Summary:One hundred fourteen patients suffering from neuropsychiatric conditions have been studied using 99ffiTc-Iabeled hexamethylpropyleneamine oxime (HM PAO) and single photon emission computed tomography (SPECT). Ninety-one patients had a firm clinical diagno sis while 23 were examined without knowledge of the clinical diagnosis. Of the 91 patients, 51 were suffering from dementia, 25 multi-infarct type and 26 Alzheimer's disease. In 19 of the Alzheimer's patients, a characteristic pattern of decreased perfusion in the parieto-occipital re gions was demonstrated while those with multi-infarct type showed varying degrees of irregular uptake in the cerebral cortex. These appearances are similar to those shown with positron emission tomography (PET) and we believe that HM-PAO will provide a widely available method for identifying patients with Alzheimer's disease. Twenty-nine patients were suffering from diseases in-