A study of serum lipoprotein (VLDL, LDL, HDL) concentration has been performed on 36 males who had undergone an aorto-coronary bypass operation before age 50. They have been compared to 33 healthy men in the same age range. The presence and severity of coronary, carotid and peripheral atherosclerosis in these patients has been evaluated on the basis of coronary angiograms, continuous wave Doppler and Duplex scanning by echo-Doppler. Lipoprotein abnormalities have been related to the occurrence of extracoronary arterial lesions in association with myocardial ischemia. Total serum cholesterol and triglycerides, LDL cholesterol and triglycerides were higher in IHD patients (p less than 0.05), while HDL cholesterol was lower (p less than 0.01). No statistically significant difference was detected in VLDL lipids or apo B and in LDL apo B. Signs of extracoronary atherosclerosis were more frequent among IHD patients than in controls. Ankle/arm pressure ratio was abnormally low in 12 patients as compared to only one control (p less than 0.01). Echo-Doppler examinations of iliac arteries demonstrated a higher prevalence of lesions among IHD patients as compared to controls (20 versus 2; p less than 0.01). All patients (4 out of 36) with audible carotid bruits had stenoses in the internal carotid artery. In order to evaluate the relationships between lipoprotein concentration and occurrence of extracoronary atherosclerosis, analysis of variance and multiple comparisons were performed on values for lipoprotein concentration in three groups: controls, IHD patients without evidence of extracoronary atherosclerosis, IHD patients with detectable extracoronary lesions. Significant differences among the three groups were demonstrated as regard to LDL cholesterol or triglycerides and HDL cholesterol.(ABSTRACT TRUNCATED AT 250 WORDS)