In a previous dose-titration study of specific immunotherapy (SIT) with a Dermatophagoides pteronyssinus extract in asthmatic patients, we proposed a dose of 3.2 micrograms of Der p and 1/1.6 micrograms of Der p 2 as an optimal maintenance dose. Changes presented by a high-dose immunotherapy group, with a maximum tolerated dose between 4 and 16 micrograms Der p 1, were compared with those of a conventional immunotherapy group, with a maximum tolerated dose of 3.2 micrograms Der p 1 or lower. After 2 years of SIT, both groups achieved the same level of clinical benefit. We now present the results of long-term monitoring of 25 of these patients, covering the 5 years of SIT in which the maintenance dose was set at 3.2 micrograms Der p 1. The aims of the study were firstly to examine if this maintenance dose could sustain the changes induced by immunotherapy in the first 2 years; and secondly, to determine if this dose is clinically effective in patients known to tolerate higher maintenance doses. The clinical severity index (CSI), medication and symptom scores, cutaneous sensitivity and specific IgE and IgG4 to D. pteronyssinus, Der p 1 and Der p 2 were measured. Positive clinical and immunological changes presented in the first 2 years of SIT were sustained (CSI, medication score, specific IgE) or even increased (symptom score, cutaneous sensitivity) after 3 additional years of SIT. In conclusion, a maintenance dose of 3.2 micrograms of Der p 1/1.6 micrograms of Der p 2 induced intense clinical and immunological changes which were sustained during a 5-year course of treatment, even in patients able to tolerate higher doses.