Ten patients with a diagnosis of acute middle cerebral artery stroke were evaluated using perfusion magnetic resonance imaging (MRI) during bolus injection of gadolinium diethylenetriaminepentaacetic acid (GdDTPA), MR angiography, and conventional MRI. Scans were performed within 24 hours of symptoms, onset, and 5 of the 10 patients had follow-up MR scans 3 or more days later to determine radiological outcome. Perfusion data were analyzed in terms of relative regional cerebral blood volume (rCBV) and bolus peak arrival times (BAT). Although relative rCBV values overall showed no significant changes compared with contralateral regions of interest, BAT was significantly increased in both infarct and peri-infarct regions. Areas of abnormal BAT significantly exceeded areas of T(2) hyperintensity in acute studies; follow-up images indicated that the size of infarction increased to include some regions with previously abnormal BAT. BAT appears to be a more sensitive parameter for the detection of abnormal cerebral perfusion than rCBV. Used in conjunction with other MR methods, perfusion MR imaging may allow visualization of ischemic tissue at risk of infarction in acute stroke.