SummaryData reported in this brief communication suggest that, despite pronounced manic behavior, morning urinary excretion levels of 17‐OHCS was reduced. 24‐hour urinary 17‐OHCS value was subsequently lowered in six manic patients studied. Amplitude of the diurnal fall in the urinary 17‐OHCS excretion levels was also slightly reduced but not significantly. These factors did not result in an absolute loss of the circadian curve of urinary 17‐OHCS excretion. The possible role of sleep disturbances in mania in forming an abnormal circadian pattern of pituitary adrenal function is