Systolic and diastolic blood pressures were compared as predictors of mortality from coronary heart disease in Norwegian men aged 35-49. A total of 39,207 men were followed up for an average of 8.9 years; 385 died of coronary heart disease. Diastolic blood pressure seemed to be the better predictor, the difference being most pronounced in the age group 35-39. At this age 26% more deaths from coronary heart disease were found in the upper quintile of diastolic blood pressure compared with the upper quintile of systolic blood pressure. At ages 45-49 there were almost the same numbers of deaths from coronary heart disease in the upper quintiles of systolic and diastolic pressures. These findings suggest that the relative predictive strength of systolic and diastolic blood pressure may be dependent on age. Furthermore, for very obese men the association between blood pressure and death from coronary heart disease is much weaker.