Changes in the specific CD4+ T-cell immunity against HCV in response to the treatment with alpha-interferon and ribavirin have been studied in 56 patients with chronic HCV infection. It was shown that after the treatment enhancement of the immune response to HCV infection was mainly due to the elevation of the numbers of NS3 and NS4 antigen-specific CD4+ T cells, which indicates that these cells play an important role in the development of the specific defense directed towards elimination of the virus from the human organism.