Changes in the luminal contents of the gastrointestinal tract modulate gastrointestinal functions, including absorption of nutrients, food intake and protection against harmful substances. The current notion is that mucosal enteroendocrine cells act as primary chemoreceptors by releasing signaling molecules in response to changes in the luminal environment, which in turn activate nerve terminals. The recent discovery that taste receptors and G-proteins subunits, -gustducin and -transducin, involved in gustatory signal transduction are expressed in the gastrointestinal mucosa supports the concept of a chemosensory machinery in the gastrointestinal tract that participates in the functional detection of harmful substances in the lumen and possibly initiates a protective response including vomiting, cessation of food intake and food aversive behavior. An understanding of luminal sensing processes responsible for the generation of the appropriate functional response to specific nutrients and non-nutrients is of clinical importance since aberrant or unsteady response to changes in luminal contents might result in disease states ranging from intoxication to feeding disorders and inflammation. The purpose of this theme article is to discuss the functional implications of bitter taste signaling molecules in the gastrointestinal tract deduced by their localization in selected populations of epithelial cells and their relationship with neural pathways responsible for the generation of specific responses to luminal contents.