Resorption of phosphate by the kidney is an important function in the maintenance of phosphate homeostasis in mammals, and a defect in renal phosphate uptake has been implicated in at least three human genetic disorders. We have isolated a cDNA encoding a human sodium-dependent phosphate transport protein (NPT1). This cDNA hybridizes to a single 2.5-kb RNA transcript from human kidney cortex, its nucleotide sequence shows 80.3% identity to the rabbit NaPi-1 sequence, and it encodes a polypeptide of 467 amino acids. Amino acid sequence comparisons indicate a 69.7% identity between human NPT1 and rabbit NaPi-1 polypeptides; the inclusion of conservative substitutions increases the homology between the two proteins to 81.5%. Alignment of both sequences also reveals several conserved potential N-glycosylation and protein kinase C phosphorylation sites. Polypeptide hydropathy analysis predicts several membrane-spanning domains. This cDNA maps the location of the gene encoding NPT1 to human chromosome 6p21.3-p23.