Previous research has suggested a role for the pineal hormone melatonin in the control of the body's sleep-wake and thermoregulatory systems. In the elderly population, there have been reports of decreased nighttime secretion of melatonin and suggestions that this may, in turn, be responsible for the increased incidence of sleep disorders reported by this age group. On this basis, it has been suggested that augmented nocturnal melatonin levels may improve sleep quality in age-related sleep disorders. Following screening assessments, 12 elderly (> 55 years) subjects with sleep maintenance insomnia were treated with either 0.5 mg transbuccal melatonin or a placebo for two sessions of 4 consecutive nights, at least 3 days apart. Subjects self-selected lights-out times, and sleep was assessed using standard polysomnographic (PSG) measures. Body temperature was measured continually from 2100 to 0700 h, and sleep quality was assessed from PSG variables measured. Nightly urine samples were assayed for the melatonin metabolite 6-sulfatoxy-melatonin (aMT.6S). Compared to the placebo, transbuccal melatonin administration significantly increased mean nocturnal aMT.6S excretion (mean +/- SEM: 194.2 +/- 16.5 vs. 42.5 +/- 7.7 nmol). In addition, there was a significant reduction in core body temperature relative to the placebo condition (p < .05). However, sustained transbuccal melatonin treatment had no positive significant effect on any PSG measure of sleep quality. The results from the present study suggest that sustained nocturnal administration of melatonin, in the low pharmacological range, might be of limited clinical benefit in this subject population.