OBJECTIVE Our objective was to evaluate the action of topical nasal steroid in nasal congestion and nasal hyper-reactivity in children and adolescents with persistent allergic rhinitis. METHODS Twenty atopic children and adolescents (6 to 18 years) with moderate-to-severe persistent allergic rhinitis (PAR) were treated with mometasone furoate (100 microg once a day) for 21 days. At the beginning and end of treatment, the following were recorded: a) nasal symptoms score; b) several parameters of nasal congestion measured by acoustic rhinometry (SRE 2000 Rhinometrics); c) degree of nasal hyper-reactivity to histamine (concentration of histamine necessary to induce at least 100% increase in total nasal resistance during nasal provocation test). Data were compared with those from 20 controls. RESULTS Compared to controls, PAR patients had significantly higher score of symptoms, as well as higher degree of nasal hyper-reactivity and lower nasal volumes. After treatment, there was a significant decrease in the mean nasal symptoms score (8.0 versus 3.8; p < 0.001) and in the nasal hyper-reactivity (histamine concentration: 0.72 mg/ml versus 2.60 mg/ml; p < 0.001). Congestion improvement was observed by the increase in all acoustic rhinometry parameters. Among all studied volumes, the volume in the segment between 2 and 5 cm showed the highest mean increase (19.8%). CONCLUSIONS Treatment with topical nasal steroid objectively reduced nasal congestion and nasal histamine hyper-reactivity in children and adolescents with PAR.