The invention relates to the treatment of inflammatory bowel disease, also termed IBD, including ulcerative colitis and Crohn's disease. To this end, the invention proposes clinoptilolite having a particle size between 0.2 and 1 μm for use in the treatment of inflammatory bowel disease, also termed IBD, in mammals and humans. In the case of such use, the clinoptilolite is preferably freed of heavy metals. In one variant, it is administered orally, optionally with pharmaceutically harmless carrier materials and/or diluents.