Artificially fed infants produce only a small amount of hydrochloric acid during digestion. The amount is not sufficient to show free hydrochloric acid, but brings the stomach contents to a hydrogen-ion concentration of, roughly, 1 × 10−5, or pH 5.0. The present study was undertaken to secure data on the pH of the gastric contents of infants; to discover the normal range on a given standard meal, and to determine the factors which cause the variations of acidity: (1) digestion time, (2) previous type of feeding, (3) the child's age, (4) the amount of test meal and (5) the concentration. Without this information, we have no basis for the interpretation of the findings of gastric analysis in pathologic conditions in infants. Work of this nature has recently been reported by Davidsohn,1 who has reviewed the literature and has also studied some of the factors in gastric