Viruses are thought to play a role in the occurrence of IgA nephropathy. In fact, cytomegalovirus (CMV) antigens have been detected in the glomerular mesangium. To clarify this relationship, we used in situ hybridization with biotin-labeled DNA probes of CMV and adenovirus (AV) in 40 patients with IgA nephropathy to determine the presence or absence of virus in affected renal tissue. Renal tissue DNA from these patients did not hybridize with the CMV or AV probes. Our results fail to support the theory that consecutive regional renal infections with CMV and/or AV are involved in the pathogenesis of IgA nephropathy.