Three-part experiment in which five subjects were exposed to lower body negative pressure (LBNP) at -50 mm Hg below the iliac crests. Duration of LBNP to earliest vagal symptoms was 7 to 21 min; all data are expressed as changes from control period to the last measurements before these symptoms. In part I, forearm blood flow (by Whitney gauge) fell 45% during LBNP. In part II, splanchnic blood flow (from arterial clearance hepatic extraction of indocyanine green) fell 32% and splanchnic vascular resistance rose 30%. In part III, cardiac output fell 28%, stroke volume 51%, and central blood volume 21%. Total peripheral resistance and heart rate rose 19% and 52%. Of the reduction in total vascular conductance, decreased splanchnic conductance accounted for approximately 33%; skin plus muscle conductance decreased similarly.