Attachment of "'Indium-oxine labeled cultured canine venous endothelial cells to expanded polytetrafluorethylene (ePTFE) grafts was evaluated in vitro. Three alternative seeding techniques were studied in grafts having different diameters, porosities, and surfaces, including: (I) manual milking of blood containing endothelial cells within the graft; (11) a two-step procedure of incubating grafts initially with blood and then with an endothelial cell suspension; and (111) mechanical spinning of grafts filled with blood containing endothelium. Method I1 had significantly higher cell attachment to the graft (11.6%) than did Method 1(1.5%) or 111 (4.7%). A somewhat higher seeding efficiency was noted in 10-mm-I. D. grafts (11.6%) compared to 6-mm-I. D. grafts (6.3%). Different graft porosity, created by altering internodal distances, did not causr significant changes in cell attachment (10 pm, 13.4%; 30 pm, 6.3%; 90 pm, 16.0%). Fibronectin-coated surfaces, which should have enhanced cell adhesion, demonstrated a 6.0% cell attachment, a lower efficiency than the 11.6% observed with a blood coating alone. Acetone-soaked surfaces, which should have predictably exhibited less hydrophobicity, produced quite variable attachments (range 3.4 to 59.7%, mean 23.4%). In the present investigation the best seeding technique was method 11, the two-step incubation procedure. Consistant differences were not noted with various ePTFE graft configurations or surfaces.