Abstract The value of intravenous lignocaine ('Xylocaine') in the management of arrhythmias after acute myocardial infarction has been assessed. Of twenty-seven patients with frequent ventricular extrasystoles, adequate suppression was achieved in twenty-four using a continuous intravenous infusion of lignocaine 1-2 mg. per minute. Ventricular tachycardia was terminated in eleven patients by a single intravenous injection of 1-2 mg. per kg. body-weight, without resort to D.C. cardioversion. Lignocaine was of little value in the management of supraventricular arrhythmias. Hæmodynamic studies in eight patients have shown no deleterious side-effects after intravenous lignocaine in this dosage. It is suggested that lignocaine is the anti-arrhythmic drug of choice in the management of ventricular arrhythmias after acute myocardial infarction.