The Second Task Force on Blood Pressure Control in Children defines "significant" hypertension as blood pressure persistently above the 95th percentile for age-sex specific distribution. In this report we present preliminary data on the prevalence of significant diastolic hypertension in pre-high school black and white children after repeated blood pressure measurements. Blood pressure was measured in 10,446 children two times at an initial screening in school and remeasured two times at a rescreening in 2,808 children from the upper 30 percentiles of the initial screening distribution. Significant hypertension was found in 653 children (6.3%) after the first screening measurement and in 475 children (4.5%) after averaging the first two screening measurements. At the rescreening, the prevalence of significant hypertension was further reduced in this cohort to 1% after one measurement and to 0.8% after averaging the two measurements. The prevalence of significant systolic hypertension had fallen to 0.47% after averaging the two rescreening measurements. These data suggest that the prevalence of significant hypertension is very low in pre-high school children.