Psoriasis is a chronic inflammatory skin disease, which is clinically characterized by scaly erythemas on the whole body. In the fully developed lesions of psoriasis, the histological features have demonstrated epidermal hyperproliferation with infiltration of T lymphocytes in the dermal papillae. Although pre-biological systemic therapies has targeted mainly proliferative keratinocytes and activated T cells, their effects were limited or these therapies could not be applied for patients with severe organ failures. Therefore, more effective agents are expected to improve quality of life （QOL） of patients with psoriasis. Recent studies have showed what kinds of cells, cell surface molecules, and cytokines should play a pivotal role in the pathogenesis of psoriasis. Biological therapies targeting these molecules have proved to be so effective for obstinate lesions of psoriasis. Here, we describe clinical features and pathogenesis of psoriasis, and the characteristics of several conventional and biological therapies for psoriasis in Japan
