When measured within 2 days of a unilateral occlusion of the middle cerebral artery (MCA) combined with tandem occlusion of the ipsilateral common carotid artery in rats, contralateral neurological deficits were detectable, with brain swelling and a consistent degree of neocortical infarction in the ipsilateral hemisphere. Oxypurinol (40 mg/kg i.p. administered 0.5 h prior to, and 24 h after, the onset of focal ischemia) significantly reduced the development of the ischemic infarct (P less than 0.001); attenuated tissue swelling (P less than 0.01) and ameliorated the neurological deficits (P less than 0.05). These findings suggest that this compound may be useful for the prevention or treatment of ischemic brain injuries, such as those occurring during stroke.