Alpha interferon is the only effective therapy in patients with chronic non-A, non-B hepatitis. Alpha interferon administration during 6 months, in a dosage of 3 millions units, three times per week, induces a complete response defined by the normalisation of transaminases in about 50 % of the patients. The normalisation of transaminases is correlated to an improvement of liver histologic activity. A relapse, with the reincrease of transaminases, is often observed after withdrawal of interferon. One year after therapy, less than 20 % of the patients treated have a sustained complete response defined by persistently normal transaminases. Studies are in progress about the efficacy of higher dosage or longer duration of alpha interferon administration.