A total of 70 patients undergoing replacement of the aortic bifurcation between October 1983 and June 1985, were studied 5 years postoperatively for graft patency. In 35 cases a collagen-coated knitted Dacron prosthesis (group I) was implanted, while an identical, but uncoated, Dacron graft was used in a second group of 35 patients (group II). Distribution of vascular risk factors were similar in both patient groups. The underlying disease was aortoiliac occlusive disease in 24 patients of group I and in 33 of group II. Aortoiliac aneurysmal disease was present in 10 patients of group I and in 2 patients of group II. One patient of group I was suffering from Takayasu's disease of the descending type. At follow-up, all grafts were patent in group I, while in group II 8 distal limb occlusions occurred between 6 and 46 months postoperatively. This represents a 5-year limb patency rate of 100% for collagen-presealed grafts versus 88.6% for uncoated prostheses (p less than 0.01). A higher incidence of distal anastomotic aneurysms was found in group I (7/70 limbs) compared to group II (1/70 limbs) (p less than 0.05). It is concluded that long-term patency of knitted Dacron prostheses in aortic bifurcation replacement is not reduced by presealing with collagen. It appears that this type of coating may actually enhance long-term patency after reconstruction of the aortoiliac axis. The higher rate of distal anastomotic aneurysm formation in patients with presealed grafts, however, could not be correlated with a failure of the sealant material or with the underlying disease of the patients involved.