Background/aims: There is little information in the literature about colonic permeability in ulcerative colitis. In this study, the differential urinary excretion of orally administered markers was used to evaluate intestinal permeability in inflammatory bowel disease, especially in Crohn's disease. The aim was to investigate the absorption of 51Cr-Labelled ethylene-diaminetetraacetic acid (51CrEDTA) and its relationship to disease activity in inflammatory bowel disease. Methods: Thirty-eight patients were examined: 24 had ulcerative colitis, five Crohn's disease and nine were control subjects. 95 μCi of 51CrEDTA was given orally after an overnight fast and urine was collected for the following 24 hours. Fifth and 24th hour urine samples were used to calculate urinary 51CrEDTA as a percentage of the administered dose. Results: Intestinal permeability tested five and 24 hours after 51CrEDTA administration was significantly higher in patients with ulcerative colitis than the controls (5 h: ulc col 2.93 ± 2.32; control 0.49 ± 0.47; p=0.012 / 24 h: ulc col 7.00 ± 5.03; control 1.27 ± 1.03 ; p=0.011). In addition, patients with Crohn's disease revealed increased intestinal permeability, even though the number of patients in this group was small. There was a significant correlation between intestinal permeability and disease activity in patients with ulcerative colitis (r=0.65; p=0.0006). Conclusions: Oral administration of 51CrEDTA is a simple and non-invasive method in evaluating intestinal permeability. Increased urinary excretion of 51CrEDTA reflects increased bowel permeability in both large and small bowel inflammation and relates to disease activity.