Electrolyte homeostasis is maintained by several ion transport systems. Na-(K)-Cl cotransporters promote the electrically silent movement of chloride across the membrane in absorptive and secretory epithelia. Two kidney-specific Na-(K)-Cl cotransporter isoforms are known, so far, according to their sensitivity to specific inhibitors. We have cloned the human cDNA coding for the renal Na-Cl cotransporter selectively inhibited by the thiazide class of diuretic agents. The predicted protein sequence of 1021 amino acids (112 kDa) shows a structure common to the other members of the Na-(K)-Cl cotransporter family: a central region harboring 12 transmembrane domains and the 2 intracellular hydrophilic amino and carboxyl termini. The expression pattern of the human Na-Cl thiazide-sensitive cotransporter (hTSC, HGMW-approved symbol SLC12A3) confirms the kidney specificity. hTSC has been mapped to human chromosome 16q13 by fluorescence in situ hybridization. The cloning and characterization of hTSC now render it possible to study the involvement of this cotransport system in the pathogenesis of tubulopathies such as Gitelman syndrome.