Desensitising therapy for allergic diseases has changed little over almost a century of practice. Administration of increasing doses of extracts of allergen source material has been shown to be reproducibly effective when patients are carefully selected and appropriate concentrations of allergen employed. However, specific immunotherapy is limited by the interaction of specific IgE with allergen, leading to a relatively high frequency of adverse events including anaphylaxis and death. Several strategies have been developed to tackle this issue. Most of these rely on reducing the allergenicity of the treatment, whilst maintaining the immunogenicity. The use of short, synthetic peptide sequences corresponding to T-cell epitopes from the allergen has been shown to modify surrogate markers of allergy including cutaneous responses to allergen challenge and ex vivo parameters of T-cell activation. This review discusses recent advances in our understanding of the mechanisms and potential efficacy of this form of therapy.