The development of autoantibodies and autoimmune reactions has been reported during and after interferon (IFN) therapy. Thirteen different antibodies from the sera of 32 patients with chronic hepatitis B treated with alpha-interferon (alpha-IFN) were tested. Seventeen HBeAg-positive patients received 4.5 megaunits (MU) of recombinant IFN thrice weekly for 4 months, and 15 anti-HBe and HBV-DNA positive patients were treated with 5 MU/m2 of lymphoblastoid IFN thrice weekly for 6 months. Five patients (15%) had antinuclear antibodies (ANA) and one patient (3%) had smooth muscle antibodies before treatment. ANA appeared during IFN treatment in five (18%) of 28 previously negative patients. With discontinuation of treatment, the titer of ANA fell to undetectable levels in all patients. In contrast, none of the patients developed antibodies to endocrine organs, such as thyroid microsomal, thyroglobulin, parietal cells, pancreatic islet cell, and adrenal cortex antibodies or autoantibodies specifically associated with autoimmune liver disease such as liver kidney microsomal antibodies and antimitochondrial antibodies. There was no correlation between autoantibody positivity before therapy or autoantibody occurrence during treatment and response to IFN therapy. None of the patients developed clinical signs of autoimmune disease. These results indicate that these regimens of recombinant and lymphoblastoid IFN therapy of chronic hepatitis B are associated with a low risk of clinically significant autoimmunity.