In a randomized comparative study, changes in lipoprotein metabolism during the use of two low-dose oral contraceptives with similar doses of ethinyl estradiol but with different progestogenically active compounds were evaluated for their effective estrogen/androgen balance. Sixty-eight healthy women who did not take hormonally active drugs or were pregnant the previous 3 months took either 75 micrograms of gestodene + 30 micrograms of ethinyl estradiol or 150 micrograms of desogestrel + 30 micrograms ethinyl estradiol during 12 cycles. During the first three cycles serum levels of the following parameters increased: triglycerides, cholesterol in high-density lipoprotein, and apolipoproteins A1, A2, and B. Additional increase was observed in apolipoprotein B only after three and six cycles. The induced changes were not significantly different in the two groups, and the levels generally remained within normal limits. The changes seen with both pills reflect a mild estrogenic dominance. On the basis of current knowledge, moderately altered lipoprotein metabolism is not expected to impose an extra risk of atherosclerosis.