In the past 2 years powerful evidence has emerged to suggest that nitric oxide functions as a neurotransmitter in both the central and peripheral nervous systems. Recent evidence suggests that it may play a role in mediating forms of synaptic plasticity such as long-term potentiation in the CA1 region of the hippocampus, and long-term depression in the cerebellum. Abnormal secretion of nitric oxide may be responsible for the neurotoxicity mediated by NMDA receptors that results in the pathophysiology of strokes and neurodegenerative diseases.