We studied the relationship between physical fitness and blood pressure in 228 school children. The data were collected as part of the Loma Linda Child-Adolescent Blood Pressure Study. Systolic and diastolic blood pressures were lower in children above average fitness than in children below average fitness among preadolescent and adolescent boys and girls. On multivariate analysis, adjusting for skinfold thickness, an index of lean arm mass, height and age, the relationship between fitness and systolic blood pressure was statistically significant for preadolescent boys and for adolescents of both sexes. The multivariate relationship was not clearly seen for diastolic blood pressure. Multivariate techniques showed that significant correlates of fitness were obesity in preadolescents, age in adolescent boys and height in adolescent girls. Predicted pulse rates for stages 6-10 of a modified Balke treadmill protocol are given in appendix 1 for preadolescent and adolescent boys and girls.