In the last decade, understanding of the relationship between plasma lipoprotein concentrations and arteriosclerosis has advanced considerably. Prospective and case-control epidemiologic studies in the general population have established a direct correlation between low density lipoprotein and an inverse correlation between high density lipoprotein concentrations and the risk of coronary disease. Detailed studies of patients and families with genetic hypercholesterolemia, hypertriglyceridemia, and combined hypercholesterolemia hypertriglyceridemia have identified subpopulations at particular risk. Skin fibroblast lines from patients with genetic hyperlipidemias have been used to provide important new information on the regulation by plasma lipoproteins of cellular cholesterol metabolism. We are entering a phase of investigation where epidemiological and biochemical data supplement each other in such a way that the old hypothesis linking plasma lipids to atherosclerosis has new life.