In eight male subjects the blood volume was changed (± 10%) by hemorrhage and transfusion. One cycle of blood infusion and withdrawal or hemorrhage and reinfusion was completed within 9 minutes. The effective compliance of the total circulation was calculated from the changes in central venous pressure recorded simultaneously with the changes in blood volume. The effective compliance was 2.3 ml/mm Hg kg−1body weight. This procedure was repeated while the capacity of the circulatory system was restricted by infusion of norepinephrine (15 μg/min), lower body positive pressure, or both. The compliance values thus obtained were: norepinephrine 1.7 ml/mm Hg kg−1body weight, lower body positive pressure 1.2 ml/mm Hg kg−1body weight, and both norepinephrine and lower body positive pressure 0.9 ml/mm Hg kg−1body weight. The effective compliance of the intrathoracic vascular bed was assumed to be between 1.2 ml/mm Hg kg−1body weight (lower body positive pressure) and 0.9 ml/mm Hg kg−1body weight (norepinephrine and lower body positive pressure). These values constitute 55% and 42% of the effective compliance of the total circulation, respectively.