Magnetic resonance studies frequently demonstrate increased T2-weighted signal in the nasal area. To further evaluate this phenomenon, several MRI examinations of the nasal cavity were performed within an 8- to 12-hour period. The study demonstrated that changes alternated from side to side and were interrupted by the administration of topical vasoconstriction, confirming imaging of the normal nasal cycle. Changes were also observed within the ethmoid sinuses. Signal intensity on T2-weighted images during the congested phase was similar to inflammatory mucosa. Occasionally, these changes make interpretation of the extent of pathology difficult in patients with sinus disease, and raise the possibility of inflammatory pathology in asymptomatic patients. Awareness of MRI imaging of nasal cycle should reduce the likelihood of diagnostic errors and provides another method for study of this physiologic phenomenon.