One approach to ensuring coexistence of genetically modified (GM) and conventional maize (Zea mays L.) is the understanding of maize pollen dispersal in the atmosphere in order to quantify the potential contamination of non-GM maize due to pollen-mediated gene flow from GM maize. For this purpose in our experiments the gene flow in two different commercial fields was evaluated. It was also determined that the increasing of the distance from the GM source proportionally reduce the GM contamination and the necessary distance to decrease the percent below 0.9% is 8.4 m. Our results are in accordance with the EU recommendations which proposed separation distances of 20 m and 50 m for silage and grain maize respectively, values determined based on statistical data of maize areas and aerial photographs with geographic information systems.