Epstein-Barr virus (EBV) is often associated with non-Hodgkin's T-cell lymphomas and has recently been found in the lesions of mycosis fungoides and Sézary syndrome. We sought to determine whether the anti-EBV antibody profile was disturbed in mycosis fungoides and Sézary syndrome and whether there are particular profiles characteristic of disease stage. Anti-EBV antibodies (anti-VCA, -EA and -EBNA) were studied in the sera of 64 patients. An immunoenzymatic technique was used, and the results were compared with the same number of age- and sex-matched healthy controls. Patients with mycosis fungoides and Sézary syndrome developed higher anti-VCA antibody titres (median 1200) than controls (median 320). Thirty-seven patients had anti-VCA > or = 1200 vs. 19 controls (P < 0.01). These elevated anti-VCA antibody titres were associated with positive EA in 19 patients versus three controls. No differences were found between the illness stages. Anti-EBV antibodies were most often found in mycosis fungoides and Sézary syndrome when the serological profile was similar to that of cellular immune deficiencies and EBV-related non-Hodgkin's lymphoma. EBV could be involved, either directly on lymphocytes or, more likely, indirectly by chronic antigenic stimulation.