There were few, but conflicting, reports dealing with the clinical significance of c-erbB-2 in biliary tract cancer. We evaluated the expression of c-erbB-2 in normal epithelium of bile ducts (n = 46), gallbladder cancer (n = 11), carcinoma of the ampulla of Vater (n = 18), and intrahepatic cholangiocarcinoma (CC) (n = 18). c-erbB-2 protein is present in 63% (29/46) of surface epithelium in large and septal bile ducts, but not in peripheral small ducts. Overexpression of the gene product was found in 27.8% (5/18) of intrahepatic CC, 27.8% (5/18) of carcinoma of the ampulla of Vater, and 63.6% (7/11) of gallbladder cancer. But, there was no c-erbB-2 overexpression in the hyperplasia or atypical hyperplastic bile duct epithelium (p = 0.002). In terms of prognostic implication, expression of c-erbB-2 did not correlate to the histopathological grade (p = 0.60) and tumor stage (p = 0.63). The results indicate that c-erbB-2 protein may play some roles in physiology of normal bile ducts. Overexpression of the gene product occurs in one forth to about two thirds of carcinoma of biliary tract, and may be used as phenotypic marker for neoplastic transformation. However, the gene product may not be important in the aggressive behavior of tumor.