We have cloned a cDNA from the human epithelial cell line T84 whose predicted amino acid sequence shows 93.9% identity with rat CIC-2. Mapping by somatic cell hybrids and polymerase chain reaction localizes the gene corresponding to this cDNA to chromosome 3q26-qter. The major transcription start site assessed by RNA primer extension is 100 nt upstream of the putative translation initiation codon. Analysis of the 5' flanking sequence revealed a high GC content and lack of common transcriptional elements such as TATA and CCAAT boxes. Northern blot analysis indicated wide organ distribution including tissues affected in cystic fibrosis (CF) and expression in an airway epithelial cell line derived from a CF patient. The high degree of sequence similarity and similar tissue distribution to rat CIC-2 suggests that this cDNA encodes the human CIC-2 voltage-gated chloride channel. Since this chloride channel is present in epithelial tissues it may be amenable to manipulation to circumvent the chloride secretion defect observed in CF.