[en] Single photon emission computed tomography (SPECT) with Xe-133 inhalation method was undertaken in 13 patients with mild or moderate senile dementia of Alzheimer's type (SDAT), 9 patients with multiple infarct demantia (MID), and 7 normal controls. Mean blood flow of the hemisphere was significantly decreased in both SDAT and MID groups than the control group. The decreased blood flow was correlated with the severity of SDAT, but not with MID. Regional cerebral blood flow (rCBF) of the SDAT group was significantly decreased in moderate cases than the control group, especially in the bilateral perietal areas, although this did not differ in the mild SDAT cases and the control cases. For MID, rCBF was significantly decreased in the bilateral frontal, basal nucleus, and left lateral areas. The findings led to the conclusion that SPECT is useful in the differential diagnosis of dementia and elucidation of the pathogenesis. (Namekawa, K.)