A novel gene, PiUS, was recently cloned and shown to increase phosphate uptake when expressed in oocytes, indicating that it may be an important regulator of cellular phosphate homeostasis. The phosphate wasting disease autosomal dominant hypophosphatemic rickets (ADHR) was previously mapped to chromosome 12p13 by linkage analysis. PiUS' role as a modulator of phosphate transport, as well as its intestinal and renal expression made the gene an appropriate candidate for ADHR. The purpose of our study was to determine the chromosomal localization of the human PiUS gene through the use of somatic cell hybrids and radiation hybrid mapping. In the present work, PiUS was localized to human chromosome 3p21.3 and is therefore not the ADHR gene.