To assess the feasibility of ambulatory blood pressure monitoring (ABPM) and establish reference values for ABPM in normal children and adolescents, 24-hour ABPM was performed in 120 normotensive, nonobese subjects, aged from 6 to 14 years (58 males, age 10.1 +/- 2.8 years; 62 females, age 9.7 +/- 3.1 years; mean +/- SD). The subjects were classified into three age groups: group A (6-8 years, n=40, 23 males, 17 females), group B (9-11 years, n=40, 21 males, 19 females), and group C (11-14 years, n=40, 18 males, 22 females). ABPM was carried out using an oscillometric device with appropriate cuff size. The monitor was programmed to measure BP every 15 min during the day (6 a.m. to 10 p.m.) and every 30 min during the night (10 p.m. to 6 a.m.). Successful rates (recording time=24 hours and > 40 recordings) were 83%, 88%, and 93% in groups A, B, and C, respectively. The recordings of 15 subjects (7 in group A, 5 in group B, 3 in group C) were not analyzed because of incomplete readings. The 24-hour mean systolic/diastolic blood pressure (SBP/DBP) for males and females were 106 +/- 7/65 +/- 5 and 105 +/- 6/64 +/- 5, 110 +/- 6/66 +/- 5 and 109 +/- 5/65 +/- 4, and 115 +/- 7/67 +/- 6 and 113 +/- 6/66 +/- 4 mmHg in groups A, B, and C, respectively. The daytime mean SBP/DBPfor males and females were 110 +/- 7/73 +/- 4 and 109 +/- 8/72 +/- 5, 117 +/- 5/75 +/- 4 and 115 +/- 8/74 +/- 6, and 122 +/- 6/76 +/- 4 and 120 +/- 7/75 +/- 6 mmHg in groups A, B, and C, respectively. The nighttime mean SBP/DBP for the corresponding sex and age groups were 97 +/- 8/58 +/- 5 and 95 +/- 7/57 +/- 6, 101 +/- 8/59 +/- 6 and 99 +/- 7/57 +/- 5, and 105 +/- 7/58 +/- 5 and 103 +/- 6/56 +/- 4 mmHg, respectively. The first fall in BP appeared after lunch (approximately 1:00 pm) and the second fall appeared during the night hours (11:00 pm to 6:00 am). There was a significant correlation between 24-hour mean ambulatory SBP and age (r=0.48, P < 0.001). In contrast, ambulatory DBP and age were not significantly correlated. A nocturnal fall of SBP/DBP was observed in all age- and sex-subgroups. This study showed that ABPM was reproducible and accurate. The normal ambulatory blood pressure (ABP) values in the pediatric age group have not been reported in Taiwan. The distribution of ABP observed in this study could serve as a preliminary reference. A multicenter study may be done to provide normal ranges of ABP in Taiwan for clinical purposes. Further studies are necessary to elucidate the role of ABPM in children.