Positron emission tomographic (PET) studies of regional cerebral glucose metabolism were performed in patients with various types of dementia, patients with Parkinson's disease but without dementia, and healthy normal controls. Patients with Alzheimer-type dementia showed significant decreases in glucose metabolism in frontal, temporal, parietal, sensory-motor and striatal regions. Patients with Pick's disease revealed decreased glucose metabolism in frontal and temporal regions. Parkinsonian patients with dementia had significant reductions of glucose metabolism in frontal, temporal, parietal, occipital, sensory-motor and striatal regions. Patients with Huntington's disease revealed decreased glucose metabolism in frontal, parietal and striatal regions. Patients with Creutzfeldt-Jakob's disease showed marked decreases in glucose metabolism throughout all brain regions. On the other hand, patients with Parkinson's disease but without dementia exhibited no reductions of cerebral glucose metabolism. Cerebral glucose hypometabolism in these various types of dementia might reflect neuronal dysfunction and cell death.