BACKGROUND & AIMS: Acute ischemic diseases of the small bowel are lethal emergencies with no reliable diagnostic biochemical tests available. Experimental studies have suggested rat intestinal fatty acid-binding protein (I-FABP) as a serum marker reflecting bowel ischemia; the present study evaluates the human homologue (human I- FABP) as a serum marker for the diagnosis of acute ischemic diseases of the bowel. METHODS: Enzyme immunoassay was applied to determine I-FABP levels in the sera of 96 subjects: 13 preoperative patients with ischemic bowel diseases (5 cases of mesenteric infarction and 8 cases of strangulated obstruction of the small bowel), 35 healthy subjects, and 48 hospitalized patients with acute abdominal pain. RESULTS: Serum I-FABP levels were < 65 ng/mL in healthy subjects. In patients with acute abdominal pain, levels ranged from < 20 to 87 ng/mL (mean, 27.4 ng/mL), not significantly different from findings in healthy subjects. However, patients with ischemic bowel disease showed significantly higher I-FABP levels, ranging from < 20 to 1496 ng/mL (mean, 265.8 ng/mL). All 5 patients with mesenteric infarction showed I-FABP levels of > 100 ng/mL. CONCLUSIONS: I-FABP is a useful biochemical marker for the accurate diagnosis of mesenteric infarction. (Gastroenterology 1996 Feb;110(2):339-43)