Pancreatic tissue from 16 post mortem kidney donors have been examined for the content of pepsinogens. A zymogen with electrophoretic mobility, isoelectric point and molecular weight equal to that of pepsinogen C of gastric origin was found in all specimens. A comparison between pepsinogen C extracted from pancreatic tissue and gastric mucosa demonstrated immunological identity. Quantitative measurements with a radioimmunoassay showed pepsinogen C concentrations in pancreatic tissue three to 80 times higher than those of blood serum. Immunohistochemical staining gave positive reaction for pepsinogen C only in the alpha cells of the pancreatic islets.