BACKGROUND Bilateral nasal allergen provocation usually produces more pronounced obstruction of one nasal passage. It was found that this could be related to the stage of the nasal cycle before the provocation. OBJECTIVE To discover whether the stage of the nasal cycle is decisive for asymmetry in congestive response observed during bilateral allergen nasal provocation. methods. Two bilateral nasal allergen provocations were performed in a group of 26 pollen-sensitive volunteers. Acoustic rhinometry measurements were taken during the nasal cycle, and then after the provocation. A cross-sectional area at the level of the inferior turbinate (CSA-2) was measured. Consecutive challenges were performed in the opposite phase of the nasal cycle: the side which had been wide just before the first challenge, was narrow before the second provocation. RESULTS Asymmetry in CSA-2 reduction between the nasal passages was observed in most cases. Significant difference was observed between mean CSA-2 reduction rate (reactivity) of the side that responded with greater congestion, and the opposite side. No significant difference was found in mean CSA-2 reduction rate between the side which was narrow, and the side which was wide before provocation. CONCLUSIONS Asymmetry of congestive response during bilateral nasal allergen provocation is not dependent on the stage of the nasal cycle preceding the challenge.