Forty-five extrahepatic bile duct carcinomas (i.e., tumors of the region proximal to the duct junction, including Klatskin tumors, tumors of the lower mid-region, and tumors of the ampulla of Vater) and 11 gallbladder carcinomas were immunohistochemically examined for p53 protein expression, using the DO-7 monoclonal (mAb) and the CM-1 polyvalent (pAb) antibodies and an antigen retrieval method. Because the DO-7 mAb was found to be significantly more reliable than the CM-1 pAb in detecting p53 immunoreactivity, the immunohistochemical results obtained with the former antibody were used for comparing p53 protein immunoreactivity with tumor site, tumor grade, and survival of patients. Approximately one third (3 of 10) of the proximal tumors were found to express weak p53 immunopositivity, whereas moderate immunopositivity and higher rate (18 of 29) was observed in tumors of the lower mid-region. Finally, moderate and marked p53 immunopositivity was observed in tumors of the ampulla (5 of 6) and gallbladder (8 of 11). In tumors of the lower mid-region of the ampulla and the gallbladder, a significantly higher p53 positivity was noted in high-grade compared with lowgrade neoplasms. For the cases in which complete follow-up was available (11 tumors of the low mid-region), median survival of patients with p53-negative tumors was 25.7 months, whereas survival of those with p53-positive tumors was 5.2 months. In conclusion, our findings suggest that (1) p53 protein is differentially expressed in extrahepatic bile duct carcinomas, thus stressing the clinical and histological distinction between proximal and lower duct tumors, (2) in a subset of the above carcinomas, p53 protein expression appears to be related to higher grades of malignancy, and (3) the presence of p53 immunopositivity might be associated with a shorter survival of the patients. (Hepatology 1995; 22:774–779.)