Laboratory evidence has recently confirmed clinical reports suggesting that the surfactant system is abnormal in congenital diaphragmatic hernia (CDH). Autopsy series show that, although both lungs are affected by the maldevelopment, the ipsilateral lung is more severely affected. The aim of this study was to examine the surfactant status in each lung in a lamb model of CDH. The lamb CDH model was created on the left side at 80 d of gestation and delivered near term. Subsequently, the lungs were removed and separated from each other. Bronchoalveolar lavage and type II pneumocyte isolations were performed on each side separately. Lavage analyses showed decreased phospholipid (0.12 versus 0.42 mg/g), per cent phosphatidylcholine (51% versus 79%) surfactant-associated protein A (0.20 versus 2.68 mg/g), and surfactant-associated protein-B (0.35 versus 2.21 mg/g) in CDH lungs compared with control lungs. However, no differences were seen between the ipsilateral and contralateral lungs of either CDH or control groups. This was in contrast to the phosphatidylcholine biosynthetic abilities of type II cells isolated from CDH lungs, which were not only lower than those from control lungs (0.15 versus 0.40 nmol/10(6) cells/h), but were also significantly worse in the ipsilateral CDH lung compared with the contralateral CDH lung (0.10 versus 0.20 nmol/10(6) cells/h). Further studies utilizing radiolabeled exogenous surfactant injected in the lower contralateral lung indicate that discrepancies between the presence of type II cell function differences between lungs, and the lack of biochemical differences between the two lungs in CDH, may be due to in utero mixing of lung fluid.