The diagnostic accuracy of the measurement of CA 19-9 in the serum, pure pancreatic juice, and aspirated pancreatic fluid in the diagnosis of pancreatic tumors was assessed in 32 patients with ndigmnt pancreatic tumors and 19 patients with pancreatitis. Pure pancreatic juice was collected from the pancreatic duct by endoscopic cannulation with a duodenofiberscope after intravenous administration of secretin. Pancreatic material was obtained by percutaneous lineneedle aspiration biopsy under ultrasonic @dance. Abnormally high CA 19-9 levels in the serum were significantly more frequent in patients with malignant pancreatic tumors than in those with pancreatitis: they were elevated in 71.9% of the patients with pancreatic tumors. High CA 19-9 levels were found primarily in patients with a tumor of the head of the pancreas, in those with a tumor greater than 3 cm in its greatest diameter, and in those with an unresectable cancer. Only 57.1% of seven patients with a tumor of less than 3 em in its greatest diameter showed an increase in CA 19-9 level. The CA 19-9 levels in pure pancreatic juice were significantly higher in patients with pancreatic tumors than in patients with pancreatitis without pancreatic stone. However, it was not useful for differentiating pancreatic tumors from pancreatitis with pancreatolithiasis. The CA 19-9 level in pancreatic materials obtained by aspiration biopsy was significantly higher in patients with malignant pancreatic tumors than in those with pancreatitis. Eight patients (80%) with pancreatic tumors had values above lo00 IJ/ml, whereas all five patients with pancreatitis had values of less than 30 U/ml. Although CA 19-9 levels in pancreatic materials was useful only when cytologic examination did not provide any evidence of malignancy, the combination of the CA 19-9 assay and the cytologic study of specimens obtained by percutaneous fine-needle aspiration biopsy of the pancreas increased the diagnostic rate to 100%.