Although several trials have been published evaluating intravenous magnesium sulfate as treatment for acute bronchospasm, its effectiveness for this indication remains unclear. This study is a meta-analysis that evaluated randomized controlled trials of adjuvant bolus intravenous magnesium sulfate for acute bronchospasm in the emergency department. Trials were identified using MEDLINE, EMBASE, bibliographies of selected articles, and review of abstracts of 4 scientific societies. Two reviewers abstracted data, one of whom was blinded to author and journal. Because studies used different spirometric outcome measures, effect size was calculated for each study by Hedges' method. The analysis used a fixed-effects model. One-way sensitivity analyses were performed to assess the influence of study quality and to search for publication bias. Abstracts from 210 articles were reviewed, yielding 40 trials, of which 9 were specific to bolus intravenous magnesium sulfate in the ED, in doses from 1.2 to 2 g, or an equivalent pediatric dose. Combined results across 9 studies including 859 patients showed a posttreatment effect size of 0.162 for patients treated with intravenous magnesium sulfate (95% confidence interval 0.028, 0.297; P =.02). In sensitivity analyses exploring the effects of study quality and publication bias, the summary effect ranged from 0.127 to 0.206. No serious adverse events were reported. The authors conclude that adjuvant bolus intravenous magnesium sulfate in acute bronchospasm appears statistically beneficial in improving spirometric airway function by 16% of a SD. Although the clinical significance of this is uncertain, given the safety of intravenous magnesium sulfate therapy and its relatively low cost, the authors suggest it should be considered, absent contraindications, in patients with moderate to severe acute bronchospasm.