Sublingual immunotherapy is widely recognized as a viable treatment for allergic rhinitis and asthma, but the optimal dosage is still under debate, especially with modified allergens. We assessed the clinical effects of a monomeric allergoid across 3 different maintenance doses in mite-monosensitized patients with rhinitis and intermittent asthma. Eighty-nine patients allergic to HDM were randomized to 3 maintenance doses of monomeric allergoid (Lais, Lofarma) or medications only. All the patients recorded their symptoms and rescue drug consumption in a diary card from November to February. Additionally, nasal eosinophil count, spirometry and methacholine bronchial challenge were performed at the beginning of the study and after 3 years. The symptom scores showed a clear improvement in all the three active arms versus baseline and versus the controls, irrespective of the dose. Likewise, a similar improvement versus baseline was seen for nasal inflammation and bronchial hyperreactivity. The SLIT with monomeric allergoids produces clinically significant results across a wide range of doses. The absence of significant side effects, even at high doses, is probably due to their low level of allergeni city.