ShiBASE (http://www.mgc.ac.cn/ShiBASE/) is a freely accessible online resource that is focused on the comparative genomics of Shigella. ShiBASE is able to summarize large volumes of genomic sequence and comparative genomic data in a visually intuitive format. The interspecies comparison of Shigella genomes may be carried out at several different levels within ShiBASE. One may compare basic genome features, such as, genome size, IS elements, genome structure (inversions and deletions) and order of orthologous genes. One can also compare metabolic pathways and virulence factors among Shigella genomes. Moreover, the CGH data produced from analyses on 43 different serotypes of Shigella strains are also integrated within ShiBASE. ShiBASE also provides a novel Shi-align service for visualizing BLAST hits between query sequences and known Shigella genomes, thus allowing rapid examination of synteny, genomic rearrangements and putative genomic islands.