Recently, a number of synthetic fabrics have been reported to be useful as vascular prostheses in human beings and experimental animals. Of these plastic materials, Vinyon "N," nylon, Orlon, Dacron, and Teflon have been investigated most extensively as to patency, incidence of thrombosis, method of fabrication, porosity, and tissue reactions.1,3,5,6,11Amylan (nylon 6) was studied by us as a material to replace the thoracic aorta in dogs and proved to be a satisfactory strut for blood flow. It was then transplanted into the abdominal aorta of a man with arteriosclerotic aneurysm. The graft eventually ruptured into the duodenum and caused fatal gastrointestinal bleeding a year later. Owing to the scarcity of reports on the fate of these plastic tubes in clinical cases, we felt it worth while to report our experience. Experimental Study Material. Nylon is a general denomination for a longchained synthetic polyamide, which can form a filament.