ABSTRACT BACKGROUND Beta-blockers are avoided in asthma over concerns regarding acute bronchoconstriction. Risk is greatest following acute exposure, including the potential for antagonism of beta2-agonist rescue therapy. MATERIALS AND METHODS A systematic review of databases was performed to identify all randomised, blinded, placebo-controlled clinical trials evaluating acute beta-blocker exposure in asthma. Effect estimates for changes in respiratory function, symptoms and beta2-agonist response were pooled using random effects meta-analysis with heterogeneity investigated. RESULTS Acute selective beta-blockers in the doses given caused a mean change in FEV1 of -6.9% (95%CI -8.5 to -5.2); a fall in FEV1 of =20% in 1 in 8 patients (P=0.03); symptoms affecting 1 in 33 patients (P=0.18); and attenuation of concomitant beta2-agonist response of -10.2% (95%CI -14.0 to -6.4). Corresponding values for acute non-selective beta-blockers in the doses given were -10.2% (95%CI -14.7 to -5.6); 1 in 9 patients (P=0.02); 1 in 13 patients (P=0.14); and -20.0% (95%CI -29.4 to -10.7). Following investigation of heterogeneity clear differences were found for celiprolol and labetalol. A dose-response relationship was demonstrated for selective beta-blockers. CONCLUSIONS Selective beta-blockers are better tolerated but not completely risk free. Risk from acute exposure may be mitigated using the smallest dose possible and beta-blockers with greater beta1-selectivity. Beta-blocker induced bronchospasm responded partially to beta2-agonists in the doses given with response blunted more by non-selective beta-blockers than selective beta-blockers. Use of beta-blockers in asthma could possibly be based upon a risk assessment on an individual patient basis.