A full-length cDNA clone of the hepatitis C virus (HCV) genotype 1 prototype (subtype 1a) sequence was constructed. Synthetic RNA produced from the initial cDNA clone was not infectious following intrahepatic inoculation of a chimpanzee. A consensus clone was prepared by comparison with multiple full-length HCV sequences of genotypes 1, 2 and 3. A total of 11 non-consensus amino acid residues were altered by mutagenesis. Synthetic RNA from the repaired clone initiated a typical, acute-resolving HCV infection following intrahepatic inoculation of a chimpanzee. In addition, at least one of three chimeric cDNA clones constructed between the HCV-1 and H77 genotype 1a strains of HCV was infectious in a chimpanzee. This is the first example of an infectious chimeric HCV clone. An infectious cDNA clone of HCV-1 will be of particular value, since it is the prototype HCV sequence and many commonly used reagents are based on this sequence.