Because the mechanisms that control the movement of food and digestive juices across the human pylorus are not completely understood, the aim of this study was to document the normal patterns of pressure activity in the antrum, pylorus, and duodenum and the associated pH changes in 9 healthy volunteers. Studies were carried out under fasting conditions and after ingestion of 300 ml of chocolate milk, using a unique 11-channel intraluminal probe that incorporated a sleeve sensor positioned across the pylorus and pH electrodes situated in the terminal antrum and proximal duodenum. The most common motor pattern recorded under fasting conditions consisted of regular coordinated contractions, most of which (a) involved the antrum and duodenum, (b) showed evidence of propagation through two or more adjacent channels, and (c) were associated with transient reductions in duodenal pH and transient elevations in antral pH. Ingestion of milk changed the motor pattern to one that was composed of pressure waves, which were confined to the pylorus with few or no pressure waves in the terminal antrum or proximal duodenum. Isolated pyloric pressure waves were gradually replaced by propagated antroduodenal contractions, which eventually occurred at a regular frequency that was higher than that observed under fasting conditions. After ingestion of milk, only the coordinated contractions were associated with transient reductions in duodenal pH. Isolated pyloric pressure waves were also observed under fasting conditions just before or just after phase III of the migrating motor complex, and 17% of these were accompanied by episodes of duodenal acidification.