An in vivo model of hepatitis C virus (HCV) infection is needed to enable investigation of the mechanism of the liver injury that it causes. In this study, we used asialoglycoprotein receptor mediated gene delivery to obtain expression of the complementary DNA (cDNA) coding the core and part of the envelope 1 protein of HCV because selective delivery to the hepatocytes has been reported to be attained with this method. The optimum carrier-DNA ratio was examined using in vitro transfection and found to be important for the efficiency of this method. In transfection in vivo, microautoradiographical examination showed that the transfected plasmids were delivered selectively to the liver parenchymal cells. To obtain an immunohistochemically detectable level of protein expression in rodent liver, some modifications for increasing the in vivo transfection efficiency were performed; a lysosomal enzyme inhibitor, chloroquine, was used and the administration route of the carrier-DNA complex was changed from the tail vein to the portal vein. On the bases of these results, in vivo transfection with expression vector of HCV core/E1 region was performed. In rat liver transfected by intraportal injection with chloroquine, the transcript RNA and the core protein were detected. These results indicated that the HCV core/E1 expression vector was not merely delivered but also successfully expressed in the liver using asialoglycoprotein receptor mediated gene delivery. The number of the HCV core expressing cells in the transfected liver was similar to that in patients with hepatitis C. These in vivo transfected animals should be useful for investigating the role of this region in the liver injury caused by HCV.