The BCR has undertaken a project to prepare compound-feed reference materials to provide a basis for analytical quality control for this assay. The first phase of the project, an intercomparison of methods for aflatoxin B1 in compounded feedstuffs at a level of ca 15 micrograms/kg is now described. The study involved 24 European laboratories who analysed two pairs of compounded feedstuffs. Each pair of feeds consisted of a contaminated and an almost uncontaminated sample (a near-blank) of otherwise identical composition. The feed pairs differed essentially only in their citrus-pulp and barley contents. The participants used a variety of methods of analysis, including chloroform, methanol-water and acetonitrile-water for extraction, TLC, reversed phase disposable cartridges and immunoaffinity columns for extract clean-up and TLC, HPLC and ELISA in the determinative step. Several performance characteristics were checked and the aflatoxin B1 contents were determined. Recoveries were found to range from approximately 70 to 110%. Coefficients of variation calculated from all the results obtained with the two pairs of contaminated samples were 16 and 19%. The study showed that, when properly applied, a number of methods employing variations in extraction, clean-up and end-method gave results which were in close agreement. It is concluded that there exists a sound basis for the establishment of reference values for the aflatoxin B1 content of compound feed reference materials which have been prepared in this project.