An epidemiologic follow-up of the first National Health and Nutrition Examination Survey (NHANES I), being conducted from 1982 to 1984, is expected to provide estimates of the risks of certain health conditions for a sample of the U.S. population and to make it possible to relate these conditions to the nutritional, social, demographic, and behavioral characteristics of the sample. As part of the followup study, the baseline data obtained in NHANES I have been reviewed to define hypotheses and to identify pertinent variables that can be used in studying changes over time and the relationships of these variables to outcome measures. Because the followup study provides cohort data on a large sample of the U.S. population, it presents a unique opportunity for epidemiologists.