The effects of two triphasic oral contraceptives containing the same amount of ethinylestradiol (EE) in combination with levonorgestrel (LNG) or gestodene (GES), respectively, on lipid metabolism and coagulation were studied. Serum concentrations of GES and LNG were determined at the same time. Thirty-three healthy women were randomized into two groups receiving either of the preparations. Before treatment and in the 3rd and the 6th cycle, blood samples were drawn in the morning while subjects were still in bed to obtain basal conditions. HDL₂-cholesterol decreased in the LNG group but was unchanged in the GES group, whereas apolipoprotein Al increased in the GES but not in the LNG group. Antithrombin III decreased in the GES group but was unchanged in the LNG- treated women. Factor VII increased in both groups, but more in the GES group. It is concluded that GES has a positive influence on lipid metabolism, and has a slightly negative influence on coagulation but the latter is more likely to be without clinical relevance. The positive influence of GES compared to LNG on lipids is probably due to its lower androgenicity and not to differences in bioavailability.