Recent clinical trials indicate that reduction of plasma cholesterol concentrations in individuals with increased levels of low-density lipoproteins reduces their risk of myocardial infarction and death. Therefore, the question of "whether to treat" should be shifted to "whom to treat" and "how best to treat." The understanding of normal lipid transport via the plasma lipoproteins has grown to a sophisticated level over the past 20 years. Plasma cholesterol, required for cellular membrane integrity, and plasma triglycerides, the primary mammalian energy source, are carried in lipoprotein particles that vary in size, density, lipid composition, and apolipoprotein content. Some lipoprotein particles (low-density lipoproteins) play a causal role in the atherosclerotic process, while other particles (high-density lipoproteins) appear to prevent this process. Utilizing this understanding of the plasma lipoproteins, a systematic approach to the management of the patient with hyperlipoproteinemia has been developed which may lead to the normalization of plasma lipoprotein concentrations in the majority of hyperlipoproteinemic patients.