In 1915, Dr. Anton Dilger, a German-American physician, developed a microbiology facility in Washington D.C. Dr. Anton produced large quantities of anthrax and glanders bacteria, using seed cultures provided by the Imperial German Government. At the loading docks, German agents inoculated 3000 head of horses, mules, and cattle that were destined for the Allied Forces in Europe. Reportedly, several hundred military personnel were secondarily infected.

In 1918, the Japanese formed a biological weapons section in the Japanese Army (Unit 731). In 1931, Japan expanded its territory into Manchuria and made available "an endless supply of human experiment materials" (prisoners of war) for Unit 731. Biological weapons experiments in Harbin, Manchuria, directed by Japanese General Ishii, continued until 1945. A post World War II autopsy investigation of 1,000 victims revealed that most were exposed to aerosolized anthrax. It is estimated up to 3,000 more prisoners and Chinese nationals may have died in this facility. During an investigation of Japan’s seizure of Manchuria in 1931, Japanese military officials unsuccessfully attempted to poison members of the League of Nations’ Lytton Commission by lacing fruit with cholera bacteria. In 1939, the Japanese military poisoned Soviet water sources with intestinal typhoid bacteria at the former Mongolian border. During an infamous biowarfare attack in 1941, the Japanese Military released an estimated 150 million plague-infected fleas from airplanes over villages in China and Manchuria, resulting in several plague outbreaks in those villages. Reportedly, by 1945, the Japanese program had stockpiled 400 kilograms of anthrax to be used in a specially designed fragmentation bomb. In the only known use of biowarfare by Germany, a large reservoir in Bohemia was poisoned with sewage, in 1945.

In 1942, shortly before the battle of Stalingrad, on the German-Soviet front, a large outbreak of tularemia occurred. Several thousand Soviets and Germans contracted the illness. 70% of the victims had pneumonic tularemia, evidence of an intentional release. It was determined later that the Soviets had developed a tularemia weapon during the prior year.

During World War II, with fears of the German and Japanese biological weapons programs, the U.S. and Great Britain began their own programs. The British program focused on anthrax spores and their viability and dissemination when delivered with a conventional bomb. Gruinard Island, off the coast of Scotland, was used as the site for this testing. It was thought that it was far enough off the coast to cause any contamination of the mainland. After an outbreak of anthrax in sheep and cattle in 1943 on the coast of Scotland that directly faced Gruinard, the British decided to stop testing.

In 1942, the United States began research into the offensive use of biological weapons. The United States conducted this research at Camp Detrick (now Fort Detrick) in Maryland. The U.S. program investigated the use of Bacillus anthracis (anthrax), botulinum toxin (botulism), Yersinia pestis (plague), Francisella tularensis (tularemia), Coxiella burnetii (Q fever), Venezuelan equine encephalitis virus, Brucella suis (brucellosis), and Staphylococcal enterotoxin B. Production of weapons also occurred at other sites in Arkansas and Colorado. The U.S. tested of bioweapons dispersal methods by releasing the harmless, but easily identifiable, Serratia marcescens over San Francisco, in 1950. In 1966, the U.S. conducted a test of vulnerability to covert bioterrorism by releasing Bacillus subtilis, another harmless organism, into the subway system of New York City. Results showed that the entire subway system could be infected by release in only one station due spread by the trains. 1969, President Nixon stopped all offensive biological and toxin weapon research and production by executive order, after which, all stockpiles of biological agents and munitions from the U.S. program were destroyed. Presently, the U.S. continues a bioweapons medical defensive program, which began in 1953, at USAMRIID in Ft. Detrick, Maryland.

In 1972, the United States and many other countries signed the Convention on the Prohibition of the Development, Production and Stockpiling of Bacteriological (Biological) and Toxin Weapons and on Their Destruction, commonly called the Biological Weapons Convention. This treaty prohibits the stockpiling of biological agents for offensive military purposes, and also forbids research into offensive use of biological agents.

Although the former Soviet Union was a signatory to the Biological Weapons Convention, their development of biological weapons only intensified after the accord and continued with full steam into the 1990s. From 1975-1983, Soviet-backed forces in Laos, Cambodia, and Afghanistan allegedly used tricothecene mycotoxins (T-2 toxins) in what was called "Yellow Rain." After being exposed, people and animals became disoriented and ill, and a small percentage of those stricken died. The use of T-2 toxins has been denied and the presence of the yellow spots was reported as being caused by deficating bees.

In late April of 1979, an outbreak of pulmonary anthrax occurred in Sverdlovsk (now Yekaterinburg) in the former Soviet Union. While, originally, the outbreak was described as being due to ingestion of infected meat, it was later discovered that the cause was from an accidental release of anthrax in aerosol form from the Soviet Military Compound 19, a Soviet bioweapons facility. Residents living downwind from this compound developed high fever and difficulty breathing, and a large number died. The final death toll was estimated at the time to be between 200 and 1,000. The death toll in animals living in the area was even greater. During the 1980s, more than 60,000 people were engaged in research, testing, production, and equipment design for the Soviet bioweapons program. One facility, Building 15 at Koltsovo, was capable of manufacturing between eighty and one hundred tons of smallpox virus a year. In the city of Kirov, the Soviets maintained an inventory of twenty tons of plague in their arsenals. And, by 1987, the combined production capacity of their anthrax lines throughout the country was nearly 5,000 tons a year.

In the early 1970s, the leftist terrorist group, the Weather Underground, reportedly attempted to blackmail a homosexual officer at USAMRIID into supplying organisms which would be used to contaminate municipal water supplies in the U.S. The plot was discovered when the officer requested several items "unrelated to his work." In Chicago, in 1972, members of the right-wing group Order of the Rising Sun, who were dedicated to creating "a new master race" were found in possession of 30 to 40 kilograms of typhoid bacteria cultures that were to be used to contaminate the water supplies of several mid-western cities. In 1975, the Symbionese Liberation Army was found in possession of technical manuals on how to produce bioweapons.

In 1978, a Bulgarian exile named Georgi Markov, living in London, was stabbed in the leg, with a device disguised as an umbrella which injected a tiny pellet containing ricin toxin, while he was waiting for a bus. He died several days later. This assassination, it was later revealed, was carried out by the communist Bulgarian government, and the technology to commit the crime was supplied by the former Soviet Union.

In 1980, a Red Army Faction safe house was reportedly discovered in Paris which included a laboratory containing quantities of botulinum toxin. In 1993, the U.S. House Armed Services Committee described the discovery of another home laboratory, in 1989, in Paris, in which botulinum toxin was produced. This was linked to a cell of the German Bader Mainhof organization.

The FBI arrested two brother in Northeastern U.S. in 1983 for being in possession of an ounce of nearly pure ricin. And, in 1995, two other men were the first convicted under the Biological Anti-Terrorism Act of 1989, for production of ricin. The two were members of a group called the Minnesota Patriots Council, and had planned to poison federal agents by placing ricin on doorknobs.

The most famous, and successful use of bioterrorism on U.S. soil occurred during September 1984, when followers of the Bhagwan Shree Rajneesh contaminated salad bars in The Dalles, Oregon with Salmonella Typhimurium. Over 750 cases of salmonellosis were determined to be caused by the salad bar contamination. It was later discovered that the Rajneeshpuram cult wanted to influence the local county commissioners election, so as to form their own township. The September bioterrorism act was a trial run for the planned November election attack, which was later canceled, as the plan seemed to be ineffective. The cult members obtained the Salmonella strain through the mail from the American Type Culture Collection (ATCC).

The Japanese doomsday cult, AumShinrikyo, while seeking to establish a theocratic state in Japan, released sarin gas in Tokyo subway stations in 1995. They were later discovered to have developed and attempted to use other chemical agents (VX gas and hydrogen cyanide) and biological agents (B. anthracis, Coxiella burnetii, Ebola virus, and botulinum toxin) on at least ten other occasions. Their multiple attacks using sarin gas killed at least 20 people and injured more than 1,000 others.