The outcome of the HBV and HCV infections is influenced by the status of the immune system. Both of the viruses are believed not to be directly cythopathic, and the host immune response is responsible for the viral clearance and cellular injury. An energic response of the natural immunity allows the control of the virus. Rapid development of specific neutralizing antibodies is essential for the clearance of VHB. The chronic phase of the disease is often associated with abnormal and weak T-cell response and viral persistence. The pathogenesis of the HCV infection is not yet completely understood. HCV persists in patients without any apparent evidence of immune deficits depending on virus or host-related factors. The recent studies revealed that both cellular and humoral immunity appear to be active, despite the progression of the disease.