A retrospective analysis of 25 primary adenocarcinomas of the pancreas, 16 metastatic pancreatic tumors, 8 cases of chronic pancreatitis, and 3 adult normal pancreas was performed to ascertain the reactivity of monoclonal antibody (MAb) B72.3 to malignant and nonneoplastic pancreatic lesions. Formalin-fixed, paraffin-embedded sections of pancreas were evaluated by immunohistochemical techniques (avidin-biotin-peroxidase complex [ABC] method). Twenty-one of 25 malignant primary tumors were reactive, and all 16 metastatic sites expressed the B72.3 antigen. In contrast, all cases of pancreatitis and normal pancreas were either weakly reactive or nonreactive. Ten malignant and two benign pancreatic fine-needle aspirates provided results similar to those seen with fixed tissues. Because MAb B72.3 has selective reactivity for primary and metastatic pancreatic cancer, it may be of value as a diagnostic adjunct in cytologic examination or for radioimmunodetection of regional and/or distant metastases of adenocarcinoma of the pancreas.