Herpes viruses, such as cytomegalovirus (CMV) and Epstein-Barr virus (EBV), very often occur in the nasopharynx. A pathogenetic role of these viruses in immunoglobulin A nephropathy (IgA NP) is a challenging hypothesis, since upper respiratory tract infections are frequently and closely related in time to the acute episodes of IgA NP. However, conflicting reports have been published in this field. We compared the IgA and IgG antibody (AB) titres against cytomegalovirus (CMV) in sera of 41 IgANP patients with 80 healthy controls. The prevalence rates of CMV-IgA and CMV-IgG AB were significantly higher in patients with IgA NP than in healthy controls (CMV-IgA, titre > = 8, p < 0.001; CMV-IgG, titre > = 16, p < 0.05). There was also a significant difference in the concentration of CMV-IgA AB between IgANP patients and controls (IgA NP: 0.34 +/- 0.66, healthy controls: 0.06 +/- 0.33, mean +/- SD, p = < 0.002), but not in the concentration of CMV-IgG AB between NP patients and controls. While examining 60 patients with IgA NP and 75 healthy controls a significantly elevated prevalence rate of IgA AB against EBV capsid antigen (EBV-VCA) was also detected in the sera of IgA NP patients vs controls (titre > = 16; p < 0.05). There was no significant difference in the prevalence of IgG AB to EBV-VCA between patients with IgA NP and healthy controls, except at titre = 1024 (p < 0.05). At a follow-up, CMV-IgA persisted in 4 of 5, and EBV-VCA-IgA in 8 of 12 seropositive patients with IgA NP. We could not detect virus antigens or virus deoxyribonucleic acid (DNA) in the glomeruli of NP patients either with immunohistology using a monoclonal antibody or with the DNA in situ hybridization technique.(ABSTRACT TRUNCATED AT 250 WORDS)