The trigeminal chemosensory system responds to irritation of the nasal cavity. Despite its dominant role as a sentinel in protecting the respiratory tract from harmful substances and its involvement in the perception of odorous substances, it has received relatively little attention compared to the olfactory system. Aim of the present study was the comparison of two psychophysical techniques to assess intranasal trigeminal thresholds, namely (A) responses of subjects who focused on intranasal trigeminally mediated sensations, and (B) the ability of subjects to identify the side of the nose receiving unilaterally presented stimuli. Method A (0.81 > r > 0.56) was found to show a higher test-retest reliability than Method B (0.48 > r > 0.40). Method A revealed thresholds that were approximately 32 times lower than those measured with method B. With method A women were found to have lower thresholds than men; no such difference could be detected between older and younger subjects. In conclusion, if the objective is to assess the level at which trigeminal sensations are detected with the utmost objectivity and unconfounded by smell, the obvious choice is B. If one's purpose is to assess the level at which trigeminal sensations are detected and the quality perceived, in the context of an odor one might opt for Method A. Thus, preference of one method over the other may depend on the question being asked, provided a well-instructed/trained panel of subjects is used. (c) 2004 Elsevier B.V. All rights reserved.