The group 2 allergens of Dermatophagoides spp. (house dust mite, HDM) are a major immunological target for IgE antibodies in the allergic immune response of HDM atopic individuals. In this report the heterogeneity of the T cell repertoire reactive with the group 2 allergen of Dermatophagoides pteronyssinus (Der p 2) of a HDM allergic individual was investigated using overlapping synthetic peptides. By clonal analysis four distinct T cell epitopes were identified, located within residues 16–31, 22–40, 82–100, and 111–129. The importance of these epitopes was confirmed by investigation of the peripheral T cell repertoire, with the polyclonal T cell response to Der p 2 falling to show marked variations in epitope specificity over time. Serological inhibition studies and the use of Epstein-Barr virus transformed B cell lines characterized for their expression of HLA-D region gene products demonstrated that recognition of peptides 16–31 and 111–129 was restricted by HLA-DQ (DQB1^*0301), whereas peptide 82–100 is recognized in association with HLA-DR (DRB1^*1101). Peptide 22–40 was presented by both HLA-DRB1^*1101 and -DQB1^*0301 class II molecules. The potential application of these findings lies in the design of peptide-based immunotherapeutics for the management of HDM allergic disease.