The anti-arrhythmic properties of a new drug, lorcainide, were evaluated. Lorcainide is highly efficient for the treatment of ventricular arrhythmias, especially ventricular extrasystoles and recurrent ventricular tachycardia. It is also efficient in the treatment of supraventricular extrasystoles and repetitive auricular tachycardia. It is ineffective in cases of auricular fibrillation and flutter. The drug also has effective anti-arrhythmic properties when administered orally. It has a small negative inotropic effect which was not clinically relevant in the patient group studied. Side effects were within acceptable limits and essentially consist of dizziness, tremor and blurring of vision, occurring only during rapid i.v. injection and depending upon the speed of injection.