Respiratory viruses have profound effect on airway function and the development of allergic reactions. We are particularly interested in the ability of respiratory viruses to promote the development of the inflammatory LAR. Present evidence suggests that the virus effects on LAR are multi-factorial including changes in inflammatory cell mediator release and the tissue-injurious properties of leukocytes. The end-result of these changes is reflected in the development of the late-phase allergic reaction. When this occurs in the airways, airway obstruction and reactivity will be greater. Uncovering the mechanisms of these effects will lead to a greater understanding of asthma and its pathogenesis.