The effects of 20% albumin (2.5 ml/kg) on plasma volume (PV) and hemodynamics, as well as albumin pharmacokinetics, were studied in ten spontaneously breathing patients 20 h after coronary bypass surgery. The albumin was infused over 20 min, and serial changes in PV were followed for 60 min using131I albumin dilution. Plasma albumin (P-Alb) and total protein concentrations, as well as oncotic pressure, hemodynamic, and oxygen transport variables, were followed for 90 min. Eleven patients served as controls. At baseline, 7.5% and 5.5% reductions in blood volume were found in the albumin and control groups, respectively. The maximal PV gain (4.5 ml/kg) was reached 15 min after the infusion. Coincidentally, 7.7 ml H2O was linked to 1 g of albumin retained in the circulation. The half-life of P-Alb was 16.2 h. and the distribution volume of the infused dose exceeded PV. An increased pulmonary capillary wedge pressure produced an increase in cardiac index. The right and left ventricular stroke work indices also increased. Pulmonary shunt flow, Pao2, and urinary output did not change appreciably.