Although enzymes play an important rôle in the process of digestion, there is comparatively little accurate knowledge concerning their variations in health and disease. Thus the status of pancreatic enzyme activity in pernicious anemia, sprue, diabetes, rickets, celiac disease, pancreatitis, cholecystitis and carcinoma of the pancreas is uncertain. The explanation for the retarded development of this field lies, we believe, in the fact that accurate methods of study have been applied biochemically for only a short time, and the factors influencing enzyme reactions have only recently been brought to light by the work of Sörensen, Michaelis, Northrop, Croft Hill, Willstatter and others. This study is an attempt to evaluate according to age, and to compare the duodenal enzyme activity and reactions of the gastric and duodenal contents of normal infants and children with those in adults. For this purpose over eighty children, ranging from 1 month to 12 years of