Plasma renin activity (PRA) was determined in a group of 610 Japanese schoolchildren aged 10-14 years in order to investigate the relationship between PRA distribution and a family history of hypertension. Plasma renin activity was higher in the subjects with a family history of hypertension (FH+) than in those without a family history of hypertension (FH-). Systolic blood pressure (SBP) was also higher in the FH+ group than in the FH- group. The FH- group showed a significant negative correlation between PRA and SBP (boys, r = -0.254, P less than 0.01; girls, r = -0.225, P less than 0.01), whereas the FH+ group showed no correlation between PRA and blood pressure. These results suggested that schoolchildren with a family history of hypertension might have an enhanced renin-aldosterone (R-A) system, resulting in elevation of blood pressure.