OBJECTIVE To determine the main characteristics of gastroduodenal motility in mechanically ventilated, critically ill patients. METHODS Case series; comparison with a parallel control group. METHODS Intensive care unit in a university teaching hospital. METHODS Twelve adult critically ill patients who required > 2 days of mechanical ventilation as a consequence of neurologic or respiratory disease. Control sample of 12 overnight, fasting, healthy volunteers. RESULTS Pressure changes in the gastric antrum, proximal duodenum, and distal duodenum were simultaneously recorded during a 4-hr period by a multilumen tube (perfused catheter technique). The migrating motor complex and its three successive phases were identified according to usual definitions (phase 1, period of quiescence; phase 2, period of irregular contractile activity; phase 3 or activity front, period of high-frequency, regular contractions). Contractions and activity fronts at each site were quantified. The mean duration of the migrating motor complex was determined in the duodenum, as well as the contribution of each phase (phases 1, 2, 3) to the length of the complete cycle. The propagation characteristics of each activity front were assessed visually. In the patients, the number of contractions was markedly decreased in the antrum, where activity fronts were totally absent. In the duodenum (proximal and distal), the number of contractions and the occurrence of activity fronts were comparable in both groups. Although the duration of the duodenal migrating motor complex was similar in the two groups, the relative contribution of the quiescence period (phase 1) to the total cycle length increased and the contribution of phase 2 decreased in the patients. Three patients exhibited abnormally propagated (retrograde or stationary) activity fronts in the duodenum. CONCLUSIONS Gastroduodenal motility is severely impaired in this group of mechanically ventilated patients. Activity fronts of the migrating motor complex never originated in the stomach, which was hypokinetic; qualitative disorders of the migrating motor complex were present in the duodenum. The loss of peristaltic activity in the stomach and, to a lesser degree, in the duodenum is consistent with an important role for motility disorders in the occurrence of digestive microbial overgrowth in such patients.