Background: Psoriasis is a chronic inflammatory disease of theskin. The etiology of psoriasis is not known exactly. Recently, ithas been suggested that an imbalance in the oxidant- antioxidantstatus due to an increased reactive oxygen species production and/or deficient function of the antioxidant system may be involvedin the pathogenesis of psoriasis. The aim of this study was toevaluate the antioxidant defense status in patients with psoriasisand to look for a correlation, if any, between the antioxidantdefense status and the severity of psoriasis.Method: Sixty patients with psoriasis and an equal number ofage and sex matched healthy controls were enrolled in the study.Plasma levels of malondialdehyde (MDA), reduced glutathione(GSH), and superoxide dismutase (SOD), and antioxidant potential(AOP) were measured in cases as well as controls.Result: Patients with psoriasis were found to have significantlyhigher levels of plasma SOD (P < 0.001) and MDA (P < 0.001)and lower levels of GSH (P < 0.001) than controls. Plasma AOPwas not significantly different between patients and controls(P= 0.822).Conclusion: The results of our study support the hypothesisof an imbalance in the oxidant –antioxidant status in psoriasis,which could contribute to the pathogenesis of psoriasis.