- Patients hospitalized in the intensive care unit (ICU) tend to become agitated and confused, and many even develop temporary psychoses (the ICU syndrome). We wondered whether the regulation of sleep and the secretion of melatonin is abnormal in ICU patients. Therefore, we studied the association of sleep-wake pattern in patients hospitalized in the ICU, their melatonin secretion rates, and profile compared with a control group of patients in general medical wards. Sleep was assessed by actigraphy. Urine was collected every 3 hours for 24 hours. Melatonin secretion was assessed by measuring the melatonin metabolite 6-sulphatoxymelatonin by enzyme-linked immunosorbent assay. Actigraphy suggested that the ICU patients lacked normal sleep behavior for the entire study period, except for occasional short naps. Compared with controls, the nocturnal peak of melatonin secretion was absent, except in two patients in the nonventilated group, and showed a flat curve. Our results suggest that lack of sleep is indeed a severe problem in ICU patients and is accompanied by impairment of normal melatonin secretion. The possibility that melatonin administration may prove useful in improving sleep patterns in ICU patients deserves further study.