As the most poisonous substance known, botulinum toxin poses a major threat. It can be easily produced, transported and used. The Japanese cult Aum Shinrikyo used it in Tokyo on three occasions between 1990 and 1995, but the attacks failed. Iran, Iraq, North Korea and Syria have developed or are believed to be developing botulinum toxin as a weapon. A lethal dose of the toxin for a 70-kilogram human would be approximately 0.09 to 0.15 micrograms intravenously or intramuscularly. All forms of botulism result from absorption of botulinum toxin into the circulation from either the intestine, lung, or a wound. Patients with botulism, which is not contagious, typically have problems seeing, speaking or swallowing because it causes nerve palsies. Aerosol dissemination may not be difficult to detect because many victims will share a common temporal or geographic exposure and lack common dietary exposures. Naturally occurring foodborne botulism is rare, with an average of nine cases per year. But any suspected cases of botulism should be reported immediately to authorities because contaminated food remains a threat to others or that botulinum toxin has been deliberately released. Therapy consists of supportive care and passive immunization with antitoxin as soon as possible. Botulism can be prevented by the presence of a neutralizing antibody in the bloodstream. Use of antitoxin for postexposure treatment is limited by its scarcity and its tendency to cause negative reactions. People suspected of being exposed to the toxin should be monitored and treated promptly with antitoxin at the first signs of illness. Botulinum toxin is easily destroyed and decays at a rate of about 1 to 4 percent per minute. Additional research is needed to minimize the toxin's threat as a weapon. Existing technologies could produce the necessary stockpiles of a human antibody needed to deter terrorist attacks and avoid rationing of the antitoxin. Tables. References.