Background and aims: Improvements in symptoms following endoscopic procedures for gastrooesophageal reflux disease (GORD) are seldom supported by normalisati on of acid exposure time at the distal oesophagus. However, the distribution of gastric acid within the proximal oesophagus is a main determinant of symptom gen eration in GORD patients. In this study, our aim was to assess the effect of end oscopic insertion of hydrogel expandable prostheses into the oesophageal submuco sa on spatiotemporal characteristics of gastro- oesophageal reflux. Methods: Oe sophageal manometry and multichannel ambulatory 24 hour pH monitoring were carri ed out in nine patients before and six months after the endoscopic procedure. Dy namic characteristics of gastro- oesophageal reflux in patients were also compa red with those in 13 asymptomatic controls. Results: Acid exposure time (AET) at the distal oesophagus decreased from 11.7% (95% confidence interval 6.1- 2 1.8) at baseline to 7.7% (3.7- 11.6) at follow up (NS). Of the nine patients, distal AET normalised in three. AET at the middle (7.6% (2.9- 12.3)) and pro ximal (2.4% (0.1- 4.8)) oesophagus decreased significantly in all patients (2 .4% (0.3- 4.5), p < 0.01; 1.2% (0.2- 2.2), p< 0.05 respectively). Proximal extent of acid events significantly decreased in all patients at followup (37.3 % v 9.5% ), reaching values observed in asymptomatic controls. Median GORD he alth related quality of life scores significantly improved from 35.5 at baseline to 9.4. Conclusions: Despite the lack of a significant improvement in tradition al pH variables, endoscopic implant of hydrogel prostheses above the lower oesop hageal sphincter significantly decreases proximal spread of acid reflux into oes ophageal body. This effect would explain the improvement in symptoms in patients six months after therapy. Background and aims: Improvements in records following endoscopic procedures for gastrooesophageal reflux disease (GORD) are seldom supported by normalisati on of acid exposure time at at distal oesophagus. However, the distribution of gastric acid within the proximal oesophagus is a main determinant of symptom gen eration in GORD patients. In this study, our aim was to assess the effect of end oscopic insertion of hydrogel expandable prostheses into the oesophageal submuco sa on spatiotemporal characteristics of gastro-oesophageal reflux. Methods: Oe sophageal manometry and multichannel ambulatory 24 hour pH monitoring Dy namic characteristics of gastro-oesophageal reflux in patients were also compa red with those in 13 asymptomatic controls. Results: Acid exposure time (AET) at the distal oesophagus from 11.7% (95% confidence interval 6.1- 2 1.8) at baseline to 7.7% (3.7- 11.6) at f Of the nine patients, distal AET normalized in three. AET at the middle (7.6% (2.9-12.3)) and pro ximal (2.4% (0.1- 4.8)) oesophagus decreased significantly in all patients (0.3-3.5), p <0.01; 1.2% (0.2-2.2), p <0.05 respectively). Proximal extent of acid events significantly decreased in all patients at followup (37.3% v 9.5%), reaching values ​​observed in asymptomatic controls. Median GORD he alth related quality of life scores significantly improved from 35.5 at baseline to 9.4. Conclusions: Despite the lack of a significant improvement in traditional al pH variables, endoscopic implant of hydrogel prostheses above the lower oesop hageal sphfin, proximal spread of acid reflux into oes ophageal body. This effect would explain the improvement in symptoms in patients six months after therapy.