Résumé : Aim: To evaluate the effect of infliximab induction therapy on calprotectin levels in patients with ulcerative colitis (UC). Patients and Methods: In this prospective study 53 patients with active UC from 17 centers were treated with infliximab therapy (5. mg/kg) at baseline, week 2, and week 6. Faecal calprotectin was measured every week. Sigmoidoscopies were performed at baseline, week 6 and week 10. Results: Median calprotectin levels decreased from 1260 (IQR 278.5- 3418) at baseline to 72.5 (IQR 18.5 - 463) at week 10 (p < 0.001). After 10. weeks, infliximab therapy induced endoscopic remission and a decrease in calprotectin to < 50. mg/kg or at least a 80% decrease from baseline level in 58% of patients. A significant and steep decrease of calprotectin levels was seen at week 2 for patients with an endoscopic remission at week 10 as compared to patients who did not show a remission. (p < 0.001).At week 10 an excellent correlation was found between endoscopic remission and clinical Mayo score reflected by an AUC of ROC analyses of 0.94 (0.87-1) and with calprotectin measurements (AUC 0.91 (0.81-1)) : all patients with calprotectin levels < 50 mg/kg, and a normal clinical Mayo score (= 0) were in endoscopic remission. Conclusions: Infliximab induces a fast and significant decrease of faecal calprotectin levels in anti-TNF naïve patients with ulcerative colitis predictive for remission of disease. © 2011 European Crohn's and Colitis Organisation.