Aquaporin-CHIP is the first known molecular water channel. Originally identified in red cells and renal tubules, transcripts and proteins related to AQP-CHIP are also expressed in diverse epithelia with distinct developmental patterns. Northern analyses of RNA from several tissues revealed transcripts of 3.1 kilobases and other sizes. The nucleotide sequences of human kidney AQP-CHIP cDNAs are identical to the human bone marrow AQP-CHIP cDNA. The 17-kilobase human AQP-CHIP structural gene was isolated, and restriction maps were constructed and partially sequenced. The TATA consensus sequence is located 87 bp 5' to the translation initiation site, and sequences surrounding the polyadenylation consensus were determined. Four exons were identified corresponding to amino acids 1-128, 129-183, 184-210, and 211-269, separated by introns of 9.6, 0.43, and 0.80 kilobases. Genomic Southern analyses indicated the existence of a single AQP-CHIP gene which was located at human chromosome 7p14 by in situ hybridization. Sequence comparisons of AQP-CHIP and cDNAs of similar proteins from diverse species suggested a common evolutionary origin. At least three of these proteins are now known to function as membrane water pores and are referred to as the "Aquaporins." These genomic AQP-CHIP DNA sequences should permit molecular characterization of the complex patterns of AQP-CHIP expression.