Bile acids, classically known for their roles in facilitating lipid digestion and absorption, are becoming increasingly appreciated as a family of enterocrine hormones in their own right. It is now known that bile acids are critical for maintenance of intestinal homeostasis and regulate many aspects of intestinal physiology, including epithelial barrier and transport function, smooth muscle contraction, and vascular tone. In the intestine, conditions that disrupt the enterohepatic circulation can lead to increased delivery of bile acids to the colon, thereby contributing to the onset of diseases, such as irritable bowel syndrome and inflammatory bowel disease. In our laboratory, we are most interested in elucidating the roles that bile acids play in regulating intestinal epithelial physiology and our current studies focus on the role that the nuclear bile acid receptor, farnesoid X receptor, plays in regulating colonic epithelial Cl- secretion, the primary driving force for fluid secretion. In these studies the synthetic ligand, GW4064 (5 μM; 24hours), was used to activate FXR. Cl- secretion was measured as changes in short-circuit current across T84 cell monolayers or muscle-stripped mouse colonic tissues. Protein expression was measured by western blotting or qPCR. We found that GW4064 treatment inhibited Cl- secretion in response to the Ca2+ and cAMP-dependent agonists, carbachol and forskolin, respectively. Intraperitoneal injection of GW4064 to mice (50mg/kg) attenuated Cl- secretion in colonic tissues. In contrast, epithelial absorptive pathways appeared largely unaltered, suggesting the effects of FXR activation are specific for secretory processes. Furthermore, GW4064 treatment inhibited the severity of symptoms in 2 separate mouse models of diarrhoeal disease. Studies into the molecular mechanisms by which activation of the FXR exerts its effects revealed that GW4064 decreased CFTR-mediated Cl- currents in T84 cells, an effect that was associated with a decrease in CFTR protein expression. GW4064 also inhibited Na+/K+-ATPase activity but without altering expression of this protein. These data reveal novel antidiarrhoeal actions of FXR activation in colonic epithelium. These effects are mediated by inhibition of multiple components of the Cl- secretory pathway, without altering absorptive processes. Our data suggest that FXR agonists may be useful in treating secretory diarrhoeas associated with common intestinal disorders.