PurposeWe developed a new method of endoscopic mucosal resection (EMR) using a mucinous substance of sodium hyaluronate. Its clinical application was started in June 1998. The details of this method were introduced in the 3rd ASGE video forum. This time, we developed new devices to establish a more reliable method, which enables a single-step resection of lesions larger than 4 cm in diameter.We tried this method on a large superficial gastric cancer of 4 cm in diameter. The new method will be presented on video. MethodsThe new devices we developed this time are incision forceps and a flat-ended transparent hood. The incision forceps can grasp a piece of tissue and cut the tissue with high frequency currents. The transparent hood on the tip of the scope plays two roles. One is the correction of the opening direction of the forceps, and the other is the opening and visualization of the submucosal layer at the incision line. After submucosal injections of sodium hyaluronate and a circumferential incision of the elevated mucosa with a needle knife, the thickened submucosal layer is cut with these devices instead of using a polypectomy snare. A large mucosa can be stripped off in one piece by this method. After several trials on dogs, in October 1999, we performed this method on a 71 year-old man with a large superficial gastric cancer located on the anterior wall of the antrum. The lesion arose from a pre-pylorus region and reached the angle. It also spread from the lessor curvature to the greater curvature. Results The cutting of the submucosal layer could be performed safely because the submucosal layer was maintained thick by the local injections of sodium hyaluronate. The tumor was resected in one piece. The pathological findings showed a complete resection of well differetiated intramucosal adenocarcinoma that measured 40 mm by 35 mm in diameter. The resected specimen measured 58 mm by 52 mm. The margin of the specimen was free of neoplasm along its circumference. There was no apparent vascular or lymphatic invasion. Conclusions From our experience, the main reason of failure in a single-step resection is the slipping of a part of the tumor out of the snare. It becomes almost impossible to hold an entire tumor with a snare if the tumor is large enough to locate in a round shape. The new method of EMR using sodium hyaluronate with assistance of the new devices can overcome the problems that are related to snareing. The new method enables a single-step resection of a large flat lesion greater than 4 cm in diameter.