We examined the association between 6-sulphatoxymelatonin (6-SMT) excretion and sleep in 68 volunteers 60-79 years of age who complained of insomnia or depression. An Actillume wrist monitor was worn for 5-7 consecutive days and nights in home-living conditions. Activity was used to estimate total sleep time (TST) and wake after sleep onset (WASO). Throughout two 24 hr periods, urine was collected approximately every 2 hr during the day and after any voidings during the sleep period. During the next week, subjects spent 5 nights and 4 days in the laboratory. Sleep was measured and scored with standard polysomnographic techniques. Urine was collected, as for home recording, on days 1 and 4. Urinary concentrations of 6-SMT were assayed. Cosine-fitting of urine data across both days at home and both laboratory collections established the mesors and amplitudes of 24 hr 6-SMT excretion rhythms, but neither was significantly correlated with sleep. Mean and peak 6-SMT excretion during the sleep period was also determined. Significant correlations were found between mean 6-SMT during the laboratory sleep period and TST and WASO. However, these associations were not independent of circadian timing: sleep was better when sleep occurred near the circadian acrophase of 6-SMT excretion. These data indicate that low melatonin production may not be an important factor in insomnia among the elderly.