The relationship of coronary artery disease to with plasma lipids and apolipoproteins was examined in 100 male patients aged 32-69 years undergoing coronary angiography for suspected myocardial infarction. Patients with angiographically defined coronary artery disease had significantly lower plasma levels of high density lipoprotein (HDL) cholesterol, apolipoproteins A-I and A-II, and significantly higher values of low density lipoprotein (LDL) cholesterol and apolipoprotein B than those in patients without coronary artery disease. The ratios derived from the measurements as LDL cholesterol/HDL cholesterol, apo B/apo A-I and apo B/apo A-II were highly significantly increased in the patients with coronary artery disease. Coronary score values, by which the severity of coronary artery disease was quantified, were not related to plasma levels of the HDL components, while they were positively correlated with those of the LDL components. These results suggest that, in single measurements, plasma levels of the HDL components, HDL-cholesterol and apo A-I, contribute strongly to the discrimination between patients with coronary artery disease and those without this disease, whereas the LDL components, LDL-cholesterol and apo B are more suitable parameters for the severity of the disease than are the HDL components. The ratios of LDL cholesterol/HDL cholesterol, apo B/apo A-I and apo B/apo A-II were powerful discriminators for either presence or severity of coronary artery disease.