The aim of this study done in patients with periodontitis was (a) to determine superoxide anion production in whole blood by measuring cytochrome c reduction; (b) to assess the effects of oxidative burst in periodontal disease by analyzing lipid peroxidation and degradation of DNA bases in the peripheral and gingival blood; (c) to search for associations between superoxide anion production, lipid peroxidation, 8-hydroxy-2-deoxyguanosine concentration and clinical parameters. Total antioxidant status in peripheral and gingival serum was also studied and correlated with periodontal clinical status. The effects of some risk factors of periodontitis on oxidative stress were analyzed. The study group included 56 patients with untreated periodontitis. The control group consisted of 25 healthy volunteers without any pathological changes in the periodontium. The most important findings of the study are: (a) negative correlation between cytochrome c reduction and periodontal disease index in the study group (p=0.026); (b) positive correlation between anti-ox-LDL autoantibody titres in gingival blood and 8-OHdG levels in venous blood (p<0.001); (c) negative correlation between 8-OHdG concentration in venous blood and total antioxidant status (TAS) in gingival blood serum in patients and positive correlation in controls; (d) significantly higher levels of 8-OHdG in gingival blood in each subgroup of patients as compared with controls; (e) significantly lower TAS in venous blood serum in each subgroup as compared with controls; (f) negative correlation between 8-OHdG concentration in gingival blood and TAS in venous blood serum (p=0.028). Oxidative stress in periodontitis expressed by elevated concentrations of ROS and accompanied by suppressed antioxidant activity in gingival blood may accelerate lesion formation in periodontal tissues.