The biologic agents are a more recent introduction to the management strategy for psoriasis. These agents block specific components of the immune system, such as tumour necrosis factor-α (e.g. infliximab, etanercept) and interleukin-12/23 (e.g. ustekinumab). They are reserved for more severe or refractory forms of disease and patients must meet certain criteria for provincial reimbursement. For example, Ontario Drug Benefits will reimburse infliximab in adults with severe plaque psoriasis only if there has been failure, intolerance, or a contraindication to adequate trials of several standard therapies, including at least two systemic oral agents (i.e. methotrexate, acitretin, or cyclosporine). Given the side effect profile and limitations in the use of cyclosporine, this review evaluates the clinical effectiveness and safety of this treatment for moderate to severe plaque psoriasis in adults.