Schizophrenia has been revealed to be a mental illness with alterations in a multi-transmitter system, because classical neurotransmitters are altered. Thus, due to the absence of presynaptic inhibition, dopamine and serotonin hyperactivity has been reported, this being related to acute psychosis. Also genetic techniques have shown hypoactivities of both γ-aminobutyric acid and glutamate. Recent investigations in schizophrenic patients have also indicated changes in the level of neuropeptides such as neurotensin, cholecystokinin, substance P, neuropeptide Y, galanin and methionine-enkephalin. This review focuses on the alterations observed in the level of neuropeptides in schizophrenic patients and the effect of altered neuropeptide concentrations on illness symptoms. Moreover, it addresses the role of neuropeptides in schizophrenic patients treated with neuroleptics. Finally, we discuss whether agonists or antagonists of neuropeptides might be useful in the treatment of schizophrenia, and the neuronal circuits containing the classical neuro-transmitters or neuropeptides involved in schizophrenia are suggested.