Focal cerebral ischemia initiates a series of event from the regional development of ischemic edema, loss of neural function and culminating in eventual infarction. The purpose of this study is to determine the effect of recirculation in acute focal cerebral ischemia. Sixty adult mongrel cats of either sex underwent production of focal ischemia by transorbital occlusion of the left middle cerebral artery with a Heifetz clip. The duration of ischemia was 1, 3 and 5 hours. In 5 animals in each group, the ischemic brain was reperfused for 1, 4 and 7 hours by removing the clip from the artery. It was observed that provided the restoration of cerebral blood flow in cats can be accomplished within 1 hour in cats or at least within 3 hours of the insult, the reversal of the neurological deficits and prevention of irreversible cerebral infarction can be expected. Therefore the prevention of cerebral infarction must first be directed toward improving blood flow during the insult as rapidly as possible to-minimize the time that cerebral blood flow is below threshold for the formation edema.