The sera from 62 of 68 patients with coronary heart disease (CHD) caused a two to five fold elevation in the intracellular cholesterol in primary cultures of subendothelial cells derived from grossly normal intima of human aorta. The sera from 33 of 42 healthy subjects did not show atherogenic properties in culture. Atherogenic potential correlated directly with the serum apolipoprotein-B-apolipoprotein A1 ratio, but not with the level of total cholesterol, high-density-lipoprotein cholesterol, apo-B, or apo-A1. The sera from patients with CHD also facilitated deposition of lipids in the medial smooth muscle cells of human aorta and mononuclear blood cells, though to a lesser degree. They had no such effect on endothelial cells of human aorta and umbilical vein, or human embryo fibroblasts.