Proinflammatory mediators, including leukotriene (LT) B4, are elevated in the intestinal mucosa in active chronic inflammatory bowel diseases (IBD). LTE4 is the major peptidoleukotriene metabolite and it is stable in urine. The aim of this study was to measure LTE4 levels in the urine of 27 children with Crohn's disease and 27 control subjects including 12 children with functional recurrent abdominal pain and 15 unaffected siblings of IBD patients. LTE4 levels were measured in urine using high-performance liquid chromatography separation and radioimmunoassay with specific antibody. The Pediatric Crohn's Disease Activity Index and physician global assessment were used to categorize patient groups. C-reactive protein, orosomucoid, and erythrocyte sedimentation rate were employed as laboratory markers of mucosal inflammation. Urinary LTE4 levels were elevated in the 13 children with active Crohn's disease (160.5 +/- 59.4 pg/ml; mean +/- SEM) compared with both levels in the 14 patients with inactive disease (67.1 +/- 18.1 pg/ml; p < 0.05) and controls (45.0 +/- 10.9 pg/ml; p < 0.05). We conclude that measurement of urinary LTE4 is a useful test for monitoring the activation of peptidoleukotrienes in patients with Crohn's disease. It provides a noninvasive, objective adjunct for assessment of disease activity and could be employed in future trials examining the role of the leukotriene inhibitors in the medical therapy of IBD.