The airway wall of asthmatic patients is infiltrated with inflammatory cells, consisting chiefly of eosinophils and T lymphocytes. Among these T lymphocytes, Th2 cells are involved in the regulation of the IgE immune response and local allergic inflammation, which underlie allergic diseases. Various cytokines produced and released by Th2 cells play important roles in the development of many allergic diseases, including asthma, and the exacerbations of their disease states. Therefore, targeting of Th2 cell-derived cytokines is a rational therapeutic strategy for the treatment of asthma. Corticosteroids and immunosuppressive agents can potently inhibit Th2 cytokine-mediated responses, but have no selectivity for Th2 cells: they also exert pharmacological activity against cells other than inflammatory cells, thereby potentially causing adverse side-effects. However, suplatast tosilate is the only specific Th2 cytokine inhibitor that can be used clinically and it has been used widely in Japan as a maintenance drug in the treatment of asthma, atopic dermatitis and allergic rhinitis. There is considerable evidence of the effectiveness of suplatast tosilate in patients with mild asthma or moderate persistent asthma. Furthermore, an effect on cough variant asthma and a steroid-sparing effect have also been reported for suplatast tosilate.