Socially stressed adult male cynomolgus monkeys (Macaca fascicularis) fed a low fat, low cholesterol diet developed more extensive coronary artery atherosclerosis than unstressed controls. Groups did not differ in serum lipids, blood pressure, serum glucose, or ponderosity. These results suggest that psychosocial factors may influence atherogenesis in the absence of elevated serum lipids. Psychosocial factors thus may help explain the presence of coronary artery disease (occasionally severe) in people with low or normal serum lipids and normal values for the other "traditional" risk factors.