In order to determine effects of contraceptive steroids with respect to dose, progestin type and duration of administration, on hepatic cholesterol metabolism, rats were treated with two different (ethinyl estradiol/norethisterone acetate and ethinyl estradiol/levonorgestrel) combinations orally at two different-low and high-doses and- short and long-terms. At the end of the experiments, total cholesterol and acetoacetate levels in plasma samples and HMG-CoA synthase and AcAc-CoA thiolase activities in the livers of rats were measured. In all groups, acetoacetate was found to be higher than in controls, and except in low dose- ethinyl estradiol/levonorgestrel treated groups, total cholesterol was also increased. In the short period treatments HMG-CoA synthase and AcAc-CoA thiolase (except in low dose-ethinyl estradiol/levonorgestrel group) activities were increased. But enzyme activities were either decreased or not changed in long period treatments. It is suggested that increased enzyme activities in short period treatments may increase total cholesterol levels, and that in time, these levels may lead to a suppression of enzyme activities.