We will test the hypothesis in normal men (rather than hypogonadal men) as a "proof of principle" investigation. A normal hypothalamic-pituitary-testicular axis and regulation, circulating T and DHT levels and intraprostatic androgen concentrations in healthy, normal men will permit optimal testing of the hypothesis. Exogenous DHT administration in normal men is expected to suppress endogenous gonadotropin and testosterone secretion, compared to more variable effects in hypogonadal men that depend on the degree of hypogonadism in these men and whether they have primary (testicular) or secondary (hypothalamic-pituitary) hypogonadism. Furthermore, intraprostatic T and DHT concentrations and 5 alpha-reductase activity (that is androgen-dependent) is expected to be more variable in hypogonadal men, depending on the degree of androgen deficiency and circulating T and DHT levels. If results in normal men support the hypothesis, subsequent studies could be performed in hypogonadal men. Because of the larger variability in circulating and probably intraprostatic androgen concentrations in hypogonadal men, these studies will require much larger numbers of subjects.