PCR cloning strategy was used to isolate cDNAs of ClC family members in the kidney. Three new members, named ClC-K1, ClC-K2, ClC-3, have been isolated. Functional expression studies in the Xenopus oocytes confirmed that these are chloride channel proteins. Northern blot and immunohistochemistry showed that ClC-K1 and ClC-K2 are selectively expressed in the kidney, while ClC-3 distributes in a variety of organs such as brain, lung, and kidney. Identification and characterization of new ClC channel proteins will contribute to a better understanding of chloride transport in the kidney.