Correlation of high levels of serum cholesterol with an increased incidence and prevalence of coronary heart disease (CHD) was demonstrated--prior to the inception of the Coronary Drug Project--repeatedly in prospective and cross-sectional epidemiological surveys (e.g., the Tecumseh Study, the Framingham Heart Disease Study). These findings led to the question of whether long-term lowering of serum lipids in individuals both with and without CHD would have a beneficial effect on morbidity and mortality.