Abnormalities of neurochemical systems in Alzheimer disease, which are potentially relevant to the pathophysiology of such noncognitive problems as agitation and depression, have been demonstrated. However, the role of these abnormalities in the etiology of noncognitive problem behaviors remains poorly understood. Such abnormalities in brain noradrenergic and serotonergic systems are of particular interest because of their apparent involvement in normal regulation of mood, arousal, and aggressive behavior. The nature of the noradrenergic abnormalities in Alzheimer disease is particularly complex, with evidence suggesting both structural damage and compensatory increased norepinephrine release from remaining noradrenergic neurons. Currently available drugs that alter brain noradrenergic or serotonergic activity should be evaluated for efficacy in the management of noncognitive behavioral disorders complicating Alzheimer disease.