The Hepatitis Delta Virus (HDV), a defective ribonucleic acid virus dependent on the Hepatitis B Virus (HBV) is a cause of severe liver disease that often leads to cirrhosis and death. Since the HDV finds in the HBV infection a biological niche in which to thrive indefinitely, the major victims of its infection are the carriers of HBsAg. Spontaneous resolution of chronic HDV hepatitis has been observed rarely and therapeutic attempts with steroids or azathioprine and levamisole have been discouraging. With the advent of recombinant DNA technologies several human alpha-interferons (IFNs) have been synthesized by genetic engineering and the availability of large amounts of the drug has dramatically altered the therapeutic prospects of viral hepatitis. In view of the wide range of biological activities of IFN, including inhibition of viral nucleic acid replication, we have tested the tolerance and the efficacy of this drug in chronic HDV hepatitis. The preliminary results of this study are reported.