Serum concentrations of the CA 19-9 antigen were determined in 91 patients with pancreatic cancer and in 111 patients with benign pancreatic, biliary and hepatocellular diseases. The CA 19-9 concentration was above the cut-off limit (37 U ml-1) in 78% of the patients with pancreatic cancer and high levels (greater than 500 U ml-1) were seen in 56% of these patients. Elevated levels were also seen in benign diseases (22%), especially in patients with extrahepatic cholestasis (up to 440 U ml-1). Hepatocellular jaundice and pancreatitis were associated with normal values (84% of the patients), or with only slightly elevated CA 19-9 levels (up to 88 U ml-1). The CA 19-9 test can be useful as an additional diagnostic tool for the detection of pancreatic cancer. Preliminary results suggest that the CA 19-9 assay can be used in the monitoring of surgically treated patients.