Left ventricular hypertrophy has been shown to be an independent predictor of cardiovascular morbidity and mortality. Few studies have examined the determinants of left ventricular mass (LVM) in normotensive children. Eight-four healthy children, blacks and whites, girls and boys, between 6 and 18 years of age, all with positive family histories of essential hypertension, participated in the study. Demographic and anthropometric characteristics, physical activity, and hemodynamic responses at rest and in response to the stress of forehead cold stimulation and a challenging video game were related to M-mode echocardiographic determined LVM indexed by two indices of body habitus. Hierarchical stepwise multiple regression analysis indicated that the significant independent correlates of LVM per body surface area were gender (boys were greater), baseline systolic blood pressure and heart rate, a physical activity index (sweat episodes per week) and peak systolic blood pressure responses to the forehead cold stressor (final model r2 = 0.49). For LVM/height2.7 significant independent correlates were adiposity index (weight z score--height z score), gender (boys were greater), age, resting systolic pressure, and systemic vascular resistance reactivity to forehead cold stimulation (final model r2 = 0.42). These findings with normotensive children corroborate other findings that have typically involved hypertensive children, indicating that resting heart rate and systolic pressure, gender, and adiposity are early determinants of LVM indices in children. In addition, the current findings indicate that hemodynamic responses to stress also appear to play a role in the early development of LVM.(ABSTRACT TRUNCATED AT 250 WORDS)