In primary interferon-alpha (IFN-alpha) nonresponders with chronic hepatitis C, retreatment with IFN-alpha has only limited efficacy with sustained response rates below 10%. Therefore, the aims of the present study were to compare the efficacy and safety of IFN-alpha alone or in combination with amantadine sulphate in nonresponders to previous IFN-alpha monotherapy. Fifty-five IFN-alpha nonresponders with chronic hepatitis C (mean age: 46.6 years) received IFN-alpha 6 MIU thrice weekly for 24 weeks followed by 3 MIU thrice weekly for additional 24 weeks. Amantadine sulphate (n=26) or a matched placebo (n=29) was given orally twice daily for 48 weeks. Because of a low initial response rate at week 12 (13/55 patients) and a high breakthrough rate (8/13 patients) after IFN-alpha dose reduction in week 24, a virological end-of-treatment response with undetectable serum HCV-RNA (< 1000 copies/mL) was achieved in only five patients (IFN-alpha/amantadine sulphate, one patient; IFN-alpha/placebo, four patients). After 24 weeks follow-up a sustained virological response was observed in only two patients receiving IFN-alpha and placebo. Health-related quality-of-life analysis showed a substantial improvement of the Profile of Mood States (POMS) scale concerning the subscales fatigue (P < 0.05) and vigor (P < 0.05) in patients receiving combined IFN-alpha/amantadine sulphate treatment compared with those treated with IFN-alpha alone. IFN-alpha/amantadine sulphate combination therapy was well tolerated without any serious adverse events. In conclusion, retreatment with IFN-alpha and amantadine sulphate does not increase the low sustained virological response rates of IFN-alpha therapy in primary IFN-alpha nonresponders with chronic hepatitis C, but may lead to a sustained improvement of health-related quality-of-life.