 The first was the "yellow rain" accusation by the United States against the USSR, to the effect that the Soviets enabled the Laotian army to use deadly mycotoxins to attack Hmong refugees allied with the US during the Vietnam War.This accusation had been disputed by Meselson in 1983 when he argued that the yellow material was actually bee feces mistaken for a biological weapon by those under attack and by certain US government scientists.