A method for quantification of recombinant DNA for Roundup Ready (RR) corn and RR soybean insoil samples is described. Soil DNA from experimental field samples was extracted using a soil DNAextraction kit with a modified protocol. For the detection and quantification of recombinant DNA ofRR corn and RR soybean, a molecular beacon and two pairs of specific primers were designed todifferentially target recombinant DNA in these two genetically modified crops. Soil DNA extracts werespiked with RR corn or RR soybean DNA, and recombinant DNA was quantified using real-timePCR with a molecular beacon. As few as one copy of RR corn genome or one copy of RR soybeangenome was detected in the soil DNA extract. Keywords: Agriculture; DNA; detection; environment; genetically modified; PCR amplification;persistence; soil; transgenic plants