Pancreatic oncofetal antigen (POA) was purified from fetal pancreas and migrated in beta-region electrophoretically. Its molecular weight was 80 X 10(4) daltons. Enzyme immunoassay for serum POA revealed that elevated levels of POA were found in sera of patients with pancreatic cancer. By a serological screening of 440 out-patients with combined assay of tumor markers including POA, 4 cases of pancreatic cancer were found. POA was demonstrated in the ductal cells of fetal pancreas and cancer cells of duct cell type pancreatic adenocarcinoma immunohistochemically. Elevated levels of serum POA of patients with pancreatic cancer was probably derived from cancer tissue. These findings indicate that serum POA assay is clinically useful.