Background: The aim of this study Was to determine whether the anatomicofunctional changes induced by vertical gastroplasty lead to pH alterations in the esophagus and body and antrum of the stomach. Materials and Methods: 23 non-smoking Volunteers (3 men, 20 women) mean age 35.29 +/- SD 6.85 years, mean weight 163.17 +/- 52.11 kg and mean BMI 56.06 +/- 14.01 kg/m(2) were studied. The pH of the esophagus, body and antrum of the stomach were measured preoperatively and 18 months postoperatively (after excess weight loss). Data was analyzed statistically using paired student t-test. Results: The pH values before (pH(1)) and after (pH(2)) the operation were: for the esophagus, pH(1e) SD = 6.12 +/- 0.31 and pH(2e) +/- SD = 5.92 +/- 0.37 (P=0.38), for the body of the stomach pH(1b) +/- SD 2.2 +/- 0.30 and pH(2b) +/- SD = 2.56 +/- 0.34 (P=0.30), and for the antrum pH(1a) +/- SD = 1.78 +/- 0.28, and pH(2a) +/- SD = 1.65 +/- 0.36 (P=0.011). Conclusions: Vertical gastroplasty does not affect the pH levels in the esophagus and in the body of the stomach. However, there is acidification in the antrum, which could lead to pH-related diseases.