Lipoprotein-related coronary risk factors in patients with angiographically defined coronary artery disease: relation to number of stenosed arteries. To determine whether an index estimating antagonism between low density lipoprotein (LDL) and high density lipoprotein (HDL) would improve separation between groups with and without coronary artherosclerosis, patients undergoing coronary catheterization (35 women and 99 men) were analysed for total cholesterol (TC), HDL cholesterol (HDLc), apolipoprotein A (apo A) and apolipoprotein B (apo B). The subjects were categorized as groups 0, 1, 2 or 3 according to the number of stenosed arteries (greater than 75% areal stenosis). Thirty of the patients showed no significant coronary atherosclerosis (group 0). Serum apo B and TC concentrations were directly related to the number of stenosed vessels, whereas the concentrations of apo A and HDLc were negatively correlated with the number of stenosed arteries. An 'atherogenic Index' (ATH index) calculated as the product of serum concentrations of apo B, and TC minus HDLc divided by the product of apo A and HDLc, proved more satisfactory than individual lipoprotein components for discrimination between subjects with and without stenosis. Accordingly, identification of coronary groups may be improved by using the ATH index. 