BACKGROUND The objective of this prospective, randomized, open-label, blinded-endpoint study was to compare the antihypertensive efficacy of valsartan 80 mg v irbesartan 150 mg when combined with hydrochlorothiazide (HCTZ) 12.5 mg. METHODS Untreated or uncontrolled hypertensive adults (n = 800) were enrolled by primary care physicians. After a 5-week open-label lead-in phase in which all patients received 12.5 mg HCTZ once daily, subjects whose blood pressure (BP) remained uncontrolled were randomized (n = 464) to valsartan/HCTZ (80/12.5 mg) or irbesartan/HCTZ (150/12.5 mg) for 8 weeks. Home BP monitoring (HBPM) was performed in the morning and in the evening for 5 days, at baseline, and after 8 weeks. Office BP measurements were obtained at baseline and after 8 weeks. RESULTS Irbesartan/HCTZ produced greater reductions in average systolic BP (SBP) and diastolic BP (DBP) measured by HBPM than valsartan/HCTZ (SBP: -13.0 v -10.6 mm Hg, P = .0094; DBP: -9.5 v -7.4 mm Hg, P = .0007). These differences were more pronounced in the morning (trough) than in the evening. Office BP measurements also showed greater reductions in trough seated SBP and DBP with irbesartan/HCTZ compared with valsartan/HCTZ. Normalization rates observed with HBPM (SBP <135 mm Hg and DBP <85 mm Hg) were significantly greater with irbesartan/HCTZ than with valsartan/HCTZ (50.2 v 33.2%; P = .0003). The overall safety was similar in the two groups. CONCLUSIONS The superior BP-lowering potency of the fixed combination irbesartan/HCTZ (150/12.5 mg) over valsartan/HCTZ (80/12.5 mg), evidenced independently from the investigators by HBPM, supports the use of this technique in trials with prospective, randomized, open-label, blinded-endpoint designs.