The effects of intravenous sotalol (0.5 mg/kg in 6 minutes) were studied in 23 patients with supraventricular tachycardia (ventricular rate greater than 120 bpm) after failure of placebo (isotonic dextrose). Thirteen patients had atrial flutter or fibrillation and 10 a junctional tachycardia of recent onset. Sinus rhythm was restored in 4 of the patients with atrial flutter or fibrillation and the ventricular rate was slowed significantly in 3 patients (less than 100 bpm). In 3 other patients the ventricular rate decreased (31 to 35 p. 100) but remained above 100 bpm. Sinus rhythm was restored in 3 of the 10 patients with a junctional tachycardia five to twelve minutes after beginning the injection. A slight slowing of the heart rate (13 to 27 p. 100) was observed in the other 7 patients but the frequency remained over 100 bpm. Overall, a satisfactory result was obtained in 10 patients (43 p. 100) including 7 cases in which sinus rhythm was restored. Sotalol was well tolerated in 21 patients; one patient complained of cold in the legs and one patient developed asymptomatic bradycardia (46 bpm). This study shows that intravenous sotalol may be useful in the emergency treatment of supraventricular tachycardia.