Use of both l-epinephrine and racemic epinephrine (adrenaline) has improved clinical symptoms and composite respiratory scores in acute bronchiolitis. The objective of this randomized double-blind placebo-controlled study was to assess whether there was sufficient improvement in clinical state to reduce hospital admissions. Seventy-five infants aged 1 month to 1 year with a clinical diagnosis of acute bronchiolitis were treated with either 2 ml of 1:1000 nebulized adrenaline or 2 ml of nebulized normal saline administered after baseline assessment and 30 min later. Clinical respiratory parameters were recorded at 15-min intervals for a period of 2 h following the baseline assessment. Admission to hospital was the primary end-point and changes in respiratory parameters were secondary end-points. Fifty percent (19/38) of infants treated with adrenaline were discharged home compared with 38 percent (14/37) of those treated with saline. This 12 percent reduction in rate of admission is not statistically significant (95% CI of difference: -10% to 35%). There was no difference between treated and placebo groups in respiratory rate, oxygen saturation, heart rate or a composite respiratory distress score at 30, 60 or 120 min post-treatment. In this study, nebulized epinephrine did not confer a significant advantage over nebulized saline in the emergency room treatment of acute bronchiolitis.