Twenty healthy female volunteers were treated with 35 microgram ethinyl estradiol and 0.4 mg norethindrone for a two-month period of time. Liver function tests (serum SGOT, SGPT, LDH, alkaline phosphatase, total bilirubin, total protein, albumin and prothrombin times) were measured at baseline and control prior to treatment, and at one and two months of therapy. There was a 1.25% incidence of abnormalities in the 320 tests conducted during therapy. During the first month of therapy, there was a 1.9% incidence of abnormal tests. 0.625% incidence of abnormal tests was seen in the second month of treatment. A 5% incidence of abnormalities (single episodes in each parameter) was seen in SGPT, LDH, total bilirubin and prothrombin time levels during the two-month period. This was well below the 10-30% incidence of abnormalities reported with 50-100 microgram of estrogen-containing birth control pills in previous studies. There seems to be little effect on liver function tests with use of estrogen preparations containing 35 microgram ethinyl estradiol.