Subcutaneous adrenaline and terbutaline have been compared in a double blind study of 20 patients with acute severe asthma presenting to an accident and emergency department. Ten patients received adrenaline 0.5 mg (0.5 ml) and 10 terbutaline 0.5 mg (0.5 ml) subcutaneously. Further treatment with nebulised salbutamol (5 mg), hydrocortisone (200 mg), and aminophylline (0.9 mg/kg/hour) was started 15 minutes later. All patients reported a reduction in chest tightness within three minutes of receiving both adrenaline and terbutaline and reported no adverse effects. Mean baseline values of peak expiratory flow (PEF) and forced expiratory volume in one second (FEV1) did not differ significantly between the adrenaline group (130 1 min-1 and 0.83 l) and the terbutaline group (111 1 min-1 and 0.63 l). After administration of adrenaline PEF had increased by 21% and FEV1 by 40% five minutes after the injection, and by 35% and 64% at 15 minutes. Terbutaline caused a 23% increase in PEF and a 37% increase in FEV1 at five minutes, and a 40% and 58% increase at 15 minutes. There was no significant difference in PEF, FEV1, heart rate, blood pressure, or pulsus paradoxus between the two groups at any time. Continuous electrocardiographic recording showed no abnormalities in either group. Thus in this study subcutaneous adrenaline (0.5 mg) and terbutaline (0.5 mg) produced effective rapid bronchodilatation without serious side effects.