Carbohydrate antigens representing some of the initial steps in mucin O-linked glycosylation were examined in specimens of normal pancreas, chronic pancreatitis, and pancreatic adenocarcinoma. Tn antigen, recognized by Vicia villosa lectin, was expressed by all specimens of normal pancreas (acinar cells) and pancreatic cancers and all but one case of chronic pancreatitis. Sialosyl Tn antigen, recognized by monoclonal antibody TKH2, was expressed in a cancer-associated fashion, being completely absent in normal pancreas but expressed by 56% of chronic pancreatitis and 97% of pancreatic cancers. T antigen, recognized by monoclonal antibody AH9-16, was expressed in 68% of normal pancreas (acinar cells), 67% of chronic pancreatitis, and 48% of pancreatic cancer tissues. These results indicate that normal acinar cells of the pancreas are capable of expressing selected carbohydrate structures associated with the initial steps of mucin glycosylation. The marked expression of sialosyl Tn compared with T antigen in pancreatic cancers suggests that with malignant transformation there is selective usage of glycosyltransferase enzymes involved in mucin oligosaccharide synthesis.