Prempro is indicated for use after menopause in women with a uterus to reduce moderate to severe hot flashes; to treat moderate to severe dryness, itching, and burning, in and around the vagina; and to help reduce your chances of getting osteoporosis (thin weak bones). The purpose of this study is to determine if these new formulations of Premarin and MPA provide the same levels of estrogen and MPA in the blood as Prempro in healthy postmenopausal women.