BACKGROUND House dust-mites are potent allergens of the indoor environment and are common inhabitants of houses worldwide. Free radicals are constantly produced by cells, mostly as reactive oxygen species. Once produced, free radicals are removed by antioxidant defenses, including the enzymes SOD, GPx, and CAT. METHODS The aim was to describe the importance of the antioxidant enzymes SOD, GPx, and CAT co-acting in hunan cells against toxic reactive oxygen species and their relationship with pathophysiological processes in stubjects who have dust-mites in their homes. RESULTS The activities of erythrocyte GPx and SOD in skin-test-positive (dust-mite-positive/negative) patients were significantly lower than those in dust-mite- and skin-test-negative controls (p < 0.05). Among the skin-test-positive patients, SOD activity was found to be lower in dust-mite-positive than in dust-mite-negative patients (p < 0.05). There was not a statistically significant difference between the CAT levels of skin-test-positive (dust-mite-positive/negative) patients and dust-mite- and skin-test-negative controls (p > 0.05). CONCLUSIONS This study clearly shows that dust-mite depresses the activities of SOD, GPx, and, to a small extent, CAT; which influence cellular reducing capacity and consequently may increase asthma risk more than other allergens.