1. Endothelial dysfunction is seen in patients with essential hypertension or congestive heart failure (CHF). The present study aimed to evaluate the direct effect on endothelium- dependent vasodilation (EDV) of different pharmacological drugs commonly used in the treatment of these conditions. 2. Forearm blood flow (FBF) was measured in 37 young healthy normotensive subjects with venous occlusion plethysmography during local intra-arterial infusions of methacholine (MCh; 2-4 microg/min), evaluating EDV, and sodium nitroprusside (SNP; 5-10 microg/min), evaluating endothelium-independent vasodilation (EIDV). The measurements of EDV and EIDV were undertaken under baseline conditions and were repeated after 1 h intra-arterial infusion of digoxin (0.1 mg/h), furosemide (5.0 mg/h), enalaprilat (2,4 mg/h), metoprolol (1.2 mg/h) or saline (controls). 3. Enalaprilat and digoxin improved the FBF response to MCh at 4 microg/min (from 22.7+/-2.3 to 25.5+/-2.1 mL/min per 100 mL tissue (P < 0.01) and from 18.2+/-2.4 to 22.2+/-2.0 mL/min per 100 mL tissue (P < 0.05), respectively). No significant changes where induced by furosemide or metoprolol in response to MCh at 4 microg/min (from 19.4+/-2.0 to 22.9+/-2.8 and from 15.3+/-2.4 to 14.7+/-1.1 mL/min per 100 mL tissue, respectively). No significant changes in basal FBF or EIDV were induced by the different drugs. When the endothelial function index was calculated as the MCh: SNP FBF ratio, a significant improvement was seen only with enalaprilat (1.1+/-0.1 to 1.2+/-0.1; P < 0.01) and furosemide (1.0+/-0.1 to 1.3+/-0.4; P < 0.05). 4. In conlusion, the results of the present study show that enalaprilat and furosemide improve endothelial vasodilatory function, while no major effect was induced by digoxin or metoprolol. Thus, different direct effects on the endothelium in young normotensive subjects were induced by drugs commonly used in the treatment of hypertension or CHF.