T-cell mediated immune response, toward the house dust mite (HDM) antigens in particular, has been reported to be involved in the pathogenesis of atopic dermatitis (AD). On the other hand, studies on the infiltrating lymphocytes in the skin lesion of AD revealed oligoclonal T-cell accumulation. However, it is not clear exactly what antigen(s) the accumulating T cells are exactly recognize in situ. Therefore, this study attempted to determine whether or not the clonally expanded T-cell clones in the diseased skin recognize HDM. Specifically, peripheral blood mononuclear cells (PBMC) obtained from six patients with AD, who revealed high titers of anti-HDM IgE, were stimulated with HDM antigens purified from Dermatophagoides pteronyssinus (Dp). T-cell clonotypes expanded by the stimulation were then identified by the analysis of their T-cell receptor (TCR) B-gene sequences using a combination of the reverse transcription-polymerase chain reaction and subsequent single strand conformation polymorphism separation. The Dp-responding T-cell clonotypes were compared with those that accumulated in the AD skin lesion in vivo. Nucleotide sequences of the TCR were also determined. As a result, the Dp stimulation induced oligoclonal T-cell expansion from the originally heterogeneous peripheral T-cell population of AD patients. However, only a small part of the Dp-reacting T-cell clonotypes detected in PBMC was identical to those accumulated in the AD skin lesion in vivo, and vice versa. This indicates that the frequency of the clonal expansion of Dp-specific T-cell clonotypes in the skin lesion of AD would be rather limited.