Summary: Pulmonary function was studied before and after bilateral lung lavage with oxygenated FC-80 fluorocarbon liquid in seven preterm Iambs, 134 days of gestation. Measurements of transpulmonary pressure, air flow, tidal volume, and functional residual capacity (FRC) enabled calculations of lung resistance and compliance, specific compliance, and work of breathing. Immediately postlav-age, arterial oxygen tension (PaO2) decreased significantly (P < 0.05) by 41% from control values. In addition, at 1 hr postlavage, lung compliance significantly decreased (P < 0.01) by 43% from control levels. Lung resistance, FRC, work of breathing, arterial carbon dioxide tension, and pH postlavage were not significantly different from postlavage values. The mean volume of FC-80 remaining in the lungs at 1 hr postlavage was 32% of the instilled volume. These data indicate that lung lavage with a low surface tension liquid has a relatively small effect on lung mechanics of the premature lung. Speculation: Adequate blood gas tensions and pH levels can be maintained both during and after bilateral fluorocarbon lavage with relatively small changes in lung mechanics. Based upon these findings, it is appealing to speculate that bilateral fluorocarbon lavage may be useful as a means of alveolar debridement, particularly in aspiration syndromes of the newborn.