After thermal injury, alterations in intestinal permeability have been demonstrated and have correlated with subsequent infections. We measured intestinal permeability on the second day after severe trauma and hemorrhagic shock (ruptured abdominal aneurysm). The mean (+/- SD) lactulose-mannitol (L/M) excretion ratio was 0.012 +/- 0.005 in seven healthy control subjects, 0.069 +/- 0.034 in 11 severely traumatized patients, and 0.098 +/- 0.093 in eight patients with aneurysm, indicating a significant increase of intestinal permeability in both patient groups. No significant correlation was found between L/M ratios and age, severity of injury or shock, lactate levels on admission, APACHE (acute physiology and chronic health evaluation) II score, daily pulmonary gas exchange parameters, or mean multiple organ failure scores. No difference in intestinal permeability between patients with and without subsequent infections could be demonstrated. In 11 patients we looked for endotoxin in the systemic circulation. In six patients endotoxemia was present immediately after admission and before the L/M test. However, during the L/M test and 1 day afterward no circulating endotoxin was observed. The present data provide evidence for the hypothesis that increased intestinal permeability and subsequent infectious complications are independent phenomena, frequently seen in patients after severe trauma or hemorrhagic shock.