A method for determining deoxynivalenol (DON) in wheat has been developed in conjunction with an assessment of contamination in Canada. The sample is extracted with methanol-water; the extract is treated with 30% aqueous ammonium sulfate solution and extracted with 4 portions of ethyl acetate. After further cleanup by column chromatography, the sample extract is derivatized with N-heptafluorobutyrylimidazole, and the DON tris-heptafluorobutyrate is determined by gas-liquid chromatography with electron capture detection. Mass spectrometric single ion monitoring at m/z 884 is used for confirmation. Detection limits are less than or equal to 0.01 microgram DON/g and recoveries from wheat, using the proposed method, averaged 72 and 80% in 2 different laboratories, with coefficients of variation of 10.2 and 10.0%, respectively. The method is also applicable to determining DON in barley and corn and T-2 toxin in wheat. Virtually 100% contamination by DON of the 1980 Ontario white winter wheat and Quebec red spring wheat crops was found, based on 72 analyses made in this laboratory, but western Canadian wheat contained little or no DON.