The aim of this study was to examine the influences of genetic predisposition to hypertension and of age on the sympathetic nervous system response to the cold pressor test (CPT). A total of 32 young subjects (aged 27 ± 2 years) were studied: 11 normotensive subjects without a family history of hypertension (FH), 14 normotensive subjects with a strong family history of hypertension (FH+), and eight hypertensive subjects. In addition, 21 older subjects (aged 53 ± 2 years) were studied: 13 hypertensive and eight normotensive subjects. Blood pressure (BP), heart rate (HR), and muscle sympathetic nerve activity (MSNA) were recorded at rest and during a 2-min period of a CPT. Both young and older hypertensive subjects had higher resting MSNA than did the normotensive ones (47 ± 7 v 29 ± 4 bursts per 100 heartbeats (P < .05) and 66 ± 4 v 40 ± 7 bursts per 100 heartbeats (P < .01), respectively). The CPT resulted in HR increases of similar magnitude in all groups of patients. The FH+ group displayed slightly less increase in systolic BP than that of the FH- group (P < .05). The MSNA increased to a far greater degree in FH- (103%) than in FH+ (32%) and in young hypertensive patients (12%) (P < .05). Similarly, MSNA change with the CPT was greater in older normotensive subjects than in older hypertensive patients (61% v 12%, P < .05). Our results show that a CPT induces sympathetic responses that are subnormal in hypertensive patients and those with a family history of hypertension, highlighting the importance of genetic factors in determining the sympathetic nervous reactivity to CPT.