Study to assess the efficacy of telmisartan 40-80 mg once daily compared with losartan 50-100 mg once daily in hypertensive patients evaluated by change from baseline in diastolic blood pressure (DBP) during the last 6 hours of the 24-hour dosing interval, at the end of the 12 weeks period of monotherapy treatment (ABPM - ambulatory blood pressure measurement).

Secondary objectives: Changes from baseline in BP at the end of the monotherapy period of treatment and at the end of the study, evaluated by sphygmomanometric blood pressure measurement and ABPM

Safety:

Incidence of adverse events (AE's); withdrawal due to adverse events; laboratory parameters

Inclusion Criteria:

• Age ≥ 18 years
• Mild-to-moderate essential hypertension defined as a mean diastolic blood pressure (DBP) ≥ 95 mmHg and < 110 mmHg and systolic blood pressure (SBP) < 180 mmHg measured by manual cuff sphygmomanometer at the end of the wash-out period
• Written informed consent

Exclusion Criteria:

• Nursing, pregnancy or childbearing potential women, post-menopausal women will be enrolled with last menstruation > 1 year prior to start wash-out phase or surgically sterile
• Secondary hypertension
• Malignant hypertension (retinal haemorrhage, exudates or papillary oedema)
• Clinically significant sodium depletion as defined by serum sodium level < 130 mEq/L and/or clinically significant hyperkaliemia as defined by serum potassium level > 5.5 mEq/L or clinically significant hypokaliemia as defined by serum potassium level < 3.0 mEq/L
• Atrial fibrillation or frequent ventricular ectopic beats or other arrhythmias which, in the investigator opinion could compromise patient's participation to the trial
• Congestive heart failure (CHF) (NYHA (New York Heart Association) functional class CHF III-IV)
• Angina pectoris or myocardial infarction
• Cardiac surgery within the past 3 months prior to start the wash-out period
• Stroke within the past 6 months prior to start the wash-out period
• Renal insufficiency defined as creatininaemia > 2mg/dl
• Bilateral renal artery stenosis, renal artery stenosis in a solitary kidney, post renal transplant, presence of only one functioning kidney
• Liver insufficiency, defined as bilirubinaemia > 2mg/dl and AST (aspartate aminotransferase) or ALT (alanine-aminotransferase) > twice the upper normal range
• Clinically significant metabolic and endocrine disease
• Autoimmune disease
• Previous history of angioedema
• Body mass index > 30kg/m2
• Arm circumference > 32 cm
• Any condition that may be likely to compromise patients participation to the trial (alcohol or drug abuse, disability illness, etc.)
• Concomitant therapy with antihypertensive drugs non permitted by protocol, corticosteroids or drugs known to affect blood pressure
• Concomitant use of lithium or cholestyramine or colestipol resins (potential drug interactions with HCTZ)
• Investigational drug treatment within the past 30 days before the enrolment or concurrent participation to any other trial
• Sensitivity, significant adverse reaction or contraindications to the study drugs (telmisartan, losartan, HCTZ)
• Predictable lack of patient co-operation