CA125 is a tumour marker test based on a monoclonal antibody against an antigen from an ovarian carcinoma cell line. Serum concentrations of CA125 were determined in 95 patients with pancreatic cancer and in 106 patients with benign pancreatic, biliary and hepatocellular diseases. The CA125 concentrations were compared with the CA19-9 and CEA levels. Almost half (45%) of the patients with pancreatic cancer had an elevated CA125 level (greater than 35 U ml-1). Elevated values were also found in benign diseases (24%), especially in patients with pancreatitis and benign hepatocellular diseases, but more seldom in extrahepatic cholestasis. It seems that CA125 is of limited value in the diagnosis of pancreatic cancer. Combination of the CA125 with the CA19-9 test increases the sensitivity only 6% as compared to the CA19-9 assay alone. There may, however, be a use for CA125 in differentiating between obstructive jaundice of benign and malignant origin.