The h-PRt-1 gene codes for a new phosphotyrosine phosphatase that may play an important role in the control of basic cellular processes such as: cell growth and proliferation, Using the cDNA of the h-PRL-1 gene as a probe, we examined a somatic mouse and hamster x human hybrid panel and found that chromosomes 1, 17 and Il harbor sequences homologous to h-PRL-1, By in situ hybridization of metaphase spreads, subchromosomal localizations were determined al bands 1p35-p34, 17q12-q21 and 11q24-q25: in addition, a faint signal was detected at 12q24, The chromosomal assignment of the genes homologous to h-PRL-1 will help the investigation of its possible involvement in human diseases involving genetic alteration at these chromosomal regions.