BACKGROUND Dust-mites are present in our homes, feed on dead exfoliated skin and other organic material. It is also known that oxidative stress may lead to cellular damage that can be confirmed by markers of cellular disruption. Oxidative stress in various infective processes has been documented. We investigated whether house dust-mites cause oxidative stress in patients. METHODS Products of lipid peroxidation in erythrocytes and lymphocytes were assessed by measuring malondialdehyde concentration. RESULTS Our results showed that patients who had a positive skin test for dust-mite antigens and had dust-mites present in their houses (dust-mite positive) had increased erythrocyte malondialdehyde levels (62.39 [18.56] nmol/g-Hb) compared with those who were skin test positive, dust-mite negative (45.45 [10.82]) or skin test negative, dust-mite negative (42.20 [5.68]). They also had significantly higher levels of lymphocyte malondialdehyde (4.22 [0.55] nmol/g-protein) compared with those who were skin test positive, dust-mite negative (3.46 [0.29]) or skin test negative, dust-mite negative (1.25 [0.31]; p <0.05). However, there was no statistically significant difference between the malondialdehyde levels of dust-mite negative/skin test positive and dust-mite negative/skin test negative patients. CONCLUSIONS Increased malondialdehyde activity in lymphocytes and erythrocytes in the dust-mite positive/skin test positive group shows the presence of the oxidative stress in patients with dust-mite infestation.