157 caucasian male patients undergoing vascular surgery for atherosclerosis and a matched control group of patients with high cholesterol levels were screened for antibodies to cytomegalovirus (CMV) and herpes simplex virus type 1 (HSV1) and type 2 (HSV2), indicative of persistent infection. The prevalence of CMV antibodies was higher in the surgical group than in the control group (90% and 74%, respectively), and a significantly greater percentage (p less than 0.001) of surgical cases than controls had high titres of CMV antibodies (57% and 26%, respectively). Small but not significant differences in antibodies to HSV1 were observed, and there were no differences in HSV2 antibody titres. For each virus there was no correlation between antibody titre and blood levels of total cholesterol or triglycerides. It is suggested that periodically activated virus may have a role in the pathogenesis of atherosclerosis.