The chemistry, pharmacology, pharmacokinetics, clinical uses, adverse effects, drug interactions and dosage of bretylium tosylate, a recently approved antiarrhythmic agent, are reviewed. Bretylium tosylate is used to treat life-threatening ventricular arrhythmias, principally ventricular fibrillation and ventricular tachycardia, that have not responded to treatment with first-line antiarrhythmic agents. The drug has a direct positive inotropic effect on the myocardium and blocking effect on postganglionic sympathetic nerve transmission. The drug is poorly absorbed orally, requiring either i.m. or i.v. administration. Drug excretion occurs primarily through the kidney, necessitating dosage modification in renal disease. Hypotension is the most commonly observed adverse reaction to bretylium tosylate. Rapid i.v. administration may cause severe nausea and vomiting, and i.m. injection at the same site may cause atrophy and necrosis of muscle tissue. Quinidine and procainamide may potentiate the hypotensive effects of bretylium. Bretylium will aggravate digitalis-induced arrhythmias. Bretylium's use in resistant ventricular tachyarrhythmias requires close clinical monitoring.