable.