Variations in clinical noninvasive systolic pressure at the point of symptom-limited exercise on a treadmill were examined in six groups of subjects: 5,459 men and 749 women classified into three categories each. Among the men, 2,532 were asymptomatic healthy, 592 were hypertensive and 1,586 had clinical manifestations of coronary heart disease (that is, typical angina pectoris, prior myocardial infarction or sudden cardiac arrest with resuscitation). Among the women, 244, 158 and 347 were in the corresponding clinical categories. None had had cardiac surgery; all had follow-up status ascertained by periodic mail questionnaires. Reported deaths were reviewed and classified by three cardiologists; 140 deaths were attributed to coronary heart disease, 118 of them in the men classified as having coronary heart disease. The majority of maximal systolic blood pressure readings were reported to the nearest centimeter rather than millimeter of pressure. Retesting of 156 persons from 1 to 32 months later showed that pressure values agreed within 10 percent in two thirds, the overall mean difference was only 8.6 mm Hg and the correlation at maximal exercise was superior to that of the resting observations just before exercise. Hypertensive patients had a significantly greater body weight than normotensive persons. Among men, the lowest maximal systolic pressure was observed in the group with coronary heart disease; among women, the lowest mean pressure was found in the healthy group. Patients with coronary heart disease were slightly older, and only the women showed a significant correlation in maximal pressure with age. Only 5 percent of the variation in maximal systolic pressure in the patients with coronary heart disease was due to a shortened duration of exercise. Maximal systolic pressures correlated fairly well (r equals 0.46 to 0.68 for the various groups) with resting systolic pressure, and this relation was independent of the diagnosis of cardiovascular disease in both men and women. Relations between pressure and the number of stenotic coronary arteries and imparied ejection fraction at rest were examined in 22 men without and 182 men with coronary artery disease. Lower maximal systolic pressures were often associated with two or three vessel disease or reduced ejection fraction, or both. The prognostic value of maximal systolic pressure for subsequent death due to coronary heart disease was examined in the men with coronary heart disease. The annual rate of sudden cardiac death decreased from 97.9 per 1,000 men to 25.3 and 6.6 per 1,000 men as the range of maximal systolic pressure increased from less than 140 to 140 to 199 and to 200 mm Hg or more, respectively. Cardiomegaly, Q waves in the resting electrocardiogram and persistent postexertional S-T depression were more common in men with the lowest systolic pressure at maximal exercise.