The immunocorrective activity of bonaphthon, an antiviral agent, was studied in 27 patients with chronic diseases of the buccal mucosa (recurrent aphthous stomatitis, lichen ruber planus, Melkersson-Rosenthal's syndrome). Bonaphthon therapy resulted in quite a number of patients in elevation of serum interferon titer and of the titer of specific antiherpetic antibodies. These results evidence that, besides the antiviral effect, bonaphthon is characterized by an immunomodulating effect and is conducive to fortification of the defense potential of the body in patients with stubborn chronic diseases of the buccal mucosa.