Methods: Each 20 of non-O and type O ASA 1 or 2 patients scheduled for spinal surgery involving 2 or 3 spinal levels were enrolled. 20 ml/kg of saline-based HES (130/0.4) or balanced HES (670/0.75) was administered during operation. Blood loss, coagulation and metabolic profiles were checked at pre-infusion (T0), 5 min after infusion (T1), 4 hrs after infusion (T2) and 24 hrs after infusion (T4).