OBJECTIVE--To compare risk factors in two populations of patients with advanced atheroma requiring coronary or femoropopliteal artery bypass grafting to try to account for the different localisations of vascular disease. DESIGN--Cross sectional epidemiological study. SETTING--Cardiovascular surgery department of a university hospital. SUBJECTS--464 men (mean age 59.25 (SD 8.57) years) undergoing coronary artery bypass grafting; 74 men (mean age 56.28 (13.3) years) undergoing femoropopliteal artery bypass grafting; and 204 control men (mean age 45.07 (6.59) years) who had been recruited in a preventive medicine department. INTERVENTIONS--Blood samples were drawn 24 hours before surgery. METHODS--Lipid and lipoprotein concentrations were measured for each patient and with adjustment for age were compared by analysis of covariance. The main risk factors (smoking, arterial hypertension, obesity, and diabetes) were determined by a standardised history, and the chi 2 test was used to compare the results in the two patient groups. Pairwise comparisons between the three populations were performed by logistic discriminant analysis. RESULTS--Both patient groups showed a significant rise in triglyceride concentration and in the ratio of total cholesterol to high density lipoprotein cholesterol (R1) and a drop in apolipoprotein AI and high density lipoprotein cholesterol concentrations. Disturbances were greater in patients undergoing coronary artery bypass grafting than in those undergoing femoropopliteal artery bypass grafting for the R1 ratio, apolipoprotein B concentration, and the ratio of apolipoprotein AI to apolipoprotein B (R2). A higher proportion of smokers was found in the femoropopliteal bypass group than in the coronary bypass group, whereas were often obese. Logistic discriminant analysis with adjustment for age and with the coronary bypass as the reference group selected three factors: smoking, the R2 ratio, and obesity. CONCLUSION--Disturbances in lipid and apoprotein concentrations varied with respect to bypass site. Other risk factors played a part in accelerating the atherogenic process, especially smoking in patients undergoing femoropopliteal artery bypass grafting and, to a lesser degree, obesity in patients undergoing coronary artery bypass grafting.