Fifteen patients undergoing elective thoracic surgery were studied in order to investigate the efficacy of high frequency jet ventilation of the non-dependent lung with respect to arterial oxygenation. During the study PaO2, PaCO2, arterial pressures and heart rate were recorded during ventilation of both lungs in the lateral decubitus position during one-lung ventilation and during high frequency jet ventilation of the non-dependent lung. Mean PaO2 was 28 +/- 8.75 kPa and mean PaCO2 was 5.4 +/- 0.7 kPa during control. During one-lung ventilation, PaO2 dropped to 10.8 +/- 2.57 kPa and PaCO2 rose to 6.3 +/- 0.9 kPa. With high frequency jet ventilation to the non-dependent lung, mean PaO2 increased to 25 +/- 6.75 kPa and PaCO2 decreased to 5.16 +/- 0.9 kPa respectively. Arterial pressures and heart rate remained stable during the study period. In conclusion high frequency jet ventilation of the non-dependent lung was effective in providing arterial normoxaemia and normocapnia during one-lung ventilation.