Abnormal glucocorticoid metabolism contributes to vascular dysfunction and cardiovascular disease. Cortisol activation of vascular mineralocorticoid and glucocorticoid receptors is regulated by two types of 11beta-HSD (11-beta hydroxysteroid dehydrogenase), namely 11beta-HSD2 and 11beta-HSD1 (type 2 and type 1 11beta-HSD respectively). We hypothesized that inhibition of 11beta-HSD would attenuate vascular function in healthy humans. A total of 15 healthy subjects were treated with the selective 11beta-HSD inhibitor GA (glycyrrhetinic acid) or matching placebo in a randomized double-blinded cross-over trial. 11beta-HSD activity was assessed by the urinary cortisol/cortisone ratio, and vascular function was measured using strain-gauge plethysmography. Endothelial function was measured through incremental brachial artery administration of methacholine (0.3-10 microg/min) and vascular smooth muscle function with incremental verapamil (10-300 microg/min). GA increased the 24-h urinary cortisol/cortisone ratio compared with placebo (P=0.008). GA tended to reduce the FBF (forearm blood flow) response to methacholine (P=0.09) and significantly reduced the FBF response to verapamil compared with placebo (P=0.04). MAP (mean arterial pressure) did not differ between the study conditions. 11beta-HSD inhibition attenuated vascular smooth muscle vasodilatory function in healthy humans. Disturbances in cortisol activity resulting from 11beta-HSD inactivation is therefore a second plausible mechanism for mineralocorticoid-mediated hypertension in humans.