After a screening and a 2-week washout period (screening period), the patients will enter 4-week open-label run-in period with telmisartan (Micardis) 40 mg monotherapy to assess eligibility. The study will be terminated for those who have responded to telmisartan (Micardis) 40 mg monotherapy at the end of 4-week open-label run-in period with telmisartan (Micardis) 40 mg monotherapy (mean seated DBP < 90 mmHg). About 200 patients not responding adequately to telmisartan (Micardis) 40 mg monotherapy will be randomised and treated for 8 weeks with once-daily administration of either telmisartan (Micardis) 40 mg or a fixed dose combination of telmisartan 40 mg and HCTZ 12.5 mg (double-blind treatment period).