Using biochemical, morphological, and endocrine evaluation, we hope to characterize the nature of oligospermia, one of the causes of infertility in man. The study has two components. First part is a detailed study of infertile men to establish the hormonal milieu, systemic and local, present in association with the infertility. Function of seminiferous tubules, Sertoli cells, and Leydig cells be examined in relation to morphology of the testis. The second part is an attempt to learn more about the natural history of oligospermia.