The use of the method of fluorescent antibodies and cytotoxic tests showed that the blood serum of schizophrenic patients and normals possess an antithymocytic activity. However, the level of this activity in patients exceeds the corresponding indices in normals (p less than 0.02). The use of indirect immunofluorescent methods permitted to demonstrate that the antithymic antibody titres in schizophrenic patients is much higher than in normals. The amount of the cytotoxic index is in direct correlation with the level of antithymic antibodies determined by the fluorescent antibody method.