We investigated the occurrence of an active cytomegalovirus (CMV) infection in patients with polyarteritis nodosa (PAN). Eleven patients with PAN were screened for the presence of CMV-DNA in their blood using the polymerase chain reaction (PCR). Serum anti-CMV IgG and anti-CMV IgM antibodies were determined by enzyme-linked immunosorbent assays (ELISA). The ELISA for IgM was negative in all cases whereas that for IgG was positive in eight cases. Only one patient was positive for CMV-DNA by PCR. He presented with myalgia, polyarthralgia, fever and weight loss, suggesting PAN activity. CMV infection was uncommon in our series of patients with PAN, despite disease activity and immunosuppressor therapy. The finding of a transient CMV infection in one case at the beginning of PAN activity suggests that CMV may be involved in the pathogenesis of PAN.