In this study we assessed regional cerebral blood flow in patients with signs and symptoms of acute stroke using single-photon emission computed tomography (SPECT) and N-isopropyl 1-123 p-iodoam- phetamine (IMP). Twenty-five patients with acute cerebral infarction had both IMP brain perfusion studies and CT scans performed within one week of each other; 22 had positive and three had negative perfusion studies. Of the 22 patients who had positive perfusion studies, six had negative CT studies initially. In the 16 patients who had abnormal CT studies, eight of the studies depicted areas of edema that were smaller than the perfusion deficits noted on the IMP studies and eight had areas of edema that were approximately equal in size to the perfusion defect. Of the three patients with normal IMP studies, two had normal CT studies and one had a positive CT study showing a 3-ram lacunar infarction. Using eight control patients, mean count rates per tissue volume normalized for the injected dose was calculated. Similarly, the quantitative data from regions of interest in the stroke patients were calculated and compared to the control patients or to a normal region in the uninvolved hemisphere in the same patients. SPECT with IMP was used to assess regional brain perfusion in acute cerebral infarction. Perfusion abnormalities were seen in our patients when the CT scan was normal, and quantitative data could be used to approximate regional cerebral blood flow in these patients when compared to the normal patient population. Stroke Vol 15, No I, 1984