Allergy to birch pollen is common in the Northern Europe, North America, and in Japan, mainly in Hokkaido Island. Previously, we have reported the positive association of birch pollen allergy in HLA-DR9 antigen. We also have identified the recognition sites in 17kDa protein (Bet v1), known as the major allergen of birch pollen, by using T cell proliferation assay against the trypsin digested materials of the 17kDa protein. In this study, overlapping synthetic peptides correspond to the Bet v1 sequences were used to investigate the specificity of T cell responses in two HLA-DR9 positive patients. Three of the epitopes, residues 35-52, 75-92, and 102-119, were recognized by T cells from both patients. These three epitopes include HLA-DR9 binding motifs. Then we established T cell clone specific to p75-92 residue. 78-89 peptide was the core sequence of the epitope for the T cell clone contained the anchor residues characteristic to HLA-DR9. Within the core sequence, five residues were identified as critical for recognition on the basis of inhibition of the T cell proliferative response against singly substituted analogue peptides.