Since the discovery of antibiotics, the battle between humans and drug resistant bacteria has never stopped. Bacteria have developed various ways to resist the toxic effects of antibiotics and other drugs. Multidrug efflux pumps are integral membrane proteins that utilize cellular energy to extrude antibiotics or biocides actively out of the cell. In this symposium, I first introduce the post-genomic approach to analyze all putative drug efflux genes. Next, I discuss the regulation of drug efflux pumps responding to environmental signals. I also introduce the physiological roles of drug efflux pumps in virulence, which is an ongoing research area. Multidrug efflux pumps have greater clinical relevance than has previously been thought, because there is now accumulating evidence that certain classes of efflux pumps not only confer resistance to drugs used in therapy but also have a role in bacterial pathogenicity.