Previous studies have shown blood pressure reactivity to exercise predicts future resting blood pressure. Subjects in this study were 206 healthy Mexican-American and Anglo-American families with fifth or sixth grade children. A total of 539 children (mean age = 12 years) and parents (mean age = 37 years) had complete data at baseline, and 79% were remeasured 48 months later. Blood pressure was measured during a submaximal cycle ergometer fitness test. Reactivity measures included systolic blood pressure at 70% of maximal heart rate (SBP70) and slope of the blood pressure-heart rate association during exercise (SLOPE). Stability of reactivity measures over 24 months varied from .22 to .63 (all p less than 0.001). Correlates of blood pressure reactivity in parents included resting heart rate, gender, age, and sodium intake. Correlates of reactivity in children included resting heart rate, body mass index, and age. Modest but significant levels of family aggregation of blood pressure reactivity were observed. In stepwise multiple regression analyses, SBP70 at baseline predicted resting blood pressure 48 months later in parents but not in children. The present results confirm previous studies indicating systolic blood pressure reactivity to exercise is a significant predictor of later resting blood pressure.