BACKGROUND/AIMS: Hepatitis C virus(HCV) was known to most common etiologic agent of chronic liver disease in United states and Japan. Although hepatitis B virus(HBV) was well known to be a its major etiologic agent in Korea, it has been showed that HCV and HBV are associated with liver cirrhosis and hepatocellular carcinoma as major causative agent of chronic liver disease. Interferon alpha therapy is generally accepted as effective single agent for chronic hepatitis or to decrease the chronicity of acute hepatitis C. So, we evaluated the efficacy of interferon alpha in hepatitis C. METHODS: 46 patients who were positive for anti-HCV antibody and HCV RNA were included in this study. Liver biopsy was per formed on all patients and all of them were tested as negative for serum HBsAg, anti Hbe. Patients were divided into 2 groups . 30 patients received interferon therapy(treated group) and 16 patients received no therapy(untreated group). We compared the change of liver function test and HCV RNA before and after therapy between two groups. Treated group was subdivided into 5 groups according to response to interferon therapy '. Non-response, partial response, breakthrough, relapse and sustained response. RESULTS: 1) The mean age and sex distribution were 49.9 year old, male 19, female 11 in treated group and 48.7 years, male 12, female 4 in untreated group. 2) The number of patients with acute hepatitis, chronic persistent hepatitis, chronic active hepatitis and liver cirrhosis were 1, 2, 23, 4 in treated group and 0, 1, 12, 3 in untreated group, respectively. 3) The mean follow up period was 1.7 year and 2.3 years in treated and untreated group, respectively. 4) The activity of serum ALT before and after therapy were 195+ 134.6 IU/L, 87.4+ 40.5 IU/L and 186.7+ 106.4 IU/L, 157+ 87.1 IU/L in treated and untreated group, respectively. Serum ALT after therapy in treated group was significantly lower than untreated group(P0.05). 6) The case of negative conversion for HCV RNA in treated group was 12, but there was no case in untreated group. 7) Sex distribution of sustained response was 6(31% ) of 19 male, 6(54.5%) of 11 female and 12 patients(40.0%)(1 of 1 patients with acute hepatitis, 1 of 2 chronic persistent hepatitis, 10 of 23 chronic active heaptitis) included in sustained reponse, but any patients with liver cirrhosis had response. 8) Mean total dose and duration of interferon therapy was non-response 10353.6 million unit(MU)/5.8month(M), partial response 20025.06MU/6.4 M, breakthrough 36000.0MU/5.0M, relapse 11700.0MU/3.3M, sustained response 28100.0MU/6.6M, respectively. 9) 3 of 7 patients who were followed up over 1 year in sustained response and mean time to the relapse was 2.2 years. CONCLUSION: Our results showed that interferon alpha therapy is effective in patients with hepatitis C and further study and attempts should be performed to augument the efficacy of interferon alpha for the treatment of hepatitis C.