Pancreatic acinar cells within the islets of Langerhans in human pancreas were investigated both histopathologically and electron microscopically. Acinar cells inside the islets of Langerhans were observed in all 50 adult cases investigated. Between such acinar cells and endocrine tissues, no reticular fiber was observed; they were encapsulated together instead. The acinar cells were immunostained with antiamylase similar to the "extrainsular" acinar cells and were also connected to the small pancreatic duct. Electron microscopically, intercellular junctions of the desmosomal type were found between the acinar cells and the adjacent endocrine cells. Therefore, the acinar cells within the islets of Langerhans were true acinar cells, based on the incomplete demarcation between the islets and the acinar tissue.