Using an electrochemiluminescence immunoassay, CYFRA 21-1 concentrations were measured in sera from 187 patients with primary liver cancer (164 with hepatocellular carcinoma (HCC) and 23 with intrahepatic cholangiocarcinoma (ICC)) and 87 patients with benign liver diseases. Concentrations of CYFRA 21-1 were significantly higher in patients with ICC (5.0; interquartile range 3.1-10.7 ng ml(-1)) than in those with benign liver disease (1.4; 1.0-1.9; Mann-Whitney U-test, P<0.0001) or HCC (1.7; 1.1-2.7; Mann-Whitney U-test, P<0.0001). Using cutoff values selected for 95% specificity in the benign group (3.0 ng ml(-1)), CYFRA 21-1 showed higher sensitivity for ICC (87.0%) than three commonly used markers including alpha-fetoprotein (17.4%), carcinoembryonic antigen (34.8%), and carbohydrate antigen 19-9 (60.9%). Serum CYFRA 21-1 increased in ICC from stages I/II to IV (Kruskal-Wallis test, P=0.0102). CYFRA 21-1 concentration increased with extent of local invasion, but not nodal status. Serum CYFRA 21-1 represents a useful diagnostic test for ICC that offers high sensitivity. CYFRA 21-1 reflected differences in tumour burden, suggesting applicability to staging and follow-up.