During recent years it has become apparent that the eosinophil may represent a powerful effector cell in the pathogenesis of asthma, particularly in the late asthmatic response. It can be stimulated by a number of stimuli among which PAF appears to be one of the most effective. The eosinophil is a source for a variety of proinflammatory and toxic products with profound effect in the lungs and airways. These eosinophil products mimic some of the features of asthma and the strong association of the eosinophil with asthma has led to the suggestion that asthma would be better classified as "chronic desquamating eosinophilic bronchitis." Although the evidence known to date is persuasive many questions still remain unanswered and await further investigation. Future therapeutic approaches in asthma may aim at interrupting the mechanisms leading to eosinophil bronchial accumulation and activation.