The effects of two different treatment combinations of bronchial asthma on antioxidant defense systems and serum prolidase activity were investigated. The groups were organized as follows: the first group (control) consisted of healthy subjects. The second group (treatment 1) consisted of patients with bronchial asthma inhaling budesonide (2 × 400 mcg/d, as puff) + formaterol (2 × 9 mcg/d, as puff). In the third group (treatment 2) patients with bronchial asthma were treated with montelukast (1 × 10 mg/d, as pill) + budesonide (2 × 400 mcg/d, as puff) + formaterol (2 × 9 mcg/d, as puff). The medical therapy of the patients in treatment 1 and treatment 2 lasted 12 weeks. Before and after treatment in all three groups blood samples were taken and the level of thiobarbituric acid-reactive substances (TBARS) and the activities of prolidase, superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), glutathione reductase (GSSG-Rd) and catalase (CAT) were measured. Prolidase activity was found to be significantly higher in patients compared to control (p < 0.05). Treatment 2 was successfully reduced the prolidase activity (p < 0.05). Before treatments, SOD activity was significantly decreased whereas TBARS level and other antioxidant enzymes were increased in both treatment groups comparing with control (p < 0.05). Both of different treatments given in treatment 1 and treatment 2 groups caused significant increase in SOD whereas decrease in TBARS, CAT, GSSG-Rd, GSH-Px (p < 0.05). When compared the treatment groups after treatments, SOD activity was significantly higher in treatment 2 group than treatment 1 group (p < 0.05). No significant difference was seen in other parameters. The balance between oxidant-antioxidant system is impaired in patients with asthma. © 2005 Elsevier B.V. All rights reserved.