PURPOSE: Acute bronchiolitis is a lower respiratory tract disease, resulting from inflammatory obstruction of the small airway. The main treatment of acute bronchiolitis is supportive but, numerous investigators have examined the efficacy of beta agonist as bronchodilators. In acute bronchiolitis, mucosal edema in the bronchioles may be an important cause of airway obstruction therefore, an alpha and beta agonist might be useful in the treatment of this disease. So we examined the efficacy and safety of repeated nebulized epinephrine compared to fenoterol. METHODS: This randomized double blind study involved 106 hospitalized infants with wheezing, under one year age and acute onset of respiratory distress. They were randomly separated into two groups, and treated with either nebulized 0.1% epinephrine 0.5 mg in 3.5 mL of 0.9% saline solution (group 1; n=50) or nebulized fenoterol 0.5 mg in 2 mL of 0.9% saline solution(group 2; n=50). This therapy was repeated at six hour intervals after hospital admission. Observations were made at admission and just before, 30 minutes after nebulization. The primary outcome measures used were the degree of change in clinical scores. The secondary outcome measures used were the length of the hospital stay. RESULTS: A significant improvement in the clinical score was noted during 72 hours of hospitalization in both groups(P<0.001). But, there were no significant differences between the groups in clinical score improvement. There were no significant differences between the groups in the length of the hospital stay(P=0.055). No adverse effects were associated with nebulized therapy. CONCLUSION: There were no group differences in the effectiveness of therapy for infants hospitalized with acute bronchiolitis.