In order to investigate whether hypertension-related structural vascular changes may be influenced by antihypertensive treatment, 10 patients were studied suffering from essential arterial hypertension, five males and five females, aged between 34 and 61 years (mean age: 46.9 +/- 8.13 years). All patients received a placebo for 1 week and then captopril, 75 mg b.i.d. for 3 months. After placebo and captopril treatments, the following parameters were evaluated: SBP, DBP, mean blood pressure (MBP), by the formula 1/3 (SBP + 2 x DBP) and basal and minimal vascular resistances, respectively obtained by the ratios MBP/rest flow and MBP/peak flow. Blood flows have been obtained by strain gauge plethysmography. A significant decrease in systolic (P less than 0.025), diastolic (P less than 0.01) and mean blood pressure (P less than 0.01), basal vascular resistances (52 +/- 19 vs 28 +/- 12 A.U., P less than 0.01) and minimal vascular resistances (6.3 +/- 2.2 vs 3.9 +/- 2.8 A.U., P less than 0.025) has been observed after captopril treatment in comparison to placebo, whereas rest (2.9 +/- 0.7 vs 4.1 +/- 0.9 ml.min-1.100 g-1, P less than 0.01) and peak blood flows (21.3 +/- 5.8 vs 29.7 +/- 9.4 ml.min-1.100 g-1) significantly increased. These data seem to indicate that antihypertensive treatment with the angiotensin-converting enzyme inhibitor, captopril, is not only efficacious in inducing a significant blood pressure decrease, consequent to the reduction of basal vascular resistance (due to the vasodilating effects of the drug), but is also able to reduce minimal vascular resistance.(ABSTRACT TRUNCATED AT 250 WORDS)