Complex clinical and laboratory examination of patients with HCV infection revealed that the use of cycloferon provided earlier normalization of the clinical and biochemical parameters and lower immunological imbalance vs. the basic therapy alone. High antiviral effect of the drug was shown. There was observed a positive impact of the cycloferon therapy on the late aftereffects hepatitis C, evidemt from higher frequency of the remissions in the patients with chronic hepatitis B and less frequent transformation of the acute form to the chronic one. Higher interferon-inducing and antiviral activities of cycloferon in the patients with acute hepatitis C and possible less frequent unfavourable aftereffects in the therapy with cycloferon in a dose of 500 mg were demonstrated.