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This overview summarizes some recent studies on the balance of oxidants to antioxidants in patients with asthma. The aim of the review is to compare studies on the changes in oxidants/antioxidants in stable asthma or in acute exacerbation of asthma.Our review of the recent literature in this field seems to indicate conflicting findings. Increased release of reactive oxygen species such as superoxide anion and hydrogen peroxide has been reported in exhaled breath condensates and from circulating granulocytes, and from the bronchoalveolar lavage cells of patients with asthma. In asthma, bronchial obstruction is associated with an increased spontaneous and stimulus-induced production of oxygen free radicals. The primary defense against reactive oxygen species is endogenous antioxidants, which are found to be altered in asthma. A marked decrease in plasma antioxidant capacity occurs. Superoxide dismutase activity is higher in erythrocytes and serum of asthmatic than in normal subjects and is diminished in cells from lavage and brushing samples of patients with asthma. Higher level of erythrocyte catalase activity has only been found in Chinese asthmatic patients while decreased glutathione peroxidase activity has been well documented.Since there are considerable discrepancies in erythrocyte or plasma antioxidant enzyme activity in patients with asthma, the problem at this time is attempting to sort out these conflicting results and to find their roles in the pathogenesis of asthma. There is good evidence that antioxidant compounds may have a potential role in the treatment of asthma, especially of asthma exacerbation.