The effects of two monophasic oral contraceptives containing ethinylestradiol 20 microg in combination with levonorgestrel 100 microg (EE20/LNG100) or 30 microg and 150 microg (EE30/LNG150), respectively, on lipoprotein metabolism was investigated in a double-blind, randomized study of 12 treatment cycles in healthy female volunteers. Total triglycerides (+32% to +46%, p < 0.05 in comparison to baseline) increased significantly. Triglycerides were highest after six cycles of treatment, decreasing thereafter. Total cholesterol (+1% to +7%), apolipoprotein (apo) B (+21% to +29%) and low-density lipoprotein (LDL) cholesterol (+7% to +17%) increased slightly. High-density lipoprotein (HDL) cholesterol decreased slightly (-11% and -5%), HDL triglycerides increased (+16% and +26%). Apo AI did not change during the study, suggesting that the molar concentration of HDL particles did not change. Apo E (-23% to -14%) decreased, and there was a transitory decrease of lipoprotein (a). Essentially, there was no difference regarding the changes in lipoprotein metabolism between the two treatment groups. The effects of the two combinations of ethinylestradiol and levonorgestrel on triglyceride-rich lipoproteins appear less pronounced than those produced by preparations containing third-generation progestins. It is not likely that the changes in lipoprotein metabolism brought about by the two preparations will alter the risk of future cardiovascular disease in a clinically relevant fashion.