Understanding of the pathogenesis of asthma has increased considerably during the past few years. These advances were possible through scientific progress in three areas which contribute to this complex and multifaceted disease: (a) the much clearer understanding of eosinophil function; (b) the defining of lipid mediators in tissue inflammation and bronchial obstruction; and (c) the growing knowledge about the biological action of a new class of protein hormones, collectively called cytokines. In line with this, evidence has accumulated of how these components may interact with each other in providing the basis of inflammatory processes in asthma. Hence it seems appropriate to review the potential implications of this new information for the pathogenesis and therapy of this disease.