Treatment for alleviating ischemia-reperfusion injury which has minimized risk of side effects and which can suppress neutrophilic infiltration and activation of platelets during ischemia reperfusion comprises administration by inhalation of a mixed gas comprising 21% - 98% oxygen, 0.1% - 4% hydrogen, 40 - 80 ppm nitrogen monoxide, and a remainder of inert gas such as nitrogen or helium to a patient undergoing reperfusion from immediately before the start of ischemia reperfusion until shortly after the start of reperfusion.
