Sixty four cases of autoimmune hemolytic anemia (AIHA) referred to our laboratory from 1985 to 1993 consisted of 51 warm type AIHA, 9 cold agglutinin disease (CAD), one paroxysmal cold hemoglobinuria, and 3 mixed type AIHA. There were 5 patients who had all clinical features of AIHA except for a positive direct-antiglobulin test (DAT). These patients were diagnosed as DAT-negative AIHA because of the elevation of red blood cell-associated IgG (RBC-IgG). The mean RBC-IgG of 100 healthy individuals was 33 +/- 13 (SD) molecules per one RBC. On the other hand, the RBC-IgG of patients with DAT-positive and with DAT-negative warm type AIHA were ranged from 257 to 12,421 and from 126 to 256 molecules per one RBC, respectively. One of 9 patients with CAD had a hemolytic anemia associated with only a cold agglutinin titer of 32 using saline-suspended RBCs, but a titer of 4,096 in the presence of bovine albumin. This case was diagnosed as low titer CAD. All of patients with DAT-negative AIHA or low titer CAD showed a good response to corticosteroid treatment.