The aim of this study was to evaluate the ability of plasma levels of apo A-I and apo B to discriminate between male patients with and without angiographically determined coronary artery disease (CAD) in comparison to the levels of cholesterol, HDL-cholesterol and triglycerides. The plasma apo A-I and B levels were measured by a radial immunodiffusion assay that made use of well characterized monoclonal antibodies. Univariate statistical analysis showed that the mean values for HDL-cholesterol and apo A-I were significantly lower in patients with single-, double- and triple-vessel disease than in the control subjects. The mean values for plasma cholesterol and apo B were significantly higher in the group with double- and triple-, but not single-vessel disease, than in the group without CAD. No statistically significant difference among groups was found for plasma triglyceride values. Since the considered variables failed to assess the severity of the disease, as determined by the number of vessels involved, the 3 groups of patients with CAD were combined into one group. A multiple logistic analysis, performed in order to assess the independent role of the variables and to estimate the corresponding odds ratio, indicated an independent association of HDL-cholesterol, apo A-I and apo B with CAD. When the multiple logistic analysis was repeated with a stepwise procedure, only apo A-I and B entered into the model. The results of our study indicate that plasma levels of apo A-I and B are more useful than plasma lipid in detecting the presence or absence of coronary artery disease in a group of male patients undergoing coronary angiography.