This article provides a science-based, decision tree approach to assess the allergenic concerns associated with the introduction of gene products into new plant varieties. The assessment focuses on the source from which the transferred gene was derived. Sources fall into 3 general categories: common allergenic food proteins; less common allergenic foods or other known allergen sources; and sources with no allergenicity. Information concerning the amino acid sequence identity to known allergenic proteins, in vitro and/or in vivo immunologic assays, and assessment of key physiological properties are included in reaching a recommendation on whether food derived from the genetically modified plant variety should be labelled as to the source of the transferred gene.