Psoriasis is a chronic skin disorder that affects approximately 2% of the US and European population. Over the last several years one of the major foci in psoriasis research has been the development of biological therapies for this disease. The aim of these therapies is to provide selective, immunologically directed intervention with fewer side effects than traditional therapies. This article will review the progress of four biological agents that are available or under investigation for clinical use: infliximab (Centocor Inc), etanercept (Amgen Inc/Wyeth), efalizumab (Genentech Inc/XOMA Ltd/Serono SA) and alefacept.