On the red blood cell membrane in a patient with autoimmune hemolytic anemia (AIHA) several glycophorin class blood group antigens were assumed to be acquired in relation to the disease. When the red blood cells were treated with Dispase, all of the acquired antigens were released to the supernatant in company with the native glycophorin class antigens and disappeared on the red blood cell membrane. Then a trial was made to analyze the supernatant of the red blood cell suspension with Dispase and the serum which contained the red cell autoantibody by capillary isotachophoresis. In each of the isotachopherogram, a specific peak which was not detected in the sample from normal human was found in the acidic zone. The protein substances expressed by these peaks will be available as a marker to diagnose AIHA because they are thought to be formed in association with AIHA.