It is known that progressive supranuclear palsy (PSP) shows subcortical dementia. The diagnosis of PSP is sometimes difficult because this disorder mimics the clinical features of parkinsonian syndrome. Several PET studies demonstrated frontal hypo-metabolism in PSP patients. We studied the cerebral blood flow (CBF) pattern by single-photon-emission-computed tomography (SPECT) using 123I-isopropyl-iodoamphetamine (IMP) in 5 patients of PSP including one autopsy case. Five PSP patients were 3 men and 2 women, mean age of 67.6 years old. Control groups were 3 normal controls (Normal), 7 patients of Parkinson's disease (PD), 5 patients of olive-pontocerebellar atrophy (OPCA), and 4 patients of dementia of Alzheimer's type (DAT). CBF was measured by 123I-IMP SPECT using 400 AC/T Starcam (GE). CBF was measured by semi-quantitative methods. Regions of Interest (ROI's) were located at cerebellar, basal ganglion, and lateral ventricle levels. Each count of ROI was divided by the count of occipital ROI. In all PSP patients, the ratio of relative blood flow to occipital lobe in the frontal and fronto-temporal regions were most markedly affected, showing average reduction rates of 66.6% and 65.5%. These rates showed statistically significant differences to other control degenerative neurological diseases. Our these results correspond to the former PET studies. Moreover, frontal hypoperfusion progressed with advancing clinical stage. The results indicate that CBF study with SPECT is useful to confirm the diagnosis of PSP. It is necessary to clarify the role of the damage in basal ganglia for frontal hypometabolic pattern.