✓ The development of ischemic edema and blood-brain barrier (BBB) disruption during the 1st day of experimental cerebral infarction induced by transorbital occlusion of the middle cerebral artery (MCA) in cats was evaluated by computerized tomography (CT) scanning and compared to gravimetric and pathological studies. Regional cerebral blood flow was measured using the hydrogen clearance technique or stable xenonenhanced CT scanning. Edema was observed gravimetrically and microscopically as early as 1 hour after the onset of ischemia in the cortex and at 3 hours or later in both the cortex and white matter. However, a significant decrease of Hounsfield numbers on the CT scans was not detectable at 1 or 3 hours and was scarcely visible at 9 hours after occlusion. Disruption of the BBB was detected by leakage of Evans blue dye at 3 hours after the occlusion in two of six animals and at 9 hours in five of five animals. However, CT scanning after infusion of contrast material showed no significant increase in Hounsfield number even 24 hours after MCA occlusion. These discrepancies should be emphasized when the dynamics of ischemic edema and BBB disruption are evaluated for clinical therapy by CT scanning.