BACKGROUNDS/AIMS: We investigated the concentration of fibronectin (FN) in the human bile to differentiate malignant and benign pancreatobiliary tract disorders and evaluate its possibility as tumor marker for the malignant pancreatobiliary tract tumors. METHODS: We obtained the biles from 65 patients with various obstucting pancrea- tobiliary tract disorders during the endoscopic retrograde cholangiopancreatography (ERCP) and percutaneous transhepatic cholangiography (PTC). Then, the concentration of FN was determined by turbidimetric immunoassay. RESULTS: The benign group consisted of 12 patients with choledocholithiasis and the malignant group consisted of 35 patients with biliary tract cancer and 18 patients with pancreatic cancer. The median concentration of FN was 16.83 microgram/mL in the benign group and 29.53 microgram/mL in the maliganant group (p=0.0002). In the malignant group, 17.77 microgram/mL in the biliary cancer group and 41.28 microgram/mL in the pancreatic cancer group (p=0.001). So, the median concentration of FN in the malignant group was significantly higher than that of the benign group. In the malignant group, the pancreatic cancer group had significantly a higher concentration of FN than biliary tract cancer group (p<0.05). CONCLUSIONS: Our results show that the bile concentration of FN can differentiate the benign and maligant pancreatobiliary obstructing disorders, and it also can differentiate the biliary tract cancer and pancreatic cancer among malignant pancreatobiliary tract disorders. However, further study will be needed to elucidate the mechanism of high expression of FN in pancreatic cancer.