In order to investigate the duodenal motor response to continuous enteral feeding during critical illness, we recorded the duodenal contractions of 12 mechanically ventilated critically ill patients during a 4 h fasting period immediately followed by another 4 h period of continuous (100 kcal/h) nasogastric feeding with a polymeric diet. Duodenal motility was recorded by manometry (perfused catheter technique) and the migrating motor complexes (MMC) were identified by their activity front (period of high frequency, regular contractions). The incidence and the mean duration of activity fronts as well as the mean duration of the MMC (time interval separating two successive activity fronts) recorded during both periods were compared. The incidence of activity fronts (fasting: median: 2.5, interquartile range: 5.5; feeding: median: 2, interquartile range: 3.5), their duration (fasting: 6.2 +/- 1.6 min; feeding: 5.8 +/- 1.6 min), and the mean duration of the MMC (fasting: 50.9 +/- 24.7 min; feeding: 49.1 +/- 20.3 min) were similar during both periods. We conclude that in these patients, the fasting pattern of motility is not interrupted by the continuous nasogastric administration of a polymeric diet. Since the activity fronts of the MMCs are highly propulsive, we suggest that their abnormal persistence during feeding may play a role in the pathophysiology of unexplained diarrhoea in some critically ill patients.