Although anthrax occurs most commonly in herbivores, it has caused serious illness in humans worldwide. Research on anthrax as a biological weapon began 80 years ago. At least 17 nations today are believed to have offensive biological weapons programs. In humans, three types of anthrax infection occur: inhalational, cutaneous and gastrointestinal. Cutaneous is the most common with an estimated 2,000 cases reported annually. Gastrointestinal infection is uncommon, and no case of inhalational anthrax has been reported in the U.S. since 1978 and only 18 cases since 1900. Once Bacillus anthracis is inhaled and germinates, disease, including hemorrhage and necrosis, follows rapidly. The mortality rate of occupationally acquired cases in the U.S. is 89 percent, but the majority of cases occurred before the development of critical care units and in some cases before the advent of antibiotics. Without antibiotics, the mortality rate of cutaneous anthrax is 20 percent, but death with antibiotics is rare. Given the difficulty of early detection of gastrointestinal anthrax, mortality rates would be high. The first suspicion of anthrax illness must lead to immediate notification of the local and State health department. The sudden appearance of a large number of patients in a city or region with acute-onset of flu-like illnesses and fatality rates of 80 percent or more within 24 to 48 hours is highly likely to be anthrax or pneumonic plague. A microbiological test should show growth in six to 24 hours. Vaccine supplies are limited and administered usually only on military staff. Penicillin has been the preferred therapy for the treatment of anthrax. Doxycycline is the preferred option from the tetracycline class of antibiotics. Because some anthrax strains have been developed to resist antibiotics, ciprofloxacin or other fluoroquinolone therapy should be used until testing shows the anthrax is not resistant. Therapy should continue for 60 days. Tables, references