The effect of an oral immunostimulant on adult periodontitis was evaluated in a pilot study. The preparation is successfully administered in respiratory tract infections but has not been used in oral medicine. 11 patients were treated with a bacterial lysate for three months after completing a hygiene phase preceding the study protocol. At day 0 and after 30, 60, and 90 days of medication, parameters characterizing disease activity (bleeding on probing, probing depth, clinical attachment loss and suppuration) and oral hygiene (plaqueindex) were recorded and compared to 10 controls. The treatment resulted in reduced gingival inflammatory activity and diminishing probing depths which was significant compared to the controls (p < 0.001). The exact mechanism of action induced by immunostimulant therapy remains to be clarified. The promising results of this pilot study offer a new aspect in the therapy of periodontal disease. Further investigations are necessary to define the therapeutic value of this treatment in oral medicine.