Intestinal permeability in inflammatory bowel disease and its relation to periods of disease activity has been investigated by measuring the urinary excretion of DTPA labeled with 99mTc. Urine excretion in 10 control subjects was 2.7 +/- 1% of the test dose. Twelve patients with ulcerative colitis excreted 5.08 +/- 1.6% in remission, 10.61 +/- 2% during periods of mild activity, 19.41 +/- 0.9% during moderate activity, and 15.41 +/- 6.3% with severe activity. Sixteen patients with Crohn's disease excreted 5.7 +/- 1.9% in remission, 8.47 +/- 2.8% during mild activity of the disease, and 14.29 +/- 5.8% during moderate activity. No differences were observed between ulcerative colitis and Crohn's disease, or between ileal and colonic forms of Crohn's disease. Excretion in remission was significantly greater than in control subjects and there was a correlation between excretion and disease activity. In serial determinations done in seven patients we found that urine excretion of the test substance correlated with disease activity. We also studied DTPA excretion in 10 cases with gastric or duodenal ulcer (2.28 +/- 1.4%), six cases of acute gastroenteritis (4.87 +/- 3.1%) and nine cases with other intestinal diseases (3.6 +/- 1.1%). In all these cases, DTPA excretion was lower than in inflammatory bowel disease. Our results show that the urinary excretion of DTPA is a simple test that measures accurately the degree of activity of inflammatory bowel disease. The test is useful in Crohn's disease as well as in ulcerative colitis, and detects intestinal permeability abnormalities even in clinical remission. Significantly lower excretions are found in other intestinal diseases. The test may be recommended as a screening test for use in clinical practice.