Outcome measures: Results from medical and neurological evaluation, neuropsychological testing, laboratory tests, and brain MRI will be used to determine if patients meet NINDS criteria for probable Alzheimer s disease. In patients who undergo brain imaging with [18F]FDG and PIB PET, PET data will be used for investigational purposes in subjects who participate in other protocols with the Molecular Imaging Branch. Results from brain imaging from healthy volunteers will be used to compare to that from AD patients. [18F]FDG and PIB PET may also be useful for determining if patients meet criteria for probable Alzheimer s disease.