This study was undertaken to test the hypothesis that external stimuli acting through the central nervous system perturb the normal gastrointestinal response to meals. Thus, in 4 healthy volunteers we used a multilumen gastroduodenal tube system that allowed simultaneous measurements of gastroduodenal motility, gastric emptying rate, gastric acid secretion, and pancreatic trypsin output. Blood pressure, pulse rate, and skin temperature were also monitored for autonomic response. All subjects were studied on 2 days, receiving on each day two identical test meals. After one of the meals on each day, vertigo was induced by labyrinthine stimulation (ear irrigation with ice water) while the other meal was followed by one of two controls, ear irrigation at 37 degrees C (control stimulation) on 1 day and no stimulation on the other, the order of the tests being randomized. Labyrinthine stimulation at subnauseant levels resulted in a consistent and reproducible delay in gastric emptying of the meal. Further, in 2 of the 4 subjects a marked and reproducible alteration of the postprandial duodenal motility pattern occurred, with a change to one resembling the fasted state, even though nutrients continued to be present in the stomach. Duodenogastric reflux and gastric acid output remained unchanged. Trypsin output decreased initially but later returned to control values. These studies emphasize the role of the central nervous system in the control of gut function after feeding. Labyrinthine stimulation nay be a useful method for investigating inhibitory and disruptive effects of centrally acting stimuli on the human upper gut.