The paper reviews the medical literature concerning the occurrence and several possible explanations of the origin nature of pancreatic intermediate cells present. Electron microscopic studies of the human pancreas and results of animal experiments in the last years strongly suggest that cells in the wall of small pancreatic ducts (ductules) may develop into duct cells, exocrine pancreatic cells (acinar cells), endocrine islet cells, and hepatocytes even in the adult organism. This suggests that transitional cells arise from the known types of pancreatic intermediate cells during this process. The development of the different cells may start from a pool of omnipotent cells (entodermal stem cells of the foregut) present in the walls of the ductules, or from undifferentiated cells, reflecting their embryonic potential as a result of proliferation of duct cells (i.e. indirect cellular transformation = metaplasia of duct cells).