THE elegant studies reported by Led-better, Homma, and Farhi in this issue are entitled `'Readjustment in Distribution of Alveolar Ventilation and Lung Perfusion in the Newborn." It must come as a great surprise to the reader to discover that the only measurement actually made was the partial pressure of nitrogen in the infants' urine. How could one conclude that there were significant imbalances between the distribution of alveolar ventilation and pulmonary blood flow (VA/Q) in the first days of life in normal infants from a urine sample? It is all the more astounding in the light of previous (and seemingly more direct) studies of alveolar-arterial oxygen and carbon dioxide differences which led others to consider the differences largely explained by anatomical right-to-left shunts.