The threat: infectious diseases remain a major threat to mankind. Bacterial diseases emerge or reemerge such that, during the past 20 years, over forty new pathogenic microorganisms have been described. Several possibilities: Many of these microorganisms may have been present but simply not recognized, such as Helicobacter pylori, whereas others now occur at a dramatically increased incidence because of their ability to exploit new man-made niches (Legionella pneumophila) or following man's increased encroachment into nature (Borrelia burgdorferi). Renewed interest: However the increasing number of identifications of new pathogenic bacteria is also due to increased scientific and medical interest in the field and improved laboratory methods, particulary the advent of molecular biological tools. The progress made to dale in understanding emerging infections could, however, be significantly improved upon if increased research funds were made available.