Cognate sites in genomes that diverged approximately 100 million years ago can be detected by PCR assays based on primer pairs from unique sequences. The great majority of such syntenically equivalent sequence-tagged sites (STSs) from human DNA can be used to assemble and format corresponding maps for other primates, and some based on gene sequences are shown to be useful for mouse and rat as well. Universal genomic mapping strategies may be possible by using sets of STSs common to many mammalian species.