Sympathetic vasoconstrictor activity increases with exercise. Previously we demonstrated sex differences in modulation of vasomotor sympathetic outflow during isometric forearm exercise in healthy young humans (Jarvis et al., 2011). The purpose of this study was to determine whether sympathetic activation during rhythmic forearm exercise differed in women compared with men. To accomplish this, responses to 6 minutes of non-fatiguing dynamic hand grip (DHG) were compared in supine healthy women (n=8, age: 26 [21, 32] years; mean [95% CI]) and men (n=9, 30 [26, 34] years). Exercise was performed at 40 % of the maximal voluntary contraction (MVC) using the dominant hand with a cycle of 2 seconds of contraction, 2 seconds of release. Beat-by-beat heart rate (HR), blood pressures (BP), and muscle sympathetic nerve activity (MSNA) were determined using electrocardiography, finger photoplethysmography and microneurography respectively. Perceived exertion was assessed upon completion of the exercise task using the Borg (6-20) scale. Baseline heart rate and blood pressures were similar for both sexes (Table 1). However, baseline MSNA was lower in women compared with men. As expected, heart rate, blood pressures and MSNA increased during forearm exercise for both women and men. The responses of heart rate and blood pressures were similar in magnitude. However, the increase in MSNA was greater for women compared with men. Rating of perceived exertion was not different (13 [12, 15] for women versus 12 [11, 14] for men). These findings suggest sex differences in sympathetic activation during rhythmic forearm exercise. Young women experience a greater increase of vasomotor outflow during dynamic exercise compared with young men. This probably reflects the difference in baseline resting sympathetic vasoconstrictor activity.