Here we describe the detection of T-cell epitope region on the house dust mite allergen Mag 3, which has been shown to trigger T-cell proliferation in mite-allergic asthmatic patients. We first examined murine T-cell epitope using T-cell fraction prepared from recombinant Mag 3 (r-Mag 3)-primed H-2k mice. Initial proliferation assay with truncated r-Mag 3 indicated that N-terminal 113 amino acid region was required for triggering T-cell activation. Subsequent epitope scanning with synthetic overlapping peptides revealed that T-cell reactive region was assigned within amino acid range 56-75. We also explored human T-cell determinant using specific T-cells from mite-allergic patients. Intriguingly, we found that amino acid range 56-85, a portion partially overlapping with that identified in r-Mag 3-primed mice, was exclusively recognized by T-cells from different patients. Further investigation of unique T-cell epitope region found in this study would provide insight into the development of animal therapeutic model and/or peptide vaccine for asthma.