The WCGS began in 1960 with 3,524 male volunteers who were employed by 11 California companies. Subjects were 39 to 59 years old and free of heart disease as determined by electrocardiogram. After the initial screening, the study population dropped to 3,154 and the number of companies to 10 because of various exclusions. The cohort comprised both blue- and white-collar employees. At baseline the following information was collected: socio-demographic including age, education, marital status, income, occupation; physical and physiological including height, weight, blood pressure, electrocardiogram, and corneal arcus; biochemical including cholesterol and lipoprotein fractions; medical and family history and use of medications; behavioral data including Type A interview, smoking, exercise, and alcohol use. Later surveys added data on anthropometry, triglycerides, Jenkins Activity Survey, and caffeine use. Average follow-up continued for 8.5 years with repeat examinations. During the 8.5 year follow-up, coronary heart disease occurred in 257 of the initially disease-free group, of whom 50 died of coronary heart disease. There were 90 non-coronary disease deaths. Multiple logistic analyses confirmed the roles of blood pressure, serum cholesterol and cigarette smoking as risk factors. The study also found that Type A behavior, as assessed by a Structured Interview, was associated independently with the risk of coronary heart disease and constituted a 2:1 risk.