In this study, the internal position of a nasogastric/orogastric tube was determined in 72 children, prior to an abdominal radiograph, by measuring CO2 and pH and bilirubin of tube aspirate. Fifteen of the 72 tubes (20.8%) were incorrectly placed on radiograph. Using the suggested adult cutoff of pH 5, pH of aspirate correctly predicted misplacement outside the stomach in 7/28 (25%) of children and correctly predicted correct placement in the stomach in 34 of 40 children (85%). Using the suggested adult cutoff of bilirubin > or = 5 mg/dL, bilirubin monitoring failed to identify either of two incorrectly placed tubes. In this study, using an algorithm of assuming stomach placement if the pH of aspirate is < or = 5 and obtaining an abdominal radiograph when either no aspirate is obtained or the pH is >5 would have resulted in 92% accuracy. Alternatively, obtaining an abdominal radiograph would result in nearly 100% accuracy.