To study the prognostic significance of proliferative cell nuclear antigen(PCNA)in bile duct carcinoma,expression of PCNA protein was studied immunohistochemically in 30 patients with bile duct carcinoma.Results:86.7 percent of bile duct carcinomas showed PCNA positive staining and significiant difference was observed between malignant and benign tissues.These results suggest that proliferative activity of malignant tissues was ber than that of the benign ones.In patients with cancer of stages 3,the mean survial time for those with high proliferative activity was 13 months in constrast with 26 months for those with low activity.PCNA is of prognostic significance for bile duct carcinoma patients.