We have isolated HFREP-1, a gene that is overexpressed in a hepatocellular carcinoma from a lambda gt10 cDNA library constructed from the mRNA of the hepatocellular carcinoma specimen using subtractive and differential cDNA cloning. The largest cDNA insert contained 1231 base pairs encoding 312 amino acids. The deduced protein sequence contained a hydrophobic leader peptide and the putative protein sequence showed marked homology with beta- and gamma-subunits of fibrinogen and other fibrinogen-related proteins. However, the HFREP-1 protein lacked a platelet-binding site, a cross-linking region and a thrombin-sensitive site, which are crucial for fibrin clot formation. The expression of the gene was studied in various organs in the rat and in several human carcinoma cell lines, and was found to be specific to liver and hepatocellular carcinoma cell lines. We suggest that the HFREP-1 gene is a new member of the fibrinogen family and that further data on the gene are important for a better understanding of the development of hepatocellular carcinomas.