This report summarizes advances in the understanding of Alzheimer's disease, the major cause of mental disability among older Americans. The demography of the disease is discussed, noting that approximately 2.5 million American adults are afflicted with the disease and that the large increase in the number of Alzheimer's disease patients is due to the growth in numbers of older people, a better approach to diagnosis, better training of health care professionals regarding the problems of old age, and the public's awareness of Alzheimer's disease. A cost estimate of $35 billion for the care of Alzheimer's disease patients is given. Research advances in diagnosis of Alzheimer's disease are reviewed, including advances using magnetic resonance imaging, and a test for a protein in the blood of victims. Biological mechanisms of the disease including differences in healthy and diseased brains and changes in brain chemistry are discussed. Theories about the cause of Alzheimer's disease are reviewed, including an examination of the role of aluminum, infectious agents, and genes as well as risk factors for the disease. Assessment and treatment approaches are summarized. The report concludes with future research directions. (ABL)