Eosinophils are the most characteristic inflammatory cells in the airway mucosa in asthma. Eosinophils release highly toxic products and cytokines which may influence the immune system, amplify the inflammatory response and participate in damaging and remodeling processes that occur in the airway mucosa. Eosinophilic inflammation in asthma is related to the blunted perception of bronchoconstriction. The magnitude of eosinophil influx and the degree of activation of these cells in the airway mucosa are related to the severity of asthma and appear to play a key role in some cases of asthma death. The number and activation of eosinophils in the airway mucosa are related to the magnitude of airway hyperresponsiveness to bradykinin but not to an agonist acting directly on smooth muscle such as methacholine. Inhaled corticosteroids reduce eosinophil inflammation in asthma whereas beta 2-agonists appear to increase the magnitude of eosinophilic inflammation induced by allergen exposure. The eosinophilic inflammation can be assessed by non-invasive methods using sputum analysis and, indirecly, by measuring the airway reactivity to bradykinin.