The effects of 4% plasma protein solution (group P), 6% dextran-70 (group D), and 5.5% oxypolygelatin (group G) on plasma volume and hemodynamics were compared with each other and with controls (group C) who received only maintenance infusion 20 h after coronary bypass surgery. After infusing 10 ml/kg of colloid at 1 g/min, the immediate increases in plasma volume were 6.1 ml/kg in group P, 8 ml/kg in group D, and 7.9 ml/kg in group G. After one hour, the corresponding increases were 4.2 ml/kg (group P), 8.2 ml/kg (group D) and 6.2 ml/kg (group G). The increases in pulmonary capillary wedge pressure and stroke index were greatest and most persistent in group D, second largest but shortest in duration in group G, and lowest in group P. In conclusion, the volume effects of these three colloid solutions in coronary bypass patients are comparable to those obtained in other elective surgical patients.