It is disclosed that a long elevation time is obtained and the efficiency of resection can be improved by providing an endoscopic injectable preparation using high molecular weight hyaluronic acid having an average molecular weight of 1,500,000 to 3,000,000 or its salt.In treating early cancer or other neoplastic mucosal lesion, the lesion is resected with handling of an endoscope ("endoscopic mucosal resection") instead of performing a major surgical operation such as laparotomy, thoracotomy or organ excision. In performing endoscopic mucosal resection, physiological saline, or a solution of low molecular weight hyaluronic acid or its salt is injected into a stratum below the site of lesion scheduled for resection to elevate the site of lesion, thereby increasing the efficiency of resection. To raise the efficiency of endoscopic mucosal resection, however, the development of an injectable preparation presenting a longer elevation time and requiring a low injection pressure has been desired.
