Intravenous salbutamool or aminophylline was administered under double-blind conditions to 20 asthmatic patients presenting with severe dyspnoea and needing urgent treatment with bronchodilators. Ten patients received salbutamol and ten patients received aminophylline. Objective measurements showing improvement were recorded in nineteen patients. A greater response was produced by salbutamol although this failed to reach statistical significance. Neither drug affected pulse or blood pressure. It is suggested that intravenous salbutamol is an effective bronchodialtor in the treatment of acute exacerbation of asthma or bronchitis.