This study investigated the addition of the direct renin inhibitor aliskiren to amlodipine in patients with mild to moderate hypertension that was inadequately controlled with amlodipine alone. Following once-daily treatment with amlodipine 5 mg for 4 weeks, patients whose hypertension responded inadequately to therapy (mean sitting diastolic blood pressure [DBP] 90–109 mm Hg) (n=545) were randomized to 6 weeks of double-blind treatment with amlodipine 5 mg plus aliskiren 150 mg, amlodipine 5 mg, or amlodipine 10 mg. At the study's end, mean systolic blood pressure and DBP reductions with the combination of aliskiren 150 mg and amlodipine 5 mg (11.0/8.5 mm Hg) were significantly greater (P<.0001) than with amlodipine 5 mg (5.0/4.8 mm Hg)—the comparator group—but similar to amlodipine 10 mg (9.6/8.0 mm Hg). All treatments were well tolerated. Edema occurred more frequently with amlodipine 10 mg (11.2%) than with combination therapy (2.1%) or amlodipine 5 mg (3.4%). In conclusion, aliskiren 150 mg plus amlodipine 5 mg shows similar but not better blood pressure-lowering efficacy when compared with amlodipine 10 mg in patients not completely responsive to amlodipine 5 mg; less edema was noted with combination therapy.