Background: Three antireflux operations—gastroplasty, fundoplication, and anterior gastropexy—were developed for performance at flexible endoscopy without laparotomy or laparoscopy. Methods: An endoscopic sewing machine mounted on a standard gastroscope, endoscopic knotting devices, overtube, and nylon thread were used to perform these operations in adult beagle dogs. Results: Gastroplasty (n = 10) was accomplished by suturing the anterior and posterior wall of the stomach to create a gastric tube (neoesophagus) along the lesser curve. An anatomic arrangement similar to fundoplication (n = 6) was achieved by invaginating the esophagus and fixing it to the stomach 2 cm distal to the cardioesophageal junction. Anterior gastropexy (n = 6) was performed using a technique similar to that used in creating percutaneous gastrostomies. There was no mortality. Ninety percent of sutures were seen atrepeat endoscopy at 4 to 8 week intervals. The gastroplasty group was selected for more extensive evaluation. Manometry using a three-channel perfused catheter system before and after the procedures showed an increase in the lower esophageal sphincter pressure (preoperative median 4.6 mm Hg; postoperative median 13.33 mm Hg, p = 0.008) and cardiac yield pressures (preoperative median 10 mm Hg; postoperative median 19 mm Hg, p = 0.007). Conclusions: This study demonstrates the feasibility of performing antireflux operations at flexible endoscopy, without laparoscopy or laparotomy, by use of endoluminal suturing techniques. (Gastrointest Endosc 1996;44:133-43.)