The use of lower extremity tourniquets for procedures of the lower leg is considered routine in orthopedic surgery, yet, lower extremity tourniquets are not benign. While the tourniquet is inflated, metabolic changes such as increased PaCO2, lactic acid, and serum potassium and decreased level of PaO2. and pH occur in the ischemic limb. Deflation of tourniquet results in release of anaerobic metabolic products during ischemia into systemic circulation. In this ischemia/reperfusion situation, oxygen free radicals could potentially be produced during the reperfusion period by several mechanisms. One of these mechanisms is release of intracellular superoxide or hydrogen peroxide by activated neutrophils in the area. These reactive oxygen species(ROS) could be a causative factor for the postreperfusion no-flow, lung injury, induction of tourniquet shock, etc, The purpose of this clinical study was to investigate the effect of tourniquet deflation on the hemodynamic changes, changes of blood gas analysis, and hydrogen peroxide production using flow cytometric analysis of fluorescent DCF(Dichlorofluorescein). Quantitative Analysis of fluorescent DCF was performed in resting and fMLP(N-formyl-methyonyl-leucyl-phenylalanine) or PMA(phorbol myristate acetate) stimuliated neutrophils. The results were as follows: 1)The hemodynamic changes (systolic and diastolic BP, pulse rate) did not show any significant difference before and after tourniquet release(P>0.05). 2)Arterial pH deceased significantly until 10min and PaC was increased significantly until Smin after toumiquet release(P<0.05). 3) Arterial PO2, bicarbonate, base excess showed no significant change before and after tour- niquet release(P>0.05). 4) Hydrogen peroxide production which was estimated by fluorescent DCF in neutrophils did not show any significant change before and after tourniquet release(P>0.05). These results indicate that tourniquet application(400mmHg, less than 2hours) could not release significant hydrogen peroxide during reperfusion period after tourniquet release.