Patients suffering from moderate-to-severe psoriasis may be treated with a variety of systemic agents and treatment modalities, including retinoids, phototherapy and/or immunomodulatory drugs, including methotrexate, ciclosporin and fumarates. Patients are regularly monitored to determine the efficacy of treatment and to detect signs of systemic toxicity. Indeed, lack of efficacy and/or therapeutic toxicity are factors which require a re-evaluation of therapy. In addition to the conventional systemic treatments, systemic "biologic" therapies are playing an increasingly important role in the management of moderate to severe psoriasis.These treatments have resulted from advances in the understanding of the patho-physiology of psoriasis, combined with advances in molecular biology, in order to provide a more targeted therapy. Biologics include drugs targeting the production or signal transduction of tumour necrosis factor alpha (TNFα), and more recently, agents which target specific cytokines known to play an important role in the disease, including interleukin (IL) 12/23.