Herpes simplex viruses were isolated from 40.8 to 56.0 per cent of the patients with genital herpes. The frequency of recovery seemed to be higher in females than in males, particularly during the first episode of infection. Asymptomatic shedding of the virus from female genitalias was approximately 0.7 per cent. Herpes simplex virus type 2 represented 98.4 per cent of all isolates and the remaining isolates were type 1. These isolates exhibited a wide range of sensitiveness to 9-(2-hydroxyethoxymethyl) guanine (acyclovir) as demonstrated by antiviral inhibition assay and no single strain exhibited high in vitro drug ID50 value.