The rate of acute liver failure due to hepatitis A virus (HAV) has not decreased [Hepatology 39 (2004) 572], and therapy of severe infections is still of major interest. Using a DNA-based HAV replicon Cell Culture system, we demonstrate that small interfering RNAs (siRNAs) targeted against viral sequences or a reporter gene contained in the vital genome specifically inhibit HAV RNA replication in HuhT7 cells. Combinations of siRNAs were more effective suppressors of HAV RNA replication. Also, siRNAs targeted against HAV 2C and 3D inhibited the expression of the respective protein. Expressions of endogenous beta-actin and double-stranded-specific RNA-activated serin/threonine kinase (PKR) were unaltered, demonstrating that the siRNA inhibitory effect was not connected to interferon inhibition, but rather was specifically targeted against HAV RNA. These results Suggest that RNA interference might ultimately be useful in treatment of severe HAV infection with or without chronic liver diseases. (C) 2004 Elsevier Inc. All rights reserved.