Recent clinical observations support the hypothesis that persistent parvovirus B19 is a triggering factor of rheumatoid arthritis (RA) in certain genetically predisposed individuals. If this hypothesis is correct, a number of RA patients may exhibit parvovirus B19 DNA in their synovial membranes. We tested the synovial tissue and peripheral blood leukocytes of 20 patients with RA, 24 patients with other arthritides or osteoarthritis (non-RA), and 34 healthy blood donors for the presence of parvovirus B19 DNA using specific DNA amplification by polymerase chain reaction (PCR). Using this technique, parvovirus B19 DNA was demonstrated in the synovial biopsies of 75% of patients with RA but in those of only 16.7% of patients with non-RA. In autologous peripheral blood mononuclear cells the percentage of PCR-positive patients was about 15% in both RA and non-RA groups and did not differ from that in healthy controls. When the PCR data were correlated with the presence of anti-parvovirus B19 IgG antibodies in serum and synovia all patients with parvovirus B19 DNA in peripheral blood alone or in both peripheral blood and synovial membrane were seropositive. In contrast, about 40% of patients with parvovirus B19 DNA restricted to the synovial membrane were seronegative. These data indicate a highly disease-related persistence of parvovirus B19 in the rheumatoid synovium.