This study evaluated the anti-hypertensive efficacy, tolerability and effects on left ventricular mass of losartan, a selective angiotensin II receptor antagonist, after 22 months in patients with essential hypertension. The study included 77 hypertensive patients who were randomised at baseline to 22 months double-blind once-daily treatment with losartan 50 mg (L group n = 44 patients, mean age 54+/-9 years) or hydrochlorothiazide 25 mg (HCTZ group, n = 33 patients, mean age 56+/-7 years). Routine haematology, blood chemistry, standard electrocardiography, echocardiography and ambulatory non-invasive 24-h blood pressure (BP) monitoring were performed at baseline and after 10 and 22 months. The results showed good tolerability and a significant mean systolic and diastolic BP reduction in all groups (L group: 22 mm Hg and 11 mm Hg; HCTZ group: 11 mm Hg and 7 mm Hg, respectively for systolic and diastolic mean BP). Moreover, a remarkable reduction in left ventricular mass index was reached after 10 and 22 months only in the L group (L group: delta = -11 g/m2, P<0.02; HCTZ group: delta = -5 g/m2, P= 0.38). In conclusion, losartan was well tolerated and produced a significant reduction in BP and left ventricular mass in hypertensive patients