Testosterone concentrations in the blood of CBA/Lac and PT mice and its content in the testes under normal conditions and during stimulation with chorionic gonadotropin were measured by enzyme immunoassay. Genetic differences in reactivity of the testes to chorionic gonadotropin were revealed: PT mice were characterized by more pronounced hormonal reaction compared to CBA/Lac mice. An optimal dose of chorionic gonadotropin (10 U) and time interval (120 min) for evaluation of potentialities of testicular hormonal function were determined.