A general mapping strategy is described in which the 3'untranslated regions of human cDNAs are used to design PCR primers which will selectively amplify human genomic sequences in a rodent background. When applied to panels of human x hamster somatic cell hybrid DNAs, this approach provides a PCR-based method for rapidly assigning genes to specific chromosomes and chromosomal regions. In addition, it follows from the virtual absence of introns in the 3'untranslated region of vertebrate genes that within this region the cDNA sequences almost always will be identical to those of the genomic DNA and can therefore be used to automatically generate gene-specific sequence-tagged sites (STSs). We have applied this strategy to six human cDNAs and demonstrate that 1) the primers selectively amplify human genomic DNA and 2) the PCR product is of the size predicted from the cDNA. To test this approach further we have utilized it to confirm the known chromosomal location of the retinoblastoma gene. Lastly, we describe how this strategy can readily be applied to unknown human cDNAs, and thereby be integrated into efforts to generate a human STS expression map of the genome. A strategy for production of such a map, using human brain cDNAs as a model, is described.