Regression of cardiovascular structural changes is a main goal of antihypertensive treatment. Two recent meta-analyses of relatively small noncomparative studies have suggested that angiotensin-converting enzyme (ACE) inhibitors may be more effective than other classes of drugs in inducing regression of left ventricular hypertrophy (LVH). The effect of different antihypertensive drugs on arteriolar structural changes has not yet been properly investigated. The aim of this study was to evaluate the effect of 6 months of treatment with amlodipine (5-10 mg o.d.) or enalapril (10-20 mg o.d.) on blood pressure (BP) (ambulatory monitoring), heart rate (HR), LV mass and function (M-mode echo, two-dimensionally guided), forearm minimal vascular resistance (min VR = BP/max blood flow-venous occlusion plethysmography, taken as an index of vascular structural changes) in 24 hypertensive patients in a comparative single-blind, randomized study, with blind reading of echocardiograms and plethysmographic tracings. After 6 months of treatment with amlodipine 5-10 mg o.d., significant reductions in LV mass index (p = 0.004) and forearm min VR (p = 0.02) were observed. Before and during treatment, LV systolic function, both at rest and during stress (handgrip test), evaluated by fractional shortening as related to end-systolic stress, was in every case within 95% confidence limits calculated in normal subjects. Similar results were observed with enalapril. No significant differences were observed for Doppler indices of diastolic filling after 6 months of treatment with either drug. These results indicate that a significant regression of structural changes in the heart and in the small resistance vessels can be observed after long-term treatment with amlodipine in essential hypertensive patients.(ABSTRACT TRUNCATED AT 250 WORDS)