We have analyzed the impact of a single needle puncture of the fetal rat membranes on day 15 of gestation on growth and development at term (day 21). Untouched littermate fetuses served as controls. The procedure led to persistent oligohydramnios. The experimental fetuses weighed less, 94% of the weight of controls, P less than 0.01. Both lungs and liver weighed significantly less, 72% (P less than 0.01) and 89% (P less than 0.03) of controls respectively and there was no effect on brain weight. When the values were expressed as organ/body weight ratio only the lung/body weight ratio was significantly lower, 77% of controls, P less than 0.01. DNA per lung was less, 83%, as was lung DNA per gram of fetal weight, 89%, and the lung protein/DNA ratio was lower, 79%, indicating lung hypoplasia and hypotrophy (all three P values less than 0.01). There were no significant differences in either liver or brain biochemical analysis. We conclude that pulmonary hypoplasia associated with oligohydroamnios in the rat is a suitable animal model of the human condition.