I. Introduction Eosinophils are believed to be crucial effector cells in the chronic inflammation and bronchial hyperresponsiveness (BHR) underlying asthma. Eosinophil basic proteins can damage airway epithelium, and the eosinophil is increasingly seen as a source of inflammatory cytokines. However, it also produces a distinctive profile of autacoids, which includes the cysteinyl-leukotrienes, the only mediators so far proved beyond doubt to have a significant role in asthma. as well as platelet-activating factor (PAF) and 15-hydroxyeicosatetraenoic acid (15-HETE) (Fig. I). This chapter will describe the ways in which eosinophils produce and respond to these autacoids and outline the evidence implicating them in inflammation in the asthmatic lung.