Of four groups of chickens, two (groups I and II) were infected with MDV and two were not (groups III and IV). Groups I and III were fed diets low in lipid, and groups II and IV were fed cholesterol-supplemented diets. Striking grossly visible atherosclerotic lesions were seen in large coronary arteries, aortas, and major aortic branches of infected normocholesterolemic and hypercholesterolemic chickens (groups I and II). In contrast, grossly visible atherosclerotic lesions were not seen in uninfected normocholesterolemic chickens (group III), nor in uninfected hypercholesterolemic chickens (group IV). Microscopically, arterial changes in the infected animals were characterized by occlusive fibromuscular intimal thickening which formed fibrous caps overlying areas of atheromatous change. This change closely resembled chronic atherosclerosis in man. These results may have important bearing on our understanding of the etiology and pathogenesis of human arteriosclerosis since there is widespread and persistent infection of human populations with up to five different herpes-viruses.