The vestibular ganglia of rats having no clinical symptoms after inoculation of HSV-I were examined by Polymerase Chain Reaction (PCR) in order to prove latent HSV-I infection. The rats were divided into two groups: one inoculated with HSV-I into the middle ear cavity (m.i. group), and the other into the peritoneal space (i.p. group). In the m.i. group, 67% of the vestibular ganglia on the inoculated side and 0% on the opposite side were positive. In the i.p. group, 60% of the vestibular ganglia on both sides were positive. These data indicate that HSV-I can establish latent infection in the vestibular ganglia. Furthermore, we assumed that reactivation of HSV-I genomes in the vestibular ganglia might lead to disorders of the vestibular system.