We assessed the long-term outcome in 24 patients with chronic hepatitis C who responded to alpha interferon. All patients were followed up for 12 months, and 16 patients were followed up 41 +/- 9 months. During the follow-up period, 18 of the 24 patients (75%) relapsed (serum ALT levels increased again); 16 had an early relapse within the 6 months and two had a late relapse 21 and 36 months after therapy; one cirrhotic patient with relapse died. Serum HCV RNA remained detectable in the two patients before the late relapse and in three of the six patients with sustained biochemical response. Histologic assessment 13 to 31 months after therapy showed a decrease in activity in most patients, even in some of those with relapse, but the decrease in portal inflammation was more marked (p < 0.05) in patients with sustained biochemical response. Liver HCV RNA was not detectable in the two sustained responders who were negative for serum HCV RNA. Despite biochemical remission induced by interferon therapy, HCV replication persists in many patients with a potential risk of late relapse. In contrast, some patients have no long-term detectable HCV RNA, suggesting clearance of HCV. Long-term histologic improvement of portal inflammation in most patients confirms the beneficial effect of interferon.