Blood pressure levels were measured in 626 children (138 Japanese, 477 Bolivian and 11 of mixed blood) in a Japanese agricultural settlement in Bolivia. Systolic (SBP) and diastolic (DBP) blood pressure was higher in Japanese children than in Bolivian children at each measured age by 4.09 mmHg (P = 0.0001) and 2.25 mmHg (P = 0.0038), respectively, using analysis of covariance. Although the slope of the regression line both for SBP and for DBP with age tended to be greater in Japanese, this was not statistically significant. There were no ethnic differences in height, weight or body mass index, however, which are usually indicators that correlate well with blood pressure. Ethnic differences in blood pressure were also shown at each of the measured values of height (SBP: 3.93, DBP: 2.19) and weight (SBP: 4.03, DBP: 2.23). Factors causing these ethnic differences are discussed in relation to cultural and genetic considerations.