Diseases of the memory, including dementia and Alzheimer's disease, are a primary health concern of the aging population. In just the last 30 years, the number of Americans diagnosed with memory diseases has doubled. The beginning signs and symptoms of Alzheimer's and dementia include mild forgetfulness, confusion, and disorientation with time and place. As the diseases advance, people often experience difficulty in carrying out normal activities, recognizing family and friends, and eventually speaking and comprehending. Early identification and treatment for dementia and Alzheimer's may help prevent and slow the progression of symptoms, but the most beneficial means of treatment is still unknown. Previous studies have suggested a link between menopause and reduced memory function in women, possibly attributed to the dramatic decline in the levels of the female hormones estrogen and progesterone. HRT in postmenopausal women may help to curb memory loss and reduce risk of developing memory-related diseases. This study will evaluate the effects of female HRT on the development and progression of memory loss in older women enrolled in the WHI study.