A recently developed hollow fiber membrane oxygenator, made of microporous polypropylene (Capiox, Terumo, 1.6 m2) was tested to evaluate the hemocompatibility and the ease and safety of operation. Two types of this oxygenator were tested: one with and one without an integral heat exchanger. Each type was tested in 6 dogs during a partial bypass of 2 hours at a flow rate of 2 l/min. In addition, gas transfer measurements were carried out. The Terumo oxygenator preserved the blood cells and the platelet function very well. In addition, neither the Wu-Hoak index, a method to measure platelet aggregates, nor inspection of the oxygenator revealed platelet aggregates. Operation and debubbling procedure were easy and safe. The estimated rated blood flow for O2 was 1.5 l/min with a corresponding CO2 removal of 90 ml/min. The integral heat exchanger did not affect the results significantly. Our data show that this oxygenator is easy and safe to use. Clinical evaluation is recommended.