Background-Elevated renin-angiotensin-aldosterone system activity correlates with left ventricular hypertrophy (LVH) and cardiovascular risk, but the relative contributions of angiotensin II and aldosterone remain unclear. This study compared LVH regression during treatment with the selective aldosterone blocker eplerenone, enalapril, and their combination in patients with hypertension. Methods and Results-A 9-month, double-blind, randomized study was performed in 202 patients with LVH and hypertension who received eplerenone 200 mg daily, enalapril 40 mg daily, or eplerenone 200 mg and enalapril 10 mg daily. At week 8, hydrochlorothiazide 12.5 to 25 mg and/or amlodipine 10 mg was added if diastolic blood pressure was Ͼ90 mm Hg. Change in left ventricular (LV) mass as assessed by MRI was the primary end point. Change in blood pressure, renin-angiotensin-aldosterone system hormones, albuminuria, and safety were also assessed. Eplerenone significantly reduced LV mass from baseline (Ϫ14.5Ϯ3.36 g; nϭ50) similarly to enalapril (Ϫ19.7Ϯ3.20 g; nϭ54; Pϭ0.258), but eplerenone/enalapril (Ϫ27.2Ϯ3.39 g; nϭ49) was more effective than eplerenone alone (Pϭ0.007). All treatments reduced systolic blood pressure and diastolic blood pressure from baseline (eplerenone, Ϫ23.8 and Ϫ11.9 mm Hg; enalapril, Ϫ24.7 and Ϫ13.4 mm Hg; and eplerenone/enalapril, Ϫ28.7 and Ϫ14.4 mm Hg, Pϭ0.048, in systolic blood pressure compared with eplerenone alone). Cough was more common with enalapril than with eplerenone (Pϭ0.033), and elevated potassium was more common with eplerenone. Conclusions-Eplerenone was as effective as enalapril in LVH regression and blood pressure control. The combination of eplerenone and enalapril was more effective in reducing LV mass and systolic blood pressure than eplerenone alone. (Circulation. 2003;108: 1831-1838.)