To assess the combined influence of blood pressure (BP), serum cholesterol level, and cigarette smoking on death from coronary heart disease (CHD) and to describe how these associations vary with age, data on those factors and on mortality for 316,099 men screened for the Multiple Risk Factor Intervention Trial (MRFIT) were examined. Vital status of participants has been determined after an average follow-up of 12 years; 6327 deaths from CHD have been identified. Strong graded relationships between serum cholesterol levels above 4.65 mmol/L (180 mg/dL), systolic BP above 110 mm Hg, and diastolic BP above 70 mm Hg and mortality due to CHD were evident. Smokers with serum cholesterol and systolic BP levels in the highest quintiles had CHD death rates that were approximately 20 times greater than nonsmoking men with systolic BP and cholesterol levels in the lowest quintile. Systolic and diastolic BP, serum cholesterol level, and cigarettes per day were significant predictors of death due to CHD in all age groups. Systolic BP was a stronger predictor than diastolic BP. These results, together with the findings of clinical trials, offer strong support for intensified preventive efforts in all age groups.