Coronary Artery Disease Risk Development in Young Adults (CARDIA) is a longitudinal study designed to trace the development of risk factors for coronary heart disease in 5100 individuals 18-30 years old. The study will compare, by cross-sectional and longitudinal analyses, trends and processes involved in risk factor development by sex, race, age, and other sociodemographic characteristics. Participants for the approximately 4 1/2-hour baseline examination were randomly selected and recruited by telephone from census tracts in Minneapolis and Chicago, by telephone exchanges within the Birmingham city limit, and from lists of the Kaiser-Permanente Health Plan membership in Oakland and Berkeley. A major issue was the desirability of sampling approximately equal numbers by age, race, sex, and education as compared with sampling numbers representative of the population base. The recruitment goal of 5100 was achieved on schedule.