Psoriasis is a chronic inflammatory, proliferative skin disease characterized by pathological skin lesions due to various exogenous and endogenous factors. It is associated with a number of biochemical and immunological disturbances. Recently, it has been suggested that increased reactive oxygen species (ROS) production and compromised function of antioxidant system may be involved in the pathogenesis of this disease. In the present study, 90 psoriasis patients were selected. Disease severity was assessed by psoriasis area severity index score and grouped as mild, moderate and severe (each group consists of 30 subjects) and compared with 30 healthy controls. Serum levels of malondialdehyde, nitric oxide end products and the activities of antioxidant enzymes such as erythrocyte-superoxide dismutase, catalase and total antioxidant status were investigated in these groups/subjects. As compared to controls, we found severitywise significantly increased serum malondialdehyde, nitric oxide end products with decrease in erythrocyte-superoxide dismutase activity, catalase activity and total antioxidant status in patients with psoriasis suggesting worsening of the disease. It seems to be linked with the enhancement of Reactive Oxygen Species production and decreased antioxidant potential in psoriasis.