In 23 acute, unmedicated, schizophrenic patients, psychotic behaviour and beta-endorphin serum level were measured before and during four weeks of neuroleptic therapy. Prior to drug treatment, beta-endorphin level of all patients was within the normal range. Neuroleptic therapy induced marked elevations of beta-endorphin in eight subjects; statistical analysis revealed a slight but significant increase for the whole group. This endocrine effect was not correlated with therapeutic efficacy of neuroleptic treatment.