To clarify the physiologic roles of granulocyte colony stimulating factor (G-CSF) in increasing granulocyte after extracorporeal circulation (ECC). The serum levels of G-CSF, C3a, granulocyte elastase and granulocyte count were examined in 26 patients undergone open heart surgery. These patients were divided into two groups, the long perfusion group (11 patients) and the short perfusion group (15 patients). Granulocyte increased immediately after ECC and reached maximum 48 hours after ECC in both groups. C3a showed significant increase at the end of ECC and decreased rapidly after ECC in both group. G-CSF showed high levels 3 and 6 hours after ECC in the short perfusion group and moderate increase prolonged until 48 hours after ECC in the long perfusion group. Granulocyte elastase showed high levels 6 hours after ECC and decreased to the normal value 48 hours after ECC in the short perfusion group, and high levels prolonging until 48 hours after ECC in the long perfusion group. Increase of granulocyte count might be affected with increase of compliment (C3a) and G-CSF at the early and late phase after ECC, respectively. Granulocyte elastase increased differently by the duration of perfusion time.