We studied 63 adults with perennial allergic rhinitis and positive skin-prick tests for Dermatophagoides pteronyssinus (Dp) and Dermatophagoides farinae (Df) who had not previously received any type of immunotherapy or pharmacotherapy for their condition. We injected these patients with a 50% Dp/50% Df modified allergen intradermally in accordance with the classic immunotherapy scheme once a week for 30 months. Specific immunotherapy (SIT) was administered until the specific IgG (sIgG) concentration reached level IV (≥81% absorbance). We measured specific IgE and sIgG levels, obtained skin-prick test results, and evaluated clinical symptoms and signs before immunotherapy, at 6 months into therapy, at the completion of therapy (30 mo), and 1 year after the completion of therapy. In the group as a whole, differences between mean sIgG values and mean skin-prick test results before and after SIT were statistically significant (p < 0.05). At the 1-year follow-up, there was a negative correlation between sIgG levels and clinical symptom and sign scores, a positive correlation between skin-prick test results and clinical improvement, and a negative correlation between sIgG levels and skin-prick test results. Individually, at the 1-year follow-up, 50 of the 63 patients (79%) had experienced a resolution of clinical symptoms and/or signs and were thus deemed to have achieved clinical recovery.