Abstract: Eight normal adult males were accepted two injections of 2, 000 IU of hGG in an interval of 6 days. During each injection peripheral blood was collected at 0, 2, 4, 6, 48, 72 and/or 06, 120 （h） for meassuring progesterone （p）, 17-OHprogesterone （17-OHP）, androstanedione（△₄A）, dehydroepiandrosterone（DHEA）, testosterone （T） and estradiol （E 2）. It was found that after the second injection, the delayed secretion peak （DSP） of 17-OHP in response to hCG was significantly higher than that of △₄A, suggesting the blockage of 17, 20-lyase. The DSP of E2 in each of two injections was significantly higher than that of △₄A or T, indicating that the aromatese in testes was activated by hCG. Some evidences showed that the blockage of 17, 20-lyase was related to the level of E2. Our data also prompted that the △₄ and △₅ pathways were equal importance in the biosynthesis of T.