Pleuroamniotic shunting was performed at 22-35 weeks' gestation in 11 fetuses with pleural effusions. Eight of the infants, born two to 16 weeks after shunting, had no evidence of pulmonary hypoplasia. Three died in the neonatal period; one because of pseudomonas septicemia, one because of pulmonary hypoplasia caused by an associated diaphragmatic hernia, and the third because of a major cardiac defect. Pleural effusions and their prenatal decompression offer an experimental human model for the study of the effect of intrathoracic compression on pulmonary development.