The Normative Aging Study is a comprehensive interdisciplinary longitudinal study located in the VA Outpatient Clinic in Boston, Mass. The study was inaugurated in 1963 by the VA because of its statutory responsibility for the medical care of 25 million war veterans of whom 2 million are now 65 years of age and over, a figure which will rise to over 7 million in the next 20 years. Approximately 2,000 male veterans are enrolled for their lifetime as research subjects and undergo recurrent examinations administered on an outpatient basis. The focus of the study is on non-pathological aging, so that the subjects were carefully screened in advance to satisfy rigid health criteria regardless of age. The study is distinctive because of its large N and the socioeconomic diversity of its population. Parameters include clinical medicine, biochemistry, special senses, oral medicine, anthropometry and behavior. The study is designed to investigate the relationship between normal aging and the natural history of chronic diseases. The investigation of environmental correlates of age change throughout the logitudinal design will also suggest the intrinsic or extrinsic nature of the aging process. The hybrid cross-sectional-longitudinal design will also enable the partialing of secular from true aging effects. Functional ages pertaining to various aspects of aging are being developed as a tool for assessing relative aging rates and the relationship among such differences in aging.