The mechanism of recurrent cyanotic episodes in infants and children is not known, but a deficiency of surfactant is a possible cause. We have measured the amount of surfactant collected by bronchoalveolar lavage from two children with recurrent cyanotic episodes and from two controls with anatomical airway obstructions. We also assessed the physical properties of the surfactant by changing the surface area (A) of a monolayer and measuring its surface tension (gamma). The cases had lower amounts of surfactant extracted, which could explain some of the abnormalities of the gamma/A loops. However, the finding that the cases had reversed loops (ie, the surface tension is higher during monolayer compression than during expansion) shows that there is also a qualitative abnormality. These features suggest a possible diagnostic test if not a mechanism for this disorder.