The causative agent of tularemia, Francisella tularensis, is one of the most infectious pathogenic bacteria known, requiring inoculation or inhalation of as few as ten organisms to cause disease. Humans become incidentally infected through diverse environmental exposures and can develop severe and sometimes fatal illness but do not transmit infection to others. It is considered to be a dangerous potential biological weapon because of its extreme infectivity, ease of dissemination, and substantial capacity to cause illness and death. A working group has developed recommendations for measures to be taken by medical and public health professionals if tularemia is used against a civilian population. This group consisted of 25 representatives from academic medical centers, civilian and military governmental agencies, and other public health and emergency management institutions and agencies. Results showed that a weapon using airborne tularemia would likely result three to five days later in an outbreak of acute, undifferentiated febrile illness with incipient pneumonia, pleuritis, and hilar lymphadenopathy. Specific epidemiological, clinical, and microbiological findings should lead to early suspicion of intentional tularemia in an alert health system. Laboratory confirmation of the agent could be delayed. Without treatment, the clinical course could progress to respiratory failure, shock, and death. Prompt treatment with streptomycin, gentamicin, doxycycline, or ciprofloxacin is recommended. Prophylactic use of doxycycline or ciprofloxacin may be useful in the early postexposure period. Simple, rapid, and reliable diagnostic tests that could be used to identify persons infected with F tularensis in the mass exposure setting need to be developed. 4 figures, 3 tables, and 102 references