Epidemiologic studies in castrates strongly support the key role of the testis in the pathogenesis of benign prostatic hyperplasia (BPH). Since the testis secretes androgen and estrogen, both of these hormones have been implicated in BPH. Much information supports the important role of dihydrotestosterone (DHT) in BPH, including intraprostatic activities of enzymes that regulate DHT. Although controversy still exists, DHT levels in BPH may be higher than in normal prostate tissue. Based upon these findings and the ability to quantitate prostate size and function with reliable new techniques, suppression of androgen-mediated action has been tested to assess the validity of the DHT theory. A variety of drugs has been demonstrated to decrease prostate size by approximately 30% by either blocking secretion of circulating testosterone and adrenal androgen, inhibiting 5 alpha-reductase to prevent DHT formation, or blocking DHT binding to androgen receptors. Accompanying these changes in size was significant improvement in clinical symptoms of prostatism in about 50% of patients, when double-blind, large multicenter studies were conducted with one of these drugs. Although these results suggest a very important role for androgen, particularly DHT, in the pathogenesis of BPH, other abnormalities may coexist since significant numbers of patients do not show a total reversal of disease. There is strong indirect evidence for a possible role for estrogen in the pathogenesis of BPH, and studies are under way to test the effects of estrogen withdrawal on prostate size and symptoms. Similarly, dynamic aspects of prostatic obstruction, which are under alpha-adrenergic regulation, may also be a component of this disease and amenable to therapy with alpha-adrenergic blockers.(ABSTRACT TRUNCATED AT 250 WORDS)