The current status of interferon (IFN) therapy in chronic hepatitis C is presented, focusing on the results of studies in Japan. Depending on the IFN treatment regimen used in chronic hepatitis C, it is possible to eradicate HCV in a relatively high percentage of patients (about 40%) and to achieve a cure for chronic hepatitis C. The objective of treatment should therefore be the eradication of HCV. The efficacy of IFN in chronic hepatitis C is dependent on the dosage of IFN, duration of treatment, liver histology findings, serum HCV-RNA levels, and HCV genotype. Besides a flu-like syndrome, many adverse reactions are associated with high-dose, long-term IFN treatment. However, as a rule, full recovery or improvement follows prompt withdrawal of IFN. By modification of the IFN, it will be possible to reduce adverse reactions and to create a more effective IFN to further enhance the effect of IFN in chronic hepatitis C.