Twenty patients with severe or medium severe asthma were given atenolol (Atenol ICI-Pharma) and/or metoprolol (Seloken Hässle) for tachycardia, hyperkinetic tremor, arterial hypertension or symptoms of angina pectoris. These cardioselective beta-blocking drugs caused only a very slight decrease in PF values. There was no difference between atenolol and metoprolol as regards the PF values. A 24 hourly dose of 100 mg atenolol caused a distinct fall in diastolic fall in diastolic pressure as compared with the same amount of metoprolol. Both these two beta1-blockers moderated the tachycardia which occurs in asthma; atenolol in this dose had a slightly stronger action. The subjective condition of five patients with severe or medium severe asthma was considerably relieved by atenolol and/or metoprolol. The relief manifested as a lessening of dyspnoea and improvement of the general status. No essential change was observed in the PF values despite the subjective effects. The most noteworthy change was the amelioration of tachycardia which had continued longer than expected in these patients. The heart rate dropped from 140-120/min to 90-70/min and dyspnoea was relieved at the same time.