There is good evidence that physiological arousal, associated with sustained activation of the hypothalamic-pituitary axis and the sympathetic nervous system, is an underlying cause of chronic insomnia. Accordingly, relaxation and meditation treatments that address elevated cognitive and somatic arousal have been effective for insomnia. Yoga is a multicomponent discipline including physical exercises, postures, breathing and meditation that is known to be an effective relaxation technique. Previous studies have documented the effectiveness of yoga in reducing activation of the hypothalamic-pituitary axis and the sympathetic nervous system and in the treatment of specific medical disorders including insomnia. The aim of this proposal is to evaluate the hypothesis that improvements in chronic psychophysiological insomnia following a yoga treatment are tightly associated with reduction of arousal in the hypothalamic-pituitary axis, as measured by plasma cortisol, and in the sympathetic nervous system, as measured by urinary catecholamines. Objective measures of sleep will be derived from polysomnographic recordings from subjects randomized into a 10-week yoga treatment or sleep hygiene control treatment group. Continuous 24-hour evaluation of cortisol and catecholamines will be performed under controlled laboratory conditions before and after treatment. We anticipate significant reductions in cortisol and catecholamines in the yoga treatment group as compared with the control group. We also anticipate that yoga will yield reductions in related measures of arousal including heart rate, autonomic arousal (as determined from heart rate variability), and body temperature. Given reported evidence that melatonin levels are chronically low in insomnia, and that meditation/yoga may enhance melatonin secretion, we anticipate an increase in the sleep-related hormone melatonin in the yoga treatment group. If achieved, these results will provide a novel demonstration of a reduction of arousal in a behavioral insomnia treatment and a behaviorally enhanced melatonin secretion under controlled laboratory conditions.