The genetic map location of the recently discovered imprinted gene U2afbpL has been verified and refined in several mouse crosses. RI strain analysis had previously shown that the gene is located on mouse chromosome 11. This assignment has been verified using interspecific backcrosses. Moreover, the location of the gene relative to a fixed order of markers in the proximal region of mouse chromosome 11 has been established. The location of the gene on mouse chromosome 11 corresponds to a homologous linkage group that is conserved on human chromosome 5q. The location of the human homologue has been determined using both somatic cell hybrid genetic analysis and fluorescence in situ hybridization. These analyses have mapped the human locus U2AFBPL to human chromosome 5q23→q3