1. Despite intensive research, the cause of Alzheimer's disease is unknown. 2. Glutamate is the major excitatory transmitter of the cerebral cortex and hippocampus and it appears to have an important role in learning and memory. In addition to its transmitter function, glutamate is a neurotoxin which has been implicated in the pathogenesis of a variety of neurodegenerative disorders. 3. Glutamate toxicity may play a role in the pathogenesis of Alzheimer's disease. 4. Disruption of glutamatergic neurotransmission may account, in part, for the learning and memory deficits of Alzheimer's disease. 5. Labeling of the glutamate receptor complex may allow in vivo diagnosis by positron emission tomography. 6. Glutamate receptor ligands may provide a means of therapeutic intervention in Alzheimer's disease.