Endothelial cell-seeded bilateral carotid ePTFE grafts were studied in 11 dogs to determine the source of their eventual luminal linings. One graft was prepared with autologous cells and the other with nonautologous cells. Immunosuppression was accomplished with cyclosporin and prednisolone. At 2 and 3 weeks post implantation, grafts were removed, revealing 9 of 11 autologous and 8 of 11 nonautologous seeded conduits to be patent. Linings were harvested enzymatically and grown in tissue culture, with karyotype analysis limited to cultures that exhibited greater than or equal to 50% endothelium (n5 autologous, n7 nonautologous). Sex type was classified in 20 cells from each graft. All five autologous cell-seeded grafts revealed host cells. Among the seven nonautologous cell-seeded grafts, one harbored only non-autologous cells, three revealed only autologous cells, and three exhibited a predominance of autologous cells with lesser numbers of nonautologous endothelium. All 100 cells from the autologous-seeded grafts were the same sex as seeded cells, while only 28 of the 140 cells from the nonautologous seeded grafts were the same sex as seeded cells (P less than 0.001). Thus, nonautologous endothelial cell seeding with immunosuppression did not uniformly produce nonautologous cell linings, but was more often associated with autologous endothelial cell linings that may have been promoted by the nonautologous cell seeding.