It is the purpose of this report to present observations on certain changes in the behavior of gastric acidity which follow experimental diminution in the activity of the pyloric sphincter (pyloric insufficiency). In previous communications1 from this laboratory experiments were described which indicated that reflux of alkaline pancreatic juice into the stomach was probably an important factor in the regulation of the level of gastric acidity. One might expect as a corollary that the pyloric sphincter governs this regurgitation in a decisive way. Direct roentgenologic observations of such a phenomenon have been made in human beings by Salamond.2 The present experiments add further support to the theory. PREVIOUS WORK That there is a relationship between gastric acidity and the pyloric muscle has long been noted from a great variety of evidence,3 which need not be reviewed here. A succinct statement of this relationship was advanced in 1907