In this prospective clinical study, we investigated the effect of the nasal decongestant tramazoline on nasal airway patency in 30 subjects with perennial nasal allergy to housedust mites and in six non-allergic volunteers who served as controls. The allergic subjects were further subdivided into groups, the severe group and the moderate group, according to the level of specific IgE. We used acoustic rhinometry as an objective method, and the nasal cavity volume (NCV) and the minimum cross-sectional area (MCA) were measured before and 10 minutes after nasal spraying. Before mucosal decongestion, the average NCV in the severe group was 5.94 cm3, which was significantly lower than those in the other two groups: 7 cm3 in the control group and 8.13 cm3 in the moderate group, respectively (P = 0.02). A more significant difference was found when the first 3-cm area of the NCV was evaluated (P = 0.009). Pharmacologic decongestion caused an increase in nasal patency by 54% from the baseline NCV values in the control group, 38% in the moderate group and 48% in the severe group. There was no significant difference among the three groups. Changes in nasal symptoms were also determined by questionnaire. The degree of improvement in subjective nasal congestion was more pronounced in the allergic groups than in the control group.