Previous studies have suggested that exposure to heavy metals may be a risk factor in coronary atherosclerotic heart disease in humans as well as in experimental animals. Little is known however on the mechanism underlying the effect of heavy metals on the development of atherosclerosis. In this study we tried to ascertain whether exposure to lead might: (a) alter plasma lipoprotein in normally fed rabbits; and (b) aggravate the hyperlipidemia usually found in cholesterol-fed animals. Rabbits were fed a normal diet or a diet containing 1% cholesterol in the presence or in the absence of 0.5% of lead subacetate for 45 days. This produced an accumulation of lead in plasma and bone. While in cholesterol-fed rabbits, lead exposure did not modify the plasma lipoprotein pattern, in normally fed animals it induced a striking elevation of cholesterol esters. This was associated with an increased concentration of VLDL (1.006 g/ml), LDL1 (1.006-1.020 g/ml), LDL2 (1.020-1.050 g/ml) and HDL1 (1.050-1.210 g/ml). These lipoproteins had an elevated content of cholesterol esters and apolipoprotein B. It is suggested that some of these lipoproteins may be important in the development of atherosclerosis in subjects chronically exposed to lead.