STUDY DESIGN: Prospective randomized clinical trial. OBJECTIVES: To determine the minimal effective pretreatment dosage of recombinant human erythropoietin for preoperative autologous donation in lumbar stenosis surgery. SUMMARY OF LITERATURE REVIEW: Preoperative autologous donation is one of the most widely used methods of autotransfusion. However securing predetermined amount may be difficult due to falling hematocrit with repeated donation especially in patients with low basal hematocrit. In this situation recombinant human erythropoietin(Epoetin alfa) may be used. MATERIALS AND METHODS: Forty five lumbar stenosis patients requiring posterior wide decompression and posterolateral fusion with instrumentation, who had basal hematocrit less than 40% were selected and alloted randomly into 3 groups. Group I(n=15) had pretreatment with Epoetin alfa 50 unit/kg. Group II(n=15) was pretreated with 25 unit/kg. Group III(n=15) had no pretreament. Patients were excluded from donation when their hematocrit values were less than 33%. RESULTS: The mean number of units collected per patient(mean+/-SD) was 3 for group I(P<0.05), 2.84 for group II and 2.67 for the control group. The red cell volumes in pretreated groups(347 ml, 325 ml) were greater than in group III(255 ml, P<0.05). The differences between hematocrits of the first and the third preoperative donations were significantly less in group I(1.50) and group II(1.51) than that of control group(3.73). Two patients in group II and 3 patients in group III required additional homologous transfusion postoperatively. And there were no significant differences in the pattern of postoperative changes of hemoglobin among the groups. There were no significant differences in amount of intraoperative saved blood, postoperative reinfused blood, and postoperative drainage. CONCLUSION: Fifty units/kg of Epoetin alfa seems to be more effective than twenty-five units/kg for preoperative autologous donation in patients requiring posterior wide decompression, posterolateral fusion with instrumentation.