The serum carbohydrate antigenic determinant (CA 19–9) was assayed in patients with various diseases, and it provides excellent sensitivity for adenocarcinoma of the pancreas (25/27, 93%), while only 4% (2/54) of the patients with benign diseases and none of the 40 healthy subjects showed elevated CA 19–9 concentrations over 37 units/ml as upper normal value. Increased serum carcinoembryonic antigen (CEA) levels over 2.5 ng/ml were observed in patients with pancreatic cancer (18/22, 82%), compared to 22% (12/54) of the patients with benign diseases and 10% (4/40) of the healthy subjects. 12 of the 19, 6 of the 19 and none of the 22 patients with pancreatic cancer exhibited high serum ferritin, β2-microglobulin, or α-fetoprotein levels, respectively. A significant difference in CA 19–9 was found between patients with pancreatic cancer and gastric cancer, other gastrointestinal (GI) malignancies, other non-GI malignancies, benign digestive diseases or normal popu