OBJECTIVES: To explore by a case-control study factors of possible etiologic significance to the occurrence of Alzheimer's disease. Variables relevant to viral, genetic and immunological hypotheses will be explored, and data on occupational and environmental exposures, drug use, psychological stress, smoking and alcohol consumption also will be collected. METHODS: A total of 100 cases of Alzheimer's disease will be identified from patients at the Veteran's Administration Medical Center and the University of Minnesota Medical Center, both in Minneapolis. For each case a hospital control matched for age, sex, race and admission date, and a neighborhood control, matched for age, sex and race, will be selected. For each subject as informant will be identified and interviewed with a structured questionnaire about variables and data mentioned above in "Objectives". Data from existing records will also be abstracted and analyzed.