The author carried out researches on the amount of pepsin secreted in the gastric juice following stimulation with caffein and histamine in 41 infants and children. The results are summarized as follows : 1. The amount of pepsin was found to be in the normal range (64-256 according to Mett\u27s method) not only in children but also in babies under one year old. 2. The amount ofpepsin reached the highest levels in the latter half of the period of secretion of the gastric juice. 3. Caffein had an action to cause secretion of considerably large amounts of pepsin, while histamine showed an action to cause secretion of considerably large amounts of hydrochloric acid (histamine is also capable of causing the secretion of pepsin within the normal range). 4. Not a single cases of 41 infants and children under study was proved negative for pepsin of the gastric juice
