PURPOSE: To evaluate the usefulness of a new model of the stent graft, and of tissue response related to placement of the stent graft. MATERIALS AND METHODS: The stent graft was constructed from polyurethane (Pellethane) graft and Hanaro stent (12 mm in diameter, 45 mm in length, 10 bends). A stent grafts was inserted into the lower thoracic aorta in each of six adult mongrel dogs (body weight, 12-16 kg). At one, two, four, and six months, follow-up studies of angiography and spiral CT angiography were performed to evaluate vascular patency, vascular stenosis, and thrombus formation. Two dogs were sacrificed at 1 month, 2 months, and 6 months after insertion of the stent graft and macroscopic, light microscopic, and scanning electron microscopic examinations of the aortic segment including the stent graft were performed to evaluate intimal hyperplasia, endothelial growth to the graft, and thrombus formation. RESULTS: During follow-up at one, two, four, and six months, angiography or spiral CT angiography showed 20-100% luminal stenosis or occlusion of the lower thoracic aorta by the thrombus and perigraft leaks in three dogs (50%), and collateral vessels caused by occlusion of the aorta in two (33.3%). On gross examination, there were thrombi of 1-5 mm thickness at the graft portions in all dogs, and this thickness gradually increased. The mean thickness of intimal hyperplasia at the stent portion gradually increased from 120um to 227um and the mean thickness of intimal hyperplasia at the graft portion from 93um to 914um. This thickness was greater at the graft portion than at the stent portion. Scanning electron microscopy showed elliptical endothelial lining on the neointimal surfaces at each end of the graft. CONCLUSION: Thrombi caused stenosis or occlusion of the stent graft. In order for such a graft to be ideal, further study is needed.