Autoimmune reactivity against corneal antigens is described in two patients with Cogan's syndrome, a nonsyphilitic deep interstitial keratitis with vestibuloauditory symptoms. In both cases corneal antibodies were found at the beginning or during an exacerbation of the disease. After administration of high doses of corticosteroids the corneal antibodies diminished. Interstitial keratitis can generally be controlled by local or systemic corticosteroids. The effect of corticosteroid therapy on the audiovestibular symptoms is variable. The possibility of an autoimmune pathogenesis of Cogan's syndrome is discussed.