Most membrane oxygenators are built with microporous fibers known for plasma leakage in long-term use such as extracorporeal life support or extracorporeal membrane oxygenation. The current study was designed to evaluate the Quadrox oxygenator in which the fibers have been coated with silicone (Jostra). Six calves (mean weight, 62 +/- 4 kg) were connected to cardiopulmonary bypass (CPB) by jugular venous and carotid arterial cannulation, with a mean flow rate of 3 L/min for 6 hours. They were randomly assigned to a standard Quadrox oxygenator (standard group, n = 3) or a siliconized Quadrox oxygenator (silicone group, n = 3). After 7 days, the animals were sacrificed. A standard battery of blood samples was taken before bypass, after mixing for 10 minutes, and after 1, 2, 5, and 6 hours of perfusion. Analysis of variance was used for repeated measurements. Total oxygen transfer and carbon dioxide transfer did not differ between groups (p = 0.5 for comparison). Blood trauma, evaluated by plasma hemoglobin (Hb), did not detect any significant hemolysis in either group. Thrombocyte and white blood cell count profiles in both groups were parallel and without significant differences (p = 0.1 and 0.6, respectively). At the end of testing no clot deposition was found in the oxygenator. At postmortem, there were no signs of peripheral emboli. The results of this study suggest that this silicone coating of hollow fibers allows for good gas transfer, while preserving all the mechanical advantages of a conventional hollow fiber oxygenator.