1-year or longer treatment of juvenile respiratory papillomatosis (JRP) with alpha-2 interferons (A21) leads to emergence of antibodies to A21 in 54.3% of the patients. The greatest percentage of the antibody positives (94.4%) was found among JRP patients treated with intramuscular recombinant human A21 (reaferon). The proportion of the antibodies carriers fell to 15.4% if reaferon was used as a component of the new preparation viferon. JRP patients have also autoantibodies to A21 and gamma-interferon (8.74 and 33.3%, respectively). Patients with autoantibodies to gamma-interferon responded well to treatment with A21. Antibodies to A21 seem to have no negative effect on interferon therapy of JRP. Reaferon and viferon can be effectively used in JRP treatment.