Arterial tissues from carotid artery plaques or from punch-biopsy samples of uninvolved areas of the aorta were removed from 132 patients with atherosclerosis during blood-vessel surgery. Cells morphologically identical to smooth muscle cells were cultured from 26 to 126 plaque samples and from 6 of 6 punch-biopsy samples. Immunofluorescence tests of these cells showed that more than 25% of the cell cultures from both types of sample contained antigens of human cytomegalovirus (CMV) but not of herpes simplex virus type 1 or type 2. Replicating CMV was not detected by electron microscopy in the antigen-positive cells, suggesting that the artery walls may be a site of CMV latency.