This Seminar is based on PubMed, ISI Web of Knowledge search for articles with "interleukin-13" in conjunction with "asthma," "airway hyperreactivity," "fibrosis," "single nucleotide polymorphism," "chitin," "aspirin exacerbated respiratory disease," "aspirin," "signaling," "mucus," glucocorticoid," "infection" in combination with "treatment" keywords, and other review articles and references from those review articles deemed relevant. This evidence concerns the gene IL13 and respiratory system disorder.