Reperfusion after a transient ischemia is a frequently encountered clinical condition that often causes greater tissue damage than persistent ischemia itself. Reperfusion to rabbit brain, after a transient focal ischemia, induced neutrophil infiltration and aggregation--neither of which were observed in rabbit brain rendered ischemic alone for the same time interval--thereby leading to severe brain edema and infarct. Brain tissue levels of interleukin-8 (IL-8), a potent neutrophil chemotactic cytokine (chemokine), increased significantly at 6 hours after reperfusion, but without a noticeable elevation of plasma IL-8 levels. Moreover, we detected IL-8 protein immunohistologically in the vascular wall and, to a lesser degree, in infiltrated neutrophils, suggesting a local production of IL-8 in reperfused brain tissues. Furthermore, a neutralizing anti-IL-8 antibody significantly reduced brain edema and infarct size in comparison to rabbits receiving a control antibody. These results implicate locally produced IL-8 as a pivotal mediator of cerebral reperfusion and suggest that IL-8 is a novel target for the intervention of this injury.