A 20mer peptide representing the N-terminus of a major allergen, Alt a I, of Alternaria alternata was synthesized and examined for its antibody binding and antibody induction activities. Alt a I peptide-BSA conjugate reacted with both human IgE and rabbit anti-Alt a I IgG in ELISA, albeit the binding of the peptide to IgE was relatively weak. Control conjugate showed no antibody binding. These results indicated that the N-terminus of Alt a I is an antibody binding site. Moreover, peptide-KLH conjugate and nonconjugated peptide induced both IgG and IgE antibodies in Balb/c mice that recognized both native Alt a I allergen and peptide-BSA conjugate. Since the free peptide was able to induce antibodies in vivo, the peptide may also possess a T cell epitope.