Intraluminal impedance recording has made it possible to record fluid transport across the pylorus during the interdigestive state without filling the stomach. During antral phase II fluid transport occurs with and without manometrically detectable antral contraction. Our aim was to investigate the relationships between ultrasonographic patterns of antral contraction, manometric pressure waves and transpyloric fluid transport during antral phase II. Subjects and methods: Antral wall movements were recorded by real-time ultrasound (US) in 8 healthy volunteers (mean age 24±7 years) during 17±5 minutes of antral phase II. Concomitantly a catheter positioned across the pylorus, monitored by transmucosal potential difference measurement, recorded 5 impedance signals (1 antral, 1 pyloric and 3 duodenal) and 6 manometric signals (2 antral, 1 pyloric and 3 duodenal). Antral contractions detected by US at the level of the two antral impedance electrodes were classified according to their association with a pyloric opening or a duodenal contraction. Transpyloric liquid transport events (impedance drop of more than 40 % of the baseline with an antegrade or retrograde propagation) and manometric pressure waves (amplitude and duration) were identified during the whole study and especially during each period of US antral contraction. Results: A total of 110 antral contractions were detected by US. Of these, 79 were also recorded by manometry. Fluid transport across the pylorus was observed in 70.9 % of the US- detected antral contractions. Pyloric opening was observed in 98.6 % of the contractions associated with fluid transport as compared to 50 % in the absence of fluid transport (p<0.05). Antral contractions associated with fluid transport were significantly (p<0.05) more often propagated to the duodenum (92%) than those without fluid transport (53%). Pressure waves associated with fluid transport were of higher amplitude (208 mmHg, range 22-493)and longer duration (7 seconds, range 2.5-13.5)than those not associated with fluid transport (102 mmHg, range 18-329 and 4.1 s, range 2-8.5, p<0.05). The propagation of the antral contractions in the duodenum in US was always associated with a pyloric opening whereas only 8 of the 25 contractions without duodenal propagation were associated with a pyloric opening (p<0.05). The presence of duodenal contractile activity before the onset of an antral contraction in US was always accompanied by pyloric opening and with fluid transport in 93.3 %, as compared to 56.8 % in its absence (p<0.05). Conclusion: In antral phase II, ultrasound is the most sensitive technique to detect antral contractions. Transpyloric fluid transport observed in relation with antral contractions occurs mainly in association with contractions of high amplitude, long duration, and is associated with pyloric opening and/or duodenal propagation.