The effects of quinapril (an angiotensin converting enzyme inhibitor) on cardiac hypertrophy were evaluated in a noncomparative study of 98 patients with mild to moderate hypertension over 4 months. Left ventricular hypertrophy (LVH) was diagnosed using echocardiography in 60% of patients at baseline. Combination therapy with hydrochlorothiazide (HCTZ) was initiated after 1 month in patients with inadequate blood pressure control to achieve a target diastolic pressure reduction from baseline (≥ 10mm Hg) and/or reduction to < 90mm Hg. Left ventricular mass index (LVMI) was significantly reduced for patients of either sex with a baseline diagnosis of LVH, but not for those in whom LVH was not detected at enrolment. Systolic and diastolic blood pressures were also significantly reduced. The response rate was 83%, while 28% of patients required combination therapy with HCTZ. There was no correlation between the hypotensive effects of quinapril and change in LVMI. Furthermore, the addition of a diuretic did not appear to affect the LVMI response. Thus, the amelioration of LVH noted in this investigation appears to be attributable to quinapril.