The primary rationale for this study is to evaluate the effect of once daily montelukast on duration of acute illness in infants with first-time bronchiolitis.

Inclusion Criteria:

• Male or female infants aged 3 to 12 months of age
• Diagnosis by emergency physician of bronchiolitis

Exclusion Criteria:

• Any previous episode, as determined by a physician, of wheezing, bronchiolitis or asthma
• Any history of previous bronchodilator use prior to this illness
• Treatment with corticosteroids in the 14 days prior to the current illness
• Immunosuppression
• Immunodeficiency
• Caregiver does not speak English
• Diagnosis by the treating ED physician of croup
• Diagnosis by the treating ED physician of pneumonia
• Caregiver does not have access to a telephone

4 weeks

Assessment was made via weekly follow up telephone interviews