This project is a component of a larger study of the immunological, biological and physical correlates of the structure of human chorionic gonadotropin, a peptide hormone secreted by normal and neoplastic trophoblasts and used as indicator of pregnancy and trophoblastic tumors. This hormone assayed in vivo appears to possess Thyroid Stimulating (TSA), Follicle Stimulating (FSA) and Interstitial Stimulating Activities, and these studies are directed toward determining the molecular basis of these activities.