Oral administration of felodipine to 10 patients with mild essential hypertension acutely reduced the brachial artery pressure by 15/13mm Hg. The tachycardia which occurred was sustained for 90 minutes together with an elevated plasma noradrenaline concentration. Addition of intravascular metoprolol after 90 minutes decreased heart rate. The felodipine-induced increase of plasma renin activity (100%; p less than 0.001) was completely reversed by metoprolol. Plasma angiotensin II (PA II) rose by 15% (p less than 0.05) during felodipine, whereas plasma aldosterone concentration was not significantly affected.