Serum antibody titres to herpes-simplex (HSV-1, 2), cytomegalovirus (CMV), and Epstein–Barr virus capsid antigen (EBV-VCA) were determined in 38 unrelated chronic schizophrenic patients, 11 nuclear families with at least 2 schizophrenic members, and 2 control groups. The distributions of antibody titres to herpes simplex and cytomegalovirus were similar among all groups. Patients had higher anti-EBV-VCA titres than non-hospitalized controls; however, hospital staff members in contact with the patients also had significantly higher antibody titres to EBV-VCA. Antibodies to EBV early antigen (EBV-EA) were also determined for 27 unrelated patients and 24 mental hospital employees. The schizophrenic patients had significantly higher antibody titres to EBV-EA than the hospital worker control group. These data do not support the hypothesis that herpes viruses are associated with the aetiology of schizophrenia. Although elevated anti-EBV early antigen titres may suggest persistent active EBV infection, it is unlikely to be related to the aetiology of the disorder, since discordance for EBV seropositivity was present among sibling pairs concordant for schizophrenia.