Thirty newborns with hyaline membrane disease were treated by mechanical ventilation with individualized appropriate positive end-expiratory pressure (APEEP) from inspiratory pressure-volume curves of the total respiratory system. APEEP was started before H24 in group 1 (19 patients), and after H24 in group 2 (11 patients). Until APEEP, the 2 groups had classical PEEP levels (lower than 0.8 kPa) either without or with incomplete improvement in arterial hypoxia. The mean APEEP of each group was greater than classical PEEP (p less than 0.001). In group 1 the time of exposure to FiO2 greater than 0.4 was shorter (23.8 +/- 13.7 h) than in group 2 (88.6 +/- 56.9 h) (p less than 0.001) and rapid improvement in blood gas exchanges was seen in group 1 compared to group 2 that was independent of the severity of the disease. Tolerance was excellent. APEEP ventilation started before H24 is of special interest in the management of newborns with severe alveolar injury.