The pharmacological actions of gamma-type endorphins show similarities to those of the neuroleptics. Two fragments of gamma-endorphin (beta-LPH 61-77) were therefore tested in patients with schizophrenic and schizo-affective psychoses who had shown an insufficient response to neuroleptics. The fragments were DT gamma E (beta-LPH 62-77) and DE gamma E (beta-LPH 66-77). Some of the patients studied responded favorably to this treatment. A number of criteria of differentiation between responders and nonresponders are discussed. The influence of DT gamma E on the central DA metabolism differs from that of the neuroleptics. It is therefore conceivable that gamma-type endorphins represent a different principle of action. The therapeutic efficacy of these compounds lends support to the hypothesis that disorders of central endorphin metabolism may play a role in the pathogenesis of psychoses of the schizophrenic type.