Sixteen rabbits were anaesthetized and subjected to saline lavage of the lungs to produce surfactant deficiency. This resulted in an arterial oxygen tension of less than 12 kPa on 100% inspired oxygen and an inflection point on the pressure-volume curve at a pressure of 8-12 mmHg. After lavage the animals were randomly assigned to receive either conventional mechanical ventilation (CMV) with a positive end-expiratory pressure (PEEP) of 1-2 mmHg (group I - low PEEP) or CMV with PEEP equal to the inflection point pressure (group II - high PEEP). Mean airway pressures were kept at 14-16 mmHg in both groups by increasing the inspiratory:expiratory time ratios in the low PEEP group. The 5-h protocol was completed by 4 animals in group I and 6 animals in group II, early death usually being associated with a metabolic acidosis. On 100% oxygen, the mean PaO2 at 2-h post-lavage was 15.2 +/- 8.3 kPa in group I and 39.6 +/- 21.8 kPa in group II. Group I had much lower end-expiratory lung volumes (3.0 +/- 1.5 ml above FRC) than group II (34.9 +/- 12.2 ml above FRC). Histological examination of the lungs revealed significantly less hyaline membrane formation in group II (p = 0.001). Thus, the prevention of alveolar collapse by the use of high PEEP levels appears to reduce lung damage in this preparation.