To determine the predictive risk factors of the severity of the coronary artery disease, the serum levels of lipoprotein cholesterol and apolipoprotein were measured in 103 patients undergoing coronary angiography examination for suspected myocardial ischemia. The extent and severity of the coronary artery disease (CAD) were assessed by assigning scores to each lesion. Twenty-six female patients (59 +/- 8 yrs.) showed a stronger relationship of apo B and apo A-I/B to the coronary scores than the 77 male patients (57 +/- 8 yrs.). The male patients were divided into four groups based on the coronary scores: H-CAD (range: over 11 points), M-CAD (5-10 points), L-CAD (1-4 points) and N-CAD (0 point). The atherogenic risk factors other than the abnormalities in lipid metabolism (obesity index, fasting plasma glucose, smoking and blood pressure) were well matched in the four groups. T.C., LDL-C., HDL-C., HDL2-C., apo B, apo A-I/B ratio and apo A-II/B ratio significantly differed in the H-CAD and N-CAD groups. These results indicate that T.C., LDL-C., HDL-C., HDL2-C., apo B, apo A-I/B ratio and apo A-II/B ratio are predictive risk factors of the coronary heart disease. Furthermore, apo B and apo A-I/B ratio significantly differed in the H-CAD and L-CAD groups. These results suggest that apo B and apo A-I/B ratio may be good discriminators of the severity of the coronary heart disease.