We investigated the effect of stimuli activate the sympathetic nervous system on plasma catecholamines, renin activity, urinary metanephrine and normetanephrine, and various hemodynamic parameters in normal subjects (NIs) and borderline hypertensive (BH) subjects. No differences were observed in sympathetic nervous system activity or renin activity when the subjects were in the resting state on a 150 mEq sodium diet. However, the BH group exhibited greater responses in terms of plasma catecholamines and plasma renin activity in response to sodium deprivation and treadmill exercise. Although hemodynamic differences in the cold pressor test and handgrip exercise did not emerge, the radio of atrial size decrement to venous tone increment during the Valsalva maneuver was significantly reduced in the BH group. The investigations suggest that in the basal state, BH subjects have appropriate levels of activation of the sympathetic and renin systems for a normal level of pressure but that perturbations of pressure and volume factors lead to unmasking of abnormalities in regulation of both systems. The data are also consistent with the suggestion that venous compliance is reduced in these patients.