Noninvasive ambulatory blood pressure monitoring (NABPM) has been playing an increasing role in the diagnosis of hypertension and in the evaluation of antihypertensive drugs. NABPM data for the normal Chinese population has not yet been established. However, data obtained from 25 young male Chinese adults has been analysed. Average ambulatory blood pressure was 120 +/- 8/74 +/- 7 mmHg for the whole-day monitoring. There was an evident diurnal change of blood pressure during the 24-hour monitoring period with higher blood pressure levels being recorded during the daytime, rather than during the nighttime (7.8 +/- 9.7/4.4 +/- 4.8 mmHg; p less than 0.001). Maximal hourly blood pressure averages occurred during the late morning, while minimal hourly blood pressure averages occurred around midnight. The variability in blood pressure was 11 +/- 3/9 +/- 2 mmHg for the daytime and 11 +/- 3/8 +/- 2 mmHg for the nighttime. The incidence of abnormally high blood pressure ranged widely. Eating would raise both the systolic and diastolic blood pressure, while sleep caused a significant fall in blood pressure. This study offers basic data for the study of NABPM in young normotensive Chinese adults.