The allergenicity of four hazelnut varieties (Runde Römer, Levantiner, Neapler, Contorta) and different types of heat treated and stored hazelnuts was examined and compared by SDSPAGE/immunoblotting and EAST-inhibition experiments using sera of 19 hazelnut allergic individuals. The immunoblot and EAST-inhibition investigations of the four varieties revealed only slight differences with regard to the allergenic activities. Heat treatment at 100°C for up to 90 min had no influence on the allergenicity of hazelnut prote ins. The IgE binding activity of the main hazelnut allergens decreased after 15 min heat treatment at temperatures between 100 and 185°C and was no longer detectable at 170°C. A protein < 14 kDa appeared to be very stable to heat and could be detected even after treatment at 185°C. Microwave treatment and storage of ground hazelnuts up to 19 weeks at room temperature had no influence on the allergenicity of hazelnut proteins.