The purpose of this study was to compare sympathetic nerve activity responses to the cold presser test in black and white normotensive subjects. We recorded muscle sympathetic nerve activity (microneurography of the peroneal nerve), arterial blood pressure, and heart rate in 9 normotensive American blacks (24±2 years, mean±SEM) and 10 normotensive American whites (28±2 years) at rest and during hand immersion in ice water (cold pressor test). Body weight was not different in the two groups (72.4±3.7 versus 74.1±3.8 kg, black versus white subjects). During supine rest, mean arterial pressure (92±2 versus 93±3 mm Hg, black versus white), heart rate (66±4 versus 62±3 beats per minute, black versus white), and muscle sympathetic nerve burst frequency (12±2 versus 17±3 bursts per minute, black versus white) were not different in the two groups. During the cold pressor test, mean arterial pressure, heart rate, and muscle sympathetic nerve activity increased from supine rest in both groups. The magnitudes of increases in mean arterial pressure and total minute muscle sympathetic nerve activity were significantly greater in blacks than whites (33.5±3 versus 22.4±3 mm Hg and 416±24% versus 243±31% of control, respectively, black versus white, P<.05). The increases in heart rate were not significantly different for the two groups. These data suggest that the enhanced presser response to cold stress observed in normotensive blacks is attributable to greater increases in peripheral sympathetic nerve activity. This heightened sympathetic response to stress may predispose blacks to the development of hypertension.