The airway obstruction is asthma results not only from bronchospasm but also from inflammatory edema, desquamation of ciliated epithelium and plugs in the lumen of airways. A final explanation for the characteristic hyperreactivity of the airways will include not only an explanation for the bronchospasm but also for this exuberant inflammation. One hypothesis to explain the hypersensitivity is a defect in stimulus-response coupling that renders not only smooth muscle cells but other cells overreactive. Isolated leukocytes have been used as a model to identify and begin to characterize possible abnormalities in stimulus-response coupling. Information thus for available indicates that leukocytes from patients with asthma respond poorly to agonists that activate adenylate cyclase and that a similar abnormality arises in normal cells exposed in vitro to supernates of respiratory virus infected tissue cultures.