BACKGROUND: Melanoma differentiation-associated gene-7 (MDA-7)/interleukin-24 (IL-24) is a novel tumor suppressor gene, which has suppressor activity in a broad spectrum of human cancer cells. We investigated the effect of the replication-competent oncolytic adenovirus SG600-IL24 and replication-incompetent adenovirus Ad.IL-24, both expressing human MDA-7/IL-24 on the hepatocellular carcinoma cell lines HepG2, Hep3B, SMMC-7721, HCCLM3, and the normal liver cell line L02. METHODS: Hepatocellular carcinoma cell lines and the normal liver cell line were infected with SG600-IL24 and Ad.IL-24. The mRNA and protein expression of MDA-7/IL-24 in infected cells was confirmed by RT-PCR, ELISA, and Western blotting. MTT assay was used to investigate the proliferation effect. Hoechst staining and Annexin-V and PI staining were performed to study the MDA-7/IL-24 gene expressed in HCC cell lines and the normal liver cell line. Flow cytometry was used to analyse the cell cycle. RESULTS: RT-PCR, ELISA and Western blotting confirmed that the exogenous MDA-7/IL-24 gene was highly expressed in cells infected with SG600-IL24. MTT and apoptosis detection indicated that SG600-IL24 induced growth suppression, promoted apoptosis, and blocked cancer cell lines in the G2/M phase in hepatocellular carcinoma cell lines but not in the normal liver cell line. CONCLUSIONS: SG600-IL24 selectively induces growth suppression and apoptosis in hepatocellular carcinoma cell lines in vitro but not in the normal liver cell line L02. Compared with Ad.IL-24, SG600-IL24 dramatically enhances antitumor activity in hepatocellular carcinoma cell lines. (Hepatobiliary Pancreat Dis Int 2010; 9:615-621)