The author succeeded in producing vestibular ganglionitis by inoculating herpes simplex virus type 1 (HSV-1) into the back of the auricle of a new-born mouse. Postural deviation to the inoculated side was observed in 14 of 275 mice (5.1%) 6 to 10 days after the inoculation. In 6 of the 14 mice (42.9%) with postural deviation, HSV antigens were demonstrated immunohistochemically in the vestibular ganglion cells of the inoculated side. No antigens were identified in the animals with normal posture or in controls. Vestibular functions were evaluated in 5 animals suffering from postural deviation by the following test procedures. 1. behavior in an open field, 2. righting reflex, 3. transversing a narrow path, 4. ascending a rope, 5. negative geotaxis, 6. grasping a rod, 7. swimming. None could perform these tasks due to impairment of vestibular function. Histopathological and immunohistochemical examinations showed degeneration of the vestibular ganglion cells in 4 of the 5 mice, while HSV-1 antigens were recognized in 2 of them. The results of the present study show that inoculation of HSV into the back of the auricle of a new-born mouse can cause infection of the vestibular ganglion resulting in symptoms similar to those of vestibular neuritis, though the incidence is low compared to that of facial paralysis.