Advances in genetics and biotechnology offer great promise in the fight against infectious diseases. But the same technologies will also increase the threat from bioterrorism. Governments must accord 'biosecurity' a higher priority in defence and foreign policies to reduce the risk of major societal disruptions and international political instabilities caused by infectious diseases, whether of natural or malignant origins. Longer term, technological progress will expand the biothreat spectrum beyond microbial attacks to embrace diverse manipulations of key body functions, including cognition. Meeting these challenges will require profound changes in national security policy, military doctrine, intelligence acquisition and law enforcement, a renewed focus on public health and disease surveillance, the evolution of new private-public partnerships to produce new diagnostics, drugs and vaccines and improved international co-operation to outlaw biological weapons.