Yellow rain

Yellow rain was the subject of a 1981 political incident in which the United States Secretary of State Alexander Haig accused the Soviet Union of supplying T-2 mycotoxin to the Communist states in Vietnam and Laos for use in counterinsurgency warfare.

Refugees described many different forms of attacks, including a sticky yellow liquid falling from planes or helicopters, which was dubbed "yellow rain". The US government alleged that over ten thousand people had been killed in attacks using these chemical weapons. The Soviet Union denied these claims and an initial United Nations investigation was inconclusive.

Some samples of the supposed chemical agent that were supplied to a group of independent scientists turned out to be honeybee feces, suggesting that the "yellow rain" was due to mass defecation of digested pollen grains from large swarms of bees. Other scientists questioned the accuracy of the refugee accounts and the reliability of the chemical analyses presented by the US government. The majority of the scientific literature on this topic now regards the hypothesis that yellow rain was a Soviet chemical weapon as disproved. However, the issue remains disputed and the US government has not retracted these allegations, arguing that the issue has not been fully resolved.

Many of the US documents relating to this incident remain classified.

The charges stemmed from events in Laos and North Vietnam beginning in 1975, when the two governments, which were allied with and supported by the Soviet Union, fought against Hmong tribes, peoples who had sided with the United States and South Vietnam during the Vietnam War. Refugees described events that they believed to be chemical warfare attacks by low-flying aircraft or helicopters; several of the reports were of a yellow, oily liquid that was dubbed "yellow rain". Those exposed claimed neurological and physical symptoms including seizures, blindness, and bleeding. Similar reports came from the Vietnamese invasion of Cambodia in 1978.

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