The present invention relates to nucleic acid sequence which comprises the genome of an infectious GB virus B clone. The invention also relates to the use of the nucleic acid sequence of the infectious GB virus B clone to indirectly study the molecular properties of HCV, and in the production of HCV/GBV-B chimeras. The invention further relates to the use of the infectious nucleic acid sequence of GB virus B clone and the HCV/GBV-B chimeras in the development of vaccines and therapeutics for HCV.