The Victoria Hospital for Children, London, S.W.3, is one of the smaller paediatric units with 110 beds and a yearly outpatient attendance of 25,000 infants and children. From the material of this hospital I wish to give examples of the benefits derived from studying plain radiographs of the abdomen and subject them to a critical survey. The main source of contrast is provided by air swallowed during feeding and crying. The contrast is in no way inferior to that provided by barium, yet interest in air contrast studies has lagged behind and occupied second place to barium technique. The reason has to be sought for in the great many variables which affect the presence and distribution of gas in the intestine (Table I).The amount of gas is determined by the balance between intake and elimination. The intake dependsinter aliaupon the vigour and efficiency of sucking movements, the position in which the infant is held during and between feeds, type and consistency of food, skill in handling and nervous factors (Magnusson and Engström, 1932; Snow and Cassasa, 1935; Soveri, 1939). The intake is considerably increased in cases of oesophageal atresia, where air is actively pressed into the stomach through the lower tracheo-oesophageal fistula while the glottis is closed during crying and choking.