The aim of this study was to comparatively assess the effects of irbesartan and amlodipine monotherapies on left ventricular mass index (LVMI) in patients with mild to moderate untreated hypertension and echocardiographically determined left ventricular hypertrophy (LVH). Sixty hypertensive patients (35 men, 25 women; mean age, 52.8 years +/- 12.6) with diastolic blood pressure (BP) > or = 100 mm Hg were randomized to irbesartan 150 mg once daily or amlodipine 5 mg once daily for a 4-week titration period. Dosage of both drugs was increased to irbesartan 300 mg once daily or amlodipine 10 mg once daily in case of sitting diastolic BP still >90 mm Hg after the first 2 weeks of treatment. Dosage doubling was necessary in more than 50% of patients in both treatment groups. After the titration period, only the responders (sitting diastolic BP < or = 90 mm Hg) entered a 5-month maintenance period. After 3 months, echocardiographically estimated LVMI decreased by 23.2% in the irbesartan-treated patients and 11.4% in the amlodipine-treated patients, with an adjusted mean difference of 11.8% in favor of irbesartan (P < 0.0001). After 6 months, it decreased by 24.7% in the irbesartan-treated patients and 13.0% in the amlodipine-treated patients, with an adjusted mean difference of 11.6% in favor of irbesartan (P < 0.0001).