MON 810 corn is a genetically modified line of insect-protected corn (maize, Zea mays) sold commercially by Monsanto as YieldGard. The protection is con-ferred by the protein Cry1Ab, a delta endotoxin produced from a gene derived from the soil bacterium Bacillus thuringiensis (Bt). This method quantifies the relative amount of MON 810 DNA in corn flour. It makes a relative quantitation of a specific part from the taxon-specific maize gene (i.e., the high mobility group [HMG] protein gene) (Ref. 5) and of the single-copy DNA integration-border region of the genomic sequence and the inserted sequence element. This element originates from the CaMV (35S promoter) and is the result of in vitro recombination. Real-time polymerase chain reaction (PCR) in a TaqMan assay is used (Ref. 3). The method is calibrated to estimate the copy number percent of modified corn in corn flour by using a reference material certified for its MON 810 mass fraction (Ref. 2). Copy number percents are estimated on the basis of the DNA extracted from the reference material and an assumed average genome size. The method is suitable for enforcement purposes with respect to its true-ness and interlaboratory variability (Ref. 1). It is annexed to standard ISO 21570:2005 (Ref. 4).