1. Haemodynamic effects of adrenaline were studied in 27 hypertensive patients, successively during treatment with propranolol and metoprolol. In 12 patients β-adrenoreceptor blockade was combined with diuretics and in 15 patients the blockade was combined with vasodilators.
2. During propranolol adrenaline caused a marked pressor effect: there was a considerable rise in systolic as well as in diastolic blood pressure and a marked fall in heart rate. During metoprolol there was only a slight rise in blood pressure and an increase in heart rate.
3. Forearm blood flow was decreased by adrenaline during propranolol and was increased during metoprolol. Calculated vascular resistance showed opposite changes.
4. Results were essentially the same when β-adrenoreceptor blockade was combined with diuretics or with vasodilators and did not differ from previous results obtained in patients treated by blockade alone.
5. If adrenaline infusion can be considered as a model for acute stress, our results seem to favour a selective β-adrenoreceptor blocking agent over a non-selective one, even when the blocker is combined with a diuretic or a vasodilator.