The development of a new device and techniques for its use have made it possible to endoscopically decompress acute, malignant colorectal obstruction in 17 patients (5 with rectal carcinoma, 4 with carcinoma of the sigmoid colon, 3 with carcinoma of the descending colon, 2 with carcinoma of the transverse colon, 2 with carcinoma of the ascending colon, and 1 with carcinoma of the cecum). Following adequate cleansing of the colon, a definitive surgery was carried out in all patients. We describe here the techniques based upon the above experiences. 1) When abdominal CT suggests acute, malignant colorectal obstruction, colonoscopy should be carried out using a colonoscope equipped with an auxiliary water inlet under fluoroscopy. 2) Following the advance of a colonoscope to the site of the tumor, a hydrophilic guide wire is then introduced through the tumor beyond the point of obstruction using a water-soluble contrast medium and a biliary guide catheter. 3) A drainage tube whose tip is tapered is placed transanally with the aid of a dilator or a sliding tube. When difficulty is encountered in inserting the tube beyond the obstruction, the tube should be introduced into the stenotic segment holding the tube by grasping forceps.