Plague and melioidosis are both potentially fatal bacterial infections found mainly in the tropics. Up to 2000 cases of plague are reported to the World Health Organization each year, although this is probably inaccurate. Melioidosis is known to be prevalent in north-east Thailand and northern Australia, but we have little idea of its true worldwide importance. Molecular techniques are improving our understanding of the pathogenesis and epidemiology of both diseases and providing new, rapid diagnostic tests. Clinical trials are helping to define the role of new β lactams such as ceftazidime and co-amoxiclav in the management of melioidosis, but the treatment of plague has not advanced since the end of the Vietnam War.