One hundred and fifteen patients with chronic type B, D and non-A, non-B hepatitis treated with recombinant alpha-interferon were tested for six different autoantibodies prior to or during therapy, and the course of treatment was compared in autoantibody-positive and -negative patients. Three out of 25 (12%) hepatitis B patients, 14 out of 30 (47%) hepatitis D patients and 19 out of 60 (32%) chronic non-A, non-B hepatitis carriers had baseline or post-therapy autoantibodies. The rate of response between patients with and without autoantibodies among B, D and non-A, non-B patients was, respectively, 67 vs. 79%, 23 vs. 25%, 70 vs. 61% (p = N.S.). No adverse reaction was observed in the 36 patients who had or developed nuclear, smooth muscle, parietal cells and thyroid autoantibodies during therapy. A patient with baseline antibodies against liver and kidney microsomes developed an icteric acute hepatitis at the fourth month of therapy, but five other patients with this reactivity responded to therapy uneventfully. The presence of autoantibodies before therapy or their induction following therapy is not a contraindication to the use of interferon in patients with chronic viral hepatitis.