Changes in circulating lipoproteins, which may be related to the risk for atherosclerotic vascular disease, were studied in a control group and in two groups of 24 or 26 women using different preparations of low-dose oral contraceptives for 3 months. One preparation contained 150 μg levo-norgestrel and 30 μg ethinylestradiol (Stediril-d 150/30); the other contained 750 μg lynestrenol and 37.5 μg ethinylestradiol (Ministat). No significant changes were found with either of the preparations in serum cholesterol or high density lipoprotein cholesterol (HDL-C) levels. Apolipoprotein A-II levels increased during Ministat treatment from 50.4 to 61.4 mg/dL and during Stediril-d 150/30 treatment from 52.7 to 58.9 mg/dL (both P < 0.001). These changes differed significantly from each other (P < 0.01). Apolipoprotein A-I levels increased significantly during use of Ministat only. Apoliprotein B in low density lipoprotein increased by about 20% (P < 0.001) in both groups. Post-heparin lipoprotein lipase activity did not change, but hepatic lipase activity decreased to the same extent in both groups (P < 0.001). Reductions in post-heparin lipase activity were not correlated with increases in HLD-C. Chemicals/CAS: ethinylestradiol plus lynestrenol, 53682-16-9, 8064-76-4; ethinylestradiol plus norgestrel, 8056-51-7; ethinylestradiol, 57-63-6; lynestrenol, 52-76-6; norgestrel, 6533-00-2; Apolipoproteins; Cholesterol, 57-88-5; Contraceptives, Oral; Contraceptives, Oral, Combined; Contraceptives, Oral, Sequential; Ethinyl Estradiol, 57-63-6; Ethinyl Estradiol-Norgestrel Combination, 8056-51-7; Lipase, EC 3.1.1.3; Lipoprotein Lipase, EC 3.1.1.34; Lipoproteins; Lynestrenol, 52-76-6; Ministat, 8064-76-4; Norgestrel, 6533-00-2; Triglycerides