The isolation of a cDNA encoding a receptor-like protein tyrosine phosphatase, termed RPTP mu, and the assignment of the human gene to chromosome 18 has recently been reported (Gebbink et al., 1991). Using a genomic clone and fluorescence in situ hybridization, we now show that the human gene, designated PTPRM (formerly PTPRL1; LeBeau and Geurts van Kessel, 1991), maps in band 18p11.2.