Background: It is important to study the crossreactivity between orange tree pollen (OTPE) and orange fruit (OFE) due to the high incidence of pollen/food-related allergies worldwide. The aim of the present study was to determine the antigenic relationship between OTPE and OFE. Methods: OTPE and OFErabbit antisera as well as sera from patients allergic to OTPE and OFE were comparatively applied in IgG- and/or IgE-specific ELISA inhibition, crossover or inhibition immunoblotting assays using OTPE and OFE allergenic extracts as solid phase. Periodate and proteinase K treatments were used for carbohydrate and protein depletion, respectively. Results: The antigenicity of OTPE and the presence of common structures between OTPE and OFE extracts were demonstrated by rabbit IgG-specific ELISA inhibition and crossover immunoblotting assays. A 30-kDa protein, common target of the IgE response on OTPE, OFE and mandarin extract, but absent in lemon extract, was identified by ELISA and immunoblot inhibition assays in patients suffering from primary sensitization to OTPE in the context of occupational exposure. Moreover, biochemical treatments showed that antigenic epitopes on the 30-kDa protein contain polypeptidic but no carbohydrate moieties. Conclusions: The antigenicity of OTPE, the presence of common antigenic determinants between pollen and citrus fruits and an IgE-specific crossreactive protein band of 30 kDa sharing carbohydrate-free epitopes were described. After isolation and purification, this common antigen might be useful for allergen immunotherapy in pollen/fruit-related allergic patients.