Many patients with schizophrenia and schizoaffective disorder have symptoms that persist, including hallucinations or delusions, despite adequate pharmacotherapy with antipsychotic drug. Glutamate is a major excitatory neurotransmitter in the brain that has been implicated in several brain diseases. NMDA antagonist drugs cause symptoms of psychosis in otherwise normal persons. It is postulated that reduced NMDA receptor mediated neurotransmission leads to an increase in synaptic glutamate. Excessive synaptic concentrations of glutamate can produce excitatory neurotoxicity. Agents which reduce excess glutamate activity are neuroprotective. This therapeutic strategy has been applied to schizophrenia through the use of compounds that reduce presynaptic release of glutamate or otherwise decrease excessive postsynaptic stimulation, including lamotrigine, memantine and a m-GLU-R2 agonist (LY354740) with the hypothesized result of a reduction in psychotic symptoms.