1. Labetalol, a compound with both α- and β-adrenoreceptor-blocking actions, was given intravenously (1·5–2·0 mg/kg) in twenty recumbent hypertensive patients.
2. There was a rapid reduction in systolic and diastolic pressures in all, maintained up to 24 h in some subjects.
3. Severe hypotension was not seen in recumbent subjects, but postural hypotension was common.
4. Labetalol caused significant lowering of heart rate.
5. Labetalol induced significant and related lowering of plasma angiotensin II and aldosterone concentrations, most obviously when these were initially high.
6. In a cross-over comparison in five patients against 10 mg of propranolol intravenously, labetalol was more effective in lowering blood pressure, but less effective in lowering pulse rate or plasma angiotensin II.
