The gastrointestinal tract is the most important of the three major routes of entry (and clearance) of xenobiotics and biologic entities into the bodies of mammals. As such, it is also the major route for administration of pharmaceuticals to humans. Gastrointestinal Toxicology, Second Edition describes the mechanism for entry and clearance of xenobiotics, as well as the barriers, immunologic and metabolic issues, and functions present in the GI tract.