Studies on the functional activity of interferon (IF) system (interferon status and serum immunoglobulins levels) and its changes in the course of interferon therapy of juvenile respiratory papillomatosis are presented. The initial disorders in alpha-IF production and levels of circulating IF came to normal after interferon therapy. Correlative changes of the following parameters occurred: a decrease in the level of circulating IF and IgM and simultaneous increase in the level of alpha-IF and IgG which, however, did not always correlate strictly with the course of the disease and the kind of preparation used.