Indium-111 autologous leucocyte scanning is a non-invasive and reliable technique for the detection of abdominal abscesses. In the past decade several papers have been published concerning the use of this technique in the assessment of inflammatory bowel disease (IBD) with variable results. We conducted a prospective study of 62 patients with IBD attending the Leiden University Hospital, to assess the diagnostic value of indium-111 tropolonate autologous granulocyte scanning. Fifty-one patients had Crohn's disease (CD) (30 with involvement of the small bowel, 18 the colon only, and 3 patients had both localizations), and 11 had ulcerative colitis (UC). Twenty-one of 26 patients with evidence of active disease of the small intestine had a true-positive scan (sensitivity, 80%). However, accurate assessment of localization and extent of disease were often difficult. The other five patients had a false-negative scan. Seven patients had a true-negative scan. No false-positive scans were found. Thus, the diagnostic accuracy for small-intestinal Crohn's disease was 85%. In contrast, of 32 patients with colonic disease (CD and UC), 26 had a true-positive scan corresponding in localization and extent with standard investigations, 3 patients had a false-negative scan (sensitivity, 90%), and 3 had a true-negative scan (diagnostic accuracy, 91%). The patients' acceptability of this procedure was definitely superior to that for radiology and endoscopy. In conclusion, this technique has a definite place in evaluating localization and extent of active colonic disease and in severely ill patients in whom invasive techniques are contraindicated.(ABSTRACT TRUNCATED AT 250 WORDS)