Bile acids have experimentally been found to damage the gastric mucosa and, thus, may be involved in stress lesion pathogenesis. We therefore measured intragastric bile acid concentrations in 26 critically ill, artificially ventilated patients. The control group consisted of eight healthy volunteers, whose treatment was similar to that of the patients with respect to bed rest, enteral feeding, and administration of H2-blockers. Gastric contents were aspirated via a gastric tube every hour for 24 h. Patients had higher intragastric bile acid concentrations than healthy controls, whether fasting [median 1.3 mmol/L (range 0.7-2.5) versus 0.3 (0.2-0.5) (p less than 0.05)] or fed via a gastric tube [1.3 (0.4-4.0) versus 0.4 (0.2-0.7) (p less than 0.05)]. Physiotherapy, nursing, and drugs (opiates, benzodiazepines, dopamine, pirenzepine, and metoclopramide) had no detectable influence on intragastric bile acid concentrations and pH in patients. We conclude that patients at risk to develop stress lesions have largely increased gastric bile acid concentrations that probably are due to increased duodenogastric reflux. This might be relevant for stress lesion pathogenesis.