Around the world, stroke is the second most common cause of death and a major cause of disability. The main direct cause of stroke is the occlusion of intracranial artery, which leads to cell death in the core suffered region, or cell functional impairment surrounding the dead core (termed ischemic penumbra). Opening the occluded artery to save the ischemic penumbra is the aim of thrombolysis therapy. But the reperfusion induced injury counteracts the potential profit by thrombolysis. Herein, we assume that gradual reperfusion can reduce the reperfusion injury by reducing the production of free radicals during reperfusion. The reason is: free radicals are critical in the reperfusion injury; free radicals come from the penumbra during reperfusion; the respiratory chain is the main source of free radical; the enzyme activity of the respiratory chain is upgraded during ischemia; once reperfused, the activity upgraded enzymes in the respiratory chain meet normal amount of oxygen and glucose, which produces exceeding intermediates (free radicals); while gradual reperfusion reduces the production of free radicals, because it can confine the amount of oxygen and glucose. (c) 2012 Elsevier Ltd. All rights reserved.