The human menstrual cycle is a monthly (circatrigantan) biological rhythm in which some of the component hormonal processes have circadian (about 24 h) and ultradian (less than 24 h) rhythms. Much of the previous work on the menstrual cycle focused on measuring a single type of variable, such as hormones, temperature, sleep, performance or mood. Furthermore, once daily sampling of these variables has often been the mode of investigation. However, several studies indicate that gonadal steroids modulate the amplitude and phase of circadian and ultradian hormonal rhythms. A study is currently ongoing to examine the circadian rhythms of a number of hormones, temperature, and mood and performance in 12 normally cycling female subjects across the menstrual cycle. The research planned in this proposal will examine the circadian rhythms of the same hormones, temperature, mood and performance in 12 healthy women who suffer from premenstrual syndrome (PMS), a disorder which effects sleep patterns. The control group for this study will be 12 healthy women without PMS who will be studied by the same method funded in a separate grant. In order to control for the known evoked effects of activity and sleep on the parameters listed above, a protocol that eliminates or "unmasks" the influence of these factors will be used to examine the phase and amplitude changes that are expected to occur at various times in the cycle. Prior to each unmasking session, the same variables will be recorded during subjects' normal sleep-wake cycle and their sleep will be recorded during the night. These studies will extend the sparse existing knowledge regarding the interaction of the human menstrual cycle in women with PMS with circadian and ultradian hormone and temperature rhythms, and help clarify the neglected area of the interaction of the menstrual cycle and sleep.