Monoclonal antibody to duct cell surface marker (HP-DU-1), produced by hybridoma, was shown to be specific to duct cell surface antigen when tested against normal adult and 12-20-week-old fetal human pancreases. There were no common HLA antigens for locus A, B, C and DR among the 10 pancreas donors; nor did HP-DU-1 reveal any affinity for lymphocytes of donors whose pancreases were used as antigen for immunization of BALB/c mice. Seven out of 7 human pancreas adenocarcinomas including a poorly differentiated human pancreatic tumor expressed surface determinants detectable by HP-DU-1. Cell lines CAPAN-1 and CAPAN-2, derived from human pancreatic adenocarcinoma, also revealed the same antigenic determinants.