Ventricular tachycardia was produced in the dog by intravenous injection of 2–3μg/kg of adrenaline during nitrous oxide-halothane anaesthesia. On a weight basis, propiomazine was found to be as effective as perphenazine in preventing the arrhythmias. Promethazine and promazine showed similar effects in much higher doses. The protection provided by all these drugs could be surmounted by doses of adrenaline of 4–6μg/kg. Propiomazine did not produce any action on blood pressure whereas the other drugs tested produced a prolonged fall in pressure in all the experiments. Since the clinical dose of propiomazine is 2–4 times that of perphenazine, it is possible that the former may prove superior to the latter in clinical