The purpose of the study is to compare the efficacy, safety and tolerability of valsartan 80 mg (with a starting dose of 40 mg) to irbesartan 150 mg (with a starting dose of 75 mg) in patients on long-term haemodialysis with mild to moderate increased mean supine systolic blood pressure (MSSBP).

Inclusion Criteria:

• Patients with mild and moderate hypertension defined by a MSSBP ≥ 140 mmHG and < 180 mmHG at Visits 1 and 2 for treated and untreated patients
• Chronic hemodialysis for at least 6 months prior to Visit 1 as substitution therapy.
• If treated with epoetin: patients with a stable hematocrit ≤ 40% (± 5%).

Exclusion Criteria:

• Inability to discontinue angiotensin II receptor blockers (ARBs) safely for a period of 1 week, as required by the protocol.
• Treatment with more than 3 different compounds for the treatment of hypertension at Visit 1.
• Atrial fibrillation

Other protocol-defined exclusion criteria may apply.