Regional cerebral blood flow (rCBF) was evaluated in 12 children ranging in age from 2.7 to 10.0 yr using 99mTc-HMPAO SPECT. For quantitative analysis, 13 pairs of homologous regions of interest (ROIs) were created on three attenuation-corrected 18,8 mm thick transverse slices matching the cerebral cortical regions, deep gray matter, cerebellar hemisphere, and vascular territories, and the semiquantitative indices including "right to left ratio [(mean countjvoxel of homologous right ROI) /(mean count/voxel of homologous left ROI) ] and regional index "(RI) [ (mean count/voxel of a ROI) /(rnean count/voxel of all ROIs of each hemisphere)] were calculated. Mean values of right to left ratios of homologous tegions ranged frorn 0.984 to 1.028 in children under 5 yr (group 1) and from 0.982 to 1.012 in children between 5 and 10 yr (group 2), and the mean value +-2 S.D. for each region did not exceed 11%. and 12% in group 1 and group 2, respective]y. There were no statis- tically significant differences between the RIs of the homologous right and left regions. Significant differences of RIs were found both between vascular regions (p<0,0005 for goup 1, and p=0,0001 for goup 2) and between regions of cerebral cortices (p<0,0005 for group 1, and p<0,005 for group 2) with a relatively high value in the occipital cortex and the Iower values in the r.erebellum and deep gray matter among the regions of cerebral cortices in both groups. There were no significant differences between the Rls of corresponding regions of group 1 and group 2, except a significantly higher value of right deep gray matter in group 2 than in group 1(p=0.0301). The RIs of the superior frontal cortex and deep gray matter showed to be positively correlated with age (superior frontal cortex; right: rs=0.5254, p =0.0814, left: rs=0.5919, p=0.0496/deep gray matter; right: rs=0.8246, p=0.0062, left: rs=0.6266, p=0,0377). The results suggest that the rCBF pattern of children approaches that of adults in an occipito-rostraJ direction. This time course of rCBF changes is in agreement with behavioral, neurophysiological, and anatomical alterations known to occur in the developing brain.