Background and objective : We performed a retrospective study of the differences in the renal protective effects of strict antihypertensive therapy for essential hypertension between a high dose of valsartan and a combination of the standard dose of valsartan and the diuretic trichlormethiazide by evaluating the changes in the estimated glomerular filtration rate and the urinary albumin : creatinine ratio. Patients and methods : The subjects were 47 outpatients with hypertension who received either a high dose (160 mg/day) of valsartan (n=32) or combination therapy with the standard dose (80 mg/ day) of valsartan and 1 mg/day of trichlormethiazide (n=15). Results : Systolic and diastolic blood pressures were significantly reduced by 19 mm Hg (13%) and 13 mm Hg (-15%) in patients treated with a high dose valsartan and by 17 mm Hg (12%) and 6 mm Hg (-7%) in patients treated with valsartan plus trichlormethiazide. A positive correlation was found between changes in the estimated glomerular filtration rate and changes in the urinary albumin : creatinine ratio in patients treated with high dose valsartan, but not in patients treated with valsartan plus trichlormethiazide. Conclusions : Strict antihypertensive therapy either with a high dose valsartan (160 mg/ day) or with the standard dose of valsartan (80 mg/day) plus a diuretic agent was found to be highly effective for reducing poorly controlled blood pressure. However, the diuretic agent appears to have a different mechanism of renal protection in patients treated with valsartan. (Jikeikai Med J 2011 ; 58 : 69-76)