In a randomized controlled trial of Interferon (IFN) in 60 patients (30 treated and 30 controls) with cryptogenic chronic active liver disease, 70% of treated patients showed complete response, but a high rate of biochemical relapse (62%) was noted. In these cases, a second response to higher doses of IFN has been more difficult and less frequent. A response to IFN was found in 88.5% of anti-HCV positive treated patients and only in 25% of anti-HCV negative. We suggest that serum anti-HCV is a suitable test to predict the response to IFN.