All patients will enter a one-week screening phase prior to starting the eight-week open-label T80 mg period. At the end of four weeks, only patients who fail to respond to T80 mg (DBP >= 90 mm Hg) will continue the treatment with T80 mg for another four weeks. At the end of eight weeks, only patients who fail to respond to T80 mg (DBP >= 90 mm Hg) will be randomized, double-blind, to receive either T80 mg alone or the fixed dose combination of T80 mg plus HCTZ 12.5 mg for eight weeks. Seated BP will be taken 24 hours post-dose at each visit. Labs, ECG, and physical examination will be done at screening, at baseline and at the final visit.