Although the occurrence of disruptive agitation behaviors likely are influenced by environmental/ interpersonal factors, it is also likely that behaviorally relevant neurobiologic abnormalities lower the threshold for the expression of such behavior in Alzheimer's disease. Because of the success prazosin has had in the treatment of Posttraumatic Stress Disorder, it is thought that it could be used similarly with disruptive agitation. Originally designed to evaluate Alzheimer's disease patients in nursing homes, the study now includes outpatients. It is a 9-week placebo-controlled trial.