The aim of this study was to evaluate the expression of blood group Tn and sialyl-Tn antigens in the pancreas to determine whether they could help to interpret histochemically needle biopsies obtained from the pancreas. Lectin and immunohistochemistry was carried out using the biotin-labeled Vicia villosa agglutinin isolectin B4 and the mouse monoclonal antibody MLS102 to detect the Tn and sialyl-Tn blood-group antigens in the pancreas. All the pancreatic ductal adenocarcinomas (11/11) were positively stained by V. villosa agglutinin and MLS102 monoclonal antibody. None of the normals or chronic pancreatitics bound MLS102 monoclonal antibody. The acini of all the normals and chronic pancreatitics were V. villosa agglutinin positive, which was absent in the normal ductal cells and present only sparingly in the chronic pancreatitis ductal tissues (10/16). Thus, both the Tn and the sialyl-Tn blood-group antigens are present in pancreatic ductal tissues that have undergone malignant transformation. MLS102 is superior to V. villosa agglutinin in distinguishing malignant from normal and nonmalignant pancreatic tissues in needle biopsies.