ECMO with a roller-pump employs two potentially thrombogenic devices: the servoregulator bladder and heat exchanger. To eliminate these we used an 0.8 m2 Capiox II hollow-fiber oxygenator ventilated with warmed humidified oxygen and a Bio-Medicus centrifugal pump with a 1/4 inch head at a flow of 250 cc/min in six sheep during 96 hr of ECMO each. Oxygenator performance and plasma Hgb were determined, as were the volume, electrolyte, and protein content of fluid accumulating in the gas phase of the oxygenator. Mean oxygen transfer was 15.78 +/- 3.15 ml/min, and mean differences in PaO2 between blood entering and leaving the oxygenator was 360 +/- 49 mmHg. Mean plasma Hgb was 24.7 +/- 12.8 mg/dl. Fluid in the gas phase of the oxygenator was less than 75 ml/day and contained no albumin, protein, sodium, potassium, or chloride. Centrifugal pumps have been associated with hemolysis at low flows, but this may have been due to the simultaneous use of silastic membrane oxygenators that have high resistance. Hollow-fiber oxygenators have been associated with early failure of gas exchange and fluid accumulation in the gas phase. This may have been due to ventilation with dry gas. We conclude that a hollow-fiber oxygenator and a centrifugal pump can provide excellent gas exchange, acceptable hemolysis, and little fluid loss.