The seed multiplication of genetically modified (GM) plants requires a modification of the multiplication process used for conventional seed. The difference compared to conventionally-bred varieties involves the detection of the modified character during variety maintenance, seed multiplication and processing, the need for separate storage, processing and transportation, the extra cleaning required for the transportation, storage and processing equipment, and the extra administration necessary for the documentation and labelling of GM seed lots. All in all this results in the lower exploitation of seed producing capacity and in additional costs. The appearance of GM plants also has an effect on the breeders and seed multipliers of conventional varieties, however, since the possibility of contamination cannot be excluded. The producers of seed free of GMs (within the tolerance threshold) are forced to employ costly cultivation techniques (temporal and spatial isolation, removal of volunteer plants) and laboratory tests (for GM contamination) if their varieties are to stay on the market and if it is to remain possible to produce GM-free products in the future.