To reveal the presence of atherogenic potential in the blood serum obtained from patients with angiographically assessed coronary atherosclerosis we used primary cultures of subendothelial cells isolated by collagenase from unaffected human aortic intima. Earlier, we have demonstrated that such cultures are made up mostly of typical and modified smooth muscle cells. Within 24 hours of cultivation with a 40% sera of patients suffering from coronary atherosclerosis, the total intracellular cholesterol level increased twofold to fivefold. Cultivation with the sera of healthy subjects had no effect on the intracellular cholesterol level. The sera of patients were separated by ultracentrifugation into two fractions: total lipoprotein fraction containing the main classes of lipoproteins and a lipoprotein-deficient fraction. The former, but not the lipoprotein-deficient fraction, was characterized by atherogenicity (i.e., the ability to induce the accumulation of intracellular cholesterol). Lipoproteins of the patients' serum were separated into main classes: low density lipoproteins (LDL), very low density lipoproteins (VLDL), and high density lipoproteins (HDL2 and HDL3). An atherogenic component of the serum capable of stimulating the deposition of intracellular cholesterol was represented by LDL and, in one case, by VLDL, but not by other classes of lipoproteins. LDL and other lipoproteins isolated from the blood serum of healthy subjects failed to raise the cholesterol content in cultured cells; that is, they were nonatherogenic.(ABSTRACT TRUNCATED AT 250 WORDS)