In a double-blind, double-dummy, placebo-controlled crossover design, the renal hemodynamic and tubular effects of 2-month specific vasodilation with a converting enzyme inhibitor (enalapril, 40 mg once daily) was compared with that of a calcium antagonist (verapamil slow release, 240 mg twice daily) in 15 patients with established essential hypertension. Enalapril and verapamil treatment induced a 9% reduction in mean blood pressure (BP). Heart rate (HR) was similar after placebo (66 beats/min), enalapril (63 beats/min), and verapamil (63 beats/min). Plasma norepinephrine (P-NE) was unaltered after enalapril and verapamil as compared with placebo (0.92, 0.88, and 1.33 nM, respectively). Plasma angiotensin II and aldosterone decreased and plasma renin activity (PRA) increased after enalapril but were unaltered after verapamil. Glomerular filtration rate (51Cr-EDTA) was not altered by either enalapril or verapamil, whereas renal blood flow (125I-hippurate) was reduced 9% by verapamil. Renal vascular resistance (RVR) was unchanged after enalapril as well as verapamil. Fractional excretion of electrolytes and diuresis were unaltered and body weight was similar after enalapril, verapamil, and placebo (81.0, 82.5, and 80.2 kg, respectively). Long-term treatment with enalapril and verapamil had a comparable antihypertensive effect. Neither enalapril nor verapamil appeared to induce reflex activation of the sympathetic nervous system. Renal hemodynamic and tubular function was well preserved with both drugs without signs of sodium and water retention.