A new means of studying vessel wall pathology is presented. This technique utilizes Procion yellow, a vital fluorescent dye, to stain and delineate the connective elements, matrix, and elastic tissue within the arterial wall. In addition, penetration of the dye into cells provides evidence of membrane pathology. A canine model was used, and clamped segments of femoral artery were stained and examined. The appreciation of this approach for the examination of the vessel wall shows alterations in tissue elements that have not been reported previously. This technique makes possible a unique means of studying connective tissue elements as well as membrane integrity.