Evidence suggests both the arterial baroreflex and vestibulosympathetic reflex contribute to blood pressure regulation, and both autonomic reflexes integrate centrally in the medulla cardiovascular center. A previous report indicates increased sympathetic baroreflex sensitivity during the mid-luteal (ML) phase of the menstrual cycle compared to the early follicular (EF) phase. Based upon this finding, we hypothesize an augmented vestibulosympathetic reflex during the ML phase of the menstrual cycle. Muscle sympathetic nerve activity (MSNA), mean arterial pressure (MAP), and heart rate responses to head-down rotation (HDR) were measured in 10 healthy females during the EF and ML phases of the menstrual cycle. Plasma estradiol (72±13 pg/ml; P<0.01) and progesterone (8±2 ng/ml; P<0.01) were significantly greater during the ML phase compared to the EF phase. The menstrual cycle did not alter resting MSNA, MAP, and heart rate (EF: 13±3 bursts/min, 80±2 mmHg, 65±2 beats/min versus ML: 14±3 bursts/min, 81±3 mmHg, 64±3 beats/min). During the EF phase, HDR increased MSNA (3±1 bursts/min; P<0.02), but did not change MAP or heart rate (0±1 mmHg and 1±1 beats/min). During the ML phase, HDR increased both MSNA and MAP (4±1 bursts/min and 3±1 mmHg; P<0.04) with no change in heart rate (0±1 beats/min). MSNA and heart rate responses to HDR were not different between the EF and ML phases, but MAP responses to HDR were augmented during the ML phase (P<0.03). Our results demonstrate that the menstrual cycle does not influence the vestibulosympathetic reflex, but appears to alter MAP responses to HDR during the ML phase.