In the past over twenty years the Japan Medical Association Quality Control Survey Committee has experienced various types of problems in preparing a large amount of different control survey materials with some matrix effects. This may have caused inappropriate evaluation for some of the participated laboratory. Not only the participated laboratories but also some industrial companies should participate to identify the exact matrix effects, so that the Committee may be able to avoid some inappropriate decisions on evaluation of the reported results. However, at the present time, no standard is available for the identification of matrix effects. The Japanese Committee for Clinical Laboratory Standards, in 1991, organized the research group on external quality control, and suggested a proposal to identify some matrix effects of survey materials for a particular assay system.