Human cervical cancer oncogene (HCCR) was identified and appeared to function as a negative regulator of p53 gene. The objective of this study was to validate HCCR expression as a candidate marker for human hepatocellular carcinoma. HCCR epitope was identified as Y(355)LGTRR(360). According to immunofluorescence study, HCCR was predominantly localized in the plasma membrane and cytoplasm of hepatocellular carcinoma. HCCR proteins were overexpressed in the tumorous compared with the nontumorous cirrhosis tissues. However, HCCR was not detected in normal liver tissue. Concentration of HCCR protein in the serum was measured in a total of 570 subjects, and comparisons were made to alpha-fetoprotein. Serological studies revealed 78.2% sensitivity of HCCR (cutoff value, 15 microg/ml), which was significantly higher than 64.6% of alpha-fetoprotein (P = 0.0098) and 95.7% specificity for hepatocellular carcinoma. Forty of 52 (76.9%) patients with carcinoma negative for alpha-fetoprotein showed positive values for HCCR. A positive rate of 69.2% in carcinoma patients with tumor sizes <2 cm was found to be a higher rate than measurement of alpha-fetoprotein. Furthermore, HCCR expression was also detected in liver cirrhosis at an intermediate level between carcinoma and normal groups, which gave 88.1% sensitivity and 79.0% specificity using 8 microg/ml as a cutoff value. In summary, the HCCR assay may have an advantage over the alpha-fetoprotein assay in that it is elevated according to disease progression from liver cirrhosis to carcinoma, and it is more frequently positive in patients with early, small hepatocellular carcinoma.