In this report the antigen and restriction specificity of human T-cell clones induced with Dermatophagoides farinae (D. farinae) and isolated from an atopic individual with perennial rhinitis has been investigated. Of the six clones analysed, four were species specific and two showed cross-reactivity for the closely related Dermatophagoides pteronyssinus (D. pteronyssinus). Inhibition of antigen-dependent proliferation by murine monoclonal antibodies directed against HLA-D-region gene products revealed that all the clones were restricted by HLA-DR molecules. The restriction specificity was investigated further using a panel of histocompatible and allogeneic-presenting cells. Of the clones tested, one appeared to be DR5 restricted while the remainder showed complex patterns suggesting that DRw52 and DRw53 supertypic specificities may be the restriction elements presenting antigen.