Allergens in plant foods are extremely complicated. In the course of investigation of the allergens in latex, most of the allergens in plant foods have been shown to be involved in defense-related proteins, particularly in six of the fourteen well-known pathogenesis-related proteins. Also many other allergens are classified into bioactive proteins such as protease/α-amylase inhibitor and seed storage proteins. Recently, asparagine-linked sugar chains have been found to be common epitopes in allergens that possess their sugar moieties.