Specific immunotherapy (SIT) is the only treatment able to modify the natural history of allergic subjects. Several aspects of the immunopathological response modified by sublingual immunotherapy (SLIT), which is an alternative route of administration for SIT, have been investigated. A shift from Th2-polarized immune response toward Th1-oriented pattern has been reported after SLIT. More recently, a crucial role for a subpopulation of T cells has been evidenced: T regulatory cells (Treg). Allergic patients have a defect of Tregs, and SLIT should be able to induce a specific Treg response. This issue is very relevant as the Treg-dependent cytokines, namely IL-10 and TGF-beta, are involved in the regulation of IgG and IgA antibodies production. Recent evidence shows that SLIT is also able of inducing a Treg response as detected by IL-10 production. IFNgamma is a typical Th1-dependent cytokine. SLIT may induce a significantly increased production of this cytokine and it may be considered as an early marker of SLIT response. Therefore, also SLIT is able of exerting the effects on immune response as well as the subcutaneous route.