Attention has been focused on role of a genetically determined skin barrier dysfunction in the pathogenesis of psoriasis. A study has provided evidence for the correlation of psoriasis with a low expression of genes encoding filaggrin and loricrin in skin biopsies taken from both psoriatic plaques and perilesional skin and analyzed by real-time PCR method. Family of genes encoding late cornified envelope proteins (LCE proteins) which is located within on chromosome 1q21.3 complex has shown abnormalities in patients with psoriasis. The objectives of the present study were to evaluate the serum levels of nitric and to investigate single nucleotoide polymorphism in nitric oxide