Racemic epinephrine has been advocated for the treatment of croup, but controlled studies have not proved it more effective than saline. Twenty patients (aged 4 months to 5 years) hospitalized with acute croup and persistent inspiratory stridor at rest were randomly assigned to one of two treatment groups: saline or racemic epinephrine, both nebulized and delivered by intermittent positive pressure breathing. Clinical scores were significantly improved (P less than .01) at ten and 30 minutes following the treatment with racemic epinephrine but not at 120 minutes. Racemic epinephrine was significantly more effective than saline at 10 (P less than .01) and 30 minutes (P less than .05) but not at 120 minutes after the treatment. We conclude that nebulized racemic epinephrine is effective treatment for the acute signs of croup.