This International Standard specifies a gas chromatographic method for the determination of the residues of organophosphorus pesticides in animal feeding stuffs. The method is applicable to animal feeding stuffs containing residues of one or more of the following organophosphorus pesticides: azinphos-ethyl, azinphos-methyl, bromophos, carbophenothion, chlorpyrifos, chlorpyrifosmethyl, diazinon, dimethoate, ethion, fonofos, malathion, methidathion, parathion, parathion-methyl, pirimiphos-ethyl and pirimiphos-methyl. The lower limit of determination for these organophosphorus pesticides is 0,01 μg/g. NOTE The method is probably equally applicable to other organophosphorus pesticides such as methaccrifos and fenitrothion, but it has not been validated for these pesticides.