Chronic insomnia affects up to 30% of the elderly and significantly impairs quality of life and daytime functioning. It is often secondary to other medical conditions, such as pain from osteoarthritis. Recent work has suggested that melatonin, a neurohormone produced by the pineal gland and regulated by the suprachiasmatic nucleus, the primary circadian pacemaker, is decreased in elderly insomniacs. However, treatment trials in primary insomniacs have been equivocal. This has raised many questions regarding the function of melatonin such as its role in sleep-wake regulation and whether it has nocturnal sleep-promoting effects. Interestingly, pain and non-steroidal anti-inflammatory drugs blunt melatonin rhythms. Thus, I believe that melatonin secretion is impaired in the elderly with chronic pain and that this contributes to their insomnia. To address the hypothesis, the applicant proposes the following aims: 1) A case-control study to test the hypothesis that melatonin deficiency is a risk factor for insomnia in the elderly with osteoarthritis pain and identify a threshold level to distinguish melatonin deficient patients; 2) A randomized, double-blind, placebo controlled trial of melatonin replacement therapy in elderly insomniacs with osteoarthritis pain to test the hypothesis that melatonin deficiency is a causal factor for their development of insomnia. Analysis will include univariable and multivariable models, and receiver operator curve analysis for Aim 1, and comparison of melatonin vs. placebo treatment arms on l objective parameters for Aim 2. This protocol may provide new insights into the neurohormonal risk factors for the development of insomnia, test the model that melatonin deficiency is a causal factor for insomnia, provide a mechanistic basis for targeted melatonin replacement therapy, and provide the training necessary to conduct rigorous, independently-funded, patient-oriented research.