An epidemiological survey of blood pressure was carried out in 2301 pre-schoolers aged 2-6 years in 11 kindergartens of Guangzhou during 1984. Judging from the chart of selected percentile of blood pressure in relation to age plotted according to the mean blood pressure, the authors suggest that the upper limit of pre-schoolers' blood pressure is 115/75 mmHg. The blood pressure of growing children rises with increases in age, weight and height. Ponderosity Index (W/H3) reflects more precisely the influence of body weight and height on blood pressure. The results show that the percentage of children with high normal pressure is obviously higher in those with a family history of hypertension than in those without such a history. It is of great importance, in the prevention of primary hypertension, to practise medical surveillance and health care in children with high normal blood pressure, especially in those with a family history of hypertension.