Alternaria alternata protein, Alt a 1 is a major allergen associated with allergy in atopic patients. Although the molecule binds strongly to IgE antibody from patients, the epitopes involved have not been identified or defined. In the present study, we synthesized overlapping peptides spanning the whole sequence and evaluated their IgE binding with sera from patients with Alternaria-induced allergy. The results identified four IgE binding linear regions. Two of these regions K41-P50 and Y54-K63 showed consistent reactivity with all four patients studied. The specific epitopes involved in the immune response may be of value in the immunodiagnosis and probably also in specific immunotherapy. (C) 2003 Elsevier Science Inc. All rights reserved.