The aim of the Saga Challenge Antihypertensive Study (S-CATS), a single-arm, prospective and multi-center trial, was to evaluate the effectiveness of combined antihypertensive treatment with losartan and hydrochlorothiazide (HCTZ). Enrolled in the study were a total of 161 patients with hypertension, who in spite of treatment with an angiotensin receptor blocker (ARB) alone or an ARB and calcium channel blocker (CCB), had not been able to reach blood pressure control goals set by the Japanese Society of Hypertension Guidelines (JSH 2004). The ARBs were replaced with a combination pill containing losartan (50 mg) and HCTZ (12.5 mg), and this treatment was continued for 3 months. This change in therapy resulted in significant decreases in systolic (158±14 to 137±15 mm Hg, P<0.001) and diastolic (85±11 to 76±10 mm Hg, P<0.001) blood pressure and heart rate (73±3 to 72±3) during the study. The patients' quality of life (QOL) score, the EuroQol 5 dimensions (EQ-5D) and the visual analog scale (VAS) (n=96; 70.0 (68.8-80.0) to 80.0 (70.0-90.0), P<0.01) all improved significantly. Another QOL score, the hypertension symptom score (HSS), which we originally developed for the S-CATS trial, decreased significantly (n=93; 4.0 (1.0-9.0) to 2.0 (1.0-8.0), P<0.05). The Pittsburgh sleep quality index (PSQI), which is a psychometric assessment of subjective sleep quality, also decreased significantly (n=45; 4.0 (2.0-7.0) to 3.0 (2.0-5.0), P<0.05). There was a significant correlation between a change in HSS (baseline value -3-months value) and a decrease in systolic blood pressure (n=93; R=0.241, P<0.05). These results suggest that an anti-hypertensive treatment combined with an ARB and a thiazide diuretic may improve patients' QOL, including sleep quality.