Type 1 allergies are recognized as an important disease affecting around 25% of the population of industrialized countries of the Northern hemisphere. Allergic patients produce specific IgE antibodies after frequent exposure to either inhaled or nutritive allergens. Of the plant allergens listed in the Official Allergen Database of the International Union of Immunological Societies, approx. 25% belong to the group of pathogenesis-related proteins (PR-proteins). PR-proteins are defined as proteins that are induced upon stress, pathogen attack and abiotic stimuli. This inhomogeneous group of proteins has been classified into 14 PR-protein families. So far, plant-derived allergens have been identified with sequence similarities to PR-protein families 2, 3, 4, 5, 8, 10 and 14. In general, both protein groups, i.e. PR-proteins and allergens, comprise rather small proteins, which are stable at low pH and resistant to proteolysis. These features, and their level of expression, make PR-proteins good candidates for evoking an immune response in predisposed humans, when coming into contact with mucosal surfaces. The identification of PR-proteins with allergenic potential and their homologues is of importance for the allergic patient and the management of this disease. Firstly, plant foods derived from genetically modified plants could represent new allergen sources, and therefore should be evaluated carefully for their potential allergenicity. Secondly, complex plant-derived foods should be analysed for hidden allergens and labelled accordingly.