We evaluated oral ribavirin as therapy for chronic hepatitis C infection in a pilot study including 10 patients. Patients (7 men, 3 women; mean age 40 years, range 23-54) all had biopsy-proven chronic non-A, non-B hepatitis and were repeatedly positive for antibodies to hepatitis C virus. Treatment was with oral ribavirin 1000-1200 mg per day in two divided doses for 12 weeks. The median serum alanine aminotransferase concentration for all patients at enrollment was 3.15 mu kat/l (range 1.22-7.79) and decreased significantly (p less than 0.005) to 1.25 mu kat/l (0.78-2.04) after 12 weeks of treatment. Within 6 weeks of the end of treatment the median serum alanine aminotransferase concentration was not significantly different from that before treatment. Side-effects were mild and fully reversible after cessation of therapy. We conclude that ribavirin is the first drug to offer a potentially effective oral treatment for chronic hepatitis C. It should be further evaluated in controlled trials, possibly in combination with interferon alpha.