Mucosal administration of antigens in experimental animals leads to the induction of peripheral T cell tolerance. We have previously reported that in H-2b mice, intranasal (i.n.) or oral administration of a peptide containing the immunodominant T cell epitope will down-regulate the function of CD4+ T cells reactive with Der P 1, a major target antigen in both B and T cell responses to house dust mite. In the present study we have investigated the tolerogenicity of peptides containing both dominant and subdominant determinants when given i.n. to nalve mice. Induction of tolerance by the nasally administered immunodominant peptide leads to a diminution in all T cell-derived cytokines and modulation of delayed-type hypersensitivity responses, but IgE production did not seem to be affected, furthermore the induction of T cell tolerance was stable, lasting beyond 6 months. We have also examined the specificity of intramolecular epitope suppression which is a feature of mucosal tolerance induced by nasally administered peptides and demonstrate that regulatory CD4+ T cells may exert their suppressive effect by linked recognition of epitopes on the same or neighbouring antigen-presenting cells.