Nonhemolytic transfusion reactions, especially urticaria and anaphylactoid reaction, are believed to be due to plasma protein antigen in the blood products. We have investigated the frequency of transfusion reactions in 59 administrated patients who were interviewed after transfusion. 79(21.5%) of 367 transfusions were associated with transfusion reactions. Transfusion reactions were urticaria (41%), itching (34%) and fever (17%), and no hemolytic transfusion reaction, transfusion-associated graft-versus-host disease or anaphylactoid reaction was observed. We investigated the relationship between the nonhemolytic transfusion reactions and anti-C2,-C4, -albumin and -fibrinogen antibodies. The significant relationship between anti-C2 and -C4 antibodies, but not anti-albumin and -fibrinogen antibodies, were observed with transfusion reactions, especially with urticaria and itching.