Exciting recent data from our laboratory show that bright light stimulates secretion of luteinizing hormone (LH, lutropin), the pituitary hormone which regulates testosterone, estrogen production and ovulation. The basic science significance of the finding may be that photoperiodic mechanisms are active in humans. One hour of bright light stimulation per day from 0500-0600 produced a 69.5 percent increase in urinary luteinizing hormone (LH) excretion in young men. It is possible to replicate and extend these findings in conjunction with ongoing studies. The investigators are currently testing bright light effects in three protocols: A) a study of circadian phase response curves in adults ages 18-30 and 60-75, B) a clinical trial of bright light for depressed patients 60-79, and C) a study of early-night versus early-morning light stimulation in patients with premenstrual dysphoric disorder and normal controls. For this project, 8792 urine samples already being collected for these three protocols will be assayed for LH, using radioimmunoassay. In each study, 24-hour urinary LH excretion will be measured both before and after bright light treatment. Results will be analyzed to determine the optimal times of day for light stimulation of LH, to compare the responsiveness of young men and menstruating women versus older men and menopausal women, and to consider the relationship of LH response to baseline depression ratings and to remission of depressive symptoms. Bright light effects on LH may ultimately be useful for augmenting testosterone in men and for stimulating ovulation in women, for regulating puberty, menarche and menopause, and for reducing endocrine risk factors for mood disorders, heart disease, and cancer.