Cerebral perfusion monitoring is an important component of hyperacute stroke treatment. Arterial spin labeling (ASL) perfusion magnetic resonance (MR) imaging provides a noninvasive method of cerebral perfusion observation. Rapid changes in cerebral perfusion were demonstrated in two patients admitted one hour after onset of hyperacute stroke who underwent recombinant tissue plasminogen activator (rt-PA) treatment. Serial MR images and ASL images were taken on admission and after rt-PA administration. Cerebral blood flow (CBF) values were obtained using the CBF workstation and analysis software. Interpretable ASL images were taken in both patients. Perfusion deficits were consistent with symptoms and/or MR angiography imaging abnormalities. Delayed arterial transit effect was present in one patient; serial imaging showed improvement of CBF after rt-PA treatment in both patients. ASL perfusion MR imaging can provide rapid noninvasive multislice imaging in hyperacute ischemic stroke, and can depict early perfusion deficit and quantify regional CBF concomitantly.