We studied cardiovascular and noncardiovascular sympathetic nervous system (SNS) responses to a vigilance task in patients with borderline (BT) or established hypertension (HT). Twelve patients in each group and twelve normotensive controls (NT) were subjected to a signalled reaction-time (RT) task which included the presentation of a noxious 110 dB white noise contingent upon RT-performance at the end of a 30 sec foreperiod. During this foreperiod recordings were made of: systolic and diastolic blood pressures, heart rate, skin- and muscle-blood flows. Skin and muscle vascular resistances were calculated from mean blood pressure and regional blood flows. Skin conductance level, fluctuations and responses were recorded as noncardiovascular SNS-responses. Compared to NT both HT and BT had higher resting blood pressures, heart rate, skin- and muscle-vascular resistances. BT showed higher resting skin conductance levels than HT and NT who were not different from one another. During stimulation HT and BT evidenced pressor hyperreactivity compared to NT. The electrodermal effects did not parallel the cardiovascular ones. Skin conductance and cardiovascular variables were more closely related in NT than HT or BT. The presence of cardiovascular hyperreactivity together with the absence of noncardiovascular hyperreactivity in HT indicates heightened SNS-activity specific to the cardiovascular system and not part of generalized SNS-arousal. The similarity between HT and BT is consistent with the notion that the differences between BT and HT are quantitative rather than qualitative.