With the indirect immuno fluorescence technique (IFT), the authors examined sera from 16 patients with Mooren's ulcer for the presence of antibodies against normal rabbit and human corneal epithelial cells, and determined the percentages of peripheral T-lymphocyte subsets in the patients and 20 controls. The results indicated that (1) antibodies against rabbit corneal epithelial cells were positive in 75% of the patients, and antibodies against human corneal epithelial cells were positive in 37.5%, whereas both antibodies were negative in the controls, and (2) the percentage of OKT8+ in patients was significantly lower, and the OKT4+/OKT8+ ratio significantly higher than in the controls. The authors concluded that regulatory imbalance existed in the immune system of the patients, and Mooren's ulcer was an autoimmunologic eye disease.