Dose-response Study With Subcutaneous Immunotherapy of an Standardized Dermatophagoides Pteronyssinus (DPT) Extract

Inclusion Criteria: 1. Patients must sign the Informed Consent Form. 2. Patients must be between 18 and 60 years of age. 3. Patients with perennial allergic rhinoconjunctivitis produced by Dermatophagoides pteronyssinus during at least 2 years prior to participating in the study. Although the pathology being studied is allergic rhinoconjunctivitis, patients who have concomitant mild or moderate asthma may be included. 4. Patients who have had a skin prick test result greater or equal to 3 mm in diameter against Dermatophagoides pteronyssinus. 5. Patients who have specific Immunoglobulin E (IgE) greater or equal to class 2 (CAP/PHADIA) to Dermatophagoides pteronyssinus. 6. Patients will preferably be monosensitized to Dermatophagoides pteronyssinus. Polysensitized patients may only be included in the study if their other sensitizations are produced by: * Pollens whose season period does not overlap with the study treatment or, if overlap, whose specific IgE levels are less than class 2. * Perennial allergens with specific IgE levels less than class 2. * Allergens that do not cohabit with the patient or whose environmental levels are not high enough to produce symptoms during the study period. 7. Women of child-bearing potential must have a negative urine pregnancy test at the time they begin the study. 8. Furthermore, women of child-bearing potential must agree to use adequate contraceptive methods during this study if they are sexually active. Exclusion Criteria: 1. Patients with stable and continued use of medication to treat their allergic condition during the 2 weeks prior to their inclusion in the study. 2. Patients sensitized and with specific IgE levels greater or equal to class 2 to other perennial or seasonal allergens clinically relevant including other mites unless they are cross reactive with Dermatophagoides pteronyssinus. 3. Patients who have received immunotherapy in the 5 years prior to the study against either the allergen being tested or an allergen which is cross-reactive, or who are currently receiving immunotherapy for any other allergen. 4. Patients with severe asthma or FEV1\< 70% or with asthma which requires treatment with inhaled or systemic corticoids at the time of the study or in the 8 weeks immediately prior to the onset of treatment. 5. Patients with immunological, cardiac, renal or hepatic diseases or with any other illness which the investigators deem may interfere with the study. 6. Patients with a prior history of anaphylaxis. 7. Patients with chronic urticaria. 8. Patients with moderate-severe atopic dermatitis. 9. Patients with clinically relevant malformations of the upper respiratory tract. 10. Patients who have participated in another clinical trial within 3 months prior to this study. 11. Patients being treated with tricyclic antidepressants, psychotropic drugs, beta-blockers, or angiotensin-converting enzyme inhibitors (ACEIs). 12. Women who are pregnant or breast-feeding or are of child-bearing age and who do not agree to use adequate contraception if they are sexually active and who have not demonstrated that they have been surgically sterilized or have other means of not bearing children. 13. Patients who cannot attend study visits. 14. Patients who are uncooperative or refuse to participate in the study.