Studies investigating the efficacy of the opiate antagonists naloxone and naltrexone in the treatment of schzophrenia are reviewed. Naloxone tended to ameliorate psychotic symptoms of noncatatonic schizophrenic patients when a dose of at least 4 mg was administered, although some of the high-dose studies produced conflicting results. Possible factors relating to the nonresponder issue are discussed, including concomitant neuroleptic medication, interindividual dose sensitivity, and subject selection criteria and target symptoms. Recommendations are made for more intensive study of single cases and experimental designs aimed at delineating the interactions between naloxone and neuroleptics, and assessing the need for stringent subject selection criteria. Naloxone also enhanced movement in stuporous and catatonic schizophrenics. Naltrexone, on the other hand, had more negative than positive effects on schizophrenic patients, possibly because of opiate agonist properties.