The study was longitudinal in design and consisted of three examinations of the cohort over a period of eighteen years. Data collected in examination one in 1969-1973 included: a twin history questionnaire; personal, family and medical histories; a diet history; a physical examination; numerical data on anthropometry, hematology, and pulmonary function; supplemental lab data; an X-ray; clinical diagnostic impression; electrocardiogram; and blood analysis-fasting lipids. Data collected in examination two in 1981-1982 included: a personal and family history; deceased twin information; residence and occupational history; Thurstone Activity Scale; leisure time physical activity; social support; medical history; physical examination; clinical diagnostic impression; job mobility and stress; retirement information; Jenkins Activity Survey; blood lipid measurements. Data collected in examination three in 1986-1987 included the same data as collected in examination two plus an assessment of the prevalence for all twins and the incidence for a subgroup of twins of preclinical cardiovascular disease detected through noninvasive techniques.