Purpose of study is (1) to determine if 12 months of estrogen replacement therapy improves cognitive and affective function in hysterectomized females with Alzheimer's disease compared to placebo; (2) to determine if there is a differential response to high and low dose estrogen; (3) to evaluate physiological mechanisms by which estrogen may have an effect in these patients; and (4) to establish the safety and tolerability of estrogen replacement therapy in elderly female Alzheimer's disease patients. The study is a double-blind, placebo-controlled pilot study of two doses of estrogen (Premarin .625 mg/day and 1.25 mg/day) versus placebo in hysterectomized women with Alzheimer's disease over the age of 60. This multi-centered study plans to enroll 120 subjects from 26 sites. Outcome measures include clinical global impressions, neuropsychological measures, mood and affect measures, functional abilities, quality of life and health and economic indicators.