BACKGROUND A late complication of pancreaticoduodenectomy is anastomotic ulcer, and the complication is lessened when pancreaticoduodenectomy is accompanied by preservation of the pylorus. However, the results of some reports suggest that acid levels are not significantly different between patients who undergo pylorus preserving pancreaticoduodenectomy (PPPD) and those having standard pancreaticoduodenectomy. In this study, we measured gastric acidity in the same patients both before and after PPPD. STUDY DESIGN Twelve patients participated in the study. Acid was measured by monitoring pH levels for 24 hours. Average pH values were calculated for two time periods: during the day (6 AM to 6 PM) and night (6 PM to 6 AM). In addition, the percentages of time during day and night hours that gastric acid was above pH 3 and above pH 4 were calculated and designated as pH holding times. RESULTS Average pH values and pH holding times during the day revealed no significant differences between patients preoperatively and postoperatively. At night, however, pH holding times significantly decreased in patients postoperatively when compared with patients preoperatively. Of 29 patients who underwent PPPD in our clinic, only one had an ulcer. The gastric acidity of this patient was similar to the others. CONCLUSIONS These results indicate that gastric acidity, as it relates to pH 3 and pH 4 holding times, increases after PPPD and that gastric acidity, per se, may not be involved in ulcer formation in these PPPD patients. Furthermore, the results of the study indicate that measuring gastric acidity for longer periods of time during the day and during the night might be important in studies on acid secretion.