The aim of the present study was to investigate the bilateral sensory changes to chemical noxious stimuli in the trigeminally innervated areas following unilateral nasal inflammation. Twenty healthy volunteers took part in five experiments. Intranasal inflammation was induced by means of a constant flow of cold air (145 ml/s); temperature and humidity of the airstream were varied across experiments. For the non-inflamed (NOI) condition, air temperature was 36 degrees C and its humidity 80%. In the other experiments the airstream's humidity was either 25% or 80% with a constant temperature of 20 degrees C; the airstream was applied to the left or right nostril. In order to produce noxious chemical stimuli, gaseous CO2 was applied to the left nostril (36 stimuli of 200 ms; 65% v/v CO2; interstimulus interval 30 s). Subjects rated the pain intensity of the stimuli by means of a visual analogue scale (VAS). As an indicator for hyperalgesia, the subjective pain ratings to CO2 stimuli increased not only while they were applied at the inflamed site, but also during their application contralaterally to the inflamed side. These results demonstrate the occurrence of bilateral hyperalgesia to noxious chemical stimuli in the nasal mucosa following unilateral inflammation which indicates the involvement of central changes. (C) 1997 International Association for the Study of Pain. Published by Elsevier Science B.V.