Most studies of the regression of left ventricular hypertrophy by antihypertensive treatment have methodological weaknesses and have not shown if regression of left ventricular hypertrophy can be obtained independently of blood pressure reduction. In the HYCAR study, after an inclusion phase of 4 to 6 weeks on furosemide (20 mg/day), 115 patients with left ventricular hypertrophy were randomised in a double blind manner to placebo group (N = 40), ramipril, 1.25 mg/day, (N = 38) or 5 mg/day (N = 37) for a period of 6 months. Furosemide was continued during the double blind treatment period. Echocardiography and ambulatory blood pressure monitoring were performed just before the randomisation and at 6 months. At the end of the study, there was no significant difference between the casual and ambulatory blood pressure changes. Expressed in g/m, the left ventricular mass index decreased significantly with respect to placebo in the ramipril 5 mg group (-12.2 +/- 3.9 versus +5.5 +/- 4.3 g/m2, p = 0.003) and in the 1.25 mg group (-7.5 +/- 4.6 g/m2, p = 0.04). The reduction in left ventricular mass index expressed in g/m2 was significant in the 5 mg ramipril (p = 0.008) but not in the 1.25 mg ramipril group (p = 0.06).(ABSTRACT TRUNCATED AT 250 WORDS)