There is a need for new methods to study the dynamics of the esophagogastric junction (EGJ). The aims were to verify the efficacy and usefulness of a "functional lumen imaging probe" (FLIP) for the evaluation of the EGJ. Eight healthy volunteers (6 men), median age 26 (21-35) yr, and two achalasia patients underwent the FLIP procedure. The EGJ was located by manometry. The FLIP measured eight cross-sectional areas (CSAs) 4 mm apart together with the pressure inside a saline-filled cylindrical bag. The data showed the geometric profile of the EGJ reconstructed in a video animation of its dynamic activity. A plot of curve-fitted data for the smallest CSA vs. pressure after balloon distension indicated that the pressure increased from 18 cmH2O at a CSA of 38 mm2 to a pressure of 37 cmH2O at a CSA of 230 mm2 for the healthy controls. In one achalasia patient (unsuccessfully treated with dilations), the CSA never rose above the minimal measurable value despite the pressure increasing to 50 cmH2O. In another achalasia patient (successfully treated with dilations), the pressure only reached 15 cmH2O despite opening to a CSA of 250 mm2. In conclusion, FLIP represents the first dynamic technique to profile the function and anatomy of the EGJ. The method can be used practically to evaluate difficult cases of EGJ dysfunction and may provide a role in evaluating patients before and after therapies for diseases affecting the EGJ such as achalasia and gastroesophageal reflux disease.