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.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.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).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.