The chromosomal localization of the gene encoding aquaporin 1 (previously called CHIP28), which acts as a water channel in erythrocytes and in the renal proximal tubules and descending limbs of Henle, was determined. Southern blot hybridizations on chromosomal DNA of a panel of 25 different human x rodent hybrid cell lines localized the aquaporin 1 gene to human chromosome 7. Additionally, in situ hybridization on R-banded metaphase chromosomes sublocalized the aquaporin 1 gene (AQP1) to 7p15-->p14, and some sequence-tagged sites in this region were identified.