It has been believed that the increased release of free oxygen radicals ($O_2^-,H_2O_2$, and $OH^-$) might be a factor in the pathogenesis of periodontal diseases. Antioxidant enzymes such as glutathione peroxidase(GSH-PX) and catalase can protect the tissue damage from the $H_2O_2$. In order to investigate the GSH-PX and catalase activity in the blood plasma and red blood cells(RBCs) of the patients with periodontitis, 19 patients who had good general health, attachment loss more than 6 mm and bone loss were selected as periodontitis group, 7 patients who had severely inflamed gingiva were selected as gingivitis group, and 15 volunteers with good general and periodontal health were selected as normal group. 17 of 26 patients were performed scaling and root planing to reduce the gingival inflammation for gingivitis and periodontitis groups, and were selected as posttreatment group. After blood plasma and RBCs were collected and separated 1 ml of peripheral blood from each subject, GSH-PX activity in blood plasma and RBCs was measured by the same method that Stefan et al. did, and catalase activity in RBCs was measured by the same method that Beers et al. did. The difference of GSH-PX and catalase activity between normal, gingivitis, and periodontitis groups was statistically analyzed by ANOVA with SPSS/PC+ program, and the difference between pretreatment and posttreatment groups was analyzed by Student t-test. The results were as follows : 1. GSH-PX activity in blood plasma was significantly lower in the gingivitis group($0.8683{pm}0.0658$), periodontitis group($0.7130{pm}0.1333$) than in the normal group($1.0241{pm}0.0801$)(p<0.05), and GSH-PX activity in RBCs was significantly lower in the gingivitis groupt. $0.8156{pm}0.1167$), periodontitis group($0.7533{pm}0.1185$) than in the normal group($l.1963{pm}0.2044$)(P<0.05), but there was no statistical significance in the difference of GSH-PX activity in RBCs between the gingivitis group and periodontitis group(p>0.05). 2. Catalase activity in RBCs was siginficantly lower in the periodontitis group($117.34{pm}35.01$) than in the normal group($l52.38{pm}32.09$)(p<0.05). 3. GSH-PX activity in blood plasma was significantly increased in the posttreatment groupe $1.0376{pm}0.2820$) compared to the pretreatment group(0.7608 0.1600) (p<0.05), and GSH-PX activity in RBC was significantly increased in the posttreatment group($1.0421{pm}0.2330$) compared to the pretreatment group($0.7728{pm}0.1210$)(p<0.05). 4. There was no statistical significance in the difference of catalase activity in RBCs between the pretreatment group($112.04{pm}43.65$) and posttreatment group($l33.41{pm}39.16$)(p>0.05).The results, within the limits of the present experiment, suggest that the lowered activity of GSH-PX and catalase in blood plasma and RBCs may be related with periodontopathogenesis.