The presence and titres of specific serum IgG and IgM antibodies to cytomegalovirus, herpes simplex virus and varicella-zoster virus were evaluated in 50 haemodialysis patients by complement fixation, immunofluorescence and Elisa tests. A second serum sample was tested in 24 patients after four weeks. Specific serum IgG antibodies to Epstein-Barr virus were also measured by immunofluorescence in 26 patients. By immunofluorescence and Elisa tests, the prevalence of cytomegalovirus, herpes simplex virus and Epstein-Barr virus infection is approximately 100 per cent, and varicella-zoster virus 60 per cent. High titres of IgG specific antibodies found by Elisa tests, detection of IgM antibodies in 16-18 per cent of patients and sero-conversion in 25 per cent of patients, suggests continuous antigenic stimulation.