We studied clinical significance of99mTc-ECD SPECT study in dementia and aphasia, and compared it with99mTc-HMPAO SPECT study. The subjects consisted of 13 patients, including 10 patients with dementia and 3 patients with aphasia. Hypoperfusion areas were detected in 5 out of 10 patients with dementia and 2 out of 3 patients with aphasia in99mTc-ECD SPECT, and in 4 out of 10 patients with dementia and all of 3 patients with aphasia in99mTc-HMPAO SPECT. The count rate ratios in99mTc-ECD and99mTc-HMPAO SPECT were correlated well with each other, and the contrast of the99mTc-ECD SPECT image was equivalent or slightly higher as compared with99mTc-HMPAO. Therefore, 99mTc-ECD SPECT study was considered to be useful for the evaluation of cerebral perfusion in dementia and aphasia.