The presence of aflatoxin in airborne grain dusts collected from the Superior/Duluth region of the United States was investigated. Dusts were collected with an industrial vacuum cleaner during transportation of grains over conveyer belts. Samples were extracted in chloroform, chloroform/water, and methylene- chloride/water mixtures. Extracts were spotted along with reference standards of aflatoxin-B1, aflatoxin-B2, aflatoxin-G1, and aflatoxin- G2 on thin layer plates and developed in a variety of solvents using conventional procedures. The plates were examined under ultraviolet light (UV). Following UV examination, the compounds were visualized by treatment with trifluoroacetic-acid or 25 percent sulfuric-acid. The limits of detection were 2 parts per billion. All dust samples contained four chloroform soluble red, blue, blue/green, and red fluorescence. Each sample contained the blue fluorescent compound with an Rf value similar to aflatoxin-B1. All dust extracts also showed a green fluorescent compound whose Rf was greater than the standards. The Rf of the red fluorescent compound present in chloroform extracts of all dusts did not correspond to those for the reference standards, but a blue fluorescent compound with an Rf value similar to aflatoxin-B2 was seen with spring wheat. The methylene-chloride soluble substance from barley and spring wheat dusts exhibited a blue fluorescence with an Rf between aflatoxin-B1 and aflatoxin-B2. There was also a substance with green fluorescence whose Rf value was below that of any of the standards. Trifluoroacetic-acid treatment did not reveal the presence of blue compounds with Rf values resembling any of the standards. The authors conclude that the grain dust examined did not contain any of the aflatoxins; the compounds which exhibited blue fluorescence were not aflatoxins.