This International Standard specifies a method for the determination of the aflatoxin M1 (AFM1) content of milk and milk powder by a method including a clean-up step using immunoaffinity chromatography followed by a thin-layer chromatography (IAC-TLC). The method is applicable to raw milk, low fat or skimmed liquid milk and milk powder. The lowest quantity of AFM1 that can commonly be determined is 2 ng, which corresponds to a limit of quantification close to 0,10 µg/l for liquid milk or dissolved milk powder (for a spot of 20 µl).