A 24-hour rhythm in serum dopamine-β-hydroxylase (DBH) activity in chronic schizophrenic patients showed a similar change as that in normal subjects: the highest activity during day time with a peak at 12.00 h and the lowest activity at night with a bottom at 24.00 h, 4 h after sleep onset. Between a group of schizophrenic patients who have sleep disturbance and another group of patients who have normal sleep patterns, no significant difference was observed in the 24-hour rhythm in serum DBH activity. Very low but significant DBH activity was found in cerebrospinal fluid of neuropsychiatric patients, and the values were approximately 1/1,000 of the serum activity. A case after cerebral injury showed a high DBH activity in cerebrospinal fluid.