Most vascular endothelial cells at the edge of experimentally induced wounds have their centrosomes oriented toward the wound in the direction of cell migration. The finding that the centrosomes in endothelial cells of nonwounded aorta and vena cava are also oriented toward the heart suggested the hypothesis that endothelial cells are normally migrating in this direction. To test this hypothesis, endothelial cells in a segment of the rat abdominal aorta were labeled with a relatively nontoxic dye, 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate (DiI), and the position of the labeled cells was determined 3 and 6 weeks later. The results obtained showed that in 6 of the 9 rat aortas examined at 3 weeks and 15 of the 20 rat aortas examined at 6 weeks, DiI-labeled endothelial cells had migrated various distances up to 5000 μm toward the heart. In contrast, no migration of endothelial cells was detected at the opposite end of the labeled segment, in the direction away from the heart. These results demonstrate that vascular endothelial cells in the abdominal aorta of the rat are not stationary but are migrating toward the heart. The significance of the migration of endothelial cells toward the heart is presently unknown; however, it would be interesting to explore whether or not the impairment of this migration may contribute to disease processes in which the ability to maintain an intact and normally functioning endothelial cell lining is compromised as in atherosclerosis.