Over the past two decades, the central role of the endothelium in the initiation, progression, and clinical sequelae of atherosclerosis has been recognized. Increased endothelial permeability and impaired function precedes and portends the development of atherosclerotic lesions and their clinical manifestations. We have previously shown that quantitative assessment of albumin leakage into the vessel wall, using a clinically approved albumin-binding contrast agent, and endothelial-dependent dysfunction associated with lesion progression and instability in animal models. Here, we translated this technique in man to test whether endothelial permeability and dysfunction associate with carotid atherosclerosis risk in patients undergoing endarterectomy.