Calprotectin is a protein released especially from neutrophilic leukocytes and secreted into the intestine during inflammation of the intestinal mucosa. It can be assayed from the feces. Faecal calprotectin has proven to be a useful marker in the diagnostics and monitoring of inflammatory bowel diseases, and application of the assay has been extended from pediatric patients also to adults. Faecal calprotectin is highly elevated in active inflammatory bowel disease, and elevated values in symptomless patients seem to be predictive of exacerbation especially in ulcerative colitis and in Crohn's disease colitis.