To assess whether the risk of chronic disease in patients with acute non-A, non-B/type C (NANB/C) hepatitis after transfusion could be reduced by treatment with interferon, patients were randomised to receive 3 million units interferon (IFN) alfa-2b three times a week for three months or no therapy. At the end of treatment, IFN had significantly reduced the number of patients with abnormal alanine aminotransferase activities compared with untreated patients but this difference was not maintained during a 15 month follow up. Treatment with IFN alfa-2b was considered safe and was well tolerated.