AIMS: To evaluate the vascular effects of doxazosin, an alpha-1 antagonist, in hypertensive patients with metabolic syndrome in whom the drug has previously been shown to exert beneficial metabolic actions on lipids and insulin metabolism. EXPERIMENTAL PROTOCOL: Twelve untreated non-diabetic hypertensive patients with National Cholesterol Education Program (NCEP) ATP-III defined metabolic syndrome were assigned to three-months of treatment with doxazosin (5.5 +/- 1.9 mg/die). Study variables were measured at baseline and after treatment. End-points: forearm blood flow (strain-gauge plethysmography) responses to graded intra-arterial acetylcholine and sodium nitroprusside infusion to test endothelium-dependent and independent vasodilatation respectively. Minimum forearm vascular resistance, the ratio of mean blood pressure and post-ischaemic maximal blood flow, as an index of arteriolar structure; transcapillary albumin escape rate (the 1-h decay rate of I-albumin, 6-8 microC ev) as a measure of systemic capillary permeability. Lipids, fasting and post-glucose insulin were measured at baseline and after treatment. RESULTS: Doxazosin reduced blood pressure, augmented acetylcholine-mediated vasodilatation, decreased minimum resistance and, although not to a statistically significant extent, transvascular albumin leakage increased high-density lipoprotein (HDL) cholesterol while triglycerides and post-stimulative hyperinsulinemia decreased. CONCLUSIONS: Doxazosin improved endothelial-mediated vasomotor function and reversed abnormal arteriolar structure in hypertensive patients with metabolic syndrome while improving lipid profile and blunting post-glucose hyperinsulinemia.