OBJECTIVE : The aim of this open multicentric study was to investigate the efficacy and safety of the addition of an angiotensin converting enzyme (ACE) inhibitor (benazepril, 10 mg/day) or a diuretic (hydrochlorothiazide, 12.5 mg/day) for 4 weeks in patients with mild to moderate essential hypertension having been treated for 4 weeks by an angiotensin II antagonist (valsartan, 80 mg/day) but still having a diastolic blood pressure (BP) > 90 mmHg on this medication given alone. METHODS : A total of 327 patients were included in the trial and 153 patients (46%) had their diastolic BP </= 90 mmHg after 4 weeks of valsartan monotherapy. These patients continued the same treatment regimen for the next 4 weeks, but no further blood pressure reduction was observed. The remaining patients were randomized to either the valsartan-hydrochlorothiazide or the valsartan-benazepril combination. RESULTS : The two combinations induced an additional significant BP reduction, which was of similar magnitude for diastolic BP (-4.5 during valsartan-hydrochlorothiazide treatment and -3.3 mmHg during valsartan-benazepril treatment), but of greater magnitude for systolic BP during valsartan-hydrochlorothiazide (-6.77 mmHg) than during valsartan-benazepril co-administration (-3.2 mmHg). At the end of the trial, the BP of the responders to the valsartan monotherapy was lower than that of patients having required a combination therapy. Valsartan given alone or in association with hydrochlorothiazide or benazepril was well tolerated. CONCLUSION : These data therefore show that in patients not responding sufficiently to angiotensin II receptor blockade BP can be further and safely lowered by adding a small dose of a diuretic or an ACE inhibitor, with the diuretic-containing combination tending to being more effective in controlling systolic BP.