T helper (Th) type 2 cytokines, particularly interleukin (IL)-4, IL-5, and IL-13, may be important in the development of allergic asthma. Humanized monoclonal antibodies (MoAbs) against IL-5 and a recombinant human soluble IL-4 receptor (sIL-4R) have been developed as possible treatments. These approaches have not yet proven to be successful in patients with persistent asthma. This may suggest that neither IL-4 nor IL-5 is important in asthma pathogenesis. There is, however, insufficient information about the efficacy of sIL-4R and the anti-IL-5 MoAbs in asthma to draw any firm conclusions about the importance of these Th2 cytokines. Also, the administration of the potentially antiinflammatory cytokines IL-12 and interferon-γ has not shown benefit in asthmatic patients. By contrast, the treatment of severe oral steroid-dependent asthma with soluble tumor necrosis factor-α receptor has demonstrated very promising results, suggesting that this cytokine plays an important role in the persistence of severe asthma.