The gastrointestinal tract shares with the skin and lung the distinction of being of a major route of both exposure and systemic absorption for environmental chemicals as well as being a target for their adverse intestinal toxins that result from interactions of chemicals, nutrients, and microorganisms add another dimension to the possible alterations of intestinal function by chemical exposure. The principal function of the gastrointestinal tract is to modify ingested food so that the nutrients can be absorbed by the intestines, passed into the bloodstream/lymph, and transported throughout the organism. Interactions of the chemicals within the gastrointestinal tract reflect the properties of the tract per se, the chemicals, and the organisms. Drugs which modify intestinal transit include atropine, morphine, clonidine, papaverine, and isoproterenol. Inflammatory bowel disease is a group of chronic inflammatory intestinal conditions which has become more prevalent in first world populations and which have been associated with a range of drugs.