trial with blinding of investigators, health care providers, and parents. • Setting – A single urban tertiary care pediatric ED during 2 bronchiolitis seasons, from November 1 to April 30 of 2010 and 2011. • Patients – Inclusion: (1) Aged 2 to <24 months, (2) first episode of bronchiolitis (wheezing with signs and symptoms of respiratory distress and upper respiratory infection), (3) Respiratory Distress Assessment Instrument (RDAI) score of 4-15 after albuterol treatment. – Exclusion: (1) History of wheezing or asthma, or bronchodilator therapy before current illness, (2) chronic lung or heart disease, (3) critical illness, (4) inability to receive nebulized medications, (5) non–English- speaking guardians. Methods