P soriasis is a hyperproliferative disorder in which both adaptive and innate immunity play important roles. Traditionally, the treatment of moderate to severe psoriasis has been limited by the safety of many of the drugs that are effective in clearing the disease. As greater understanding of the immunopathology of psoriasis has developed, more targeted therapies have emerged with apparently fewer toxic side effects. The biologic agents act on precise steps in the immunologic cascade to control psoriasis. The hope for using biologics in moderate to severe psoriasis is to have safe and effective longterm management of this disease. In addition, for psoriatic arthritis, the goal is to inhibit structural damage and prevent disability. The 3 biologics that have been approved by the Food and Drug Administration (FDA) for the treatment of moderate to severe chronic plaque psoriasis are alefacept (LFA3TIP) and efalizumab (antiCD11a), both of which act via inhibition of T-cell activation, and etanercept, which is a soluble tumor necrosis factor (TNF) receptor drug. Etanercept is also FDA approved for controlling signs and symptoms and inhibition of radiographic progression of psoriatic arthritis. Two other TNF antagonists, infliximab and adalimumab, are in clinical trials for psoriasis. This article reviews the clinical trials that show efficacy of the biologics in psoriasis. We also