The influence of reperfusion after complete global brain ischemia (CGBI) on blood brain barrier (BBB) permeability to evans blue dye (EB) was studied in dogs. The various durations of CGBI, from 10 to 18 minutes, were produced by clamping the ascending aorta with the aorta to the right atrium and the aorta to the femoral vein bypass circuit. Dogs were divided into four groups according to the duration of CGBI : dogs in group A, B, C, and D(n=6, in each group) suffered 10, 12, 15, and 18 minutes of CGBI, respectively. EB was injected 15 minutes after the reperfusion, and extravasation of EB in the cerebral cortex. thalamus, hippocampus, cerebellum and the brain stem were observed 30 minutes after the reperfusion. In this study, cerebral blood flow (CBF) and intracranial pressure (ICP) were also measured for the first 20 minutes after the reperfusion. Extravasation of EB were observed in three dogs except for group A, and a tendency toward extravasation of EB in the cerebellum was recognized in group C and D. Reactive hyperemia and increase in ICP within 20 minutes after the reperfusion were also observed. In conclusion, not only ischemia but also the reactive hyperemia might increase BBB permeability.