Interferon-alpha (IFN-alpha) induces sustained remission of chronic hepatitis C in approximately 25% of patients. In patients who are non-responders to the first course of therapy, retreatment with IFN-alpha is of limited efficacy. Ribavirin has also been used to treat chronic hepatitis C, but it induces only a transient response. In this study, we evaluated the efficacy of ribavirin and IFN-alpha combination therapy for IFN-alpha resistant chronic hepatitis C. Twenty-four IFN-alpha non-responders and 24 relapsers were randomized to receive either ribavirin (1000 mg per day) together with IFN-alpha (3-6 million units (MU) thrice weekly) or the same dose of IFN-alpha alone, for 6 months. Both at the end of treatment and 6 months later, normal transaminase levels were more common in the patients receiving combination therapy than in the group receiving IFN-alpha alone: 17 (70.8%) vs seven (29.2%) patients (P = 0.009) and six (25%) vs one (4.2%) patient (P = 0.034), respectively. At the end of treatment and 6 months later, serum HCV RNA was no longer detectable in eight (33.3%) and five (20.8%) patients in the combination therapy group and in six (25%) and one (4.2%) patient in the IFN-alpha therapy group, respectively. Three patients (12.5%) were withdrawn prematurely from combination therapy because of side-effects; ribavirin therapy was ceased or dosage reduced in six other patients (25%), again because of side-effects. In conclusion, this combination treatment was more effective than retreatment with IFN-alpha, alone, in inducing sustained biochemical remission of chronic hepatitis C that was resistant to a previous course of IFN-alpha. The combination treatment, however, was frequently associated with significant side-effects.