225 patients with hazel pollen allergy were examined by means of cutaneous tests and RAST. In the scratch test, 92% of the patients revealed a sensitization to hazelnuts; clinically manifest or latent, only detectable by skin tests and RAST. A significant incidence of the manifest hazelnuts allergy can be seen only in patients with a polyvalent sensitization and in patients, whose complaints of pollinosis start in the flowery of hazel, i.e. February/March, and who are very strongly sensitive to hazel pollen. The results of our study indicate, that an antigenic relationship between hazel pollen and hazel-nuts exists. Very frequently we found an additional allergy to the botanically related pollen of white beech, alder, birch, beech and oak and an allergy to several fruits and vegetables.