Comparative genomics is emerging as a powerful approach for assessing the similarities and differences between species. In the September Genome Research Band et al. compare cows and humans to generate mapping information about the bovine genome (Genome Res 2000, 10:1359-1368). The authors combined parallel radiation hybrid (RH) mapping analysis with express sequence tag (EST) sequence information and a bioinformatic methodology called COMPASS (comparative mapping by annotation and sequence similarity). They were able to create a whole-genome RH map with 768 cattle genes and 319 anchored microsatellite markers. Over 80% of these genes had human orthologs and the two genomes had at least 105 conserved chromosomal segments in common. The coverage of the cattle-human comparative map is predicted to be about 60%. These results provide a framework for future comparative studies. Clearly men and cows are more similar than they look.