The lipid and apolipoprotein states of 74 men (mean age 49.96 +/- 5.9 years) were studied 24 h before coronary bypass surgery and their results were compared with those of a control group of 78 men (mean age 48.88 +/- 5.41 years). Apolipoproteins C-III (apo C-III) and E (apo E) were determined in particles with (LpB) and without (nonLpB) apo B separated using a concanavalin A reagent. Apo C-III was significantly increased in LpB particles (P less than 0.001), and apo E in LpB (P less than 0.001) and nonLpB (P less than 0.001) particles. The significant variables selected in logistic discriminant stepwise analysis were total cholesterol/HDL-cholesterol, apo E-nonLpB and apo C-III-LpB. This last parameter, which is more discriminant than triglycerides, provides a more specific indication of dyslipoproteinemia in coronary bypass patients; in association with the other two variables, it significantly improved the percentage of correctly classified individuals.