Smallpox is not known to occur outside of the human species, and it is difficult to obtain and cultivate. Since its eradication in the last 30 years, there are only two known repositories of the virus, one at the Centers for Disease Control in Atlanta and the other in the Russian counterpart located in Moscow. Anthrax, like most other pathogens, can be found occurring naturally in the environment. Information on where to find these pathogens and how to isolate and grow them can be found in libraries, bookstores, and on the Internet. Creating a military-grade anthrax, however, would require a seed stock, thousands of dollars worth of equipment, and the technical expertise of a few microbiologists. Regarding bacteria, the most important factor in weapon use is whether the bacteria are gram-negative or gram-positive. Gram-positive bacteria are generally susceptible to penicillin and are slow to develop a resistance to it. Gram-negative bacteria are more difficult to kill with antibiotics. The toxins produced by the bacterium cause the most damage. Botulinum, for example, is the most potent toxin known and is more lethal than chemical nerve agents. Viruses differ from bacteria in several ways, most notably in being smaller than bacteria and in not being able to reproduce on their own. Antibiotics are not effective against viruses. Antiviral medicines are available, but they are not effective against all viruses and may be more toxic to human cells than antibiotics. Rickettsiae are organisms smaller than bacteria but larger than viruses. They are constructed like bacteria and can be controlled or killed with antibiotics, but, like viruses, they can live and multiply only inside host cells. The most common disease caused by rickettsiae is Rocky Mountain spotted fever. Fungal infections caused by inhalation of fungal spores, can be lethal, although they are typically easy to identify and treat effectively. Toxins are not living organisms, but are derived form living organisms; they are many times more stable and effective than their chemical weapon counterparts. Naturally occurring sources of toxins are described in this article. The possibility of a terrorist attack with biological agents carries a higher probability than most people usually accept. The raw materials, knowledge, and equipment necessary to create such agents are available to the layperson. The problems that will be encountered with their use should be addressed now in a cooperative endeavor that involves the government and the medical community in the creation of a capacity to treat a significant number of persons infected in the case of a terrorist attack. 6 references and 3 additional sources