We studied 40 subjects, 20 under 60 yrs old (10 normotensive and 10 hypertensive) and 20 over 60 yrs old (10 normotensive and 10 hypertensive). Each patient underwent a 24-hour ambulatory blood pressure monitoring (8:00 a.m. to 8:00 a.m.), by a noninvasive method using an ICR 5300 apparatus. Systolic blood pressure was significantly higher on random measurement and during the daytime in the older patients. Although comparison of the other parameters did not reveal significant differences, we noted a tendency to higher systolic values among the older group, and higher diastolic values in the younger one. The variability of the values was slightly higher, although not significantly, among the older patients. In both groups random systolic measurements, and in the younger group diastolic values as well, were significantly higher than mean 24 hour values. The incidence of abnormal systolic BP values ranged from 18.8% to 100% (mean 60.2% +/- 28.9) in younger hypertensives, and from 54% to 100% (mean 76.5% +/- 14.4) in older patients. The incidence of abnormal diastolic BP values ranged from 64.5% to 100% (mean 80.4% +/- 15.6) in younger patients and from 47.2% to 96% (mean 67.8% +/- 15.8) in older patients. The correlation between mean systolic and diastolic values recorded from 8:00 to 10:00 a.m., and mean 24-hour values was significant in young hypertensives, while in the older group there was a significant correlation only for diastolic BP. The lack of significance for systolic values is probably due to a greater variability in systolic pressure in elderly subjects during the morning.(ABSTRACT TRUNCATED AT 250 WORDS)