BACKGROUND Small intestinal canine submucosa has been used in previous studies as a large diameter arterial graft and has shown acceptable patency rates. The aim of our experimental study was to assess its effectiveness when it is used as an autogenous medium-sized diameter arterial graft (5-7 mm). METHODS Fifteen mongrel dogs were included and underwent laparotomy under general anaesthesia. The mucosa, tunica muscularis and serosa were removed from a resected intestinal segment. The remaining tube, which consisted of the submucosa and the basilar tunica mucosa, represented the experimental graft which was used to replace a proportional gap of the canine infrarenal aorta. Ascertainment of peripheral pulses, measurement of the intra-aortic pressures, aortography and in vivo/in situ observation before the sacrifice of the animals, were the procedures used for verification of the graft's patency. RESULTS The resistance to thrombogenicity of the graft was considered satisfactory: nine out of 10 grafts remained patent for postoperative intervals ranging from one day to one year; one graft showed partial obstruction due to a technical perioperative error. The grafts showed also excellent physical characteristics (ease of handling and suturing, blood impermeability and durability), resistance to infection and showed no tendency to develop myointimal hyperplasia. CONCLUSIONS Small intestinal canine submucosa showed satisfactory haemodynamic properties, long-term patency and resistance to infection, when used as a medium-diameter arterial substitute.