Although interferon-a (IFK-a) has been used for the treatment of chronic hepatitis C, its effectiveness is often limited Ribavirin, a nucleoside analog agent with a broad spectrum of antiviral activity, has been reported to decrease serum ALT levels in chronic hepatitis C patients. Ribavirin (600 mg/day) was given to 34 patients with type C chronic liver diseases (20 chronihepatitis, 14 cirrhosis) for 3 months (19 patients) and 6 rnonths (15 patients), respectively. The efficacy was evaluated by measuring serum alanine aminotransferase (ALT) levels. Serum ALT levels gradually decreased in both groups after administration cf ribavirin, but statistical significance could not be observed. After treatment, decrease of serum ALT more than 50% of pretreatment level was found in 32% in 3 months group and in 20% in 6 months group. 3 to 6 rnonths after cessation of ribavirin therapy, sustained normal ALT was observed in 15% among 26 patients. No significant side effect was found during ribavirin therapy. It is suggested that although ribavirin decreases serurn ALT levels in chronic HCV-related liver disease, it is not effective in controlling disease activity as a single agent.