Burkholderia pseudomallei is a Gram-negative bacillus inhabiting the soil and water of tropical and sub-tropical regions. Infection by B. pseudomallei causes a broad spectrum of diseases in humans and animals, collectively termed melioidosis. Infection occurs through inhalation, ingestion or percutaneous acquisition of bacteria. Melioidosis is associated with a high mortality rate and a high rate of relapse and can affect almost every host organ. Melioidosis has been suggested to be an emerging disease worldwide and the molecular basis of disease is poorly understood. The ability to sequence whole genomes has advanced research significantly. Comparisons between pathogenic and non-pathogenic organisms can be achieved more readily and can provide insights into possible virulence mechanisms. Analysis of the genomes of three Burkholderia species, B. pseudomallei, B. mallei and B. thailandensis, has revealed many differences and similarities. The differences contribute to the divergence between the three species and may suggest which genes are involved in virulence in the pathogenic species and those required for survival in the environment in avirulent species. Possibly, B. pseudomallei virulence is both multi-factorial and combinatorial and does not involve just a few virulence-associated genes...