These studies seek to assess the effects of environmental agents on spermatogenesis, function of accessory sex organs, and male and female reproductive capacity. Mechanisms of toxicity are studied and new approaches to toxicity testing are proposed and validated in order to extrapolate more reliably from laboratory animals to man and to improve our ability to analyze risk. The following studies are ongoing: (A) the mechanisms by which DNA-damaging agents increase the induction of aryl hydrocarbon hydroxylase activity by TCDD in the prostate glands; (B) the effects of TCDD on preovulatory oocytes and preimplantation embryos; (C) protein analysis of epithelial cells from precaput, caput, corpus, and cauda epididymides to identify sperm maturation factors; (D) correlation of improved histopathologic assessment (ultra-thin sections) of testicular damage induced by antineoplastic agents with testicular and epididymal sperm counts and fertilizing capacity determined in vivo; and (E) susceptibility of testicular tissues to early postnatal treatment with antineoplastic agents.