The sleep of elderly people is characterized by frequent awakenings and almost total disappearance of deep sleep. As a group, the elderly are high utilizers of sleep medications which can have serious adverse effects. The overall goal of this project is to develop melatonin administration as a safe means of improving sleep in the elderly. The project will meet four specific aims: 1.Describe melatonin pharmacokinetics in the elderly as compared to young adults. 2.Test the effect of high-dose melatonin administration on the sleep of healthy old people. 3.Test the effect of low-dose, sustained release melatonin administration on the sleep of healthy old people. 4.Determine the effects of melatonin administration on the overnight core body temperature curve in healthy old people. These aims will be met by three experiments conducted over the five year period of the grant. The first experiment will compare melatonin pharmacokinetics in twelve old and twelve young research subjects. The second experiment will be a placebo-controlled, two period cross-over study of high-dose melatonin's effects on the sleep of eighteen very healthy elderly persons participating in the Oregon Brain Aging Study. The third experiment will also be a placebo-controlled, two period cross-over study of sleep in eighteen people participating in the Oregon Brain Aging Study, but low-dose, sustained release melatonin will be used. this will assess the strategy of "physiologic replacement" of declining melatonin levels to restore youthful sleep in old people.