OBJECTIVE We sought to investigate the pattern, duration, and amplitude of nasal cycle and its response to nasal decongestant. METHODS Ten adult volunteers attended 2 sessions (with and without nasal spray of 0.1% xylometazoline) for consecutive examinations by rhinomanometry and acoustic rhinometry every 10 minutes over 6 hours. RESULTS A spontaneous fluctuation in nasal minimum cross-sectional area, volume, and nasal resistances (inspiration and expiration) could be observed in every consecutive measurement. A significant negative correlation (r = -0.33 to -0.70, P < 0.05) between both nasal passages was shown in 5 subjects by rhinomanometry and in 2 subjects by acoustic rhinometry but was not detectable after nasal spray with 0.1% xylometazoline. CONCLUSIONS A spontaneous fluctuation in nasal patency can be documented every 10 minutes with irregular pattern, frequency, and amplitude. Classic nasal cycle is not a universal phenomenon, which can be abolished by the application of decongestant.