The particular substances that are ingested by individuals are the consequence of their environmental, residential, and occupational exposures. The possible effects of these exposures on intestinal functions can beexamined by the evaluation ofin vivo orin vitro exposure followed by an in vivo and/or in vitro monitoring of effects. Several examples of the in vivo exposure and in vitro monitoring approach are presented to demonstrate the consequences oforal exposure to either a heavy metal (arsenic), or a herbicide contaminant (2,3,7,8-tetrachlorodibenzo-p-dioxin) or a jet fuel propellant (hydrazine) and the subsequent measurement of either a particular metabolic pathway, or a cell-specific enzyme induction or the development of brush border enzymes are presented.