We believe that genetic factors also influence response to β2-AR agonist therapy in children with bronchiolitis. Specifically, we believe that β2-AR polymorphisms at amino acid position 16 affect response to acute β2-AR agonist therapy in children with bronchiolitis. Our hypothesis is that children with bronchiolitis who are homozygous for glycine at amino acid position 16 (Gly/Gly) will have improved response to inhaled β2-AR agonist therapy.