Sensitivity to house dust mite allergens in the development of allergic rhinitis has a key role. In this study, the clinical and immunological effects of high dose Dermatophagoides farinae sublingual immunotherapy (SLIT) versus placebo were compared. Forty poly-sensitized patients, ages 6-33 years, with allergic rhinitis and positive allergic reaction to the mites were enrolled in the study. Twenty-one patients were placed in the SLIT group and 19 in the placebo group. Expression levels of IL-10, TGF-β, FOXP3 and IL-17 were measured by using real-time PCR before and after the administration of sublingual immunotherapy. Clinical efficacy was estimated by the reduction rate of symptom/medication scores in the SLIT group compared with placebo treatment. After 6 months of SLIT, TGF-β expression levels were increased compared to pre-treatment (P less than 0.05). SLIT with D. Farinae extract is an effective treatment for poly-sensitized patients with allergic rhinitis. TGF-β mediated T-cell suppression may be an important mechanism in the first 6 months of SLIT.