Endothelial cell integrity (coverage and quality) of large donor vessels is important because these vessels are used for vascular reconstructions in solid-organ transplantation. Disruption of the endothelial cell monolayer will initiate blood coagulation and may lead to thrombosis of large vessels, often resulting in the loss of the transplanted organ. Iliac arteries and veins, removed from 10 heart-beating multi-organ donors at the end of the donor procedure, were analyzed using scanning electron microscopy at three different time points of preservation. Endothelial cell coverage and quality were determined immediately after removal from the donor, after 10 h (time of transplantation) and 7 d storage in 'University of Wisconsin' cold preservation solution (UW). Endothelial cell coverage decreased during the preservation of arteries, but was maintained in veins. Storage of the veins for 7 d in plastic bags showed a decreased endothelial cell coverage compared to storage in glass vials. Early removal of the blood vessels and proper storage, free floating and in clean UW, may improve maintenance of the endothelial cell integrity. These findings may be important in order to reduce the risk of thrombosis and, consequently, organ failure after transplantation. Furthermore, vessels with maintained endothelial cell integrity after 7 d may be used for in vitro research.