The inactivation of endogenous steroids and foreign compounds by the liver hydroxylative pathway, can be modified by androgenic substances. The inhibitory or inductory activity, can be estimated by measuring the half‐life of antipyrine. Androgens (testosterone propionate, 5α‐dihydro‐testosterone and mesterolone) reduce antipyrine metabolism in male rabbits. In females, androgens are not inhibitors, but one of them, 5α‐dihydrotestosterone, shows an inductive effect on liver oxidative mechanisms.