An open-label study was conducted to characterize the pharmacokinetics and antihypertensive response to irbesartan in children (1-12 years) and adolescents (13-16 years) with hypertension. Patients received single once-daily oral doses of irbesartan 2 mg/kg (maximum of 150 mg once daily) for 2 to 4 weeks (+/- nifedipine or hydrochlorothiazide). Plasma irbesartan concentrations were determined by a validated high-performance liquid chromatography/fluorescence method from blood samples taken predose, up to 24 hours after dosing on Day 1, and up to 48 hours after the final dose. The plasma concentration-time profiles were similar between the 6- to 12-year and the 13- to 16-year age groups and to that previously determined from a study of adult subjects receiving approximately 2 mg/kg (i.e., 150 mg) oral irbesartan once daily. Mean reductions in systolic/diastolic blood pressure were 16/10 mmHg at Day 28 with irbesartan monotherapy (n = 8). Irbesartan was well tolerated and may be a treatment option for pediatric hypertensive patients.