. 2006. Adventitious presence of GMOs: Scientific overview for Canadian grains. Can. J. Plant Sci. 86: 1-23. The global expansion in the development and cultivation of genetically modified (GM) crops has increased international concern about adventitious presence of GM materials in non-GM seeds and grains. GM events in canola, corn, soybean, cotton, flax, papaya, potato, squash, sugar beet, and tomato have received regulatory approval in Canada. However, GM cultivars are only in commercial production for canola, corn and soybean. More than 30 GM events have been approved in these three crops. Cases of unapproved adventitious presence of GM materials that have impacted grain trading and handling in Canada and other countries include StarLink⹠corn, GT200 canola, GM canola in mustard and recently Bt10 corn. Some countries have established tolerance and traceability requirements for adventitious presence of GMOs, while others are in the process of developing or adopting legislation. The threshold for labeling of adventitious presence of approved GM material in non-GM grain varies from 0.9% (e.g., EU) to 5% (e.g., Japan). Progress has been made in the development of DNA-and proteinbased GMO detection methods. However, only a limited number of these detection methods have been internationally validated. The challenges for detection methods include sampling, a lack of certified reference material, a lack of DNA sequence information for the design of event-specific primers, and the sheer number of individual events that may be present and tested for. Current efforts by ISO and CEN will be valuable for establishing harmonized and standardized GMO detection methods.Key words: List of GM events, cases of AP, tolerance, traceability, detection methods, challenges Demeke, T., Perry, D. J. et Scowcroft, W. R. 2006. Présence de matériel génétiquement modifié adventif : survol de la situation des grains au Canada. Can. J. Plant Sci. 86: 1-23. Le développement et la culture de matériel génétiquement modifié (GM) connaissent une expansion mondiale si bien que, partout sur terre, on s'inquiÚte de la présence de matériel GM adventif dans les semences et les grains non GM. La modification génétique du canola, du maïs, du soja, du coton, du lin, de la papaye, de la pomme de terre, de la courge, de la betterave sucriÚre et de la tomate a été autorisée par les organismes de réglementation au Canada. Les cultivars GM cultivés commercialement se limitent néanmoins au canola, au maïs et au soja. Plus de 30 modifications génétiques ont été approuvées pour ces trois cultures. Parmi les cas de matériel GM adventif non autorisé qui ont posé des problÚmes au niveau des échanges commerciaux et de la manutention du grain au Canada et ailleurs, on retrouve le maïs StarLink MC , le canola GT200, le canola GM dans la moutarde et, plus récemment, le maïs Bt10. Certains pays tolÚrent ou exigent qu'on puisse retracer le matériel GM adventif, mais d'autres ont entrepris l'élaboration ou l'adoption de lois en la matiÚre. Le seuil de tolérance concernan...