The etiology of rheumatic arthritis (RA) is associated with a number of genetic and environmental factors, but is not definitively elucidated. Recently, more attention has been paid to the possibility of microbial etiology in the pathogenesis of RA, because many different infectious agents have been reported to precede the onset or exacerbation of RA. Adenovirus (ADV) may be one cause of persistent or recurrent inflammatory arthritis. Varicella zoster virus (VZV) arthritis is detected frequently in RA patients treated with low dose methotrexate. The demonstration of simultaneous presence of both viral agents of specific viral nucleic acid in synovial fluids from synovitis patients would provide more direct evidence for arthritis etiological relationship, but there are no confirmed results. Therefore, we studied the ability of adenovirus and VZV to establish coinfection and persistent infection in synovial fluid from synovitis patients. The presence of viral agents in the synovial fluid demonstrated by isolation of cell culture, enzyme immunoassay and nested-PCR. The synovial fluids were also investgated for the presence of viral nucleic acid by nested-PCR using specific primer. ADV produced 220 bp and VZV produced 447 bp by each nested-PCR with specific primers. We detected 4/6 cases (66.7%) with persistent infection of ADV and 5/6 cases (83.3%) of VZV with 13 synovial fluids (between 7 to 52 day intervals) from synovitis patients by monoclonal ErA and nested-PCR. 21/28 cases (75%) with coinfection of adenovirus and VZV with synovial fluids from synovitis patients by nested-PCR. ADV and VZV coinfection and persistent infection of synovial fluids may provide a chronic antigenic stimuli to the immune system therefore provoking a continuing inflammatory response and caused the possibility of synovitis and arthritis.