Efalizumab (Raptiva, Genentech/Xoma) is a humanized monoclonal antibody of CD11a that exerts its effect through the blockade of the interaction between leukocyte function-associated antigen-1 (LFA-1) and intercellular adhesion molecule-1 (ICAM-1). FDA recently granted approval for efalizumab in the treatment of chronic moderate-to-severe plaque psoriasis in adults aged 18 years and older. Efalizumab does not achieve clinical response rates equal to cyclosporine or methotrexate, but it lacks the systemic organ toxicities of these agents and is associated with a more rapid onset of action (significant improvements in Psoriasis Area and Severity Index [PASI] response after 2 doses). In addition, efalizumab will likely compete with another approved biologic, alefacept, and off-label use of 2 other biologics currently on the market, etanercept and infliximab. At this time, until further studies comparing efalizumab to other drugs indicated for the treatment of psoriasis are completed and post-marketing surveillance is conducted, the agent?s place on the formulary remains unclear.