It has been believed that the increased release of free oxygen radicals and their tissue damaging potency might be a contributing factor in the pathogenesis of periodontal disease. Antioxidant enzymes such as superoxide dismutase(SOD) and catalase can protect the tissue damage from the free oxygen radicals($O_2^-,H_2O_2$, and $OH^-$). In order to investigate the SOD- and catalase - activity in the blood plasma and red blood cells(RBCs) of the patients with perodontitis, 19 male periodontitis patients($25{sim}35$ years old) who had good general health, more than 10 teeth with severely inflamed gingiva, attachment loss more than 6mm and bone loss were selected as periodontitis group, and 13 male volunteers($22{sim}29$ years old) with good general and periodontal health were selected as normal group. After blood plasma and RBC were separated from peripheral blood of 2ml collected from antecubital vein of each subject, SOD- activity in blood plasma and RBCs was measured by the same method that Paoletti et al. did, and catalase - activity in RBC was measured by the same method that Beers et al, did. The difference of SOD- and catalase - activity between the normal and the periodontitis groups was statistically analyzed by Student t-test with SPSS/PC program.The results were as follows : 1. SOD activity in blood plasma was significantly lower in the periodontitis group($1.986{pm}0.893$) than in the normal group($3.324{pm}1.044$)(p<0.05). 2. There was no statistical significance in the difference of SOD- activity in RBCs between the periodontitis group($7.753{pm}3.206$) and the normal group($8.116{pm}1.192$)(p<O.05). 3. Catalase activity in RBCs was siginficantly lower in the periodontitis group($242.8{pm}45.6$) than in the normal group($280.2{pm}32.6$)(p<O.O5). The results, within the limits of the present experiment, suggest that the lowered activity of SOD in blood plasma and catalase in RBCs may be related with periodontal destruction.