Blood group A, B, H, Le, Le^b, Le^x, and Le^y antigenicity as well as the expression of CA 19-9 were examined in pancreatic cancer specimens from 30 patients, using monoclonal antibodies to the respective antigen and immunohistochemical techniques, and the findings were correlated with the blood group types (ABO and Lewis) of the individuals. Compatible antigen expression was found in 82, 75, and 50% of tumors from patients with A, B, and O blood group types, respectively. Deletion of the compatible antigen was found in 10 (33%) of the cases, predominantly in patients of blood group O type, and incompatible expression (of B antigen only) in 4 (13%). Le^a was detected in 87%, Le^b in 90%, Le^x in 30%, and Le^y in 43% of the specimens, regardless of ABH and Lewis phenotype of the patients. Coexpression of Le^a and Le^b was found in 87%, of Le^x and Le^y in 13%, of Le^a and Le^x in 23%, and of Le^b and Le^y in 40% of the cases. CA 19-9 was expressed in 80% of the tumors; it was present in the tumor tissue of 21 of 22 patients from Le^a-b+, in all 4 individuals from Le^a+b-, but in none of the 4 patients from Le^a-b- phenotype (P < 0.01). Heterogeneity in the expression of each of the antigens was found. The overall results indicate that blood group antigen expression in pancreatic tumor differs from that of other gastrointestinal cancers and that the Lewis antigen expression in pancreatic cancer cells is independent of the blood group phenotype of the patients and thus may be useful as a tumor marker.