The presence of cytomegalovirus (CMV) nucleic acids was demonstrated in arterial walls of patients with grade III and with maximally grade I atherosclerosis by dot blot and in situ DNA hybridization and by polymerase chain reaction (PCR) using probes and primers derived from immediate early (IE) and late (L) genomic regions. The presence of the complete viral genome could be demonstrated by both dot blot DNA hybridization and PCR. IE mRNA but not L mRNA could be demonstrated by in situ DNA hybridization, indicating the presence of latent CMV in the human arterial wall. By PCR 90% of the samples obtained from atherosclerotic patients were shown to contain viral nucleic acids as compared to 53% of patients with maximally grade I atherosclerosis, thus substantiating a role for this virus in the pathogenesis of atherosclerosis.