This study describes the immunohistologic distribution of carcinoembryonic antigen (CEA) in 30 fetal pancreata, 5 normal adult pancreata, 11 cases of chronic pancreatitis without carcinoma, 16 cases of chronic pancreatitis with carcinoma, and 20 cases of primary pancreatic adenocarcinoma. The position of CEA-cross-reacting antigen, especially of nonspecific cross-reacting antigen (NCA), was also studied in the case of chronic pancreatitis and pancreatic adenocarcinoma. For this purpose, both monospecific antibodies to CEA and NCA, as well as cross-reacting antibodies, were used in an indirect immunoperoxidase technique. CEA reactivity could not be detected, neither during pancreatic development nor in chronic pancreatitis with or without associated adenocarcinoma. In 15 of 20 pancreatic adenocarcinomas, CEA positivity was found both with membranous and cytoplasmic localization. With the use of the cross-reacting antibodies, all cases of chronic pancreatitis and pancreatic adenocarcinomas showed positive staining of both ductal and tubular structures. Antibodies to NCA closely mimicked the results obtained with the cross-reacting antibodies both in pancreatitis and adenocarcinoma. From the authors' results it can be concluded that CEA is not a developmental antigen of the pancreas. Furthermore, NCA cross-activity of anti-CEA antibodies is an important reason of false positive reaction in chronic pancreatitis. Moreover, true CEA positivity in the pancreas appears to be restricted to adenocarcinoma of the exocrine pancreas.