Twenty-one patients with cerebrovascular disease (5 with hemorrhage, 10 with infarction, 2 with TIA, 4 with motor disturbance of unknown cause) were studied using N-isopropyl-p-(123I)iodoamphetamine (123I-IMP) and single photon emission CT. In 3 of 5 cases with cerebral hemorrhage, perfusion defects were shown in and around the region of hematomas, furthermore, one of the cases with internal capsular hematoma, the perfusion defect extended to the cortical area corresponding to the neurological pathway. In one case with MCA infarction, the perfusion defect was greater and clearer than the low density area on X-ray computed tomography (CT). These results revealed the 123I-IMP study provides physiological information in contrast with X-ray CT which provides anatomical information. In 3 of 9 cases with multiple small deep hemispheric infarctions on X-ray CT, the perfusion to the basal ganglia was suspected to be decreased on 123I-IMP images. However, this visual findings was not definitive and, in fact, the diseased side was not always consistent with the clinical findings. For quantitative analysis, symmetrical regions of interest (ROIs) were constructed both basal ganglia and the ratio of average counts over the ROI to those over the whole slice was calculated. In the small infarction group, the mean +/- S.D. of the values was 0.89 +/- 0.09 in right and 0.89 +/- 0.08 in left. Although the values were not significantly different from those of normal subjects (0.99 +/- 0.02 in right, 0.97 +/- 0.03 in left), they distributed in the range less than normal in 5 of 9 cases. This method was thought to be useful and practical to evaluate the cerebral blood flow in basal ganglia of patients with deep hemispheric infarction.