BACKGROUND: Hypersensitivity to Rosaceae fruits, especially apple, is often associated with birch pollinosis. As the sensitization to pollens has increased, apple allergy is more prevalent. However, the immunologic mechanism has not yet been evaluated in Korean adult patients. OBJECTIVE: This study was conducted to characterize the clinical features of apple allergy and to identify its IgE- binding components. Method: Ten patients having apple allergy were enrolled. Skin prick tests to common allergens and pollens were performed. Serum specific IgE to apple was measured by ELISA, and IgE-binding components of apple allergen were identified by IgE immunoblot analysis. RESULT: Most patients showed positive responses to alder/birch pollens by skin prick tests and high serum levels of specific IgE to apple by ELISA. The IgE-binding component of apple allergen with a molecular weight of 17 kDa was identified by IgE immunoblot in most patients. There was no significant difference in the level of specific IgE to apple between the patient group having oral allergy syndrome and the other group with additional systemic symptoms. CONCLUSION: We confirmed that apple allergy can develop in pollen-sensitized patients because a 17-kDa allergen is assumed as Mal d 1 which shares a common allergenic determinant with Bet v 1 of birch pollen.