We investigated the oxidant-antioxidant balance and the effect of inhaled corticosteroids on this balance in mild stable asthmatics. Included in the study were 30 mild asthmatic patients (I I male, 19 female, mean age (year) +/- SD: 35.1 +/- 9.7) and 26 healthy adults (7 male, 19 female, mean age (year) +/- SD: 40.8 +/- 13.3). In all study groups, the peripheral venous blood samples were taken for plasma malonyldialdehyde (MDA), a parameter of lipid peroxidation caused by the oxidants, and erythrocyte superoxide dismutase (SOD), an antioxidant enzyme. The mean plasma MDA level was lower in the asthmatic group (5.7 +/- 1.2 nmol/ml) than in the healthy group (6.3 +/- 1.7 nmol/ml); and the mean erythrocyte SOD level was higher in asthmatic group (1086.4 +/- 247.4 U/gHb) than in the healthy group (1028.0 +/- 230.0 U/gHb). However, there were no significant differences in measurements of both plasma MDA levels and erythrocyte SOD enzyme activities between the groups (respectively, p = 0.1 and p = 0.4). When asthmatic patients were divided into subgroups as "inhaled steroid user" and "no inhaled steroid user", no significant differences were observed in the measurements of either plasma MDA level or erythrocyte SOD enzyme activity between the mentioned subgroups. According to the results of our study, we can say that oxidant-antioxidant balance is not significantly affected in mild asthmatics or measurement of plasma level of MDA and erythrocyte SOD enzyme activity is not sensitive to the oxidant-antioxidant balance in mild asthmatics.