Since the terrorist attack on the United States in September 2001 attention has been focused on the threat of biological warfare. The disruptive effects of deliberate release of anthrax in civilian settings have been well documented, and several other pathogens could also be used as biological weapons. We have described the key features of such pathogens, how they might be used in biological warfare, and the clinical syndromes they cause. We also discuss the medical and logistic response to their possible use. #### Summary points Appropriate dispersion of even a small volume of biological warfare agent may cause high morbidity and mortality, which may be exacerbated by public panic and social disruption Early symptoms of disease induced by a biological warfare agent may be non-specific or difficult to recognise Healthcare workers should be alert for unusual single cases or clusters of illness, especially in otherwise healthy adults Unusual illness should be notified immediately to public health authorities Strategic responses to the deliberate release of biological warfare agents must be rehearsed locally and nationally with multiple agencies Healthcare professionals should familiarise themselves with national and local sources of advice on deliberate release Biological warfare agents are defined as “living organisms, whatever their nature, or infected material derived from them, which are used for hostile purposes and intended to cause disease or death in man, animals and plants, and which depend for their efforts on the ability to multiply in the person, animal or plant attacked.”1 Many such agents are zoonotic and have a considerable impact on agriculture as well as on human health. Biological warfare agents are well suited for use in bioterrorism or for attack by poorer nations against the rich (so called “asymmetric methods” of attack2) as they are cheap and easy to obtain and disperse, although full scale use …