Studies of the myenteric (Auerbach) plexus of esophagus, stomach, small intestine, colon, and rectum, by microdissection and pointcount morphometry, for 18 patients with Alzheimer disease (AD), eight with other types of dementia of the elderly, non-demented elderly patients, and younger control patients, show a normal loss of enteric neurons and plexus mass with age, comparable to that reported by others for rats and guinea pigs. Values for patients with AD or other non-AD dementias did not differ from those for elderly controls. Enteric neurons in AD or the other dementias studied showed no definite stain with ALZ-50, a monoclonal antibody to a derivative of the microtubule-associated protein tau, which stains degenerating cerebral neurons in AD. Although the processes in the central nervous system in AD affect some neurons derived from the neural plate, the results of this study suggest that the enteric neurons, which are of neural crest origin, are not affected in AD. Enteric neurons, at least by the methods of this study, do not provide a useful peripheral marker for AD.