BACKGROUND: Understanding of the effects of adjustments to laparoscopic adjustable gastric band (LAGB) volume is limited. Changes in intraluminal pressure may be important and explain patients reporting a tighter LAGB after saline is removed and an identical volume replaced. METHODS: Using high-resolution manometry, changes in the basal intraluminal pressure at the level of the LAGB in response to sequential, small alterations in LAGB volume were recorded. All fluid was removed from the LAGB and replaced, pressures and motility were reassessed. RESULTS: Sixteen patients (four males, age 45.4 +/- 13.2 years) participated. A linear increase (r (2) = 0.87 +/- 0.12) in intraluminal pressure was observed after a threshold volume was reached. The threshold volume varied considerably (1.0 to 5.8 ml). The gradient of the linear increase was 21.2 +/- 8.7 mmHg/ml. The mean basal intraluminal pressure at the level of the LAGB was initially 19.1 +/- 8.9 mmHg and increased to 37.0 +/- 20.4 mmHg (p = 0.001) after removing and replacing the same volume of saline. There was an increase in distal esophageal peristaltic pressure (123.5 +/- 34.7 vs. 157.4 +/- 52.6 mmHg, p = 0.003) and a decrease in the proportion of normal swallows (0.85 +/- 0.22 vs. 0.53 +/- 0.47, p = 0.02). Nine patients also developed adverse symptoms. CONCLUSIONS: Intraluminal pressure at the level of the LAGB is an objective measure of the restriction produced by LAGBs. The addition of fluid to the LAGB results in a linear increase in intraluminal pressure once a threshold volume is reached. The removal and replacement of the same volume of saline from the LAGB may temporarily increase intraluminal pressure.