This review consists of an explanation of the significance and sources of blood lipids and lipoproteins and an evaluation of the effects on triglycerides, cholesterol, and phospholipids of estrogens and progestagens taken combined or separately by normal or hyperlipidemic subjects. Normal blood contains alpha and beta lipoproteins (binding cholesterol and phospholipids) in morning, and chylomicrons (with dietary triglycerides) and prebeta-lipoproteins (with endogenous triglycerides) after a meal. Estrogens or combined pills raise triglycerides to 1.5 gm per 100 ml, the upper range of normal limits, due to an elevation of heavy prebeta-lipoproteins (0-12 SF). Th is elevation may be related to decreased lipoprotein lipase (post-heparin-lipolytic activity) seen in women taking estrogen. Heightened triglycerides have been observed in mixed and endogenous hyperlipidemia and types 1, 4, 5 (Frederickson classification), but not essential or type 2 hyperlipidemia. Progestogens lower triglycerides and raise lipoprotein lipase in normal subjects and in those with endogenous hyperlipidemia type 5. Results of studies of total cholesterol are variable: androgenic progestogens decrease cholesterol, but other progestagens increased it in some studies. A norethisterone and ethinyl estradiol combination has been shown to raise high- and very high-density lipoproteins, cephalin and lecithin, but to depress lyso-le cithin. Besides altered lipoprotein lipase, these lipoprotein changes c ould be due to elevated insulin, cortisol, thyroxin, or growth hormone, or their protein carriers.