The prevalence of herpes simplex virus (HSV) antibodies has been investigated in 123 child psychiatric patients and 86 normal children. HSV antibodies were measured by ELISA technique. The prevalence of HSV antibodies in different diagnostic groups (conduct disorder, emotional disorder, hyperkinetic syndrome, anorexia nervosa, infantile autism and borderline schizophrenia in childhood) was compared with age-matched normal children, but no significant differences were found.