Cardiovascular responses to sympathetic stimulation may be altered in the early phases of life of subjects with a family history of hypertension. The possible influence of physical activity on adrenergic modulation in children is still not well known. In this study we evaluated, in a group of 162 11-year-old children from a secondary school near Naples, blood pressure and heart rate measured 4 times at 3-week intervals at rest and during adrenergic system stimulation by mental arithmetic stress and isometric exercise. Children were divided into sedentary and physically active groups according to the levels of a Saltin modified questionnaire. Family history of hypertension was also investigated. Systolic and diastolic blood pressure at rest were slightly higher in the sedentary group at each control (107/75 +/- 11/11 vs 105/73 +/- 11/11 mmHg at the first and 100/70 +/- 14/14 vs 98/69 +/- 9/9 at the last control); heart rate in the same group was higher as well (91 +/- 11 vs 87 +/- 12 beats/min, p less than 0.02 at the first and 80 +/- 9 vs 77 +/- 11 at the last control). Systolic and diastolic blood pressure increased by 7/15% during mental stress and by 23/45% during isometric exercise in the sedentary group. The corresponding blood pressure increases in the physically active group were 6/12% and 20/40%, respectively. These responses were independent of sex, body weight and family history of hypertension. These results support the hypothesis that regular physical activity in young adolescents only mildly influences resting blood pressure and cardiovascular responses during the stimulation of the sympathetic nervous system.