Subjects with minimal-to-mild chronic hepatitis C may suffer long-term consequences of hepatitis C virus (HCV) infection. Nonetheless, they are not candidates for antiviral treatment, mainly because little data are available concerning the efficacy and safety of therapy. Thirty-two HCV RNA positive individuals aged 18-45 years, who had a histological activity index score < or = 8 and alanine aminotransferase (ALT) levels < or = 1.5 times lower than the normal limit for at least 1 year, were prospectively enrolled among a cohort of 35358 candidate blood donors, and treated with 4.5 mega units (MU) of recombinant interferon-alpha2a (IFN-alpha2a) thrice weekly for 6 months, and for an additional 6 months if a virological response was observed. Twelve months after the completion of treatment, 13 of 31 evaluable patients were HCV RNA negative, accounting for a sustained response rate of 42%. Patients without fibrosis had a lower response rate than those with mild fibrosis (two of 14 vs 11 of 17; P=0.012). In responders, median aminotransferase levels were significantly lower after therapy than before (11.04 +/- 3.98 vs 27.3 +/- 12.32 U l-1, respectively; P < 0. 005). When the analysis was limited to the six responders whose pretreatment aminotransferase levels were consistently normal, this difference was still significant (9.33 +/- 4.12 vs 20.58 +/- 6.73 U l-1; P=0.002). In conclusion, a durable suppression of viraemia can be obtained by IFN monotherapy in a relatively high proportion of young subjects with minimal-to-mild chronic hepatitis C, especially when portal fibrosis is found on liver biopsy. The disappearance of viraemia always leads to a reduction in the degree of hepatocellular necrosis.