Rats with spontaneous periodontitis develop lipid peroxidation in the blood and periodontal tissues, that is associated with hypercoagulation and fibrinolysis inhibition, reduced antiaggregation activity of the periodontal tissues. Administration of periodontal cytomedin results in normalization of lipid peroxidation, blood coagulation, and euglobulin lysis, as well as in increase in the activities of periodontal antioxidant enzymes and antiaggregation properties. Cytomedin effect on lipid peroxidation and antioxidant enzymes was more manifest in periodontal tissues than in the blood. Visual examination has shown an improvement of the periodontal tissue status, thus indicating good prospects for such therapy.