Hepatocellular carcinoma (HCC) is a major complication of chronic viral hepatitis C. Therapy for HCC is still disappointing. It is thus of great importance to identify novel HCC markers for early detection of the disease, and tumor-specific proteins as potential therapeutic targets. We have used a proteomic approach to identify new proteins involved in HCC development. Four cases of HCC developing from chronic viral hepatitis C were analyzed by two-dimensional electrophoresis (2-DE), and results were compared to those of paired adjacent non-tumorous liver tissues. For MS fingerprinting, protein spots with differential intensity between HCC and non-tumorous liver were directly cut out of gels and processed for MALDI-MS and nano-LC-ESI-MS/MS analysis. Approximately 850 spots were visualized in each gel. The comparative analysis of paired samples indicated that 345 protein spots showed significant differences in expression level between non-tumor and tumor tissue. Among the 345 protein spots analyzed, 238 spots corresponding to 155 different proteins were identified; 49 proteins were up-regulated, whereas 106 proteins were down-regulated. Among these 155 proteins, 91 proteins were regulated in at least three cases. Although 52 out of these 91 proteins have been already described by previous proteomic or transcriptomic studies, or are already known to be involved in hepatocarcinogenesis, this experiment revealed 39 new proteins differentially expressed in HCC developing from viral hepatitis C. Variations in protein accumulation were confirmed for two selected proteins (apolipoprotein E, chloride intracellular channel 1) by Western blotting in ten additional cases of HCC developing in patients with viral hepatitis C