Stroke is the third most common cause of death in Western countries and the most important cause of adult disability (1). In spite of massive efforts to reduce the risk of death or disability and to improve outcome in stroke patients, there is still no effective drug treatment (1-5). In the West, most strokes (-85%) result from cerebral infarction after arterial occlusion. Besides the core of dead neurons in the vascular territory of the occlusion, the adjacent tissue—the so-called penumbra—may survive or die depending on early reoxygenation after stroke and the establishment of appropriate treatment. Current treatments include thrombolytic agents, anticoagulants, antithrombotic drugs, and vasodilators, the main function of which is to improve tissue reperfusion. Although early reperfusion is required to maintain tissue viability, it may in fact cause further damage by triggering a cascade of events where free radicals appear to play a major role (6,7). Thus, recent therapeutic strategies have included neuroprotective agents (glutamate antagonists, calcium antagonists, and free radical scavengers) to minimize reperfusion injury. Free radicals have been implicated in a wide variety of neurological disorders and brain dysfunctions (8-11). A considerable body of evidence mainly generated from studies using animal models of brain ischemia/reperfusion indicates that reperfusion injury is associated with the formation of reactive oxygen species (ROS) and that free radical scavengers may have neuroprotective effects. In these studies, several criteria for the establishment of the pathophysiologic significance of free radical mediated processes have been met. These include (a) the demonstration of post-ischemic levels of oxygen radicals and lipid peroxidation products, (b) the spatial and temporal correlation between oxygen radical formation and functional alterations, (c) the similarity between damage produced by ischemia/reperfusion and that caused by chemical generation of ROS, and (d) the protective effect of antioxidants.