Our concept of asthma has changed dramatically in the past decade. Although many factors contribute to airflow obstruction in asthma, there is now an expanded focus on all events in bronchial obstruction including bronchospasm, edema, mucous formation, and inflammation. The last of these airway changes, bronchial inflammation, not only causes symptoms of asthma but also contributes or is the cause of a basic characteristic of asthma: airway hyperresponsiveness. It has become apparent that asthma is a complex disease in which the causes of airflow obstruction are multi-factorial, multicellular, and redundant. It is important to identify the cellular mechanisms involved in airway inflammation and to understand how they contribute to changes in airway responsiveness and obstruction.