In order to determine the effect of dihydrotestosterone on the feed back mechanisim of the hypothalamo-pituitary-testis axis, nine healthy subjects were subjected to LH-RH tests before and after treatment with 5alpha-DHT. A double antibody radio-immunoassay technique was used to measure the concentration of LH and FSH in the plasma. Our results clearly show that the pituitary LH release by LH-RH after pre-treatment with 5alpha-DHT is more prononeced. In the light of actual findings from several laboratories it is not possible to interpret clearly the results of our own experiments, and hence we advance only some hypotheses.