Seventy-two patients with chronic hepatitis C were included in a randomised trial of lymphoblastoid interferon versus no treatment. Thirty-six patients entered each group. Interferon was given in a step-down schedule for 12 months. Aminotransferase activities became normal during treatment in 30 of 36 (83.3%) treated patients, but in only 1 out of 36 (2.7%) non-treated cases (p < 0.001). However, a reactivation of the disease during the interferon course was observed in 12 patients after a mean of 5.58 +/- 1.55 months of therapy, and a post-treatment relapse was observed in 5 additional cases. The remaining 13 patients (36%) had sustained normalization of the aminotransferase levels for 15.27 +/- 10.34 months (range 3-30) after discontinuation of interferon, thus representing a long-term sustained remission of the disease. Knodell's histological activity index decreased in all treatment patients, except for 3 non-responders (91.5%), but in only 9 of 36 non-treated cases (25%) (p < 0.001). Procollagen type III peptide levels normalized in most cases (83%) with a sustained response. A significant decrease in the detection of hepatitis C virus RNA was observed in patients with a sustained response (p < 0.05). Anti-interferon antibodies were only detected in one non-responder. Thus, interferon diminishes inflammatory and fibrogenic activity in the majority of patients with chronic hepatitis C and abolishes viremia in most of the patients with a sustained response.