A randomized, double-blind, placebo-controlled trial of ebselen was conducted in patients with complete occlusion of the middle cerebral artery. Ebselen or placebo granules suspended in water (150 mg b.i.d. ) were orally administered within 12 h of onset and continued for 2 weeks. The major end points were the maximum volume of cerebral infarct measured on follow-up computed tomography and the Glasgow Outcome Scale score at 1 month. One hundred and five patients were enrolled in this trial. Although the intent-to-treat analysis of 99 patients (43 given ebselen and 56 given placebo) did not reach statistical significance in reduction of the infarct volume (p = 0. 099), the protocol-compatible analysis of 83 patients with complete occlusion of the middle cerebral artery (34 given ebselen and 49 given placebo) determined a significant reduction using ebselen treatment (p = 0.034). A good outcome was seen in approximately 15% more patients from the ebselen group, but the difference between the 2 groups was not significant (p = 0.129). There was a corresponding significant reduction in the volume of cerebral infarct and an improvement in the outcome of patients who started treatment within 6 h of onset. These findings may suggest that ebselen protected the brain from ischemic damage in the acute stage.