In a randomized double-blind trial an intravenous injection of salbutamol (100mug) was compared with an intravenous injection of aminophylline (250mg) in 23 patients with acute exacerbations of asthma. Salbutamol (11 cases) and aminophylline (12) produced a mean proportionate increase in FEV of 26% and 23% respectively. Blood gas pressures showed a trend to improvement with a mean rise in oxygen tension of 2mm Hg(0-2kPa) in the aminophylline group and of 6mm Hg (0-8kPa) in the salbutamol group. Electrocardiogram patterns also showed overall improvement, and mean decreases in pulse rate of 8 beats per minute and 2 beats per minute were noted in the aminophylline and salbutamol groups respectively. Differences in results did not reach conventional levels of significance and no serious side effects were noted. It was concluded that in the doses and routes of administration compared, salbutamol was as effective as aminophylline.