BACKGROUND The pathogenetic mechanisms in vitiligo have not been clarified completely. One of the major hypotheses in the pathogenesis of vitiligo is the oxidative stress hypothesis. The active and stable phases of vitiligo are defined as the progression or appearance of new lesions in the last 3 months and the absence of new lesions or progression in the last 6 months, respectively. METHODS We examined the levels of malondialdehyde, catalase, glutathione peroxidase, and superoxide dismutase in the tissues of 10 patients with active vitiligo, 10 patients with stable vitiligo, and 20 matched healthy controls. RESULTS The results revealed that the levels of superoxide dismutase, glutathione peroxidase, and malondialdehyde in tissues were increased significantly in patients with active vitiligo relative to those in patients with stable vitiligo and matched controls; however, the levels of catalase in tissues were decreased significantly in patients with active vitiligo relative to those in patients with stable vitiligo and matched controls. CONCLUSIONS Our study shows that oxidative stress is involved in the pathophysiology of both active and stable vitiligo, but an increased imbalance of antioxidants is observed in the tissues of patients with active vitiligo.