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Nasal irritation and associated symptoms (e.g., nasal congestion, rhinorrhea, sinus headache) are important air-pollution-related health complaints, particularly in so-called problem buildings. Individual differences in nasal irritant sensitivity are therefore of both clinical and regulatory interest. To document such differences, one must first functionally define perceptual acuity to airborne irritants. In an adaptation of an established sensory testing method, the authors used the odorless irritant carbon dioxide in an electronically controlled dilution apparatus to deliver brief (≃ 3 s) pulses at controlled levels (10%-70%, vol/vol), synchronized with the inspiratory phase of the respiratory cycle. Investigators who use this apparatus can use a variant of the forced-choice paradigm for threshold determination to document nasal irritant sensitivity. The authors recruited 30 adult volunteers (17 males, 13 females; average age = 41 y, range = 19-79 y) from a university laboratory complex and from the general community. Within this group, there was a skewed distribution of carbon dioxide thresholds(arithmetic mean = 28%, geometric mean = 27% [vol/vol]). In univariate analyses, geometric mean carbon dioxide thresholds differed significantly with respect to smoking status (36% carbon dioxide in smokers versus 25% in nonsmokers; p < .005), but not with respect to age, gender, or self-reported history of allergic rhinitis. In a multivariate analysis, gender also approached significance; females tended to show better perceptual acuity than males (p = .06). Neither self-reported"vasomotor rhinitis" symptoms nor self-reported symptomatic reactivity to environmental tobacco smoke predicted carbon dioxide thresholds. Pulsed carbon dioxide is well tolerated by subjects who participate in a threshold detection task; the procedure yields a potential endpoint with which to compare individuals (and groups) with respect to nasal irritant perceptual acuity. The relationship between such acuity and nasal physiologic reactivity-as well as the generalizability of such measures to other, more environmentally realistic irritants-has yet to be defined.