Background: Three kinds of conditions should be considered to reduce free hemoglobin production using an autologous cell salvage device. They are the negative suction pressure, the size of suction tip, and the air contact during suction. We want to examine which condition is the most important factor to produce free hemoglobin. Methods: One pack of red blood cell and one pack of fresh frozen plasma with the same blood type were mixed. They were aspirated based on the two suction pressure (-150 mmHg or -300 mmHg), three sizes of suction tips, and the two conditions of air contact, in which the suction tip was located in the surface of blood or in the middle of the blood. Seven ml sized EDTA tube was used to collect 5 ml blood. All the procedure repeated ten times. Free hemoglobin, total hemoglobin, and hematocrit were measured. Hemolysis ratio was calculated with following formula. Hemolysis ratio = (new free hemoglobin production) × (100-hematocrit) / (total hemoglobin). Results: Free hemoglobin production and hemolysis ratio were increased when the suction tip was positioned in the surface than when it was in the middle of the blood. The pressure of negative suction and three kinds of the suction tips did not influence the production of free hemoglobin nor the hemolysis ratio. Conclusions: The air contact is the most important factor to reduce hemolysis using autologous cell salvage device. Suction pressure or suction tip diameter have little influence to produce hemolysis. (Korean J Anesthesiol 2011; 60: 266-271)