Background: Apricots are widely grown in Europe, and allergic reactions are becoming more common, especially oral allergy syndrome. Apricot belongs to the botanical subfamily of Prunoideae, which includes peach, the major allergen of which was identified as a 9-kd protein, a lipid transfer protein (LTP). Objective: The aim of the study was to evaluate the IgE reactivity pattern to an apricot extract in subjects with allergic reactions to apricot, as demonstrated by a positive oral challenge response. Methods: Thirty patients were investigated. All the patients displayed oral allergy syndrome (2 with systemic reactions) to apricot, with positive open food challenge responses, skin prick test responses, and serum-specific IgE antibodies to apricot. The IgE reactivity pattern to apricot extract was identified by using SDS-PAGE and immunoblotting. The major allergen, a 9-kd protein, was then purified by HPLC and characterized by periodic acid–Schiff stain, isoelectric point determination, and N-terminal amino acid sequencing. Results: The sera from all patients allergic to apricot recognized the 9-kd protein, whereas none of the other allergens, with molecular weights from 15 to 80 kd, acted as a major allergen. The 9-kd allergen has an isoelectric point of 8.7 and is not glycosylated. Determination of the N-terminal 34 amino acid sequence showed that it belongs to the LTP family, with a 94% homology with the LTP from peach. IgE blotting of the apricot extract was completely inhibited by the 9-kd purified LTP from peach. Conclusions: The major allergen of apricot is an LTP, which is highly cross-reactive with the LTP from peach. (J Allergy Clin Immunol 2000;105:371-7.)