objective:to study the expression,distribution and biological significance of ribonucleotide reductase m2 subunit(rrm2) in human cholangiocarcinoma tissues and qbc939 cell line. methods:the expression of rrm2 was evaluated immunohistochemically in 40 cholangiocarcinoma samples,40 cases of adjacent histologically noncancerous bile duct,and 10 specimens of normal bile duct tissue. the expression of rrm2 in human cholangiocarcinoma cell line qbc939 and human normal bile duct epithelial cell line hibec were also detected by rt-pcr and western blot analysis. results:rrm2 was expressed in 72.5%(29 of 40) samples of carcinoma tissues,but it was undetectable in all adjacent histologically noncancerous bile and normal bile duct tissue. rrm2 was also expressed in cholangiocarcinoma cell line qbc939 but not in hibec. conclusion:the high expression of rrm2 in human cholangiocarcinoma tissue and cell line suggest that rrm2 may be a key gene in initiation and progress of cholangiocarcinoma.