Sperm acquire the ability to fertilize ova during their passage through the epididymis and are stored in the epididymis until ejaculated. The acquisition of fertilizing ability by and their survival in the epididymis are dependent upon the hormonally modulated melieu the epididymis. We propose to obtain information on how androgens and estrogens are involved in regulating the structure and function of the epididymis and how the epididymis in turn provides a suitable environment for sperm maturation and survival. We propose: a) to examine androgen and estrogen receptors in the epididymis, b) to examine the segmental distribution of these receptors and determine if the segmental distribution correlates with known physiological or morphological parameters, c) to investigate the ontogeny of androgen and estrogen receptors in the epididymis to determine if these hormones act individually or in concert to bring about the developmental changes that occur in the epididymis during sexual maturation, and d) to develop an estrogen nuclear exchange assay to quantitate changes in the concentration of nuclear acceptor sites. Understanding the role of the epididymis in sperm maturation and survival is of importance in devising extratesticular methods of male contraception and in providing means for alleviating infertility problems arising from epididymal malfunction.