In the EU the presence of genetically modified organisms (GMO) in food is controlled by the Member States official laboratories within their national inspection and monitoring programs.  The most frequently used approach to detect the presence of GMO material in different food matrices is the PCR-based screening for the CaMV 35S promoter and the nos terminator (T-nos) DNA sequence from Agrobacterium tumefaciens.  A real-time PCR method for detection of T-nos and its validation in a collaborative trial study is described in this paper.  The PCR system amplifies a 84 bp fragment and showed to be sensitive to detect at least 5 copies of the T-nos DNA sequence.  The assay was adapted for use in real-time PCR instruments using plastic reaction vials and glass capillaries, respectively.  A total of 24 laboratories participated in the study and each laboratory received 18 DNA blind samples prepared from GMO certified reference materials (0.1 % and 0.5 % NK601 maize) and from a non-GM maize flour.  All samples containing NK603 maize DNA were correctly classified as T-nos positive by the participating laboratories.  For the blank samples (0 % GMO) only three false-positive results were reported. A detailed evaluation of the results of the collaborative trial study is described.