Three lines of evidence suggest that the novel neurotransmitter Nitric Oxide (NO) play a central role in pathophysiology of schizophrenia. First, schizophrenia-like syndromes can be induced in humans by phencyclidine (PCP), a drug with marked psychomimetic properties. Recent studies indicate that the behavioral and biochemical effects of PCP in rats are blocked by Nitric Oxid synthase (NOS) inhibitors, suggesting that NO plays an important role in the pharmacological effects of PCP. Second, Postmortem brain tissue obtained at autopsy from schizophrenia and control demonstrate increased in NOS in the cerebellum and brainstem of schizophrenic patients. Third, NO play a role in learning and memory, which severly impaired in schizophrenia.