Blood samples were obtained from 20 women, aged 18 to 30 years, before and during the use of selected oral contraceptives. The contraceptive preparation containing 100 μg mestranol induced increases in triglycerides, esterified cholesterol, free cholesterol, and phospholipids. Ethinyl estradiol with norgestrol, on the other hand, tended to decrease the lipid levels, while preparations containing only 50 μg mestranol produced no significant change in the levels of the four substances. The levels produced by each of these three preparations did not exceed the normal limits. A cyclic fluctuation was observed in the monthly cycles.