A collaborative study was conducted to test a method, proposed in the European Community (EC) as a candidate‐official method for the determination of aflatoxin B1in compounded feeding stuffs. The study was undertaken on behalf of the European Commission's Community Bureau of Reference (BCR). It involved 25 laboratories from 11 EC countries. The method, based on chloroform extraction and Sep‐Pak Florisil and C18cartridge clean‐up, offered either reverse‐phase high performance liquid chromatography (HPLC) with iodine post‐column derivatization, or two‐dimensional thin‐layer chromatography (TLC) as determinative steps. In the study, 22 laboratories applied HPLC, three laboratories applied TLC. The study involved six unknown samples. These consisted of blind duplicate samples of compounded feeding stuff, with target concentrations of aflatoxin B1at < 2, 8 and and 14 μg/kg. Statistical analysis of the HPLC data was carried out according to ISO 5725. For the < 2μg/kg sample, all reported aflatoxin concentrations were < 2 μg/kg. At the 8 and 14μg/kg level (pooled), repeatability(r)and reproducibility(R)expressed as ratios, were 1.4 and 1.7 respectively, and within‐laboratory and between‐laboratory coefficients of variation were 11% and 18% respectively. The study revealed that admittance of daylight in the laboratory caused losses of aflatoxin B1and must be avoided. New glassware coming into contact with aqueous solutions containing aflatoxin B1was found to be a potential cause of loss of aflatoxin B1. The method has been recommended to the European Commission to be considered for adoption in EC regulations.