Nine dogs and one primate were placed on total cardiopulmonary bypass and subjected to a simulated hemorrhagic shock procedure. Venous compliance was determined by occluding the venous outflow catheters; venous flow and pressure drop were used to calculate resistance. Individual measurements were made for the superior (SVC) and inferior vena caval (IVC) beds. During hypotension, compliance increased equally in the SVC and IVC; following reinfusion, IVC compliance was consistently lower than SVC compliance. Resistance of the sVC system increased slightly more rapidly during early hypotension than did that of the IVC, but SVC resistance then decreased and remained significantly below that of the IVC system throughout the posthypotension period. These results are interpreted as indicating a different response of the two vascular beds, particularly an increase in IVC arteriolar resistance with a decrease in venous tone. To the extent that the splanchnic bed contributes to the IVC system changes, they are contrary to the concept of a maintained venous tone and decreased arteriolar tone after hemorrhagic shock.