Regional cerebral perfusion was evaluated in 15 normal controls by single photon emission comput- ed tomography using ""Tc HM-PAO. For quantitative analysis, 13 pairs of hornologous region of interest (ROI) were drawn on three transverse slices matching the vascular territories and cerebral cortices, and normal values of '3 semiqunatitative indices including Right to left ratio (R/L ratio), 'Regional index' (RI), and 'Region to cerebellum ratio (R/cbll ratio) were calculated. Mean values of R/L ratios of homologous regions were ranged frorn 0.985 to 1.023, and mean +- 2 s.d. of ali regions did not exceed 11% of mean. Significant difference of Rls (mean count per voxel of a ROJ/mean count per voxel of total ROls) between regions were found (p<0.001) with highest values in occipital cortex and cerebellum. After attenuation correction, Rls in deep gray, cranial portion of anterior cerebral artery and vascular territories in the 2nd siice increased significantly (p< 0.05 0.001). hut vise versa in other ROIs. Reginn to cerebellum ratios also showed regional difference siinifar to Rls.