After the heart-lung machine was used for the open heart surgery, it was hypothesized that the extracorporeal circulation might be applicable to the management of acute respiratory failure. The development of silicone membrane minimized the possible physical or chemieal damages to blood perfused into the oxygenator. Extracorporeal lung assist(ECLA) using a membrane oxygenator has been recognized as a therapeutic modality for acute respiratory failure, To simplify and reduce the voulme of the ECLA circuit, a small oxygenator, surface area 0.3 m2, was developed by Kurare Co., Japan. It was composed of non-microporous hollow fibers. We performed venoarterial(VA) ECLA to evaluate the gas transfer of the Kurare oxygenator. The priming volume of the ECLA circuit was about 150 ml. Venous blood was drained via the right external jugular vein. The maximum bypass flow rate was about l060 ml/min. Oxygenated blood was perfused into aortic arch via the right carotid artery. The increase of arterial oxygen tension was about 58 mmHg during VA ECLA. It was confirmed that Kurare oxygenator was adequate for the oxygenation support on hypoxic dogs. We tried this ECLA circuit on a postoperative cardiac patient on May, 20, 1991. After 90 hours VA ECLA, she recovered without any complicatioris.