Objectives: To determine the effect of regular prophylactic inhaled corticosteroids on wheezing episodes associated with viral infection in school age children.

Design: Randomised, double blind, placebo controlled trial.

Setting: Community based study in Southampton.

Subjects: 104 children aged 7 to 9 years who had had wheezing in association with symptoms of upper and lower respiratory tract infection in the preceding 12 months.

Interventions: After a run in period of 2-6 weeks children were randomly allocated twice daily inhaled beclomethasone dipropionate 200 micrograms or placebo through a Diskhaler for 6 months with a wash out period of 2 months. Children were assessed monthly.

Main outcome measures: Forced expiratory volume in 1 second (FEV1); bronchial responsiveness to methacholine (PD20); percentage of days with symptoms of upper and lower respiratory tract infection with frequency, severity, and duration of episodes of upper and lower respiratory symptoms and of reduced peak expiratory flow rate.

Results: During the treatment period there was a significant increase in mean FEV1 (1.63 v 1.53 1; adjusted difference 0.09 1 (95% confidence interval 0.04 to 0.14); P = 0.001) and methacholine PD20 12.8 v 7.2 mumol/l; adjusted ratio of means 1.7 (1.2 to 2.4); P = 0.007) in children receiving beclomethasone dipropionate compared with placebo. There were, however, no significant differences in the percentage of days with symptoms or in the frequency, severity, or duration of episodes of upper or lower respiratory symptoms or of reduced peak expiratory flow rate during the treatment period between the two groups.

Conclusions: Although lung function is improved with regular beclomethasone dipropionate 400 micrograms/day, this treatment offers no clinically significant benefit in school age children with wheezing episodes associated with viral infection.