The authors measured total opioid activity by radioreceptor assay in the CSF of 41 normal subjects and 89 unmedicated psychiatric patients, including schizophrenic, schizoaffective, depressed, and manic diagnostic groups. Schizophrenic men had significantly lower levels of opioid activity than the normal men, although these levels did not significantly differ from levels of other male patients. The authors observed higher opioid activity during mania than during depression in paired samples for 4 manic-depressive patients. beta-Endorphin immunoreactivity in a subsample of the same subjects was no different in the patient group than in the normal group, suggesting that the differences in CSF opioid activity between schizophrenic men and normal patients may be related to opioids other than beta-endorphin.