Plasma-levels of major lipids (cholesterol, triglyceride, high-density-lipoprotein cholesterol), two major apolipoproteins (apo-B and apo-A1), and two ratios (total-cholesterol/apo-B and apo-A1/apo-B) were studied in 218 survivors of myocardial infarction and 160 controls. Apolipoproteins were as good as lipids as discriminators between the populations under the age of 50 and better in the sixth to eighth decades.. Furthermore, values of total-cholesterol/apo-B and apo-A1/apo-B obtained from controls and normolipaemic survivors of myocardial infarction gave a bimodal distribution. The protein moiety of lipoproteins is a better discriminator than lipids between atherosclerotic subjects and controls.