Melatonin supplements have been reported to be an effective treatment for circadian rhythm sleep disorders, including shift work dyssomnia, jet-lag, delayed sleep phase syndrome, and sleep disruption suffered by many blind individuals. However, the mechanism(s) by which melatonin affects the timing of sleep are not well-understood. The purpose of this study is to determine if melatonin improves sleep and performance on a schedule simulating eastward travel. This study will provide information regarding the mechanism of action of melatonin that will be critical for the use of melatonin as a treatment for circadian rhythm sleep disorders.