Interferon (IFN) has been demonstrated to be effective against chronic hepatitis C. However, it has been believed that IFN treatment is generally ineffective in cases that have already progressed to cirrhosis. It is highly important to develop a treatment modality that will stop the progression of compensated to decompensated cirrhosis. We have carried out a randomized controlled study of human lymphoblastoid interferon in patients with compensated type C cirrhosis. There were no serious side effects, and treatment with 3 MU IFN daily for 2 wk and three times weekly for 24 wk thereafter is more effective than treatment with 1 MU, or no treatment. IFN administration can be effective and safe in patients with compensated type C cirrhosis, and it would be worthwhile to evaluate IFN therapy for such patients further.