['The optimal combination treatment for hypertension has not been established. We investigated the effect of a calcium channel blocker or a diuretic added to angiotensin II receptor blockers (ARBs) on the augmentation index (AI), as a marker of arterial stiffness and wave reflection, in hypertensive patients.', 'Thirty-seven patients treated with ARBs were randomly allocated to either of the 2 groups receiving an ARB plus azelnidipine (AZ group) or trichlormethiazide (TCM group). Changes in brachial blood pressure (BP), AI, high-sensitive C-reactive protein (hsCRP), and serum asymmetric dimethylarginine, as an endogenous nitric oxide synthase inhibitor, were determined.', 'Systolic and diastolic blood pressure after 6 months were significantly reduced in both the groups similarly; however, after adjustment for baseline covariates, the extent of the reduction in AI (%) in the AZ group was significantly greater than in the TCM group (between-group difference was 3.2; 95%CI: 0.2-6.3; P = 0.03). The reduction of high-sensitive C-reactive protein (mg/L) and serum asymmetric dimethylarginine (micromol/L) was significantly greater in the AZ group than in the TCM group (between-group difference was 0.18 and 0.05; 95%CI: -0.01 to 0.36 and -0.01 to 0.11; P = 0.04 and 0.02, respectively). Further, when patients were analyzed according to age younger than 60 years or older than 60 years, the reduction in AI in the AZ group aged older than 60 years was significantly greater than in the TCM group.'] Does combination therapy of calcium channel blocker and angiotensin II receptor blocker reduce augmentation index in hypertensive patients?