OBJECTIVE The purpose of the present study was to examine the keratitis detected in these mice after the xenogeneic thymus gland transplantation. METHODS The thymus glands were collected from F 344 rat embryos and transplanted under the renal capsules of BALB/c nude mice (rat TG nude mice). Histological and immunohistological examinations and a transfer experiment of keratitis was also conducted. RESULTS The histological image was characterized by the infiltration of mononuclear cells and neutrophils and the marked angiogenesis. The autoantibodies reacting specifically to corneal epithelial cells and corneal stroma were recognized in the blood. The deposits of immunoglobulins and complements were simultaneously observed in the corneal stroma and around the basement membrane. Corneal lesions of rat TG nude mice were therefore successfully transferred into naive nude mice by host splenic CD 4 positive cells. CONCLUSIONS The present study demonstrated that autoimmunity was involved in the development of keratitis in rat TG nude mice and that these mice were the first animal models to develop autoimmune keratitis spontaneously.