Bronchiolitis is an acute, highly communicable lower respiratory tract infection. Bronchodilators are commonly used in the management of bronchiolitis in North America, but not in the United Kingdom. The objective of this review was to assess the effects of bronchodilators for bronchiolitis.We searched MEDLINE, EMBASE, Reference Update, reference lists of articles, and the files of two of the authors up to June 1998.Randomised trials comparing bronchodilators with placebo in the treatment of bronchiolitis.Two reviewers independently assessed trial quality and extracted data. Unpublished data were requested from authors when necessary.In eight trials with 394 children, 46% demonstrated an improved clinical score with bronchodilators compared to 75% with placebo (odds ratio for no improvement 0.29, 95% confidence interval 0.19 to 0.45). However, the inclusion of studies that enrolled people with recurrent wheezes may have biased these results in favour of bronchodilators. Bronchodilator recipients did not show improvement in measures of oxygenation, the rate of hospitalisation (18% versus 26%, odds ratio 0.70, 95% confidence interval 0.36 to 1.35) or duration of hospitalisation (weighted mean difference 0.12, 95% confidence interval -0.3 to 0.5).Bronchodilators produce modest short-term improvement in clinical scores. This small benefit must be weighed against the costs of these agents.