In Alzheimer disease (AD), dysfunction in several neuronal systems is associated with alterations in neurotransmitter receptors. Although receptors are important components of normal neural circuitry, their role in the pathophysiology of AD is only beginning to be clarified. For example, despite the consistent loss of presynaptic cholinergic markers in cortex in AD, the pattern of changes in cortical muscarinic cholinergic receptors is unclear, although the density of nicotinic receptors appears to be reduced. In AD, reductions in serotonin, glutamate, and somatostatin receptors also occur in cortex, and an increase in corticotropin-releasing factor (CRF) receptors has been reported. Studies of neurotransmitter receptor alterations in AD are contributing to the characterization of the biology of this disorder and could result in the development of better diagnostic tests and therapeutic agents.