It is hypothesized that gonadal steroids modulate circadian rhythms and the sleep-wake cycle in humans, as they do in animals. This hypothesis will be tested by performing chronobiologic evaluations on women enrolled in protocol 92-M-0174 ("The central nervous system effects of pharmacologically induced hypogonadotropic hypogonadism with and without estrogen and progesterone") and on men enrolled in protocol 94-M-0037 (The central nervous system effects of pharmacologically induced hypogonadotropic hypogonadism with and without testosterone replacement"). Based on the animal literature, we hypothesize that melatonin and sleep onset will be phase-advanced in women on estrogen, compared with those on progesterone or in a hypogonadal state. We also hypothesize that the amplitude of the activity cycle will be decreased in the progesterone, as compared with the estrogen, condition. Based on findings in amenorrheic women and in those on oral contraceptives, we hypothesize that the amplitude of melatonin secretion will be increased in the hypogonadal state, compared with the other two conditions. Finally, based on literature cited below, we hypothesize that mean prolactin levels will be higher in the testosterone plus Lupron condition and in the estrogen plus Lupron condition than in the other hormonal conditions.