Six children conventionally ventilated for acute pulmonary parenchymal failure developed severe hypoxemia (mean PaO2 48 +/- 7 mmHg at an FiO2 of 0.95 +/- 0.08) persisting for more than 6 h despite a progressive increase in positive end expiratory pressure (PEEP) to 14.7 +/- 1.5 cmH2O. Combined high-frequency jet ventilation (HFJV, mean rate 225 b/min superimposed on small tidal volume conventional ventilation) resulted in a sustained increase in PaO2 to 93 +/- 21 mmHg, p less than 0.05 while peak inspiratory pressure decreased from 47 +/- 8 to 35 +/- 6 cmH2O and positive end expiratory pressure could be reduced to 5.8 +/- 4.5 cmH2O, p less than 0.05 and FiO2 to 0.88 +/- 0.10. This improvement occurred without new barotrauma nor deleterious effects on hemodynamic function or diuresis. After a mean of 62 h of combined function or diuresis. After a mean of 62 h of combined HFJV, persistent improvement in gas exchange allowed us to resume conventional mechanical ventilation at lower airway pressures in 4 children who continued to improve and survived. The 2 other children maintained satisfactory gas exchange on combined HFJV, but ultimately died from multiple organ failure. We conclude that combined HFJV might prove helpful to relieve profound hypoxemia and possibly decrease the risk of barotrauma in children with catastrophic pulmonary failure.