Since the use of synthetic vascular grafts there has been the general impression that synthetic grafts do not develop atheromatous changes. This general impression was supported by the experimental work of Creech and associates1 in 1955 with nylon and Orion grafts in dogs, and of Rustad3 in 1958 with nylon-Teflon grafts in rabbits. They concluded that synthetic vascular grafts do not develop atherosclerosis. In 1958 Jordan2 described atheromatous changes in the pseudointima of a nylon and Orlon graft in 2 of 6 hypothyroid dogs with hypercholesterolemia for more than 1 year. The purpose of this investigation was to determine whether synthetic vascular grafts composed of Dacron, Teflon, nylon, and a combination of Dacron-Teflon and nylon-Teflon, would develop atherosclerosis. The adult albino rabbit was selected as the experimental animal because of the relative ease in producing atherosclerosis by hypercholesterolemia. The dog would technically be ideal for vascular grafting,