This study was designed to investigate the effect of preoperative collection of blaod and acute normovolemic hemodilution(ANH) on the requirement of homologous transfusion, perioperative blood loss and hematological parameters in patients undergoing open heart surgery. Ninety two adult patients for elective open heart surgery were randomly assigned to one of three groups. Group I, ANH group, had blood withdrawn to a hematocrit of 33%o after induction of anesthesia(n =54). In Group II preoperative collection of blood in accordance with hospital protocol and ANH were performed(n=16). Ciroup III was control group(n=22). Autologous blood was replaced post bypass. The patients whose hematocrit fell below 25% were transfused with homologous blood. The use of homologous transfusion was 2.2+/-0.4 units in group I, 0.1+/-0.1 units in group II and 4.1+/-0.8 units in group III. Requirement of homologous transfusion in group II was reduced compared with group II and III with statistical significance(P<0.05). There was statistical significance between group I and group III(P<0.05) in homologous transfusion. Postoperative blood loss was 760.7+/-74.6 ml in group I, 675.6+101.5 ml in group II and 819.3+/-91.3 rnl in group III. There was no statistical significance among 3 groups. There was no difference in hematocrit or platelet count, and total blood loss on immediately post surgery or on day 1. Our data show that preoperative collection of blood and ANH can reduce the amount of homologous transfusion.