The purpose of this project is to define the morphological changes occurring in the vestibular sense organs and nerves following transtympanic labyrinthectomy. Emphasis will be placed on evaluating the magnitude and consistency of degenerative change occurring in the vesitbular nerves as a function of time following labyrinthectomy. The principal question is whether vestibular nerve section has any advantage, in terms of completeness of morphological ablation, over transtympanic labyrinthectomy. The clinical significance lies in the fact that vestibular nerve section, which requires invasion of the subarachnoid space, subjects the patient to greater risks of surgical complications than transtympanic labyrinthectomy. Twenty cats have been subjected to unilateral labyrinthectomy. The temporal bones are being prepared for histological study as the animals are sacrificed at predetermined survival times. IDEN*