Objective : To find out if there was a relationship between increased intestinal permeability and the development of multiple organ failure (MOF) after multiple injuries, we correlated the extent of injury and MOF with intestinal permeability on the second and fourth day after injury. Design : Prospective open study. Setting : University hospital, Slovenia. Patients : 29 multiply injured patients, injury severity score (ISS) over 25, admitted shocked. Intervention : Intestinal permeability measured by giving lactulose and mannitol solution enterally on days 2 and 4. Main outcome measures : The lactulose: mannitol ratio calculated from the urinary portion of the probe molecules. ISS and the acute physiology and chronic health evaluation (APACHE II) calculated on admission. Results : The median lactulose: mannitol ratio for five volunteers was 0.014 (range 0.008-0.017) and that for 29 patients was 0.03 (0.01-0.1). On day 2 it was 0.03 (0.02-0.1), on day 4 0.02 (0.01-0.2). The ratio calculated on day 2 correlated with average and late MOF scores ( r = 0.41 R 2 = 0.1681, p < 0.03 and r = 0.38, R 2 = 0.1444, p < 0.04) and that measured on day 4 correlated with overall, early, and late MOF scores ( r = 0.47, R 2 = 0.2209, p < 0.01; r = 0.51, R 2 = 0.2601, p < 0.005; r = 0.39, R 2 = 0.1512, p < 0.04). No correlation was found between ISS, transport time, shock index, APACHE II, and days in intensive care. Conclusions : Even if intestinal permeability is invariably increased after injury, it seems to have some predictive value for MOF in multiply injured patients because it correlates with its development.