We investigated the effects of antigen and histamine on the nasal passage patency in guinea pigs with or without nasal allergy. The change of nasal patency was measured by acoustic rhinometry and nasal airway resistance. Acoustic reflections have been used in adult humans to determine nasal cavity dimensions in terms of cross-sectional areas as a function of the distance from the nostril. In order to measure nasal cavity dimensions in guinea pigs, we modified equipment for use in humans by decreasing sound tube dimensions, increasing sampling frequency, and applying a special nosepiece. The percent change of volume, minimum cross-sectional area, and nasal airway resistance showed the largest changes at 10 minutes after antigen challenge in sensitized guinea pigs. There was a significant correlation between the individual percent change of nasal airway resistance and volume or minimum cross-sectional area. Histamine, 10(2) to 10(5) micrograms/mL, caused a dose-dependent reduction in percent change of volume in the challenged side of nonsensitized guinea pigs, but not in the opposite side. These results indicate that the noninvasive acoustic reflections technique is useful in small experimental animals, especially to assess the effect of nasal cavity dimensions after the challenge of antigen or nonspecific stimuli.