Genome maps have been constructed for the mycobacterial pathogens Mycobacterium leprae and Mycobacterium tuberculosis, as well as for the attenuated vaccine strain Mycobacterium bovis BCG Pasteur. While the chromosomes of M. tuberculosis and M. bovis BCG Pasteur show extensive conservation at the gross level, comparison with M. leprae revealed a high degree of diversification, with a mosaic-like pattern apparent. The ordered libraries of M. tuberculosis and M. leprae produced during the course of these studies played a central role in the genome sequencing projects of these two bacilli, showing the utility of this approach for systematic sequencing of bacterial genomes.