Trigeminal nerve endings of the human nasal mucosa are activated by chemical, physical or thermal stimuli. Activation of these A(delta) and C fibers can be quantified through the recording of chemo-somatosensory event-related potentials (ERP). The aim of this study was to investigate whether allergy-related activation of trigeminal nerve endings leads to changes in their responsiveness to intranasal trigeminal stimulation. Gaseous carbon dioxide (CO(2)) stimuli were applied in three sessions (baseline, after NaCl solution and after allergen application) to the nasal mucosa of 13 subjects with allergic rhinitis. Chemo-somatosensory ERP were recorded, and subjects rated the intensity of rhinitis symptoms. Administration of allergen produced a significant shortening of chemo-somatosensory ERP peak latencies P1 and N1. Observed changes of latencies were in line with rhinitis symptoms subjects indicated during the session. In addition, there was a negative relation between the general symptom score and ERP peak latencies, obtained both at baseline and after allergen exposure. In conclusion, it is hypothesized that in patients suffering from allergic rhinitis, nasal itching and sneezing after allergen exposure are, at least in part, clinical correlates of the activation of trigeminal nerve endings due to local inflammatory mechanisms. The correlations between ERP latencies and the patients' symptoms indicate that ERP latencies may possess a predictive value of the subjects' responsiveness to allergens.