 This study will compare the bioavailabity of three new investigational combination formulations of Premarin and medroxyprogesterone acetate MPA with a currently marketed formulation of Premarin and MPA, PremproTM. PremproTM 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 PremarinMPA provide the same levels of estrogen and MPA in the blood as Prempro in healthy postmenopausal women. 