In this 12-week phase 2 trial, a humanized anti–interleukin-17 monoclonal antibody was effective for chronic plaque psoriasis. Larger studies of longer duration are necessary to assess the safety and efficacy of long-term treatment. Psoriasis vulgaris (plaque psoriasis) is a chronic, frequently painful, and often debilitating skin disorder. The estimated prevalence of diagnosed psoriasis in the United States is 3%, with approximately 17% of these patients having moderate-to-severe plaque psoriasis. 1 Psoriasis is characterized by inflammation and keratinocyte hyperproliferation 2 thought to be the pathological consequence of a T-cell–mediated immune response to an as-yet unidentified autoantigen. Studies have shown that a subgroup of CD4+ T cells, type 17 helper T (Th17) cells, may play a specific pathological role in psoriasis. 3 Type 17 helper T cells secrete a number of proinflammatory cytokines, including interleukin-17A, a member of . . .