Hemodynamic, plasma volume, and oxygen transport effects were measured after administration of 500 ml of 5% albumin or 6% hydroxyethyl starch (HES) in hypovolemic postoperative patients using a prospectively randomized crossover design. Both agents produced marked and significant improvement in plasma volume and flow as well as small transient increases in arterial and venous pressures, urine output, colloidal osmotic pressure (COP), and oxygen transport. The authors conclude that HES is a safe, inexpensive, effective plasma expander that has hemodynamic effects similar to those of other colloids. It was apparent from these and other studies that clinically stable postoperative patients may have appreciable blood volume deficits. Routine vital signs correlated poorly with the preinfusion control hemodynamic values or the changes in blood volume status after volume loading. Normal cardiac output, central venous pressure (CVP), and pulmonary arterial wedge pressure (WP) values are commonly seen in critically ill postoperative patients who, nevertheless, may be hypovolemic. Measurement of changes in these variables after a fluid challenge is a useful way to assess plasma volume status.