Correction of a left congenital diaphragmatic hernia in a human fetus with a large volume of liver in the chest requires reduction of liver and viscera into the abdomen. This can kink the ductus venosus and cause the death of the fetus. Therefore, we have repaired surgically created diaphragmatic hernias in fetal lambs by leaving viscera in the chest wrapped in a silastic chimney. With fetal growth there is a relative reduction of hernia volume over weeks, potentially avoiding kinking the ductus venosus. In four groups of lambs lung size and static respiratory system compliance at birth were compared. Lambs treated by this new technique (silo, n = 7) were compared with lambs that had undergone immediate complete correction with a flat silastic patch in the diaphragm plus an abdominal patch (patch, n = 8), with lambs with uncorrected hernias (n = 6), and with normals (n = 8). There was no significant difference between total lung weights (131 +/- 6 g v 157 +/- 13 g, mean +/- SEM, silo v patch) and lung displacement volumes (142 +/- 7 mL v 162 +/- 14 mL) in either surgically corrected group. Lungs from those corrected by silo were significantly heavier than those with uncorrected herniae (131 +/- 6 g v 56 +/- 5 g, P < .01), but were not as heavy as normal lungs (131 +/- 6 g v 257 +/- 16 g, P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)