The authors assess the therapeutic efficacy of kemantan, an immunomodulator, used in the treatment of 30 patients with severe stubborn recurrent aphthous stomatitis (RAS). The blood immunological and biochemical characteristics were checked up over the course of treatment. Clinical and laboratory studies have shown that this immunocorrective agent is sufficiently effective for fibrous and cicatrizing RAS running a permanent course: the periods of the pathologic elements epithelialization are shortened, the permanent course of the condition is interrupted and the remissions are prolonged; clinical cure has been achieved in a number of cases. Kemantan is indicated for RAS patients only in cases with immunologic insufficiency, with immunologic responses monitored over the course of the treatment.