Intestinal chloride secretion is stimulated during diarrhea. Cholera toxin is secreted by bacterium Vibrio cholera and is responsible for the watery diarrhea after cholera infection. Mechanistically, cholera toxin increases intracellular cyclic AMP, which subsequently activates protein kinase A and the cystic fibrosis transmembrane regulator chloride channel (CFTR). However, we recently identified an intestinal cAMP-Ca cross-talk signaling pathway that is initiated by elevation of intracellular cAMP and subsequently elevates intracellular Ca concentrations through the exchange protein activated by cAMP (Epac). This observation suggests that both CFTR and calcium-activated chloride channels are targets of elevated intracellular cAMP signaling molecule. Therefore, we are studying the role of calcium-activated Cl channels in intestinal chloride secretion under physiological conditions and during diarrhea. We are also determining whether the recently identified transmembrane protein 16 family of proteins, which are calcium-activated chloride channels, is also involved in intestinal chloride secretion in addition to the well characterized CFTR channel. Increased understanding of regulation of intestinal Cl secretion provides the necessary background information for the development of therapeutic drugs for the treatment of diarrhea, constipation and cystic fibrosis. The discovery that calcium-activated chloride channels are involved in intestinal chloride secretion provides additional targets for anti-diarrhea drug development.