The effects of the monophasic oral contraceptive preparation desogestrel plus ethinyloestradiol (EE) and triphasic levonorgestrel plus EE on lipid metabolism were compared. Sixteen young healthy female volunteers received monophasic desogestrel plus EE (21 X 150/30), whereas eighteen women received triphasic levonorgestrel plus EE (6 X 50/30 + 5 X 75/40 + 10 X 125/30) for six consecutive cycles. The lipid composition of the various lipoprotein fractions was estimated after separation in a density gradient by ultracentrifugation. In addition, the apolipoproteins A-I and B were assessed. HDL-cholesterol (precipitation method), HDL-2 cholesterol, HDL-2 phospholipids and the ratio apolipoprotein A-I to apolipoprotein B were significantly higher in the monophasic desogestrel group than in the triphasic levonorgestrel group after three and six treatment cycles. HDL-cholesterol (gradient), HDL-phospholipids (gradient), HDL-3 phospholipids and apolipoprotein A-I were only significantly higher after six treatment cycles. No differences between the groups were observed for the other lipid variables studied including triglycerides and VLDL-triglycerides.