Background: New thread-cutting techniques were developed for use at flexible endoscopy. A guillotine was designed to follow and cut thread at the endoscope tip. A new method was developed for guiding suture cutters. Efficacy of Nd:YAG laser cutting of threads was studied. Experimental and clinical experience with thread-cutting methods is presented. Methods: A 2.4 mm diameter flexible thread-cutting guillotine was constructed featuring two lateral holes with sharp edges through which sutures to be cut are passed. Standard suture cutters were guided by backloading thread through the cutters extracorporeally. A snare cutter was constructed to retrieve objects sewn to tissue. Efficacy and speed of Nd:YAG laser in cutting twelve different threads were studied. Results: The guillotine cut thread faster (p < 0.05) than standard suture cutters. Blackloading thread shortened time taken to cut thread (p < 0.001) compared with free-hand cutting. Nd:YAG laser was ineffective in cutting uncolored threads and slower than mechanical cutters. Results of thread cutting in clinical studies using sewing machine (n = 77 cutting episodes in 21 patients), in-vivo experiments (n = 156), and postsurgical cases (n = 15 over 15 years) are presented. Conclusions: New thread-cutting methods are described and their efficacy demonstrated in experimental and clinical studies. (Gastrointest Endosc 1996;44:667-74.)