HLA antibodies were studied in 88 patients with chronic hemolytic anemia who received multitransfusions of red blood cells prepared by conventional (PRC-C), inverted centrifugation (LR-I) and leukocyte filter (LR-F) techniques. Their mean age was 8 years and 4 months with a duration of transfusion of 8 years. The patients were divided into five groups: group 1, receiving PRC-C (n=20); group 2, receiving LR-I (n=33); group 3, receiving LR-F (n=11); group 4, subsequently receiving LR-I and LR-F (n=10); and group 5, receiving PRC-C followed by LR-I and LR-F (n=14). The HLA class I antibodies were found in 30 out of 88 patients (34%). All were against HLA antigens commonly found in the Thai population. The patients receiving PRC-C exhibited HLA antibodies of 65%, which was significantly higher than those of patients receiving LR-I (24%) and LR-F (0%). Consequently, the transfusion reactions of fever, chill, rash and urticaria were also commonly found in patients receiving PRC-C (13.4%), which was significantly higher than patients receiving LR-I (0.4%) and LR-F (0%). The leukocyte filter technique has been shown to be effective in preventing HLA alloimmunization and transfusion reactions but the price is rather high. For the inverted centrifugation technique, only transfusion reactions were effectively prevented and the HLA alloimmunization continued to develop. A more effective and low-cost method for the removal of leukocytes should be investigated for these multitransfusion patients.