Angiotensin II (Ang II) receptor blockers are the newest class of antihypertensive drugs to be developed. No large-scale clinical trials have been performed to evaluate their efficacy alone, or in combination with other drugs. A large-scale, eight week, open-label, non-placebo-controlled, single-arm trial evaluated the efficacy, tolerability and dose-response of candesartan cilexetil, 16-32 mg once-daily, either as monotherapy or as part of combination therapy, in a diverse hypertensive population in actual practice settings. 6465 patients with high blood pressure, of whom 52% were female and 16% African American, with a mean age of 58 years, were included. 5446 patients had essential hypertension and 1014 patients had isolated systolic hypertension. In order to be included in this study, patients had either untreated or uncontrolled hypertension (systolic blood pressure (SBP) 140-179 mmHg and/or diastolic blood pressure (DBP) 90-109 mmHg inclusive at baseline), despite a variety of other antihypertensive drugs. Of the 5156 patients with essential hypertension and at least one post baseline efficacy measurement, the mean pretreatment blood pressure (BP) was 156/97 mmHg. Candesartan cilexetil monotherapy reduced mean SBP/DBP by 18.0/12.2 mmHg. Similarly, in the 964 patients with isolated systolic hypertension and at least one post baseline efficacy measurement, candesartan cilexetil monotherapy reduced SBP/DBP from 158/81 by 16.5/4.5 mmHg. Candesartan cilexetil was similarly effective when employed as add-on therapy. When added to baseline antihypertensive medication in 51% of the patients with essential hypertension not achieving BP control, additional reduction in BP was achieved regardless of the background therapy, including diuretics (17.8/11.7 mmHg) calcium antagonists (16.6/11.2 mmHg), beta-blockers (16.5/10.4 mmHg), angiotensin-converting enzyme inhibitors (ACE-I) (15.3/10.0 mmHg), and alpha blockers (16.4/10.4 mmHg). Likewise, when candesartan cilexetil was used as add-on therapy in patients with isolated systolic hypertension, there was a consistent further reduction of mean SBP/DBP, regardless of the background therapy. Moreover, these monotherapeutic or add-on efficacy benefits were seen regardless of age (<65 or >65 years), gender, or race. Despite the open-label design of the study which enhances efficacy owing to the placebo effect, the Ang II receptor blocker, candesartan cilexetil either alone, or as an add-on therapy, is highly effective for assisting in the control of systolic and diastolic hypertension.