Excessive memory decline or dementia affects an increasing number of women as they become older. The frequency of dementia doubles every 5 years beginning at age 60, making the discovery of ways to prevent or slow the disease imperative. Previous studies have indicated that changes in memory may be associated with the female hormonal decline that occurs after menopause, but more research is needed to establish the link between menopause and poorer memory function. It is believed that taking the female hormones estrogen and/or progesterone may help improve women's health by protecting against memory decline. This study will evaluate the effects of female hormone replacement therapy (HRT) on the development and progression of memory loss in older women enrolled in the Women's Health Initiative (WHI) study.