Biological agents as weapons are not new to mankind. For centuries and into the present, biological warfare has been the subject of much research and speculation, but little action. Their limited use has probably been due to fear of unexpected counter-effects and doubts about their efficiency as weapons. Recently a new form of terrorism employing infectious agents has emerged slowly and without much fanfare, until the recent events with Bacillus anthracis in the United States. Smallpox is potentially the most devastating of these agents. Less than 25 years after the eradication of smallpox, the public health field is now forced to deal with the possibility of its re-introduction. The author discusses the scenario of smallpox re-introduction into Brazil.17615191523