['Hepatitis B virus (HBV) infection is a world-wide health problem. The major obstacles for current anti-HBV therapy are the low efficacy and the occurrence of drug resistant HBV mutations. Recent studies have demonstrated that combination therapy can enhance antiviral efficacy and overcome the shortcomings. Here, the inhibitory effect mediated by combination of small interfering RNAs (siRNAs) targeting different sites of HBV nuclear localization signal (NLS) was monitored in HepG2.2.15 cells.', 'Recombinant plasmid psil-HBV was constructed and transfected into HepG2.2.15 cells. At 48, 72 and 96 h after transfection, culture media were collected and cells were harvested for HBV replication assay. HBsAg and HBeAg in the cell culture medium were detected by enzyme-linked immunoadsorbent assay. Intracellular viral DNA and covalently closed circular DNA (cccDNA) was quantified by real-time PCR. HBV viral mRNA was reverse transcribed and quantified by reverse-transcript PCR.', 'Our data demonstrated that three used siRNAs showed marked anti-HBV effects. The expression of HBsAg and the replication of HBV DNA could be specifically inhibited in a dose-dependent manner by siRNAs. Furthermore, combination of siRNAs, compared with individual use of each siRNA, exerted a stronger inhibition on antigen expression and viral replication, even though the final concentration of siRNA in the therapy was the same. More importantly, we showed that combination therapy significantly suppressed HBV cccDNA amplification.'] Does combination therapy of siRNAs mediate greater suppression on hepatitis B virus cccDNA in HepG2.2.15 cell?