OBJECTIVE: To examine the influence of viral respiratory infection (VRI) on treatment response in acute asthma in children. STUDY DESIGN: A total of 218 children (mean age, 6.6 years) with acute asthma were recruited. Symptoms were recorded, an asthma severity score was determined, and whenever possible, a per-nasal aspirate was obtained for detection of viruses. Each child\'s response to inhaled beta(2)-agonists was assessed after 6, 12, and 24 hours. RESULTS: The 168 children with VRI symptoms received more treatment with inhaled beta(2)-agonists after 6 hours (P = .010), 12 hours (P = .002), and 24 hours (P = .0005) compared with the 50 children without such symptoms. Asthma severity did not differ between the 2 groups. A per-nasal aspirate was obtained from 77% of the children. The most frequently identified virus was rhinovirus (61.4%). Among children with symptoms of a VRI, those with rhinovirus had an impaired response to beta(2)-agonists at 6 hours (P = .032). CONCLUSION: Children with acute asthma and symptoms of VRI respond less effectively to beta(2)-agonists after 6, 12, or 24 hours and thus may benefit from more intense therapy and monitoring.