Sixteen males and sixteen females were recruited for this study; eight of each gender were aerobically trained athletes; the remaining eight were untrained control subjects. Each subject performed a maximal exercise stress test for aerobic capacity (VO2max). On a separate day the blood volume and the cardiovascular responses to progressive (0 to -50 torr) lower body negative pressure (LBNP) were determined. The female subjects were observed to be significantly more tolerant of the LBNP than the male subjects. No differences between groups were observed in changes in leg volume, cardiac index, blood pressure, or heart rate during LBNP. However, the females, in comparison to the males, maintained stroke index at a higher level, and increased regional vasoconstriction more, during the LBNP induced hypotensive stress. These findings suggest that female subjects withstand LBNP to -50 torr better than male subjects.