Strains (338) of herpes simplex virus (HSV) were isolated in Stockholm during 1965-1974. By immunoelectroosmophoresis it was possible to identify all strains as either HSV type 1 (HSV-1) or 2 (HSV-2). No strains of intermediate antigenic type or with untypable characteristics were found. The antigenic type of HSV was correlated with body site and clinical features of infection. A case of severe, recurrent, abdominal pain in association with HSV-2 infection is described. In one patient with acute aseptic meningitis, both coxsackievirus A9 and HSV-2 were isolated from the same specimen of cerebrospinal fluid. Serology suggested a primary infection with coxsackievirus A9 and a recurrent HSV-2 infection. HSV-1 was isolated from specimens of cerebrospinal fluid. Serology suggested a primary infection with coxsackievirus A9 and a recurrent HSV-2 infection. HSV-1 was isolated from specimens of cerebrospinal fluid from two of four adults with HSV encephalitis.