BACKGROUND: Combination of the antiviral drug amantadine with interferon (IFN) may be more effective than IFN monotherapy for treatment of chronic hepatitis C. METHODS: We randomised 93 patients with chronic hepatitis C to IFNIFN 6 MU 3 times/week for 24 weeks, followed by IFN 3 MU 3 times/week for further 24 weeks given in combination with amantadine 100 mg t.i.d. (regimen A, n=48) or as monotherapy (regimen B, n=45). Control liver biopsies were obtained 6 months post treatment. RESULTS: At the end of the trial a similar proportion of patients had normal serum ALT levels (35% for regimen A, and 44% for regimen B) as measured by intention to treat criteria. Sustained biochemical response at 6 months post treatment was 15 and 20%, and sustained virological response was 10 and 20% for regimen A and B, respectively. The effect on liver histology was also similar: the inflammatory components of the Knodell score decreased by 1.3+/-0.6 points for regimen A and by 1.6+/-0.6 for regimen B, and score for fibrosis remained unchanged with both regimens. CONCLUSIONS: Combination of IFN therapy with amantadine does not enhance the effect of IFN as shown by biochemical, virological and histological criteria.