The major contribution of Positron Emission Tomography (PET) has been to bring into the clinical arena many aspects of neurophysiology and pharmacology that were previously considered to be solely the domain of basic laboratory research. The applications of PET have forced the clinician to consider regional brain physiology not as an abstract concept but as a quantifiable reality. This achievement symbolizes the transition of the traditional view of neurological diseases as distortions of structure, to one of physiological or functional alterations from normality. This transition is particularly important for an understanding of the mechanisms by which diseases of the brain cause dementia. This volume explores current data, obtained with PET, on patients with demands of the Alzheimer type (DAT) and related neurological disorders. The influences on measurements of brain atrophy and the activation state are examined in detail, as are specific aspects of the PET procedure.