This study used 24-h ambulatory blood pressure (BP) monitoring to investigate the effectiveness of a novel low-dose combination of bisoprolol/hydrochlorothiazide in adult patients with mild to moderate essential hypertension. Thirty-six patients with stable mild to moderate hypertension (sitting diastolic BP 95-114 mmHg) after a placebo run-in phase received oral bisoprolol/hydrochlorothiazide 5 mg/6.25 mg once daily for 4 weeks in a single-blind regimen. At office visits, BP and pulse were measured with statistically significant reductions (p < 0.01) recorded after 2 and 4 weeks of treatment. Twenty-four-h ambulatory BP monitoring at the completion of therapy revealed significant reductions (p < 0.01) in both systolic and diastolic 24-h, daytime, and nighttime BP, compared with the end of the placebo treatment phase. Systolic and diastolic load were also reduced (p < 0.01). The combination was well tolerated, and overall quality-of-life questionnaire scores indicated an improvement after bisoprolol/hydrochlorothiazide therapy (p = 0.02). No clinically significant changes from baseline in laboratory parameters were observed; in particular, serum potassium was unchanged. This is the first study to demonstrate the 24-h effectiveness of the bisoprolol/hydrochlorothiazide 5 mg/6.25 mg combination, using 24-h ambulatory BP monitoring. In addition, antihypertensive therapy with low doses of bisoprolol/hydrochlorothiazide in combination may improve tolerability.