In this phase 2, randomized, double-blind, placebo-controlled forced dose-titration study, 115 patients with resistant hypertension, receiving background therapy with >/=3 antihypertensive medications including a diuretic at full doses, were randomized 2:1 to increasing doses of darusentan (10, 50, 100, 150, and 300 mg), a selective endothelin receptor antagonist, or matching placebo once daily for 10 weeks. Darusentan treatment decreased mean systolic and diastolic blood pressure levels in a dose-dependent fashion compared with placebo; the largest reductions were observed at week 10 (300-mg dose) (systolic, -11.5+/-3.1 mm Hg [P=.015;] diastolic, -6.3+/-2.0 mm Hg [P=.002]). Darusentan (300 mg) also decreased mean 24-hour, daytime, and nighttime ambulatory blood pressures from baseline to week 10. Darusentan was generally well tolerated; mild to moderate edema and headache were the most common adverse events. This study demonstrates a clinical benefit from a new class of antihypertensive agent in patients classified as resistant by the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure guidelines.