IN various accounts of histochemical studies on the presence of alkaline phosphatase (substrate: sodium-β-glycerophosphate, pH. 9) in homologous organs, correspondences (for example, in kidney and intestine) have usually been stressed rather than differences. It seems, however, appropriate to direct attention to the latter in order to place the value of experiments on animals in its proper perspective. If the pancreas is selected for discussion, it is because of the confusion which seems to exist in the literature concerning the phosphatase content of this organ. It is often stated in a general way that the enzyme occurs or has been shown to be present in pancreatic tissue1,2. The fact is that Grosser and Husler3, who investigated the pancreas of cattle, sheep, cat and man biochemically, expressly emphasize the complete absence of the enzyme. Again, Takamatsu4, and Kabat and Furth5 failed to produce histochemical evidence for the presence of phosphatase in the pancreas of man. Gomori6 reported that only in the pancreas of the dog are the smallest ducts strongly outlined in black (phosphatase-positive). I found7, in histochemical tests, the epithelial cells, which are related to the duct system of the external secretion of the pancreas, entirely negative in the guinea pig and rat, but strongly positive in the dog (from the centro-acinar cells to the epithelium of large ducts; Fig. 1), thus confirming and extending Gomori's observation.