The motor responses of the human duodenum to saline solutions of varying osmolality were examined in order to investigate the possible role played by the upper intestine in the control of gastric efflux of hyperosmolar material. During fasting, delivery of the solutions into the duodenum increased duodenal motor activity and intraduodenal pressure, the magnitude of the response increasing with osmolality. At the highest osmolalities, a regular duodenal motor pattern was induced in some individuals which was indistinguishable from fasting phase III activity. After feeding, hyperosmolar saline again increased motor activity. In addition, the transit of an intraduodenal marker to the caecum was accelerated. These findings support the concept that the duodenum is both sensitive and responsive to its intraluminal content. The motor responses additionally appear to function to clear excessively stimulating intraluminal material from the duodenal lumen and may also contribute to the 'postpyloric' resistance which is known to exert control of normal gastric emptying.