Although the use of 24-h ambulatory blood pressure monitoring has been recommended in the study of blood pressure and exercise, consistent results have not been found for average 24-h systolic or diastolic blood pressures. Systolic load and diastolic load (the percentage of pressures >140/90 mm Hg during daytime hours and >120/80 mm Hg during sleep) have recently been identified as an important variable, but has had limited use with exercise. The purpose of this study was to compare the average systolic and diastolic pressures to systolic and diastolic loads from 24-h data recorded after a 50-min treadmill walk at 50% VO2max to data from a nonexercise control day. Subjects were 36 normotensive (116.9 +/- 10.7/77.0 +/- 8.9 mm Hg) and 25 hypertensive (141.0 +/- 13.7/96.6 +/- 9.0 mm Hg) adults. No significant differences were found for systolic and diastolic pressures or loads between the control and exercise days for normotensives. Even though no significant changes were found for any of the average systolic and diastolic pressures between the control and exercise days for the hypertensives, significant reductions were found in systolic load for 24-h (-25.7%), day (6 AM to 10 PM, -23.1%), work (6 AM to 5 PM, -22.9%), and leisure (5 PM to 10 PM, -26.7%) periods; and in diastolic load for the work (-22.5%) period. Thus, the measurement of systolic and diastolic load may be more sensitive than average systolic and diastolic blood pressures for the detection of 24-h ambulatory blood pressure changes with exercise in borderline hypertension.