The research carried out at the Center for Population Research of the Population Council's Biomedical Division includes both applied and fundamental studies on the biology of reproduction and contraceptive development. There is work in progress (1) to determine the feasibility of regulating fertility by immunological procedures, (2) to establish the function and periodicity of corpus luteum and to determine hormonal factors influencing ovulation in the rhesus monkey, (3) to elucidate the intracellular events consequent to sex hormone stimulation of target tissues, (4) to observe the effects of androgens on protein synthesis of rat epididymis explants, (5) to characterize the nature of the interaction of HCG with membrane fractions of testicular and luteal cells, (6) to establish the conditions affecting the release rates from polymers of steroids in vitro and in vivo, (7) to screen compounds as antifertility agents in the rat and monkey for possible use as contraceptives in human beings, (8) to determine the factors participating in the control of DNA synthesis in eukaryotic cells during mitosis and meiosis, (9) to determine morphologic and biochemical changes in the uterus induced by copper-containing IUD, (10) to evaluate the efficacy of copper-bearing IUD in fertility control, (11) to study the ultrastructure of reproductive tissues under different hormonal conditions.