We plan to explore the endocrine physiology of the testis with the ultimate goal of gaining insight into the mechanisms for idiopathic oligospermia in man. These investigations involve study of rodents, subhuman primates and men. Altered testicular steroidogenesis may be causal in a subgroup of infertile men. Accordingly, studies are underway to compare in vivo and in vitro steroidogenesis with other clinical properties in a population of men attending an infertility clinic. Basic studies are also performed using orchiectomy tissue from untreated men with prostatic cancer. Androgen binding protein appears to be a product of sertoli cells and may function to maintain high levels of intratesticular testosterone needed for spermatogenesis and sperm maturation and transport in the epididymis. Our laboratories are involved in the study of ABP in men. Having measured this protein using a binding assay in orchiectomy specimens, we plan to refine our assays to permit study of this material in the testis biopsies of our infertile male population. We also plan to extend our studies of intratesticular steroidogenesis and androgen binding protein to subhuman primates. Such experiments will permit us to explore the control of testicular hormones in a fashion not possible in man.