INTRODUCTIONHepatocellular carcinoma (HCC) is one of the major causes ofdeath in the world.The mechanism of carcinogenesis isunknown,although it is widely accepted that HBV and HCVare closely related to liver cancer.Previously,a varietyof studies have described the differences in gene expressionwhich distinguished tumor from nontumor.Cloning ofthe genes,especially the genes associated with HBV andHCV,is still very important to account for the developmentof liver cancer.Traditionally,several methods were used to clone thenew genes,which means to compare two population of mRNAand obtain clones of genes that expressed in one population butnot in the other.Although these methods have been successfulin some cases,they require many rounds of hybridization andare not well suited for the identification of rare messages.The INTRODUCTION Hepatocellular carcinoma (HCC) is one of the major causes ofdeath in the world. The mechanism of carcinogenesis isunknown, although it is widely accepted that HBV and HCVare closely related to liver cancer .Previously, a varietyof studies have described the differences in gene expressionwhich distinguished tumor from nontumor. Cloning of the genes, especially the genes associated with HBV and HCV, is still very important to account for the developmentof liver cancer .Traditionally, several methods were used to clone the new genes, which means to compare two population of mRNA and obtain clones of genes that expressed in one population butnot in the other .Although these methods have been successfulin some cases, they require many rounds of hybridization andare not well suited for the identification of rare messages.The