Abstract: This study describes method for extraction and quantification of calprotectin (L1 protein) in feces by enzyme immunoassay. This protein is a prominent antimicrobial component of neutrophils, monocytes, macrophages and squamous epithelia. Calprotectin was stable in feces during storage for seven days at room temperature. Fecal calprotectin quantitated in a five gram sample taken from a 24 hours feces collection gave a reliable estimate of calprotectin found in the pooled collection. The assay had a within assay precision (=CV) of 1,9% and a between assay precision of 14,8%. The following mean fecal calprotectin levels were found: Healthy subjects (n=33) 3095 .mu.g/l, hospital controls (n=40): 14697 .mu.g/l, patients with inflammatory bowel disease (Crohn's disease and ulcerative colitis), (n=28) 40850 .mu.g/l. The differences between the means are highly significant.