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Background: Acoustic rhinometry (AR) uses sonar principles to map the anatomy of the nasal cavity and has been used in other studies to assess acute airway responses to allergen exposure. Objective: The purpose of this study was to evaluate the utility of AR in assessing acute airway responses to cat allergen exposure by using a well-characterized cat exposure model. Methods: Thirty subjects with a history of cat-induced rhinitis and a positive skin prick test response to cat allergen underwent an environmental cat challenge. Of these 30 subjects, 10 also had repeat challenges at lower levels of antigen to determine whether there was a dose response. Five subjects with negative skin test responses to cat were recruited as control subjects. During the 1-hour cat exposure, upper and lower respiratory symptoms were scored every 5 minutes, and spirometry and AR were obtained every 15 minutes. Results: Although 29 of 30 subjects had changes in AR measurements, no correlations were detected between upper respiratory symptom scores and any of the changes observed in AR. In comparing the baseline challenges with lower antigen level challenges, upper respiratory symptom scores differed significantly (P = .002), whereas AR responses were nearly identical. Subjects without cat allergy did exhibit less response by AR (P = .05 to .13), but the greatest differences remained in the upper respiratory symptoms scores (P < .0001). Conclusion: We conclude that although AR does provide an objective measure of nasal response to allergen exposure, it has significant limitations. These are evidenced by the lack of correlation with symptoms, the inability to measure a dose response, and the changes noted even among the control subjects. (J Allergy Clin Immunol 1998;102:896-901).