Thirty-one strains of herpesvirus (HSV), isolated from patients presenting with the clinical features of herpes genitalis, were typed by polypeptide analysis of virus proteins in sodium dodecyl sulphate polyacrylamide gels. Nineteen (61.3%) of the isolates were shown to be HSV type 1 and 12 (38.7%) HSV type 2. There was no obvious difference in the incidence of HSV-1 in primary or recurrent infections and no apparent correlation between the genital site of isolation and virus type. The high incidence of genital HSV-1 infection in this group of patients is probably due to the increased practice of oro-genital contact and has possible implications for the future development of drugs and vaccines in the control of genital herpes.