The intestinal electroneutral Na + absorptive processes account for most small intestinal Na + absorption in the period between meals and also for the great majority of the increase in ileal Na + absorption that occurs postprandially. In most diarrheal diseases, there is inhibition of neutral NaCl absorption. Elevated levels of intracellular calcium ([Ca 2+] i) are known to inhibit NaCl absorption and involve multiple components of the Ca 2+ signaling pathway. The BB Na +H + exchanger NHE3 accounts for most of the recognized digestive changes in neutral NaCl absorption, as well as most of the changes in Na + absorption that occur in diarrheal diseases. Previous studies have examined several aspects of Ca 2+ regulation of NHE3 activity. These include phosphorylation, protein trafficking, and multiprotein complex formation. In addition, recent studies have demonstrated the role of the NHERF family of PDZ domain-containing proteins in Ca 2+ regulation of NHE3 activity, thereby adding a new level of complexity to understanding Ca 2+-dependent inhibition of Na + absorption. In this article, we will review the current understanding of (1) Ca 2+ signaling events in intestinal epithelial cells; (2) Ca 2+ regulation of intestinal electroneutral sodium absorption, which includes NHE3; and (3) the role of the NHERF family of PDZ domain-containing proteins in Ca 2+ regulation of NHE3 activity. We will also present new data on using advanced imaging showing rapid BB NHE3 endocytosis in response to elevated [Ca 2+] i.