Estrogen (EST) may have significant benefits in preserving cognitive functioning in normal aging after menopause and in decreasing the incidence of Alzheimer's disease (AD). On a molecular level, EST has effects on a variety of cholinergic neuronal and receptor-mediated mechanisms that may be responsible for these beneficial effects. These neurons have critical relevance for the development of age-related cognitive changes and dementing disorders. However, little is known about the clinical relevance of EST-cholinergic interactions, either in normal aging or in AD.