Gastrointestinal permeability. Intestinal permeability was determined using lactulose and mannitol. After a fasting period of 12 hours GvHD-mice (n = 20), control animals (n = 18) and non irradiated B6D2F1 mice (n = 8) received 1 ml of the lactulose/mannitol solution by orogastral tube. One hour after feeding serum concentrations of lactulose (representative for paracellular permeability) and mannitol (representative for transcellular permeability) were determined using melibiose as internal standard as described. A) mean and SD of mannitol and lactulose serum concentrations normalized to melbiose. * indicates p-values < 0.05 and ** p-values < 0.01. B) Lactulose/mannitol quotient. * indicates p-value < 0.05.