Studies indicate that women with PMS experience improvement in symptoms following treatment with leuprolide acetate, when estrogen and progesterone levels are low. Women with PMS, but not women without the disorder, experience a return of symptoms within approximately a week after re-exposure to either estrogen or progesterone. The cause of this hormone-induced depression remains unclear. It is not known whether this depressed mood is due simply to the change in the levels of estrogen and progesterone and whether it would remit following continued exposure to stable levels of estrogen and progesterone. This study will determine whether the maintenance of stable hormone levels will prevent mood disturbances in women with PMS.