Ten patients without cardiac disease or pulmonary dysfunction were exposed to an inspiratory pressure of 0, 10 and 20 cmH2O, in random order, via a nasal mask during the first postoperative day after scoliotic surgery. These patients were in the supine position, and a BiPAP respiratory assist device was used. Arterial oxygen saturation increased significantly during the application of 10 and 20 cmH2O, while none of the haemodynamic parameters (cardiac output, central venous pressure, right ventricular ejection fraction, right ventricular end diastolic volume, mean pulmonary artery pressure, pulmonary artery wedge pressure, pulmonary vascular resistance) changed significantly, contrary to the findings during continuous positive airways pressure treatment. In addition, the BiPAP was generally well tolerated by the patients.