Whole-genome bacterial artificial chromosome (BAC) libraries for approximately 40 representative species of mammals provide unique resources for the construction of high-resolution ordered genomic maps, the development of species genetics, and multispecies genome comparisons. Herein we describe procedures to construct high-quality radiation hybrid comparative maps using BAC-end sequences (BESs). This approach has been applied to the construction of approximately 1 Mbp resolution porcine-human and cattle-human comparative maps. High-resolution ordered comparative maps built with BESs and whole-genome sequences have been shown to be an invaluable resource for the analysis of mammalian chromosome evolution, and as a backbone for the assembly of whole-genome shotgun sequences.