Asthma is a chronic inflammatory lung disease in which eosinophils are one of the most important involved cells. These cells accumulate in the lung because of cytokines, which are able to regulate cellular responses. The role of cytokines is well known in allergic asthma: IL4, IL5, IL3, GMCSF are the principally cytokine involved. IL4 regulate IgE synthesis while IL5, (and IL3) cause the activation and accumulation of eosinophils. In non allergic asthma, whilst only IL5 seemed to be important recent data, shows that also IL4 plays an important role. Therefore nowadays no relevant difference seems to exist between allergic and non allergic asthma; instead the primer is different: the allergen in allergic asthma and often an unknown factor in the non allergic asthma. Recently other cytokines have been proved to play a role in the pathogenesis of asthma. IL8 is chemotactic not only for neutrophils but also for eosinophils and might cause chronic inflammation in severe asthma. IL13 works like IL4, while RANTES seems to be a more important chemotactic agent than IL5. Finally IL10, which immunoregulates T lymphocyte responses, may reduce asthma inflammation. In conclusion cytokine made us to learn more about the pathogenesis of asthma even if we do not yet know when and how asthma inflammation develops.