Hepatocellular carcinoma (HCC) is the eighth most frequent cancer worldwide, iipidemiologically-studied risk factors include hepatitis B virus (greater than 80%), hepatitis C virus and aflatoxins. Molecular mechanisms of hepatocarcinogenesis are poorly understood. The only gene known to be consistently involved in these tumors is the p53 tumor suppressor gene. However, this gene was found to be mutated or ifiactivated in about 30% of HCC. There is a need to study additional genes in order to fully understand hepatocellular carcinogenesis. p73 has been identified recently as a p5i -homolog gene. In this study, we analyzed the possible involvement of this gene in HCC. We investigated both the expression and structure of p73 gene in HCC for possible alterations.We first developed a novel method to analyze the expression of alternatively spliced transcripts of p73 (p73a and p73p) simultaneously. This technique, based on RT-PCR, allows the analysis of p73 transcripts semi-quantitatively. We found that p73a was expressed ubiquituously in 8 cell lines derived from normal liver or HCC tumors. Interestingly, p73|3 was present only in 5 differentiated but not in 3 undifferentiated cell lines. The differentiation status of these cell lines were tested by the analysis of albumin and a-fetoprotein transcripts by RT-PCR. These transcripts were present in 3/5 differentiated but not in 3 undifferentiated cell lines. Next, we screened 25 HCC samples for possible mutations of p73 gene at selected exons with non-radioactive heteroduplex test, radioactive SSCP analysis, restriction enzyme analysis and DNA sequencing. No alterations were found in exons homologous to those of p53 known to harbor mutational hotspots.From these observations, we conclude that i) /3 gene is not mutated in HCC, but it may play a critical role in hepatocellular differentiation. As p73p was found in differentiated cell lines, this form may be involved in transcriptional regulation of liver-specific genes. Additional studues are needed to confirm this hypothesis.