The efficiency of posterior hemifundoplication (Toupet's procedure) in the treatment of gastroesophageal reflux was studied prospectively in 25 patients. Surgery was performed because of resistance to medical therapy and/or ulcerated esophagitis (12 cases). Clinical symptoms were evaluated three times: preoperatively, from 2 to 4 months after surgery and thirdly at a late post-operative interview (mean 21 months). Esophageal pH was recarded through a 3-h period after a standard meal and acid peptic reflux was expressed using a scoring index taking into account the duration and magnitude of pH fall. Esophageal pH was assessed in all the patients before and shortly after surgery and in 10 patients at the late postoperative control. Twenty-four of the 25 patients, had a dramatic improvement or were symptom-free, from 2 to 4 months after operation; the gastroesophageal reflux score decreased in all but 1 patient, but returned to physiological values in only 19 patients (group A), and remained above the normal range in 6 patients (group B). In the latter subjects, the preoperative score was significantly higher and the time elapsed below pH 3 significantly longer than those in group A. At the late postoperative control, clinical symptoms of gastroesophageal reflux were noted in 10 of the 23 patients interviewed. The incidence of late postoperative deterioration was more frequent in group B patients (4 among 6 subjects) than in group A (6 out of 17), and in patients presenting with severe esophagitis before surgery. In conclusion, while they confirm the immediate clinical efficiency of posterior hemifundoplication in gastroesophageal reflux, these results indicate that an abnormal esophageal pH test persists in 25 p. 100 of patients, and seems to carry an increased risk of further clinical deterioration.