The aim of this study was to determine the frequency of various metabolic risk factors for coronary artery disease (CAD) in 246 male patients studied over a 2-year period. CAD was diagnosed on the basis of a history indicative of angina pectoris, an electrocardiogram diagnostic of myocardial ischaemia, and a positive coronary angiogram. Thirty-eight per cent of this population had diabetes, hypertension or both. Of the remaining individuals, 39% had a plasma cholesterol concentration greater than 5.2 mmol l-1, whereas 23% had a cholesterol concentration less than 5.2 mmol l-1. Plasma lipid and lipoprotein levels of a non-smoking subset of those subjects with a total cholesterol concentration less than 5.2 mmol l-1 were compared with values of a matched group of individuals who did not have significant vessel disease as revealed by angiography. The results of these investigations indicated that patients with CAD and a plasma cholesterol concentration less than 5.2 mmol l-1 exhibited an increase in plasma triglyceride concentration and a decrease in plasma HDL-cholesterol concentration. Since these subjects were not diabetic, hypertensive or hypercholesterolaemic, it is suggested that the observed changes in triglyceride and HDL metabolism made a major contribution to the CAD in these individuals.