Aflatoxin B2 is the minor analogue of the blue fluorescent family of bisfuranocoumarin mycotoxins produced by Aspergillus flavus and related species. Aflatoxins are one of the most potent mycotoxins known but are in fact "pre-toxins", requiring metabolic activation to the toxic principle. Aflatoxins are found widely in nature in trace amounts, particularly in grains and nuts. The toxicity of these metabolites was first recognised in the 1950s and their structures elucidated in 1963. Aflatoxins have been extensively reviewed.