In hypertensive patients, the development of left ventricular hypertrophy seems to increase the risk of cardiovascular death. Although some antihypertensive agents have been associated with regression in left ventricular hypertrophy, diuretics, the most widely used ones, have not. Indapamide is a new, nonthiazide diuretic and vasodilator. To test its effects on left ventricular hypertrophy, patients with essential hypertension and left ventricular hypertrophy were studied before and at the end of 6 months of therapy with 2.5 mg of indapamide daily. Candidates had to have moderate, uncontrolled essential hypertension with echocardiographically documented left ventricular hypertrophy (left ventricular mass index greater than or equal to 130 gm/m2 for men and greater than or equal to 110 gm/m2 for women). Patients with complicated hypertension or with significant cardiovascular or metabolic diseases were excluded. Patients could remain on antihypertensive drugs other than diuretics, provided doses remained stable for 3 months before entry and there was no know regression of left ventricular hypertrophy. Of 13 patients selected, 2 dropped out. The remaining 11 patients successfully completed 6 months of therapy. The average age was 56 +/- 10 years. Indapamide was associated with a significant reduction of mean systolic blood pressure from 172 to 142 mm Hg (p less than 0.001), diastolic blood pressure from 101 to 83 mm Hg (p less than 0.001), and left ventricular mass index from 146 +/- 22 to 124 +/- 22 gm/m2 (mean +/- SD) (p less than 0.003).(ABSTRACT TRUNCATED AT 250 WORDS)