Context: Both light and melatonin can be used to phase shift the human circadian clock, but the phase advancing effect of the combination has not been extensively investigated.

Objective: To determine if phase advances induced by morning intermittent bright light and a gradually advancing sleep schedule could be increased with afternoon melatonin.

Participants: Healthy adults (25 m, 19 f, between 19 and 45 y).

Design: There were 3 days of a gradually advancing sleep/dark period (waketime 1 h earlier each morning), bright light upon awakening (four 30 min bright light pulses (5000 lux) alternating with 30 min room light < 60 lux) and afternoon melatonin, either 0.5 or 3.0 mg melatonin timed to induce maximal phase advances, or matching placebo. The dim light melatonin onset (DLMO) was measured before and after the treatment to determine the phase advance.

Results: There were significantly larger phase advances with 0.5 mg (2.5 h, n = 16) and 3.0 mg melatonin (2.6 h, n = 13) compared with placebo (1.7 h, n = 15), but there was no difference between the two melatonin doses. Subjects did not experience jet-lag-type symptoms during the 3 day treatment

Conclusion: Afternoon melatonin, morning intermittent bright light and a gradually advancing sleep schedule advanced circadian rhythms almost an hour a day and thus produced very little circadian misalignment. This treatment could be used in any situation in which people need to phase advance their circadian clock, such as before eastward jet travel or for delayed sleep phase syndrome.