AbstractThe effect of varying bile acid output on fasting small intestinal motility was investigated in healthy male volunteers. Biliary output was manipulated by jejunal infusion of isotonic mannitol, which resulted in increased output, and by prolonged drainage of duodenal contents, which resulted in decreased output. Intestinal motility was measured by manometric recordings performed at four levels in the proximal small intestine. A marker dilution technique was used to measure pancreatico‐biliary output. There were three experimental groups: duodenal drainage, non‐drainage and control. Both duodenal drainage and non‐drainage groups underwent jejunal saline infusion, followed by mannitol infusion. The control group did not receive drainage or infusions. In the drainage group, 0.41 (0.13‐0.68) activity fronts of the migrating motor complex (MMC) per hour were recorded during saline infusion, but only 0.06 (0‐0.19) activity fronts per hour were observed during mannitol infusion. In the nondrainage group, 0.71 (0.61‐0.81) activity fronts per hour were observed during saline infusion and 0.50 (0.18‐0.82) activity fronts per hour were recorded during mannitol infusion. In the control group, 0.58 (0.33–0.84) activity fronts per hour were recorded during the first 4‐h session and 0.58 (0.45‐0.71) activity fronts per hour during the second session. There was no difference between the number of activity fronts per hour observed in the control group and those observed in the saline infusion of the drainage group. In contrast, there was a significant decrease in the number of activity fronts per hour in the drainage group during mannitol infusion, compared to both non‐drainage group during mannitol infusion (P<0.01) and controls (P<0.05). In conclusion, decreased biliary output caused by duodenal drainage in combination with mannitol infusion is associated with inhibition of the cyclic activity of MMC in the proximal s