The disruption of multiple neurotransmitter systems in Alzheimer's disease plays an important role in the pathophysiology of cognitive and behavioral disturbances associated with the illness. The central cholinergic system is significantly disrupted in a fashion that correlates with cognitive impairment. This article describes drugs, such as scopolamine, that selectively affect the cholinergic system and model aspects of Alzheimer's disease phenomenology in both animals and humans. Drugs that induce cognitive changes but whose chemical mechanisms are not well understood are presented as alternative pharmacologic models of Alzheimer's disease.