Intestinal permeability was assessed in patients with inflammatory bowel disease by measuring the urine excretion of 51chromium-labeled ethylenediaminetetraacetate over periods up to 24 h after oral administration. Twenty-eight control subjects and 10 patients with ulcerative colitis excreted less than 2.6% of the test dose in 24 h. Ten patients with small bowel Crohn's disease excreted 3.3%-14.0%, and 10 of 11 patients with ileocolonic involvement had increased excretion. At the same time, 5 of 11 patients with Crohn's colitis were clearly outside the normal range, suggesting small bowel involvement. The 24-h urine excretion of 51chromium-labeled ethyl-enediaminetetraacetate after oral administration appears to be a sensitive, noninvasive test for assessing small intestinal integrity, and may be a valuable adjuvant in the differential diagnosis of inflammatory bowel disease.