Using the indirect immunofluorescence test (IFT), the authors examined the sera of 16 patients with Mooren's ulcer for the presence of antibodies against normal rabbit and human corneal epithelial cells, and determined the percentages of T-lymphocyte subsets in the peripheral blood of the patients and controls. The results indicate that (1) serum antibodies against rabbit corneal epithelial cells were positive in 75% of the patients, serum antibodies against human corneal epithelial cells were positive in 37.5%, whereas in 20 normal controls the above serum antibody against both were negative; (2) the percentage of OKT8+ in patients was significantly lower and the OKT4+/OKT8+ ratio significantly higher than those in the controls (P < 0.01). The etiopathogenesis of Mooren's ulcer is discussed and the authors especially point out that regulatory imbalances exist in the patient's immune systems and Mooren's ulcer is an autoimmunological eye disease.