The immunological localization of kallikrein in human pancreatic tissue was studied at the optical and subcellular levels. Data obtained by light microscopy, using indirect immunofluorescence and immunoperoxidase techniques, demonstrate the presence of kallikrein in pancreatic acinar cells. Ultrastructural localization was performed by using the immunocytochemical protein A-gold technique. Kallikrein was found at the level of the rough endoplasmic reticulum and mainly in the zymogen granules of pancreatic acinar cells. Kallikrein was not found in the centro-acinar or duct cells.