To determine the tolerance of an allergen extract standardized in mass units, we closely monitored the side-effects, during the buildup phase of immunotherapy treatment, in 88 patients with well-documented respiratory allergy to house-dust mite (Dermatophagoides pteronyssinus). Thirty-four patients (38.6%) suffered from moderate perennial rhinitis, and 54 had mild to moderate bronchial asthma (61.4%). For the desensitizing treatment, we used a depot extract adsorbed in aluminum hydroxide of D. pteronyssinus (Pangramin Depot UM), biologically standardized and having the major allergens Der p 1 and Der p 2 quantified in micrograms. A total of 1244 doses were administered. All patients except one (98.9%) reached the expected maximum dose of 4 micrograms Der p 1. Only five patients suffered mild adverse reactions (5.7%). All adverse reactions except one appeared to be related to the vial of maximum concentration: vial III (4 micrograms Der p 1). Considering the number of patients who had adverse reactions and the frequency of adverse reactions per dose, we found no significant differences between rhinitis and asthma sufferers. We think that immunotherapy in doses of 4 micrograms Der p 1 and 2 micrograms Der p 2 is well tolerated and should not be avoided in mildly to moderately asthmatic patients when treating house-dust mite allergy.